Cell surface recycling of internalized antigen permits dendritic cell priming of B cells

Dendritic cells process internalized antigens to present degradative products on MHC for TCR recognition. Because antigen-exposed DCs also induce humoral immunity, DCs must also retain antigen in its native state for the engagement of BCR on B cells. Here, we demonstrate that antigen endocytosed by the inhibitory Fc receptor, Fc gamma RIIB, accesses a nondegradative intracellular vesicular compartment that recycles to the cell surface, enabling interaction of native antigen with BCR on B cells. Immunization with IgG-opsonized, T independent antigens leads to enhanced humoral responses in a FcyRIIB and complement dependent manner. IC-loaded DCs trafficking to the splenic marginal zone can prime a T independent response in an Fc gamma RIIB-dependent manner. Thus dendritic cells are equipped with both nondegradative and degradative antigen uptake pathways to facilitate antigen presentation to both B and T cells.