Serum IL-40 increases in patients with rheumatoid arthritis and correlates with some clinical characteristics and comorbidities.

The role of Interleukin-40 (IL-40) in rheumatoid arthritis (RA) is not well understood, and this study was designed to explore serum IL-40 levels in RA patients to assess its potential as a disease biomarker. In this research, serum IL-40 levels were determined using enzyme-linked immunosorbent assay in 116 patients with RA, 40 with osteoarthritis (OA), 29 with systemic lupus erythematosus (SLE), and 66 healthy controls (HCs). Paired serum samples were collected from 86 of the 116 patients treated during follow-up visits at week 12. Group comparison analysis showed that serum IL-40 levels were significantly higher in patients with RA than in HCs, and the areas under the curve for IL-40 were 0.688, 0.865, and 0.870 for distinguishing patients with RA from HCs and those with OA and SLE, respectively. Furthermore, in RA, serum IL-40 levels were lower in patients with comorbidities of cardiovascular diseases or OA. Correlation analyses revealed that serum IL-40 levels were positively associated with RA-related autoantibodies and coagulation-related indicators, whereas no correlation was observed with disease activity-associated factors. When comparing paired samples, treatment with TNF inhibitors (TNFi) significantly reduced serum IL-40 levels, emphasizing its potential as a treatment guide.