NOVEL FAS (CD95 APO-1) MUTATIONS IN INFANTS WITH A LYMPHOPROLIFERATIVE DISORDER/

Fas is an apoptosis-signaling receptor important for homeostasis of th e immune system. In this study, Fas-mediated apoptosis and Fas mutatio ns were analyzed in three Japanese children from two families with a l ymphoproliferative disorder characterized by lymphadenopathy, hepatosp lenomegaly, pancytopenia, hypergammaglobulinemia and an increase in TC R alpha beta(+)CD4(-)CD8(-) T cells, Apoptosis induced by anti-fas mAb was defective in both activated T cells and a cells, and granulocytes from these patients. Truncated Fas receptor lacking the cytoplasmic d eath domain caused by a point mutation in the splice region of intron 7 were demonstrated in two siblings, A homozygous point mutation in th e splice acceptor of intron 3 was found in the Fas gene of the third p atient, which resulted in the skipping of exon 4 and complete loss of Fas expression, Corresponding to these mutations, soluble Fas concentr ations were decreased and reciprocally soluble Fas ligands were increa sed in patients' sera, Interestingly, co-stimulation by immobilized an ti-fas mAb in T cells from the two siblings was comparable to that see n in normal T cells, These results suggest that Fas-mediated apoptosis plays a pivotal role in immunological homeostasis in vivo, especially regarding clonal deletion of immune cells in humans.