Abstract: Objective To compare the difference of programmed cell death receptor-1 （PD-1） receptor on peripheral blood follicular helper T lymphocyte （Tfh） surface in chronic hepatitis C （CHC） patients with low and high serum viral loads. Methods 180 patients with CHC were divided into two group,and 76 had serum HCV RNA level of less than 6 lg copies/ml and 104 had serum HCV RNA level of greater than 6 lg copies/ml. The percentage of PD-1 on peripheral blood Tfh cell surface,percentage of Tfh,peripheral blood T and B lymphocyte subsets and serum interleukin 21 （IL-21） level were detected. Results In patients with low and high viral load groups,serum HCV RNA levels were （4.5±1.2） lg copies/ml and （6.4±0.7） lg copies/ml,the percentages of PD-1 on Tfh cell surface were （26.2±2.2）% and （37.2±1.1）%,the percentages of Tfh cells were （7.9±0.7）% and （5.1±0.4）%,and serum IL-21 levels were（46.8±1.3） ng/l and（21.7±1.1） ng/l,all significantly different between the two groups （P<0.05）;the percentages of CD4⁺T lymphocyte were （51.1±4.6）% and （37.6±4.4）%], the percentages of CD8⁺T cell were （24.0±3.1）% and （31.7±3.9）%],the ratios of CD4⁺T/CD8⁺T cells were （3.3±0.2） and （2.3±0.1）],the percentage of CD19⁺B cell were（16.7±3.9）% and（11.8±3.2）%,all significantly different between the two groups（P<0.05）;the percentages of PD-1 on CD4⁺T lymphocyte surface were（10.1±2.3）% and （2.4±0.6）%],and the percentages of PD-1 on CD8⁺T cell surface were （6.3±2.2）% and（1.0±0.3）% （both P<0.01）. Conclusion There were significant differences between patients with low and high serum HCV RNA loads as respect to their peripheral blood Tfh and PD-1 expression,which might be important in evaluating the response to antiviral therapy and prognosis.

Key words: Chronic hepatitis C, Viral loads, Follicle helper T lymphocytes, Programmed cell death receptor-1, Interleukin 21