Antibody responses initiated by Clec9A-bearing dendritic cells in normal and Batf3^-/- mice

Injection of antigens coupled to antibodies against the dendritic cell (DC) surface molecule Clec9A has been shown to produce strongly enhanced antibody responses even without co-administration of adjuvants, via antigen presentation by DC on MHC class II and consequent production of follicular helper T cells. A series of mutant mice were tested to determine the DC subtypes responsible for this MHC II presentation of targeted antigen, compared to presentation of antigen on MHC I. A new clec9A null mouse was developed; these mice did not give enhanced antibody production, confirming the response was dependent on Clec9A-expressing DC. However targeting of antigen to Clec9A in batf3 null mice produced enhanced antibody responses despite the marked reduction in CD8⁺ DC, the major Clec9A-expressing DC subtype. This was shown to be dependent on efficient MHC II presentation by minor Clec9A-expressing DC subtypes in the environment of the Batf3^-/- mice, namely early cells of the CD8 DC lineage and the plasmacytoid-related CD8⁺ DC subset, but not by plasmacytoid cells themselves. However in normal mice most MHC II presentation of the Clec9A-targeted antigen was by the major CD8⁺ DC population, the DC also responsible for presentation on MHC I.