The extrinsic pathway begins when death receptors on the cell membrane bind to their corresponding ligands. These receptors are part of the tumor necrosis factor (TNF) receptor superfamily and include Fas receptor (CD95) and TNF-related apoptosis-inducing ligand (TRAIL) receptors. The binding of ligands to these receptors leads to the formation of a signaling complex known as the death-inducing signaling complex (DISC), which recruits and activates initiator caspases, primarily caspase-8.
