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 into 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 319 amino acid type I transmembrane protein, which contains a 157 amino acid extracellular domain, a 17 amino acid transmembrane domain, and a 145 amino acid cytoplasmic domain. Recombinant Human soluble Fas (sFas Receptor) is a 157 amino acid polypeptide (17.6 kDa) corresponding to the TNFR-homologous cysteine-rich extracellular Fas domain.