Objective To investigate the role of Th17/Treg balance in immune mechanism in severe exacerbation of hepatitis B.Methods The clinical data of 41 patients with chronic hepatitis B were collected,and according to the conditions during hospitalization,these patients were divided into exacerbation group (19 patients) and improvement group (22 patients).On admission,at weeks 1 and 2 of treatment,and at the end of treatment,flow cytometry was used to measure the frequencies of Th 17 and Treg cells in peripheral blood,and enzyme-linked immunosorbent assay was used to determine the serum levels of interleukin-17 (IL-17),interleukin-10 (IL-10),and transforming growth factor-β (TGF-β).The dynamic changes in the frequencies of Th17 and Treg cells were compared between the two groups,and the correlation between clinical indices for hepatitis and cytokines was analyzed.The t-test was used for comparison between groups,a one-way analysis of variance was used for comparison within one group across different time points,and Pearson correlation analysis was performed.Results With disease progression,the exacerbation group showed an increase in the frequency of Th 17 cells and a relatively low frequency of Treg cells;compared with the improvement group,the exacerbation group had a higher frequency of Th 17 cells and a lower frequency of Treg cells.Th1 7/Treg ratio gradually increased with exacerbation and decreased with improvement in conditions;in the exacerbation group and the improvement group,Th17/Treg ratio was positively correlated with total bilirubin and negatively correlated with prothrombin activity.In the exacerbation group and the improvement group,Th 17 cells were positively correlated with IL-17,and Treg cells were positively correlated with IL-10 and TGF-β.Conclusion Th1 7 and Treg cells play important roles in severe exacerbation of hepatitis B,and Th1 7/Treg ratio may be used as an immunobiological marker for the judgment of severity during severe exacerbation of hepatitis B.