PRTN3 and rheumatoid arthritis: •MAA adducts increased in RA vs. OA synovium•Anti-MAA Ab (IgA, IgG, IgM) increased in RA (ACPA+ and ACPA-) vs. Control•Correlations of Anti-MAA with RF and ACPA (beta coefficient 0.33-0.61; p<0.001) variable associations of Anti-MAA Ab with RA disease activity•No cross reactivity with ACPA