Susceptibility of activated T cells to killing by pDCs from HIV-1 viremic patients. (A) Cytotoxic activity of isolated pDCs from viremic patients infected with HIV-1 was tested against nonstimulated and PHA-stimulated CD4⁺ T cells from healthy HIV-1–seronegative persons, and CD4⁺ T cells from a viremic patient infected with HIV-1 served as positive control target cells. Data represent means of duplicate wells ± SEM from 4 independent experiments of europium-TDA release assays. (B) pDCs derived from a viremic patient infected with HIV-1 were incubated with anti-TRAIL, anti-Fas ligand, anti–IFN-α, anti-TRAIL plus anti–IFN-α, or of an IgG1 isotype mAbs and, thereafter, with PHA-stimulated CD4⁺ T cells from HIV-1–seronegative persons. CD4⁺ T cells from a HIV-1 viremic patient served as positive control. Data represent means of duplicate wells ± SEM from 2 independent experiments of europium-TDA release assays. (C) TRAIL receptors were analyzed on nonstimulated and PHA-stimulated CD4⁺ T cells from healthy HIV-1–seronegative persons, HIV-1 viremic CD4⁺ T cells, and HIV-negative and HIV-positive H9 cells by FACS staining. The data are given as mean percentages of positive cells ± SEM from 2 independent experiments. (D) pDCs from a viremic patient infected with HIV-1 (viremic pDCs) or healthy HIV-1–seronegative control (normal pDCs) were preincubated with IgG1 isotype, anti-TRAIL, anti-Fas ligand, anti–IFN-α, or anti-TRAIL plus anti–IFN-α mAbs. HIV-1–infected or –uninfected H9 cell lines served as target cells. Data represent means of duplicate wells ± SEM from 1 of 2 independent experiments of europium-TDA release assays.