U83A inhibits R5 HIV-1 infection. (A) Using HIV-1 R5 strain on MAGI-CCR5 cells, U83A-N and U83A inhibit HIV-1 foci of infection in the same range of positive control as CCL5/RANTES. The deletion U83A-Ndel had no effect. Results (means ± SDs) are representative of 3 independent experiments. (B) U83A and U83A-N did not inhibit infection by CXCR4 using HIV-1 strain on MAGI-CXCR4 cells. (C) U83A-N and CCL5/RANTES inhibit infection of HIV-1 strain SF2 (dual tropic) on MAGI-CCR5 cells. (D) U83A-N and CCL5/RANTES inhibit infection of HIV-1 strain SF162 (CCR5 specific) on MAGI-CCR5 cells.