Objective:To explore the roles of the expression of the co-stimulatory molecule,B7-2,and the co-inhibitory molecule,PD-L1,on peripheral blood mononuclear cells in the mechanism of immunotolerance in chronic hepatitis B virus infection.Methods:Thirty HBV infected patients in the immunoreactive phase and 20 patients in the immunotolerant phase were enrolled in the study,while 20 healthy volunteers were used as controls.RT-PCR and real-time PCR methods were used to detect the expression levels of B7-2 and PD-L1 mRNA in peripheral blood mononuclear cells in chronic HBV infected patients.Results:The B7-2 expression in immunoreactive and immunotolerant patients was significantly lower than that in the controls(P all < 0.01);B7-2 expression in immunoreactive patients was significantly lower than in immunotolerant patients(P < 0.01).PD-L1 expression in immunoreactive patients and immunotolerant patients was significantly higher than that in normal controls(P all < 0.01).The PD-L1/B7-2 ratios in immunoreactive and immunotolerant patients were significantly higher than that of the healthy controls(P all < 0.01);the PD-L1/B7-2 ratio was significantly higher in the immunoreactive patients than in the immunotolerant patients(P < 0.01).Conclusion:In chronic HBV infection,changes in the expression of co-stimulatory and co-inhibitory molecules imply a protective adjustment against the patient’s immune response that may result in increased immunotolerance and persistent HBV infection. Objective: To explore the roles of the expression of the co-stimulatory molecule, B7-2, and the co-inhibitory molecule, PD-L1, on peripheral blood mononuclear cells in the mechanism of immunotolerance in chronic hepatitis B virus infection. Methods: Thirty HBV infected patients in the immunoreactive phase and 20 patients in the immunotolerant phase were enrolled in the study, while 20 healthy volunteers were used as controls. RT-PCR and real-time PCR methods were used to detect the expression levels of B7-2 and PD-L1 mRNA in peripheral blood mononuclear cells in chronic HBV infected patients. Results: The B7-2 expression in immunoreactive and immunotolerant patients was significantly lower than that in the controls (P all <0.01); B7-2 expression in immunoreactive patients were significantly lower than in immunotolerant patients (P <0.01). PD-L1 expression in immunoreactive patients and immunotolerant patients was significantly higher than that in normal controls (P <0.01). The PD-L1 / B7-2 ratios i The immunoreactive and immunotolerant patients were significantly higher than that of the healthy controls (P all <0.01); the PD-L1 / B7-2 ratio was significantly higher in the immunoreactive patients than in the immunotolerant patients (P <0.01) .Conclusion: In chronic HBV infection, changes in the expression of co-stimulatory and co-inhibitory molecules imply a protective adjustment against the patient’s immune response that may result in increased immunotolerance and persistent HBV infection.