Opposing roles of dectin-1 expressed on human plasmacytoid dendritic cells and myeloid dendritic cells in TH² polarization

Dendritic cells (DCs) can induce and control host immune responses. DC subset-dependent functional specialties and their ability to display functional plasticity, which is mainly driven by signals via pattern recognition receptors, identify DCs as immune orchestrators. A pattern recognition receptor, Dectin-1, is expressed on myeloid DCs and known to play important roles in Th17 induction and activation during fungal and certain bacterial infections. In this study, we first demonstrate that human plasmacytoid DCs express Dectin-1 in both mRNA and protein levels. More interestingly, Dectin-1-activated plasmacytoid DCs promote TH²-type T cell responses, whereas Dectin-1-activated myeloid DCs decrease TH²-type T cell responses. Such contrasting outcomes of TH²- type T cell responses by the two DC subsets are mainly due to their distinct abilities to control surface OX40L expression in response to b-glucan. This study provides new insights for the regulation of host immune responses by Dectin-1 expressed on DCs.