Fas (CD95/APO-1) is a transmembrane glycoprotein belonging to the tumor necrosis factor (TNF) receptor superfamily. It can mediates apoptosis by ligation with an agonistic anti-Fas antibody or Fas ligand. Stimulation of Fas results in the aggregation of its intracellular death domains, leading to the formation of the death-inducing signaling complex (DISC). FAS-mediated apoptosis may have a role in the induction of peripheral tolerance, in the antigen-stimulated suicide of mature T-cells,or both. The molecular mass of native Fas is 38 kDa, the high molecular weight form (40-55 kDa) of Fas is due to glycosylation.