Cross-recognition by CD4+ T cells of an epitope (DERAA) that is found both in synovial citrullinated vinculin and in several microbes (including gut bacteria such as Lactobacillus, enriched in RA) (232, 254, 255) and which is presented by predisposing HLA-DQ molecules (HLA-DQ5, DQ-7.3 and DQ8, all in tight linkage disequilibrium with HLA-DR SE alleles), leads to increased ACPA production and, eventually, RA (265). The gene discussed is PRTN3; the disease is rheumatoid arthritis.