CD40 on salivary gland epithelial cells: high constitutive expression by cultured cells from Sjögren’s syndrome patients indicating their intrinsic activation

Abstract

CD40 has been identified in an expanding list of haematopoietic and non‐haematopoietic cells and has received an increased interest based on its role in a variety of cell‐mediated responses and its potential to participate in the pathogenesis of chronic inflammatory disorders. Sjögren’s syndrome (SS) is an autoimmune exocrinopathy, which is characterized by chronic lymphocytic infiltration of exocrine glands and aberrant activation of epithelial tissues. We studied the expression of CD40 protein in cultured non‐neoplastic salivary gland epithelial cell (SGEC) lines as well as in minor SG biopsies obtained from 17 SS patients and 12 controls. Immunocytochemical and flow cytometric analyses had revealed the occurrence of constitutively expressed CD40 molecules on the surface of long‐term cultured SGEC lines, which could be further induced by interferon‐gamma (IFN‐γ) and IL‐1β cytokines, but not tumour necrosis factor‐alpha (TNF‐α), IL‐4, IL‐6, granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) or IFN‐α. Triggering of SGEC through CD40 enhanced the surface expression of the adhesion molecule intercellular adhesion molecule‐1 (ICAM‐1)/CD54, but not MHC class I and class II (HLA‐DR) molecules. Spontaneous CD40 expression was significantly higher in SGEC lines derived from SS patients, compared with controls (P < 0·001), which is suggestive of their intrinsically activated status. In SG biopsies, CD40 was constitutively expressed by lymphocytes, ductal epithelial cells and endothelial cells but not by other glandular cell types, such as acinar cells, myoepithelial cells and fibroblasts. In addition, CD40L staining was also detected in 30–50% of the infiltrating lymphocytes in the biopsies of SS patients. Our findings indicate the immunoregulatory potential of SGEC and lend further support to a model of intrinsic activation in salivary epithelia in SS, whereby these cells actively participate in the induction and maintenance of lymphocytic infiltrates of patients.