The FAS ligand (Fas-L) belongs to the tumor necrosis factor family. The full length Fas-L protein has a cytoplasmic domain, transmembrane (Type II) domain and extracellular domain. The membrane-bound form of Fas-L is proteolytically cleaved to produce soluble Fas-L. There are at least 2 known isoforms of Fas-L produced by alternate splicing.