Fig. (2) The effect of HHA and T-20 on syncytium formation between Env⁺ and SupT1 cells. Env+ cells were incubated with the reagents for 30 min before the addition of the SupT1 cells. The cells were then incubated for 3 h at 37°C, washed twice with PBS, and then observed by fluorescence microscopy. (A) Fluorescence micrograph of cells incubated with HHA at 1 µg/ml. HHA inhibited both the attachment of SupT1 cells to the Env⁺ cells and their fusion. (B) Inhibition of cell-cell fusion by HHA at varying concentrations. (C) Fluorescence micrograph of cells incubated with T-20 at 1 µg/ml. T-20 inhibited cell-cell fusion, but not the attachment of the red-orange SupT1 cells to the Env⁺ cells. (D) Inhibition of cell-cell fusion by T-20 at varying concentrations. The vertical bars indicate the spread of duplicate determinations.