The ACPA+RF+ RA group of patients revealed a negative correlation between the level of CICs and the titer of serum ACPAs (r = −0.62, p = 0.003; Table S3, Supplementary Materials) and a positive correlation between the titer of serum RFs and the CIC IgG level (r = 0.46, p = 0.04; Table S3, Supplementary Materials). Here, PRTN3 is linked to rheumatoid arthritis.