Role of type 1 IFN and DR5 in T-cell apoptosis. (A) Effect of monoclonal RIK-2 anti-TRAIL antibody, anti-DR5 antibody, and anti–IFN-α/β antibodies on the percentages of annexin V⁺ cells resulting from 24-hour cultures of CD4⁺ T cells with AT-2 HIV-1_MN. (B) Two-color flow cytometric analysis of annexin V/DR5 double-positive CD4⁺ T cells cultured for 24 hours with microvesicles plus anti-DR5 (control), AT-2 HIV-1MN plus isotype, or AT-2 HIV-1 plus anti-DR5 antibody. Control and AT-2 HIV-1 plus anti-DR5–treated cells were then stained using an anti–mouse PE antibody, and cells cultured with AT-2 HIV-1 plus isotype were stained using an anti-DR5 PE antibody. (Top left) Cells are nonapoptotic but DR5⁺. (Top right) Cells are apoptotic (annexin V⁺) and DR5⁺. (C) Effect of IFN-α/β–specific antibodies on TRAIL expression by CD4⁺ T cells cultured with AT-2 HIV-1_MN. (D) Effect of anti–IFN-α/β antibodies on TRAIL mRNA expression induced by culture with AT-2 HIV-1_MN for 24 hours. (E) Activated caspase-3 levels in CD4⁺ T cells cultured for 6 hours with or without AT-2 HIV-1_MN (top panel) and in the presence or absence of anti–IFN-α/β antibodies (bottom panel). (F) IFN-α levels, measured by ELISA, in supernatants of isolated pDCs, cultured for 24 hours with microvesicles, AT-2 HIV-1_MN, or AT-2HIV-1_Ada. (A,D,F) Mean values (± SD) of 6 experiments. (B-C,E) Representative results of 4 independent experiments. (A,D) P values were determined by 2-tailed Student t test.