The extrinsic signalling pathway results in apoptosis when tumor necrosis factor (TNF) receptor gene superfamily receptors are activated by extrinsic (extracellular) signals. Fas ligand on the surface of CTLs and TNFα and TNF-related apoptosis-inducing ligand (TRAIL) that are secreted by activated macrophages and lymphocytes are examples of extrinsic signals that interact with Fas receptor, TNF receptor 1 (TNFR1), and TRAIL receptor 1, respectively, on the surface of a target cell