Interleukin-18 in Brazilian Rheumatoid Arthritis Patients: Can Leflunomide Reduce It?

Abstract

Objectives. Rheumatoid arthritis affects about 1% of the world’s population. This is a chronic autoimmune disease. It is predominant in females with progressive joint damage. Immune cells are involved, especially Th1/Th17 lymphocytes and their inflammatory cytokines. These proteins have different functions in the immune system, such as IL-16 is a chemotactic factor; IL-18 can activate NFκB transcription producing inflammatory proteins; IL-31 can activate the JAK/STAT pathway which leads to the production of inflammatory factors in chronic diseases; IL-33 promotes IL-16 secretion which causes lymphocyte recruitment, and IL-32 and IL-34 appear to increase TNF secretion by macrophages activation in AR. The aim of this study was to evaluate serum levels of IL-16, IL-18, IL-31, IL-32, IL-33, and IL-34 and compare them with the severity and treatment of RA patients if there are any correlations. Methods. A total of 140 RA patients and 40 healthy donors were recruited from the Department of Rheumatology at Hospital das Clínicas from the Federal University of Pernambuco. 60 AR patients were naïve for any treatment. Serum cytokine levels were determined using an ELISA kit. Results. Serum IL-16 ( $p$  = 0.0491), IL-18 ( $p$  < 0.0001), IL-31 ( $p$  = 0.0004), and IL-32 ( $p$  = 0.0040) levels were significantly increased in RA patients compared with healthy donors. It was observed that patients using leflunomide had the lowest IL-18 levels, close to controls levels ( $p$  = 0.0064). Conclusion. IL-16, IL-18, IL-31, and IL-32 are increased in the serum of RA patients. IL-18 is at lower levels in those AR who are taking leflunomide as treatment.