Dendritic Cells Rapidly Recruited into Epithelial Tissues via CCR6/CCL20 Are Responsible for CD8 + T Cell Crosspriming In Vivo

The nature of dendritic cell(s) (DC[s]) that conditions efficient in vivo priming of CD8 + CTL after immunization via epithelial tissues remains largely unknown. Here, we show that myeloid DCs rapidly recruited by adjuvants into the buccal mucosa or skin are essential for CD8 + T cell crosspriming. Recruitment of circulating DC precursors, including Gr1 + monocytes, precedes the sequential accumulation of CD11c + MHC class II + DCs in dermis and epithelium via a CCR6/CCL20-dependent mechanism. Remarkably, a defect in CCR6, local neutralization of CCL20, or depletion of monocytes prevents in vivo priming of CD8 + CTL against an innocuous protein antigen administered with adjuvant. In addition, transfer of CCR6-sufficient Gr1 + monocytes restores CD8 + T cell priming in CCR6 °/° mice via a direct Ag presentation mechanism. Thus, newly recruited DCs likely derived from circulating monocytes are responsible for efficient crosspriming of CD8 + CTL after mucosal or skin immunization.