INCREASED FAS ANTIGEN EXPRESSION IN MURINE RETROVIRUS-INDUCED IMMUNODEFICIENCY SYNDROME, MAIDS

The Fas antigen (Fas), which is a cell surface protein belonging to th e tumor necrosis factor receptor family, mediates apoptosis. To assess the contribution of Fas to the pathogenesis of retrovirus-induced imm unodeficiency, we examined the kinetics of Fas expression on the lymph ocytes during the course of murine acquired immunodeficiency syndrome (MAIDS) induced by a defective LP-BM5 murine leukemia virus. The Fas-p ositive cells were increased in proportion both in alpha beta T cells and B cells with the progression of MAIDS, The appearance of Fas-posit ive cells in alpha beta T cells preceeded those in B cells during the course of MAIDS. Among alpha beta T cells, about half of the Thy1.2(+) alpha beta T cells were positive for Fas, while almost all of Thy1.2( -) CD4+ alpha beta T cells were of the Fas-positive phenotype. The Fas -positive cells in MAIDS mice, especially unique Thy1.2(-) CD4(+) alph a beta T cells,were easily rendered apoptotic by stimulation via Fas, indicating that Fas expressed on the lymphocytes is functional. Furthe rmore, concomitant infection with Mycobacterium avium in MAIDS mice ca used a marked increase in Fas-positive cells accompanied by a severely impaired T cell reactivity to polyclonal stimuli. Taken together, the se results suggest the possible participation of the Fas system in the pathogenesis of retrovirus-induced immunodeficiency.