HIV-1 down-modulates NTB-A and CD48 on infected cells. Primary T-cell blasts either were left uninfected or were infected with 10³ TCID₅₀ HIV-1_SF162 or HIV-1_SF128A. Cells were surface-stained for (A,C,D) CD48, or (B,E,F) NTB-A followed by intracellular staining for the HIV-1 p24 capsid protein using the human 71-31 monoclonal antibody and goat antihuman secondary antibody. Data are representative of at least 3 different experiments with different donors. In panels A and B, the numbers in the corners of the plot quadrants are the percentage of viable cells that express the specific markers. Histogram representation of all viable cells is shown in panels C through F (■ represents isotype control staining, ——— represents surface staining of viable uninfected cells, and ▔▔▔ represents surface staining of viable HIV-infected cells).