Fas and Fas Ligand (FasL) belong to the TNF superfamily and are type I and type II transmembrane proteins, respectively. Binding of FasL to Fas triggers apoptosis in Fas-bearing cells. The mechanism of apoptosis involves recruitment of pro-caspase 8 through an adaptor molecule called FADD followed by processing of the pro-enzyme to active forms. These active caspases then cleave various cellular substrates leading to the eventual cell death. sFasR is capable of inhibiting FasL-induced apoptosis by acting as a decoy receptor that serves as a sink for FasL. The full length Fas (receptor) is a 319aa type I transmembrane protein, which contains a 157aa extracellular domain, a 17aa transmembrane domain, and 145aa cytoplasmic domain. Recombinant human soluble Fas (sFas Receptor) is a 157aa polypeptide,17.6kD, corresponding to the TNFR homologous cysteine rich extracellular domain Fas.