Development of interstitial lung disease in rheumatoid arthritis patients and the connection between interleukin-9 and interleukin-22

Rheumatoid arthritis is an autoimmune disease characterized by chronic inflammation in the joints, leading to joint deformities. Although the major clinical presentation of rheumatoid arthritis is joint inflammation, lung involvement is a significant cause of morbidity and mortality. Recent studies have shown that interleukin-9 and interleukin-22 levels are elevated in the serum and synovial fluids of patients with rheumatoid arthritis and are associated with the development of inflammation. The levels of interleukin-9 and interleukin-22 have not been studied in rheumatoid arthritis patients with interstitial lung disease. The aim of our study is to investigate whether interleukin-9 and interleukin-22 levels play a role in the development of interstitial lung disease in patients with rheumatoid arthritis. The study included patients diagnosed with rheumatoid arthritis according to the 2010 American College of Rheumatology/ European League Against Rheumatism classification criteria who were referred to the Rheumatology Clinic of Trakya University, as well as healthy volunteers. The rheumatoid arthritis patients were divided into two groups: those with interstitial lung disease and those without. During routine blood collection, an additional 2 cc of blood was taken from both the patient and control groups into gel serum separation tubes, centrifuged, and the samples were stored at -80°C. The demographic and clinical characteristics of the patients, lung imaging and functional characteristics, disease activity, and treatments they received were recorded. Interleukin-9 and interleukin-22 levels were measured in the serum of patients and healthy volunteers using enzyme-linked immunosorbent assay. The obtained results were analyzed to determine whether there was any relationship between the clinical and lung characteristics of the rheumatoid arthritis groups and were compared to those of the healthy volunteers. A total of 76 participants were included in the study, consisting of 24 patients with rheumatoid arthritis, 26 patients with rheumatoid arthritis-related interstitial lung disease, and 26 healthy volunteers. While the average age was similar between the rheumatoid arthritis groups, the healthy volunteers were younger. There was no difference between disease activity score-28 and acute phase reactants in patients with rheumatoid arthritis. When comparing interleukin-9 levels in the patient groups, the rheumatoid arthritis-related interstitial lung disease group had higher interleukin-9 levels compared to the control group. Although there was no statistical significance between the rheumatoid arthritis and rheumatoid arthritis-related interstitial lung disease groups, interleukin-9 levels were higher in the rheumatoid arthritis related interstitial lung disease group. There was no difference in interleukin-22 levels between the groups. Interleukin-22 levels were higher in patients with a high disease activity score-28. Patients who were rheumatoid factor positive had higher interleukin-9 levels. Although various genetic and environmental factors are implicated in the development of interstitial lung disease in patients with rheumatoid arthritis, its etiopathogenesis is not yet fully understood. Some studies have shown that interleukin-9 levels play a significant role in the pathogenesis of rheumatoid arthritis. In our study, the higher interleukin-9 levels observed in patients with rheumatoid arthritis and interstitial lung disease suggest that interleukin-9 may play an active role in the development of interstitial lung disease, and it could potentially serve as a marker for the development of interstitial lung disease in patients with rheumatoid arthritis. The lack of statistical significance for interleukin-22 may be due to the small number of patients in the study and the potential influence of disease activity on its levels.