AIM:To investigate peripheral T-lymphocyte subpopulation profile and its correlation with hepatitis B virus (HBV) replication in patients with chronic hepatitis B (CHB).METHODS:Distribution of T-lymphocyte subpopulations in peripheral blood was measured by flow cytometry in 206 CHB patients.HBV markers were detected with ELISA.Serum HBV DNA load was assessed with quantitative real-time polymerase chain reaction (PCR).The relationship between HBV replication and variation in peripheral T-cell subsets was analyzed.RESULTS:CHB patients had significantly decreased CD3,and CD4+ cells and CD4+/CD8+ ratio,and increased CD8+ cells compared with uninfected controls (55.44±12.39 vs 71.07±4.76,30.92±7.48 vs 38.94±3.39,1.01±0.49 vs 1.67±0.33,and 34.39±9.22 vs 24.02±4.35;P＜0.001,respectively).Univariate analysis showed a similar pattern of these parameters was significantly associated with high viral load,presence of serum hepatitis B e antigen (HBeAg) expression,liver disease severity,history of maternal HBV infection,and young age at HBV infection,all with P＜0.01.There was a significant linear relationship between viral load and these parameters of T-lymphocyte subpopulations (linear trend test P＜0.001).There was a negative correlation between the levels of CD3+ and CD4+ cells and CD4+/CD8+ ratio and serum level of viral load in CHB patients (r=-0.68,-0.65 and-0.75,all P＜0.0001),and a positive correlation between CD8+ cells and viral load (r=0.70,P＜0.0001).There was a significant decreasing trend in CD3+ and CD4+ cells and CD4+/CD8+ratio with increasing severity of hepatocyte damage and decreasing age at HBV infection (linear trend test P＜0.01).In multiple regression (after adjustment for age at HBV infection,maternal HBV infection status and hepatocyte damage severity) log copies of HBV DNA maintained a highly significant predictive coefficient on T-lymphocyte subpopulations,and was the strongest predictor of variation in CD3+,CD4+,CD8+ cells and CD4+/CD8+ ratio.However,the effect of HBeAg was not significant.CONCLUSION:T-lymphocyte failure was significantly associated with viral replication level.The substantial linear dose-response relationship and strong independent predictive effect of viral load on T-lymphocyte subpopulations suggests the possibility of a causal relationship between them,and indicates the importance of viral load in the pathogenesis of T cell hyporesponsiveness in these patients.