Possible role for IL-40 and IL-40-producing cells in the lymphocytic infiltrated salivary glands of patients with primary Sjögren's syndrome

Objectives: Aim of this study was to investigate the expression of interleukin (IL)-40, a new cytokine associated with B cells homoeostasis and immune response, in primary Sjögren syndrome (pSS) and in pSS-associated lymphomas. Methods: 29 patients with pSS and 24 controls were enrolled. Minor salivary gland (MSG) biopsies from patients, controls and parotid gland biopsies from pSS-associated lymphoma were obtained. Quantitative gene expression analysis by TaqMan real-time PCR and immunohistochemistry for IL-40 were performed on MSG. MSG cellular sources of IL-40 were determined by flow-cytometry and immunofluorescence. Serum concentration of IL-40 was assessed by ELISA and cellular sources of IL-40 were determined by flow-cytometry. An in vitro assay with recombinant IL-40 (rIL-40) was performed to detect the effect on cytokine production from peripheral blood mononuclear cells (PBMCs). Results: IL-40 was significantly increased in the lymphocytic infiltrated MSG of patients with pSS and correlated with focus score and with IL-4 and transforming growth factor-β expression. In addition, IL-40 was increased in the serum of pSS and its levels correlated with the EULAR Sjögren's Syndrome Disease Activity Index score. B cells from patients were shown to be the major source of IL-40 at both tissue and peripheral level. PBMCs from patients, exposed to rIL-40 in vitro, released proinflammatory cytokines, specifically interferon-γ from B cells and T-CD8+ and tumour necrosis factor-α and IL-17 from both T-CD4+ and T-CD8+. IL-40 expression in parotid glands of pSS-associated lymphomas was also increased. Moreover, IL-40-driven NETosis was evidenced in neutrophils obtained from pSS. Conclusion: Our results suggest that IL-40 may play a role in pSS pathogenesis and pSS-associated lymphomas.