C1q-Dependent Dendritic Cell Cross-Presentation of In Vivo-Formed Antigen-Antibody Complexes

Dendritic cells (DCs) are specialized in Ag engulfment via a wide variety of uptake receptors on their cell surface. In the present study we investigated Ag uptake and presentation of in vivo-formed Ag-Ab complexes by i.v. injecting mice with Ag-specific Abs followed by the cognate Ag. We show by this natural Ab-mediated Ag targeting system that uptake by splenic APC subsets is severely hampered in mice lacking complement factor C1q (C1qa (-/-)). Moreover, no detectable Ag cross-presentation by CD8 alpha(+) DCs from C1qa (-/-) mice was found. On the contrary, Ag uptake was not hampered by APCs in FcgRI/II/III/IV-deficient (FcgR quadruple (-/-) ) mice, and the cross-presentation ability of CD8 alpha(+) DCs was not affected. In conclusion, we show that C1q rather than FcgRs controls the Ab-mediated Ag uptake and its presentation by spleen APC subsets to T cells.