FIG 1.

Neutralization assays. (A) Frozen CD4⁺ cells were thawed, stimulated overnight with IL-2, and infected with one of the four GFP-labeled HIV-1 Env variants to prepare cell-associated virus. Cell-free HIV-1 or HIV-1-infected donor cells were incubated with virus-directed antibodies or inhibitors for 1 h and then added to uninfected TZM-bl target cells. DEAE-dextran was used for cell-free virus infection but not for cell-associated infection. After 96 h, Steady-Glo luciferase expression was used to quantify the amount of infection of TZM-bl cells. (B) Cell-free HIV-1 or HIV-1-infected donor cells stained with Far Red DDAO-SE were incubated with virus-directed antibodies or inhibitors for 1 h and then added to uninfected A3R5 target cells. DEAE-dextran was used for cell-free virus infection only. Flow cytometry was performed to determine the number of newly infected target cells from cell-associated (GFP⁺ Far Red⁻) or cell-free (GFP⁺) virus. FITC, fluorescein isothiocyanate.