FAS is a receptor and contains three TNFR-Cys repeats and one death domain. It has been shown that FAS is involved in the physiological regulation of programmed cell death, and has been implicated in the pathogenesis of various malignancies and diseases of the immune system. FADD (adapter molecule) recruits caspase-8 to the activated receptor, the resulting death-inducing signaling complex (DISC) performs caspase-8 proteolytic activation which initiates the subsequent cascade of caspases mediating apoptosis. FAS-mediated apoptosis may play a role in the induction of peripheral tolerance, in the antigen-stimulated suicide of mature T-cells, or both.