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Open Access Research article

NK cells mediate the cumulative analgesic effect of electroacupuncture in a rat model of neuropathic pain

Yong-Hui Gao1, Jun-Ying Wang1, Li-Na Qiao1, Shu-Ping Chen1, Lian-Hong Tan1, Qiu-Ling Xu2 and Jun-Ling Liu1*

Author Affiliations

1 Department of Physiology, Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China

2 Hainan Medical University, Haikou, Hainan Province 571101, China

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BMC Complementary and Alternative Medicine 2014, 14:316  doi:10.1186/1472-6882-14-316

Published: 26 August 2014

Abstract

Background

Cumulating evidence has revealed the effectiveness of acupuncture therapy in relieving pain via immunoregulation. However, its underlying mechanism remains unknown. The present study was designed to determine the changes of immunogenic responses at different time-points of electroacupuncture (EA) interventions in neuropathic pain rats.

Methods

The neuropathic pain model was established by ligature of the left sciatic nerve to induce chronic constriction injury (CCI). EA was applied at Zusanli (ST36) and Yanglingquan (GB34) for the EA groups. The thermal pain threshold was detected with an algesia-detector. The subgroups of plasma and splenic lymphocytes were determined via fluorescence-activated cell sorting. Specific inflammatory cytokines were assayed using an ELISA-based bead multiplex assay. The activities of splenic natural killer (NK) cells and cytotoxic T lymphocytes were detected by methyl thiazolyl tetrazolium colorimetric method. For confirming the involvement of NK cell in EA-analgesia, anti-asialo-ganglio-N-tetraosylceramide (anti-asialo-GM1) antibody was given to CCI rats before EA.

Results

Following CCI, the thermal pain threshold of the affected hind footpad was significantly decreased, and increased from the 3rd day to the 12th day after EA interventions, presenting a time-dependent tendency from the 5th day on. From day 3 to 5 of EA interventions, the percentages and activity of splenic NK cells, concentrations of splenic interleukin-2 (IL-2) and beta-endorphin (β-EP) were significantly increased. Meanwhile, the concentrations of plasma IL-2, IL-1β and gamma-interferon (IFN-γ) were significantly decreased and returned to the normal level on day 12 following EA. Plasma transforming growth factor-β (TGF-β) levels were considerably upregulated on day 5 and 12 following EA. The CD4+/CD8+ T cell ratio was markedly downregulated compared with the control and CCI groups on day 5 and returned to the normal level on day 12 following EA. After depleting NK cells by anti-asialo-GM1 antibody, the increased thermal pain threshold following EA intervention was obviously reduced.

Conclusions

Repeated EA interventions have a time-dependent cumulative analgesic effect in neuropathic pain rats, which is closely associated with its regulatory effects on NK cells, splenic IL-2, β-EP, and plasma IL-2, IL-1β, IFN-γ and TGF-β levels.

Keywords:
Acupuncture analgesia; Cumulative effect; Chronic constriction injury; Innate immunity; Acquired immunity; NK cells