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

The HLA-DR15 haplotype is the strongest genetic risk factor for multiple sclerosis (MS), but our understanding of how it contributes to MS is limited. Because autoreactive CD4+ T cells and B cells as antigen-presenting cells are involved in MS pathogenesis, we characterized the immunopeptidomes of the two HLA-DR15 allomorphs DR2a and DR2b of human primary B cells and monocytes, thymus, and MS brain tissue. Self-peptides from HLA-DR molecules, particularly from DR2a and DR2b themselves, are abundant on B cells and thymic antigen-presenting cells. Furthermore, we identified autoreactive CD4+ T cell clones that can cross-react with HLA-DR-derived self-peptides (HLA-DR-SPs), peptides from MS-associated foreign agents (Epstein-Barr virus and Akkermansia muciniphila), and autoantigens presented by DR2a and DR2b. Thus, both HLA-DR15 allomorphs jointly shape an autoreactive T cell repertoire by serving as antigen-presenting structures and epitope sources and by presenting the same foreign peptides and autoantigens to autoreactive CD4+ T cells in MS. [Display omitted] •HLA-DR15 present abundant HLA-DR-derived self-peptides on B cells•Autoreactive T cells in MS recognize HLA-DR-derived self-peptides/DR15 complexes•Foreign peptides/DR15 complexes trigger potential autoreactive T cells in MS•HLA-DR15 shape an autoreactive T cell repertoire by cross-reactivity/restriction The immunopeptidome presented by HLA-DR15 molecules links the most important genetic and environmental risk factors for multiple sclerosis, the HLA-DR15 haplotype and Epstein-Barr virus, by shaping a cross-reactive CD4+ T cell repertoire.