Antigen-stimulated apoptotic T-cell death in HIV infection is selective for CD4+ T cells, modulated by cytokines and effected by lymphotoxin

Objective: To characterize the mechanism of in vitro antigen-induced apoptotic T-cell death in the peripheral blood mononuclear cells (PBMC) of HIV-1-infected individuals. Design and methods: PBMC from HIV-1-infected and uninfected individuals were unstimulated or stimulated with HIV-1 envelope synthetic peptides (Env) or influenza A virus to determine the extent of antigen-stimulated apoptotic T-cell death, whether this death was limited to the CD4+ subset, and the effects of cytokines on T-cell death. Death was assessed by apoptotic nuclear morphology after 7 days of culture by fluorescence microscopy using a DNA-specific dye. Transwell cultures and supernatant transfers were utilized to test whether a soluble factor produced by HIV-positive PBMC induced death of HIV-negative T cells. Exogenous cytokines [interleukin (IL)-12, interferon (IFN)-γ, IL-4 and IL-10], as well as antibodies against endogenously produced cytokines (IL-4, IL-10, IL-12, and lymphotoxin) were tested for their ability to modulate death. Results: Antigenic stimulation induced death in PBMC from HIV-positive donors, but not in PBMC from HIV-negative donors. Antigen-stimulated death was seen in CD4+ but not CD8+ T-cell subset from the HIV-positive patients. Apoptotic death was blocked by IL-12, IFN-γ, anti-IL-4, anti-IL-10, and anti-lymphotoxin, but not by anti-IL-12. Transwell and supernatant transfer experiments indicated that antigen stimulated HIV-positive PBMC produced a factor that killed T-cell blasts. The factor was inhibited by anti-lymphotoxin, but not by anti-IL-10. Conclusions: Stimulation of HIV-positive PBMC with CD4-dependent antigens results in selective death of CD4+ T cells that is modulated by cytokines. Our results suggest that apoptotic death is not limited to HIV-infected or HIV-specific T cells, but occurs in bystander cells. Lymphotoxin is a mediator of antigen-stimulated T-cell death in this in vitro model.