[Apoptosis in human diseases: role of Fas system in liver cell injury by viral hepatitis].

Hepatitis C virus (HCV) and hepatitis B virus (HBV) are major causative agents of chronic liver disease. However, the mechanisms responsible for liver cell injury remain to be clarified. Cytotoxic T lymphocytes play a crucial role in liver cell injury by HCV or HBV infection. Recently, perforin and Fas ligand have been shown to be the only molecules causing T cell-mediated cytotoxicity in short term assays. Therefore, we examined the implication of the Fas system-mediated apoptosis in the liver cell injury. When examined by immunohistochemical method, Fas antigen expression in chronic hepatitis C or B was upregulated in accordance with the severity of liver inflammation. Furthermore, Fas ligand expression was detected in liver-infiltrating mononuclear cells obtained from patients with chronic hepatitis C. These observations suggest that the Fas system plays a dominant role in liver cell injury by viral hepatitis.