While the serum RF titer correlated with the level of all classes of CIC immunoglobulins (IgA r = 0.51, p = 0.004; IgG r = 0.37, p = 0.046; IgM r = 0.38, p = 0.036; Table S3, Supplementary Materials), the serum ACPA titer correlated only with the level of CIC IgA in the RA group (r = 0.45, p = 0.012; Table S3, Supplementary Materials). Here, PRTN3 is linked to rheumatoid arthritis.