Both necrosis and apoptosis contribute to HIV-1-induced killing of CD4 cells

Background: Data currently available on HIV-1-induced cytopathology is unclear regarding the mechanism of cell killing. Objective: To clarify the extent to which apoptosis or necrosis is involved in HIV-1-induced cell death in view of conflicting exiting data. Methods: T lymphoblastoid cells or peripheral blood mononuclear cells were infected by various strains of HIV-1 and the number of apoptotic or necrotic cells were quantified at various times after infection using video-image analysis techniques; the results were compared with the amount of fragmented DNA using a quantitative method. Measurement of mitochondrial transmembrane potential (ΔΨ(m)) and intracellular calcium concentrations [Ca²⁺](i) was performed with fluorescent probes and fluorescence concentration analysis (FCA). Results: Although lymphoblastoid and monocytoid cells acutely infected by HIV-1 had increased levels of fragmented DNA, a marker of apoptotic cell death, few (< 12%) had condensed chromatin and fragmented nuclei, the morphological features of apoptosis. The predominant alterations in acutely infected cells were distended endoplasmic reticulum and abnormal mitochondria; these ultrastructural changes are consistent with necrosis, although some infected cells simultaneously displayed features of both necrosis and apoptosis. Viability of cells persistently infected by HIV-1 was only minimally reduced from that of uninfected cells. This reduction was accounted for by an increased propensity of the persistently infected cells to die by apoptosis. Alterations in [Ca²⁺](i) and ΔΨ(m) occurred in both acutely and persistently infected cells. Conclusion: Both necrosis and apoptosis contribute to HIV-1-induced killing of CD4 cells.