Mechanism of activation-induced cell death of T cells and regulation of FasL expression.

Activation-induced cell death (AICD) of T cells is a process for regulating the peripheral immune system. The fate of a T cell is controlled by numerous signals derived from various stimuli, such as antigens, cytokines, and chemokines. In healthy humans, overactivated or autoreactive T cells are harmful and are eliminated to maintain the immune system. AICD in T cells by Fas/FasL-mediated apoptosis is triggered by the switch from life to death through several signaling molecules. The control or distribution of Fas or FasL expression largely affects AICD of T cells. Although autoimmune diseases are considered to be induced by multiple factors, an impaired immune system with AICD by Fas/FasL-mediated apoptosis leads to the onset or development of autoimmunity. Based on published reports, this review describes the regulatory mechanisms involved in AICD of T cells by Fas/ FasL-mediated apoptosis and the associations between AICD and autoimmunity in humans and animal models.