Fas Ligand (FasL) is a member of the TNF superfamily that is expressed on the cell surface of activated T cells. Binding of FasL to Fas Receptor triggers apoptosis in Fas-bearing cells. FasL has the ability to kill T cells and activated B cells, which leads to down-regulation of the immune response. The mechanism of Fas-induced 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. Both human and murine sFasL are fully active on human and murine cells. Recombinant Human sFas Ligand is a 17.9 kDa protein comprising the TNF-homologous region of FasL and contains an 8-residue N-terminal His-Tag.