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Mean levels of anti‐citrullinated protein antibodies (ACPA) immunoglobulin (Ig)G, IgA, IgM and secretory IgA (SIgA) in rheumatoid arthritis (RA) patients at inclusion and during the 36 months of follow‐up. ****P = 0·0001 (Friedman’s test). Error bars represent standard error of the mean (s.e.m.) (n = 231).
