In hepatitis B virus (HCV) infection-induced liver fibrosis, the expression of PD-1 and PD-L1 in liver tissue is significantly increased, which together with other immune checkpoint molecules such as CTLA-4, T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) and lymphocyte activation gene 3 (LAG3), promotes the formation of immunosuppressive microenvironment in liver (173). This evidence concerns the gene PDCD1 and Hepatic fibrosis.