J Rheum Dis 2020; 27(2): 96-99  
Clinical Significance of Elevated Serum Immunoglobulin G4 Levels in Patients With Rheumatoid Arthritis
Sang-Hyon Kim, M.D., Ph.D.1, Hye-Jin Jeong, M.D.1, Ji-Min Kim, M.D., Ph.D.1, Jae-Bum Jun, M.D., Ph.D.2, Chang-Nam Son, M.D., Ph.D.1
1Division of Rheumatology, Department of Internal Medicine, Keimyung University School of Medicine, Daegu, 2Department of Rheumatology, Hanyang University Hospital for Rheumatic Diseases, Seoul, Korea
Correspondence to: Chang-Nam Son http://orcid.org/0000-0002-1722-2190
Division of Rheumatology, Department of Internal Medicine, Keimyung University School of Medicine, 1035 Dalgubeol-daero, Dalseo-gu, Daegu 42601, Korea.
Received: September 4, 2019; Revised: January 14, 2020; Accepted: January 14, 2020; Published online: April 1, 2020.
© Korean College of Rheumatology. All rights reserved.

This is a open Access article, which permits unrestricted non-commerical use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective. This study aimed to evaluate the relationship between serum immunoglobulin G4 (IgG4) levels and the presence and disease activity of rheumatoid arthritis (RA). Methods. The study enrolled 128 participants (RA, 96; healthy controls, 17; osteoarthritis, 11; and IgG4-related disease, 4) between March 2014 and July 2017. Blood samples were collected prior to the commencement of treatment, and serum IgG4 levels were determined using a nephelometric assay (levels ≥135 mg/dL were considered elevated). The levels of serum IgG4 and the ratio of IgG4/total IgG in patients with RA were compared with those in healthy controls, patients with osteoarthritis, and patients with IgG4-related disease. Furthermore, the relationship between serum IgG4 levels and RA disease activity was evaluated. Results. Among the 96 patients with RA, the mean (±standard deviation) serum IgG4 level was 48.0±45.4 mg/dL; 6 (6.3%) patients had elevated serum IgG4 levels. However, none of the healthy controls or patients with osteoarthritis had elevated serum IgG4 levels. The mean serum IgG4/IgG ratio in patients with RA was 3.5%±2.8% (range, 0.2%∼16.9%). Using Spearman’s correlation coefficient analysis, a significant correlation was found between serum IgG4 levels and the Disease Activity Score-28 with erythrocyte sedimentation rate (r, 0.245; p=0.016). Conclusion. There was an increased frequency of elevated serum IgG4 levels in patients with RA, and the levels were correlated with RA disease activity.
Keywords: Rheumatoid arthritis, Immunoglobulin G4

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