Objective:To investigate the action mechanisms of electroacupuncture(EA)on postoperative immunosuppression.Methods:Male C57BL/6 mice(5-7 weeks old)were randomly divided into:the sham injury group,the surgical trauma stressed group,the EA group[surgery+2/100 Hz EA at Neiguan(PC 6)],and the EA+Nal(surgery+EA+intraperitoneal injection of naloxone).Abdominal surgical trauma stress mice model was established.EA was performed on bilateral PC 6 acupoints by an EA apparatus(2/100 Hz)for 20 min once a day for 3 days.The mRNA expressions of MOR,DOR,and KOR in thymus and L3-L5 dorsal root ganglions(DRG)were determined by quantitative real-time polymerase chain reaction(qRT-PCR)and the protein expressions of MOR,DOR,and KOR in thymus were measured by Western blot.Flow cytometry assay was used to detect the levels of T lymphocyte subtypes in the peripheral blood.Results:Surgical trauma induced decreased the mRNA expression level of MOR in both thymus(P＜0.01)and L3-L5 DRGs(P＜0.05).Moreover,EA treatment not only significantly attenuated the MOR protein and mRNA expression in the thymus(both P＜0.05),but also markedly increased expression of DOR and KOR opioid receptor in thymus(P＜0.01).However,the mRNA expressions of opioid receptors were not regulated by EA in the DRG(all P＞0.05).Furthermore,T lymphocyte population of CD3+and CD4+was decreased in the peripheral blood after surgical trauma(both P＜0.01).EA treatment can significantly elevate the population of CD3+(P＜0.01),CD4+(P＜0.05)and CD8+T cells(P＜0.01).Intraperitoneal injection of the non-selective opioid receptor antagonist naloxone blocked the up-regulation of T lymphocytes by EA.Conclusion:EA may improve postoperative immunosuppression through the peripheral opioid system.