Plasmacytoid Dendritic Cells Take Up Opsonized Antigen Leading to CD4+ and CD8+ T Cell Activation In Vivo

Abstract

Plasmacytoid dendritic cells (pDC) are the body’s main source of IFN-α, but, unlike classical myeloid DC (myDC), they lack phagocytic activity and are generally perceived as playing only a minor role in Ag processing and presentation. We show that murine pDC, as well as myDC, express Fcγ receptors (CD16/CD32) and can use these receptors to acquire Ag from immune complexes (IC), resulting in the induction of robust Ag-specific CD4+ and CD8+ T cell responses. IC-loaded pDC stimulate CD4+ T cells to proliferate and secrete a mixture of IL-4 and IFN-γ, and they induce CD8+ T cells to secrete IL-10 as well as IFN-γ. In contrast, IC-loaded myDC induce both CD4+ and CD8+ T cells to secrete mainly IFN-γ. These results indicate that pDC can shape an immune response by acquiring and processing opsonized Ag, leading to a predominantly Th2 response.