Fas/FasL-Independent Activation-Induced Cell Death of T Lymphocytes from HIV-Infected Individuals Occurs without DNA Fragmentation

We assessed the effects of activation with phorbol myrystic acetate (PMA) and ionomycin on peripheral blood mononuclear cells (PBMC) from HIV-infected individuals by 51Cr release, propidium iodide (PI) uptake, electron microscopy, and DNA analysis. Up to 70% 51Cr release was induced from PBMC of HIV-infected individuals, versus up to 26% 51Cr release from PBMC of non-HIV-infected volunteers. Flow cytometry identified mostly T cells undergoing activation-induced cell death (AICD). The kinetics of 51Cr release and the effects of cold target inhibitors were consistent with cell-mediated cytotoxicity. Certain anti-CD3 antibodies or extracellular Ca2+ chelation prevented AICD, but antagonistic anti-Fas antibodies, caspase inhibitors, and cycloheximide had no effect. The antioxidants thiourea and N-acetylcysteine reduced AICD, indicating a role for oxidative stress. Electron microscopy revealed plasma membrane disruption with nuclear integrity, while DNA analysis showed intact chromosomal DNA. This form of T cell AICD triggered by PMA and ionomycin differs from classical apoptosis in the absence of either caspase involvement or DNA fragmentation.