CXCR4 blocker attenuated HIV-1 but not combined TNF-α and HIV-1-induced astrocyte toxicity. (A) HFA pretreated with CXCR4 blocker (AMD3100) (0.5 or 5.0 μM) were given HIV-1 treatment; 48 h later, LDH release was estimated in cell supernatants (P < 0.05). Inset shows overlay histogram of CXCR4 receptor expression in HFA after treatment with TNF-α for 16 h analyzed by flow cytometry, with the percentage of cell population shown relative to isotype control. (B) HFA were pretreated with AMD3100 (CXCR4 blocker) for 30 minutes at the indicated concentrations, then treated with a combination of HIV-1 (250 ng/ml) and TNF-α (10 ng/ml) and monitored for LDH release as before. HFA, human fetal astrocytes; LDH, lactate dehyrdrogenase.