Increased Fas antigen expression in murine retrovirus‐induced immunodeficiency syndrome, MAIDS

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