Cytokine that binds to TNFRSF6/FAS, a receptor that transduces the apoptotic signal into cells. Involved in cytotoxic T-cell-mediated apoptosis, natural killer cell-mediated apoptosis and in T-cell development . Initiates fratricidal/suicidal activation-induced cell death (AICD) in antigen-activated T-cells contributing to the termination of immune responses. TNFRSF6/FAS-mediated apoptosis has also a role in the induction of peripheral tolerance. Binds to TNFRSF6B/DcR3, a decoy receptor that blocks apoptosis.