In chronic viral hepatitis, immunosuppressive checkpoints, including PD-1/PD-L1, cytotoxic T-lymphocyte associated protein 4 (CTLA4), and T cell immunoglobulin and mucin domain 3 (TIM3), play an important role in immunosuppression by downregulating the T cell response (57). The gene discussed is CTLA4; the disease is animal viral hepatitis.