TNF-related apoptosis-inducing ligand (TRAIL) belongs to the tumor necrosis factor (TNF) cytokine family and induces rapid apoptosis in a wide variety of tumor cell lines upon binding to the death-signalling receptors on the cell membrane. TRAIL binds to one of four receptors that have been identified in humans, including TRAIL-R1/DR4, TRAIL-R2/KILLER/DR5, TRAIL-R3/DcR1/TRID, and TRAIL-R4/DcR2/TRUNDD. Both DR4 and DR5 are pro-apoptotic receptors, which contain a cytoplasmic death domain and mediate apoptosis on binding to TRAIL. By contrast, TRID and TRUNDD do not contain a cytoplasmic death domain and block the function of TRAIL by competing with DR4 and DR5 for binding of TRAIL. Recombinant human TRAIL was expressed in E.coli and purified by using conventional chromatography techniques.