HLA-DR15 Molecules Jointly Shape an Autoreactive T Cell Repertoire in Multiple Sclerosis

Autoimmune diseases are often associated with HLA molecules. Multiple sclerosis (MS) is a prototypical example with the HLA-DR15 haplotype as strongest genetic factor. How it contributes to MS is not clear, but key to understand this and other autoimmune diseases. Autoreactive CD4+ T cells and proinflammatory B cells are central pathogenetic factors, and since HLA-DR molecules present peptides to CD4+ T cells, we characterized the peptidomes of the two HLA-DR15 allomorphs DR2a and DR2b on B cells. Self-peptides from HLA-DR α- and β-chains themselves are abundantly presented on B cells. We identified autoreactive CD4+ T cell clones, which recognize HLA-DR-derived self-peptides and peptides from the MS-related infectious agents EBV and Akkermansia and the autoantigen RAS guanyl-releasing protein 2. Our data demonstrate how the two MS-associated HLA-DR15 allomorphs function as antigen-presenting structures and source of peptides during peripheral maintenance of autoreactive T cells and activation by MS-associated pathogens.