lymphocytes from patients with HIV infection have been shown to undergo accelerated apoptosis. Fas antigen is a cell surface protein known to initiate an apoptotic signal. Therefore, we undertook a study to examine the expression of the Fas antigen during HIV infection. Using three color flow cytometry, expression of the Fas antigen on lymphocytes of 23 HIV infected individuals (CDC category 2, CD4 200499 cells/pL, n = 10; CDC category 3, CD4 < 200 cells/pl, n = 13) and 10 healthy controls was examined. Both CD3+CD4+ and CD3+CD8+ subsets were examined for their expression of this marker. In lymphocytes of healthy controls, 47% of the CD3+CD4+ and 45% of the CD3+CD8+ cells were Fas antigen positive. This percentage was significantly increased in CD4 cells from HIV infected patients belonging to CDC category 3, but was unchanged from normal values in CDC category 2 subjects. The increase in the percentage of CD4+ T cells expressing Fas antigen in patients correlated significantly with the decrease in circulating CD4T cell count ( P < 0.009). In addition, by examining mean fluorescence intensity, we found that the amount of Fas expression per cell was increased threefold in CD3+CD4+ cells and increased twofold in CD3+CD8+ cells in category 3 patients. These results demonstrate that an increase in Fas antigen expression occurs during HIV infection. o 1995 Wiley-Liss, Inc.
Key terms: Fas, HIV, apoptosis, flow cytometryThe Fas antigen is a protein expressed on the surface of lymphocytes (12) which resides in a superfamily of proteins containing nerve growth factor (NGF) receptor (9) and tumor necrosis factor (TNF) receptor (20). Fas is identical to the Apo-1 antigen (1 3). Engagement of the Fas antigen by anti-Fas antibody has been shown to trigger DNA fragmentation and apoptotic cell death (15). A Fas mediated signal is not sufficient by itself to induce apoptosis in T cells (1,12). However, a mutation in Fds (26) or Fas ligand (22) results in massive lymphocyte accumulation in the periphery, suggesting a pivotal role for Fas in physiologic peripheral T cell death.Our laboratory has previously demonstrated that PBMC from HIV patients undergo accelerated apoptosis, and that crosslinking the CD4 molecule can induce apoptosis in human PBMC from normal controls (16). In addition, we have recently found that this crosslinking process upregulates the expression of Fas antigen in normal lymphocytes ( 17); others have shown that crosslinking human CD4 T cells with HIV gp120 followed by signalling through the TCR resulted in activation-dependent apoptosis (2). Further investigation demonstrated that both interferon-y (IFN-y ) and TNF-a contributed to this process and that antibodies directed against these cytokines were able to block both CD4 crosslinking-induced Fas upregulation and lymphocyte apoptosis ( 17). 0 1995 Wiley-Liss, Inc. This current report examines the expression of Fas antigen on CD4+ and CD8+ T lymphocyte subsets isolated from HIV infected patients. Our findings reveal that a greater percentage of CD4 lymp...