The role of plasmacytoid dendritic cells in immunity and tolerance

Purpose of review Plasmacytoid dendritic cells are key effectors in host innate immunity and orchestrate adaptive immune responses. The role of plasmacytoid dendritic cells in regulating immunity and tolerance is a subject of immense research interest. This review summarizes the current literature regarding the role of plasmacytoid dendritic cells in the induction of regulatory T cells and the maintenance of immunologic tolerance. Recent findings Dendritic cells are critical to the development and peripheral expansion of regulatory T cells. Recent studies have shown that plasmacytoid dendritic cells induce the generation of interleukin-10-producing CD8(+) T suppressor and CD4(+)CD25(+)Foxp3(+) regulatory T cells that potently suppress autologous and allogeneic T cell proliferation. Plasmacytoid dendritic cells express indoleamine 2,3-dioxygenase and produce large amounts of type I interferons that may contribute to regulatory T cell generation and tolerance induction. Increasing evidence in both experimental and clinical transplantation studies demonstrates that plasmacytoid dendritic cells enhance engraftment and prevent graft-versus-host disease. Summary Considerable new evidence suggests that plasmacytoid dendritic cells play an important role in regulatory T cell generation and the maintenance of immune tolerance. Understanding the immune regulatory functions and the mechanisms of plasmacytoid dendritic cells may lead to the development of novel therapies for infectious diseases, autoimmune diseases, cancer, and organ transplantations.