Type 1 regulatory cells suppress T-cell cytotoxicity to alleviate liver injury during acute hepatitis B virus infection in mice

Hepatitis B virus (HBV) exclusively infects hepatocytes and produces large quantities of subviral particles containing its surface antigen (HBsAg). T cells play a central role in controlling HBV infection but can also mediate liver injury and contribute to disease progression. However, the mechanisms that regulate T-cell responses to eliminate the virus without causing immunopathology during acute HBV infection remain poorly defined. In this study, we established acute HBV infection models in mice by delivering the HBV genome to the liver via hydrodynamic injection or high-dose adenoviral vector administration. Single-cell RNA sequencing was performed to characterize the heterogeneity of HBsAg-specific CD4+ T cells, revealing distinct functional subsets, including follicular helper (Tfh), cytotoxic, and type 1 regulatory (Tr1) cells. These subsets were further validated by flow cytometry using representative phenotypic markers. Our findings demonstrate that Tr1 cells attenuate the cytotoxicity of both CD4+ and CD8+ T cells in response to HBsAg. Neutralization of interleukin-10 (IL-10) impaired Tr1-mediated suppression of cytotoxic T-cell responses. Notably, IL-10 deficiency in Tr1 cells led to substantial liver injury without enhancing HBsAg clearance. Together, these results highlight the critical function of Tr1 cells in safeguarding against liver immunopathology by modulating T-cell cytotoxicity during acute HBV infection in mice.