TNF-α synergized HIV-1-induced toxicity in astrocytes. (A) TNF-α with HIV-1 increased toxicity on astrocytes (HFA). LDH release was estimated in culture supernatants from HFA after treatment with increasing concentrations of TNF-α (0–10 ng/ml) and HIV-1 NL4-3 (50 ng/ml, 250 ng/ml p24 concentrations) or TNF-α alone for 48 h. Controls were left untreated (negative control). H2O2 was used as a positive control (P < 0.05). (B) HFA were treated with HIV-1 alone (250 ng/ml) or in combination with TNF-α (10 ng/ml). At 48 h after treatment, cell death was monitored by Trypan blue dye exclusion. Untreated HFA served as a negative control. Results were plotted as mean ± standard error of the mean (SEM) after counting 20 high-power fields for each treatment (n = 3). HFA, human fetal astrocytes; LDH, lactate dehyrdrogenase.