HIV-1 Nef does not modulate TNF-alpha decreased viability of astrocytes. U251MG-parental, -pNeo and -Nef cells were treated with TNF-alpha for 24 h at indicated concentrations. The medium was then exchanged and cell viability assay was performed as described in the Material section. The times indicated are relative to the moment of adding AlamarBlue® reagent to the cell culture medium. The relative fluorescence represents the ratio of the fluorescence intensity of study cells versus mock-treated cells at 1 h after start of the assay. Data represent mean ± s.e.m. (n = 5).