Crossreactivity to vinculin and microbes provides a molecular basis for HLA-based protection against rheumatoid arthritis

The HLA locus is the strongest risk factor for anti-citrullinated protein antibody (ACPA) + rheumatoid arthritis (RA). Despite considerable efforts in the last 35 years, this association is poorly understood. Here we identify (citrullinated) vinculin, present in the joints of ACPA + RA patients, as an autoantigen targeted by ACPA and CD4 + T cells. These T cells recognize an epitope with the core sequence DERAA, which is also found in many microbes and in protective HLA-DRB1*13 molecules, presented by predisposing HLA-DQ molecules. Moreover, these T cells crossreact with vinculin-derived and microbial-derived DERAA epitopes. Intriguingly, DERAA-directed T cells are not detected in HLA-DRB1*13 + donors, indicating that the DERAA epitope from HLA-DRB1*13 mediates (thymic) tolerance in these donors and explaining the protective effects associated with HLA-DRB1*13. Together our data indicate the involvement of pathogen-induced DERAA-directed T cells in the HLA–RA association and provide a molecular basis for the contribution of protective/predisposing HLA alleles. Autoantibodies targeting citrunillated proteins are common in rheumatoid arthritis patients. Here the authors show that vinculin (a human protein) and some microbial proteins are recognized by these antibodies and by CD4 + T cells, and this response is absent in patients carrying a protective HLA allele.