The deaths of neurons, astrocytes and endothelial cells have been described in patients with HIV (human immunodeficiency virus) dementia. HIV-1 does not infect neurons; instead, neurotoxic substances shed by infected glia and macrophages can induce a form of programmed cell death called apoptosis in neurons. These neurotoxins include the HIV-1 proteins Tat and gp120, as well as pro-inflammatory cytokines, chemokines, excitotoxins and proteases. In this article we review the evidence for apoptosis of various cell types within the brain of HIV-infected patients, and describe in vitro and in vivo experimental studies that have elucidated the mechanisms by which HIV causes apoptosis of brain cells.

An indirect immunofluorescence procedure was developed for the measurement of cyclobutyl dithymidine dimers in DNA of individual Syrian hamster embryo cells using a specific monoclonal antibody. A fluorescein-labeled secondary antibody and a fluorochrome which binds to DNA were used to measure the photoproduct and total DNA in the same nucleus. Fluorescence intensity was quantitated with a computer-assisted microfluorometric system which was calibrated with a uranyl oxide impregnated glass slide. Similar dose-response curves, i.e. normalized fluorescence intensity plotted as a function of dose of germicidal irradiation, were obtained with two different cell types. Normalized fluorescence intensity per nucleus was related to thymidine dimer content with a competitive enzyme-linked immunosorbent assay using DNA isolated from cells given doses of germicidal irradiation identical to those used in the immunofluorescence assay. Thymidine dimer levels produced by 10 J/m2 of germicidal irradiation (approximately 8 x 10(5)/nucleus) and which allow for 15-30% cell survival can readily be detected. The specific monoclonal antibody was labeled with tritium and used in the immunofluorescence assay to relate the number of antibodies bound to the number of thymidine dimers per cell. The data revealed that approximately 45% of the thymidine dimers in cells exposed to 100 J/m2 of germicidal irradiation and essentially all the T mean value of T in cells receiving 20 J/m2, were being detected in the indirect immunofluorescence assay. This technique can provide a sensitive means for measuring various types of DNA damage in individual cells given that the appropriate probes are available. It can be especially useful for monitoring occupationally or environmentally exposed populations where usually only small samples of cells or tissues are available.