Objective To investigate the induction and function of circulating CD4+ CD25+ regulatory T cells(CD4+CD25+ Treg cells)in patients with chronic hepatitis B,and their role in the progress of chronic HBV infection.Methods Twenty two patients with chronic hepatitis B(CHB),11 patients with acute hepatitis B(AHB)and 20 healthy blood donators were enrolled in the study.After stimulating with recombinant HBV antigen or anti-CD3 mAb,the fraction of CD4+ CD25+Treg cells in peripheral blood mononuclear cells(PBMC)from different subjects was analyzed using flow cytometry.CD4+CD25+ Treg cells and effector cells(PBMC-Treg)were sorted out and cultured alone or together in vitro,and the cell proliferation and cytokines production were measured. Serum HBV titers,HBV markers and liver function were also evaluated.Results The fraction of circulating CD4+CD25+ Treg cells induced in PBMC from CHB patients under the stimulation of recombinant HBsAg was much higher than that in AHB patients(F=3.47,P＜0.05)and normal controls(F=4.98,P＜0.05).With HBsAg stimulation,cell proliferation and cytokines production (IFN-γand IL-10)of CD4+ CD25+ Treg cells either from patients or from normal controls was very low when cultured alone,and there was no significant difference between two groups(P＞0.05).Cell proliferation and IFN-γproduction of effector cells from AHB patients were higher than those from CHB patients,however,when effector cells were cultured with CD4+Cd25+Treg cells at a ratio of 5:1,the cell proliferation and IFN-γ production were significantly inhibited (F=4.66,5.24,P＜0.05).Conclusion Circulating nificantly suppress the production and IFN-γ production of effector T Cells,which may be associated with the progress of chronic HBV infection.