Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the Tumor Necrosis Factor (TNF) family of cytokines. TRAIL is widely produced by a variety of cell types including tumor cells, smooth muscle of the lung and spleen, cerebellar glial cells, and thyroid follicular cells. TRAIL is a cytotoxic protein that induces apoptosis in tumor cells through the activation of the death receptors DR4 and DR5. TRAIL also binds the neutralizing decoy receptors, DcR1 and DcR2. Human TRAIL is active on mouse cells.