Fig 1.

Fas apoptotic pathway. Patients with ALPS have defective Fas-mediated apoptosis. During downregulation of the immune response, activated B and T lymphocytes upregulate expression of Fas ligand, and activated T lymphocytes up-regulate expression of Fas. Fas ligand and Fas interact, activating the intracellular Fas-associated death domain (FADD) and triggering the caspase cascade with subsequent proteolysis, DNA degradation, and apoptosis. Apoptotic signalling mediated by Fas is part of the extrinsic pathway as it is activated through engangement of cell surface death receptors. The intrinsic apoptotic pathway is activated by cellular stressors, leading to alterations in mitochondrial membrane permeability and release of apoptosis-inducing substances. © Sue Seif, MA (used with permission).