Immunoglobulin (Ig) G4 accounts for 4–6% of the total IgG in a healthy human. Several evidence-based studies have suggested that level IgG4 is significantly elevated autoimmune diseases, including rheumatoid arthritis (RA). The clinical significance RA with regard to disease activity, severity, and treatment response remains elusive. We consecutively recruited 174 patients from our rheumatology...