Interleukin-15 as a potential new target in Sjögren's syndrome-associated inflammation

IL-15 is a key regulatory cytokine that shares many biological properties with IL-2. Recently, it has been shown that IL-15 could be up-regulated in T cell-mediated inflammatory disorders, such as rheumatoid arthritis and inflammatory bowel diseases. However, the role and expression of IL-15 in the inflammatory autoimmune disease Sjögren's syndrome (SS) has not been investigated. In the present study we evaluated the expression of IL-15 mRNA and protein in minor salivary gland (MSG) biopsy specimens and in human salivary gland epithelial cell (SGEC) cultures obtained from patients with primary SS (pSS) and compared their expression with that seen in normal healthy control subjects. IL-15 gene and protein analysis revealed that SGEC are able to produce IL-15. Results obtained demonstrated that the number of IL-15(+) cultured SGEC was significantly higher in cells derived from patients with pSS in comparison with SGEC from healthy subjects; similar results were obtained for IL-15 immunoreactivity by using immunohistochemistry that revealed a strong expression both in acinar and in ductal cells from pSS MSG. These studies could provide a rational basis to determine whether IL-15 could be a good candidate for anti-cytokine therapy in chronic inflammatory pSS diseases.