Programmed cell death (mainly apoptosis) is involved in all fundamental processes of the immune system. Furthermore, apoptosis is essential for elimination of autoreactive lymphocytes and is, therefore a mechanism to guarantee self-tolerance. There are several genes directly implicated in the regulation of lymphoid apoptosis. However, certain mouse strains expressing the defective mutants of those genes exhibit immunological dysfunctions resembling human autoimmune disease conditions. Thus, further analyses of such animal models could facilitate the better understanding of immunopathological abnormalities developing in humans.