Re: 한의학의 역사를 바꿀 전침(교감-부교감신경 항염증 자극) 탐구를 위한 염증반응의 이해!!

[문형철]

ReviewVolume 232102793May 2021Open access

Download Full Issue

Acupuncture modulates immunity in sepsis:

Toward a science-based protocol

Wei-Xing Pana panw@hhmi.org ∙ Arthur Yin Fanb,c ArthurFan@ChineseMedicineDoctor.us ∙ Shaozong Chend,1 zjyjs1980@sdutcm.edu.cn ∙ Sarah Faggert Alemib,e

Affiliations & Notes

aJanelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA

bAmerican TCM Association, Vienna, VA 22182, USA

cMcLean Center for Complementary and Alternative Medicine, PLC, Vienna, VA 22182, USA

dAcupuncture Research Institute, Shandong University of Chinese Medicine, Jinan 250355, China

eEastern Roots Wellness, PLC, McLean, VA 22101, USA

1

Dr. Chen is the lead corresponding author of this paper.

Article Info

Publication History:

Received November 26, 2020; Revised January 26, 2021; Accepted February 25, 2021; Published online February 27, 2021

DOI: 10.1016/j.autneu.2021.102793 External LinkAlso available on ScienceDirect External Link

Copyright: © 2021 The Authors. Published by Elsevier B.V.

User License: Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | Elsevier's open access license policy

• Download PDF
• Cite
•  
• Set Alert
• Get Rights
• Reprints

Download Full Issue

Previous articleNext article

Show Outline

Highlights

•

Acupuncture modulates immunity and improves organ functions in sepsis, emerging as a promising therapy of immunomodulation.

•

Acupuncture obtains its regulatory effect via the somatic-autonomic-immune reflexes.

•

Such reflexes include the sympathetic-splenic, sympathetic-adrenal, vagal-splenic and vagal-adrenal reflexes, inducing systemic effects.

•

There are also local reflexes activated by acupuncture, such as the somatic-sympathetic-lung-reflex, inducing local effects.

•

A comprehensive EA protocol is designed based on the evidenced mechanisms.

Abstract

Sepsis is a serious medical condition in which immune dysfunction plays a key role. Previous treatments focused on chemotherapy to control immune function; however, a recognized effective compound or treatment has yet to be developed. Recent advances indicate that a neuromodulation approach with nerve stimulation allows developing a therapeutic strategy to control inflammation and improve organ functions in sepsis. As a quick, non-invasive technique of peripheral nerve stimulation, acupuncture has emerged as a promising therapy to provide significant advantages for immunomodulation in acute inflammation. Acupuncture obtains its regulatory effect by activating the somatic-autonomic-immune reflexes, including the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex and the somatic-vagal-adrenal reflex, which produces a systemic effect. The peripheral nerve stimulation also induces local reflexes such as the somatic-sympathetic-lung-reflex, which then produces local effects. These mechanisms offer scientific guidance to design acupuncture protocols for immunomodulation and inflammation control, leading to an evidence-based comprehensive therapy recommendation.

주요 요점

• 침술은 패혈증 환자의 면역을 조절하고 장기 기능을 개선하며, 유망한 면역 조절 요법으로 부상하고 있습니다.
• 침술의 조절 효과는 **체성-자율신경-면역 반사(Somatic-autonomic-immune reflexes)**를 통해 이루어집니다.
• 이러한 반사에는 교감-비장, 교감-부신, 미주-비장, 미주-부신 반사가 포함되며, 이는 전신적인 효과를 유발합니다.
• 또한 침술에 의해 활성화되는 체성-교감-폐 반사와 같은 국소 반사는 국소적인 효과를 유발합니다.
• 입증된 메커니즘을 바탕으로 종합적인 전침(EA) 프로토콜이 설계되었습니다.

---

국문 초록

패혈증은 면역 기능 장애가 핵심적인 역할을 하는 심각한 의학적 상태입니다. 이전의 치료법들은 면역 기능을 조절하기 위한 화학 요법에 집중해 왔으나, 아직 공인된 효과적인 화합물이나 치료법은 개발되지 않은 상태입니다.

최근의 연구 진전은

신경 자극을 통한 신경 조절(Neuromodulation) 접근법이

패혈증의 염증을 조절하고 장기 기능을 개선하는 치료 전략 개발을 가능하게 함을 시사합니다.

빠르고 비침습적인 말초 신경 자극 기술인 침술은

급성 염증의 면역 조절에 있어 상당한 이점을 제공하는 유망한 치료법으로 떠오르고 있습니다.

침술은

체성-교감-비장 반사, 체성-교감-부신 반사, 체성-미주-비장 반사, 체성-미주-부신 반사를 포함한 

체성-자율신경-면역 반사를 활성화함으로써

전신적인 조절 효과를 얻습니다.

또한 말초 신경 자극은 체성-교감-폐 반사와 같은 국소 반사를 유도하여 국소적인 효과를 만들어냅니다.

이러한 메커니즘은

면역 조절 및 염증 제어를 위한 침술 프로토콜 설계에 과학적 지침을 제공하며,

근거 기반의 종합적인 치료 권고안으로 이어집니다.

Abbreviations

1. Acupoint (acupuncture point)
2. APS (antigen-presenting cells)
3. ARDS (acute respiratory distress syndrome)
4. APACHE II (acute physiology and chronic health score)
5. CARS (compensatory anti-inflammatory response)
6. COVID-19 (coronavirus disease 2019)
7. CRP (C reactive protein)
8. EA (electroacupuncture)
9. ICU (Intensive Care Unit)
10. IL (interleukin)
11. MODS (multiple organ dysfunction syndrome)
12. LAC (blood lactic acid)
13. NK (natural killer)
14. PCT (procalcitonin)
15. SARS (severe acute respiratory syndrome)
16. TNF (tumor necrosis factor)
17. SOFA (systemic infection-related organ failure score)
18. VNS (vagus nerve stimulation)

Keywords

1. Nerve stimulation
2. Acupuncture
3. Electroacupuncture
4. Sepsis
5. Inflammation
6. Anti-inflammation
7. Inflammatory reflex
8. Immune dysfunction
9. Somatic-sympathetic reflex
10. Somatic-vagal reflex

1 Introduction

Sepsis is defined as life-threatening organ dysfunction, caused by a dysregulated host response to infection (Gotts and Matthay, 2016; Singer et al., 2016), which clinically manifests as severe systemic inflammatory response, Acute Respiratory Distress Syndrome (ARDS), Septic Shock, or Multiple Organ Dysfunction Syndrome (MODS). It is the number one killer in the Intensive Care Unit (ICU). Globally, there are approximately 30 million cases of sepsis each year, with a fatality rate as high as 30% (Reinhart et al., 2017). The Coronavirus Disease 2019 (COVID-19), which has developed into a global pandemic, is a current example of a manifestation of severe sepsis. Similar to other infections, deaths resulting from COVID-19 have been related to sepsis, which causes septic shock, MODS, and ARDS in particular (C. Wang et al., 2020; D. Wang et al., 2020; Z. Wu and McGoogan, 2020). Reducing inflammation and correcting organ dysfunction are the core strategies of clinical treatment of sepsis. However, due to the lack of a specific and effective antiviral drug, how to effectively treat sepsis has been a clinical challenge for a long time, especially for sepsis caused by viral infection. Traditionally, steroids, i.e. adrenocortical hormones, were once the major anti-inflammatory drugs used for this condition; however, they were unsatisfactory due to their serious side effects and sequelae. Recent immunotherapy drugs, such as siltuximab and tocilizumab, present hope but are yet to be eval‎uated and summarized for further development and clinical application. Fortunately, experimental animal studies in recent years have shown that a simple non-pharmacological approach shows the effect of anti-septicemia (for a review, see Lai et al., 2020). That approach is peripheral nerve stimulation done through both electroacupuncture (EA) and manual acupuncture (in short, acupuncture). Studies have shown that acupuncture is a promising alternative clinical anti-inflammatory therapy. Several lines of evidence published in recent years, from the researches of immunomodulatory mechanisms (for reviews, see, i.g. Tracey, 2002; Ulloa, 2005; Huston et al., 2006; Behrens and Koretzky, 2017; Pavlov et al., 2018; Berlot and Passero, 2019), the experiments of acupuncture in animal models (for a review, see Lai et al., 2020) and in patients of clinical trials (for a review, see Tang et al., 2020), support the antiseptic effect of acupuncture. Such a non-pharmacological and non-invasive approach has attracted the attention of the clinical medicine community and has been advocated by some leading researchers (Ulloa et al., 2017; Pavlov and Tracey, 2017). However, the clinical translation in practice with details is still lacking. This article aims to offer a brief comprehensive review and develop an evidence-based EA therapy for immunomodulation in acute inflammation to promote further research and clinical application.

1. 서론

패혈증은

감염에 대한 인체의 조절되지 않은 반응으로 인해 발생하는

생명을 위협하는 장기 기능 장애로 정의되며(Gotts and Matthay, 2016; Singer et al., 2016),

임상적으로는

심각한 전신 염증 반응, 급성 호흡곤란 증후군(ARDS),

패혈성 쇼크 또는 다발성 장기 기능 부전 증후군(MODS)으로 나타납니다.

Multiple Organ Dysfunction Syndrome

패혈증은

중환자실(ICU) 내 사망 원인 1위입니다.

전 세계적으로 매년 약 3,000만 건의 패혈증 사례가 발생하며,

사망률은 30%에 달합니다(Reinhart et al., 2017).

전 세계적 팬데믹으로 발전한 **코로나바이러스 감염증-19(COVID-19)**는

중증 패혈증이 나타나는 최신 사례입니다.

다른 감염과 마찬가지로, COVID-19로 인한 사망은

패혈성 쇼크, MODS,

특히 ARDS를 유발하는 패혈증과 관련이 있습니다(C. Wang et al., 2020; D. Wang et al., 2020; Z. Wu and McGoogan, 2020).

염증을 줄이고

장기 기능 장애를 교정하는 것이

패혈증 임상 치료의 핵심 전략입니다.

그러나 특이적이고 효과적인 항바이러스제의 부재로 인해,

특히 바이러스 감염에 의한 패혈증을 어떻게 효과적으로 치료할 것인가는

오랫동안 임상적 과제였습니다.

전통적으로 부신피질 호르몬과 같은 스테로이드제가

주요 항염증제로 사용되어 왔으나,

심각한 부작용과 후유증으로 인해 그 결과는 만족스럽지 못했습니다.

실투심맙(siltuximab)이나 토실리주맙(tocilizumab)과 같은

최신 면역 요법 약물들이 희망을 제시하고 있지만,

추가적인 개발과 임상 적용을 위한 평가 및 정리가 더 필요한 실정입니다.

다행히 최근 몇 년간의 실험 동물 연구에 따르면,

단순한 비약물적 접근법이 항패혈증 효과를 보이는 것으로 나타났습니다(검토는 Lai et al., 2020 참조).

그 방법은

바로 **전침(EA)과 수침(Manual acupuncture)을 통한

말초 신경 자극(이하 침술)**입니다.

연구들은 침술이 유망한 대안적 항염증 요법임을 보여주었습니다.

최근 발표된 면역 조절 메커니즘 연구,

동물 모델 실험, 그리고 임상 시험 데이터들은 침술의 항패혈증 효과를 뒷받침합니다.

이러한 비약물적·비침습적 접근법은

임상의학계의 관심을 끌었으며,

일부 주요 연구자들에 의해 옹호되어 왔습니다(Ulloa et al., 2017; Pavlov and Tracey, 2017).

그러나

실제 임상 현장에서의 세부적인 적용(Translation)은 여전히 부족한 상태입니다.

본 논문은

간략하고 포괄적인 검토를 제공하고,

추가 연구와 임상 적용을 촉진하기 위해 급성 염증의 면역 조절을 위한 

근거 기반의 전침 요법을 개발하는 것을 목표로 합니다.

2 Pathophysiology of sepsis

Sepsis is initiated by an infection. However, it has been known that the clinical manifestations and pathological complications of sepsis are not caused directly by invading pathogens, but rather by a disorder of the host's immune reaction (Hamers et al., 2015; Behrens and Koretzky, 2017). The main pathophysiological process of infectious diseases is the body's response to bio-immunogenic substances, that is, inflammatory reactions with defense properties. With the advancement of immunopathology research, more details of the inflammatory process have been understood (Gotts and Matthay, 2016; Singer et al., 2016; Reinhart et al., 2017; Sladkova and Kostolansk, 2006; Tisoncik et al., 2012; Wiersinga et al., 2014). The body's immune system is functionally divided into innate immunity and acquired adaptive immunity. When pathogenic microorganisms invade the body for the first time, the innate immune system responds accordingly, starting the inflammatory process. First, macrophages recognize and engulf the pathogens. While destroying and inactivating them, some antigen-presenting cells (APCs) can recognize the antigenic characteristics of pathogens and then transmit to B cells; the adaptive immune system is then activated to generate specific antibodies, which can more accurately and efficiently kill pathogens. Long-term memory of antigen information forming, and then lifelong immunity will be generated. However, antibody production takes a long time, around 5–10 days. Fortunately, the innate immune system immediately goes forward to start the battle of non-specific immunity, rather than waiting for the arrival of specific antibodies. Immune cells and infected tissue cells quickly release a batch of cytokines and pro-inflammatory substances under the stimulation of pathogens, such as interleukin IL-1, IL-8, IL-18, tumor necrosis factor TNF-α, IL-6, IL-33, type I and III Interferons (IFN), etc. which are called primary cytokine storms (Behrens and Koretzky, 2017). These cytokines exert a variety of different immune functions. For example, IL-1 is an important initiator of the inflammatory response; TNF has a strong killing effect; IFN has an antiviral effect and can limit virus replication and spread, protecting uninfected cells from being affected by virus invasion; chemokines IL-8 can induce the recruitment of more immune cells toward the infection site; some cytokines can activate the neuroendocrine system, leading to increased body temperature, breathing, circulation, metabolism and other functions. At the same time, these cytokines have a positive feedback effect, which can activate immune cells to release more cytokines, forming a secondary wave of cytokine storms and further strengthening the inflammatory response in order to effectively kill the pathogens (Guo and Thomas, 2017). If this process is successful, the pathogen may be eliminated, or at least prevented from spreading until the specific antibodies (IgM) are produced and the pathogen is destroyed. Once this occurs, the body enters the rehabilitation phase, removing necrotic cells and repairing damaged tissue. This is the general clinical process of many inflammatory infections, which generally last for 1–2 weeks and end through self-healing alone. Unfortunately, a significant proportion of patients progress to a worsening course of disease and develop sepsis. In severe cases, ARDS, septic shock, and MODS are fatal. The core problem of sepsis is a disturbance of the functioning of the immune system. Its pathophysiological mechanism is that the patient is prone to excessive inflammatory reactions in the early stage of the infection, which is the aforementioned cytokine storm phenomenon, also clinically called cytokine release syndrome (CRS). During the normal inflammatory response, when a large number of pro-inflammatory factors are released, the release of anti-inflammatory factors such as IL-4, IL-10, IL-11, IL-13, and IL-1Ra are also initiated, as a self-balance regulation of the immune system, called “compensatory anti-inflammatory response” (CARS) (Berlot and Passero, 2019). The emergence of sepsis is caused by a disorder in the dynamic balance between pro-inflammatory and anti-inflammatory factors, the excessive secretion of multiple pro-inflammatory factors, and the intensification under the positive feedback mechanism. While attacking the pathogen, it also damages the normal tissue cells of the body, leading to important organs or system dysfunction or even failure. However, that is not all that occurs during sepsis. It has recently been discovered that the mechanism behind sepsis is more complicated than previously thought. Not only does the immune response become hyperactive in the early stage, but also CARS is activated at the same time to limit the tissue damage. However, the CARS can represent a double-edged sword. It might be beneficial to restore immune balance; yet, it might cause the shutdown of the immune response if it over responds, inducing the status of immune-paralysis (Hamers et al., 2015; Berlot and Passero, 2019). With immune-paralysis, there can be a reduction of immune-related receptors, apoptosis of various immune cells (T cells, B cells, macrophages, dendritic cells), weakened antigen presentation function of APCs, and increased suppressive lymphocytes, etc., leading to both innate and adaptive immune functions that are severely weakened. This makes it difficult to clear the damaged tissues in later stages. It is also easier to activate latent pathogens and cause a secondary infection. Even worse is that some patients might have problems with immune-paralysis at the early stage, or multiple hits of the cytokine storm phenomenon ultimately leading to the exhaustion of the immune response, which makes treatment more difficult. Therefore, it is necessary to enhance immunity in the later stage as well, which has become a new focus of both basic science and clinical studies. The patterns of inflammatory reaction have been proposed theoretically (Berlot and Passero, 2019), shown in Fig. 1.

패혈증(sepsis)은

감염에 의해 시작됩니다.

그러나

패혈증의 임상 증상과 병리학적 합병증은

침입하는 병원체에 의해 직접적으로 발생하는 것이 아니라,

숙주의 면역 반응 장애에 의해 일어난다는 것이 알려져 있습니다 (Hamers et al., 2015; Behrens and Koretzky, 2017).

감염성 질환의 주요 병태생리 과정은

생체 면역원성 물질에 대한 신체의 반응,

즉 방어적 성질을 가진 염증 반응입니다.

면역병리학 연구의 발전으로

염증 과정의 더 많은 세부 사항이 이해되었습니다

(Gotts and Matthay, 2016; Singer et al., 2016; Reinhart et al., 2017; Sladkova and Kostolansk, 2006; Tisoncik et al., 2012; Wiersinga et al., 2014).

신체의 면역 체계는

선천 면역(innate immunity)과 후천 적응 면역(acquired adaptive immunity)으로

기능적으로 나뉩니다.

병원성 미생물이 처음 침입할 때

선천 면역 체계가 이에 대응하여 염증 과정을 시작합니다.

먼저 대식세포(macrophages)가

병원체를 인식하고 포식합니다.

이를 파괴하고 비활성화하는 동안

일부 항원 제시 세포(APCs)는 병원체의 항원 특성을 인식한 후 B 세포에 전달합니다.

그러면

적응 면역 체계가 활성화되어

특이적 항체를 생성하며,

이는 병원체를 더 정확하고 효율적으로 사멸시킬 수 있습니다.

항원 정보에 대한 장기 기억이 형성되어

평생 면역이 생깁니다.

그러나

항체 생산에는 시간이 오래 걸리며,

대략 5–10일 정도 소요됩니다.

다행히

선천 면역 체계는

특이적 항체가 도착하기를 기다리지 않고

즉시 비특이적 면역 전투를 시작합니다.

면역 세포와 감염된 조직 세포는

병원체 자극 하에 IL-1, IL-8, IL-18, 종양괴사인자 TNF-α, IL-6, IL-33, I형 및 III형 인터페론(IFN) 등

다양한 사이토카인과 전염증 물질을 빠르게 방출합니다.

이를

1차 사이토카인 폭풍(primary cytokine storm)이라고

합니다 (Behrens and Koretzky, 2017).

https://www.nature.com/articles/s41392-025-02178-y

CytokinesMain cell typeMajor Function

IL-1	Macrophages, epithelial cells, pyroptic cells	Pro-inflammatory; pyrogenic; macrophage activation; Th17 cells differentiation.563
IL-2	T cells	Autoimmunity regulation; T cell proliferation and differentiation; Teff generation; Treg maintenance.564
IL-4	Mast cells, Th2 cells, eosinophils, and basophils	Anti-inflammatory; IgE production; Th2 differentiation; M2 macrophage polarization155
IL-6	Macrophages, T cells, fibroblasts, endothelial cells	Pro-inflammatory; acute phase response; pyrogenic; angiogenic; T cell differentiation; enhanced antibody production, increased vascular permeability.565
IL-9	Th9 cells, type 2 innate lymphoid cells, Tc9 cells, Vδ2 T cells, mast cells	Pleiotropic; anti-tumor; T cells and B cells regulation; mast cells activation.566
IL-10	Th2 cells, Treg cells, CD8+ T cells, B cells	Anti-inflammatory; suppression of immune response; inhibition of macrophage activation; inhibition of Th1 cells; Treg response.567
IL-12	DCs, macrophages	Th1 cell differentiation; activation of T and NK cells; inhibition of immunosuppressive cells; induction of IFN-γ production; action in synergy with IL-18.568
IL-13	Th2 cells	Anti-inflammatory; B cell proliferation; activation of eosinophils, basophils, and mast cells.569
IL-17	Th17 cells, Tc17 cells, NK cells, γδ T cells, type 3 innate lymphoid cells	Pro-inflammatory; bacterial elimination; induction of cytokines and chemokines; immune cell recruitment.570
IL-18	Macrophages, DCs	Pro-inflammatory; activation of Th1 cells; action in synergy with IL-12.571
IL-21	Tfh cells	Pro-inflammatory; B cell activation; CD8+ T differentiation and activation.572
IL-22	Th1, Th17, Th22, CD8+ T cells, γδ T cells, NK cells, neutrophils	Regulation of host defense and epithelial homeostasis; antimicrobial.573
IL-31	Th2 cells, macrophages, DCs, eosinophils, mast cells, fibroblasts and keratinocytes	Pro-inflammatory; cell mediated immunity; itch mediator.574
IL-33	Endothelial cells, epithelial cells, macrophages, DCs, mast cells	Pro-inflammatory; activation of Th1, Th2, NK cells, CD8+ T cells; allergic inflammation.575
IL-37	Macrophages, DCs, epithelial cells, Treg cells	Anti-inflammatory; suppression of innate inflammatory and immune responses.576
Type I IFN	Virtually all body cells	Antimicrobial activity; modulation of innate immune responses; activate the adaptive immune system.577
Type II IFN	NK cells, Th1 cells, cytotoxic T cells	Proinflammatory; antiviral immunity, regulation of innate and adaptive immune responses.578
TGF-β	Almost every tissue and cell type	Immunosuppressive; oncogenic; regulation of cell proliferation, embryonic development, wound healing, and immune response.579
TNF	T cells, NK cells, macrophages, mast cells	Pyrogenic; increasing vascular permeability.580

이러한 사이토카인은

다양한 면역 기능을 발휘합니다.

예를 들어

IL-1은 염증 반응의 중요한 개시자이며,

TNF는 강력한 살상 효과를 가지며,

IFN은 항바이러스 효과를 발휘하여 바이러스 복제와 확산을 제한하고 감염되지 않은 세포를 보호합니다.

케모카인 IL-8은

더 많은 면역 세포를 감염 부위로 유도합니다.

일부 사이토카인은

신경내분비계를 활성화하여

체온 상승, 호흡, 순환, 대사 등의 기능을 증가시킵니다.

동시에 이러한 사이토카인은 양성 피드백 효과를 가지며,

면역 세포를 활성화하여

더 많은 사이토카인을 방출하게 하여

2차 사이토카인 폭풍을 형성하고

염증 반응을 더욱 강화하여 병원체를 효과적으로 사멸시킵니다 (Guo and Thomas, 2017).

이 과정이 성공하면

병원체가 제거되거나

적어도 특이적 항체(IgM)가 생성되어 병원체를 파괴할 때까지 확산이 방지됩니다.

일단 이렇게 되면 신체는

회복 단계에 들어가

괴사 세포를 제거하고 손상된 조직을 복구합니다.

이는 많은 염증성 감염의 일반적인 임상 과정으로,

보통 1–2주 정도 지속되며 자가 치유로 끝납니다.

불행히도 상당수의 환자는

질병이 악화되어 패혈증으로 진행됩니다.

심한 경우

ARDS, 패혈성 쇼크, 다발성 장기 부전(MODS)이 치명적입니다.

패혈증의 핵심 문제는

면역 체계 기능의 장애입니다.

그 병태생리 기전은

감염 초기 단계에서 과도한 염증 반응이 일어나기 쉬운 것으로,

앞서 언급한 사이토카인 폭풍 현상이며,

임상적으로는 사이토카인 방출 증후군(cytokine release syndrome, CRS)이라고도 합니다.

정상적인 염증 반응에서는

다량의 전염증 인자가 방출될 때 IL-4, IL-10, IL-11, IL-13, IL-1Ra 등의 항염증 인자 방출도 시작되어

면역 체계의 자가 균형 조절을 이루는

'보상성 항염증 반응(compensatory anti-inflammatory response, CARS)'이

일어납니다 (Berlot and Passero, 2019).

패혈증의 발생은

전염증과 항염증 인자 간의 동적 균형 장애,

다중 전염증 인자의 과도한 분비,

양성 피드백 기전에 의한 강화로 인해 일어납니다.

병원체를 공격하면서 동시에 신체의 정상 조직 세포를 손상시켜

중요한 장기나 계통의 기능 장애 또는 부전을 초래합니다.

그러나

패혈증에서 일어나는 것은 이것만이 아닙니다.

최근 발견된 바에 따르면 패혈증의 기전은

이전에 생각했던 것보다 훨씬 복잡합니다.

초기 단계에서 면역 반응이 과활성화되는 것뿐만 아니라

동시에 CARS가 활성화되어 조직 손상을 제한합니다.

그러나

CARS는 양날의 검일 수 있습니다.

면역 균형 회복에 도움이 될 수 있지만,

과도하게 반응하면 면역 반응의 셧다운을 유발하여

면역 마비(immune-paralysis) 상태를 초래할 수 있습니다 (Hamers et al., 2015; Berlot and Passero, 2019).

면역 마비 상태에서는

면역 관련 수용체 감소,

다양한 면역 세포(T 세포, B 세포, 대식세포, 수지상 세포)의 세포 사멸,

APC의 항원 제시 기능 약화,

억제성 림프구 증가 등으로 선천 및 적응 면역 기능이 심각하게 약화됩니다.

이로 인해 후기 단계에서 손상된 조직을 제거하기 어려워지며,

잠복 병원체가 활성화되어

2차 감염이 발생하기 쉽습니다.

더 나쁜 것은

일부 환자는 초기부터 면역 마비 문제가 있거나,

다중 사이토카인 폭풍 현상이 반복되어

결국 면역 반응의 소진으로 이어져 치료를 더 어렵게 만듭니다.

따라서

후기 단계에서 면역을 강화하는 것이 기본 과학과 임상 연구의 새로운 초점이 되었습니다.

염증 반응의 패턴은 이론적으로 제안되었으며 (Berlot and Passero, 2019),

Fig. 1에 나타나 있습니다.

Figure viewer

Fig. 1 The immune reaction patterns (reproduced from Berlot and Passero, 2019).

A. Possible clinical trajectories of patients with sepsis shock. Line 1, intense hyper-inflammatory reaction followed by CARS and the return to the baseline immune state. Line 2, weak hyper-inflammatory reaction followed by immune-paralysis and immune restoration. Line 3, immune-paralysis not preceded by a hyper-inflammatory reaction. B. The multiple hits phenomenon ultimately leading to the exhaustion of the immune response.

Fig. 1 면역 반응 패턴 (Berlot and Passero, 2019에서 재현).

A. 패혈성 쇼크(septic shock) 환자의 가능한 임상 경과(trajectories).

• Line 1: 강렬한 과염증 반응(hyper-inflammatory reaction)이 일어난 후 CARS가 뒤따르고, baseline 면역 상태로 회복되는 경로.
• Line 2: 약한 과염증 반응이 일어난 후 면역 마비(immune-paralysis)가 발생하고, 이후 면역 회복(immune restoration)이 일어나는 경로.
• Line 3: 과염증 반응 없이 바로 면역 마비가 발생하는 경로.

B. 다중 타격 현상(multiple hits phenomenon)이 결국 면역 반응의 소진(exhaustion of the immune response)으로 이어지는 과정.

3 Difficulties in regulating immune function in the treatment of sepsis

The treatment of sepsis needs to address three aspects: reducing the pathogens (such as fighting the bacterial or viral infection, if applicable), reducing inflammation, and correction of various physiological dysfunctions. Multiple organ dysfunctions are closely related to inflammation, so reducing inflammation is an important aspect to be dealt with in its early and middle stages. Anti-inflammation or reducing inflammation means regulating immune function. The immune system consists of a variety of functional cells and molecular signaling pathways that form an extremely complex regulatory network. Normal inflammatory response is a dynamic equilibrium process of immune cells and molecular networks. The imbalance of septicemia manifests as early immune hyperactivity and late immune paralysis (Berlot and Passero, 2019) Theoretically, treatment should be to give inhibitory intervention in the early stages, followed by a strengthening intervention. However, it is difficult to make a decision in delivering the specific interventions in real clinical settings. There have been large numbers of anti-inflammatory medications previously used, including corticosteroids, aspirin, monoclonal antibodies, anti-cytokines, anti-chemokines, etc., the effectiveness of which is inconclusive, with some also leading to worsening of the condition. There are several reasons for this. First, in terms of the magnitude of the immune response, how much cytokine release during the inflammatory response can be determined to be “excessive”? It is difficult to define because of the physical condition of patients, such as age, gender, and possible chronic underlying disease. Second, in terms of phases, the turning point of the immune response from the hyper-phase to the hypo-phase is difficult to predict. Unlike antibiotics that advocate early use, immuno-suppressants are generally considered only when clinical symptoms are severe. At this time, immune hyperactivity may have peaked and begun to show a downward trend. Immuno-suppressants may be redundant and even cause immune paralysis quickly. This may be one of the reasons why traditional steroids (adrenal cortex hormones) or targeted therapies that target specific cytokines (for example, antagonists such as the IL-6 blocker siltuximab and the IL-6R blocker tocilizumab) often fail. Clinical effect has not been reached on the effects of these two types of therapy on reducing mortality. Third, regardless of the overall inhibition of steroids (adrenocortical hormones) or single-factor targeted therapy, they are not the normal physiological regulation. This makes it easy to create new imbalances. For example, reducing the recruitment and activation of neutrophils can reduce the damage to normal tissues, but also reduce the lethality to pathogens, leading to the spread of infection. Fourth, in recent explorations, the administration of immune stimulators in later phases is said to be promising, although biomarkers to stratify the immune status are still in development (Peters van Ton et al., 2018). However, once into the late phase, multiple organ dysfunctions may be enough to cause death and immune stimulators may seem meaningless. The only significance of immune stimulators is that of patients with direct immune paralysis in the early phases, but reliable diagnostic indicators are needed. Therefore, the ideal approach is the therapy closest to physiological regulation. Perhaps turning to the neuromodulation of immune responses is a promising direction.

패혈증 치료에서 면역 기능 조절의 3가지 어려움

패혈증 치료는

세 가지 측면을 다루어야 합니다:

병원체 감소(예: 세균 또는 바이러스 감염에 대한 치료, 해당되는 경우),

염증 감소, 그리고

다양한 생리적 기능 장애의 교정입니다.

다발성 장기 기능 장애는

염증과 밀접하게 관련되어 있으므로,

초기 및 중기 단계에서 염증을 줄이는 것이 중요한 과제입니다.

항염증 또는 염증 감소는 

면역 기능 조절을 의미합니다.

면역 체계는

다양한 기능 세포와 분자 신호 전달 경로로 구성되어 있으며,

이는 극도로 복잡한 조절 네트워크를 형성합니다.

정상적인 염증 반응은

면역 세포와 분자 네트워크의 동적 평형 과정입니다.

패혈증에서의 불균형은

초기의 면역 과활성화(hyperactivity)와

후기의 면역 마비(paralysis)로 나타납니다 (Berlot and Passero, 2019).

이론적으로 치료는

초기 단계에서 억제적 개입을 하고,

이후 강화적 개입을 하는 것이어야 합니다.

그러나 실제 임상 현장에서 구체적인 개입 시점을 결정하는 것은 매우 어렵습니다.

이전에 사용된

수많은 항염증 약물들(코르티코스테로이드, 아스피린, 단클론 항체, 항사이토카인, 항케모카인 등)의 효과는

아직 명확하지 않으며, 일부는 오히려 상태를 악화시키기도 했습니다.

그 이유는 여러 가지입니다.

첫째, 면역 반응의 강도 측면에서 염증 반응 중 사이토카인 방출이 어느 정도여야 “과도한(excessive)” 것인지 판단하기 어렵습니다.

환자의 나이, 성별, 만성 기저 질환 여부 등 신체 상태에 따라 다르기 때문에 명확한 기준을 정하기 힘듭니다.

둘째, 단계(phase) 측면에서 면역 반응이 과활성 단계(hyper-phase)에서 저활성 단계(hypo-phase)로 전환되는 전환점을 예측하기 어렵습니다. 항생제는 조기 사용을 권장하는 것과 달리, 면역억제제는 일반적으로 임상 증상이 심각할 때에만 고려됩니다. 이 시점에서는 이미 면역 과활성화가 정점에 도달했거나 하강 국면에 들어갔을 가능성이 높아, 면역억제제가 불필요하거나 오히려 면역 마비를 빠르게 유발할 수 있습니다. 이것이 전통적인 스테로이드(부신피질 호르몬)나 특정 사이토카인을 표적으로 하는 치료(예: IL-6 차단제 siltuximab, IL-6 수용체 차단제 tocilizumab 등)가 종종 실패하는 이유 중 하나일 수 있습니다. 이 두 가지 유형의 치료가 사망률 감소에 미치는 임상 효과는 아직 입증되지 않았습니다.

셋째, 스테로이드의 전반적인 억제나 단일 인자 표적 치료 모두 정상적인 생리적 조절 방식이 아닙니다. 이로 인해 새로운 불균형이 쉽게 발생할 수 있습니다. 예를 들어 호중구의 모집과 활성화를 줄이면 정상 조직 손상은 감소하지만, 병원체에 대한 살상 능력도 떨어져 감염이 확산될 위험이 있습니다.

넷째, 최근 연구에서는 후기 단계에서 면역 자극제(immune stimulators)를 투여하는 것이 유망하다고 여겨지지만, 면역 상태를 층화(stratify)할 수 있는 바이오마커는 아직 개발 중입니다 (Peters van Ton et al., 2018). 그러나 이미 후기 단계에 들어가면 다발성 장기 기능 장애가 사망을 초래할 정도로 심각해져 면역 자극제가 무의미해 보일 수 있습니다. 면역 자극제의 유일한 의미는 초기부터 직접적인 면역 마비가 있는 환자에게만 해당되지만, 이를 위한 신뢰할 수 있는 진단 지표가 필요합니다.

따라서

이상적인 접근법은 생리적 조절에 가장 가까운 치료법입니다.

아마도 면역 반응의 신경 조절(neuromodulation)이 유망한 방향이 될 수 있습니다.

4 Neural regulation of immunity

The immune system was once thought to be an independent regulatory system in the body. The role of the nervous system in regulating immune function has not been known until recent decades, although it has an ancient existence in the history of biological evolution. For example, there are simple organisms, such as C elegans, whose immune cells have been affected by neural signals. In higher animals the brain has been regarded as an immune privileged organ with powerful influence in immunity. The immune system, nervous system and endocrine systems constitute a functional regulatory network (Fig. 2). Based on the functional organization of neuroendocrine and autonomic control, the nervous system can efficiently affect immune function in two ways: through central control and peripheral reflex. The effect of psychological stress on immune function is an example of central control. Peripheral reflex regulation is a more common process, such as inflammatory reflexes (Borovikova et al., 2000; Tracey, 2002). The inflammatory cytokines can stimulate peripheral sensory nerves, including somatic and visceral sensory nerves, or they can directly enter the brain to activate the center integrative effects on immune function, acting through the neuroendocrine or autonomic outputs. The neuroendocrine output is mainly the hypothalamic-pituitary-adrenal (HPA) axis, which has an inhibitory regulating effect on immune function. However, recently it has been noticed that the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamic-pituitary-gonadal (HPG) axis, and the hypothalamic-growth-hormone (HGH) axes are also involved in modulating immune activities (Eskandari et al., 2003). These axes need to be further studied. Autonomic outputs include the sympathetic and vagus nerves, both of which control the immune system and inflammation, which is the focus of this article.

4 면역의 신경 조절

면역 체계는

한때 신체 내에서 독립적인 조절 시스템으로 여겨졌습니다.

신경계가 면역 기능을 조절하는 역할은

생물 진화 역사상 오래전부터 존재했음에도 불구하고,

최근 수십 년이 되어서야 알려지기 시작했습니다.

예를 들어,

C. elegans와 같은 단순한 생물에서도

신경 신호가 면역 세포에 영향을 미치는 것이 관찰되었습니다.

고등 동물에서는

뇌가 강력한 면역 영향력을 가진 면역 특권 기관(immune privileged organ)으로 간주됩니다.

면역 체계, 신경계, 내분비계는

기능적 조절 네트워크를 구성합니다 (Fig. 2).

신경내분비 및 자율신경 조절의 기능적 조직에 기반하여,

신경계는 두 가지 주요 경로를 통해 면역 기능을 효율적으로 영향을 미칩니다:

중추 조절(central control)과 말초 반사(peripheral reflex).

심리적 스트레스가

면역 기능에 미치는 영향은 중추 조절의 대표적인 예입니다.

말초 반사 조절은

더 흔한 과정으로, 염증 반사(inflammatory reflex)가 이에 해당합니다

(Borovikova et al., 2000; Tracey, 2002).

염증성 사이토카인은

체성 감각 신경(somatic sensory nerves)과

내장 감각 신경(visceral sensory nerves)을 포함한 말초 감각 신경을 자극하거나,

뇌로 직접 들어가 중추 통합 효과를 활성화하여

신경내분비 또는 자율신경 출력을 통해 면역 기능에 작용합니다.

신경내분비 출력은

주로 시상하부-뇌하수체-부신 축(HPA axis, hypothalamic-pituitary-adrenal axis)으로,

면역 기능에 억제적 조절 효과를 발휘합니다.

그러나

최근에는

시상하부-뇌하수체-갑상선 축(HPT axis, hypothalamic-pituitary-thyroid axis),

시상하부-뇌하수체-생식선 축(HPG axis, hypothalamic-pituitary-gonadal axis), 그리고

시상하부-성장호르몬 축(HGH axis, hypothalamic-growth-hormone axis)도

면역 활동 조절에 관여한다는 사실이 주목받고 있습니다 (Eskandari et al., 2003).

https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2023.1291856/full

https://www.mdpi.com/1422-0067/24/7/6492

https://www.nature.com/articles/s41392-019-0036-y

이러한 축들에 대한 추가 연구가 필요합니다.

자율신경 출력으로는

교감신경(sympathetic nerve)과 미주신경(vagus nerve)이 있으며,

둘 다 면역 체계와 염증을 조절합니다.

이는 본 논문의 주요 초점입니다.

Figure viewer

Fig. 2 The immune network. The immune system, nervous system and endocrine systems constitute a functional regulatory network. The dynamic balance of immune activity is controlled by the interactions of immune cells and cytokinesis (the left part of the figure adapted from Sladkova and Kostolansk, 2006), which accepts the regulation of the brain (the right part of the figure). The brain regulates the immune system with two major outputs: one is the hormonal system including the HPA, HPTs, HPG, and HGH axes (Eskandari et al., 2003); and the other is the autonomic nervous system consisting of sympathetic norepinephrine and vagal acetylcholine pathways. The immune system can also regulate the nervous system through cytokines which activate the afferent nerves or enter the brain directly.

Fig. 2 면역 네트워크.

면역 체계, 신경계, 내분비계는

기능적 조절 네트워크를 구성합니다.

면역 활동의 동적 균형은

면역 세포와 사이토카인 간의 상호작용에 의해 조절됩니다(그림의 왼쪽 부분은 Sladkova and Kostolansk, 2006에서 차용).

이 부분은 뇌의 조절을 받습니다(그림의 오른쪽 부분).

뇌는 두 가지 주요 출력 경로를 통해 면역 체계를 조절합니다.

하나는 HPA 축, HPT 축, HPG 축, HGH 축을 포함하는 호르몬 시스템(Eskandari et al., 2003)이고,

다른 하나는 교감신경의 노르에피네프린 경로와 미주신경의 아세틸콜린 경로로 구성된 자율신경계입니다.

면역 체계는

또한 사이토카인을 통해 신경계를 조절할 수 있습니다.

사이토카인은 구심성 신경(afferent nerves)을 활성화하거나 뇌로 직접 들어가 작용합니다.

It has been known for a long time that the sympathetic nerves regulate the immune system extensively and complexly, but they have gained increasing interest and attention in recent years. As a result, new knowledge has developed (Eskandari et al., 2003; Olofsson et al., 2012; Jänig, 2014; Jänig and Green, 2014; Bellinger and Lorton, 2014; Pavlov and Tracey, 2017; Chavan and Tracey, 2017). In brief, sympathetic nerves contains nerve fibers (from postganglionic neurons) that specially innervate immune organs including the primary lymphoid organs, i.e. marrow and thymus, and the secondary lymphoid organs, i.e. spleen, lymph nodes, and mucosa-associated lymphatic tissue (Jänig, 2014; Bellinger and Lorton, 2014; Chavan and Tracey, 2017). The sympathetic postganglionic neurons release norepinephrine transmitters which activate β- and α- adrenergic receptors on immune cells, producing the regulatory effects (Bellinger and Lorton, 2014). The β- and α2-adrenergic receptors have opposite effects on immune responses to inflammation (Szelényi et al., 2000; Liu et al., 2020). The hypothalamic area has been thought as a high level center of the autonomic nervous system, which is also known to have extensive influence on immune functioning (for reviews, see Wrona, 2006). Some sub-areas of the hypothalamus might play specific roles in modulating immune functions, e.g. in animal model, electrical stimulation of the lateral hypothalamic area increased natural killer cell cytotoxicity in spleen, while stimulation of the ventromedial hypothalamic area showed suppression effect (Wrona and Trojniar, 2003, 2005). Such hypothalamic-splenic immune modulation is mediated by the sympathetic efferent pathway; therefore, the “hypothalamic-sympathetic-splenic axis” was proposed (Okamoto et al., 1996). The hypothalamus might be involved in the peripheral reflex to modulate immunity (Son et al., 2002; Hahm et al., 2004). Martelli and colleagues (Martelli et al., 2014a, 2014b, 2016, 2019), with a series of experiments in rodents, have identified the greater splanchnic nerve as the sympathetic efferent arm of the inflammatory reflex to inhibit inflammatory cytokines in the spleen as well as in other inner organs innervated by the nerve such as liver, gastrointestinal tract and importantly, the adrenal, as systemic immune cell function can also be regulated through the adrenal medulla with catecholamine releasing. In addition, recent studies have shown that selective somatic local effects of sympathetic innervations on immune functions are available via a direct interaction of the postganglionic nerves with local immune cells. Bassi et al. (2017) showed that direct stimulation of the lumbar sympathetic trunk reduced neutrophil recruitment in arthritic knee joints, and the same effect resulted from direct injection of norepinephrine into the joint. Given the well-known function of the somatic-sympathetic reflex, one might predict that selective stimulation of somatic nerve connecting to the same segment of the spinal cord from which the sympathetic efferent fibers innervate a specific organ or tissue, might produce a local effect of immune regulation of the specific organ or tissues. Indeed, Kim et al. (2007, 2008) have found that electroacupuncture (EA) at Zusanli (ST36) acupoints suppressed zymosan- or carrageenan-induced paw inflammation. Interestingly, they found that low frequency (1 Hz) EA obtained the local suppression effect via activation of sympathetic postganglionic neurons, the simple somatic-sympathetic reflex; while high-frequency (120 Hz) EA suppression is mediated by the sympathoadrenal medullary axis to induce systemic catecholamines for whole body effects. A very recent study (S.B. Liu et al., 2020) showed that selective stimulation of acupoint Tianshu (ST25), which connects to the same segment of the spinal cord sending sympathetic innervation to spleen, evoked the somatic-sympathetic-splenic reflex, produced systemic effect of immune modulation. This new knowledge of different immune reflex paths is very valuable to selective treatment of specific organs and local tissue with inflammation and dysfunction.

More recent knowledge shows that the vagus nerve controls immune function by dominating the spleen and adrenal medulla. The first discovery is the “cholinergic anti-inflammatory pathway” (Borovikova et al., 2000) and then developed the concept of “inflammatory reflex”(Tracey, 2002). In brief (for full reviews, see Ulloa, 2005; Huston et al., 2006; Olofsson et al., 2012; Inoue et al., 2016; Pavlov and Tracey, 2017; Pavlov et al., 2018; Huh and Veiga-Fernandes, 2020), the vagal nerve center can be activated by an immune challenge, and then the vagus nerve efferent terminals releasing cholinergic transmitters, innervate the spleen, perhaps relayed by the splenic nerve (Komegae et al., 2018) (but see Martelli et al., 2014c, 2016), and through the α7 nicotinic receptor on macrophages and other immune cells, inhibit the release of pro-inflammatory cytokines such as TNFα and IL-1 etc. Activation of this pathway by electrical or pharmacological stimulation suppresses excessive inflammation in the gastrointestinal tract (de Jonge et al., 2005; Ghia et al., 2006, 2007), pancreas (van Westerloo et al., 2006), liver (Guarini et al., 2003) and heart (Bernik et al., 2002), inhibiting systemic inflammation. Recent experiments in mice model (Torres-Rosas et al., 2014) have found that the vagus nerve can also dominate the adrenal medulla and activate the latter to release dopamine to inhibit the release of pro-inflammatory cytokines and increase the survival rate of the animals with sepsis. Kwan et al. (2016) have systematically reviewed 36 eligible studies from 290 identified records of vagus nerve stimulation (VNS) for treatment of inflammation in animal models and clinical trials, suggesting that VNS is a very promising approach of inflammation reduction. This immunomodulatory effect produced by stimulating efferent nerves may be an ideal therapy closer to normal or natural physiological regulation without the side effects seen in some drugs. The anti-inflammatory effects of implanted electrodes to stimulate the vagus nerve have been tried for the treatment of chronic immune diseases (De Ferrari et al., 2011; Howland et al., 2011; Howland, 2014; Koopman et al., 2016; Noller et al., 2019). For acute infections, implanting electrodes is not a viable option. Fortunately, stimulating peripheral somatic nerves can also produce the effects of autonomic-immune reflexes, including vagal-immune reflex and the above-mentioned sympathetic-immune reflex (Ulloa et al., 2017; Pavlov and Tracey, 2017). This opens a convenient window of hope for the treatment of acute inflammation in infectious diseases. Not surprisingly, this approach is just how acupuncture therapy works. There is a long history in China of acupuncture being used to treat various emergencies such as acute fever, shock and coma, etc. Acupuncture has been applied even more frequently and sometimes might be considered more important than traditional Chinese herbal medicine, which needs to be prepared or cooked and takes time to see results (L.G. Liu et al., 2004). Acupuncture works rapidly and can often quickly reverse critical conditions, according to ancient and contemporary literature (L.G. Liu et al., 2004). Contemporary Chinese medicine practitioners continued this tradition and use acupuncture, combining it with modern conventional treatment, to treat epidemic diseases, including COVID-19 (R. Wang et al., 2020). Recent random control clinical studies (see following session) also show that acupuncture is a promising clinical anti-inflammatory therapy.

교감신경이

면역 체계를 광범위하고 복잡하게 조절한다는 사실은 오래전부터 알려져 있었으나,

최근 몇 년 사이에 관심과 주목이 크게 증가하면서 새로운 지식이 축적되었습니다

(Eskandari et al., 2003; Olofsson et al., 2012; Jänig, 2014; Jänig and Green, 2014; Bellinger and Lorton, 2014; Pavlov and Tracey, 2017; Chavan and Tracey, 2017).

간략히 말해,

교감신경은 교감신경절 후 신경세포(postganglionic neurons)에서 나온 신경섬유를 포함하며,

이 신경섬유는

1차 림프 기관(골수와 흉선)과

2차 림프 기관(비장, 림프절, 점막 관련 림프 조직)을 포함한 면역 기관들을 특이적으로 지배합니다

(Jänig, 2014; Bellinger and Lorton, 2014; Chavan and Tracey, 2017).

교감신경절 후 신경세포는

노르에피네프린(norepinephrine)을 방출하여

면역 세포 표면의 β- 및 α- 아드레날린 수용체를 활성화함으로써 조절 효과를 발휘합니다

(Bellinger and Lorton, 2014).

β-아드레날린 수용체와 α2-아드레날린 수용체는

염증에 대한 면역 반응에 정반대의 효과를 나타냅니다

(Szelényi et al., 2000; Liu et al., 2020).

시상하부 영역은

자율신경계의 고위 중추로 여겨지며,

면역 기능에 광범위한 영향을 미치는 것으로 알려져 있습니다 (리뷰: Wrona, 2006).

시상하부의 일부 하위 영역은

면역 기능 조절에 특이적인 역할을 할 수 있습니다.

예를 들어 동물 모델에서

외측 시상하부 영역(lateral hypothalamic area)의 전기 자극은

비장의 자연살해세포(natural killer cell) 세포독성을 증가시켰으며,

복내측 시상하부 영역(ventromedial hypothalamic area)의 자극은 억제 효과를 보였습니다 (Wrona and Trojniar, 2003, 2005).

이러한 시상하부-비장 면역 조절은

교감신경 유출 경로를 매개로 이루어지며,

따라서 “시상하부-교감신경-비장 축(hypothalamic-sympathetic-splenic axis)”이 제안되었습니다 (Okamoto et al., 1996).

시상하부는

말초 반사를 통해 면역을 조절하는 데에도 관여할 수 있습니다 (Son et al., 2002; Hahm et al., 2004).

Martelli와 동료들(Martelli et al., 2014a, 2014b, 2016, 2019)은 설치류 실험 시리즈를 통해 대내장신경(greater splanchnic nerve)을 염증 반사의 교감신경 유출 경로로 확인하였습니다. 이 신경은 비장에서 염증성 사이토카인을 억제하며, 간, 위장관, 그리고 특히 부신을 포함한 신경이 지배하는 다른 내장 기관에서도 동일한 효과를 발휘합니다. 부신수질을 통한 카테콜아민 방출로 전신 면역 세포 기능도 조절될 수 있습니다.

또한 최근 연구에서는 교감신경의 선택적 국소 효과가 후신경절 신경과 국소 면역 세포의 직접적인 상호작용을 통해 가능하다는 것이 밝혀졌습니다. Bassi et al. (2017)은 요추 교감신경줄기(lumbar sympathetic trunk)의 직접 자극이 관절염 무릎 관절에서 호중구 모집을 감소시켰으며, 동일한 관절에 노르에피네프린을 직접 주사해도 같은 효과가 나타났습니다.

체성-교감 반사(somatic-sympathetic reflex)의 잘 알려진 기능으로 미루어,

특정 장기나 조직을 지배하는 교감신경 유출 섬유가 나오는 척수 분절과 연결된 체성 신경을 선택적으로 자극하면

해당 장기나 조직에 국소적인 면역 조절 효과를 낼 수 있을 것으로 예측됩니다.

실제로 Kim et al. (2007, 2008)은

족삼리(Zusanli, ST36) 혈자리에 전침(electroacupuncture, EA)을 시행하여

자이모산(zymosan) 또는 카라기난(carrageenan)으로 유도된 발 염증을 억제하였습니다.

흥미롭게도

저주파(1 Hz) EA는

교감신경절 후 신경세포를 활성화하는 단순 체성-교감 반사를 통해

국소 억제 효과를 나타냈으며,

고주파(120 Hz) EA 억제는

교감-부신수질 축(sympathoadrenal medullary axis)을 매개로

전신 카테콜아민을 유도하여 전신 효과를 발휘하였습니다.

매우 최근 연구(S.B. Liu et al., 2020)에서는

비장에 교감신경을 보내는 척수 분절과 연결된 천추(Tianshu, ST25) 혈자리의 선택적 자극이

체성-교감-비장 반사를 유발하여

전신 면역 조절 효과를 나타냈습니다.

이러한 다양한 면역 반사 경로에 대한 새로운 지식은

특정 장기와 국소 조직의 염증 및 기능 장애를 선택적으로 치료하는 데 매우 가치 있습니다.

더 최근의 지식에 따르면,

미주신경(vagus nerve)은

비장과 부신수질을 지배함으로써 면역 기능을 조절합니다.

최초 발견은

“콜린성 항염증 경로(cholinergic anti-inflammatory pathway)”

(Borovikova et al., 2000)이며,

이후 “염증 반사(inflammatory reflex)” 개념으로 발전하였습니다 (Tracey, 2002).

간략히 설명하면 (전체 리뷰: Ulloa, 2005; Huston et al., 2006; Olofsson et al., 2012; Inoue et al., 2016; Pavlov and Tracey, 2017; Pavlov et al., 2018; Huh and Veiga-Fernandes, 2020),

면역 도전에 의해 미주신경 중추가 활성화되고,

미주신경 유출 말단에서 콜린성 전달물질을 방출하여

비장을 지배합니다(아마도 비장신경을 경유하여; Komegae et al., 2018; 그러나 Martelli et al., 2014c, 2016 참조).

이 과정은

대식세포 및 기타 면역 세포의 α7 니코틴 수용체를 통해

TNFα, IL-1 등의 전염증성 사이토카인 방출을 억제합니다.

이 경로를

전기적 또는 약리학적으로 자극하면

위장관(de Jonge et al., 2005; Ghia et al., 2006, 2007),

췌장(van Westerloo et al., 2006), 간(Guarini et al., 2003), 심장(Bernik et al., 2002) 등에서

과도한 염증을 억제하고 전신 염증을 감소시킵니다.

최근 생쥐 모델 실험(Torres-Rosas et al., 2014)에서는

미주신경이 부신수질을 지배하여 도파민을 방출하게 하고,

이는 전염증성 사이토카인 방출을 억제하며

패혈증 동물의 생존율을 증가시킨다는 것이 밝혀졌습니다.

Kwan et al. (2016)은

동물 모델과 임상 시험에서

미주신경 자극(VNS)이 염증 치료에 미치는 효과를 체계적으로 검토한 36개 적격 연구(290건 식별 기록 중)를 분석하여,

VNS가 매우 유망한 염증 감소 접근법이라고 결론지었습니다.

유출 신경을 자극함으로써 얻어지는 면역 조절 효과는

일부 약물에서 나타나는 부작용 없이 정상적 또는 자연적인 생리적 조절에 더 가까운

이상적인 치료법이 될 수 있습니다.

미주신경을 자극하는 이식형 전극의 항염증 효과는

만성 면역 질환 치료를 위해 시도되었습니다

(De Ferrari et al., 2011; Howland et al., 2011; Howland, 2014; Koopman et al., 2016; Noller et al., 2019).

그러나

급성 감염에서는 전극 이식이 현실적이지 않습니다.

다행히 말초 체성 신경을 자극하면

자율-면역 반사(미주-면역 반사 및 앞서 언급한 교감-면역 반사)를

유발할 수 있습니다 (Ulloa et al., 2017; Pavlov and Tracey, 2017).

이는 감염성 질환의 급성 염증 치료에 편리한 희망의 창을 열어줍니다.

놀랍지 않게도,

이러한 접근법은 바로 침술 요법의 작용 기전입니다.

중국에는

급성 발열, 쇼크, 혼수 등의 다양한 응급 상황을

침술로 치료해 온 오랜 역사가 있습니다.

침술은

전통 한약(준비하거나 달여야 하며 효과가 나타나는 데 시간이 걸림)에 비해 더 자주 사용되었고,

때로는 더 중요하게 여겨졌습니다 (L.G. Liu et al., 2004).

고대 및 현대 문헌에 따르면

침술은 신속하게 작용하며 위중한 상태를 빠르게 호전시킬 수 있습니다 (L.G. Liu et al., 2004).

현대 중의학자들은

이 전통을 이어가며 침술을 현대적 기존 치료와 병행하여 전염병,

심지어 COVID-19까지 치료하였습니다 (R. Wang et al., 2020).

https://pmc.ncbi.nlm.nih.gov/articles/PMC8168732/

Clinical features and outcomes of hospitalized COVID-19 patients in a low burden region - PMC

최근 무작위 대조 임상 연구(다음 섹션 참조)에서도

침술이 유망한 임상 항염증 요법임을 보여주고 있습니다.

5 Regulatory effects of acupuncture on immune function

Modern studies have demonstrated that acupuncture modulates multiple physiological systems of the body, including the immune system, to reestablish homeostasis by activating peripheral nerves to evoke physiological reflexes (spinal and supraspinal reflex) and the brain central integration (as reviewed elsewhere, Ma, 2004; Zhao, 2008; Kagitani et al., 2010; Uchida et al., 2017; Pan, 2018, 2019). The experimental research on the effects of acupuncture on immune function can be traced back to the middle of the last century (S.Z. Liu, 1959; Yan, 1959). Studies over the decades have shown that acupuncture has a wide range of regulatory effects on the immune system (Den, 1981).

5. 침술의 면역 기능 조절 효과 요약

현대 연구에 따르면

침술은 말초 신경을 활성화하여

척수 및 상위 반사(spinal and supraspinal reflex)와 뇌 중추 통합을 유발함으로써

신체의 여러 생리 시스템, 특히 면역계를 조절하여 항상성(homeostasis)을 회복시킵니다.

침술의 면역 조절 효과 연구는

지난 세기 중반부터 시작되었으며,

수십 년간의 연구에서 면역계에 광범위한 조절 효과가 확인되었습니다.

5.1 Enhancement effects of acupuncture on immunity under physiological conditions

Most of the early studies showed that acupuncture enhanced immunity of normal humans or physiological model animals (S.Z. Liu, 1959; Den, 1981; Du et al., 1995; Johansen et al., 2004; Sato et al., 1996). Acupuncture can enhance the innate immune functions. For example, a large number of studies in rodent models (Sato et al., 1996; Liu et al., 1997; Choi et al., 2002; Kim et al., 2005; Rho et al., 2008) showed that EA at ST36 (Zusanli) upregulated the function of natural killer (NK) cells and macrophages, which play a central role in the innate immune response, especially in killing virus-infected cells. Acupuncture also increases the weight of mouse thymus (L.J. Liu et al., 1997), suggesting an effect of enhancing innate immune function. The effect of acupuncture on adaptive immunity is also supported by many experimental results. Acupuncture can increase the number of lymphocytes in the peripheral blood and the lymphocyte transformation rate in animals (Cao et al., 1982) and humans (Wu, 1983; Jong et al., 2006). In the aging animal model, acupuncture increased the functions of T lymphocytes (J.M. Liu et al., 2009). It has been reported that acupuncture for 20 days can increase the level of IgG and IgM in the elderly (Han, 1993). A few studies have shown that the lateral hypothalamus plays a role in the enhancement effect of EA. EA increased natural killer cell activity in the spleen, correlating with the activation of hypothalamus (Rho et al., 2008). Selective destruction of the lateral hypothalamic area (Choi et al., 2002) cancelled various immune enhancement effects of acupuncture. The general enhancement effects of acupuncture on immunity might benefit the prevention of infections and immune suppression status of sepsis. However, acupuncture effects on immunity show state-dependent features. For example, under disease conditions, the effects of acupuncture might be different from that under normal conditions, which is elaborated below.

5.1 정상(생리적) 상태에서의 면역 강화 효과 초기 연구 대부분에서 침술은 정상인이나 생리적 모델 동물의 면역력을 강화하는 것으로 나타났습니다.

• 선천 면역 강화: 특히 족삼리(ST36, Zusanli) 전침(EA)은 설치류 모델에서 자연살해세포(NK cell)와 대식세포(macrophage)의 기능을 상향 조절하며, 바이러스 감염 세포 사멸 등 선천 면역의 핵심 역할을 강화합니다. 또한 흉선 무게 증가 등 효과도 관찰되었습니다.
• 적응 면역 강화: 말초 혈액 림프구 수 증가, 림프구 변환율 상승, T 림프구 기능 향상(노화 모델 포함), 노인에서 IgG·IgM 수준 증가 등이 보고되었습니다.
• 기전: 외측 시상하부(lateral hypothalamus) 활성화가 NK 세포 활성 증가와 관련되며, 이 부위 손상 시 침술 효과가 소실됩니다. 이러한 강화 효과는 감염 예방과 패혈증에서의 면역 억제 상태 개선에 유익할 수 있습니다. 그러나 침술 효과는 상태 의존적(state-dependent)입니다.

5.2 Bidirectional regulations of immune function by acupuncture under pathological conditions

Previous studies have shown that the most interesting feature of acupuncture is the bidirectional regulation effect on the body's homeostasis, either in hyper- or hypo- functional states (dual regulation, normalization, or restoring homeostasis) in either patients or pathological models of animals (for a review, Pan, 2019). For instance, EA at ST36 showed stimulation of stress-induced delayed gastric emptying and inhibition of stress-induced acceleration of colonic transit (Iwa et al., 2006). Such state-dependent effect also is observed on immune modulation by acupuncture. Acupuncture can enhance the suppressed innate immune functions, such as up-regulating the decreased function of NK cells and macrophages (Zhao et al., 1994; Wu, 1995; Hisamittsu et al., 2002; Yamaguchi et al., 2007; Johnston et al., 2011). Conversely, acupuncture can also downregulate the activity of these immune cells and related cytokines when they are in a hyperactivity state such as inflammation (see the following section). Studies (as reviewed elsewhere, Kim and Bae, 2010; Dai et al., 2018) also showed that acupuncture has bidirectional regulating effects on adaptive immunity, such as T lymphocytes functions. T helper cells, a type of T lymphocytes, play an important role in the immune modulation. There are two main subsets of T helper cells, Th1 and Th2, which respectively produce Th1 type cytokines (e.g. IL-2, INFγ) and Th2 type cytokines (e.g. IL-4, IL-10). The former tends to produce the pro-inflammatory responses, and the latter, anti-inflammatory responses. The balance of Th1/Th2 is changed in different diseases and that can be modulated by acupuncture (Yamaguchi et al., 2007; Dai et al., 2018; Silvério-Lopes and da Mota, 2013). For example, acupuncture can downregulate Th2-specific cytokines (Park et al., 2004; Kim et al., 2011) to improve Th2 dominant disorders, such as allergic rhinitis (Shiue et al., 2008) and chronic fatigue syndrome (C. Wang et al., 2014). In contrast, for the Th1 dominant disorders such as rheumatoid arthritis (Yim et al., 2007), ulcerative colitis (Tian et al., 2003) and depression (Lin et al., 2014), acupuncture can modulate the Th1/Th2 balance with inhibiting Th1 responses. Such bidirectional regulatory effects suggest some interesting mechanisms that need further study (Pan, 2019). Generally speaking The bidirectional regulatory effect of acupuncture mirrors the activation and reinforcement of the body's self-healing or biological adaptive mechanism, which is a unique effect that no specific drug can reach at this time. Thus, acupuncture is a patient-tailored approach, although controlled by the body per se.

5.2 병리적 상태에서의 양방향 조절 효과 (Bidirectional regulation) 

침술의 가장 흥미로운 특징은

과기능(hyper-) 또는 저기능(hypo-) 상태에서

신체 항상성을 정상화하는 양방향 조절(dual regulation)입니다.

이는

약물로는 달성하기 어려운 환자 맞춤형(self-healing) 메커니즘으로

평가됩니다.

• 선천 면역: 억제된 상태(예: NK 세포·대식세포 기능 저하)에서는 기능을 상향 조절하고, 과활성 상태(염증 시)에서는 활동과 관련 사이토카인을 하향 조절합니다.
• 적응 면역: T 림프구 기능, 특히 T helper 세포(Th1/Th2) 균형을 조절합니다.
  • Th1형 사이토카인(IL-2, IFNγ): 염증 촉진 → Th1 우세 질환(류마티스 관절염, 궤양성 대장염, 우울증)에서 Th1 반응 억제.
  • Th2형 사이토카인(IL-4, IL-10): 항염증 → Th2 우세 질환(알레르기 비염, 만성 피로 증후군)에서 Th2 특이적 사이토카인 하향 조절.
  • 결과: Th1/Th2 불균형을 질환에 따라 정상화하여 면역 과민(알레르기) 또는 과도한 염증(자가면역)을 개선합니다.

결론적으로

침술은 병리 상태에 따라 면역계를 양방향으로 조절하여

과도한 염증은 억제하고,

억제된 면역은 강화함으로써 신체의 자가 치유·적응 메커니즘을 활성화합니다.

이는 패혈증 같은 면역 불균형 질환에서

특히 유망한 비약물적 접근법으로 여겨집니다.

5.3 The anti-inflammatory effect of acupuncture

There is growing interest in the anti-inflammatory effect of acupuncture in the research field. In recent decades, the anti-inflammatory effects of acupuncture in septic animals and patients are highlighted. The most common problem of immune response in sepsis is a hyper-reactive cytokine storm. Silvério-Lopes and da Mota (2013) systematically eval‎uated 67 relevant papers published between 2001 and 2011, and concluded that acupuncture and EA are effective in modulation of immunity in animals and humans. Lai et al. (2020) systematically reviewed 54 studies up to May 2019 on acupuncture at ST36 (Zusanli) for the treatment of the experimental sepsis in animal models crossing species (rodents and rabbits). They used 17 criteria to estimate the study quality and risk of bias. The average quality scores of the studies is 6.3 varying from 2 to 9.5, with 13 studies (15%) accepted quality scores ≥7.0. Those studies support that acupuncture benefits to protecting multiple organs against injuries by sepsis and maintaining the immune balance to attenuate inflammation. A very new study (S.B. Liu et al., 2020), published in Neuron online, July 2020, further confirmed that acupuncture has a reliable anti-inflammatory effect, and revealed new features and mechanisms by using genetic strategy. Those results, especially from the quite a few quality studies (Scognamillo-szabo et al., 2004; Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Villegas-Bastida et al., 2014; Yu et al., 2014; Zhu et al., 2015; Chen et al., 2016; Liu et al., 2020), have shown that the efficacy of acupuncture on experimental sepsis has the following characteristics:

5.3 침술의 항염증 효과

최근 연구 분야에서

침술의 항염증 효과에 대한 관심이 크게 증가하고 있습니다.

최근 수십 년 동안 패혈증 동물 모델과 환자에서 침술의 항염증 효과가 강조되어 왔습니다.

패혈증에서 면역 반응의 가장 흔한 문제는 과도한 사이토카인 폭풍(cytokine storm)입니다.

Silvério-Lopes와 da Mota(2013)는

2001년부터 2011년까지 발표된 67편의 관련 논문을 체계적으로 평가한 결과,

침술과 전기침(EA)이 동물과 인간에서 면역 조절에 효과적이라고 결론지었습니다.

Lai et al.(2020)은 2019년 5월까지의 54편 연구를 체계적으로 검토하여,

족삼리(ST36) 혈자리에 대한 침술이 설치류와 토끼 등 다양한 종의 실험적 패혈증 동물 모델에서

치료 효과를 보인다고 밝혔습니다.

이들은 연구 품질과 편향 위험을 평가하기 위해 17개 기준을 사용하였으며,

연구들의 평균 품질 점수는 6.3점(2~9.5점 범위)이었고,

13편(15%)의 연구가 7.0점 이상의 양호한 품질 점수를 받았습니다.

이러한 연구들은

침술이 패혈증으로 인한 다발성 장기 손상을 보호하고,

면역 균형을 유지하여 염증을 완화하는 데 도움이 된다는 것을 뒷받침합니다.

매우 최근 연구(S.B. Liu et al., 2020)는 Neuron 저널 온라인판(2020년 7월)에 게재되었으며,

유전자 전략을 활용하여 침술의 신뢰할 수 있는 항염증 효과를 확인하고,

새로운 특징과 메커니즘을 밝혔습니다.

이러한 결과들, 특히 다수의 양질의 연구(Scognamillo-szabo et al., 2004; Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Villegas-Bastida et al., 2014; Yu et al., 2014; Zhu et al., 2015; Chen et al., 2016; Liu et al., 2020)에서 실험적 패혈증에 대한 침술의 효능은 다음과 같은 특징을 보입니다:

1.  

1.

EA improved the survival rate of animals with sepsis. The survival rate of rats or mice with sepsis increased significantly, with a maximum survival increase up to 80% (S.B. Liu et al., 2020; Torres-Rosas et al., 2014; Chen et al., 2016; Song et al., 2012; Zhu et al., 2015; Villegas-Bastida et al., 2014). EA inhibited the release of important pro-inflammatory factors. The blood levels of pro-inflammatory factors such as TNF, IL-6, MCP-1 and INFγ in the acupuncture group were significantly reduced. The level of anti-inflammatory factor IL-10 either increased (da Silva et al., 2011; Ramires et al., 2020) or did not change significantly (Song et al., 2012). It suggests that acupuncture does not simply suppress the immune response but modulates its balance. The anti-inflammation effect of acupuncture is clear. A study (Ramires et al., 2020) showed that acupuncture obtained similar levels of effect as that of indomethacin (a classical nonsteroidal anti-inflammatory drug) in suppressing peripheral and brainstem cytokines.

2.

EA reduced injuries induced by sepsis in multiple inner organs such as lung, cardiac, kidney, liver and gastrointestinal tract (Lai et al., 2020).

3.

The time-window of treatment exists. The earlier that acupuncture treatment is given, the better the results, with results from preventive care even better (Torres-Rosas et al., 2014; Liu et al., 2020). Even one treatment or pretreatment of EA can cause the effect, and the effect lasts at least 6 h (Torres-Rosas et al., 2014). However, the effects from daily EA, in which there are a consecutive three days of treatment, may have more stable and effective results (Torres-Rosas et al., 2014). A new finding (S.B. Liu et al., 2020) is that time-window plays the role depending on the intensity of stimulation (see below for the details). However, these results perhaps depend on the inflammatory model. It seems that the pretreatments are better than post treatments to lipopolysaccharide (LPS) model (Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Chen et al., 2016; S.B. Liu et al., 2020; Ramires et al., 2020), but no matter to the cecal ligation and puncture (CLP) model (Song et al., 2012; Torres-Rosas et al., 2014). This might arouse future studying of the treatment windows for various inflammations with different pathogens, e.g. bacteria or virus.

4.

The parameter of EA stimulation is important, which consists of frequency, intensity and the model of pulse trains including generally “continuing trains”, “bursting trains” and “alternating trains” with a common commercial EA stimulator. Most experiments obtained show clear effects with simple stimulation of continuing trains of low frequency (<15 Hz). However, a study (Chen et al., 2016) comparing the effects of three types of trains has shown that the alternating trains (2/15 Hz) is the best, then the bursting trains (2/0 Hz), and then the continuing trains (2 Hz). As mentioned above, another study showed that that low frequency (1 Hz) EA produce the local anti-inflammatory effect via activation of the simple spinal somatic-sympathetic reflex; while high-frequency (120 Hz) EA is mediated by the sympathoadrenal medullary axis to induce systemic effects (Kim et al., 2007, 2008). This frequency effect is consistent with some other acupuncture effects depending on frequency of stimulation (Han, 2003).

1. 전기침(EA)은 패혈증 동물의 생존율을 향상시켰습니다. 패혈증이 유발된 쥐나 생쥐의 생존율이 유의하게 증가하였으며, 최대 80%까지 생존율이 향상되었습니다(S.B. Liu et al., 2020; Torres-Rosas et al., 2014; Chen et al., 2016; Song et al., 2012; Zhu et al., 2015; Villegas-Bastida et al., 2014). EA는 중요한 전염증 인자(pro-inflammatory factors)의 방출을 억제하였습니다. 침술군에서 TNF, IL-6, MCP-1, INFγ 등의 혈중 전염증 인자 수준이 유의하게 감소하였습니다. 항염증 인자인 IL-10은 증가하거나(da Silva et al., 2011; Ramires et al., 2020) 유의한 변화가 없었습니다(Song et al., 2012). 이는 침술이 단순히 면역 반응을 억제하는 것이 아니라 균형을 조절한다는 것을 시사합니다. 침술의 항염증 효과는 명확하며, 한 연구(Ramires et al., 2020)에서는 침술이 주변부 및 뇌간 사이토카인을 억제하는 효과가 고전적인 비스테로이드성 항염증제인 인도메타신(indomethacin)과 유사한 수준임을 보여주었습니다.
2. EA는 패혈증으로 인한 다발성 내장기(폐, 심장, 신장, 간, 위장관 등)의 손상을 감소시켰습니다(Lai et al., 2020).
3. 치료 시간 창(time-window)이 존재합니다. 침술 치료를 조기에 시행할수록 결과가 좋으며, 예방적 치료(preventive care)가 더욱 우수한 결과를 보입니다(Torres-Rosas et al., 2014; Liu et al., 2020). 단 한 번의 치료나 사전 치료(pre-treatment)만으로도 효과가 나타나며, 효과는 최소 6시간 지속됩니다(Torres-Rosas et al., 2014). 그러나 3일 연속 매일 EA 치료는 더 안정적이고 효과적인 결과를 보일 수 있습니다(Torres-Rosas et al., 2014). 새로운 발견(S.B. Liu et al., 2020)에 따르면 시간 창은 자극 강도(intensity)에 따라 달라집니다(아래 상세 참조). 그러나 이러한 결과는 염증 모델에 따라 다를 수 있습니다. 리포폴리사카라이드(LPS) 모델에서는 사전 치료가 사후 치료보다 우수한 것으로 보입니다(Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Chen et al., 2016; S.B. Liu et al., 2020; Ramires et al., 2020). 반면, 맹장결찰천공(CLP) 모델에서는 사전/사후 치료 모두 효과가 있습니다(Song et al., 2012; Torres-Rosas et al., 2014). 이는 향후 세균이나 바이러스 등 다양한 병원체에 의한 염증 모델별 치료 시간 창 연구를 촉진할 수 있습니다.
4. EA 자극 매개변수(주파수, 강도, 펄스 열차 모델 — 일반적으로 “연속 열차(continuing trains)”, “버스트 열차(bursting trains)”, “교대 열차(alternating trains)” 등 상용 EA 자극기 사용)는 중요합니다. 대부분의 실험에서 저주파(<15Hz) 연속 열차 자극으로 명확한 효과가 확인되었습니다. 그러나 세 가지 열차 유형을 비교한 연구(Chen et al., 2016)에서는 교대 열차(2/15Hz)가 가장 우수하고, 그 다음 버스트 열차(2/0Hz), 연속 열차(2Hz) 순이었습니다. 앞서 언급한 바와 같이, 저주파(1Hz) EA는 단순 척수 체성-교감 신경 반사를 통해 국소 항염증 효과를 일으키며, 고주파(120Hz) EA는 교감-부신 수질 축(sympathoadrenal medullary axis)을 매개로 전신 효과를 유발합니다(Kim et al., 2007, 2008). 이는 Han(2003)의 다른 침술 효과에서 주파수 의존성을 확인한 것과 일치합니다.

5.

There are large varieties of the intensity of EA stimulation used in different experiments. A problem is that different laboratories used different stimulators which indicate the intensity with different scales: current (mA) or voltage (V), that limits to compare the intensities between the different studies. However, some studies included investigating the effects of intensities, providing valuable data. Torres-Rosas et al. (2014), using mice lipopolysaccharide (LPS) model, compared the pretreatments with stimulations of 0.4 V and 4 V at ST36, and the results showed that the anti-inflammatory effect of 4 V stimulation was clearly stronger than that of 0.4 V. Similarly, Liu et al. (2020) compared the pretreatment with stimulations of 0.5 mA, 1.0 mA and 3.0 mA at ST36 or ST25 (Tianshu, at abdomen) in LPS mice, conforming the results, i.e. the stronger the stimulation, the better the anti-inflammatory effect. A surprising funding by Liu et al. is that post-treatment with the 3.0 mA produced oppositely pro-inflammatory effects, i.e. increased the serum TNF-α level and decreased in survival rate. That is because that LPS increased the expression‎ of α2-ARs (adrenergic receptors) in splenic cells, which mediate pro-inflammatory effects, and the post-treatment with high intensity EA activated the spinal sympathetic-splenic pathway (demonstrated with genetic strategy) that further enhanced the α2-ARs effect. They further demonstrated that Yohimbine (α2-ARs antagonist) or splenectomy allowed 3.0 mA EA to promote survival and to suppress serum TNFα level. However, they found that post-treatment of 0.5 mA weak stimulation at ST36 is not enough to activate this sympathetic-splenic pathway, but it is sufficient to activate the vagal-splenic pathway to obtain the anti-inflammatory effects. But EA at ST25 (either 0.5 mA or 3 mA) did not activate the vagal reflex. Those findings are consistent with the previous results that stimulating acupoints at abdomen area produced the sympathetic reflex on the inner organs, while stimulating acupoints of limbs produced the vagal reflex (Sato, 1997; Li et al., 2007). Those results suggest that we need to consider the stimulation site (acupoint), stimulation intensity and time window of treatment (pre- or post- treatment) together for a clinical therapy. Especially, the time-window dependent effect of stimulation intensity is not easy to control in clinical practice because that almost all treatments are post-treatment on patients. However, this result was from the LPS model. Another data showed that the post-treatment of high intensity EA on CLP model obtained the anti-inflammatory effects and promoted the survival rate (Torres-Rosas et al., 2014). On the other hand, EA applying to patients in real clinical practice might rarely reach the intensity of stimulation as high as that in animals in the laboratory. The EA stimulation of 3 mA is over the threshold (>2 mA) (Kagitani et al., 2010) activating Aδ and C fibers of the peripheral nerves (but see Zhou et al., 1985), that will produce pain feelings in conscious animals and humans. The general situation in a clinic is that a stimulation of EA applying to a patient without uncomfortable feeling, especially without pain, that generally induces slight twitch of the local muscles. This general clinic EA intensity is roughly equal to moderate stimulation in animal experiments, which perhaps might or might not activates the peripheral Aδ fibers (threshold 1.5 mA)(Kagitani et al., 2010; Li et al., 2007) but not C fibers. We might not need to concern too much on above pro-inflammatory effect induced by high intensity post-EA, rather, we might use this feature to benefit to patients, e.g. using relative high stimuli at very early stage (before sepsis happening) to prevent serious sepsis, or promote immunity at late stage with the immune-paralysis.

6.

The selection of acupoints has certain significance. As mentioned above, to control inner organ function, the acupoints at abdomen or back mediate the somatic-sympathetic reflex, while the acupoints of limbs mediate the somatic-vagal-reflex (for an individual organ, the exact and maximal reflex effect is obtained following the spinal segmental dominance rule). However, there is still some variety between acupoints within trunk group or limbs group, e.g. LI4 (Hegu) and PC6 (Neiguan) are both effective acupoints of anti-inflammation, but the former is more effective (Song et al., 2012). This difference might be related to the distinction of the nerves distribution under the acupoints.

5. 전침(EA) 자극 강도의 다양성과 문제점

전침(EA) 자극 강도는 실험마다 매우 다양하게 사용됩니다. 문제는 각 연구실에서 사용하는 자극기가 서로 달라 강도를 표시하는 단위가 전류(mA) 또는 전압(V)으로 나뉘어 있어, 서로 다른 연구 간 강도를 직접 비교하기 어렵다는 점입니다. 그러나 일부 연구에서는 강도별 효과를 비교 조사하여 귀중한 데이터를 제공했습니다.

• Torres-Rosas et al. (2014)은 생쥐 LPS 모델에서 ST36 혈자리에 0.4 V와 4 V 자극을 사전(pre) 치료로 비교한 결과, 4 V 자극의 항염증 효과가 0.4 V보다 훨씬 강하게 나타났습니다.
• Liu et al. (2020)은 LPS 생쥐에서 ST36 또는 ST25(천추, 복부) 혈자리에 0.5 mA, 1.0 mA, 3.0 mA 자극을 사전 치료로 비교하였으며, 자극 강도가 강할수록 항염증 효과가 더 우수하다는 결과를 확인했습니다.

그러나 Liu et al. (2020)의 놀라운 발견은 사후(post) 치료에서 3.0 mA 고강도 자극이 오히려 염증 촉진(pro-inflammatory) 효과를 나타냈다는 점입니다. 즉, 혈청 TNF-α 수준이 증가하고 생존율이 감소하였습니다. 이는 LPS가 비장 세포에서 α2-아드레날린 수용체(α2-ARs)의 발현을 증가시켜 염증 촉진 효과를 매개하기 때문이며, 고강도 EA 사후 치료가 척수 교감-비장 경로(spinal sympathetic-splenic pathway)를 활성화(유전자 전략으로 입증)하여 α2-ARs 효과를 더욱 강화한 결과였습니다.

이들은 추가로 α2-ARs 길항제인 요힘빈(Yohimbine) 투여 또는 비장 절제(splenectomy)를 하면 3.0 mA EA가 생존율을 촉진하고 혈청 TNF-α를 억제할 수 있음을 입증했습니다. 반면, ST36에서 0.5 mA 약한 자극의 사후 치료는 교감-비장 경로를 활성화할 만큼 강하지 않았으나, 미주-비장 경로(vagal-splenic pathway)를 충분히 활성화하여 항염증 효과를 나타냈습니다. 그러나 ST25(복부) 혈자리에서는 0.5 mA나 3.0 mA 모두 미주 반사를 활성화하지 않았습니다.

이 결과는 이전 연구와 일치합니다: 복부·등 부위 혈자리 자극은 체성-교감 반사(somatic-sympathetic reflex)를 통해 내장 기관을 조절하고, 사지(팔다리) 혈자리 자극은 체성-미주 반사(somatic-vagal reflex)를 매개합니다 (Sato, 1997; Li et al., 2007).

따라서 임상 치료 시에는 혈자리 위치(자극 부위), 자극 강도, 치료 시점(사전 vs 사후)을 종합적으로 고려해야 합니다. 특히 자극 강도의 시간 창 의존적 효과(time-window dependent effect)는 임상에서 거의 모든 치료가 환자의 사후 치료이기 때문에 조절하기 어렵습니다. 그러나 이 결과는 LPS 모델에서 나온 것이며, 다른 데이터에서는 CLP 모델에서 고강도 EA 사후 치료가 항염증 효과를 나타내고 생존율을 향상시켰습니다 (Torres-Rosas et al., 2014).

한편, 실제 임상에서 환자에게 적용하는 EA 자극 강도는 동물 실험처럼 3 mA 수준에 도달하는 경우가 드뭅니다. 3 mA는 말초 신경의 Aδ 및 C 섬유를 활성화하는 역치(>2 mA)를 초과하여(Kagitani et al., 2010; 그러나 Zhou et al., 1985 참조), 의식이 있는 동물이나 사람에게 통증을 유발합니다. 일반적인 임상 상황에서는 환자가 불편함이나 통증 없이, 주로 국소 근육의 가벼운 경련(twitch)을 유발할 정도의 중간 강도가 사용됩니다. 이는 동물 실험의 중간 강도에 해당하며, Aδ 섬유(역치 약 1.5 mA)는 활성화될 수도 있고 아닐 수도 있지만 C 섬유는 활성화되지 않습니다 (Kagitani et al., 2010; Li et al., 2007).

따라서 고강도 사후 EA가 유발하는 염증 촉진 효과에 대해 과도하게 우려할 필요는 없으며, 오히려 이 특성을 활용할 수 있습니다. 예를 들어, 매우 초기 단계(패혈증 발생 전)에 상대적으로 높은 자극을 주어 중증 패혈증을 예방하거나, 후기 면역 마비(immune-paralysis) 단계에서 면역을 촉진하는 데 사용할 수 있습니다.

6. 혈자리 선택의 의의

앞서 언급한 바와 같이 내장 기관 기능을 조절하기 위해서는 복부·등 부위 혈자리가 체성-교감 반사를 매개하고, 사지 혈자리는 체성-미주 반사를 매개합니다. 개별 장기에 대해 가장 정확하고 최대의 반사 효과를 얻으려면 척수 분절 지배 규칙(spinal segmental dominance rule)을 따라야 합니다.

그러나 같은 체간(trunk) 그룹이나 사지 그룹 내에서도 혈자리 간에 차이가 있습니다. 예를 들어 LI4(합곡)와 PC6(내관)은 모두 항염증에 효과적인 혈자리이지만, LI4가 더 효과적이라는 보고가 있습니다 (Song et al., 2012). 이러한 차이는 혈자리 아래 신경 분포의 차이와 관련이 있을 가능성이 큽니다.

7.

The anti-inflammation effect of EA is mainly achieved by activating vagal-splenic pathway (Song et al., 2012; Villegas-Bastida et al., 2014; Lim et al., 2016; S.B. Liu et al., 2020), the vagal-adrenal medulla-dopamine pathway (Torres-Rosas et al., 2014) and the sympathetic-splenic pathway (Martelli et al., 2014b; S.B. Liu et al., 2020), rather than by enhancing the hypothalamic-pituitary-adrenal cortex axis, because electroacupuncture pretreatment did not increase serum corticosteroid in animal sepsis model (Song et al., 2012). The role of sympathetic-adrenal medulla pathway is thought to play the role in anti-inflammatory effect in carrageenan-induced paw inflammation model (Kim et al., 2008). However, the role of sympathetic-adrenal medulla pathway in suppressing systemic inflammation needs further investigation. Furthermore, the role of sympathetic-vagal relationship and balance are worth to be studied (Huang et al., 2010).

With these detailed results, the approach of the peripheral-autonomic-immune reflex, carried out by acupuncture, seems promising in being translated into a relative optimal clinical therapy. However, as mentioned above, in the process of sepsis, the immune system with CARS mechanism might present not only a hyper-inflammatory reaction but also immune-paralysis depending on the individual conditions. Further studies are needed to address if there is immune-paralysis at a later stage (even early stage) of the sepsis model, which can be prevented by acupuncture. Theoretically, acupuncture should have a corrective effect for both the hyper- and the insufficient immune responses in the inflammation process according to the bidirectional principle. Indeed, Guo et al. (2010) have reported that EA at Zusali (ST36) and Guanyuan (CV4) decreased the apoptosis of thymocytes in rat sepsis model, suggesting acupuncture can prevent sepsis animals from immune-paralysis. The data from other immune suppression models and clinical trials of inflammation also support the bidirectional effects of acupuncture. For instance, acupuncture reduced the increased plasma level of IL-10 in patients with chronic allergic rhinitis (Petti et al., 2002). Theoretically, when the releasing of pro-inflammatory factors is suppressed, the releasing of anti-inflammatory factors will decrease as well, due to the latter being triggered by the former. Thus, reducing the pro-inflammatory factors by acupuncture at an early stage means also reducing the anti-inflammatory factors later. This might help to avoid the up-and-down oscillation of the compensatory anti-inflammatory response to prevent immune-paralysis, that finally increases the survival rate of animals with sepsis, which needs to be confirmed in future.

7. 전침(EA)의 항염증 기전 및 임상적 함의

전침(EA)의 항염증 효과는 주로 다음 경로들을 활성화함으로써 달성됩니다:

• 미주-비장 경로(vagal-splenic pathway) (Song et al., 2012; Villegas-Bastida et al., 2014; Lim et al., 2016; S.B. Liu et al., 2020)
• 미주-부신수질-도파민 경로(vagal-adrenal medulla-dopamine pathway) (Torres-Rosas et al., 2014)
• 교감-비장 경로(sympathetic-splenic pathway) (Martelli et al., 2014b; S.B. Liu et al., 2020)

이 효과는 시상하부-뇌하수체-부신피질 축(hypothalamic-pituitary-adrenal cortex axis)을 강화하는 것이 아니라 이루어집니다. 동물 패혈증 모델에서 전침 사전 치료가 혈청 코르티코스테로이드(corticosteroid) 수준을 증가시키지 않았기 때문입니다 (Song et al., 2012).

한편, 카라기난(carrageenan)으로 유도된 발 염증 모델에서는 교감-부신수질 경로(sympathetic-adrenal medulla pathway)가 항염증 효과에 관여하는 것으로 생각됩니다 (Kim et al., 2008). 그러나 이 경로가 전신 염증 억제에 미치는 역할은 추가 연구가 필요합니다. 또한 교감신경과 미주신경 간의 상호작용 및 균형(sympathetic-vagal relationship and balance)에 대한 연구도 가치가 있습니다 (Huang et al., 2010).

이러한 상세한 결과들을 바탕으로, 침술을 통해 이루어지는 말초-자율신경-면역 반사(peripheral-autonomic-immune reflex) 접근법은 비교적 최적화된 임상 치료로 전환될 가능성이 유망해 보입니다.

그러나 앞서 언급한 바와 같이 패혈증 과정에서 면역 체계는 CARS(보상성 항염증 반응) 기전을 통해 과염증(hyper-inflammatory) 반응뿐만 아니라 개별 조건에 따라 면역 마비(immune-paralysis) 상태도 나타낼 수 있습니다. 따라서 패혈증 모델의 후기(또는 심지어 초기) 단계에서 발생할 수 있는 면역 마비를 침술이 예방할 수 있는지에 대한 추가 연구가 필요합니다.

이론적으로 침술은 양방향 조절 원칙(bidirectional principle)에 따라 염증 과정에서 과도한(hyper) 면역 반응과 부족한(insufficient) 면역 반응 모두를 교정하는 효과를 가져야 합니다. 실제로 Guo et al. (2010)은 족삼리(ST36, Zusanli)와 관원(CV4, Guanyuan) 전침이 쥐 패혈증 모델에서 흉선세포(thymocyte)의 세포 사멸(apoptosis)을 감소시켰다고 보고하였으며, 이는 침술이 패혈증 동물의 면역 마비를 예방할 수 있음을 시사합니다.

또한 다른 면역 억제 모델 및 염증 관련 임상 시험 데이터들도 침술의 양방향 효과를 뒷받침합니다. 예를 들어 만성 알레르기 비염 환자에서 침술이 증가된 혈장 IL-10 수준을 감소시켰습니다 (Petti et al., 2002).

이론적으로 전염증 인자(pro-inflammatory factors)의 방출이 억제되면, 이를 유발하는 항염증 인자(anti-inflammatory factors)의 방출도 감소합니다. 따라서 초기 단계에서 침술로 전염증 인자를 줄이면 후기 단계에서 항염증 인자도 함께 감소하게 되어, 보상성 항염증 반응(CARS)의 상하 진동(oscillation)을 피할 수 있고, 이는 결국 면역 마비를 방지하여 패혈증 동물의 생존율을 높일 수 있습니다. 이 가설은 향후 연구를 통해 확인되어야 합니다.

5.4 Clinical evidence

In real clinical conditions, patients with sepsis may also have additional complications, especially during the critical stage. Therefore, it is necessary to use different medications or therapies to deal with multiple factors to reach the best results, although animal experiments have shown that acupuncture alone significantly increases the survival rate of sepsis animals. Traditional Chinese practitioners have known for thousands of years to combine acupuncture and herbal medicine together to cure complicated diseases, including serious infections. Recently, acupuncture integrated with modern medical therapies, as a part of the comprehensive treatments of sepsis, has shown exciting values in clinical trials. Clinical reports show that the effect of adding acupuncture intervention in conjunction with conventional treatment is superior to the conventional treatment group alone. A recent study (L. Wang et al., 2019) of a randomized controlled trial on 108 patients with sepsis (54 in the control group and 54 in acupuncture group) showed that the patients in both groups were given conventional treatments, i.e. routine anti-infective medications, and supportive treatments with organ functioning monitored. The patients in the acupuncture group were treated with acupuncture at ST36 daily for 3 consecutive days in addition to conventional treatment. The results showed that, compared to the condition before the treatments, after the treatments, the plasma factor procalcitonin (PCT), blood lactic acid (Lac) expression‎ level, Acute Physiology and Chronic Health Eval‎uation (APACHE II) score, and Sequential Organ Failure Assessment (SOFA) score in both groups were significantly decreased; however, compared to the control group, after the treatment, the acupuncture group showed more decreaces significantly (P < 0.05). Another study (J.N. Wu et al., 2013) conducted a randomized control trial with 50 patients with sepsis, comparing acupuncture plus conventional treatment (n = 26) with conventional treatment alone (n = 24). The results showed that after 3 consecutive days of daily EA treatment, the plasma TNF-α, IL-6 in the “acupuncture plus conventional treatment” group were significantly lower than that in conventional treatment group, and its overall effect was also better. Similarly, F.W. Wu (2016) reported the effect of EA on the inflammatory response and immune function in sepsis patients. The 50 patients with sepsis were randomly divided into two groups of 25 each, i.e. the control group used the treatment plan recommended by the 2008 international guideline on the rescue of sepsis, and the acupuncture group used EA at ST 36 daily plus the treatment given to control group. The APACHE II scores, C reactive protein (CRP), PCT, Lac, and IL-6, IL-10 and T cell subsets (CD4+ and CD8+) were recorded before the treatments and 3 and 7 days after treatments in both groups. The rates of incidence of MODS and fatality rate during 28-day hospitalization were calculated. The results showed that after treatments, at each time point the APACHE II score, CRP, PCT, and Lac levels in both groups decreased to some extent, while the levels of CD4+ and CD8+ of T cell subsets involved in adaptive immunity increased in both groups; however, the EA group was better than the control group (P < 0.05). This indicated that EA at ST36 not only alleviated the pro-inflammatory response of patients with sepsis, but also improved adaptive immune function. This study importantly shows that the 28-day fatality rate in the EA group (8.00%) was significantly lower than that in control group (28.00%) (P < 0.05), while the incidences of MODS in EA group (24%) was lower than that in control group (36%) but not significantly (p > 0.05). Xiao et al. (2015) also obtained similar results. 90 patients with sepsis were randomly distributed to “conventional treatment” (n = 30), “conventional treatment + thymosin α1” (n = 30), and “conventional treatment + acupuncture” (n = 30). The fatality rate after treatment, and T cell subsets CD3+, CD4+, CD8+, CD4+/CD8+ ratio and the antibody IgG, IgA, IgM before and after treatment were compared between groups. The results showed that after 6 days of treatment, while the immune function with above items in all three groups of patients significantly increased (P < 0.01), that the thymosin group and the acupuncture group increased significantly more than in the conventional treatment group (P < 0.01, respectively). The ICU length of stay (days), and the rates of 28-day fatality also decreased significantly (P < 0.05, P < 0.01 respectively) in both the thymosin group and with the acupuncture group compared with the conventional treatment group. This suggests that acupuncture can improve adaptive immune function, and its effectiveness is comparable to that of thymosin, a recognized immune-stimulant used for the treatment of sepsis. This clinical data suggest that acupuncture not only decreases the pro-inflammatory factors but also enhances adaptive immune function to prevent immune-paralysis, which needs to be further confirmed.

Further, acupuncture can not only modulate immune function, but also improve organ functioning in multiple disorders. This also gives acupuncture as an advantage to treating MODS, imbalance of energy metabolism of sepsis. For example, a study by Yu et al. (2015) has shown that acupuncture can not only significantly improve the immune function of sepsis cases, but also protect the gastrointestinal function of septic patients. The incidence of vomiting, abdominal distension and gastric retention in the EA group (EA plus conventional treatment) were significantly reduced compared with the control (conventional treatment alone) group. Meng et al. (2018) also obtained the effects of attenuating inflammatory responses and intra-abdominal pressure in septic patients, but not the length of stay in intensive care unit (ICU) and 28 days fatality rate.

A recent meta-analysis (Tang et al., 2020) including 20 studies with total 1337 patients with sepsis showed that the 28 day fatality rate, the APACHE II score on the 3rd day and the 7th day after treatments, ICU length of stay, gastrointestinal function improvement, PCT and TNF-α on day 7 after treatments, in acupuncture plus conventional treatment group were all significantly superior to that in conventional treatment alone group statistically. All those research results (although still limited) indicate that acupuncture is a very promising integrative therapy for treating patients with sepsis.

5.4 임상 증거

실제 임상 환경에서 패혈증 환자는 특히 중증 단계에서 다양한 합병증을 동반할 수 있습니다. 따라서 동물 실험에서 침술 단독으로 패혈증 동물의 생존율을 유의하게 증가시켰음에도 불구하고, 최적의 결과를 얻기 위해서는 여러 요인을 다루기 위한 다양한 약물이나 치료법을 병용하는 것이 필요합니다. 전통 중의학자들은 수천 년 전부터 복잡한 질환, 특히 중증 감염을 치료하기 위해 침술과 한약을 함께 사용하는 것을 알고 있었습니다. 최근에는 침술을 현대 의학 치료와 통합하여 패혈증의 종합 치료 일부로 활용하는 것이 임상 시험에서 흥미로운 가치를 보여주고 있습니다. 임상 보고에 따르면 기존 치료에 침술을 추가한 군이 기존 치료 단독 군보다 우수한 효과를 보였습니다.

• L. Wang et al. (2019): 패혈증 환자 108명(대조군 54명, 침술군 54명)을 대상으로 한 무작위 대조 시험. 두 군 모두 기존 치료(항감염 약물, 장기 기능 지원 치료)를 받았으며, 침술군은 기존 치료에 더해 족삼리(ST36) 침술을 매일 3일 연속 시행했습니다. 치료 전후 비교 결과, 두 군 모두 혈장 프로칼시토닌(PCT), 혈중 젖산(Lac), APACHE II 점수, SOFA 점수가 유의하게 감소하였으나, 치료 후 침술군이 대조군에 비해 더 큰 감소폭을 보였습니다(P < 0.05).
• J.N. Wu et al. (2013): 패혈증 환자 50명을 대상으로 한 무작위 대조 시험(침술+기존 치료군 n=26, 기존 치료 단독군 n=24). 매일 3일 연속 전침(EA) 치료 후, 침술 병용군의 혈장 TNF-α, IL-6 수준이 기존 치료군보다 유의하게 낮았으며, 전체 효과도 더 우수했습니다.
• F.W. Wu (2016): 패혈증 환자 50명을 무작위로 두 군(각 25명)으로 나누었습니다. 대조군은 2008년 국제 패혈증 구호 지침에 따른 치료를 받았고, 침술군은 대조군 치료에 ST36 전침을 매일 추가했습니다. 치료 전, 치료 3일 및 7일 후 APACHE II 점수, CRP, PCT, Lac, IL-6, IL-10, T 세포 아군(CD4+, CD8+)을 기록하고, 28일 입원 기간 동안 다발성 장기 부전(MODS) 발생률과 사망률을 계산했습니다. 결과: 두 군 모두 치료 후 각 시점에서 APACHE II 점수, CRP, PCT, Lac이 감소하고 적응 면역 관련 CD4+ 및 CD8+ 수준이 증가하였으나, 전침군이 대조군보다 우수했습니다(P < 0.05). 이는 ST36 전침이 패혈증 환자의 전염증 반응을 완화할 뿐만 아니라 적응 면역 기능을 개선한다는 것을 보여줍니다. 특히 28일 사망률은 전침군 8.00%로 대조군 28.00%보다 유의하게 낮았습니다(P < 0.05). MODS 발생률은 전침군 24%로 대조군 36%보다 낮았으나 통계적으로 유의하지 않았습니다(p > 0.05).
• Xiao et al. (2015): 패혈증 환자 90명을 무작위로 기존 치료군(n=30), 기존 치료+티모신 α1군(n=30), 기존 치료+침술군(n=30)으로 배정했습니다. 치료 후 사망률, T 세포 아군(CD3+, CD4+, CD8+, CD4+/CD8+ 비율), 항체(IgG, IgA, IgM)를 비교했습니다. 6일 치료 후 세 군 모두 면역 기능 지표가 유의하게 증가하였으나(P < 0.01), 티모신군과 침술군이 기존 치료군보다 훨씬 더 큰 증가를 보였습니다(P < 0.01). ICU 재원 기간과 28일 사망률도 티모신군 및 침술군에서 기존 치료군에 비해 유의하게 감소했습니다(P < 0.05, P < 0.01). 이는 침술이 적응 면역 기능을 개선하며, 패혈증 치료에 사용되는 인정된 면역 자극제인 티모신과 비슷한 효과를 낸다는 것을 시사합니다.

이러한 임상 데이터는 침술이 전염증 인자를 감소시킬 뿐만 아니라 적응 면역 기능을 강화하여 면역 마비(immune-paralysis)를 예방할 수 있음을 보여주며, 이는 추가 확인이 필요합니다.

또한 침술은 면역 기능 조절뿐만 아니라 여러 장애에서 장기 기능을 개선합니다. 이는 패혈증의 다발성 장기 부전(MODS)과 에너지 대사 불균형 치료에 유리한 장점입니다.

• Yu et al. (2015): 침술이 패혈증 환자의 면역 기능을 개선할 뿐만 아니라 위장관 기능을 보호한다는 결과를 보였습니다. 전침+기존 치료군에서 구토, 복부 팽만, 위 정체 발생률이 기존 치료 단독군에 비해 유의하게 감소했습니다.
• Meng et al. (2018): 패혈증 환자에서 염증 반응 완화 및 복강 내 압력 감소 효과를 확인하였으나, ICU 재원 기간과 28일 사망률은 유의한 차이를 보이지 않았습니다.

최근 메타분석(Tang et al., 2020)은 총 1,337명의 패혈증 환자를 포함한 20편 연구를 분석하였습니다. 결과: 침술+기존 치료군이 기존 치료 단독군에 비해 통계적으로 유의하게 우수했습니다.

• 28일 사망률 감소
• 치료 3일 및 7일 후 APACHE II 점수 개선
• ICU 재원 기간 단축
• 위장관 기능 개선
• 치료 7일 후 PCT 및 TNF-α 수준 감소

이러한 연구 결과(아직 제한적이지만)는 침술이 패혈증 환자 치료를 위한 매우 유망한 통합 요법(integrative therapy)임을 강력히 시사합니다.

6 Discussion: toward a science-based design of EA protocol of immunomodulation

Given the current absence of recognized treatment protocols for immune dysfunction in the process of sepsis, based on above laboratory (i.e. preclinical studies) and clinical evidences, acupuncture could serve as an adjuvant therapy, with its advantage of being easily used, low cost, without any chemical side effects, and importantly, because of its ability to modulate both immune function and multiple organ function. All of which are beneficial to prevent the condition from worsening and to decrease the fatality rate of septic patients. We strongly recommend that acupuncture be included in the comprehensive treatment plan for sepsis. However, the therapies used in previous studies generally followed traditional theory or personal experience. Their selections of acupoints, stimulating parameters, daily dose and course of treatment might not be optimal; thus, it might limit their curative efficiency. To obtain better or maximal effects, we give an acupuncture protocol design based on the new knowledge developed from the researches described above. For the mechanism, stimulating peripheral nerves induces the somatic-autonomic reflex, which produces sympathetic or vagal effects on the functional regulation of organs or physiological systems, including the immune system we now focus on. The spinal somatic-sympathetic reflex follows the rule of the spinal cord segmental control, i.e. the effect of a somatic-sympathetic reflex on an specific organ is obtained limitedly by stimulating the somatic nerve connecting to the spinal cord segments (1–5 segments usually) as same as that the organ do. For example, the spleen is innervated by the sympathetic nerve from the spinal cord segment T5-T8, thus only the stimulation (electrical or acupunctural one) from the somatic nerve zone belonging to the T5-T8 segments can produce the reflex effect on the spleen. Similarly, T8-L1 for the adrenal medulla, and T1-T5 for the lung and so on, that a map with the details can be found in any anatomy textbook. The supraspinal somatic-sympathetic reflex might be induced by high intensity nociceptive stimulation, which is systemic, but rarely produced by acupuncture. The somatic-vagal reflex is special. Previous data showed the vagal reflex control the gastrointestinal tract can be induced by stimulation of the peripheral nerves or the acupoints at the limbs (not the trunk) with high intensity (activating Aδ and C fibers) of stimulation (Sato,1997; Li et al., 2007). However, to activate the vagal-adrenal reflex, a new data (Liu et al., 2020) showed that the stimulation of 0.5 mA (lower than the threshold of Aδ) is sufficient to do. To focus on immune function controlling, we name those reflexes as “somatic-autonomic-immune reflexes”; specifically, the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex, somatic-vagal-adrenal reflex, which induce systemic regulatory effects on immune functions because the final outputs are from the spleen or the adrenal medulla, which release cytokines or norepinephrine and dopamine into blood. However, the other somatic-sympathetic reflexes related to an organ have local effect only, e.g. the somatic-sympathetic-lung reflex, the somatic-sympathetic-kidney reflex, etc. It should be noted that stimulation of any acupoint can also produce common systemic effects or perhaps some unknown specific effects through the brain integration (both sympathetic and vagal ones) simultaneously, that need further studies. Those concepts and principles are illustrated in Fig. 3.

6. 논의: 면역 조절을 위한 전침(EA) 프로토콜의 과학적 설계 방향

현재 패혈증 과정에서 면역 기능 장애에 대한 공인된 치료 프로토콜이 없다는 점을 고려할 때, 위에서 제시된 실험실(전임상 연구) 및 임상 증거를 바탕으로 침술은 보조 요법(adjuvant therapy)으로 활용될 수 있습니다. 침술의 장점은 사용이 간편하고, 비용이 저렴하며, 화학적 부작용이 전혀 없다는 점이며, 무엇보다 면역 기능과 다발성 장기 기능을 동시에 조절할 수 있다는 점입니다. 이는 패혈증 환자의 상태 악화를 방지하고 사망률을 감소시키는 데 모두 유익합니다. 우리는 패혈증의 종합 치료 계획에 침술을 포함할 것을 강력히 권고합니다.

그러나 이전 연구에서 사용된 치료법은 대부분 전통 이론이나 개인적 경험에 기반하고 있습니다. 혈자리 선택, 자극 파라미터, 일일 용량, 치료 기간 등이 최적화되지 않았을 가능성이 크며, 이는 치료 효능을 제한할 수 있습니다. 더 나은 또는 최대한의 효과를 얻기 위해, 위에서 설명한 최신 연구 지식을 바탕으로 전침 프로토콜 설계 방향을 제안합니다.

기전 중심 원리 말초 신경 자극은 체성-자율신경 반사(somatic-autonomic reflex)를 유발하여 장기 또는 생리 시스템(특히 여기서는 면역계)의 기능 조절에 교감신경(sympathetic) 또는 미주신경(vagal) 효과를 발휘합니다.

• 척수 체성-교감 반사(spinal somatic-sympathetic reflex): 척수 분절 지배 규칙(spinal cord segmental control rule)을 따릅니다. 즉, 특정 장기에 대한 체성-교감 반사 효과는 해당 장기가 교감신경을 받는 척수 분절(보통 1~5개 분절)과 동일한 분절의 체성 신경을 자극할 때에만 제한적으로 나타납니다. 예: 비장은 T5-T8 분절에서 교감신경을 받으므로, T5-T8 분절에 속하는 체성 신경 영역(전기 또는 침 자극)만 비장에 반사 효과를 줄 수 있습니다. 유사하게: 부신수질은 T8-L1, 폐는 T1-T5 등. 자세한 지도는 해부학 교과서에서 확인할 수 있습니다.
• 상위 척수 체성-교감 반사(supraspinal somatic-sympathetic reflex): 고강도 통각 자극(nociceptive stimulation)에 의해 전신적으로 유발될 수 있으나, 침술로는 거의 일어나지 않습니다.
• 체성-미주 반사(somatic-vagal reflex): 특이합니다. 이전 데이터에 따르면 위장관을 조절하는 미주 반사는 사지(팔다리) 말초 신경 또는 혈자리 자극(체간이 아닌) + 고강도 자극(Aδ 및 C 섬유 활성화)으로 유발됩니다 (Sato, 1997; Li et al., 2007). 그러나 미주-부신 반사(vagal-adrenal reflex)를 활성화하는 데는 새로운 데이터(Liu et al., 2020)에 따르면 0.5 mA( Aδ 섬유 역치 이하) 자극만으로도 충분합니다.

면역 기능 조절에 초점 이러한 반사들을 우리는 “체성-자율신경-면역 반사(somatic-autonomic-immune reflexes)”로 명명합니다. 구체적으로:

• 체성-교감-비장 반사(somatic-sympathetic-splenic reflex)
• 체성-교감-부신 반사(somatic-sympathetic-adrenal reflex)
• 체성-미주-비장 반사(somatic-vagal-splenic reflex)
• 체성-미주-부신 반사(somatic-vagal-adrenal reflex)

이들 반사는 비장 또는 부신수질을 통해 사이토카인, 노르에피네프린, 도파민 등을 혈액으로 방출하여 전신 면역 기능에 조절 효과를 발휘합니다.

반면, 다른 장기와 관련된 체성-교감 반사(예: 체성-교감-폐 반사, 체성-교감-신장 반사 등)는 국소 효과만 나타냅니다.

추가 고려사항 어떤 혈자리를 자극하더라도 뇌 중추 통합(brain integration)을 통해 교감과 미주 모두를 포함한 공통 전신 효과(common systemic effects) 또는 아직 알려지지 않은 특이적 효과가 동시에 발생할 수 있으며, 이는 추가 연구가 필요합니다.

이러한 개념과 원리는 Fig. 3에 도식화

Figure viewer

Fig. 3 The organization of the somatic-autonomic-immune reflexes (the part of the figure showing the autonomic nervous system and organs is modified from Figure 296 of REF [Gao and Yu, 2014]). For explanation see the text.

6.1 An auxiliary acupuncture protocol

Following the above reflex principles and considering that the effects of acupuncture are state-dependent, stimulation-parameter-dependent, acupoint-dependent, and treatment-time-dependent, an auxiliary acupuncture protocol for sepsis treatment is designed as follows and summarized in Table 1:

1)

Acupoint selection: examples of acupoints we selected are listed below. It should be noted that following the segmental distribution to select acupoints is the key point here.

a.

Systemic regulation:

•

Vagal Group: ST36 (Zusangli) or LI4 (Hegu), bilaterally (the same below). They are the most effective acupoints reported from laboratorial and clinical studies, activating vagal anti-inflammatory pathway to down-regulating cytokines storm;

•

Sympathetic Group: BL17 (Geshu) and BL19 (Danshu) on the back; or ST21 (Liangmen) and ST25 (Tianshu) on the abdomen, to activate the sympathetic-splenic reflex and the sympathoadrenal medullary reflex, additionally benefiting to septic shock patients due to the norepinephrine releasing.

b.

Local regulation:

•

Thoracic group: BL13 (Feishu) and HT7 (Shenmen).

•

Abdominal group (gastrointestinal organs, liver and kidneys): BL19 (Danshu) and ST25 (Tianshu).

•

Pelvic group: BL23 (Shenshu) and SP6 (Sanyinjiao).

b.

The formula of acupoints we recommend:

Formula I: Vagal group + Local group/s (if needed);

Formula II: Sympathetic group + Local group/s (if needed).

The two formulas are used in turns.

2)

Stimulation parameters: for the intensity of EA, it is recommended to give moderate stimuli which can cause slight muscle twitching and also be tolerated by patients. To prevent sepsis in patients in the early stages of infection, high-intensity stimulation is recommended; that perhaps causes more of a pain sensation. Applying EA “continuing trains” with the frequency of 2–10 Hz for 30 min is a general EA dose. However according to the frequency effect (Chen et al., 2016), here we recommend using “alternating trains” of 2/15 Hz or 2/100 Hz, (100 Hz to enhance sympathoadrenal medullary reflex, Kim et al., 2008) for systemic effects, and “bursting trains” with high frequency (15-100 Hz) for local effects. If using the traditional manual acupuncture, we suggest mimicking the “alternating trains”, applying a light or moderate stimulation (a slow rotation) of 2–5 min/10 min for 30 min, given that manual acupuncture can activate all groups of sensory nerve fibers (Kagitani et al., 2010) and a slow rotation of needle is efficient to induce anti-inflammatory effect (Lim et al., 2016; Ramires et al., 2020).

3)

Daily dose and course of treatment: considering that the inhibitory effects of one treatment of EA on most inflammatory factors last for about 6 h (Song et al., 2012; Torres-Rosas et al., 2014), the daily dose we suggest is 2 times/day for patient with sepsis; one time/day for early stage of acute infection. Formula I and Formula II will be used in turns. Take a course of 5–7 days with a break of 1–3 days, because the toleration might happen after 7 days with continuous daily treatments (Du et al., 1995). For severe infection such as COVID-19, the sooner the intervention is performed, the better.

4)

Self-healing: for mild cases or early stages of the infection, the transcutaneous electrical stimulator (TENS) can be used by patients themselves.

EffectsReflexAcupointsPulse trainsFrequency (Hz)IntensityDose & course

Systemic	Vagal reflex	ST36 (Zusanli) LI4 (Hegu)	A B C	2/15 or 2/100 15 2	Moderate	2 times/day, 5–7 days
Systemic	Sympathetic-splenic	BL17 (Geshu) ST21 (Liangmen)	A B C	2/100 or 2/15 100 or 15 15	Moderate	2 times/day, 5–7 days
	Sympathetic-adrenal	BL19 (Danshu) ST25 (Tianshu)	Same
Local organs	Sympathetic (thoracic)	BL13 (Feishu) HT7 (Shenmen)	B	15 or 2	Moderate	2 times/day, 5–7 days
	Sympathetic (abdominal)	BL19 (Danshu) ST25 (Tianshu)	Same
	Sympathetic (pelvic)	BL23 (Shenshu) SP6 (Shanyinjiao)	Same

Table 1

An example design of evidence-based therapy of EA to modulate immunity in sepsis.

A: alternating trains; B: bursting trains; C: continuing trains.

• Open table in a new tab

6.2 Limitations and future research

As discussed above, acupuncture is supported by a large amount of research data both in clinical trials and animal studies in resolving cytokine storms during severe inflammation; however, there still exist many unsolved gaps. There are several limitations to this review aside from those discussed above. 1) Although acupuncture's anti-inflammatory storm has been repeatedly confirmed by animal experiments, and the effect of acupuncture in inhibiting inflammatory storms through neuroimmune pathway is almost certain, it should be noted that current experimental results mostly come from CLP models and LPS models. It is necessary to further compare the differences between these two and expand to other new models. In particular, a new direction is to establish an immune-paralysis model in late-stage sepsis. 2) More detailed research is needed in acupoint selection and stimulation parameters. 3) Time-window of acupuncture effect is worthy enough to do further systematic research: identifying the acupuncture effect during different development stages of sepsis, i.e. pretreatment, and its early, middle, and late stages. This needs to combine with acupoint selection and stimulation parameters. 4) Refining and deepening is needed in the bidirectional regulating effect and mechanism of acupuncture in terms of immune regulation. In particular, given that the suppressing effects of acupuncture on cytokine storms has been well addressed, next challenge is investigating the effects of acupuncture on immune-paralysis in sepsis. 5) Most of previous studies focused on systemic effects of acupuncture or other peripheral nerve stimulation. A new direction is identifying local effect produced by local segmental reflexes, that will provide scientific bases of acupoint selection to clinical therapy design. 6) Any peripheral stimulation might produce both local spinal segmental reflexes and supra-spinal reflexes. Local segmental reflexes might co-work with its supra-spinal reflexes, or have independent effect, that can be used in different situation. This is a basic question of acupuncture and very important for selecting acupoints in a therapy. The interactions and mechanisms of local spinal segmental reflexes and supra-spinal reflexes produced by acupuncture need to be further studied extensively, not only for inflammation but for all other disorders. 6) Current acupuncture clinical trials have some quality issues. The quality of most reports has been criticized due to insufficient sample sizes and lacking proper sham controls. Indeed, the feature of acupuncture different from drug's makes the design of sham acupuncture control difficult to meet the rules of double-blind clinical study. To avoid such problems, the National Institutes of Health (NIH) is currently advocating real-world clinical research in view of the characteristics of acupuncture (Zia et al., 2017). However, according to the results of current animal and clinical experiments, there are large varieties of the effects of acupoints and stimulation parameters, that some of them showed significant effects but others with little effects on same treatment targets (e.g. Chen et al., 2016; Li et al., 2015). Such little effective acupoints or stimulation parameters give an idea “sham” control manipulation. By using such parallel design, Li et al. (2015) showed the effects of long-lasting reduction of blood pressure in a group treated with specific acupoints but not in the other group with different acupoints. We strongly recommend such parallel design, that uses invalid acupoints or stimulation parameters as “sham” control group to rule out placebo effect. Parallel design is well known as the “gold standard” for phase 3 clinical trials. It is just very well for clinical study of acupuncture. Anyhow, systematic, large and rigorous clinical data will be the key for supporting in acupuncture-assisted immune adjustment in the treatment of sepsis. The acupuncture protocol designed in this article is just one example of suggestions for future clinical research, which is based on current available literature. We hope that this protocol would be inspiring and promoting the translation from scientific study to clinical application. Given that there are gaps in acupuncture mechanisms, and between acupuncture real practice and basic science study in treating sepsis, further studies in both acupuncture mechanisms and clinical trials are warranted.

7 Summary

Faced with the severe situation of the global pandemic of COVID-19, the medical community throughout the world is exploring various treatments from different approaches, including antiviral, anti-inflammatory, and controlling multiple organ functions. It has been identified that COVID-19 induces immune disorder and sepsis in severe patients (Yuki et al., 2020). A new study demonstrated that COVID-19 cytokine storms, especially a high level of TNF may make few memory B cells and prevent a durable immune response (Kaneko et al., 2020). For fatal sepsis with multiple organ failure, the imbalance of immune function is the core pathological mechanism, and the various therapies for controlling the immune function currently have no recognized best choice for various reasons. At this moment, acupuncture used to activate the somatic-autonomic-immune reflexes is a promising therapy emerging from multiple recent animal experiments and clinical studies, to provide significant clinical advantage to control inflammation and restore organ function without adverse side effects. Different from a new drug investigation needing a phase I clinical trial (screening the safety and testing the proper dose), acupuncture with its safety feature, has been carried out at least in phase II like clinical trials for a variety of diseases for years throughout the world. If acupuncture is involved in the treatment of COVID-19, the patients will not only avoid losing a promising adjunctive therapy, but it would also be a good opportunity obtaining a large number of patients to test the efficiency of acupuncture in a clinic trial. Previous studies from animal models and clinical trials have shown that acupuncture modulates immunity, but it has yet been consistent with showing that acupuncture decreases the fatality rate of sepsis patients. Besides the complicated process of sepsis, one main reason is that the efficiency of acupuncture depends on several factors such as the pathological status, the acupoints, the stimulation parameters and the time-window of treatment etc. that need well consideration together to obtain maximal effects. We recommend an evidence-based comprehensive design of EA protocol to practitioners and researchers to test it. It is worth looking forward to its contribution to the treatment of sepsis and, for the moment, to treating the urgent need of patients with COVID-19 infection as well as for future patients with various infections and other factors.

Declaration of competing interest

Author Sarah Faggert Alemi was employed by the company Eastern Roots Wellness, PLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AcknowledgmentsAcknowledgements

We thank Dr. Qiufu Ma for his feedback on the manuscript.

CRediT authorship contribution statement

This project was initiated by WX Pan and A.Y. Fan. As the primary researcher, WX Pan designed the project and protocol, structured and drafted the early version of manuscript. A.Y. Fan, SZ. Chen and S.F. Alemi participated in discussing, further drafting and editing the later versions. WX. Pan and A.Y. Fan completed the final manuscript. There was no financial support for this project. Due to the limitation of the authors' personal experience and perspective, this review may have some omissions and errors; comments or corrections are welcomed and appreciated.

References

1.

Bassi, G.S. ∙ Dias, D.P.M. ∙ Franchin, M. ...

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Brain Behav. Immun. 2017; 64:330-343

Crossref

Scopus (71)

PubMed

Google Scholar

2.

Behrens, E.M. ∙ Koretzky, G.A.

Cytokine storm syndrome: looking toward the precision medicine era

Arthritis Rheumatol. 2017; 69:1135-1143

Crossref

Scopus (226)

PubMed

Google Scholar

3.

Bellinger, D.L. ∙ Lorton, D.

Autonomic regulation of cellular immune function

Autonomic Neuroscience: Basic and Clinical. 2014; 182(15–41):2014

Google Scholar

4.

Berlot, G. ∙ Passero, S.

Immunoparalysis in Septic Shock Patients. Patients [Online First]

IntechOpen, 2019

https://www.intechopen.com/online-first/immunoparalysis-in-spetic-shock-patients

Crossref

Google Scholar

5.

Bernik, T.R. ∙ Friedman, S.G. ∙ Ochani, M. ...

Pharmacological stimulation of the cholinergic antiinflammatory pathway

J. Exp. Med. 2002; 195:781-788

Crossref

Scopus (458)

PubMed

Google Scholar

6.

Borovikova, L.V. ∙ Ivanova, S. ∙ Zhang, M. ...

Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin

Nature. 2000; 405:458-462

Crossref

Scopus (3326)

PubMed

Google Scholar

7.

Cao, J.R., Gong, Q. H., Xiang, Y. M. (1982). Effect of acupuncture on the output lymph and cell in popliteal lymph nodes in rabbits. Shanghai J Acu-moxi. 1, 35–37.

Google Scholar

8.

Chavan, S.S. ∙ Tracey, K.J.

Essential neuroscience in immunology. J Immunol. 2017; 198:3389-3397

Google Scholar

9.

Chen, Y., Lei, Y., Mo, L.Q., Li, J., Wang, M.H., Wei, J.C., et al. (2016). Electroacupuncture pretreatment with different waveforms prevents brain injury in rats subjected to cecal ligation and puncture via inhibiting microglial activation, and attenuating inflammation, oxidative stress and apoptosis. Brain Res Bull. 127, 248–259.

Google Scholar

10.

Choi, G.S. ∙ Oha, S.D. ∙ Han, J.B. ...

Modulation of natural killer cell activity affected by electroacupuncture through lateral hypothalamic area in rats

Neurosci. Lett. 2002; 329:1-4

Crossref

Scopus (26)

PubMed

Google Scholar

11.

da Silva, M.D. ∙ Guginski, G. ∙ Werner, M.F. ...

Involvement of interleukin-10 in the anti-inflammatory effect of Sanyinjiao (SP6) acupuncture in a mouse model of peritonitis

Evid. Based Complement. Alternat. Med. 2011; 2011:217946

Crossref

Scopus (50)

PubMed

Google Scholar

12.

Dai, Q.M., Shang, Y.Q., Liang, H., Yan, P.Y., Wang, M.Q., Wang, K. (2018). Research progress of effect of acupuncture therapy on T cell subsets. J Clin Acupunct. 7,78–82.

Google Scholar

13.

De Ferrari, G.M. ∙ Crijns, H.J.G.M. ∙ Borggrefe, M. ...

Chronic vagus nerve stimulation: a new and promising therapeutic approach for chronic heart failure

Eur. Heart J. 2011; 32:847-855

Crossref

Scopus (426)

PubMed

Google Scholar

14.

de Jonge, W.J. ∙ van der Zanden, E.P. ∙ The, F.O. ...

Stimulation of the vagus nerve attenuates macrophage activation by activating the Jak2-STAT3 signaling pathway

Nat. Immunol. 2005; 6:844-851

Crossref

Scopus (918)

PubMed

Google Scholar

15.

Den, G.G.

ReviewVolume 232102793May 2021Open access

Download Full Issue

Acupuncture modulates immunity in sepsis: Toward a science-based protocol

Wei-Xing Pana panw@hhmi.org ∙ Arthur Yin Fanb,c ArthurFan@ChineseMedicineDoctor.us ∙ Shaozong Chend,1 zjyjs1980@sdutcm.edu.cn ∙ Sarah Faggert Alemib,e

Affiliations & Notes

aJanelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA

bAmerican TCM Association, Vienna, VA 22182, USA

cMcLean Center for Complementary and Alternative Medicine, PLC, Vienna, VA 22182, USA

dAcupuncture Research Institute, Shandong University of Chinese Medicine, Jinan 250355, China

eEastern Roots Wellness, PLC, McLean, VA 22101, USA

1

Dr. Chen is the lead corresponding author of this paper.

Article Info

Publication History:

Received November 26, 2020; Revised January 26, 2021; Accepted February 25, 2021; Published online February 27, 2021

DOI: 10.1016/j.autneu.2021.102793 External LinkAlso available on ScienceDirect External Link

Copyright: © 2021 The Authors. Published by Elsevier B.V.

User License: Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | Elsevier's open access license policy

• Download PDF
• Cite
•  
• Set Alert
• Get Rights
• Reprints

Download Full Issue

Previous articleNext article

Show Outline

Highlights

•

Acupuncture modulates immunity and improves organ functions in sepsis, emerging as a promising therapy of immunomodulation.

•

Acupuncture obtains its regulatory effect via the somatic-autonomic-immune reflexes.

•

Such reflexes include the sympathetic-splenic, sympathetic-adrenal, vagal-splenic and vagal-adrenal reflexes, inducing systemic effects.

•

There are also local reflexes activated by acupuncture, such as the somatic-sympathetic-lung-reflex, inducing local effects.

•

A comprehensive EA protocol is designed based on the evidenced mechanisms.

Abstract

Sepsis is a serious medical condition in which immune dysfunction plays a key role. Previous treatments focused on chemotherapy to control immune function; however, a recognized effective compound or treatment has yet to be developed. Recent advances indicate that a neuromodulation approach with nerve stimulation allows developing a therapeutic strategy to control inflammation and improve organ functions in sepsis. As a quick, non-invasive technique of peripheral nerve stimulation, acupuncture has emerged as a promising therapy to provide significant advantages for immunomodulation in acute inflammation. Acupuncture obtains its regulatory effect by activating the somatic-autonomic-immune reflexes, including the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex and the somatic-vagal-adrenal reflex, which produces a systemic effect. The peripheral nerve stimulation also induces local reflexes such as the somatic-sympathetic-lung-reflex, which then produces local effects. These mechanisms offer scientific guidance to design acupuncture protocols for immunomodulation and inflammation control, leading to an evidence-based comprehensive therapy recommendation.

Abbreviations

1. Acupoint (acupuncture point)
2. APS (antigen-presenting cells)
3. ARDS (acute respiratory distress syndrome)
4. APACHE II (acute physiology and chronic health score)
5. CARS (compensatory anti-inflammatory response)
6. COVID-19 (coronavirus disease 2019)
7. CRP (C reactive protein)
8. EA (electroacupuncture)
9. ICU (Intensive Care Unit)
10. IL (interleukin)
11. MODS (multiple organ dysfunction syndrome)
12. LAC (blood lactic acid)
13. NK (natural killer)
14. PCT (procalcitonin)
15. SARS (severe acute respiratory syndrome)
16. TNF (tumor necrosis factor)
17. SOFA (systemic infection-related organ failure score)
18. VNS (vagus nerve stimulation)

Keywords

1. Nerve stimulation
2. Acupuncture
3. Electroacupuncture
4. Sepsis
5. Inflammation
6. Anti-inflammation
7. Inflammatory reflex
8. Immune dysfunction
9. Somatic-sympathetic reflex
10. Somatic-vagal reflex

1 Introduction

Sepsis is defined as life-threatening organ dysfunction, caused by a dysregulated host response to infection (Gotts and Matthay, 2016; Singer et al., 2016), which clinically manifests as severe systemic inflammatory response, Acute Respiratory Distress Syndrome (ARDS), Septic Shock, or Multiple Organ Dysfunction Syndrome (MODS). It is the number one killer in the Intensive Care Unit (ICU). Globally, there are approximately 30 million cases of sepsis each year, with a fatality rate as high as 30% (Reinhart et al., 2017). The Coronavirus Disease 2019 (COVID-19), which has developed into a global pandemic, is a current example of a manifestation of severe sepsis. Similar to other infections, deaths resulting from COVID-19 have been related to sepsis, which causes septic shock, MODS, and ARDS in particular (C. Wang et al., 2020; D. Wang et al., 2020; Z. Wu and McGoogan, 2020). Reducing inflammation and correcting organ dysfunction are the core strategies of clinical treatment of sepsis. However, due to the lack of a specific and effective antiviral drug, how to effectively treat sepsis has been a clinical challenge for a long time, especially for sepsis caused by viral infection. Traditionally, steroids, i.e. adrenocortical hormones, were once the major anti-inflammatory drugs used for this condition; however, they were unsatisfactory due to their serious side effects and sequelae. Recent immunotherapy drugs, such as siltuximab and tocilizumab, present hope but are yet to be eval‎uated and summarized for further development and clinical application. Fortunately, experimental animal studies in recent years have shown that a simple non-pharmacological approach shows the effect of anti-septicemia (for a review, see Lai et al., 2020). That approach is peripheral nerve stimulation done through both electroacupuncture (EA) and manual acupuncture (in short, acupuncture). Studies have shown that acupuncture is a promising alternative clinical anti-inflammatory therapy. Several lines of evidence published in recent years, from the researches of immunomodulatory mechanisms (for reviews, see, i.g. Tracey, 2002; Ulloa, 2005; Huston et al., 2006; Behrens and Koretzky, 2017; Pavlov et al., 2018; Berlot and Passero, 2019), the experiments of acupuncture in animal models (for a review, see Lai et al., 2020) and in patients of clinical trials (for a review, see Tang et al., 2020), support the antiseptic effect of acupuncture. Such a non-pharmacological and non-invasive approach has attracted the attention of the clinical medicine community and has been advocated by some leading researchers (Ulloa et al., 2017; Pavlov and Tracey, 2017). However, the clinical translation in practice with details is still lacking. This article aims to offer a brief comprehensive review and develop an evidence-based EA therapy for immunomodulation in acute inflammation to promote further research and clinical application.

2 Pathophysiology of sepsis

Sepsis is initiated by an infection. However, it has been known that the clinical manifestations and pathological complications of sepsis are not caused directly by invading pathogens, but rather by a disorder of the host's immune reaction (Hamers et al., 2015; Behrens and Koretzky, 2017). The main pathophysiological process of infectious diseases is the body's response to bio-immunogenic substances, that is, inflammatory reactions with defense properties. With the advancement of immunopathology research, more details of the inflammatory process have been understood (Gotts and Matthay, 2016; Singer et al., 2016; Reinhart et al., 2017; Sladkova and Kostolansk, 2006; Tisoncik et al., 2012; Wiersinga et al., 2014). The body's immune system is functionally divided into innate immunity and acquired adaptive immunity. When pathogenic microorganisms invade the body for the first time, the innate immune system responds accordingly, starting the inflammatory process. First, macrophages recognize and engulf the pathogens. While destroying and inactivating them, some antigen-presenting cells (APCs) can recognize the antigenic characteristics of pathogens and then transmit to B cells; the adaptive immune system is then activated to generate specific antibodies, which can more accurately and efficiently kill pathogens. Long-term memory of antigen information forming, and then lifelong immunity will be generated. However, antibody production takes a long time, around 5–10 days. Fortunately, the innate immune system immediately goes forward to start the battle of non-specific immunity, rather than waiting for the arrival of specific antibodies. Immune cells and infected tissue cells quickly release a batch of cytokines and pro-inflammatory substances under the stimulation of pathogens, such as interleukin IL-1, IL-8, IL-18, tumor necrosis factor TNF-α, IL-6, IL-33, type I and III Interferons (IFN), etc. which are called primary cytokine storms (Behrens and Koretzky, 2017). These cytokines exert a variety of different immune functions. For example, IL-1 is an important initiator of the inflammatory response; TNF has a strong killing effect; IFN has an antiviral effect and can limit virus replication and spread, protecting uninfected cells from being affected by virus invasion; chemokines IL-8 can induce the recruitment of more immune cells toward the infection site; some cytokines can activate the neuroendocrine system, leading to increased body temperature, breathing, circulation, metabolism and other functions. At the same time, these cytokines have a positive feedback effect, which can activate immune cells to release more cytokines, forming a secondary wave of cytokine storms and further strengthening the inflammatory response in order to effectively kill the pathogens (Guo and Thomas, 2017). If this process is successful, the pathogen may be eliminated, or at least prevented from spreading until the specific antibodies (IgM) are produced and the pathogen is destroyed. Once this occurs, the body enters the rehabilitation phase, removing necrotic cells and repairing damaged tissue. This is the general clinical process of many inflammatory infections, which generally last for 1–2 weeks and end through self-healing alone. Unfortunately, a significant proportion of patients progress to a worsening course of disease and develop sepsis. In severe cases, ARDS, septic shock, and MODS are fatal. The core problem of sepsis is a disturbance of the functioning of the immune system. Its pathophysiological mechanism is that the patient is prone to excessive inflammatory reactions in the early stage of the infection, which is the aforementioned cytokine storm phenomenon, also clinically called cytokine release syndrome (CRS). During the normal inflammatory response, when a large number of pro-inflammatory factors are released, the release of anti-inflammatory factors such as IL-4, IL-10, IL-11, IL-13, and IL-1Ra are also initiated, as a self-balance regulation of the immune system, called “compensatory anti-inflammatory response” (CARS) (Berlot and Passero, 2019). The emergence of sepsis is caused by a disorder in the dynamic balance between pro-inflammatory and anti-inflammatory factors, the excessive secretion of multiple pro-inflammatory factors, and the intensification under the positive feedback mechanism. While attacking the pathogen, it also damages the normal tissue cells of the body, leading to important organs or system dysfunction or even failure. However, that is not all that occurs during sepsis. It has recently been discovered that the mechanism behind sepsis is more complicated than previously thought. Not only does the immune response become hyperactive in the early stage, but also CARS is activated at the same time to limit the tissue damage. However, the CARS can represent a double-edged sword. It might be beneficial to restore immune balance; yet, it might cause the shutdown of the immune response if it over responds, inducing the status of immune-paralysis (Hamers et al., 2015; Berlot and Passero, 2019). With immune-paralysis, there can be a reduction of immune-related receptors, apoptosis of various immune cells (T cells, B cells, macrophages, dendritic cells), weakened antigen presentation function of APCs, and increased suppressive lymphocytes, etc., leading to both innate and adaptive immune functions that are severely weakened. This makes it difficult to clear the damaged tissues in later stages. It is also easier to activate latent pathogens and cause a secondary infection. Even worse is that some patients might have problems with immune-paralysis at the early stage, or multiple hits of the cytokine storm phenomenon ultimately leading to the exhaustion of the immune response, which makes treatment more difficult. Therefore, it is necessary to enhance immunity in the later stage as well, which has become a new focus of both basic science and clinical studies. The patterns of inflammatory reaction have been proposed theoretically (Berlot and Passero, 2019), shown in Fig. 1.

Figure viewer

Fig. 1 The immune reaction patterns (reproduced from Berlot and Passero, 2019). A. Possible clinical trajectories of patients with sepsis shock. Line 1, intense hyper-inflammatory reaction followed by CARS and the return to the baseline immune state. Line 2, weak hyper-inflammatory reaction followed by immune-paralysis and immune restoration. Line 3, immune-paralysis not preceded by a hyper-inflammatory reaction. B. The multiple hits phenomenon ultimately leading to the exhaustion of the immune response.

3 Difficulties in regulating immune function in the treatment of sepsis

The treatment of sepsis needs to address three aspects: reducing the pathogens (such as fighting the bacterial or viral infection, if applicable), reducing inflammation, and correction of various physiological dysfunctions. Multiple organ dysfunctions are closely related to inflammation, so reducing inflammation is an important aspect to be dealt with in its early and middle stages. Anti-inflammation or reducing inflammation means regulating immune function. The immune system consists of a variety of functional cells and molecular signaling pathways that form an extremely complex regulatory network. Normal inflammatory response is a dynamic equilibrium process of immune cells and molecular networks. The imbalance of septicemia manifests as early immune hyperactivity and late immune paralysis (Berlot and Passero, 2019) Theoretically, treatment should be to give inhibitory intervention in the early stages, followed by a strengthening intervention. However, it is difficult to make a decision in delivering the specific interventions in real clinical settings. There have been large numbers of anti-inflammatory medications previously used, including corticosteroids, aspirin, monoclonal antibodies, anti-cytokines, anti-chemokines, etc., the effectiveness of which is inconclusive, with some also leading to worsening of the condition. There are several reasons for this. First, in terms of the magnitude of the immune response, how much cytokine release during the inflammatory response can be determined to be “excessive”? It is difficult to define because of the physical condition of patients, such as age, gender, and possible chronic underlying disease. Second, in terms of phases, the turning point of the immune response from the hyper-phase to the hypo-phase is difficult to predict. Unlike antibiotics that advocate early use, immuno-suppressants are generally considered only when clinical symptoms are severe. At this time, immune hyperactivity may have peaked and begun to show a downward trend. Immuno-suppressants may be redundant and even cause immune paralysis quickly. This may be one of the reasons why traditional steroids (adrenal cortex hormones) or targeted therapies that target specific cytokines (for example, antagonists such as the IL-6 blocker siltuximab and the IL-6R blocker tocilizumab) often fail. Clinical effect has not been reached on the effects of these two types of therapy on reducing mortality. Third, regardless of the overall inhibition of steroids (adrenocortical hormones) or single-factor targeted therapy, they are not the normal physiological regulation. This makes it easy to create new imbalances. For example, reducing the recruitment and activation of neutrophils can reduce the damage to normal tissues, but also reduce the lethality to pathogens, leading to the spread of infection. Fourth, in recent explorations, the administration of immune stimulators in later phases is said to be promising, although biomarkers to stratify the immune status are still in development (Peters van Ton et al., 2018). However, once into the late phase, multiple organ dysfunctions may be enough to cause death and immune stimulators may seem meaningless. The only significance of immune stimulators is that of patients with direct immune paralysis in the early phases, but reliable diagnostic indicators are needed. Therefore, the ideal approach is the therapy closest to physiological regulation. Perhaps turning to the neuromodulation of immune responses is a promising direction.

4 Neural regulation of immunity

The immune system was once thought to be an independent regulatory system in the body. The role of the nervous system in regulating immune function has not been known until recent decades, although it has an ancient existence in the history of biological evolution. For example, there are simple organisms, such as C elegans, whose immune cells have been affected by neural signals. In higher animals the brain has been regarded as an immune privileged organ with powerful influence in immunity. The immune system, nervous system and endocrine systems constitute a functional regulatory network (Fig. 2). Based on the functional organization of neuroendocrine and autonomic control, the nervous system can efficiently affect immune function in two ways: through central control and peripheral reflex. The effect of psychological stress on immune function is an example of central control. Peripheral reflex regulation is a more common process, such as inflammatory reflexes (Borovikova et al., 2000; Tracey, 2002). The inflammatory cytokines can stimulate peripheral sensory nerves, including somatic and visceral sensory nerves, or they can directly enter the brain to activate the center integrative effects on immune function, acting through the neuroendocrine or autonomic outputs. The neuroendocrine output is mainly the hypothalamic-pituitary-adrenal (HPA) axis, which has an inhibitory regulating effect on immune function. However, recently it has been noticed that the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamic-pituitary-gonadal (HPG) axis, and the hypothalamic-growth-hormone (HGH) axes are also involved in modulating immune activities (Eskandari et al., 2003). These axes need to be further studied. Autonomic outputs include the sympathetic and vagus nerves, both of which control the immune system and inflammation, which is the focus of this article.

Figure viewer

Fig. 2 The immune network. The immune system, nervous system and endocrine systems constitute a functional regulatory network. The dynamic balance of immune activity is controlled by the interactions of immune cells and cytokinesis (the left part of the figure adapted from Sladkova and Kostolansk, 2006), which accepts the regulation of the brain (the right part of the figure). The brain regulates the immune system with two major outputs: one is the hormonal system including the HPA, HPTs, HPG, and HGH axes (Eskandari et al., 2003); and the other is the autonomic nervous system consisting of sympathetic norepinephrine and vagal acetylcholine pathways. The immune system can also regulate the nervous system through cytokines which activate the afferent nerves or enter the brain directly.

It has been known for a long time that the sympathetic nerves regulate the immune system extensively and complexly, but they have gained increasing interest and attention in recent years. As a result, new knowledge has developed (Eskandari et al., 2003; Olofsson et al., 2012; Jänig, 2014; Jänig and Green, 2014; Bellinger and Lorton, 2014; Pavlov and Tracey, 2017; Chavan and Tracey, 2017). In brief, sympathetic nerves contains nerve fibers (from postganglionic neurons) that specially innervate immune organs including the primary lymphoid organs, i.e. marrow and thymus, and the secondary lymphoid organs, i.e. spleen, lymph nodes, and mucosa-associated lymphatic tissue (Jänig, 2014; Bellinger and Lorton, 2014; Chavan and Tracey, 2017). The sympathetic postganglionic neurons release norepinephrine transmitters which activate β- and α- adrenergic receptors on immune cells, producing the regulatory effects (Bellinger and Lorton, 2014). The β- and α2-adrenergic receptors have opposite effects on immune responses to inflammation (Szelényi et al., 2000; Liu et al., 2020). The hypothalamic area has been thought as a high level center of the autonomic nervous system, which is also known to have extensive influence on immune functioning (for reviews, see Wrona, 2006). Some sub-areas of the hypothalamus might play specific roles in modulating immune functions, e.g. in animal model, electrical stimulation of the lateral hypothalamic area increased natural killer cell cytotoxicity in spleen, while stimulation of the ventromedial hypothalamic area showed suppression effect (Wrona and Trojniar, 2003, 2005). Such hypothalamic-splenic immune modulation is mediated by the sympathetic efferent pathway; therefore, the “hypothalamic-sympathetic-splenic axis” was proposed (Okamoto et al., 1996). The hypothalamus might be involved in the peripheral reflex to modulate immunity (Son et al., 2002; Hahm et al., 2004). Martelli and colleagues (Martelli et al., 2014a, 2014b, 2016, 2019), with a series of experiments in rodents, have identified the greater splanchnic nerve as the sympathetic efferent arm of the inflammatory reflex to inhibit inflammatory cytokines in the spleen as well as in other inner organs innervated by the nerve such as liver, gastrointestinal tract and importantly, the adrenal, as systemic immune cell function can also be regulated through the adrenal medulla with catecholamine releasing. In addition, recent studies have shown that selective somatic local effects of sympathetic innervations on immune functions are available via a direct interaction of the postganglionic nerves with local immune cells. Bassi et al. (2017) showed that direct stimulation of the lumbar sympathetic trunk reduced neutrophil recruitment in arthritic knee joints, and the same effect resulted from direct injection of norepinephrine into the joint. Given the well-known function of the somatic-sympathetic reflex, one might predict that selective stimulation of somatic nerve connecting to the same segment of the spinal cord from which the sympathetic efferent fibers innervate a specific organ or tissue, might produce a local effect of immune regulation of the specific organ or tissues. Indeed, Kim et al. (2007, 2008) have found that electroacupuncture (EA) at Zusanli (ST36) acupoints suppressed zymosan- or carrageenan-induced paw inflammation. Interestingly, they found that low frequency (1 Hz) EA obtained the local suppression effect via activation of sympathetic postganglionic neurons, the simple somatic-sympathetic reflex; while high-frequency (120 Hz) EA suppression is mediated by the sympathoadrenal medullary axis to induce systemic catecholamines for whole body effects. A very recent study (S.B. Liu et al., 2020) showed that selective stimulation of acupoint Tianshu (ST25), which connects to the same segment of the spinal cord sending sympathetic innervation to spleen, evoked the somatic-sympathetic-splenic reflex, produced systemic effect of immune modulation. This new knowledge of different immune reflex paths is very valuable to selective treatment of specific organs and local tissue with inflammation and dysfunction.

More recent knowledge shows that the vagus nerve controls immune function by dominating the spleen and adrenal medulla. The first discovery is the “cholinergic anti-inflammatory pathway” (Borovikova et al., 2000) and then developed the concept of “inflammatory reflex”(Tracey, 2002). In brief (for full reviews, see Ulloa, 2005; Huston et al., 2006; Olofsson et al., 2012; Inoue et al., 2016; Pavlov and Tracey, 2017; Pavlov et al., 2018; Huh and Veiga-Fernandes, 2020), the vagal nerve center can be activated by an immune challenge, and then the vagus nerve efferent terminals releasing cholinergic transmitters, innervate the spleen, perhaps relayed by the splenic nerve (Komegae et al., 2018) (but see Martelli et al., 2014c, 2016), and through the α7 nicotinic receptor on macrophages and other immune cells, inhibit the release of pro-inflammatory cytokines such as TNFα and IL-1 etc. Activation of this pathway by electrical or pharmacological stimulation suppresses excessive inflammation in the gastrointestinal tract (de Jonge et al., 2005; Ghia et al., 2006, 2007), pancreas (van Westerloo et al., 2006), liver (Guarini et al., 2003) and heart (Bernik et al., 2002), inhibiting systemic inflammation. Recent experiments in mice model (Torres-Rosas et al., 2014) have found that the vagus nerve can also dominate the adrenal medulla and activate the latter to release dopamine to inhibit the release of pro-inflammatory cytokines and increase the survival rate of the animals with sepsis. Kwan et al. (2016) have systematically reviewed 36 eligible studies from 290 identified records of vagus nerve stimulation (VNS) for treatment of inflammation in animal models and clinical trials, suggesting that VNS is a very promising approach of inflammation reduction. This immunomodulatory effect produced by stimulating efferent nerves may be an ideal therapy closer to normal or natural physiological regulation without the side effects seen in some drugs. The anti-inflammatory effects of implanted electrodes to stimulate the vagus nerve have been tried for the treatment of chronic immune diseases (De Ferrari et al., 2011; Howland et al., 2011; Howland, 2014; Koopman et al., 2016; Noller et al., 2019). For acute infections, implanting electrodes is not a viable option. Fortunately, stimulating peripheral somatic nerves can also produce the effects of autonomic-immune reflexes, including vagal-immune reflex and the above-mentioned sympathetic-immune reflex (Ulloa et al., 2017; Pavlov and Tracey, 2017). This opens a convenient window of hope for the treatment of acute inflammation in infectious diseases. Not surprisingly, this approach is just how acupuncture therapy works. There is a long history in China of acupuncture being used to treat various emergencies such as acute fever, shock and coma, etc. Acupuncture has been applied even more frequently and sometimes might be considered more important than traditional Chinese herbal medicine, which needs to be prepared or cooked and takes time to see results (L.G. Liu et al., 2004). Acupuncture works rapidly and can often quickly reverse critical conditions, according to ancient and contemporary literature (L.G. Liu et al., 2004). Contemporary Chinese medicine practitioners continued this tradition and use acupuncture, combining it with modern conventional treatment, to treat epidemic diseases, including COVID-19 (R. Wang et al., 2020). Recent random control clinical studies (see following session) also show that acupuncture is a promising clinical anti-inflammatory therapy.

5 Regulatory effects of acupuncture on immune function

Modern studies have demonstrated that acupuncture modulates multiple physiological systems of the body, including the immune system, to reestablish homeostasis by activating peripheral nerves to evoke physiological reflexes (spinal and supraspinal reflex) and the brain central integration (as reviewed elsewhere, Ma, 2004; Zhao, 2008; Kagitani et al., 2010; Uchida et al., 2017; Pan, 2018, 2019). The experimental research on the effects of acupuncture on immune function can be traced back to the middle of the last century (S.Z. Liu, 1959; Yan, 1959). Studies over the decades have shown that acupuncture has a wide range of regulatory effects on the immune system (Den, 1981).

5.1 Enhancement effects of acupuncture on immunity under physiological conditions

Most of the early studies showed that acupuncture enhanced immunity of normal humans or physiological model animals (S.Z. Liu, 1959; Den, 1981; Du et al., 1995; Johansen et al., 2004; Sato et al., 1996). Acupuncture can enhance the innate immune functions. For example, a large number of studies in rodent models (Sato et al., 1996; Liu et al., 1997; Choi et al., 2002; Kim et al., 2005; Rho et al., 2008) showed that EA at ST36 (Zusanli) upregulated the function of natural killer (NK) cells and macrophages, which play a central role in the innate immune response, especially in killing virus-infected cells. Acupuncture also increases the weight of mouse thymus (L.J. Liu et al., 1997), suggesting an effect of enhancing innate immune function. The effect of acupuncture on adaptive immunity is also supported by many experimental results. Acupuncture can increase the number of lymphocytes in the peripheral blood and the lymphocyte transformation rate in animals (Cao et al., 1982) and humans (Wu, 1983; Jong et al., 2006). In the aging animal model, acupuncture increased the functions of T lymphocytes (J.M. Liu et al., 2009). It has been reported that acupuncture for 20 days can increase the level of IgG and IgM in the elderly (Han, 1993). A few studies have shown that the lateral hypothalamus plays a role in the enhancement effect of EA. EA increased natural killer cell activity in the spleen, correlating with the activation of hypothalamus (Rho et al., 2008). Selective destruction of the lateral hypothalamic area (Choi et al., 2002) cancelled various immune enhancement effects of acupuncture. The general enhancement effects of acupuncture on immunity might benefit the prevention of infections and immune suppression status of sepsis. However, acupuncture effects on immunity show state-dependent features. For example, under disease conditions, the effects of acupuncture might be different from that under normal conditions, which is elaborated below.

5.2 Bidirectional regulations of immune function by acupuncture under pathological conditions

Previous studies have shown that the most interesting feature of acupuncture is the bidirectional regulation effect on the body's homeostasis, either in hyper- or hypo- functional states (dual regulation, normalization, or restoring homeostasis) in either patients or pathological models of animals (for a review, Pan, 2019). For instance, EA at ST36 showed stimulation of stress-induced delayed gastric emptying and inhibition of stress-induced acceleration of colonic transit (Iwa et al., 2006). Such state-dependent effect also is observed on immune modulation by acupuncture. Acupuncture can enhance the suppressed innate immune functions, such as up-regulating the decreased function of NK cells and macrophages (Zhao et al., 1994; Wu, 1995; Hisamittsu et al., 2002; Yamaguchi et al., 2007; Johnston et al., 2011). Conversely, acupuncture can also downregulate the activity of these immune cells and related cytokines when they are in a hyperactivity state such as inflammation (see the following section). Studies (as reviewed elsewhere, Kim and Bae, 2010; Dai et al., 2018) also showed that acupuncture has bidirectional regulating effects on adaptive immunity, such as T lymphocytes functions. T helper cells, a type of T lymphocytes, play an important role in the immune modulation. There are two main subsets of T helper cells, Th1 and Th2, which respectively produce Th1 type cytokines (e.g. IL-2, INFγ) and Th2 type cytokines (e.g. IL-4, IL-10). The former tends to produce the pro-inflammatory responses, and the latter, anti-inflammatory responses. The balance of Th1/Th2 is changed in different diseases and that can be modulated by acupuncture (Yamaguchi et al., 2007; Dai et al., 2018; Silvério-Lopes and da Mota, 2013). For example, acupuncture can downregulate Th2-specific cytokines (Park et al., 2004; Kim et al., 2011) to improve Th2 dominant disorders, such as allergic rhinitis (Shiue et al., 2008) and chronic fatigue syndrome (C. Wang et al., 2014). In contrast, for the Th1 dominant disorders such as rheumatoid arthritis (Yim et al., 2007), ulcerative colitis (Tian et al., 2003) and depression (Lin et al., 2014), acupuncture can modulate the Th1/Th2 balance with inhibiting Th1 responses. Such bidirectional regulatory effects suggest some interesting mechanisms that need further study (Pan, 2019). Generally speaking The bidirectional regulatory effect of acupuncture mirrors the activation and reinforcement of the body's self-healing or biological adaptive mechanism, which is a unique effect that no specific drug can reach at this time. Thus, acupuncture is a patient-tailored approach, although controlled by the body per se.

5.3 The anti-inflammatory effect of acupuncture

There is growing interest in the anti-inflammatory effect of acupuncture in the research field. In recent decades, the anti-inflammatory effects of acupuncture in septic animals and patients are highlighted. The most common problem of immune response in sepsis is a hyper-reactive cytokine storm. Silvério-Lopes and da Mota (2013) systematically eval‎uated 67 relevant papers published between 2001 and 2011, and concluded that acupuncture and EA are effective in modulation of immunity in animals and humans. Lai et al. (2020) systematically reviewed 54 studies up to May 2019 on acupuncture at ST36 (Zusanli) for the treatment of the experimental sepsis in animal models crossing species (rodents and rabbits). They used 17 criteria to estimate the study quality and risk of bias. The average quality scores of the studies is 6.3 varying from 2 to 9.5, with 13 studies (15%) accepted quality scores ≥7.0. Those studies support that acupuncture benefits to protecting multiple organs against injuries by sepsis and maintaining the immune balance to attenuate inflammation. A very new study (S.B. Liu et al., 2020), published in Neuron online, July 2020, further confirmed that acupuncture has a reliable anti-inflammatory effect, and revealed new features and mechanisms by using genetic strategy. Those results, especially from the quite a few quality studies (Scognamillo-szabo et al., 2004; Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Villegas-Bastida et al., 2014; Yu et al., 2014; Zhu et al., 2015; Chen et al., 2016; Liu et al., 2020), have shown that the efficacy of acupuncture on experimental sepsis has the following characteristics:

1.

EA improved the survival rate of animals with sepsis. The survival rate of rats or mice with sepsis increased significantly, with a maximum survival increase up to 80% (S.B. Liu et al., 2020; Torres-Rosas et al., 2014; Chen et al., 2016; Song et al., 2012; Zhu et al., 2015; Villegas-Bastida et al., 2014). EA inhibited the release of important pro-inflammatory factors. The blood levels of pro-inflammatory factors such as TNF, IL-6, MCP-1 and INFγ in the acupuncture group were significantly reduced. The level of anti-inflammatory factor IL-10 either increased (da Silva et al., 2011; Ramires et al., 2020) or did not change significantly (Song et al., 2012). It suggests that acupuncture does not simply suppress the immune response but modulates its balance. The anti-inflammation effect of acupuncture is clear. A study (Ramires et al., 2020) showed that acupuncture obtained similar levels of effect as that of indomethacin (a classical nonsteroidal anti-inflammatory drug) in suppressing peripheral and brainstem cytokines.

2.

EA reduced injuries induced by sepsis in multiple inner organs such as lung, cardiac, kidney, liver and gastrointestinal tract (Lai et al., 2020).

3.

The time-window of treatment exists. The earlier that acupuncture treatment is given, the better the results, with results from preventive care even better (Torres-Rosas et al., 2014; Liu et al., 2020). Even one treatment or pretreatment of EA can cause the effect, and the effect lasts at least 6 h (Torres-Rosas et al., 2014). However, the effects from daily EA, in which there are a consecutive three days of treatment, may have more stable and effective results (Torres-Rosas et al., 2014). A new finding (S.B. Liu et al., 2020) is that time-window plays the role depending on the intensity of stimulation (see below for the details). However, these results perhaps depend on the inflammatory model. It seems that the pretreatments are better than post treatments to lipopolysaccharide (LPS) model (Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Chen et al., 2016; S.B. Liu et al., 2020; Ramires et al., 2020), but no matter to the cecal ligation and puncture (CLP) model (Song et al., 2012; Torres-Rosas et al., 2014). This might arouse future studying of the treatment windows for various inflammations with different pathogens, e.g. bacteria or virus.

4.

The parameter of EA stimulation is important, which consists of frequency, intensity and the model of pulse trains including generally “continuing trains”, “bursting trains” and “alternating trains” with a common commercial EA stimulator. Most experiments obtained show clear effects with simple stimulation of continuing trains of low frequency (<15 Hz). However, a study (Chen et al., 2016) comparing the effects of three types of trains has shown that the alternating trains (2/15 Hz) is the best, then the bursting trains (2/0 Hz), and then the continuing trains (2 Hz). As mentioned above, another study showed that that low frequency (1 Hz) EA produce the local anti-inflammatory effect via activation of the simple spinal somatic-sympathetic reflex; while high-frequency (120 Hz) EA is mediated by the sympathoadrenal medullary axis to induce systemic effects (Kim et al., 2007, 2008). This frequency effect is consistent with some other acupuncture effects depending on frequency of stimulation (Han, 2003).

5.

There are large varieties of the intensity of EA stimulation used in different experiments. A problem is that different laboratories used different stimulators which indicate the intensity with different scales: current (mA) or voltage (V), that limits to compare the intensities between the different studies. However, some studies included investigating the effects of intensities, providing valuable data. Torres-Rosas et al. (2014), using mice lipopolysaccharide (LPS) model, compared the pretreatments with stimulations of 0.4 V and 4 V at ST36, and the results showed that the anti-inflammatory effect of 4 V stimulation was clearly stronger than that of 0.4 V. Similarly, Liu et al. (2020) compared the pretreatment with stimulations of 0.5 mA, 1.0 mA and 3.0 mA at ST36 or ST25 (Tianshu, at abdomen) in LPS mice, conforming the results, i.e. the stronger the stimulation, the better the anti-inflammatory effect. A surprising funding by Liu et al. is that post-treatment with the 3.0 mA produced oppositely pro-inflammatory effects, i.e. increased the serum TNF-α level and decreased in survival rate. That is because that LPS increased the expression‎ of α2-ARs (adrenergic receptors) in splenic cells, which mediate pro-inflammatory effects, and the post-treatment with high intensity EA activated the spinal sympathetic-splenic pathway (demonstrated with genetic strategy) that further enhanced the α2-ARs effect. They further demonstrated that Yohimbine (α2-ARs antagonist) or splenectomy allowed 3.0 mA EA to promote survival and to suppress serum TNFα level. However, they found that post-treatment of 0.5 mA weak stimulation at ST36 is not enough to activate this sympathetic-splenic pathway, but it is sufficient to activate the vagal-splenic pathway to obtain the anti-inflammatory effects. But EA at ST25 (either 0.5 mA or 3 mA) did not activate the vagal reflex. Those findings are consistent with the previous results that stimulating acupoints at abdomen area produced the sympathetic reflex on the inner organs, while stimulating acupoints of limbs produced the vagal reflex (Sato, 1997; Li et al., 2007). Those results suggest that we need to consider the stimulation site (acupoint), stimulation intensity and time window of treatment (pre- or post- treatment) together for a clinical therapy. Especially, the time-window dependent effect of stimulation intensity is not easy to control in clinical practice because that almost all treatments are post-treatment on patients. However, this result was from the LPS model. Another data showed that the post-treatment of high intensity EA on CLP model obtained the anti-inflammatory effects and promoted the survival rate (Torres-Rosas et al., 2014). On the other hand, EA applying to patients in real clinical practice might rarely reach the intensity of stimulation as high as that in animals in the laboratory. The EA stimulation of 3 mA is over the threshold (>2 mA) (Kagitani et al., 2010) activating Aδ and C fibers of the peripheral nerves (but see Zhou et al., 1985), that will produce pain feelings in conscious animals and humans. The general situation in a clinic is that a stimulation of EA applying to a patient without uncomfortable feeling, especially without pain, that generally induces slight twitch of the local muscles. This general clinic EA intensity is roughly equal to moderate stimulation in animal experiments, which perhaps might or might not activates the peripheral Aδ fibers (threshold 1.5 mA)(Kagitani et al., 2010; Li et al., 2007) but not C fibers. We might not need to concern too much on above pro-inflammatory effect induced by high intensity post-EA, rather, we might use this feature to benefit to patients, e.g. using relative high stimuli at very early stage (before sepsis happening) to prevent serious sepsis, or promote immunity at late stage with the immune-paralysis.

6.

The selection of acupoints has certain significance. As mentioned above, to control inner organ function, the acupoints at abdomen or back mediate the somatic-sympathetic reflex, while the acupoints of limbs mediate the somatic-vagal-reflex (for an individual organ, the exact and maximal reflex effect is obtained following the spinal segmental dominance rule). However, there is still some variety between acupoints within trunk group or limbs group, e.g. LI4 (Hegu) and PC6 (Neiguan) are both effective acupoints of anti-inflammation, but the former is more effective (Song et al., 2012). This difference might be related to the distinction of the nerves distribution under the acupoints.

7.

The anti-inflammation effect of EA is mainly achieved by activating vagal-splenic pathway (Song et al., 2012; Villegas-Bastida et al., 2014; Lim et al., 2016; S.B. Liu et al., 2020), the vagal-adrenal medulla-dopamine pathway (Torres-Rosas et al., 2014) and the sympathetic-splenic pathway (Martelli et al., 2014b; S.B. Liu et al., 2020), rather than by enhancing the hypothalamic-pituitary-adrenal cortex axis, because electroacupuncture pretreatment did not increase serum corticosteroid in animal sepsis model (Song et al., 2012). The role of sympathetic-adrenal medulla pathway is thought to play the role in anti-inflammatory effect in carrageenan-induced paw inflammation model (Kim et al., 2008). However, the role of sympathetic-adrenal medulla pathway in suppressing systemic inflammation needs further investigation. Furthermore, the role of sympathetic-vagal relationship and balance are worth to be studied (Huang et al., 2010).

With these detailed results, the approach of the peripheral-autonomic-immune reflex, carried out by acupuncture, seems promising in being translated into a relative optimal clinical therapy. However, as mentioned above, in the process of sepsis, the immune system with CARS mechanism might present not only a hyper-inflammatory reaction but also immune-paralysis depending on the individual conditions. Further studies are needed to address if there is immune-paralysis at a later stage (even early stage) of the sepsis model, which can be prevented by acupuncture. Theoretically, acupuncture should have a corrective effect for both the hyper- and the insufficient immune responses in the inflammation process according to the bidirectional principle. Indeed, Guo et al. (2010) have reported that EA at Zusali (ST36) and Guanyuan (CV4) decreased the apoptosis of thymocytes in rat sepsis model, suggesting acupuncture can prevent sepsis animals from immune-paralysis. The data from other immune suppression models and clinical trials of inflammation also support the bidirectional effects of acupuncture. For instance, acupuncture reduced the increased plasma level of IL-10 in patients with chronic allergic rhinitis (Petti et al., 2002). Theoretically, when the releasing of pro-inflammatory factors is suppressed, the releasing of anti-inflammatory factors will decrease as well, due to the latter being triggered by the former. Thus, reducing the pro-inflammatory factors by acupuncture at an early stage means also reducing the anti-inflammatory factors later. This might help to avoid the up-and-down oscillation of the compensatory anti-inflammatory response to prevent immune-paralysis, that finally increases the survival rate of animals with sepsis, which needs to be confirmed in future.

5.4 Clinical evidence

In real clinical conditions, patients with sepsis may also have additional complications, especially during the critical stage. Therefore, it is necessary to use different medications or therapies to deal with multiple factors to reach the best results, although animal experiments have shown that acupuncture alone significantly increases the survival rate of sepsis animals. Traditional Chinese practitioners have known for thousands of years to combine acupuncture and herbal medicine together to cure complicated diseases, including serious infections. Recently, acupuncture integrated with modern medical therapies, as a part of the comprehensive treatments of sepsis, has shown exciting values in clinical trials. Clinical reports show that the effect of adding acupuncture intervention in conjunction with conventional treatment is superior to the conventional treatment group alone. A recent study (L. Wang et al., 2019) of a randomized controlled trial on 108 patients with sepsis (54 in the control group and 54 in acupuncture group) showed that the patients in both groups were given conventional treatments, i.e. routine anti-infective medications, and supportive treatments with organ functioning monitored. The patients in the acupuncture group were treated with acupuncture at ST36 daily for 3 consecutive days in addition to conventional treatment. The results showed that, compared to the condition before the treatments, after the treatments, the plasma factor procalcitonin (PCT), blood lactic acid (Lac) expression‎ level, Acute Physiology and Chronic Health Eval‎uation (APACHE II) score, and Sequential Organ Failure Assessment (SOFA) score in both groups were significantly decreased; however, compared to the control group, after the treatment, the acupuncture group showed more decreaces significantly (P < 0.05). Another study (J.N. Wu et al., 2013) conducted a randomized control trial with 50 patients with sepsis, comparing acupuncture plus conventional treatment (n = 26) with conventional treatment alone (n = 24). The results showed that after 3 consecutive days of daily EA treatment, the plasma TNF-α, IL-6 in the “acupuncture plus conventional treatment” group were significantly lower than that in conventional treatment group, and its overall effect was also better. Similarly, F.W. Wu (2016) reported the effect of EA on the inflammatory response and immune function in sepsis patients. The 50 patients with sepsis were randomly divided into two groups of 25 each, i.e. the control group used the treatment plan recommended by the 2008 international guideline on the rescue of sepsis, and the acupuncture group used EA at ST 36 daily plus the treatment given to control group. The APACHE II scores, C reactive protein (CRP), PCT, Lac, and IL-6, IL-10 and T cell subsets (CD4+ and CD8+) were recorded before the treatments and 3 and 7 days after treatments in both groups. The rates of incidence of MODS and fatality rate during 28-day hospitalization were calculated. The results showed that after treatments, at each time point the APACHE II score, CRP, PCT, and Lac levels in both groups decreased to some extent, while the levels of CD4+ and CD8+ of T cell subsets involved in adaptive immunity increased in both groups; however, the EA group was better than the control group (P < 0.05). This indicated that EA at ST36 not only alleviated the pro-inflammatory response of patients with sepsis, but also improved adaptive immune function. This study importantly shows that the 28-day fatality rate in the EA group (8.00%) was significantly lower than that in control group (28.00%) (P < 0.05), while the incidences of MODS in EA group (24%) was lower than that in control group (36%) but not significantly (p > 0.05). Xiao et al. (2015) also obtained similar results. 90 patients with sepsis were randomly distributed to “conventional treatment” (n = 30), “conventional treatment + thymosin α1” (n = 30), and “conventional treatment + acupuncture” (n = 30). The fatality rate after treatment, and T cell subsets CD3+, CD4+, CD8+, CD4+/CD8+ ratio and the antibody IgG, IgA, IgM before and after treatment were compared between groups. The results showed that after 6 days of treatment, while the immune function with above items in all three groups of patients significantly increased (P < 0.01), that the thymosin group and the acupuncture group increased significantly more than in the conventional treatment group (P < 0.01, respectively). The ICU length of stay (days), and the rates of 28-day fatality also decreased significantly (P < 0.05, P < 0.01 respectively) in both the thymosin group and with the acupuncture group compared with the conventional treatment group. This suggests that acupuncture can improve adaptive immune function, and its effectiveness is comparable to that of thymosin, a recognized immune-stimulant used for the treatment of sepsis. This clinical data suggest that acupuncture not only decreases the pro-inflammatory factors but also enhances adaptive immune function to prevent immune-paralysis, which needs to be further confirmed.

Further, acupuncture can not only modulate immune function, but also improve organ functioning in multiple disorders. This also gives acupuncture as an advantage to treating MODS, imbalance of energy metabolism of sepsis. For example, a study by Yu et al. (2015) has shown that acupuncture can not only significantly improve the immune function of sepsis cases, but also protect the gastrointestinal function of septic patients. The incidence of vomiting, abdominal distension and gastric retention in the EA group (EA plus conventional treatment) were significantly reduced compared with the control (conventional treatment alone) group. Meng et al. (2018) also obtained the effects of attenuating inflammatory responses and intra-abdominal pressure in septic patients, but not the length of stay in intensive care unit (ICU) and 28 days fatality rate.

A recent meta-analysis (Tang et al., 2020) including 20 studies with total 1337 patients with sepsis showed that the 28 day fatality rate, the APACHE II score on the 3rd day and the 7th day after treatments, ICU length of stay, gastrointestinal function improvement, PCT and TNF-α on day 7 after treatments, in acupuncture plus conventional treatment group were all significantly superior to that in conventional treatment alone group statistically. All those research results (although still limited) indicate that acupuncture is a very promising integrative therapy for treating patients with sepsis.

6 Discussion: toward a science-based design of EA protocol of immunomodulation

Given the current absence of recognized treatment protocols for immune dysfunction in the process of sepsis, based on above laboratory (i.e. preclinical studies) and clinical evidences, acupuncture could serve as an adjuvant therapy, with its advantage of being easily used, low cost, without any chemical side effects, and importantly, because of its ability to modulate both immune function and multiple organ function. All of which are beneficial to prevent the condition from worsening and to decrease the fatality rate of septic patients. We strongly recommend that acupuncture be included in the comprehensive treatment plan for sepsis. However, the therapies used in previous studies generally followed traditional theory or personal experience. Their selections of acupoints, stimulating parameters, daily dose and course of treatment might not be optimal; thus, it might limit their curative efficiency. To obtain better or maximal effects, we give an acupuncture protocol design based on the new knowledge developed from the researches described above. For the mechanism, stimulating peripheral nerves induces the somatic-autonomic reflex, which produces sympathetic or vagal effects on the functional regulation of organs or physiological systems, including the immune system we now focus on. The spinal somatic-sympathetic reflex follows the rule of the spinal cord segmental control, i.e. the effect of a somatic-sympathetic reflex on an specific organ is obtained limitedly by stimulating the somatic nerve connecting to the spinal cord segments (1–5 segments usually) as same as that the organ do. For example, the spleen is innervated by the sympathetic nerve from the spinal cord segment T5-T8, thus only the stimulation (electrical or acupunctural one) from the somatic nerve zone belonging to the T5-T8 segments can produce the reflex effect on the spleen. Similarly, T8-L1 for the adrenal medulla, and T1-T5 for the lung and so on, that a map with the details can be found in any anatomy textbook. The supraspinal somatic-sympathetic reflex might be induced by high intensity nociceptive stimulation, which is systemic, but rarely produced by acupuncture. The somatic-vagal reflex is special. Previous data showed the vagal reflex control the gastrointestinal tract can be induced by stimulation of the peripheral nerves or the acupoints at the limbs (not the trunk) with high intensity (activating Aδ and C fibers) of stimulation (Sato,1997; Li et al., 2007). However, to activate the vagal-adrenal reflex, a new data (Liu et al., 2020) showed that the stimulation of 0.5 mA (lower than the threshold of Aδ) is sufficient to do. To focus on immune function controlling, we name those reflexes as “somatic-autonomic-immune reflexes”; specifically, the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex, somatic-vagal-adrenal reflex, which induce systemic regulatory effects on immune functions because the final outputs are from the spleen or the adrenal medulla, which release cytokines or norepinephrine and dopamine into blood. However, the other somatic-sympathetic reflexes related to an organ have local effect only, e.g. the somatic-sympathetic-lung reflex, the somatic-sympathetic-kidney reflex, etc. It should be noted that stimulation of any acupoint can also produce common systemic effects or perhaps some unknown specific effects through the brain integration (both sympathetic and vagal ones) simultaneously, that need further studies. Those concepts and principles are illustrated in Fig. 3.

Figure viewer

Fig. 3 The organization of the somatic-autonomic-immune reflexes (the part of the figure showing the autonomic nervous system and organs is modified from Figure 296 of REF [Gao and Yu, 2014]). For explanation see the text.

6.1 An auxiliary acupuncture protocol

Following the above reflex principles and considering that the effects of acupuncture are state-dependent, stimulation-parameter-dependent, acupoint-dependent, and treatment-time-dependent, an auxiliary acupuncture protocol for sepsis treatment is designed as follows and summarized in Table 1:

1)

Acupoint selection: examples of acupoints we selected are listed below. It should be noted that following the segmental distribution to select acupoints is the key point here.

a.

Systemic regulation:

•

Vagal Group: ST36 (Zusangli) or LI4 (Hegu), bilaterally (the same below). They are the most effective acupoints reported from laboratorial and clinical studies, activating vagal anti-inflammatory pathway to down-regulating cytokines storm;

•

Sympathetic Group: BL17 (Geshu) and BL19 (Danshu) on the back; or ST21 (Liangmen) and ST25 (Tianshu) on the abdomen, to activate the sympathetic-splenic reflex and the sympathoadrenal medullary reflex, additionally benefiting to septic shock patients due to the norepinephrine releasing.

b.

Local regulation:

•

Thoracic group: BL13 (Feishu) and HT7 (Shenmen).

•

Abdominal group (gastrointestinal organs, liver and kidneys): BL19 (Danshu) and ST25 (Tianshu).

•

Pelvic group: BL23 (Shenshu) and SP6 (Sanyinjiao).

b.

The formula of acupoints we recommend:

Formula I: Vagal group + Local group/s (if needed);

Formula II: Sympathetic group + Local group/s (if needed).

The two formulas are used in turns.

2)

Stimulation parameters: for the intensity of EA, it is recommended to give moderate stimuli which can cause slight muscle twitching and also be tolerated by patients. To prevent sepsis in patients in the early stages of infection, high-intensity stimulation is recommended; that perhaps causes more of a pain sensation. Applying EA “continuing trains” with the frequency of 2–10 Hz for 30 min is a general EA dose. However according to the frequency effect (Chen et al., 2016), here we recommend using “alternating trains” of 2/15 Hz or 2/100 Hz, (100 Hz to enhance sympathoadrenal medullary reflex, Kim et al., 2008) for systemic effects, and “bursting trains” with high frequency (15-100 Hz) for local effects. If using the traditional manual acupuncture, we suggest mimicking the “alternating trains”, applying a light or moderate stimulation (a slow rotation) of 2–5 min/10 min for 30 min, given that manual acupuncture can activate all groups of sensory nerve fibers (Kagitani et al., 2010) and a slow rotation of needle is efficient to induce anti-inflammatory effect (Lim et al., 2016; Ramires et al., 2020).

3)

Daily dose and course of treatment: considering that the inhibitory effects of one treatment of EA on most inflammatory factors last for about 6 h (Song et al., 2012; Torres-Rosas et al., 2014), the daily dose we suggest is 2 times/day for patient with sepsis; one time/day for early stage of acute infection. Formula I and Formula II will be used in turns. Take a course of 5–7 days with a break of 1–3 days, because the toleration might happen after 7 days with continuous daily treatments (Du et al., 1995). For severe infection such as COVID-19, the sooner the intervention is performed, the better.

4)

Self-healing: for mild cases or early stages of the infection, the transcutaneous electrical stimulator (TENS) can be used by patients themselves.

EffectsReflexAcupointsPulse trainsFrequency (Hz)IntensityDose & course

Systemic	Vagal reflex	ST36 (Zusanli) LI4 (Hegu)	A B C	2/15 or 2/100 15 2	Moderate	2 times/day, 5–7 days
Systemic	Sympathetic-splenic	BL17 (Geshu) ST21 (Liangmen)	A B C	2/100 or 2/15 100 or 15 15	Moderate	2 times/day, 5–7 days
	Sympathetic-adrenal	BL19 (Danshu) ST25 (Tianshu)	Same
Local organs	Sympathetic (thoracic)	BL13 (Feishu) HT7 (Shenmen)	B	15 or 2	Moderate	2 times/day, 5–7 days
	Sympathetic (abdominal)	BL19 (Danshu) ST25 (Tianshu)	Same
	Sympathetic (pelvic)	BL23 (Shenshu) SP6 (Shanyinjiao)	Same

Table 1

An example design of evidence-based therapy of EA to modulate immunity in sepsis.

A: alternating trains; B: bursting trains; C: continuing trains.

• Open table in a new tab

6.2 Limitations and future research

As discussed above, acupuncture is supported by a large amount of research data both in clinical trials and animal studies in resolving cytokine storms during severe inflammation; however, there still exist many unsolved gaps. There are several limitations to this review aside from those discussed above. 1) Although acupuncture's anti-inflammatory storm has been repeatedly confirmed by animal experiments, and the effect of acupuncture in inhibiting inflammatory storms through neuroimmune pathway is almost certain, it should be noted that current experimental results mostly come from CLP models and LPS models. It is necessary to further compare the differences between these two and expand to other new models. In particular, a new direction is to establish an immune-paralysis model in late-stage sepsis. 2) More detailed research is needed in acupoint selection and stimulation parameters. 3) Time-window of acupuncture effect is worthy enough to do further systematic research: identifying the acupuncture effect during different development stages of sepsis, i.e. pretreatment, and its early, middle, and late stages. This needs to combine with acupoint selection and stimulation parameters. 4) Refining and deepening is needed in the bidirectional regulating effect and mechanism of acupuncture in terms of immune regulation. In particular, given that the suppressing effects of acupuncture on cytokine storms has been well addressed, next challenge is investigating the effects of acupuncture on immune-paralysis in sepsis. 5) Most of previous studies focused on systemic effects of acupuncture or other peripheral nerve stimulation. A new direction is identifying local effect produced by local segmental reflexes, that will provide scientific bases of acupoint selection to clinical therapy design. 6) Any peripheral stimulation might produce both local spinal segmental reflexes and supra-spinal reflexes. Local segmental reflexes might co-work with its supra-spinal reflexes, or have independent effect, that can be used in different situation. This is a basic question of acupuncture and very important for selecting acupoints in a therapy. The interactions and mechanisms of local spinal segmental reflexes and supra-spinal reflexes produced by acupuncture need to be further studied extensively, not only for inflammation but for all other disorders. 6) Current acupuncture clinical trials have some quality issues. The quality of most reports has been criticized due to insufficient sample sizes and lacking proper sham controls. Indeed, the feature of acupuncture different from drug's makes the design of sham acupuncture control difficult to meet the rules of double-blind clinical study. To avoid such problems, the National Institutes of Health (NIH) is currently advocating real-world clinical research in view of the characteristics of acupuncture (Zia et al., 2017). However, according to the results of current animal and clinical experiments, there are large varieties of the effects of acupoints and stimulation parameters, that some of them showed significant effects but others with little effects on same treatment targets (e.g. Chen et al., 2016; Li et al., 2015). Such little effective acupoints or stimulation parameters give an idea “sham” control manipulation. By using such parallel design, Li et al. (2015) showed the effects of long-lasting reduction of blood pressure in a group treated with specific acupoints but not in the other group with different acupoints. We strongly recommend such parallel design, that uses invalid acupoints or stimulation parameters as “sham” control group to rule out placebo effect. Parallel design is well known as the “gold standard” for phase 3 clinical trials. It is just very well for clinical study of acupuncture. Anyhow, systematic, large and rigorous clinical data will be the key for supporting in acupuncture-assisted immune adjustment in the treatment of sepsis. The acupuncture protocol designed in this article is just one example of suggestions for future clinical research, which is based on current available literature. We hope that this protocol would be inspiring and promoting the translation from scientific study to clinical application. Given that there are gaps in acupuncture mechanisms, and between acupuncture real practice and basic science study in treating sepsis, further studies in both acupuncture mechanisms and clinical trials are warranted.

7 Summary

Faced with the severe situation of the global pandemic of COVID-19, the medical community throughout the world is exploring various treatments from different approaches, including antiviral, anti-inflammatory, and controlling multiple organ functions. It has been identified that COVID-19 induces immune disorder and sepsis in severe patients (Yuki et al., 2020). A new study demonstrated that COVID-19 cytokine storms, especially a high level of TNF may make few memory B cells and prevent a durable immune response (Kaneko et al., 2020). For fatal sepsis with multiple organ failure, the imbalance of immune function is the core pathological mechanism, and the various therapies for controlling the immune function currently have no recognized best choice for various reasons. At this moment, acupuncture used to activate the somatic-autonomic-immune reflexes is a promising therapy emerging from multiple recent animal experiments and clinical studies, to provide significant clinical advantage to control inflammation and restore organ function without adverse side effects. Different from a new drug investigation needing a phase I clinical trial (screening the safety and testing the proper dose), acupuncture with its safety feature, has been carried out at least in phase II like clinical trials for a variety of diseases for years throughout the world. If acupuncture is involved in the treatment of COVID-19, the patients will not only avoid losing a promising adjunctive therapy, but it would also be a good opportunity obtaining a large number of patients to test the efficiency of acupuncture in a clinic trial. Previous studies from animal models and clinical trials have shown that acupuncture modulates immunity, but it has yet been consistent with showing that acupuncture decreases the fatality rate of sepsis patients. Besides the complicated process of sepsis, one main reason is that the efficiency of acupuncture depends on several factors such as the pathological status, the acupoints, the stimulation parameters and the time-window of treatment etc. that need well consideration together to obtain maximal effects. We recommend an evidence-based comprehensive design of EA protocol to practitioners and researchers to test it. It is worth looking forward to its contribution to the treatment of sepsis and, for the moment, to treating the urgent need of patients with COVID-19 infection as well as for future patients with various infections and other factors.

Declaration of competing interest

Author Sarah Faggert Alemi was employed by the company Eastern Roots Wellness, PLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AcknowledgmentsAcknowledgements

We thank Dr. Qiufu Ma for his feedback on the manuscript.

CRediT authorship contribution statement

This project was initiated by WX Pan and A.Y. Fan. As the primary researcher, WX Pan designed the project and protocol, structured and drafted the early version of manuscript. A.Y. Fan, SZ. Chen and S.F. Alemi participated in discussing, further drafting and editing the later versions. WX. Pan and A.Y. Fan completed the final manuscript. There was no financial support for this project. Due to the limitation of the authors' personal experience and perspective, this review may have some omissions and errors; comments or corrections are welcomed and appreciated.

References

1.

Bassi, G.S. ∙ Dias, D.P.M. ∙ Franchin, M. ...

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Brain Behav. Immun. 2017; 64:330-343

Crossref

Scopus (71)

PubMed

Google Scholar

2.

Behrens, E.M. ∙ Koretzky, G.A.

Cytokine storm syndrome: looking toward the precision medicine era

Arthritis Rheumatol. 2017; 69:1135-1143

Crossref

Scopus (226)

PubMed

Google Scholar

3.

Bellinger, D.L. ∙ Lorton, D.

Autonomic regulation of cellular immune function

Autonomic Neuroscience: Basic and Clinical. 2014; 182(15–41):2014

Google Scholar

4.

Berlot, G. ∙ Passero, S.

Immunoparalysis in Septic Shock Patients. Patients [Online First]

IntechOpen, 2019

https://www.intechopen.com/online-first/immunoparalysis-in-spetic-shock-patients

Crossref

Google Scholar

5.

Bernik, T.R. ∙ Friedman, S.G. ∙ Ochani, M. ...

Pharmacological stimulation of the cholinergic antiinflammatory pathway

J. Exp. Med. 2002; 195:781-788

Crossref

Scopus (458)

PubMed

Google Scholar

6.

Borovikova, L.V. ∙ Ivanova, S. ∙ Zhang, M. ...

Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin

Nature. 2000; 405:458-462

Crossref

Scopus (3326)

PubMed

Google Scholar

7.

Cao, J.R., Gong, Q. H., Xiang, Y. M. (1982). Effect of acupuncture on the output lymph and cell in popliteal lymph nodes in rabbits. Shanghai J Acu-moxi. 1, 35–37.

Google Scholar

8.

Chavan, S.S. ∙ Tracey, K.J.

Essential neuroscience in immunology. J Immunol. 2017; 198:3389-3397

Google Scholar

9.

Chen, Y., Lei, Y., Mo, L.Q., Li, J., Wang, M.H., Wei, J.C., et al. (2016). Electroacupuncture pretreatment with different waveforms prevents brain injury in rats subjected to cecal ligation and puncture via inhibiting microglial activation, and attenuating inflammation, oxidative stress and apoptosis. Brain Res Bull. 127, 248–259.

Google Scholar

10.

Choi, G.S. ∙ Oha, S.D. ∙ Han, J.B. ...

Modulation of natural killer cell activity affected by electroacupuncture through lateral hypothalamic area in rats

Neurosci. Lett. 2002; 329:1-4

Crossref

Scopus (26)

PubMed

Google Scholar

11.

da Silva, M.D. ∙ Guginski, G. ∙ Werner, M.F. ...

Involvement of interleukin-10 in the anti-inflammatory effect of Sanyinjiao (SP6) acupuncture in a mouse model of peritonitis

Evid. Based Complement. Alternat. Med. 2011; 2011:217946

Crossref

Scopus (50)

PubMed

Google Scholar

12.

Dai, Q.M., Shang, Y.Q., Liang, H., Yan, P.Y., Wang, M.Q., Wang, K. (2018). Research progress of effect of acupuncture therapy on T cell subsets. J Clin Acupunct. 7,78–82.

Google Scholar

13.

De Ferrari, G.M. ∙ Crijns, H.J.G.M. ∙ Borggrefe, M. ...

Chronic vagus nerve stimulation: a new and promising therapeutic approach for chronic heart failure

Eur. Heart J. 2011; 32:847-855

Crossref

Scopus (426)

PubMed

Google Scholar

14.

de Jonge, W.J. ∙ van der Zanden, E.P. ∙ The, F.O. ...

Stimulation of the vagus nerve attenuates macrophage activation by activating the Jak2-STAT3 signaling pathway

Nat. Immunol. 2005; 6:844-851

Crossref

Scopus (918)

PubMed

Google Scholar

15.

Den, G.G.

ReviewVolume 232102793May 2021Open access

Download Full Issue

Acupuncture modulates immunity in sepsis: Toward a science-based protocol

Wei-Xing Pana panw@hhmi.org ∙ Arthur Yin Fanb,c ArthurFan@ChineseMedicineDoctor.us ∙ Shaozong Chend,1 zjyjs1980@sdutcm.edu.cn ∙ Sarah Faggert Alemib,e

Affiliations & Notes

aJanelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA

bAmerican TCM Association, Vienna, VA 22182, USA

cMcLean Center for Complementary and Alternative Medicine, PLC, Vienna, VA 22182, USA

dAcupuncture Research Institute, Shandong University of Chinese Medicine, Jinan 250355, China

eEastern Roots Wellness, PLC, McLean, VA 22101, USA

1

Dr. Chen is the lead corresponding author of this paper.

Article Info

Publication History:

Received November 26, 2020; Revised January 26, 2021; Accepted February 25, 2021; Published online February 27, 2021

DOI: 10.1016/j.autneu.2021.102793 External LinkAlso available on ScienceDirect External Link

Copyright: © 2021 The Authors. Published by Elsevier B.V.

User License: Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | Elsevier's open access license policy

• Download PDF
• Cite
•  
• Set Alert
• Get Rights
• Reprints

Download Full Issue

Previous articleNext article

Show Outline

Highlights

•

Acupuncture modulates immunity and improves organ functions in sepsis, emerging as a promising therapy of immunomodulation.

•

Acupuncture obtains its regulatory effect via the somatic-autonomic-immune reflexes.

•

Such reflexes include the sympathetic-splenic, sympathetic-adrenal, vagal-splenic and vagal-adrenal reflexes, inducing systemic effects.

•

There are also local reflexes activated by acupuncture, such as the somatic-sympathetic-lung-reflex, inducing local effects.

•

A comprehensive EA protocol is designed based on the evidenced mechanisms.

Abstract

Sepsis is a serious medical condition in which immune dysfunction plays a key role. Previous treatments focused on chemotherapy to control immune function; however, a recognized effective compound or treatment has yet to be developed. Recent advances indicate that a neuromodulation approach with nerve stimulation allows developing a therapeutic strategy to control inflammation and improve organ functions in sepsis. As a quick, non-invasive technique of peripheral nerve stimulation, acupuncture has emerged as a promising therapy to provide significant advantages for immunomodulation in acute inflammation. Acupuncture obtains its regulatory effect by activating the somatic-autonomic-immune reflexes, including the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex and the somatic-vagal-adrenal reflex, which produces a systemic effect. The peripheral nerve stimulation also induces local reflexes such as the somatic-sympathetic-lung-reflex, which then produces local effects. These mechanisms offer scientific guidance to design acupuncture protocols for immunomodulation and inflammation control, leading to an evidence-based comprehensive therapy recommendation.

Abbreviations

1. Acupoint (acupuncture point)
2. APS (antigen-presenting cells)
3. ARDS (acute respiratory distress syndrome)
4. APACHE II (acute physiology and chronic health score)
5. CARS (compensatory anti-inflammatory response)
6. COVID-19 (coronavirus disease 2019)
7. CRP (C reactive protein)
8. EA (electroacupuncture)
9. ICU (Intensive Care Unit)
10. IL (interleukin)
11. MODS (multiple organ dysfunction syndrome)
12. LAC (blood lactic acid)
13. NK (natural killer)
14. PCT (procalcitonin)
15. SARS (severe acute respiratory syndrome)
16. TNF (tumor necrosis factor)
17. SOFA (systemic infection-related organ failure score)
18. VNS (vagus nerve stimulation)

Keywords

1. Nerve stimulation
2. Acupuncture
3. Electroacupuncture
4. Sepsis
5. Inflammation
6. Anti-inflammation
7. Inflammatory reflex
8. Immune dysfunction
9. Somatic-sympathetic reflex
10. Somatic-vagal reflex

1 Introduction

Sepsis is defined as life-threatening organ dysfunction, caused by a dysregulated host response to infection (Gotts and Matthay, 2016; Singer et al., 2016), which clinically manifests as severe systemic inflammatory response, Acute Respiratory Distress Syndrome (ARDS), Septic Shock, or Multiple Organ Dysfunction Syndrome (MODS). It is the number one killer in the Intensive Care Unit (ICU). Globally, there are approximately 30 million cases of sepsis each year, with a fatality rate as high as 30% (Reinhart et al., 2017). The Coronavirus Disease 2019 (COVID-19), which has developed into a global pandemic, is a current example of a manifestation of severe sepsis. Similar to other infections, deaths resulting from COVID-19 have been related to sepsis, which causes septic shock, MODS, and ARDS in particular (C. Wang et al., 2020; D. Wang et al., 2020; Z. Wu and McGoogan, 2020). Reducing inflammation and correcting organ dysfunction are the core strategies of clinical treatment of sepsis. However, due to the lack of a specific and effective antiviral drug, how to effectively treat sepsis has been a clinical challenge for a long time, especially for sepsis caused by viral infection. Traditionally, steroids, i.e. adrenocortical hormones, were once the major anti-inflammatory drugs used for this condition; however, they were unsatisfactory due to their serious side effects and sequelae. Recent immunotherapy drugs, such as siltuximab and tocilizumab, present hope but are yet to be eval‎uated and summarized for further development and clinical application. Fortunately, experimental animal studies in recent years have shown that a simple non-pharmacological approach shows the effect of anti-septicemia (for a review, see Lai et al., 2020). That approach is peripheral nerve stimulation done through both electroacupuncture (EA) and manual acupuncture (in short, acupuncture). Studies have shown that acupuncture is a promising alternative clinical anti-inflammatory therapy. Several lines of evidence published in recent years, from the researches of immunomodulatory mechanisms (for reviews, see, i.g. Tracey, 2002; Ulloa, 2005; Huston et al., 2006; Behrens and Koretzky, 2017; Pavlov et al., 2018; Berlot and Passero, 2019), the experiments of acupuncture in animal models (for a review, see Lai et al., 2020) and in patients of clinical trials (for a review, see Tang et al., 2020), support the antiseptic effect of acupuncture. Such a non-pharmacological and non-invasive approach has attracted the attention of the clinical medicine community and has been advocated by some leading researchers (Ulloa et al., 2017; Pavlov and Tracey, 2017). However, the clinical translation in practice with details is still lacking. This article aims to offer a brief comprehensive review and develop an evidence-based EA therapy for immunomodulation in acute inflammation to promote further research and clinical application.

2 Pathophysiology of sepsis

Sepsis is initiated by an infection. However, it has been known that the clinical manifestations and pathological complications of sepsis are not caused directly by invading pathogens, but rather by a disorder of the host's immune reaction (Hamers et al., 2015; Behrens and Koretzky, 2017). The main pathophysiological process of infectious diseases is the body's response to bio-immunogenic substances, that is, inflammatory reactions with defense properties. With the advancement of immunopathology research, more details of the inflammatory process have been understood (Gotts and Matthay, 2016; Singer et al., 2016; Reinhart et al., 2017; Sladkova and Kostolansk, 2006; Tisoncik et al., 2012; Wiersinga et al., 2014). The body's immune system is functionally divided into innate immunity and acquired adaptive immunity. When pathogenic microorganisms invade the body for the first time, the innate immune system responds accordingly, starting the inflammatory process. First, macrophages recognize and engulf the pathogens. While destroying and inactivating them, some antigen-presenting cells (APCs) can recognize the antigenic characteristics of pathogens and then transmit to B cells; the adaptive immune system is then activated to generate specific antibodies, which can more accurately and efficiently kill pathogens. Long-term memory of antigen information forming, and then lifelong immunity will be generated. However, antibody production takes a long time, around 5–10 days. Fortunately, the innate immune system immediately goes forward to start the battle of non-specific immunity, rather than waiting for the arrival of specific antibodies. Immune cells and infected tissue cells quickly release a batch of cytokines and pro-inflammatory substances under the stimulation of pathogens, such as interleukin IL-1, IL-8, IL-18, tumor necrosis factor TNF-α, IL-6, IL-33, type I and III Interferons (IFN), etc. which are called primary cytokine storms (Behrens and Koretzky, 2017). These cytokines exert a variety of different immune functions. For example, IL-1 is an important initiator of the inflammatory response; TNF has a strong killing effect; IFN has an antiviral effect and can limit virus replication and spread, protecting uninfected cells from being affected by virus invasion; chemokines IL-8 can induce the recruitment of more immune cells toward the infection site; some cytokines can activate the neuroendocrine system, leading to increased body temperature, breathing, circulation, metabolism and other functions. At the same time, these cytokines have a positive feedback effect, which can activate immune cells to release more cytokines, forming a secondary wave of cytokine storms and further strengthening the inflammatory response in order to effectively kill the pathogens (Guo and Thomas, 2017). If this process is successful, the pathogen may be eliminated, or at least prevented from spreading until the specific antibodies (IgM) are produced and the pathogen is destroyed. Once this occurs, the body enters the rehabilitation phase, removing necrotic cells and repairing damaged tissue. This is the general clinical process of many inflammatory infections, which generally last for 1–2 weeks and end through self-healing alone. Unfortunately, a significant proportion of patients progress to a worsening course of disease and develop sepsis. In severe cases, ARDS, septic shock, and MODS are fatal. The core problem of sepsis is a disturbance of the functioning of the immune system. Its pathophysiological mechanism is that the patient is prone to excessive inflammatory reactions in the early stage of the infection, which is the aforementioned cytokine storm phenomenon, also clinically called cytokine release syndrome (CRS). During the normal inflammatory response, when a large number of pro-inflammatory factors are released, the release of anti-inflammatory factors such as IL-4, IL-10, IL-11, IL-13, and IL-1Ra are also initiated, as a self-balance regulation of the immune system, called “compensatory anti-inflammatory response” (CARS) (Berlot and Passero, 2019). The emergence of sepsis is caused by a disorder in the dynamic balance between pro-inflammatory and anti-inflammatory factors, the excessive secretion of multiple pro-inflammatory factors, and the intensification under the positive feedback mechanism. While attacking the pathogen, it also damages the normal tissue cells of the body, leading to important organs or system dysfunction or even failure. However, that is not all that occurs during sepsis. It has recently been discovered that the mechanism behind sepsis is more complicated than previously thought. Not only does the immune response become hyperactive in the early stage, but also CARS is activated at the same time to limit the tissue damage. However, the CARS can represent a double-edged sword. It might be beneficial to restore immune balance; yet, it might cause the shutdown of the immune response if it over responds, inducing the status of immune-paralysis (Hamers et al., 2015; Berlot and Passero, 2019). With immune-paralysis, there can be a reduction of immune-related receptors, apoptosis of various immune cells (T cells, B cells, macrophages, dendritic cells), weakened antigen presentation function of APCs, and increased suppressive lymphocytes, etc., leading to both innate and adaptive immune functions that are severely weakened. This makes it difficult to clear the damaged tissues in later stages. It is also easier to activate latent pathogens and cause a secondary infection. Even worse is that some patients might have problems with immune-paralysis at the early stage, or multiple hits of the cytokine storm phenomenon ultimately leading to the exhaustion of the immune response, which makes treatment more difficult. Therefore, it is necessary to enhance immunity in the later stage as well, which has become a new focus of both basic science and clinical studies. The patterns of inflammatory reaction have been proposed theoretically (Berlot and Passero, 2019), shown in Fig. 1.

Figure viewer

Fig. 1 The immune reaction patterns (reproduced from Berlot and Passero, 2019). A. Possible clinical trajectories of patients with sepsis shock. Line 1, intense hyper-inflammatory reaction followed by CARS and the return to the baseline immune state. Line 2, weak hyper-inflammatory reaction followed by immune-paralysis and immune restoration. Line 3, immune-paralysis not preceded by a hyper-inflammatory reaction. B. The multiple hits phenomenon ultimately leading to the exhaustion of the immune response.

3 Difficulties in regulating immune function in the treatment of sepsis

The treatment of sepsis needs to address three aspects: reducing the pathogens (such as fighting the bacterial or viral infection, if applicable), reducing inflammation, and correction of various physiological dysfunctions. Multiple organ dysfunctions are closely related to inflammation, so reducing inflammation is an important aspect to be dealt with in its early and middle stages. Anti-inflammation or reducing inflammation means regulating immune function. The immune system consists of a variety of functional cells and molecular signaling pathways that form an extremely complex regulatory network. Normal inflammatory response is a dynamic equilibrium process of immune cells and molecular networks. The imbalance of septicemia manifests as early immune hyperactivity and late immune paralysis (Berlot and Passero, 2019) Theoretically, treatment should be to give inhibitory intervention in the early stages, followed by a strengthening intervention. However, it is difficult to make a decision in delivering the specific interventions in real clinical settings. There have been large numbers of anti-inflammatory medications previously used, including corticosteroids, aspirin, monoclonal antibodies, anti-cytokines, anti-chemokines, etc., the effectiveness of which is inconclusive, with some also leading to worsening of the condition. There are several reasons for this. First, in terms of the magnitude of the immune response, how much cytokine release during the inflammatory response can be determined to be “excessive”? It is difficult to define because of the physical condition of patients, such as age, gender, and possible chronic underlying disease. Second, in terms of phases, the turning point of the immune response from the hyper-phase to the hypo-phase is difficult to predict. Unlike antibiotics that advocate early use, immuno-suppressants are generally considered only when clinical symptoms are severe. At this time, immune hyperactivity may have peaked and begun to show a downward trend. Immuno-suppressants may be redundant and even cause immune paralysis quickly. This may be one of the reasons why traditional steroids (adrenal cortex hormones) or targeted therapies that target specific cytokines (for example, antagonists such as the IL-6 blocker siltuximab and the IL-6R blocker tocilizumab) often fail. Clinical effect has not been reached on the effects of these two types of therapy on reducing mortality. Third, regardless of the overall inhibition of steroids (adrenocortical hormones) or single-factor targeted therapy, they are not the normal physiological regulation. This makes it easy to create new imbalances. For example, reducing the recruitment and activation of neutrophils can reduce the damage to normal tissues, but also reduce the lethality to pathogens, leading to the spread of infection. Fourth, in recent explorations, the administration of immune stimulators in later phases is said to be promising, although biomarkers to stratify the immune status are still in development (Peters van Ton et al., 2018). However, once into the late phase, multiple organ dysfunctions may be enough to cause death and immune stimulators may seem meaningless. The only significance of immune stimulators is that of patients with direct immune paralysis in the early phases, but reliable diagnostic indicators are needed. Therefore, the ideal approach is the therapy closest to physiological regulation. Perhaps turning to the neuromodulation of immune responses is a promising direction.

4 Neural regulation of immunity

The immune system was once thought to be an independent regulatory system in the body. The role of the nervous system in regulating immune function has not been known until recent decades, although it has an ancient existence in the history of biological evolution. For example, there are simple organisms, such as C elegans, whose immune cells have been affected by neural signals. In higher animals the brain has been regarded as an immune privileged organ with powerful influence in immunity. The immune system, nervous system and endocrine systems constitute a functional regulatory network (Fig. 2). Based on the functional organization of neuroendocrine and autonomic control, the nervous system can efficiently affect immune function in two ways: through central control and peripheral reflex. The effect of psychological stress on immune function is an example of central control. Peripheral reflex regulation is a more common process, such as inflammatory reflexes (Borovikova et al., 2000; Tracey, 2002). The inflammatory cytokines can stimulate peripheral sensory nerves, including somatic and visceral sensory nerves, or they can directly enter the brain to activate the center integrative effects on immune function, acting through the neuroendocrine or autonomic outputs. The neuroendocrine output is mainly the hypothalamic-pituitary-adrenal (HPA) axis, which has an inhibitory regulating effect on immune function. However, recently it has been noticed that the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamic-pituitary-gonadal (HPG) axis, and the hypothalamic-growth-hormone (HGH) axes are also involved in modulating immune activities (Eskandari et al., 2003). These axes need to be further studied. Autonomic outputs include the sympathetic and vagus nerves, both of which control the immune system and inflammation, which is the focus of this article.

Figure viewer

Fig. 2 The immune network. The immune system, nervous system and endocrine systems constitute a functional regulatory network. The dynamic balance of immune activity is controlled by the interactions of immune cells and cytokinesis (the left part of the figure adapted from Sladkova and Kostolansk, 2006), which accepts the regulation of the brain (the right part of the figure). The brain regulates the immune system with two major outputs: one is the hormonal system including the HPA, HPTs, HPG, and HGH axes (Eskandari et al., 2003); and the other is the autonomic nervous system consisting of sympathetic norepinephrine and vagal acetylcholine pathways. The immune system can also regulate the nervous system through cytokines which activate the afferent nerves or enter the brain directly.

It has been known for a long time that the sympathetic nerves regulate the immune system extensively and complexly, but they have gained increasing interest and attention in recent years. As a result, new knowledge has developed (Eskandari et al., 2003; Olofsson et al., 2012; Jänig, 2014; Jänig and Green, 2014; Bellinger and Lorton, 2014; Pavlov and Tracey, 2017; Chavan and Tracey, 2017). In brief, sympathetic nerves contains nerve fibers (from postganglionic neurons) that specially innervate immune organs including the primary lymphoid organs, i.e. marrow and thymus, and the secondary lymphoid organs, i.e. spleen, lymph nodes, and mucosa-associated lymphatic tissue (Jänig, 2014; Bellinger and Lorton, 2014; Chavan and Tracey, 2017). The sympathetic postganglionic neurons release norepinephrine transmitters which activate β- and α- adrenergic receptors on immune cells, producing the regulatory effects (Bellinger and Lorton, 2014). The β- and α2-adrenergic receptors have opposite effects on immune responses to inflammation (Szelényi et al., 2000; Liu et al., 2020). The hypothalamic area has been thought as a high level center of the autonomic nervous system, which is also known to have extensive influence on immune functioning (for reviews, see Wrona, 2006). Some sub-areas of the hypothalamus might play specific roles in modulating immune functions, e.g. in animal model, electrical stimulation of the lateral hypothalamic area increased natural killer cell cytotoxicity in spleen, while stimulation of the ventromedial hypothalamic area showed suppression effect (Wrona and Trojniar, 2003, 2005). Such hypothalamic-splenic immune modulation is mediated by the sympathetic efferent pathway; therefore, the “hypothalamic-sympathetic-splenic axis” was proposed (Okamoto et al., 1996). The hypothalamus might be involved in the peripheral reflex to modulate immunity (Son et al., 2002; Hahm et al., 2004). Martelli and colleagues (Martelli et al., 2014a, 2014b, 2016, 2019), with a series of experiments in rodents, have identified the greater splanchnic nerve as the sympathetic efferent arm of the inflammatory reflex to inhibit inflammatory cytokines in the spleen as well as in other inner organs innervated by the nerve such as liver, gastrointestinal tract and importantly, the adrenal, as systemic immune cell function can also be regulated through the adrenal medulla with catecholamine releasing. In addition, recent studies have shown that selective somatic local effects of sympathetic innervations on immune functions are available via a direct interaction of the postganglionic nerves with local immune cells. Bassi et al. (2017) showed that direct stimulation of the lumbar sympathetic trunk reduced neutrophil recruitment in arthritic knee joints, and the same effect resulted from direct injection of norepinephrine into the joint. Given the well-known function of the somatic-sympathetic reflex, one might predict that selective stimulation of somatic nerve connecting to the same segment of the spinal cord from which the sympathetic efferent fibers innervate a specific organ or tissue, might produce a local effect of immune regulation of the specific organ or tissues. Indeed, Kim et al. (2007, 2008) have found that electroacupuncture (EA) at Zusanli (ST36) acupoints suppressed zymosan- or carrageenan-induced paw inflammation. Interestingly, they found that low frequency (1 Hz) EA obtained the local suppression effect via activation of sympathetic postganglionic neurons, the simple somatic-sympathetic reflex; while high-frequency (120 Hz) EA suppression is mediated by the sympathoadrenal medullary axis to induce systemic catecholamines for whole body effects. A very recent study (S.B. Liu et al., 2020) showed that selective stimulation of acupoint Tianshu (ST25), which connects to the same segment of the spinal cord sending sympathetic innervation to spleen, evoked the somatic-sympathetic-splenic reflex, produced systemic effect of immune modulation. This new knowledge of different immune reflex paths is very valuable to selective treatment of specific organs and local tissue with inflammation and dysfunction.

More recent knowledge shows that the vagus nerve controls immune function by dominating the spleen and adrenal medulla. The first discovery is the “cholinergic anti-inflammatory pathway” (Borovikova et al., 2000) and then developed the concept of “inflammatory reflex”(Tracey, 2002). In brief (for full reviews, see Ulloa, 2005; Huston et al., 2006; Olofsson et al., 2012; Inoue et al., 2016; Pavlov and Tracey, 2017; Pavlov et al., 2018; Huh and Veiga-Fernandes, 2020), the vagal nerve center can be activated by an immune challenge, and then the vagus nerve efferent terminals releasing cholinergic transmitters, innervate the spleen, perhaps relayed by the splenic nerve (Komegae et al., 2018) (but see Martelli et al., 2014c, 2016), and through the α7 nicotinic receptor on macrophages and other immune cells, inhibit the release of pro-inflammatory cytokines such as TNFα and IL-1 etc. Activation of this pathway by electrical or pharmacological stimulation suppresses excessive inflammation in the gastrointestinal tract (de Jonge et al., 2005; Ghia et al., 2006, 2007), pancreas (van Westerloo et al., 2006), liver (Guarini et al., 2003) and heart (Bernik et al., 2002), inhibiting systemic inflammation. Recent experiments in mice model (Torres-Rosas et al., 2014) have found that the vagus nerve can also dominate the adrenal medulla and activate the latter to release dopamine to inhibit the release of pro-inflammatory cytokines and increase the survival rate of the animals with sepsis. Kwan et al. (2016) have systematically reviewed 36 eligible studies from 290 identified records of vagus nerve stimulation (VNS) for treatment of inflammation in animal models and clinical trials, suggesting that VNS is a very promising approach of inflammation reduction. This immunomodulatory effect produced by stimulating efferent nerves may be an ideal therapy closer to normal or natural physiological regulation without the side effects seen in some drugs. The anti-inflammatory effects of implanted electrodes to stimulate the vagus nerve have been tried for the treatment of chronic immune diseases (De Ferrari et al., 2011; Howland et al., 2011; Howland, 2014; Koopman et al., 2016; Noller et al., 2019). For acute infections, implanting electrodes is not a viable option. Fortunately, stimulating peripheral somatic nerves can also produce the effects of autonomic-immune reflexes, including vagal-immune reflex and the above-mentioned sympathetic-immune reflex (Ulloa et al., 2017; Pavlov and Tracey, 2017). This opens a convenient window of hope for the treatment of acute inflammation in infectious diseases. Not surprisingly, this approach is just how acupuncture therapy works. There is a long history in China of acupuncture being used to treat various emergencies such as acute fever, shock and coma, etc. Acupuncture has been applied even more frequently and sometimes might be considered more important than traditional Chinese herbal medicine, which needs to be prepared or cooked and takes time to see results (L.G. Liu et al., 2004). Acupuncture works rapidly and can often quickly reverse critical conditions, according to ancient and contemporary literature (L.G. Liu et al., 2004). Contemporary Chinese medicine practitioners continued this tradition and use acupuncture, combining it with modern conventional treatment, to treat epidemic diseases, including COVID-19 (R. Wang et al., 2020). Recent random control clinical studies (see following session) also show that acupuncture is a promising clinical anti-inflammatory therapy.

5 Regulatory effects of acupuncture on immune function

Modern studies have demonstrated that acupuncture modulates multiple physiological systems of the body, including the immune system, to reestablish homeostasis by activating peripheral nerves to evoke physiological reflexes (spinal and supraspinal reflex) and the brain central integration (as reviewed elsewhere, Ma, 2004; Zhao, 2008; Kagitani et al., 2010; Uchida et al., 2017; Pan, 2018, 2019). The experimental research on the effects of acupuncture on immune function can be traced back to the middle of the last century (S.Z. Liu, 1959; Yan, 1959). Studies over the decades have shown that acupuncture has a wide range of regulatory effects on the immune system (Den, 1981).

5.1 Enhancement effects of acupuncture on immunity under physiological conditions

Most of the early studies showed that acupuncture enhanced immunity of normal humans or physiological model animals (S.Z. Liu, 1959; Den, 1981; Du et al., 1995; Johansen et al., 2004; Sato et al., 1996). Acupuncture can enhance the innate immune functions. For example, a large number of studies in rodent models (Sato et al., 1996; Liu et al., 1997; Choi et al., 2002; Kim et al., 2005; Rho et al., 2008) showed that EA at ST36 (Zusanli) upregulated the function of natural killer (NK) cells and macrophages, which play a central role in the innate immune response, especially in killing virus-infected cells. Acupuncture also increases the weight of mouse thymus (L.J. Liu et al., 1997), suggesting an effect of enhancing innate immune function. The effect of acupuncture on adaptive immunity is also supported by many experimental results. Acupuncture can increase the number of lymphocytes in the peripheral blood and the lymphocyte transformation rate in animals (Cao et al., 1982) and humans (Wu, 1983; Jong et al., 2006). In the aging animal model, acupuncture increased the functions of T lymphocytes (J.M. Liu et al., 2009). It has been reported that acupuncture for 20 days can increase the level of IgG and IgM in the elderly (Han, 1993). A few studies have shown that the lateral hypothalamus plays a role in the enhancement effect of EA. EA increased natural killer cell activity in the spleen, correlating with the activation of hypothalamus (Rho et al., 2008). Selective destruction of the lateral hypothalamic area (Choi et al., 2002) cancelled various immune enhancement effects of acupuncture. The general enhancement effects of acupuncture on immunity might benefit the prevention of infections and immune suppression status of sepsis. However, acupuncture effects on immunity show state-dependent features. For example, under disease conditions, the effects of acupuncture might be different from that under normal conditions, which is elaborated below.

5.2 Bidirectional regulations of immune function by acupuncture under pathological conditions

Previous studies have shown that the most interesting feature of acupuncture is the bidirectional regulation effect on the body's homeostasis, either in hyper- or hypo- functional states (dual regulation, normalization, or restoring homeostasis) in either patients or pathological models of animals (for a review, Pan, 2019). For instance, EA at ST36 showed stimulation of stress-induced delayed gastric emptying and inhibition of stress-induced acceleration of colonic transit (Iwa et al., 2006). Such state-dependent effect also is observed on immune modulation by acupuncture. Acupuncture can enhance the suppressed innate immune functions, such as up-regulating the decreased function of NK cells and macrophages (Zhao et al., 1994; Wu, 1995; Hisamittsu et al., 2002; Yamaguchi et al., 2007; Johnston et al., 2011). Conversely, acupuncture can also downregulate the activity of these immune cells and related cytokines when they are in a hyperactivity state such as inflammation (see the following section). Studies (as reviewed elsewhere, Kim and Bae, 2010; Dai et al., 2018) also showed that acupuncture has bidirectional regulating effects on adaptive immunity, such as T lymphocytes functions. T helper cells, a type of T lymphocytes, play an important role in the immune modulation. There are two main subsets of T helper cells, Th1 and Th2, which respectively produce Th1 type cytokines (e.g. IL-2, INFγ) and Th2 type cytokines (e.g. IL-4, IL-10). The former tends to produce the pro-inflammatory responses, and the latter, anti-inflammatory responses. The balance of Th1/Th2 is changed in different diseases and that can be modulated by acupuncture (Yamaguchi et al., 2007; Dai et al., 2018; Silvério-Lopes and da Mota, 2013). For example, acupuncture can downregulate Th2-specific cytokines (Park et al., 2004; Kim et al., 2011) to improve Th2 dominant disorders, such as allergic rhinitis (Shiue et al., 2008) and chronic fatigue syndrome (C. Wang et al., 2014). In contrast, for the Th1 dominant disorders such as rheumatoid arthritis (Yim et al., 2007), ulcerative colitis (Tian et al., 2003) and depression (Lin et al., 2014), acupuncture can modulate the Th1/Th2 balance with inhibiting Th1 responses. Such bidirectional regulatory effects suggest some interesting mechanisms that need further study (Pan, 2019). Generally speaking The bidirectional regulatory effect of acupuncture mirrors the activation and reinforcement of the body's self-healing or biological adaptive mechanism, which is a unique effect that no specific drug can reach at this time. Thus, acupuncture is a patient-tailored approach, although controlled by the body per se.

5.3 The anti-inflammatory effect of acupuncture

There is growing interest in the anti-inflammatory effect of acupuncture in the research field. In recent decades, the anti-inflammatory effects of acupuncture in septic animals and patients are highlighted. The most common problem of immune response in sepsis is a hyper-reactive cytokine storm. Silvério-Lopes and da Mota (2013) systematically eval‎uated 67 relevant papers published between 2001 and 2011, and concluded that acupuncture and EA are effective in modulation of immunity in animals and humans. Lai et al. (2020) systematically reviewed 54 studies up to May 2019 on acupuncture at ST36 (Zusanli) for the treatment of the experimental sepsis in animal models crossing species (rodents and rabbits). They used 17 criteria to estimate the study quality and risk of bias. The average quality scores of the studies is 6.3 varying from 2 to 9.5, with 13 studies (15%) accepted quality scores ≥7.0. Those studies support that acupuncture benefits to protecting multiple organs against injuries by sepsis and maintaining the immune balance to attenuate inflammation. A very new study (S.B. Liu et al., 2020), published in Neuron online, July 2020, further confirmed that acupuncture has a reliable anti-inflammatory effect, and revealed new features and mechanisms by using genetic strategy. Those results, especially from the quite a few quality studies (Scognamillo-szabo et al., 2004; Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Villegas-Bastida et al., 2014; Yu et al., 2014; Zhu et al., 2015; Chen et al., 2016; Liu et al., 2020), have shown that the efficacy of acupuncture on experimental sepsis has the following characteristics:

1.

EA improved the survival rate of animals with sepsis. The survival rate of rats or mice with sepsis increased significantly, with a maximum survival increase up to 80% (S.B. Liu et al., 2020; Torres-Rosas et al., 2014; Chen et al., 2016; Song et al., 2012; Zhu et al., 2015; Villegas-Bastida et al., 2014). EA inhibited the release of important pro-inflammatory factors. The blood levels of pro-inflammatory factors such as TNF, IL-6, MCP-1 and INFγ in the acupuncture group were significantly reduced. The level of anti-inflammatory factor IL-10 either increased (da Silva et al., 2011; Ramires et al., 2020) or did not change significantly (Song et al., 2012). It suggests that acupuncture does not simply suppress the immune response but modulates its balance. The anti-inflammation effect of acupuncture is clear. A study (Ramires et al., 2020) showed that acupuncture obtained similar levels of effect as that of indomethacin (a classical nonsteroidal anti-inflammatory drug) in suppressing peripheral and brainstem cytokines.

2.

EA reduced injuries induced by sepsis in multiple inner organs such as lung, cardiac, kidney, liver and gastrointestinal tract (Lai et al., 2020).

3.

The time-window of treatment exists. The earlier that acupuncture treatment is given, the better the results, with results from preventive care even better (Torres-Rosas et al., 2014; Liu et al., 2020). Even one treatment or pretreatment of EA can cause the effect, and the effect lasts at least 6 h (Torres-Rosas et al., 2014). However, the effects from daily EA, in which there are a consecutive three days of treatment, may have more stable and effective results (Torres-Rosas et al., 2014). A new finding (S.B. Liu et al., 2020) is that time-window plays the role depending on the intensity of stimulation (see below for the details). However, these results perhaps depend on the inflammatory model. It seems that the pretreatments are better than post treatments to lipopolysaccharide (LPS) model (Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Chen et al., 2016; S.B. Liu et al., 2020; Ramires et al., 2020), but no matter to the cecal ligation and puncture (CLP) model (Song et al., 2012; Torres-Rosas et al., 2014). This might arouse future studying of the treatment windows for various inflammations with different pathogens, e.g. bacteria or virus.

4.

The parameter of EA stimulation is important, which consists of frequency, intensity and the model of pulse trains including generally “continuing trains”, “bursting trains” and “alternating trains” with a common commercial EA stimulator. Most experiments obtained show clear effects with simple stimulation of continuing trains of low frequency (<15 Hz). However, a study (Chen et al., 2016) comparing the effects of three types of trains has shown that the alternating trains (2/15 Hz) is the best, then the bursting trains (2/0 Hz), and then the continuing trains (2 Hz). As mentioned above, another study showed that that low frequency (1 Hz) EA produce the local anti-inflammatory effect via activation of the simple spinal somatic-sympathetic reflex; while high-frequency (120 Hz) EA is mediated by the sympathoadrenal medullary axis to induce systemic effects (Kim et al., 2007, 2008). This frequency effect is consistent with some other acupuncture effects depending on frequency of stimulation (Han, 2003).

5.

There are large varieties of the intensity of EA stimulation used in different experiments. A problem is that different laboratories used different stimulators which indicate the intensity with different scales: current (mA) or voltage (V), that limits to compare the intensities between the different studies. However, some studies included investigating the effects of intensities, providing valuable data. Torres-Rosas et al. (2014), using mice lipopolysaccharide (LPS) model, compared the pretreatments with stimulations of 0.4 V and 4 V at ST36, and the results showed that the anti-inflammatory effect of 4 V stimulation was clearly stronger than that of 0.4 V. Similarly, Liu et al. (2020) compared the pretreatment with stimulations of 0.5 mA, 1.0 mA and 3.0 mA at ST36 or ST25 (Tianshu, at abdomen) in LPS mice, conforming the results, i.e. the stronger the stimulation, the better the anti-inflammatory effect. A surprising funding by Liu et al. is that post-treatment with the 3.0 mA produced oppositely pro-inflammatory effects, i.e. increased the serum TNF-α level and decreased in survival rate. That is because that LPS increased the expression‎ of α2-ARs (adrenergic receptors) in splenic cells, which mediate pro-inflammatory effects, and the post-treatment with high intensity EA activated the spinal sympathetic-splenic pathway (demonstrated with genetic strategy) that further enhanced the α2-ARs effect. They further demonstrated that Yohimbine (α2-ARs antagonist) or splenectomy allowed 3.0 mA EA to promote survival and to suppress serum TNFα level. However, they found that post-treatment of 0.5 mA weak stimulation at ST36 is not enough to activate this sympathetic-splenic pathway, but it is sufficient to activate the vagal-splenic pathway to obtain the anti-inflammatory effects. But EA at ST25 (either 0.5 mA or 3 mA) did not activate the vagal reflex. Those findings are consistent with the previous results that stimulating acupoints at abdomen area produced the sympathetic reflex on the inner organs, while stimulating acupoints of limbs produced the vagal reflex (Sato, 1997; Li et al., 2007). Those results suggest that we need to consider the stimulation site (acupoint), stimulation intensity and time window of treatment (pre- or post- treatment) together for a clinical therapy. Especially, the time-window dependent effect of stimulation intensity is not easy to control in clinical practice because that almost all treatments are post-treatment on patients. However, this result was from the LPS model. Another data showed that the post-treatment of high intensity EA on CLP model obtained the anti-inflammatory effects and promoted the survival rate (Torres-Rosas et al., 2014). On the other hand, EA applying to patients in real clinical practice might rarely reach the intensity of stimulation as high as that in animals in the laboratory. The EA stimulation of 3 mA is over the threshold (>2 mA) (Kagitani et al., 2010) activating Aδ and C fibers of the peripheral nerves (but see Zhou et al., 1985), that will produce pain feelings in conscious animals and humans. The general situation in a clinic is that a stimulation of EA applying to a patient without uncomfortable feeling, especially without pain, that generally induces slight twitch of the local muscles. This general clinic EA intensity is roughly equal to moderate stimulation in animal experiments, which perhaps might or might not activates the peripheral Aδ fibers (threshold 1.5 mA)(Kagitani et al., 2010; Li et al., 2007) but not C fibers. We might not need to concern too much on above pro-inflammatory effect induced by high intensity post-EA, rather, we might use this feature to benefit to patients, e.g. using relative high stimuli at very early stage (before sepsis happening) to prevent serious sepsis, or promote immunity at late stage with the immune-paralysis.

6.

The selection of acupoints has certain significance. As mentioned above, to control inner organ function, the acupoints at abdomen or back mediate the somatic-sympathetic reflex, while the acupoints of limbs mediate the somatic-vagal-reflex (for an individual organ, the exact and maximal reflex effect is obtained following the spinal segmental dominance rule). However, there is still some variety between acupoints within trunk group or limbs group, e.g. LI4 (Hegu) and PC6 (Neiguan) are both effective acupoints of anti-inflammation, but the former is more effective (Song et al., 2012). This difference might be related to the distinction of the nerves distribution under the acupoints.

7.

The anti-inflammation effect of EA is mainly achieved by activating vagal-splenic pathway (Song et al., 2012; Villegas-Bastida et al., 2014; Lim et al., 2016; S.B. Liu et al., 2020), the vagal-adrenal medulla-dopamine pathway (Torres-Rosas et al., 2014) and the sympathetic-splenic pathway (Martelli et al., 2014b; S.B. Liu et al., 2020), rather than by enhancing the hypothalamic-pituitary-adrenal cortex axis, because electroacupuncture pretreatment did not increase serum corticosteroid in animal sepsis model (Song et al., 2012). The role of sympathetic-adrenal medulla pathway is thought to play the role in anti-inflammatory effect in carrageenan-induced paw inflammation model (Kim et al., 2008). However, the role of sympathetic-adrenal medulla pathway in suppressing systemic inflammation needs further investigation. Furthermore, the role of sympathetic-vagal relationship and balance are worth to be studied (Huang et al., 2010).

With these detailed results, the approach of the peripheral-autonomic-immune reflex, carried out by acupuncture, seems promising in being translated into a relative optimal clinical therapy. However, as mentioned above, in the process of sepsis, the immune system with CARS mechanism might present not only a hyper-inflammatory reaction but also immune-paralysis depending on the individual conditions. Further studies are needed to address if there is immune-paralysis at a later stage (even early stage) of the sepsis model, which can be prevented by acupuncture. Theoretically, acupuncture should have a corrective effect for both the hyper- and the insufficient immune responses in the inflammation process according to the bidirectional principle. Indeed, Guo et al. (2010) have reported that EA at Zusali (ST36) and Guanyuan (CV4) decreased the apoptosis of thymocytes in rat sepsis model, suggesting acupuncture can prevent sepsis animals from immune-paralysis. The data from other immune suppression models and clinical trials of inflammation also support the bidirectional effects of acupuncture. For instance, acupuncture reduced the increased plasma level of IL-10 in patients with chronic allergic rhinitis (Petti et al., 2002). Theoretically, when the releasing of pro-inflammatory factors is suppressed, the releasing of anti-inflammatory factors will decrease as well, due to the latter being triggered by the former. Thus, reducing the pro-inflammatory factors by acupuncture at an early stage means also reducing the anti-inflammatory factors later. This might help to avoid the up-and-down oscillation of the compensatory anti-inflammatory response to prevent immune-paralysis, that finally increases the survival rate of animals with sepsis, which needs to be confirmed in future.

5.4 Clinical evidence

In real clinical conditions, patients with sepsis may also have additional complications, especially during the critical stage. Therefore, it is necessary to use different medications or therapies to deal with multiple factors to reach the best results, although animal experiments have shown that acupuncture alone significantly increases the survival rate of sepsis animals. Traditional Chinese practitioners have known for thousands of years to combine acupuncture and herbal medicine together to cure complicated diseases, including serious infections. Recently, acupuncture integrated with modern medical therapies, as a part of the comprehensive treatments of sepsis, has shown exciting values in clinical trials. Clinical reports show that the effect of adding acupuncture intervention in conjunction with conventional treatment is superior to the conventional treatment group alone. A recent study (L. Wang et al., 2019) of a randomized controlled trial on 108 patients with sepsis (54 in the control group and 54 in acupuncture group) showed that the patients in both groups were given conventional treatments, i.e. routine anti-infective medications, and supportive treatments with organ functioning monitored. The patients in the acupuncture group were treated with acupuncture at ST36 daily for 3 consecutive days in addition to conventional treatment. The results showed that, compared to the condition before the treatments, after the treatments, the plasma factor procalcitonin (PCT), blood lactic acid (Lac) expression‎ level, Acute Physiology and Chronic Health Eval‎uation (APACHE II) score, and Sequential Organ Failure Assessment (SOFA) score in both groups were significantly decreased; however, compared to the control group, after the treatment, the acupuncture group showed more decreaces significantly (P < 0.05). Another study (J.N. Wu et al., 2013) conducted a randomized control trial with 50 patients with sepsis, comparing acupuncture plus conventional treatment (n = 26) with conventional treatment alone (n = 24). The results showed that after 3 consecutive days of daily EA treatment, the plasma TNF-α, IL-6 in the “acupuncture plus conventional treatment” group were significantly lower than that in conventional treatment group, and its overall effect was also better. Similarly, F.W. Wu (2016) reported the effect of EA on the inflammatory response and immune function in sepsis patients. The 50 patients with sepsis were randomly divided into two groups of 25 each, i.e. the control group used the treatment plan recommended by the 2008 international guideline on the rescue of sepsis, and the acupuncture group used EA at ST 36 daily plus the treatment given to control group. The APACHE II scores, C reactive protein (CRP), PCT, Lac, and IL-6, IL-10 and T cell subsets (CD4+ and CD8+) were recorded before the treatments and 3 and 7 days after treatments in both groups. The rates of incidence of MODS and fatality rate during 28-day hospitalization were calculated. The results showed that after treatments, at each time point the APACHE II score, CRP, PCT, and Lac levels in both groups decreased to some extent, while the levels of CD4+ and CD8+ of T cell subsets involved in adaptive immunity increased in both groups; however, the EA group was better than the control group (P < 0.05). This indicated that EA at ST36 not only alleviated the pro-inflammatory response of patients with sepsis, but also improved adaptive immune function. This study importantly shows that the 28-day fatality rate in the EA group (8.00%) was significantly lower than that in control group (28.00%) (P < 0.05), while the incidences of MODS in EA group (24%) was lower than that in control group (36%) but not significantly (p > 0.05). Xiao et al. (2015) also obtained similar results. 90 patients with sepsis were randomly distributed to “conventional treatment” (n = 30), “conventional treatment + thymosin α1” (n = 30), and “conventional treatment + acupuncture” (n = 30). The fatality rate after treatment, and T cell subsets CD3+, CD4+, CD8+, CD4+/CD8+ ratio and the antibody IgG, IgA, IgM before and after treatment were compared between groups. The results showed that after 6 days of treatment, while the immune function with above items in all three groups of patients significantly increased (P < 0.01), that the thymosin group and the acupuncture group increased significantly more than in the conventional treatment group (P < 0.01, respectively). The ICU length of stay (days), and the rates of 28-day fatality also decreased significantly (P < 0.05, P < 0.01 respectively) in both the thymosin group and with the acupuncture group compared with the conventional treatment group. This suggests that acupuncture can improve adaptive immune function, and its effectiveness is comparable to that of thymosin, a recognized immune-stimulant used for the treatment of sepsis. This clinical data suggest that acupuncture not only decreases the pro-inflammatory factors but also enhances adaptive immune function to prevent immune-paralysis, which needs to be further confirmed.

Further, acupuncture can not only modulate immune function, but also improve organ functioning in multiple disorders. This also gives acupuncture as an advantage to treating MODS, imbalance of energy metabolism of sepsis. For example, a study by Yu et al. (2015) has shown that acupuncture can not only significantly improve the immune function of sepsis cases, but also protect the gastrointestinal function of septic patients. The incidence of vomiting, abdominal distension and gastric retention in the EA group (EA plus conventional treatment) were significantly reduced compared with the control (conventional treatment alone) group. Meng et al. (2018) also obtained the effects of attenuating inflammatory responses and intra-abdominal pressure in septic patients, but not the length of stay in intensive care unit (ICU) and 28 days fatality rate.

A recent meta-analysis (Tang et al., 2020) including 20 studies with total 1337 patients with sepsis showed that the 28 day fatality rate, the APACHE II score on the 3rd day and the 7th day after treatments, ICU length of stay, gastrointestinal function improvement, PCT and TNF-α on day 7 after treatments, in acupuncture plus conventional treatment group were all significantly superior to that in conventional treatment alone group statistically. All those research results (although still limited) indicate that acupuncture is a very promising integrative therapy for treating patients with sepsis.

6 Discussion: toward a science-based design of EA protocol of immunomodulation

Given the current absence of recognized treatment protocols for immune dysfunction in the process of sepsis, based on above laboratory (i.e. preclinical studies) and clinical evidences, acupuncture could serve as an adjuvant therapy, with its advantage of being easily used, low cost, without any chemical side effects, and importantly, because of its ability to modulate both immune function and multiple organ function. All of which are beneficial to prevent the condition from worsening and to decrease the fatality rate of septic patients. We strongly recommend that acupuncture be included in the comprehensive treatment plan for sepsis. However, the therapies used in previous studies generally followed traditional theory or personal experience. Their selections of acupoints, stimulating parameters, daily dose and course of treatment might not be optimal; thus, it might limit their curative efficiency. To obtain better or maximal effects, we give an acupuncture protocol design based on the new knowledge developed from the researches described above. For the mechanism, stimulating peripheral nerves induces the somatic-autonomic reflex, which produces sympathetic or vagal effects on the functional regulation of organs or physiological systems, including the immune system we now focus on. The spinal somatic-sympathetic reflex follows the rule of the spinal cord segmental control, i.e. the effect of a somatic-sympathetic reflex on an specific organ is obtained limitedly by stimulating the somatic nerve connecting to the spinal cord segments (1–5 segments usually) as same as that the organ do. For example, the spleen is innervated by the sympathetic nerve from the spinal cord segment T5-T8, thus only the stimulation (electrical or acupunctural one) from the somatic nerve zone belonging to the T5-T8 segments can produce the reflex effect on the spleen. Similarly, T8-L1 for the adrenal medulla, and T1-T5 for the lung and so on, that a map with the details can be found in any anatomy textbook. The supraspinal somatic-sympathetic reflex might be induced by high intensity nociceptive stimulation, which is systemic, but rarely produced by acupuncture. The somatic-vagal reflex is special. Previous data showed the vagal reflex control the gastrointestinal tract can be induced by stimulation of the peripheral nerves or the acupoints at the limbs (not the trunk) with high intensity (activating Aδ and C fibers) of stimulation (Sato,1997; Li et al., 2007). However, to activate the vagal-adrenal reflex, a new data (Liu et al., 2020) showed that the stimulation of 0.5 mA (lower than the threshold of Aδ) is sufficient to do. To focus on immune function controlling, we name those reflexes as “somatic-autonomic-immune reflexes”; specifically, the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex, somatic-vagal-adrenal reflex, which induce systemic regulatory effects on immune functions because the final outputs are from the spleen or the adrenal medulla, which release cytokines or norepinephrine and dopamine into blood. However, the other somatic-sympathetic reflexes related to an organ have local effect only, e.g. the somatic-sympathetic-lung reflex, the somatic-sympathetic-kidney reflex, etc. It should be noted that stimulation of any acupoint can also produce common systemic effects or perhaps some unknown specific effects through the brain integration (both sympathetic and vagal ones) simultaneously, that need further studies. Those concepts and principles are illustrated in Fig. 3.

Figure viewer

Fig. 3 The organization of the somatic-autonomic-immune reflexes (the part of the figure showing the autonomic nervous system and organs is modified from Figure 296 of REF [Gao and Yu, 2014]). For explanation see the text.

6.1 An auxiliary acupuncture protocol

Following the above reflex principles and considering that the effects of acupuncture are state-dependent, stimulation-parameter-dependent, acupoint-dependent, and treatment-time-dependent, an auxiliary acupuncture protocol for sepsis treatment is designed as follows and summarized in Table 1:

1)

Acupoint selection: examples of acupoints we selected are listed below. It should be noted that following the segmental distribution to select acupoints is the key point here.

a.

Systemic regulation:

•

Vagal Group: ST36 (Zusangli) or LI4 (Hegu), bilaterally (the same below). They are the most effective acupoints reported from laboratorial and clinical studies, activating vagal anti-inflammatory pathway to down-regulating cytokines storm;

•

Sympathetic Group: BL17 (Geshu) and BL19 (Danshu) on the back; or ST21 (Liangmen) and ST25 (Tianshu) on the abdomen, to activate the sympathetic-splenic reflex and the sympathoadrenal medullary reflex, additionally benefiting to septic shock patients due to the norepinephrine releasing.

b.

Local regulation:

•

Thoracic group: BL13 (Feishu) and HT7 (Shenmen).

•

Abdominal group (gastrointestinal organs, liver and kidneys): BL19 (Danshu) and ST25 (Tianshu).

•

Pelvic group: BL23 (Shenshu) and SP6 (Sanyinjiao).

b.

The formula of acupoints we recommend:

Formula I: Vagal group + Local group/s (if needed);

Formula II: Sympathetic group + Local group/s (if needed).

The two formulas are used in turns.

2)

Stimulation parameters: for the intensity of EA, it is recommended to give moderate stimuli which can cause slight muscle twitching and also be tolerated by patients. To prevent sepsis in patients in the early stages of infection, high-intensity stimulation is recommended; that perhaps causes more of a pain sensation. Applying EA “continuing trains” with the frequency of 2–10 Hz for 30 min is a general EA dose. However according to the frequency effect (Chen et al., 2016), here we recommend using “alternating trains” of 2/15 Hz or 2/100 Hz, (100 Hz to enhance sympathoadrenal medullary reflex, Kim et al., 2008) for systemic effects, and “bursting trains” with high frequency (15-100 Hz) for local effects. If using the traditional manual acupuncture, we suggest mimicking the “alternating trains”, applying a light or moderate stimulation (a slow rotation) of 2–5 min/10 min for 30 min, given that manual acupuncture can activate all groups of sensory nerve fibers (Kagitani et al., 2010) and a slow rotation of needle is efficient to induce anti-inflammatory effect (Lim et al., 2016; Ramires et al., 2020).

3)

Daily dose and course of treatment: considering that the inhibitory effects of one treatment of EA on most inflammatory factors last for about 6 h (Song et al., 2012; Torres-Rosas et al., 2014), the daily dose we suggest is 2 times/day for patient with sepsis; one time/day for early stage of acute infection. Formula I and Formula II will be used in turns. Take a course of 5–7 days with a break of 1–3 days, because the toleration might happen after 7 days with continuous daily treatments (Du et al., 1995). For severe infection such as COVID-19, the sooner the intervention is performed, the better.

4)

Self-healing: for mild cases or early stages of the infection, the transcutaneous electrical stimulator (TENS) can be used by patients themselves.

EffectsReflexAcupointsPulse trainsFrequency (Hz)IntensityDose & course

Systemic	Vagal reflex	ST36 (Zusanli) LI4 (Hegu)	A B C	2/15 or 2/100 15 2	Moderate	2 times/day, 5–7 days
Systemic	Sympathetic-splenic	BL17 (Geshu) ST21 (Liangmen)	A B C	2/100 or 2/15 100 or 15 15	Moderate	2 times/day, 5–7 days
	Sympathetic-adrenal	BL19 (Danshu) ST25 (Tianshu)	Same
Local organs	Sympathetic (thoracic)	BL13 (Feishu) HT7 (Shenmen)	B	15 or 2	Moderate	2 times/day, 5–7 days
	Sympathetic (abdominal)	BL19 (Danshu) ST25 (Tianshu)	Same
	Sympathetic (pelvic)	BL23 (Shenshu) SP6 (Shanyinjiao)	Same

Table 1

An example design of evidence-based therapy of EA to modulate immunity in sepsis.

A: alternating trains; B: bursting trains; C: continuing trains.

• Open table in a new tab

6.2 Limitations and future research

As discussed above, acupuncture is supported by a large amount of research data both in clinical trials and animal studies in resolving cytokine storms during severe inflammation; however, there still exist many unsolved gaps. There are several limitations to this review aside from those discussed above. 1) Although acupuncture's anti-inflammatory storm has been repeatedly confirmed by animal experiments, and the effect of acupuncture in inhibiting inflammatory storms through neuroimmune pathway is almost certain, it should be noted that current experimental results mostly come from CLP models and LPS models. It is necessary to further compare the differences between these two and expand to other new models. In particular, a new direction is to establish an immune-paralysis model in late-stage sepsis. 2) More detailed research is needed in acupoint selection and stimulation parameters. 3) Time-window of acupuncture effect is worthy enough to do further systematic research: identifying the acupuncture effect during different development stages of sepsis, i.e. pretreatment, and its early, middle, and late stages. This needs to combine with acupoint selection and stimulation parameters. 4) Refining and deepening is needed in the bidirectional regulating effect and mechanism of acupuncture in terms of immune regulation. In particular, given that the suppressing effects of acupuncture on cytokine storms has been well addressed, next challenge is investigating the effects of acupuncture on immune-paralysis in sepsis. 5) Most of previous studies focused on systemic effects of acupuncture or other peripheral nerve stimulation. A new direction is identifying local effect produced by local segmental reflexes, that will provide scientific bases of acupoint selection to clinical therapy design. 6) Any peripheral stimulation might produce both local spinal segmental reflexes and supra-spinal reflexes. Local segmental reflexes might co-work with its supra-spinal reflexes, or have independent effect, that can be used in different situation. This is a basic question of acupuncture and very important for selecting acupoints in a therapy. The interactions and mechanisms of local spinal segmental reflexes and supra-spinal reflexes produced by acupuncture need to be further studied extensively, not only for inflammation but for all other disorders. 6) Current acupuncture clinical trials have some quality issues. The quality of most reports has been criticized due to insufficient sample sizes and lacking proper sham controls. Indeed, the feature of acupuncture different from drug's makes the design of sham acupuncture control difficult to meet the rules of double-blind clinical study. To avoid such problems, the National Institutes of Health (NIH) is currently advocating real-world clinical research in view of the characteristics of acupuncture (Zia et al., 2017). However, according to the results of current animal and clinical experiments, there are large varieties of the effects of acupoints and stimulation parameters, that some of them showed significant effects but others with little effects on same treatment targets (e.g. Chen et al., 2016; Li et al., 2015). Such little effective acupoints or stimulation parameters give an idea “sham” control manipulation. By using such parallel design, Li et al. (2015) showed the effects of long-lasting reduction of blood pressure in a group treated with specific acupoints but not in the other group with different acupoints. We strongly recommend such parallel design, that uses invalid acupoints or stimulation parameters as “sham” control group to rule out placebo effect. Parallel design is well known as the “gold standard” for phase 3 clinical trials. It is just very well for clinical study of acupuncture. Anyhow, systematic, large and rigorous clinical data will be the key for supporting in acupuncture-assisted immune adjustment in the treatment of sepsis. The acupuncture protocol designed in this article is just one example of suggestions for future clinical research, which is based on current available literature. We hope that this protocol would be inspiring and promoting the translation from scientific study to clinical application. Given that there are gaps in acupuncture mechanisms, and between acupuncture real practice and basic science study in treating sepsis, further studies in both acupuncture mechanisms and clinical trials are warranted.

7 Summary

Faced with the severe situation of the global pandemic of COVID-19, the medical community throughout the world is exploring various treatments from different approaches, including antiviral, anti-inflammatory, and controlling multiple organ functions. It has been identified that COVID-19 induces immune disorder and sepsis in severe patients (Yuki et al., 2020). A new study demonstrated that COVID-19 cytokine storms, especially a high level of TNF may make few memory B cells and prevent a durable immune response (Kaneko et al., 2020). For fatal sepsis with multiple organ failure, the imbalance of immune function is the core pathological mechanism, and the various therapies for controlling the immune function currently have no recognized best choice for various reasons. At this moment, acupuncture used to activate the somatic-autonomic-immune reflexes is a promising therapy emerging from multiple recent animal experiments and clinical studies, to provide significant clinical advantage to control inflammation and restore organ function without adverse side effects. Different from a new drug investigation needing a phase I clinical trial (screening the safety and testing the proper dose), acupuncture with its safety feature, has been carried out at least in phase II like clinical trials for a variety of diseases for years throughout the world. If acupuncture is involved in the treatment of COVID-19, the patients will not only avoid losing a promising adjunctive therapy, but it would also be a good opportunity obtaining a large number of patients to test the efficiency of acupuncture in a clinic trial. Previous studies from animal models and clinical trials have shown that acupuncture modulates immunity, but it has yet been consistent with showing that acupuncture decreases the fatality rate of sepsis patients. Besides the complicated process of sepsis, one main reason is that the efficiency of acupuncture depends on several factors such as the pathological status, the acupoints, the stimulation parameters and the time-window of treatment etc. that need well consideration together to obtain maximal effects. We recommend an evidence-based comprehensive design of EA protocol to practitioners and researchers to test it. It is worth looking forward to its contribution to the treatment of sepsis and, for the moment, to treating the urgent need of patients with COVID-19 infection as well as for future patients with various infections and other factors.

Declaration of competing interest

Author Sarah Faggert Alemi was employed by the company Eastern Roots Wellness, PLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AcknowledgmentsAcknowledgements

We thank Dr. Qiufu Ma for his feedback on the manuscript.

CRediT authorship contribution statement

This project was initiated by WX Pan and A.Y. Fan. As the primary researcher, WX Pan designed the project and protocol, structured and drafted the early version of manuscript. A.Y. Fan, SZ. Chen and S.F. Alemi participated in discussing, further drafting and editing the later versions. WX. Pan and A.Y. Fan completed the final manuscript. There was no financial support for this project. Due to the limitation of the authors' personal experience and perspective, this review may have some omissions and errors; comments or corrections are welcomed and appreciated.

References

1.

Bassi, G.S. ∙ Dias, D.P.M. ∙ Franchin, M. ...

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Brain Behav. Immun. 2017; 64:330-343

Crossref

Scopus (71)

PubMed

Google Scholar

2.

Behrens, E.M. ∙ Koretzky, G.A.

Cytokine storm syndrome: looking toward the precision medicine era

Arthritis Rheumatol. 2017; 69:1135-1143

Crossref

Scopus (226)

PubMed

Google Scholar

3.

Bellinger, D.L. ∙ Lorton, D.

Autonomic regulation of cellular immune function

Autonomic Neuroscience: Basic and Clinical. 2014; 182(15–41):2014

Google Scholar

4.

Berlot, G. ∙ Passero, S.

Immunoparalysis in Septic Shock Patients. Patients [Online First]

IntechOpen, 2019

https://www.intechopen.com/online-first/immunoparalysis-in-spetic-shock-patients

Crossref

Google Scholar

5.

Bernik, T.R. ∙ Friedman, S.G. ∙ Ochani, M. ...

Pharmacological stimulation of the cholinergic antiinflammatory pathway

J. Exp. Med. 2002; 195:781-788

Crossref

Scopus (458)

PubMed

Google Scholar

6.

Borovikova, L.V. ∙ Ivanova, S. ∙ Zhang, M. ...

Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin

Nature. 2000; 405:458-462

Crossref

Scopus (3326)

PubMed

Google Scholar

7.

Cao, J.R., Gong, Q. H., Xiang, Y. M. (1982). Effect of acupuncture on the output lymph and cell in popliteal lymph nodes in rabbits. Shanghai J Acu-moxi. 1, 35–37.

Google Scholar

8.

Chavan, S.S. ∙ Tracey, K.J.

Essential neuroscience in immunology. J Immunol. 2017; 198:3389-3397

Google Scholar

9.

Chen, Y., Lei, Y., Mo, L.Q., Li, J., Wang, M.H., Wei, J.C., et al. (2016). Electroacupuncture pretreatment with different waveforms prevents brain injury in rats subjected to cecal ligation and puncture via inhibiting microglial activation, and attenuating inflammation, oxidative stress and apoptosis. Brain Res Bull. 127, 248–259.

Google Scholar

10.

Choi, G.S. ∙ Oha, S.D. ∙ Han, J.B. ...

Modulation of natural killer cell activity affected by electroacupuncture through lateral hypothalamic area in rats

Neurosci. Lett. 2002; 329:1-4

Crossref

Scopus (26)

PubMed

Google Scholar

11.

da Silva, M.D. ∙ Guginski, G. ∙ Werner, M.F. ...

Involvement of interleukin-10 in the anti-inflammatory effect of Sanyinjiao (SP6) acupuncture in a mouse model of peritonitis

Evid. Based Complement. Alternat. Med. 2011; 2011:217946

Crossref

Scopus (50)

PubMed

Google Scholar

12.

Dai, Q.M., Shang, Y.Q., Liang, H., Yan, P.Y., Wang, M.Q., Wang, K. (2018). Research progress of effect of acupuncture therapy on T cell subsets. J Clin Acupunct. 7,78–82.

Google Scholar

13.

De Ferrari, G.M. ∙ Crijns, H.J.G.M. ∙ Borggrefe, M. ...

Chronic vagus nerve stimulation: a new and promising therapeutic approach for chronic heart failure

Eur. Heart J. 2011; 32:847-855

Crossref

Scopus (426)

PubMed

Google Scholar

14.

de Jonge, W.J. ∙ van der Zanden, E.P. ∙ The, F.O. ...

Stimulation of the vagus nerve attenuates macrophage activation by activating the Jak2-STAT3 signaling pathway

Nat. Immunol. 2005; 6:844-851

Crossref

Scopus (918)

PubMed

Google Scholar

15.

Den, G.G.

ReviewVolume 232102793May 2021Open access

Download Full Issue

Acupuncture modulates immunity in sepsis: Toward a science-based protocol

Wei-Xing Pana panw@hhmi.org ∙ Arthur Yin Fanb,c ArthurFan@ChineseMedicineDoctor.us ∙ Shaozong Chend,1 zjyjs1980@sdutcm.edu.cn ∙ Sarah Faggert Alemib,e

Affiliations & Notes

aJanelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA

bAmerican TCM Association, Vienna, VA 22182, USA

cMcLean Center for Complementary and Alternative Medicine, PLC, Vienna, VA 22182, USA

dAcupuncture Research Institute, Shandong University of Chinese Medicine, Jinan 250355, China

eEastern Roots Wellness, PLC, McLean, VA 22101, USA

1

Dr. Chen is the lead corresponding author of this paper.

Article Info

Publication History:

Received November 26, 2020; Revised January 26, 2021; Accepted February 25, 2021; Published online February 27, 2021

DOI: 10.1016/j.autneu.2021.102793 External LinkAlso available on ScienceDirect External Link

Copyright: © 2021 The Authors. Published by Elsevier B.V.

User License: Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | Elsevier's open access license policy

• Download PDF
• Cite
•  
• Set Alert
• Get Rights
• Reprints

Download Full Issue

Previous articleNext article

Show Outline

Highlights

•

Acupuncture modulates immunity and improves organ functions in sepsis, emerging as a promising therapy of immunomodulation.

•

Acupuncture obtains its regulatory effect via the somatic-autonomic-immune reflexes.

•

Such reflexes include the sympathetic-splenic, sympathetic-adrenal, vagal-splenic and vagal-adrenal reflexes, inducing systemic effects.

•

There are also local reflexes activated by acupuncture, such as the somatic-sympathetic-lung-reflex, inducing local effects.

•

A comprehensive EA protocol is designed based on the evidenced mechanisms.

Abstract

Sepsis is a serious medical condition in which immune dysfunction plays a key role. Previous treatments focused on chemotherapy to control immune function; however, a recognized effective compound or treatment has yet to be developed. Recent advances indicate that a neuromodulation approach with nerve stimulation allows developing a therapeutic strategy to control inflammation and improve organ functions in sepsis. As a quick, non-invasive technique of peripheral nerve stimulation, acupuncture has emerged as a promising therapy to provide significant advantages for immunomodulation in acute inflammation. Acupuncture obtains its regulatory effect by activating the somatic-autonomic-immune reflexes, including the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex and the somatic-vagal-adrenal reflex, which produces a systemic effect. The peripheral nerve stimulation also induces local reflexes such as the somatic-sympathetic-lung-reflex, which then produces local effects. These mechanisms offer scientific guidance to design acupuncture protocols for immunomodulation and inflammation control, leading to an evidence-based comprehensive therapy recommendation.

Abbreviations

1. Acupoint (acupuncture point)
2. APS (antigen-presenting cells)
3. ARDS (acute respiratory distress syndrome)
4. APACHE II (acute physiology and chronic health score)
5. CARS (compensatory anti-inflammatory response)
6. COVID-19 (coronavirus disease 2019)
7. CRP (C reactive protein)
8. EA (electroacupuncture)
9. ICU (Intensive Care Unit)
10. IL (interleukin)
11. MODS (multiple organ dysfunction syndrome)
12. LAC (blood lactic acid)
13. NK (natural killer)
14. PCT (procalcitonin)
15. SARS (severe acute respiratory syndrome)
16. TNF (tumor necrosis factor)
17. SOFA (systemic infection-related organ failure score)
18. VNS (vagus nerve stimulation)

Keywords

1. Nerve stimulation
2. Acupuncture
3. Electroacupuncture
4. Sepsis
5. Inflammation
6. Anti-inflammation
7. Inflammatory reflex
8. Immune dysfunction
9. Somatic-sympathetic reflex
10. Somatic-vagal reflex

1 Introduction

Sepsis is defined as life-threatening organ dysfunction, caused by a dysregulated host response to infection (Gotts and Matthay, 2016; Singer et al., 2016), which clinically manifests as severe systemic inflammatory response, Acute Respiratory Distress Syndrome (ARDS), Septic Shock, or Multiple Organ Dysfunction Syndrome (MODS). It is the number one killer in the Intensive Care Unit (ICU). Globally, there are approximately 30 million cases of sepsis each year, with a fatality rate as high as 30% (Reinhart et al., 2017). The Coronavirus Disease 2019 (COVID-19), which has developed into a global pandemic, is a current example of a manifestation of severe sepsis. Similar to other infections, deaths resulting from COVID-19 have been related to sepsis, which causes septic shock, MODS, and ARDS in particular (C. Wang et al., 2020; D. Wang et al., 2020; Z. Wu and McGoogan, 2020). Reducing inflammation and correcting organ dysfunction are the core strategies of clinical treatment of sepsis. However, due to the lack of a specific and effective antiviral drug, how to effectively treat sepsis has been a clinical challenge for a long time, especially for sepsis caused by viral infection. Traditionally, steroids, i.e. adrenocortical hormones, were once the major anti-inflammatory drugs used for this condition; however, they were unsatisfactory due to their serious side effects and sequelae. Recent immunotherapy drugs, such as siltuximab and tocilizumab, present hope but are yet to be eval‎uated and summarized for further development and clinical application. Fortunately, experimental animal studies in recent years have shown that a simple non-pharmacological approach shows the effect of anti-septicemia (for a review, see Lai et al., 2020). That approach is peripheral nerve stimulation done through both electroacupuncture (EA) and manual acupuncture (in short, acupuncture). Studies have shown that acupuncture is a promising alternative clinical anti-inflammatory therapy. Several lines of evidence published in recent years, from the researches of immunomodulatory mechanisms (for reviews, see, i.g. Tracey, 2002; Ulloa, 2005; Huston et al., 2006; Behrens and Koretzky, 2017; Pavlov et al., 2018; Berlot and Passero, 2019), the experiments of acupuncture in animal models (for a review, see Lai et al., 2020) and in patients of clinical trials (for a review, see Tang et al., 2020), support the antiseptic effect of acupuncture. Such a non-pharmacological and non-invasive approach has attracted the attention of the clinical medicine community and has been advocated by some leading researchers (Ulloa et al., 2017; Pavlov and Tracey, 2017). However, the clinical translation in practice with details is still lacking. This article aims to offer a brief comprehensive review and develop an evidence-based EA therapy for immunomodulation in acute inflammation to promote further research and clinical application.

2 Pathophysiology of sepsis

Sepsis is initiated by an infection. However, it has been known that the clinical manifestations and pathological complications of sepsis are not caused directly by invading pathogens, but rather by a disorder of the host's immune reaction (Hamers et al., 2015; Behrens and Koretzky, 2017). The main pathophysiological process of infectious diseases is the body's response to bio-immunogenic substances, that is, inflammatory reactions with defense properties. With the advancement of immunopathology research, more details of the inflammatory process have been understood (Gotts and Matthay, 2016; Singer et al., 2016; Reinhart et al., 2017; Sladkova and Kostolansk, 2006; Tisoncik et al., 2012; Wiersinga et al., 2014). The body's immune system is functionally divided into innate immunity and acquired adaptive immunity. When pathogenic microorganisms invade the body for the first time, the innate immune system responds accordingly, starting the inflammatory process. First, macrophages recognize and engulf the pathogens. While destroying and inactivating them, some antigen-presenting cells (APCs) can recognize the antigenic characteristics of pathogens and then transmit to B cells; the adaptive immune system is then activated to generate specific antibodies, which can more accurately and efficiently kill pathogens. Long-term memory of antigen information forming, and then lifelong immunity will be generated. However, antibody production takes a long time, around 5–10 days. Fortunately, the innate immune system immediately goes forward to start the battle of non-specific immunity, rather than waiting for the arrival of specific antibodies. Immune cells and infected tissue cells quickly release a batch of cytokines and pro-inflammatory substances under the stimulation of pathogens, such as interleukin IL-1, IL-8, IL-18, tumor necrosis factor TNF-α, IL-6, IL-33, type I and III Interferons (IFN), etc. which are called primary cytokine storms (Behrens and Koretzky, 2017). These cytokines exert a variety of different immune functions. For example, IL-1 is an important initiator of the inflammatory response; TNF has a strong killing effect; IFN has an antiviral effect and can limit virus replication and spread, protecting uninfected cells from being affected by virus invasion; chemokines IL-8 can induce the recruitment of more immune cells toward the infection site; some cytokines can activate the neuroendocrine system, leading to increased body temperature, breathing, circulation, metabolism and other functions. At the same time, these cytokines have a positive feedback effect, which can activate immune cells to release more cytokines, forming a secondary wave of cytokine storms and further strengthening the inflammatory response in order to effectively kill the pathogens (Guo and Thomas, 2017). If this process is successful, the pathogen may be eliminated, or at least prevented from spreading until the specific antibodies (IgM) are produced and the pathogen is destroyed. Once this occurs, the body enters the rehabilitation phase, removing necrotic cells and repairing damaged tissue. This is the general clinical process of many inflammatory infections, which generally last for 1–2 weeks and end through self-healing alone. Unfortunately, a significant proportion of patients progress to a worsening course of disease and develop sepsis. In severe cases, ARDS, septic shock, and MODS are fatal. The core problem of sepsis is a disturbance of the functioning of the immune system. Its pathophysiological mechanism is that the patient is prone to excessive inflammatory reactions in the early stage of the infection, which is the aforementioned cytokine storm phenomenon, also clinically called cytokine release syndrome (CRS). During the normal inflammatory response, when a large number of pro-inflammatory factors are released, the release of anti-inflammatory factors such as IL-4, IL-10, IL-11, IL-13, and IL-1Ra are also initiated, as a self-balance regulation of the immune system, called “compensatory anti-inflammatory response” (CARS) (Berlot and Passero, 2019). The emergence of sepsis is caused by a disorder in the dynamic balance between pro-inflammatory and anti-inflammatory factors, the excessive secretion of multiple pro-inflammatory factors, and the intensification under the positive feedback mechanism. While attacking the pathogen, it also damages the normal tissue cells of the body, leading to important organs or system dysfunction or even failure. However, that is not all that occurs during sepsis. It has recently been discovered that the mechanism behind sepsis is more complicated than previously thought. Not only does the immune response become hyperactive in the early stage, but also CARS is activated at the same time to limit the tissue damage. However, the CARS can represent a double-edged sword. It might be beneficial to restore immune balance; yet, it might cause the shutdown of the immune response if it over responds, inducing the status of immune-paralysis (Hamers et al., 2015; Berlot and Passero, 2019). With immune-paralysis, there can be a reduction of immune-related receptors, apoptosis of various immune cells (T cells, B cells, macrophages, dendritic cells), weakened antigen presentation function of APCs, and increased suppressive lymphocytes, etc., leading to both innate and adaptive immune functions that are severely weakened. This makes it difficult to clear the damaged tissues in later stages. It is also easier to activate latent pathogens and cause a secondary infection. Even worse is that some patients might have problems with immune-paralysis at the early stage, or multiple hits of the cytokine storm phenomenon ultimately leading to the exhaustion of the immune response, which makes treatment more difficult. Therefore, it is necessary to enhance immunity in the later stage as well, which has become a new focus of both basic science and clinical studies. The patterns of inflammatory reaction have been proposed theoretically (Berlot and Passero, 2019), shown in Fig. 1.

Figure viewer

Fig. 1 The immune reaction patterns (reproduced from Berlot and Passero, 2019). A. Possible clinical trajectories of patients with sepsis shock. Line 1, intense hyper-inflammatory reaction followed by CARS and the return to the baseline immune state. Line 2, weak hyper-inflammatory reaction followed by immune-paralysis and immune restoration. Line 3, immune-paralysis not preceded by a hyper-inflammatory reaction. B. The multiple hits phenomenon ultimately leading to the exhaustion of the immune response.

3 Difficulties in regulating immune function in the treatment of sepsis

The treatment of sepsis needs to address three aspects: reducing the pathogens (such as fighting the bacterial or viral infection, if applicable), reducing inflammation, and correction of various physiological dysfunctions. Multiple organ dysfunctions are closely related to inflammation, so reducing inflammation is an important aspect to be dealt with in its early and middle stages. Anti-inflammation or reducing inflammation means regulating immune function. The immune system consists of a variety of functional cells and molecular signaling pathways that form an extremely complex regulatory network. Normal inflammatory response is a dynamic equilibrium process of immune cells and molecular networks. The imbalance of septicemia manifests as early immune hyperactivity and late immune paralysis (Berlot and Passero, 2019) Theoretically, treatment should be to give inhibitory intervention in the early stages, followed by a strengthening intervention. However, it is difficult to make a decision in delivering the specific interventions in real clinical settings. There have been large numbers of anti-inflammatory medications previously used, including corticosteroids, aspirin, monoclonal antibodies, anti-cytokines, anti-chemokines, etc., the effectiveness of which is inconclusive, with some also leading to worsening of the condition. There are several reasons for this. First, in terms of the magnitude of the immune response, how much cytokine release during the inflammatory response can be determined to be “excessive”? It is difficult to define because of the physical condition of patients, such as age, gender, and possible chronic underlying disease. Second, in terms of phases, the turning point of the immune response from the hyper-phase to the hypo-phase is difficult to predict. Unlike antibiotics that advocate early use, immuno-suppressants are generally considered only when clinical symptoms are severe. At this time, immune hyperactivity may have peaked and begun to show a downward trend. Immuno-suppressants may be redundant and even cause immune paralysis quickly. This may be one of the reasons why traditional steroids (adrenal cortex hormones) or targeted therapies that target specific cytokines (for example, antagonists such as the IL-6 blocker siltuximab and the IL-6R blocker tocilizumab) often fail. Clinical effect has not been reached on the effects of these two types of therapy on reducing mortality. Third, regardless of the overall inhibition of steroids (adrenocortical hormones) or single-factor targeted therapy, they are not the normal physiological regulation. This makes it easy to create new imbalances. For example, reducing the recruitment and activation of neutrophils can reduce the damage to normal tissues, but also reduce the lethality to pathogens, leading to the spread of infection. Fourth, in recent explorations, the administration of immune stimulators in later phases is said to be promising, although biomarkers to stratify the immune status are still in development (Peters van Ton et al., 2018). However, once into the late phase, multiple organ dysfunctions may be enough to cause death and immune stimulators may seem meaningless. The only significance of immune stimulators is that of patients with direct immune paralysis in the early phases, but reliable diagnostic indicators are needed. Therefore, the ideal approach is the therapy closest to physiological regulation. Perhaps turning to the neuromodulation of immune responses is a promising direction.

4 Neural regulation of immunity

The immune system was once thought to be an independent regulatory system in the body. The role of the nervous system in regulating immune function has not been known until recent decades, although it has an ancient existence in the history of biological evolution. For example, there are simple organisms, such as C elegans, whose immune cells have been affected by neural signals. In higher animals the brain has been regarded as an immune privileged organ with powerful influence in immunity. The immune system, nervous system and endocrine systems constitute a functional regulatory network (Fig. 2). Based on the functional organization of neuroendocrine and autonomic control, the nervous system can efficiently affect immune function in two ways: through central control and peripheral reflex. The effect of psychological stress on immune function is an example of central control. Peripheral reflex regulation is a more common process, such as inflammatory reflexes (Borovikova et al., 2000; Tracey, 2002). The inflammatory cytokines can stimulate peripheral sensory nerves, including somatic and visceral sensory nerves, or they can directly enter the brain to activate the center integrative effects on immune function, acting through the neuroendocrine or autonomic outputs. The neuroendocrine output is mainly the hypothalamic-pituitary-adrenal (HPA) axis, which has an inhibitory regulating effect on immune function. However, recently it has been noticed that the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamic-pituitary-gonadal (HPG) axis, and the hypothalamic-growth-hormone (HGH) axes are also involved in modulating immune activities (Eskandari et al., 2003). These axes need to be further studied. Autonomic outputs include the sympathetic and vagus nerves, both of which control the immune system and inflammation, which is the focus of this article.

Figure viewer

Fig. 2 The immune network. The immune system, nervous system and endocrine systems constitute a functional regulatory network. The dynamic balance of immune activity is controlled by the interactions of immune cells and cytokinesis (the left part of the figure adapted from Sladkova and Kostolansk, 2006), which accepts the regulation of the brain (the right part of the figure). The brain regulates the immune system with two major outputs: one is the hormonal system including the HPA, HPTs, HPG, and HGH axes (Eskandari et al., 2003); and the other is the autonomic nervous system consisting of sympathetic norepinephrine and vagal acetylcholine pathways. The immune system can also regulate the nervous system through cytokines which activate the afferent nerves or enter the brain directly.

It has been known for a long time that the sympathetic nerves regulate the immune system extensively and complexly, but they have gained increasing interest and attention in recent years. As a result, new knowledge has developed (Eskandari et al., 2003; Olofsson et al., 2012; Jänig, 2014; Jänig and Green, 2014; Bellinger and Lorton, 2014; Pavlov and Tracey, 2017; Chavan and Tracey, 2017). In brief, sympathetic nerves contains nerve fibers (from postganglionic neurons) that specially innervate immune organs including the primary lymphoid organs, i.e. marrow and thymus, and the secondary lymphoid organs, i.e. spleen, lymph nodes, and mucosa-associated lymphatic tissue (Jänig, 2014; Bellinger and Lorton, 2014; Chavan and Tracey, 2017). The sympathetic postganglionic neurons release norepinephrine transmitters which activate β- and α- adrenergic receptors on immune cells, producing the regulatory effects (Bellinger and Lorton, 2014). The β- and α2-adrenergic receptors have opposite effects on immune responses to inflammation (Szelényi et al., 2000; Liu et al., 2020). The hypothalamic area has been thought as a high level center of the autonomic nervous system, which is also known to have extensive influence on immune functioning (for reviews, see Wrona, 2006). Some sub-areas of the hypothalamus might play specific roles in modulating immune functions, e.g. in animal model, electrical stimulation of the lateral hypothalamic area increased natural killer cell cytotoxicity in spleen, while stimulation of the ventromedial hypothalamic area showed suppression effect (Wrona and Trojniar, 2003, 2005). Such hypothalamic-splenic immune modulation is mediated by the sympathetic efferent pathway; therefore, the “hypothalamic-sympathetic-splenic axis” was proposed (Okamoto et al., 1996). The hypothalamus might be involved in the peripheral reflex to modulate immunity (Son et al., 2002; Hahm et al., 2004). Martelli and colleagues (Martelli et al., 2014a, 2014b, 2016, 2019), with a series of experiments in rodents, have identified the greater splanchnic nerve as the sympathetic efferent arm of the inflammatory reflex to inhibit inflammatory cytokines in the spleen as well as in other inner organs innervated by the nerve such as liver, gastrointestinal tract and importantly, the adrenal, as systemic immune cell function can also be regulated through the adrenal medulla with catecholamine releasing. In addition, recent studies have shown that selective somatic local effects of sympathetic innervations on immune functions are available via a direct interaction of the postganglionic nerves with local immune cells. Bassi et al. (2017) showed that direct stimulation of the lumbar sympathetic trunk reduced neutrophil recruitment in arthritic knee joints, and the same effect resulted from direct injection of norepinephrine into the joint. Given the well-known function of the somatic-sympathetic reflex, one might predict that selective stimulation of somatic nerve connecting to the same segment of the spinal cord from which the sympathetic efferent fibers innervate a specific organ or tissue, might produce a local effect of immune regulation of the specific organ or tissues. Indeed, Kim et al. (2007, 2008) have found that electroacupuncture (EA) at Zusanli (ST36) acupoints suppressed zymosan- or carrageenan-induced paw inflammation. Interestingly, they found that low frequency (1 Hz) EA obtained the local suppression effect via activation of sympathetic postganglionic neurons, the simple somatic-sympathetic reflex; while high-frequency (120 Hz) EA suppression is mediated by the sympathoadrenal medullary axis to induce systemic catecholamines for whole body effects. A very recent study (S.B. Liu et al., 2020) showed that selective stimulation of acupoint Tianshu (ST25), which connects to the same segment of the spinal cord sending sympathetic innervation to spleen, evoked the somatic-sympathetic-splenic reflex, produced systemic effect of immune modulation. This new knowledge of different immune reflex paths is very valuable to selective treatment of specific organs and local tissue with inflammation and dysfunction.

More recent knowledge shows that the vagus nerve controls immune function by dominating the spleen and adrenal medulla. The first discovery is the “cholinergic anti-inflammatory pathway” (Borovikova et al., 2000) and then developed the concept of “inflammatory reflex”(Tracey, 2002). In brief (for full reviews, see Ulloa, 2005; Huston et al., 2006; Olofsson et al., 2012; Inoue et al., 2016; Pavlov and Tracey, 2017; Pavlov et al., 2018; Huh and Veiga-Fernandes, 2020), the vagal nerve center can be activated by an immune challenge, and then the vagus nerve efferent terminals releasing cholinergic transmitters, innervate the spleen, perhaps relayed by the splenic nerve (Komegae et al., 2018) (but see Martelli et al., 2014c, 2016), and through the α7 nicotinic receptor on macrophages and other immune cells, inhibit the release of pro-inflammatory cytokines such as TNFα and IL-1 etc. Activation of this pathway by electrical or pharmacological stimulation suppresses excessive inflammation in the gastrointestinal tract (de Jonge et al., 2005; Ghia et al., 2006, 2007), pancreas (van Westerloo et al., 2006), liver (Guarini et al., 2003) and heart (Bernik et al., 2002), inhibiting systemic inflammation. Recent experiments in mice model (Torres-Rosas et al., 2014) have found that the vagus nerve can also dominate the adrenal medulla and activate the latter to release dopamine to inhibit the release of pro-inflammatory cytokines and increase the survival rate of the animals with sepsis. Kwan et al. (2016) have systematically reviewed 36 eligible studies from 290 identified records of vagus nerve stimulation (VNS) for treatment of inflammation in animal models and clinical trials, suggesting that VNS is a very promising approach of inflammation reduction. This immunomodulatory effect produced by stimulating efferent nerves may be an ideal therapy closer to normal or natural physiological regulation without the side effects seen in some drugs. The anti-inflammatory effects of implanted electrodes to stimulate the vagus nerve have been tried for the treatment of chronic immune diseases (De Ferrari et al., 2011; Howland et al., 2011; Howland, 2014; Koopman et al., 2016; Noller et al., 2019). For acute infections, implanting electrodes is not a viable option. Fortunately, stimulating peripheral somatic nerves can also produce the effects of autonomic-immune reflexes, including vagal-immune reflex and the above-mentioned sympathetic-immune reflex (Ulloa et al., 2017; Pavlov and Tracey, 2017). This opens a convenient window of hope for the treatment of acute inflammation in infectious diseases. Not surprisingly, this approach is just how acupuncture therapy works. There is a long history in China of acupuncture being used to treat various emergencies such as acute fever, shock and coma, etc. Acupuncture has been applied even more frequently and sometimes might be considered more important than traditional Chinese herbal medicine, which needs to be prepared or cooked and takes time to see results (L.G. Liu et al., 2004). Acupuncture works rapidly and can often quickly reverse critical conditions, according to ancient and contemporary literature (L.G. Liu et al., 2004). Contemporary Chinese medicine practitioners continued this tradition and use acupuncture, combining it with modern conventional treatment, to treat epidemic diseases, including COVID-19 (R. Wang et al., 2020). Recent random control clinical studies (see following session) also show that acupuncture is a promising clinical anti-inflammatory therapy.

5 Regulatory effects of acupuncture on immune function

Modern studies have demonstrated that acupuncture modulates multiple physiological systems of the body, including the immune system, to reestablish homeostasis by activating peripheral nerves to evoke physiological reflexes (spinal and supraspinal reflex) and the brain central integration (as reviewed elsewhere, Ma, 2004; Zhao, 2008; Kagitani et al., 2010; Uchida et al., 2017; Pan, 2018, 2019). The experimental research on the effects of acupuncture on immune function can be traced back to the middle of the last century (S.Z. Liu, 1959; Yan, 1959). Studies over the decades have shown that acupuncture has a wide range of regulatory effects on the immune system (Den, 1981).

5.1 Enhancement effects of acupuncture on immunity under physiological conditions

Most of the early studies showed that acupuncture enhanced immunity of normal humans or physiological model animals (S.Z. Liu, 1959; Den, 1981; Du et al., 1995; Johansen et al., 2004; Sato et al., 1996). Acupuncture can enhance the innate immune functions. For example, a large number of studies in rodent models (Sato et al., 1996; Liu et al., 1997; Choi et al., 2002; Kim et al., 2005; Rho et al., 2008) showed that EA at ST36 (Zusanli) upregulated the function of natural killer (NK) cells and macrophages, which play a central role in the innate immune response, especially in killing virus-infected cells. Acupuncture also increases the weight of mouse thymus (L.J. Liu et al., 1997), suggesting an effect of enhancing innate immune function. The effect of acupuncture on adaptive immunity is also supported by many experimental results. Acupuncture can increase the number of lymphocytes in the peripheral blood and the lymphocyte transformation rate in animals (Cao et al., 1982) and humans (Wu, 1983; Jong et al., 2006). In the aging animal model, acupuncture increased the functions of T lymphocytes (J.M. Liu et al., 2009). It has been reported that acupuncture for 20 days can increase the level of IgG and IgM in the elderly (Han, 1993). A few studies have shown that the lateral hypothalamus plays a role in the enhancement effect of EA. EA increased natural killer cell activity in the spleen, correlating with the activation of hypothalamus (Rho et al., 2008). Selective destruction of the lateral hypothalamic area (Choi et al., 2002) cancelled various immune enhancement effects of acupuncture. The general enhancement effects of acupuncture on immunity might benefit the prevention of infections and immune suppression status of sepsis. However, acupuncture effects on immunity show state-dependent features. For example, under disease conditions, the effects of acupuncture might be different from that under normal conditions, which is elaborated below.

5.2 Bidirectional regulations of immune function by acupuncture under pathological conditions

Previous studies have shown that the most interesting feature of acupuncture is the bidirectional regulation effect on the body's homeostasis, either in hyper- or hypo- functional states (dual regulation, normalization, or restoring homeostasis) in either patients or pathological models of animals (for a review, Pan, 2019). For instance, EA at ST36 showed stimulation of stress-induced delayed gastric emptying and inhibition of stress-induced acceleration of colonic transit (Iwa et al., 2006). Such state-dependent effect also is observed on immune modulation by acupuncture. Acupuncture can enhance the suppressed innate immune functions, such as up-regulating the decreased function of NK cells and macrophages (Zhao et al., 1994; Wu, 1995; Hisamittsu et al., 2002; Yamaguchi et al., 2007; Johnston et al., 2011). Conversely, acupuncture can also downregulate the activity of these immune cells and related cytokines when they are in a hyperactivity state such as inflammation (see the following section). Studies (as reviewed elsewhere, Kim and Bae, 2010; Dai et al., 2018) also showed that acupuncture has bidirectional regulating effects on adaptive immunity, such as T lymphocytes functions. T helper cells, a type of T lymphocytes, play an important role in the immune modulation. There are two main subsets of T helper cells, Th1 and Th2, which respectively produce Th1 type cytokines (e.g. IL-2, INFγ) and Th2 type cytokines (e.g. IL-4, IL-10). The former tends to produce the pro-inflammatory responses, and the latter, anti-inflammatory responses. The balance of Th1/Th2 is changed in different diseases and that can be modulated by acupuncture (Yamaguchi et al., 2007; Dai et al., 2018; Silvério-Lopes and da Mota, 2013). For example, acupuncture can downregulate Th2-specific cytokines (Park et al., 2004; Kim et al., 2011) to improve Th2 dominant disorders, such as allergic rhinitis (Shiue et al., 2008) and chronic fatigue syndrome (C. Wang et al., 2014). In contrast, for the Th1 dominant disorders such as rheumatoid arthritis (Yim et al., 2007), ulcerative colitis (Tian et al., 2003) and depression (Lin et al., 2014), acupuncture can modulate the Th1/Th2 balance with inhibiting Th1 responses. Such bidirectional regulatory effects suggest some interesting mechanisms that need further study (Pan, 2019). Generally speaking The bidirectional regulatory effect of acupuncture mirrors the activation and reinforcement of the body's self-healing or biological adaptive mechanism, which is a unique effect that no specific drug can reach at this time. Thus, acupuncture is a patient-tailored approach, although controlled by the body per se.

5.3 The anti-inflammatory effect of acupuncture

There is growing interest in the anti-inflammatory effect of acupuncture in the research field. In recent decades, the anti-inflammatory effects of acupuncture in septic animals and patients are highlighted. The most common problem of immune response in sepsis is a hyper-reactive cytokine storm. Silvério-Lopes and da Mota (2013) systematically eval‎uated 67 relevant papers published between 2001 and 2011, and concluded that acupuncture and EA are effective in modulation of immunity in animals and humans. Lai et al. (2020) systematically reviewed 54 studies up to May 2019 on acupuncture at ST36 (Zusanli) for the treatment of the experimental sepsis in animal models crossing species (rodents and rabbits). They used 17 criteria to estimate the study quality and risk of bias. The average quality scores of the studies is 6.3 varying from 2 to 9.5, with 13 studies (15%) accepted quality scores ≥7.0. Those studies support that acupuncture benefits to protecting multiple organs against injuries by sepsis and maintaining the immune balance to attenuate inflammation. A very new study (S.B. Liu et al., 2020), published in Neuron online, July 2020, further confirmed that acupuncture has a reliable anti-inflammatory effect, and revealed new features and mechanisms by using genetic strategy. Those results, especially from the quite a few quality studies (Scognamillo-szabo et al., 2004; Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Villegas-Bastida et al., 2014; Yu et al., 2014; Zhu et al., 2015; Chen et al., 2016; Liu et al., 2020), have shown that the efficacy of acupuncture on experimental sepsis has the following characteristics:

1.

EA improved the survival rate of animals with sepsis. The survival rate of rats or mice with sepsis increased significantly, with a maximum survival increase up to 80% (S.B. Liu et al., 2020; Torres-Rosas et al., 2014; Chen et al., 2016; Song et al., 2012; Zhu et al., 2015; Villegas-Bastida et al., 2014). EA inhibited the release of important pro-inflammatory factors. The blood levels of pro-inflammatory factors such as TNF, IL-6, MCP-1 and INFγ in the acupuncture group were significantly reduced. The level of anti-inflammatory factor IL-10 either increased (da Silva et al., 2011; Ramires et al., 2020) or did not change significantly (Song et al., 2012). It suggests that acupuncture does not simply suppress the immune response but modulates its balance. The anti-inflammation effect of acupuncture is clear. A study (Ramires et al., 2020) showed that acupuncture obtained similar levels of effect as that of indomethacin (a classical nonsteroidal anti-inflammatory drug) in suppressing peripheral and brainstem cytokines.

2.

EA reduced injuries induced by sepsis in multiple inner organs such as lung, cardiac, kidney, liver and gastrointestinal tract (Lai et al., 2020).

3.

The time-window of treatment exists. The earlier that acupuncture treatment is given, the better the results, with results from preventive care even better (Torres-Rosas et al., 2014; Liu et al., 2020). Even one treatment or pretreatment of EA can cause the effect, and the effect lasts at least 6 h (Torres-Rosas et al., 2014). However, the effects from daily EA, in which there are a consecutive three days of treatment, may have more stable and effective results (Torres-Rosas et al., 2014). A new finding (S.B. Liu et al., 2020) is that time-window plays the role depending on the intensity of stimulation (see below for the details). However, these results perhaps depend on the inflammatory model. It seems that the pretreatments are better than post treatments to lipopolysaccharide (LPS) model (Gu et al., 2011; Song et al., 2012; Torres-Rosas et al., 2014; Chen et al., 2016; S.B. Liu et al., 2020; Ramires et al., 2020), but no matter to the cecal ligation and puncture (CLP) model (Song et al., 2012; Torres-Rosas et al., 2014). This might arouse future studying of the treatment windows for various inflammations with different pathogens, e.g. bacteria or virus.

4.

The parameter of EA stimulation is important, which consists of frequency, intensity and the model of pulse trains including generally “continuing trains”, “bursting trains” and “alternating trains” with a common commercial EA stimulator. Most experiments obtained show clear effects with simple stimulation of continuing trains of low frequency (<15 Hz). However, a study (Chen et al., 2016) comparing the effects of three types of trains has shown that the alternating trains (2/15 Hz) is the best, then the bursting trains (2/0 Hz), and then the continuing trains (2 Hz). As mentioned above, another study showed that that low frequency (1 Hz) EA produce the local anti-inflammatory effect via activation of the simple spinal somatic-sympathetic reflex; while high-frequency (120 Hz) EA is mediated by the sympathoadrenal medullary axis to induce systemic effects (Kim et al., 2007, 2008). This frequency effect is consistent with some other acupuncture effects depending on frequency of stimulation (Han, 2003).

5.

There are large varieties of the intensity of EA stimulation used in different experiments. A problem is that different laboratories used different stimulators which indicate the intensity with different scales: current (mA) or voltage (V), that limits to compare the intensities between the different studies. However, some studies included investigating the effects of intensities, providing valuable data. Torres-Rosas et al. (2014), using mice lipopolysaccharide (LPS) model, compared the pretreatments with stimulations of 0.4 V and 4 V at ST36, and the results showed that the anti-inflammatory effect of 4 V stimulation was clearly stronger than that of 0.4 V. Similarly, Liu et al. (2020) compared the pretreatment with stimulations of 0.5 mA, 1.0 mA and 3.0 mA at ST36 or ST25 (Tianshu, at abdomen) in LPS mice, conforming the results, i.e. the stronger the stimulation, the better the anti-inflammatory effect. A surprising funding by Liu et al. is that post-treatment with the 3.0 mA produced oppositely pro-inflammatory effects, i.e. increased the serum TNF-α level and decreased in survival rate. That is because that LPS increased the expression‎ of α2-ARs (adrenergic receptors) in splenic cells, which mediate pro-inflammatory effects, and the post-treatment with high intensity EA activated the spinal sympathetic-splenic pathway (demonstrated with genetic strategy) that further enhanced the α2-ARs effect. They further demonstrated that Yohimbine (α2-ARs antagonist) or splenectomy allowed 3.0 mA EA to promote survival and to suppress serum TNFα level. However, they found that post-treatment of 0.5 mA weak stimulation at ST36 is not enough to activate this sympathetic-splenic pathway, but it is sufficient to activate the vagal-splenic pathway to obtain the anti-inflammatory effects. But EA at ST25 (either 0.5 mA or 3 mA) did not activate the vagal reflex. Those findings are consistent with the previous results that stimulating acupoints at abdomen area produced the sympathetic reflex on the inner organs, while stimulating acupoints of limbs produced the vagal reflex (Sato, 1997; Li et al., 2007). Those results suggest that we need to consider the stimulation site (acupoint), stimulation intensity and time window of treatment (pre- or post- treatment) together for a clinical therapy. Especially, the time-window dependent effect of stimulation intensity is not easy to control in clinical practice because that almost all treatments are post-treatment on patients. However, this result was from the LPS model. Another data showed that the post-treatment of high intensity EA on CLP model obtained the anti-inflammatory effects and promoted the survival rate (Torres-Rosas et al., 2014). On the other hand, EA applying to patients in real clinical practice might rarely reach the intensity of stimulation as high as that in animals in the laboratory. The EA stimulation of 3 mA is over the threshold (>2 mA) (Kagitani et al., 2010) activating Aδ and C fibers of the peripheral nerves (but see Zhou et al., 1985), that will produce pain feelings in conscious animals and humans. The general situation in a clinic is that a stimulation of EA applying to a patient without uncomfortable feeling, especially without pain, that generally induces slight twitch of the local muscles. This general clinic EA intensity is roughly equal to moderate stimulation in animal experiments, which perhaps might or might not activates the peripheral Aδ fibers (threshold 1.5 mA)(Kagitani et al., 2010; Li et al., 2007) but not C fibers. We might not need to concern too much on above pro-inflammatory effect induced by high intensity post-EA, rather, we might use this feature to benefit to patients, e.g. using relative high stimuli at very early stage (before sepsis happening) to prevent serious sepsis, or promote immunity at late stage with the immune-paralysis.

6.

The selection of acupoints has certain significance. As mentioned above, to control inner organ function, the acupoints at abdomen or back mediate the somatic-sympathetic reflex, while the acupoints of limbs mediate the somatic-vagal-reflex (for an individual organ, the exact and maximal reflex effect is obtained following the spinal segmental dominance rule). However, there is still some variety between acupoints within trunk group or limbs group, e.g. LI4 (Hegu) and PC6 (Neiguan) are both effective acupoints of anti-inflammation, but the former is more effective (Song et al., 2012). This difference might be related to the distinction of the nerves distribution under the acupoints.

7.

The anti-inflammation effect of EA is mainly achieved by activating vagal-splenic pathway (Song et al., 2012; Villegas-Bastida et al., 2014; Lim et al., 2016; S.B. Liu et al., 2020), the vagal-adrenal medulla-dopamine pathway (Torres-Rosas et al., 2014) and the sympathetic-splenic pathway (Martelli et al., 2014b; S.B. Liu et al., 2020), rather than by enhancing the hypothalamic-pituitary-adrenal cortex axis, because electroacupuncture pretreatment did not increase serum corticosteroid in animal sepsis model (Song et al., 2012). The role of sympathetic-adrenal medulla pathway is thought to play the role in anti-inflammatory effect in carrageenan-induced paw inflammation model (Kim et al., 2008). However, the role of sympathetic-adrenal medulla pathway in suppressing systemic inflammation needs further investigation. Furthermore, the role of sympathetic-vagal relationship and balance are worth to be studied (Huang et al., 2010).

With these detailed results, the approach of the peripheral-autonomic-immune reflex, carried out by acupuncture, seems promising in being translated into a relative optimal clinical therapy. However, as mentioned above, in the process of sepsis, the immune system with CARS mechanism might present not only a hyper-inflammatory reaction but also immune-paralysis depending on the individual conditions. Further studies are needed to address if there is immune-paralysis at a later stage (even early stage) of the sepsis model, which can be prevented by acupuncture. Theoretically, acupuncture should have a corrective effect for both the hyper- and the insufficient immune responses in the inflammation process according to the bidirectional principle. Indeed, Guo et al. (2010) have reported that EA at Zusali (ST36) and Guanyuan (CV4) decreased the apoptosis of thymocytes in rat sepsis model, suggesting acupuncture can prevent sepsis animals from immune-paralysis. The data from other immune suppression models and clinical trials of inflammation also support the bidirectional effects of acupuncture. For instance, acupuncture reduced the increased plasma level of IL-10 in patients with chronic allergic rhinitis (Petti et al., 2002). Theoretically, when the releasing of pro-inflammatory factors is suppressed, the releasing of anti-inflammatory factors will decrease as well, due to the latter being triggered by the former. Thus, reducing the pro-inflammatory factors by acupuncture at an early stage means also reducing the anti-inflammatory factors later. This might help to avoid the up-and-down oscillation of the compensatory anti-inflammatory response to prevent immune-paralysis, that finally increases the survival rate of animals with sepsis, which needs to be confirmed in future.

5.4 Clinical evidence

In real clinical conditions, patients with sepsis may also have additional complications, especially during the critical stage. Therefore, it is necessary to use different medications or therapies to deal with multiple factors to reach the best results, although animal experiments have shown that acupuncture alone significantly increases the survival rate of sepsis animals. Traditional Chinese practitioners have known for thousands of years to combine acupuncture and herbal medicine together to cure complicated diseases, including serious infections. Recently, acupuncture integrated with modern medical therapies, as a part of the comprehensive treatments of sepsis, has shown exciting values in clinical trials. Clinical reports show that the effect of adding acupuncture intervention in conjunction with conventional treatment is superior to the conventional treatment group alone. A recent study (L. Wang et al., 2019) of a randomized controlled trial on 108 patients with sepsis (54 in the control group and 54 in acupuncture group) showed that the patients in both groups were given conventional treatments, i.e. routine anti-infective medications, and supportive treatments with organ functioning monitored. The patients in the acupuncture group were treated with acupuncture at ST36 daily for 3 consecutive days in addition to conventional treatment. The results showed that, compared to the condition before the treatments, after the treatments, the plasma factor procalcitonin (PCT), blood lactic acid (Lac) expression‎ level, Acute Physiology and Chronic Health Eval‎uation (APACHE II) score, and Sequential Organ Failure Assessment (SOFA) score in both groups were significantly decreased; however, compared to the control group, after the treatment, the acupuncture group showed more decreaces significantly (P < 0.05). Another study (J.N. Wu et al., 2013) conducted a randomized control trial with 50 patients with sepsis, comparing acupuncture plus conventional treatment (n = 26) with conventional treatment alone (n = 24). The results showed that after 3 consecutive days of daily EA treatment, the plasma TNF-α, IL-6 in the “acupuncture plus conventional treatment” group were significantly lower than that in conventional treatment group, and its overall effect was also better. Similarly, F.W. Wu (2016) reported the effect of EA on the inflammatory response and immune function in sepsis patients. The 50 patients with sepsis were randomly divided into two groups of 25 each, i.e. the control group used the treatment plan recommended by the 2008 international guideline on the rescue of sepsis, and the acupuncture group used EA at ST 36 daily plus the treatment given to control group. The APACHE II scores, C reactive protein (CRP), PCT, Lac, and IL-6, IL-10 and T cell subsets (CD4+ and CD8+) were recorded before the treatments and 3 and 7 days after treatments in both groups. The rates of incidence of MODS and fatality rate during 28-day hospitalization were calculated. The results showed that after treatments, at each time point the APACHE II score, CRP, PCT, and Lac levels in both groups decreased to some extent, while the levels of CD4+ and CD8+ of T cell subsets involved in adaptive immunity increased in both groups; however, the EA group was better than the control group (P < 0.05). This indicated that EA at ST36 not only alleviated the pro-inflammatory response of patients with sepsis, but also improved adaptive immune function. This study importantly shows that the 28-day fatality rate in the EA group (8.00%) was significantly lower than that in control group (28.00%) (P < 0.05), while the incidences of MODS in EA group (24%) was lower than that in control group (36%) but not significantly (p > 0.05). Xiao et al. (2015) also obtained similar results. 90 patients with sepsis were randomly distributed to “conventional treatment” (n = 30), “conventional treatment + thymosin α1” (n = 30), and “conventional treatment + acupuncture” (n = 30). The fatality rate after treatment, and T cell subsets CD3+, CD4+, CD8+, CD4+/CD8+ ratio and the antibody IgG, IgA, IgM before and after treatment were compared between groups. The results showed that after 6 days of treatment, while the immune function with above items in all three groups of patients significantly increased (P < 0.01), that the thymosin group and the acupuncture group increased significantly more than in the conventional treatment group (P < 0.01, respectively). The ICU length of stay (days), and the rates of 28-day fatality also decreased significantly (P < 0.05, P < 0.01 respectively) in both the thymosin group and with the acupuncture group compared with the conventional treatment group. This suggests that acupuncture can improve adaptive immune function, and its effectiveness is comparable to that of thymosin, a recognized immune-stimulant used for the treatment of sepsis. This clinical data suggest that acupuncture not only decreases the pro-inflammatory factors but also enhances adaptive immune function to prevent immune-paralysis, which needs to be further confirmed.

Further, acupuncture can not only modulate immune function, but also improve organ functioning in multiple disorders. This also gives acupuncture as an advantage to treating MODS, imbalance of energy metabolism of sepsis. For example, a study by Yu et al. (2015) has shown that acupuncture can not only significantly improve the immune function of sepsis cases, but also protect the gastrointestinal function of septic patients. The incidence of vomiting, abdominal distension and gastric retention in the EA group (EA plus conventional treatment) were significantly reduced compared with the control (conventional treatment alone) group. Meng et al. (2018) also obtained the effects of attenuating inflammatory responses and intra-abdominal pressure in septic patients, but not the length of stay in intensive care unit (ICU) and 28 days fatality rate.

A recent meta-analysis (Tang et al., 2020) including 20 studies with total 1337 patients with sepsis showed that the 28 day fatality rate, the APACHE II score on the 3rd day and the 7th day after treatments, ICU length of stay, gastrointestinal function improvement, PCT and TNF-α on day 7 after treatments, in acupuncture plus conventional treatment group were all significantly superior to that in conventional treatment alone group statistically. All those research results (although still limited) indicate that acupuncture is a very promising integrative therapy for treating patients with sepsis.

6 Discussion: toward a science-based design of EA protocol of immunomodulation

Given the current absence of recognized treatment protocols for immune dysfunction in the process of sepsis, based on above laboratory (i.e. preclinical studies) and clinical evidences, acupuncture could serve as an adjuvant therapy, with its advantage of being easily used, low cost, without any chemical side effects, and importantly, because of its ability to modulate both immune function and multiple organ function. All of which are beneficial to prevent the condition from worsening and to decrease the fatality rate of septic patients. We strongly recommend that acupuncture be included in the comprehensive treatment plan for sepsis. However, the therapies used in previous studies generally followed traditional theory or personal experience. Their selections of acupoints, stimulating parameters, daily dose and course of treatment might not be optimal; thus, it might limit their curative efficiency. To obtain better or maximal effects, we give an acupuncture protocol design based on the new knowledge developed from the researches described above. For the mechanism, stimulating peripheral nerves induces the somatic-autonomic reflex, which produces sympathetic or vagal effects on the functional regulation of organs or physiological systems, including the immune system we now focus on. The spinal somatic-sympathetic reflex follows the rule of the spinal cord segmental control, i.e. the effect of a somatic-sympathetic reflex on an specific organ is obtained limitedly by stimulating the somatic nerve connecting to the spinal cord segments (1–5 segments usually) as same as that the organ do. For example, the spleen is innervated by the sympathetic nerve from the spinal cord segment T5-T8, thus only the stimulation (electrical or acupunctural one) from the somatic nerve zone belonging to the T5-T8 segments can produce the reflex effect on the spleen. Similarly, T8-L1 for the adrenal medulla, and T1-T5 for the lung and so on, that a map with the details can be found in any anatomy textbook. The supraspinal somatic-sympathetic reflex might be induced by high intensity nociceptive stimulation, which is systemic, but rarely produced by acupuncture. The somatic-vagal reflex is special. Previous data showed the vagal reflex control the gastrointestinal tract can be induced by stimulation of the peripheral nerves or the acupoints at the limbs (not the trunk) with high intensity (activating Aδ and C fibers) of stimulation (Sato,1997; Li et al., 2007). However, to activate the vagal-adrenal reflex, a new data (Liu et al., 2020) showed that the stimulation of 0.5 mA (lower than the threshold of Aδ) is sufficient to do. To focus on immune function controlling, we name those reflexes as “somatic-autonomic-immune reflexes”; specifically, the somatic-sympathetic-splenic reflex, the somatic-sympathetic-adrenal reflex, the somatic-vagal-splenic reflex, somatic-vagal-adrenal reflex, which induce systemic regulatory effects on immune functions because the final outputs are from the spleen or the adrenal medulla, which release cytokines or norepinephrine and dopamine into blood. However, the other somatic-sympathetic reflexes related to an organ have local effect only, e.g. the somatic-sympathetic-lung reflex, the somatic-sympathetic-kidney reflex, etc. It should be noted that stimulation of any acupoint can also produce common systemic effects or perhaps some unknown specific effects through the brain integration (both sympathetic and vagal ones) simultaneously, that need further studies. Those concepts and principles are illustrated in Fig. 3.

Figure viewer

Fig. 3 The organization of the somatic-autonomic-immune reflexes (the part of the figure showing the autonomic nervous system and organs is modified from Figure 296 of REF [Gao and Yu, 2014]). For explanation see the text.

6.1 An auxiliary acupuncture protocol

Following the above reflex principles and considering that the effects of acupuncture are state-dependent, stimulation-parameter-dependent, acupoint-dependent, and treatment-time-dependent, an auxiliary acupuncture protocol for sepsis treatment is designed as follows and summarized in Table 1:

1)

Acupoint selection: examples of acupoints we selected are listed below. It should be noted that following the segmental distribution to select acupoints is the key point here.

a.

Systemic regulation:

•

Vagal Group: ST36 (Zusangli) or LI4 (Hegu), bilaterally (the same below). They are the most effective acupoints reported from laboratorial and clinical studies, activating vagal anti-inflammatory pathway to down-regulating cytokines storm;

•

Sympathetic Group: BL17 (Geshu) and BL19 (Danshu) on the back; or ST21 (Liangmen) and ST25 (Tianshu) on the abdomen, to activate the sympathetic-splenic reflex and the sympathoadrenal medullary reflex, additionally benefiting to septic shock patients due to the norepinephrine releasing.

b.

Local regulation:

•

Thoracic group: BL13 (Feishu) and HT7 (Shenmen).

•

Abdominal group (gastrointestinal organs, liver and kidneys): BL19 (Danshu) and ST25 (Tianshu).

•

Pelvic group: BL23 (Shenshu) and SP6 (Sanyinjiao).

b.

The formula of acupoints we recommend:

Formula I: Vagal group + Local group/s (if needed);

Formula II: Sympathetic group + Local group/s (if needed).

The two formulas are used in turns.

2)

Stimulation parameters: for the intensity of EA, it is recommended to give moderate stimuli which can cause slight muscle twitching and also be tolerated by patients. To prevent sepsis in patients in the early stages of infection, high-intensity stimulation is recommended; that perhaps causes more of a pain sensation. Applying EA “continuing trains” with the frequency of 2–10 Hz for 30 min is a general EA dose. However according to the frequency effect (Chen et al., 2016), here we recommend using “alternating trains” of 2/15 Hz or 2/100 Hz, (100 Hz to enhance sympathoadrenal medullary reflex, Kim et al., 2008) for systemic effects, and “bursting trains” with high frequency (15-100 Hz) for local effects. If using the traditional manual acupuncture, we suggest mimicking the “alternating trains”, applying a light or moderate stimulation (a slow rotation) of 2–5 min/10 min for 30 min, given that manual acupuncture can activate all groups of sensory nerve fibers (Kagitani et al., 2010) and a slow rotation of needle is efficient to induce anti-inflammatory effect (Lim et al., 2016; Ramires et al., 2020).

3)

Daily dose and course of treatment: considering that the inhibitory effects of one treatment of EA on most inflammatory factors last for about 6 h (Song et al., 2012; Torres-Rosas et al., 2014), the daily dose we suggest is 2 times/day for patient with sepsis; one time/day for early stage of acute infection. Formula I and Formula II will be used in turns. Take a course of 5–7 days with a break of 1–3 days, because the toleration might happen after 7 days with continuous daily treatments (Du et al., 1995). For severe infection such as COVID-19, the sooner the intervention is performed, the better.

4)

Self-healing: for mild cases or early stages of the infection, the transcutaneous electrical stimulator (TENS) can be used by patients themselves.

EffectsReflexAcupointsPulse trainsFrequency (Hz)IntensityDose & course

Systemic	Vagal reflex	ST36 (Zusanli) LI4 (Hegu)	A B C	2/15 or 2/100 15 2	Moderate	2 times/day, 5–7 days
Systemic	Sympathetic-splenic	BL17 (Geshu) ST21 (Liangmen)	A B C	2/100 or 2/15 100 or 15 15	Moderate	2 times/day, 5–7 days
	Sympathetic-adrenal	BL19 (Danshu) ST25 (Tianshu)	Same
Local organs	Sympathetic (thoracic)	BL13 (Feishu) HT7 (Shenmen)	B	15 or 2	Moderate	2 times/day, 5–7 days
	Sympathetic (abdominal)	BL19 (Danshu) ST25 (Tianshu)	Same
	Sympathetic (pelvic)	BL23 (Shenshu) SP6 (Shanyinjiao)	Same

Table 1

An example design of evidence-based therapy of EA to modulate immunity in sepsis.

A: alternating trains; B: bursting trains; C: continuing trains.

• Open table in a new tab

6.2 Limitations and future research

As discussed above, acupuncture is supported by a large amount of research data both in clinical trials and animal studies in resolving cytokine storms during severe inflammation; however, there still exist many unsolved gaps. There are several limitations to this review aside from those discussed above. 1) Although acupuncture's anti-inflammatory storm has been repeatedly confirmed by animal experiments, and the effect of acupuncture in inhibiting inflammatory storms through neuroimmune pathway is almost certain, it should be noted that current experimental results mostly come from CLP models and LPS models. It is necessary to further compare the differences between these two and expand to other new models. In particular, a new direction is to establish an immune-paralysis model in late-stage sepsis. 2) More detailed research is needed in acupoint selection and stimulation parameters. 3) Time-window of acupuncture effect is worthy enough to do further systematic research: identifying the acupuncture effect during different development stages of sepsis, i.e. pretreatment, and its early, middle, and late stages. This needs to combine with acupoint selection and stimulation parameters. 4) Refining and deepening is needed in the bidirectional regulating effect and mechanism of acupuncture in terms of immune regulation. In particular, given that the suppressing effects of acupuncture on cytokine storms has been well addressed, next challenge is investigating the effects of acupuncture on immune-paralysis in sepsis. 5) Most of previous studies focused on systemic effects of acupuncture or other peripheral nerve stimulation. A new direction is identifying local effect produced by local segmental reflexes, that will provide scientific bases of acupoint selection to clinical therapy design. 6) Any peripheral stimulation might produce both local spinal segmental reflexes and supra-spinal reflexes. Local segmental reflexes might co-work with its supra-spinal reflexes, or have independent effect, that can be used in different situation. This is a basic question of acupuncture and very important for selecting acupoints in a therapy. The interactions and mechanisms of local spinal segmental reflexes and supra-spinal reflexes produced by acupuncture need to be further studied extensively, not only for inflammation but for all other disorders. 6) Current acupuncture clinical trials have some quality issues. The quality of most reports has been criticized due to insufficient sample sizes and lacking proper sham controls. Indeed, the feature of acupuncture different from drug's makes the design of sham acupuncture control difficult to meet the rules of double-blind clinical study. To avoid such problems, the National Institutes of Health (NIH) is currently advocating real-world clinical research in view of the characteristics of acupuncture (Zia et al., 2017). However, according to the results of current animal and clinical experiments, there are large varieties of the effects of acupoints and stimulation parameters, that some of them showed significant effects but others with little effects on same treatment targets (e.g. Chen et al., 2016; Li et al., 2015). Such little effective acupoints or stimulation parameters give an idea “sham” control manipulation. By using such parallel design, Li et al. (2015) showed the effects of long-lasting reduction of blood pressure in a group treated with specific acupoints but not in the other group with different acupoints. We strongly recommend such parallel design, that uses invalid acupoints or stimulation parameters as “sham” control group to rule out placebo effect. Parallel design is well known as the “gold standard” for phase 3 clinical trials. It is just very well for clinical study of acupuncture. Anyhow, systematic, large and rigorous clinical data will be the key for supporting in acupuncture-assisted immune adjustment in the treatment of sepsis. The acupuncture protocol designed in this article is just one example of suggestions for future clinical research, which is based on current available literature. We hope that this protocol would be inspiring and promoting the translation from scientific study to clinical application. Given that there are gaps in acupuncture mechanisms, and between acupuncture real practice and basic science study in treating sepsis, further studies in both acupuncture mechanisms and clinical trials are warranted.

7 Summary

Faced with the severe situation of the global pandemic of COVID-19, the medical community throughout the world is exploring various treatments from different approaches, including antiviral, anti-inflammatory, and controlling multiple organ functions. It has been identified that COVID-19 induces immune disorder and sepsis in severe patients (Yuki et al., 2020). A new study demonstrated that COVID-19 cytokine storms, especially a high level of TNF may make few memory B cells and prevent a durable immune response (Kaneko et al., 2020). For fatal sepsis with multiple organ failure, the imbalance of immune function is the core pathological mechanism, and the various therapies for controlling the immune function currently have no recognized best choice for various reasons. At this moment, acupuncture used to activate the somatic-autonomic-immune reflexes is a promising therapy emerging from multiple recent animal experiments and clinical studies, to provide significant clinical advantage to control inflammation and restore organ function without adverse side effects. Different from a new drug investigation needing a phase I clinical trial (screening the safety and testing the proper dose), acupuncture with its safety feature, has been carried out at least in phase II like clinical trials for a variety of diseases for years throughout the world. If acupuncture is involved in the treatment of COVID-19, the patients will not only avoid losing a promising adjunctive therapy, but it would also be a good opportunity obtaining a large number of patients to test the efficiency of acupuncture in a clinic trial. Previous studies from animal models and clinical trials have shown that acupuncture modulates immunity, but it has yet been consistent with showing that acupuncture decreases the fatality rate of sepsis patients. Besides the complicated process of sepsis, one main reason is that the efficiency of acupuncture depends on several factors such as the pathological status, the acupoints, the stimulation parameters and the time-window of treatment etc. that need well consideration together to obtain maximal effects. We recommend an evidence-based comprehensive design of EA protocol to practitioners and researchers to test it. It is worth looking forward to its contribution to the treatment of sepsis and, for the moment, to treating the urgent need of patients with COVID-19 infection as well as for future patients with various infections and other factors.

Declaration of competing interest

Author Sarah Faggert Alemi was employed by the company Eastern Roots Wellness, PLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AcknowledgmentsAcknowledgements

We thank Dr. Qiufu Ma for his feedback on the manuscript.

CRediT authorship contribution statement

This project was initiated by WX Pan and A.Y. Fan. As the primary researcher, WX Pan designed the project and protocol, structured and drafted the early version of manuscript. A.Y. Fan, SZ. Chen and S.F. Alemi participated in discussing, further drafting and editing the later versions. WX. Pan and A.Y. Fan completed the final manuscript. There was no financial support for this project. Due to the limitation of the authors' personal experience and perspective, this review may have some omissions and errors; comments or corrections are welcomed and appreciated.

References

1.

Bassi, G.S. ∙ Dias, D.P.M. ∙ Franchin, M. ...

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Brain Behav. Immun. 2017; 64:330-343

Crossref

Scopus (71)

PubMed

Google Scholar

2.

Behrens, E.M. ∙ Koretzky, G.A.

Cytokine storm syndrome: looking toward the precision medicine era

Arthritis Rheumatol. 2017; 69:1135-1143

Crossref

Scopus (226)

PubMed

Google Scholar

3.

Bellinger, D.L. ∙ Lorton, D.

Autonomic regulation of cellular immune function

Autonomic Neuroscience: Basic and Clinical. 2014; 182(15–41):2014

Google Scholar

4.

Berlot, G. ∙ Passero, S.

Immunoparalysis in Septic Shock Patients. Patients [Online First]

IntechOpen, 2019

https://www.intechopen.com/online-first/immunoparalysis-in-spetic-shock-patients

Crossref

Google Scholar

5.

Bernik, T.R. ∙ Friedman, S.G. ∙ Ochani, M. ...

Pharmacological stimulation of the cholinergic antiinflammatory pathway

J. Exp. Med. 2002; 195:781-788

Crossref

Scopus (458)

PubMed

Google Scholar

6.

Borovikova, L.V. ∙ Ivanova, S. ∙ Zhang, M. ...

Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin

Nature. 2000; 405:458-462

Crossref

Scopus (3326)

PubMed

Google Scholar

7.

Cao, J.R., Gong, Q. H., Xiang, Y. M. (1982). Effect of acupuncture on the output lymph and cell in popliteal lymph nodes in rabbits. Shanghai J Acu-moxi. 1, 35–37.

Google Scholar

8.

Chavan, S.S. ∙ Tracey, K.J.

Essential neuroscience in immunology. J Immunol. 2017; 198:3389-3397

Google Scholar

9.

Chen, Y., Lei, Y., Mo, L.Q., Li, J., Wang, M.H., Wei, J.C., et al. (2016). Electroacupuncture pretreatment with different waveforms prevents brain injury in rats subjected to cecal ligation and puncture via inhibiting microglial activation, and attenuating inflammation, oxidative stress and apoptosis. Brain Res Bull. 127, 248–259.

Google Scholar

10.

Choi, G.S. ∙ Oha, S.D. ∙ Han, J.B. ...

Modulation of natural killer cell activity affected by electroacupuncture through lateral hypothalamic area in rats

Neurosci. Lett. 2002; 329:1-4

Crossref

Scopus (26)

PubMed

Google Scholar

11.

da Silva, M.D. ∙ Guginski, G. ∙ Werner, M.F. ...

Involvement of interleukin-10 in the anti-inflammatory effect of Sanyinjiao (SP6) acupuncture in a mouse model of peritonitis

Evid. Based Complement. Alternat. Med. 2011; 2011:217946

Crossref

Scopus (50)

PubMed

Google Scholar

12.

Dai, Q.M., Shang, Y.Q., Liang, H., Yan, P.Y., Wang, M.Q., Wang, K. (2018). Research progress of effect of acupuncture therapy on T cell subsets. J Clin Acupunct. 7,78–82.

Google Scholar

13.

De Ferrari, G.M. ∙ Crijns, H.J.G.M. ∙ Borggrefe, M. ...

Chronic vagus nerve stimulation: a new and promising therapeutic approach for chronic heart failure

Eur. Heart J. 2011; 32:847-855

Crossref

Scopus (426)

PubMed

Google Scholar

14.

de Jonge, W.J. ∙ van der Zanden, E.P. ∙ The, F.O. ...

Stimulation of the vagus nerve attenuates macrophage activation by activating the Jak2-STAT3 signaling pathway

Nat. Immunol. 2005; 6:844-851

Crossref

Scopus (918)

PubMed

Google Scholar

15.

Den, G.G.