Apoptosis mediated by the Fas system.

Fas is a cell-surface protein mediating apoptosis. Fas ligand is a type II membrane protein and induces apoptosis by binding to Fas. Fas ligand is expressed in activated T cells, and works as an effector of cytotoxic lymphocytes. Molecular and genetic analysis of Fas and Fas ligand indicated that mouse lymphoproliferation mutation (lpr) and generalized lymphoproliferative disease (gld) are mutations of Fas and Fas ligand respectively. The lpr of gld mice develop lymphadenopathy, and suffer from autoimmune disease. Based on these phenotypes and other studies, it was concluded that the Fas system is involved in the apoptotic process during T-cell development, specifically peripheral clonal deletion or activation-induced suicide of mature T cells. In addition to the activated lymphocytes, Fas is expressed in the liver, heart and lung. Administration of agonistic anti-Fas antibody into mice induced apoptosis in the liver and quickly killed the mice, causing liver damage. These findings suggest that the Fas system plays a role not only in the physiological process of lymphocyte development, but also in the cytotoxic T-lymphocyte-mediated disease such as fulminant hepatitis.