AB0211 The relationship between the elevated serum immunoglobulin g4 level and disease activity in patients with rheumatoid arthritis
Authors: C.-N. Son, H.-J. Jeong, J.-N. Chae, J.-M. Kim, S.-H. Kim
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> High levels of serum immunoglobulin G4 (IgG4) would comprise a useful diagnostic tool in IgG4-related disease, but little information is available about IgG4 in conditions other than IgG4-related disease, including rheumatic diseases. Previous studies indicate that the elevated serum IgG4 in rheumatoid arthritis (RA) is common and disproportional to total IgG. <h3>Objectives</h3> The aim of study is to evaluate the level of serum IgG4 and IgG4/total IgG ratio in patients with RA. <h3>Methods</h3> Ninety-six patients with RA and one hundred and thirty-five non-RA controls were enrolled between <sup>March 2014</sup> and July 2017. All samples were collected before the treatments. The levels of Serum total IgG and IgG4 were determined by nephelometric assay. The cut-off value of serum IgG4 was 135 mg/dL. Data on clinical variables and disease activity markers, such as numbers of tender and swollen joints, levels of acute phase reactants and disease activity score 28 (DAS28) were recorded in RA patients. We compared the levels of serum IgG4 and the ratio of IgG4/total IgG in rheumatoid arthritis with healthy controls and other rheumatic diseases. This study also investigated the difference the relationship between levels of serum IgG4 and disease activity in RA. <h3>Results</h3> Among 96 RA patients, the mean of serum IgG4 was 48.0±45.4 mg/dL and 6.3% had elevated serum IgG4. The mean serum IgG4/IgG ratio of RA patients was 3.5%±2.8% (range 0.2%∼16.9%). There was no patient with elevated serum IgG4 in ankylosing spondylitis, systemic lupus erythematosus, Sjogren's syndrome, and inflammatory myositis. When the patients were divided according to clinical activity, the percentages of the positive serum IgG4 were 25% in active disease group and 4% in low activity group. However, the serum IgG4 levels of the RA patients with active disease activity were not significantly higher than those of the RA patients with low disease activity (58.3±44.3 mg/dL vs. 39.9±30.1 mg/dL). No significant relationship was observed between the ratio of IgG4/total IgG and disease activity. The IgG4 concentrations and total IgG/IgG4 ratios were similar between RA and the other autoimmune diseases (p&gt;0.05). <h3>Conclusions</h3> Our results showed that elevated serum IgG4 in RA is relatively common. However the presence of the elevated serum IgG4 was not associated with disease activity of RA. Further investigations are needed to explore the clinical significance in a larger study population. <h3>References</h3> [1] Lin G, et al. Elevation of serum IgG subclass concentration in patients with rheumatoid arthritis. Rheumatol Int2010;30:837–40. [2] Yamamoto M, et al. Value of serum IgG4 in the diagnosis of IgG4-related disease and in differentiation from rheumatic diseases and other diseases. Mod Rheumatol2012;22:419–25. [3] Chen LF, et al. Elevated Serum IgG4 Defines Specific Clinical Phenotype of Rheumatoid Arthritis. Mediators Inflamm2014;2014:635293. <h3>Disclosure of Interest</h3> None declared