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

Abstract

SUMMARYCD40 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-g) and IL-1b cytokines, but not tumour necrosis factor-alpha (TNF-a), IL-4, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) or IFN-a. 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.

Immune receptors CD40 and CD86 in oral keratinocytes and implications for oral lichen planus

“…CD40 is a 45-50 kDa phosphorylated type I integral membrane glycoprotein that belongs to the tumor necrosis factor receptor superfamily, which is expressed on various hematopoietic and non-hematopoietic cells (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). CD40 is involved in several biological functions, such as cell-mediated immunity and cell growth regulation.…”

A-fodrinAutoantigen Detection in Saliva and on Salivary Ductal Cells in Sjögren Syndrome

“…As stated earlier, in an in vitromodel using HSG cells that α-fodrin, caspase-3, poly(ADP-ribose) polymerase protease (PARP), SS-A, and SS-B were all cleaved in response to stimulation by TNF-α, a known inducer of apoptosis [21].Therefore, it is possible that TNF, which is increased systemically in SS, contributes in vivo to apoptosis and destruction of salivary gland tissue. TNF-α and other cytokines such as IFN-γ are known to be increased in vivoin the parenchyma of salivary and lacrimal glands of patients with SS [22][23][24][25][26].The cellular source of TNF in the salivary glands is unknown, however, although it is presumably released by infiltrating CD4 lymphocytes.…”

“…TNF-α and other cytokines such as IFN-γ are known to be increased in vivoin the parenchyma of salivary and lacrimal glands of patients with SS [22][23][24][25][26].The cellular source of TNF in the salivary glands is unknown, however, although it is presumably released by infiltrating CD4 lymphocytes. Interestingly, all proteins except PARP are cleaved in vitroand transported to the ductal or acinar cell membrane; PARP, however, is cleaved but remains in the intracellular space [21].Perhaps this intracellular location of PARP where it appears protected from antigen processing by the immune system, is one factor contributing to why PARP is infrequently associated with autoantibody production in SS.…”

“…Such cleaved products could then be presented to ductal epithelial or endothelial cells, which express HLA-DR antigens or CD40, and could then undergo antigen processing. This could result in an immune response with T cell proliferation and the production of the autoantibodies detected in many SS patients [21].This observation also provides a possible explanation for a central role of epithelial cells in SS implied by the location of the periductal and perivascular location of lymphocytic infiltrates in salivary gland ducts and vessels [21,27].It is interesting that cleaved PARP fragments have been reported on the ducts and acini but minimally detected in the area of the lymphocytic infiltrate compared with α-fodrin [11]. This is consistent with the proposal that PARP, a nuclear antigen, we have shown is not expressed on the cell surface during apoptosis and therefore not expected to undergo antigen processing by infiltrating lymphocytes [7].…”

Chemokine (C-X-C Motif) Ligand 1 (CXCL1) Expression in the Minor Salivary Glands of Sjögren's Syndrome Patients

“…Epithelial cells are thought to participate in and modulate the inflammatory process in SS, as supported by previous immunohistochemical studies of the salivary gland tissue of SS patients that demonstrated an increased expression of various immunoactive molecules in the ductal and acinar salivary gland epithelial cells (SGEC) [4][5][6][7][8][9]. Additionally, several studies of cultured SGEC from SS patients found that various molecules associated with innate and acquired immune responses were expressed [10][11][12][13][14]. These results strongly suggest the implication of epithelial cells in the induction and promotion of chronic inflammation and that they have an important role to play in the pathogenesis of SS.…”