Clinical significance of IL-33 and soluble ST2 in patients with axial spondyloarthritis and primary sjögren's syndrome

IL-33 is a newly identified cytokine belonging to the IL-1 family. It is expressed in epithelial, endothelial, smooth muscle cells, cardiomyocytes, fibroblasts, keratinocytes, adipocytes, dendritic cells and activated macrophages and it has an important role in innate immune system. ST2 is the only known receptor of IL-33. The ST2 receptor is a member of the Toll-like receptor and IL-1 receptor superfamily. There are 2 forms of ST2: Soluble ST2, which is found in dissolved form, traps only excess IL-33 molecules as a trap receptor for IL-33 and does not generate a signal, and ST2-L form, which is membrane bound and stimulates the function of mast cells, Thelper2, Tregulatory cells and naive lymphoid cells. The relationship of IL-33 and sST2 with autoimmune and chronic inflammatory diseases has been studied before. Sixty followed-up patients with primary Sjögren's syndrome (PSS), 60 patients with axial spondyloarthritis (axSpA) and 40 healthy volunteers were included in the study. Serum samples were taken to measure serum IL-33 and soluble ST2 (sST2) levels from a total of 160 participants consisting of PSS, axSpA and control groups. ELISA measurements were made as specified in the operating procedures found in the kits' catalogs. Obtained patient data were analyzed with appropriate statistical methods and p<0.05 was accepted as statistically significant. Among the groups included in the study, serum sST2 levels were found to be significantly higher in patients in PSS and axSpA groups (p<0.001), but there was no statistically significant difference between serum IL-33 levels. When the patient groups were compared with each other, serum sST2 levels were higher in the axSpA group than in PSS group. While there was a significant difference in serum sST2 levels between the patient and healthy control groups, the lack of significant difference in serum IL-33 levels was explained by the fact that sST2 is a decoy receptor for IL-33. No significant correlation was found between disease activities and serum IL-33 and sST2 levels. As a result, it was concluded that serum IL-33 and sST2 levels may change in autoimmune and chronic inflammatory diseases, but comprehensive studies are needed to better clarify and obtain more detailed information.