CD4+ T-lymphocytes infected with HIV-1 express NKG2D ligands. CD4⁺ T cells (B,F) uninfected or (A,C,D) infected with HIV-1_SF162 or (E,F) HIV-1_SF128A were stained with NKG2D/IgG Fc fusion proteins and goat antihuman secondary reagent followed by staining with mouse anti–HIV-1 p24 antibodies. Numbers in the dot plots represent the percentage of viable cells within each quadrant. Histograms (panels B-D) show expression of NKG2D ligand on uninfected, HIV-1 p24 Ag⁻ infected cells and HIV-1 p24 Ag⁺ infected cells, respectively. (F) The histogram with the dotted line represents cells stained with secondary antibodies alone, the histogram with the thin line represents uninfected cells, and the histogram with the bold line represents HIV-1 p24 Ag⁺ cells. These are representative of 5 separate experiments.