IGHG3 and rheumatoid arthritis: For ACPA-positive RA, a higher proportion of patients were positive for anti-CarP antibodies with 24, 74, and 53% positive for the IgM, IgG, and IgA, and 73, 39, 10, and 43% positive for IgG1, IgG2, IgG3, and IgG4, respectively (Fig. 1c).