Loss of the Class II Accessory Molecule HLA-DO leads to presentation of lower abundance of DM-resistant epitopes

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 function remains 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 the thymic deletion, and peripheral activation of CD4 T cells. Here, using in vivo antigen presentation in an autoimmune as well as infectious model, we found that DO-KO mice present a lower abundance of MOG(35-55)/I-Ab and H5N1-HA(259-274)/DR1 complexes by B cells. Using 2D2 Tg T cells specific for MOG(35-55)/I-Ab as a readout system, we observed a less effective T cell activation upon co-culture of brain recovered APCs from diseased DO-KO mice. When we vaccinated DR1+DO-KO and DR1+DO-WT mice with flu vaccine, we found that HA(259-274)/DR1 specific CD4 T cells had a less avid interaction with B cells presenting HA(259-274)/DR1 from DR1+DO-KO as compared to B cells from vaccinated DR1+DO-WT mice as measured by a novel avidity measurement tool, z-MoviTM.