Expression of CD4, HIV p24 antigen, and MHC class I molecules on HIV-infected primary CD4^- T-cell blasts. HIV-1_SF162-infected primary T-cell blasts were depleted of CD4⁺ cells before their use as target cells in the cytotoxicity assay. CD4-depleted HIV-infected cells (bold lines) were stained with fluorochrome-conjugated anti-CD4 antibody (A,C) or human anti-HIV p24 antibody, together with fluorochrome-conjugated goat anti-human IgG antibody (B,D). Cells were then stained with fluorochrome-conjugated anti-MHC class I antibody (C-D). As controls, uninfected CD4⁺ T cells (thin solid lines) were also stained with the same antibody. MHC class I molecules expressed on 10⁴ uninfected CD4⁺ control cells (C-D), 10⁴ HIV p24 antigen-positive cells (D), and 10⁴ CD4^- cells (C) were determined. Dotted lines indicate isotype control antibody (Ab).