The interleukin 33/ST2 axis in patients with primary Sjögren syndrome: Expression in serum and salivary glands, and the clinical association

Objective. To evaluate the expression of interleukin 33 (IL-33) and its receptor in sera and salivary tissues of patients with primary Sjögren syndrome (pSS), and to investigate the association with clinical profiles. Methods. Serum IL-33 and soluble ST2 (sST2) of 55 patients with pSS and 48 controls were determined by ELISA and assessed for clinical correlation. The expression of IL-33/ST2 in salivary tissues was investigated by immunohistochemical staining and was further characterized by confocal microscopy. We also measured IL-33 production in salivary glandular epithelial cells by proinflammatory stimuli. Results. Serum levels of IL-33 and sST2 were higher in patients with pSS compared to those in controls (p = 0.018 and p < 0.0001, respectively). Among patients with pSS, sST2 concentration was associated with thrombocytopenia (p = 0.029) and correlated with disease duration (p = 0.013) and the European League Against Rheumatism Sjögren Syndrome Disease Activity Index (p = 0.042). The expression of IL-33 and ST2 was elevated in salivary glands of patients with pSS with grade 2 inflammation, and diminished in advanced inflammation. In patients with pSS, IL-33 was mainly observed in epithelial and endothelial cells of glandular tissue. The production of IL-33 mRNA by salivary gland epithelial cell line increased under stimulation with interferon-γ. Conclusion. The expression of IL-33 and its receptor was elevated in sera and salivary tissues of patients with pSS. These results suggest that the IL-33/ST2 axis might have a role in the pathogenesis of pSS.