Langerin+ CD8alpha+ dendritic cells are critical for cross-priming and IL-12 production in response to systemic antigens

Distinct dendritic cell (DC) subsets differ with respect to pathways of Ag uptake and intracellular routing to MHC class I or MHC class II molecules. Murine studies suggest a specialized role for CD8alpha(+) DC in cross-presentation, where exogenous Ags are presented on MHC class I molecules to CD8(+) T cells, while CD8alpha(-) DC are more likely to present extracellular Ags on MHC class II molecules to CD4(+) T cells. As a proportion of CD8alpha(+) DC have been shown to express langerin (CD207), we investigated the role of langerin(+)CD8alpha(+) DC in presenting Ag and priming T cell responses to soluble Ags. When splenic DC populations were sorted from animals administered protein i.v., the ability to cross-present Ag was restricted to the langerin(+) compartment of the CD8alpha(+) DC population. The langerin(+)CD8alpha(+) DC population was also susceptible to depletion following administration of cytochrome c, which is known to trigger apoptosis if diverted to the cytosol. Cross-priming of CTL in the presence of the adjuvant activity of the TLR2 ligand N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-[R]-Cys-[S]-Serl-[S]-Lys4-trihydrochloride or the invariant NKT cell ligand alpha-galactosylceramide was severely impaired in animals selectively depleted of langerin(+) cells in vivo. The production of IL-12p40 in response to these systemic activation stimuli was restricted to langerin(+)CD8alpha(+) DC, and the release of IL-12p70 into the serum following invariant NKT cell activation was ablated in the absence of langerin(+) cells. These data suggest a critical role for the langerin(+) compartment of the CD8alpha(+) DC population in cross-priming and IL-12 production.