Evaluation of Serum and Synovial Fluid Interleukin-33 Levels in Patients with Active Rheumatoid Arthritis: The Association with Disease Activity and Clinical Findings

Abstract

Aim of work: To evaluate serum and synovial fluid (SF) interleukin-33 (IL-33) levels in patients with active rheumatoid arthritis (RA) and to investigate the association with the disease activity, clinical and laboratory findings. Patients and Methods: Fifty RA patients with disease activity score 28 (DAS28) >3.2 and 30 patients with osteoarthritis (OA) serving as a control group were included in this cross-sectional study. Matched serum and SF were obtained from both patients and controls. Measurement of serum and SF IL-33 was done using the Human IL-33 Enzyme-linked immunosorbent assay. Results: Median serum and SF IL-33 levels in RA patients were higher than OA control group (82.3 pg/ml (range 27.7-180) vs. 21 pg/ml (range 6-65) and 135.75 pg/ml (range 79.7-228.9) vs. 23 pg/ml (range 7-42) respectively) with a high statistically significant difference between them (p<0.001). SF IL-33 levels showed higher results than matched serum samples in the RA group with a positive significant correlation (p<0.001). A statistically insignificant association was found between serum and SF IL-33 levels with erythrocyte sedimentation rate, C-reactive protein, tender joint count, swollen joint count, DAS28, disease duration, anti-cyclic citrullinated peptide antibody, rheumatoid factor and modified Sharp Score. Conclusion: IL-33 levels showed an increase in serum and SF in RA patients supporting the notion of its involvement in the pathogenesis of RA; however, it may not be a sensitive marker of disease activity.