memory T cells Plasmacytoid DCs regulate recall responses by rapid induction of IL-10 in

Abstract Dendritic cells (DCs) are believed to regulate T-cell mediated immunity primarily by directing differentiation of naive T cells. Here, we show that a large fraction of CD4 + memory cells produce IL-10 within the first hours after interaction with plasmacytoid DCs (PDCs). In contrast, CD11c + DCs induce IFN-γ and little IL-10. IL-10-secreting T cells isolated after 36 h of culture with PDCs, suppressed antigen-induced T cell proliferation by an IL-10-dependent mechanism, but were distinct from natural and type 1 regulatory T cells. They proliferated strongly and continued to secrete IL-10 during expansion with PDCs, and after re-stimulation with immature monocyte-derived DCs or CD11c + DCs. The IL-10-producing T cells acquired the ability to secrete high levels of IFN-γ after isolation and subsequent co-culture with PDCs or CD11c + DCs. Compared to CD11c + DCs, PDCs were superior in their ability to selectively expand T cells that produced cytokines upon repeated antigenic challenge. The DC-dependent differences in cytokine profiles were observed with viral recall antigen or staphylococcal enterotoxin B and were independent of extracellular type I interferon or IL-10. Our results show that DCs can regulate memory responses, and that PDCs rapidly induce regulatory cytokines in effector T cells that can suppress bystander activity. From bloodjournal.hematologylibrary.org by guest on December 31, 2011. For personal use only.