PRTN3 and rheumatoid arthritis: The mean number of IgA (0.37 ± 0.7 vs. 0.96 ± 0.93; p < 0.001) and IgM (0.22 ± 0.46 vs. 0.44 ± 0.6; p = 0.04) ACPA isotypes was lower in PR than in RA patients.