AUTOIMMUNE LYMPHOPROLIFERATIVE SYNDROME
During lymphocyte development, autoreactive cells are culled by undergoing apoptotic death. During the life span of mature lymphocytes, activation and effector function is followed by activation-induced cell death by apoptosis. Apoptosis thus maintains homeostasis in the immune system by minimizing autoimmune reactions to self-antigens, as well as limiting the total size of the peripheral lymphocyte pool. Antigen-mediated activation of T cells induces them to express a surface receptor FAS (CD95) as well as its ligand, the FAS-ligand. FAS/FAS-ligand interaction activates a biochemical pathway culminating in cell death by apoptosis. Mice that are FAS-/-(lpr) or FAS-ligand-/- (gld) develop autoimmunity and develop expansion of their their lymphocyte pool.