Cytokines produced by infiltrating hematogenous cells or by glial cells activated during the course of central nervous system disease or trauma are implicated as mediators of tissue injury. In this study, we have assessed the extent and mechanism of injury of human-derived CNS oligodendrocytes and neurons in vitro mediated by the cytokines tumor necrosis factor alpha and beta and compared these with the tumor necrosis factor independent effects mediated by activated CD4+ T-cells. We found that activated CD4+ T-cells, but not tumor necrosis factor alpha or beta, could induce significant release of lactate dehydrogenase, a measure of cell membrane lysis, from oligodendrocytes within 24 hr. Neither induced DNA fragmentation as measured using a fluorescence nick-end labelling technique. After a more prolonged time period (96 hr), tumor necrosis factor alpha did induce nuclear fragmentation changes in a significant proportion of oligodendrocytes without increased lactate dehydrogenase release. The extent of DNA fragmentation was comparable to that induced by serum deprivation. Tumor necrosis factor beta effects were even more pronounced. In contrast to oligodendrocytes, the extent of DNA fragmentation, assessed by propidium iodide staining, induced in neurons by tumor necrosis factor alpha was less than that induced by serum deprivation. In-situ hybridization studies of human adult glial cells in culture indicated that astrocytes, as well as microglia, can express tumor necrosis factor alpha mRNA.