Fas ligand is also known as FasL, CD178, CD95L, or TNFSF6, is a homotrimeric type-II transmembrane protein that belongs to the tumor necrosis factor （TNF） family. Its ability to induce apoptosis in target cells plays an important role in the development, homeostasis, and function of the immune system. Interaction of FAS with fas Ligand is critical in triggering apoptosis of some types of cells such as lymphocytes. Fas Ligand may be involved in cytotoxic T-cell mediated apoptosis and in T-cell development. TNFRSF6/FAS-mediated apoptosis may have a role in the induction of peripheral tolerance, in the antigen-stimulated suicide of mature T-cells, or both.