The Role of Interleukin-22 in The Diagnosis and Evaluation of Disease Activity in Rheumatoid Arthritis

Background: Rheumatoid Arthritis (RA) is a chronic autoimmune disease that primarily affects small joints, resulting in joint inflammation, pain, and limited mobility. The identification of novel biomarkers specific to RA could enhance early diagnosis and treatment and also improve the monitoring of the disease activity and treatment response. In this study, the levels of IL-22 were measured in 133 patients with inflammatory arthritis using the ELISA method with the aim of assessing the diagnostic value of IL-22 in the diagnosis of RA and evaluating the disease activity. The findings revealed that serum IL-22 levels were significantly higher in RA patients compared to patients with other types of inflammatory arthritis. Additionally, positive correlations were observed between IL-22 and disease activity scores as determined by CDAI, DAS-28 ESR, and DAS-28 CRP. Notably, when IL-22 was used as a diagnostic tool, with a cut-off value of ≥ 26.9 pg/ml, it exhibited a sensitivity of 83%, specificity of 75%, and an AUC of 0.838. Furthermore, significant associations were found between IL-22 levels and the age of RA patients, while no significant correlations were observed with gender, BMI, and smoking index. It is noteworthy that IL-22 levels were significantly correlated with ESR, RF titer, and ACPA levels. Consequently, IL-22 can be regarded as a valuable biomarker for diagnosing RA and evaluating disease activity. Subjects and method: This cross-sectional study was conducted from September 2022 to January 2023, involving 133 patients with inflammatory arthritis, including RA and other forms of inflammatory arthritis. All patients were recruited from As-Sader Teaching Hospital in Najaf. The ages of the patients included in the present study range  from 20 to 70 years, with a sample comprising 116 females and 17 males. Results: The higher median (IQR) value of IL-22 was observed among the RA patients [36.9 (28.6-63.7) pg/ml] compared to that of the other patients with inflammatory arthritis [23.6 (19.8-26.8) pg/ml]. The difference between the two groups of patients was highly significant (P < 0.0001). Among the RA patients, a highly significant difference in the median (IQR) level of IL-22 was observed among the disease activity groups according to CDAI, DAS-28 ESR, and DAS-28 CRP (P < 0.0001). Conclusion: Interleukin-22 can be regarded as a reliable biomarker for the diagnosis of RA and holds potential for assessing disease activity.