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IFN-γ secretion by Ag-specific T cells is known to be tightly regulated by engagement of the TCR. Human plasmacytoid dendritic cells (pDC) can cross-present Ags from apoptotic HIV-infected cells or tumor cells to CD8 + T cells. As pDC respond to HIV virions by maturing and secreting cytokines, we hypothesized that this might affect cross-presentation from HIV-infected cells. Purified blood DC were incubated with apoptotic HIV-infected H9 cells in the presence of saquinavir, after which the activation process of HIV-specific cloned CD8 + T cells was studied. IFN-γ secretion by HIV-specific T cells was stimulated by pDC and conventional DC (cDC1) more than by cDC2 and was strictly MHC class I restricted. Surprisingly, intracellular production of IFN-γ was only partly MHC class I restricted for pDC, indicating a noncognate CD8 + T cell activation. pDC, but not cDC, matured and secreted IFN-α in the presence of apoptotic H9HIV cells. A mixture of IFN-α, IFN-β, and TNF-α induced intracellular production of IFN-γ but not granzyme B, mimicking the noncognate mechanism. Neutralization of type I IFN signaling blocked noncognate intracellular production of IFN-γ. Moreover, cognate stimulation was required to induce IFN-γ secretion in addition to the cytokine mixture. Thus, IFN-γ secretion is tightly regulated by engagement of the TCR as expected, but in the context of virus-infected cells, pDC can trigger intracellular IFN-γ accumulation in CD8 + T cells, potentializing IFN-γ secretion once CD8 + T cells make cognate interactions. These findings may help manipulate type I IFN signaling to enhance specifically Ag-specific CD8 + T cell activation against chronic infections or tumors.

Cell-Associated HIV Cross-Presentation by Plasmacytoid Dendritic Cells Is Potentiated by Noncognate CD8+ T Cell Preactivation