Abstract
Introduction: A novel immunomodulatory cytokine IL-41 is associated with the pathogenesis of Graves disease, Kawasaki disease, gout, psoriatic arthritis, and rheumatoid arthritis (RA). We aimed to evaluate serum IL-41 level as a biomarker of the RA and disease activity treatment efficacy and patient responses. We also wanted to determine eventual potential predictors of IL-41 concentrations. Methods and analysis: This observational clinical trial will enrol 189 patients rheumatology clinics of the Clinical Center Kragujevac, Serbia. Participants will be divided into three groups: patients on methotrexate monotherapy (MTX), (n=31), those treated with combined therapy of MTX plus TNF inhibitors (TNFi) (n=70), and patients treated with monotherapy with IL-6 inhibitor tocilizumab (TCZ) (n=43). Newly diagnosed RA or patients who for some reason were excluded from the DMARDs for a minimum of 3 months were considered as the control group (n=45). Results: TCZ reduced the IL-41 level the most. All treatment options significantly reduced clinical signs, symptoms and the scores of disease activity composite indices, TCZ the most. The only statistically significant predictor of higher IL-41 values was smoking. Conclusion: IL-41 may be a new potential biomarker that can help physicians evaluate treatment efficacy and predict patient responses. Smoking status is associated with the higher concentration of IL- 41 and clinical presentation of patients with RA.