Update on the role of plasmacytoid dendritic cells in inflammatory/autoimmune skin diseases

Plasmacytoid dendritic cells ( pDC s) represent a specialized dendritic cell population that exhibit plasma cell morphology, express CD 4, CD 123, blood‐derived dendritic cell antigen‐2 ( BDCA ‐2) and Toll‐like receptor ( TLR )7 and TLR 9 within endosomal compartments. When activated, pDC s are capable of producing large quantities of type I IFN s (mainly IFN ‐ α / β ), which provide antiviral resistance and link the innate and adaptive immunity. While generally lacking from normal skin, pDC s infiltrate the skin and appear to be involved in the pathogenesis of several inflammatory, infectious (especially viral) and neoplastic entities. In recent years, pDC role in inflammatory/autoimmune skin conditions has been extensively studied. Unlike type I IFN ‐mediated protective immunity that pDC s provide at the level of the skin by regulated sensing of microbial or self‐nucleic acids upon skin damage, excessive sensing may elicit IFN ‐driven inflammatory/autoimmune diseases. In this review, focus will be on the role of pDC s in cutaneous inflammatory/autoimmune dermatoses.