CCR6/CCR10-mediated plasmacytoid dendritic cell recruitment to inflamed epithelia after instruction in lymphoid tissues.

Absent in peripheral tissues during homeostasis, human plasmacytoid dendritic cells (pDCs) are described in inflamed skin or mucosa. Here, we report that, unlike blood pDCs, a subset of tonsil pDCs express functional CCR6 and CCR10, and their respective ligands CCL20 and CCL27are detected in inflamed epithelia contacting blood dendritic cell antigen 2(+) pDCs. Moreover, pDCs are recruited to imiquimod-treated skin tumors in WT but not CCR6-deficient mice, and competitive adoptive transfers reveal that CCR6-deficient pDCs are impaired in homing to inflamed skin tumors after intravenous transfer. On IL-3 culture, CCR6 and CCR10 expression is induced on human blood pDCs that become responsive to CCL20 and CCL27/CCL28, respectively. Interestingly, unlike myeloid DC, blood pDCs initially up-regulate CCR7 expression and CCL19 responsiveness on IL-3 ± CpG-B and then acquire functional CCR6 and CCR10. Finally, IL-3-differentiated CCR6(+) CCR10(+) pDCs secrete high levels of IFN-α in response to virus. Overall, we propose an unexpected pDCs migratory model that may best apply for mucosal-associated lymphoid tissues. After CCR7-mediated extravasation into lymphoid tissues draining inflamed epithelia, blood pDCs may be instructed to up-regulate CCR6 and/or CCR10 allowing their homing into inflamed epithelia (in mucosae or skin). At this site, pDCs can then produce IFN-α contributing to pathogen clearance and/or local inflammation.