Elevated expression of interleukin‐37 in patients with rheumatoid arthritis

Aim This study aims to discuss plasma and messenger RNA (mRNA) levels of interleukin (IL)‐37 in rheumatoid arthritis (RA) patients and evaluate the potential of plasma IL‐37 as a biomarker for RA. Method Plasma IL‐37 levels and IL‐37 mRNA relative concentrations were measured by enzyme‐linked immunosorbent assay (ELISA) and quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR). We discussed the association of IL‐37 levels and clinical, laboratory parameters in RA patients in a training cohort. Plasma IL‐37 levels were tested for discriminatory capacity by receiver operating characteristic (ROC) curve analysis. We then validated plasma IL‐37 expression in a cohort of 598 patients (230 RA, 107 systemic lupus erythematosus [SLE], 100 osteoarthritis [OA], 62 gout, 51 primary Sjögren's syndrome [pSS], 48 ankylosing spondylitis [AS]). Results Both plasma levels of IL‐37 and mRNA levels of IL‐37 were elevated in RA patients compared to those in healthy controls in the training cohort, and there was a good diagnostic ability to predict RA (area under the curve [AUC] = 0.97). Plasma IL‐37 levels were significantly related to Disease Activity Score of 28 joints ‐ erythrocyte sedimentation rate (DAS28‐ESR) (rs = 0.459, P