Loss of the Class II Accessory Molecule HLA-DO leads to altered TCR avidity

Abstract

Abstract HLA-DO (DO in human; H2-O in mice) is a highly conserved non-classical MHC class II accessory molecule. Unlike the main Class II peptide editor HLA-DM, expression of DO is restricted to the thymic medulla, B cells and certain dendritic cell subsets. Although DO forms a stable complex with HLA-DM, its biological functions remain poorly understood. Previously, our lab provided biochemical evidence in support of a model where DO enhances the binding of DM-resistant peptides, and reduces the binding of DM-sensitive peptides to the HLA-DR1 (DR1) molecules in vitro. Changes in the quantities of either DM-resistant of DM-sensitive peptides could therefore lead to alterations in both thymic deletion, and peripheral activation of CD4 T cells. Here, using both in vivo antigen presentation as well as a novel avidity measurement tool, z-Movi™ (LUMICKS), we found that: (1) brain recovered APCs from diseased DO-KO mice present less of the MOG(35–55) epitope, (2) naïve DO-KO CD4 T cells have a more avid interaction with their own APCs, and (3) that hemagglutinin specific, DR1 restricted CD4 T cells had a less avid interaction with B cells from flu vaccinated DR1+DO-KO mice as compared to B cells from vaccinated DR1+DO-WT mice. These avidity changes could explain two things: (1) why we find that despite DR1+DO-KO mice have similar precursor levels of collagen specific CD4 T cells as DR1+DO-WT mice, they are more susceptible to the development of Collagen Induced Arthritis, even though we previously showed that the immunodominant collagen epitope is DM-sensitive. And, (2) why we find increased levels of regulatory T cells in the absence of DO.