Salivary gland epithelial cell exosomes: A source of autoantigenic ribonucleoproteins

Abstract

Objective. Exosomes are membrane vesicles of endosomal origin that are distinct from apoptotic bodies and are thought to represent an acellular mechanism for antigen transfer to classic antigen-presenting cells, as well as for direct antigen presentation with the capacity to induce immune response or tolerance. Nevertheless, it is not known whether exosomes are involved in the induction or regulation of immune responses against intracellular autoantigens that characterize autoimmune diseases. Exosomes have been shown to be secreted by several types of cells, whereas studies of non-neoplastic epithelial cells are lacking. This study was undertaken to investigate the capacity of nonneoplastic salivary gland epithelial cells (SGECs) to release exosomes, and to determine whether epithelial exosomes contain RNPs, which are major autoantigens in systemic rheumatic diseases.Methods. Exosomes were isolated by ultracentrifugation from culture supernatants of 26 non-neoplastic SGEC lines established from patients with various rheumatic disorders. They were analyzed by electron microscopy, immunoblotting, or immunoprecipitation.Results. All SGEC lines were found to release comparable and significant amounts of exosomes. Similar to other cell systems, exosome secretion was constitutive and was unrelated to activation or apoptotic processes. SGEC-derived exosomes were found to contain the autoantigenic Ro/SSA, La/SSB, and Sm RNPs, as well as epithelial-specific cytokeratins.Conclusion. SGECs constitutively secrete exosomes that contain the major autoantigens Ro/SSA, La/SSB, and Sm. This mechanism may represent a pathway whereby intracellular autoantigens are presented to the immune system with an immunogenic or tolerogenic outcome.Autoimmune diseases are characterized by the development of humoral responses against self antigens, most of which are intracellular proteins. Although thought to involve typical antigen-driven responses, the precise mechanism(s) involved in the presentation of such intracellular autoantigens to the immune system is unclear (1). Apoptosis and the resulting release of autoantigen-containing apoptotic vesicles are considered potential pathways for the generation of autoimmune responses (2).During the last decade, a novel cell-free mechanism of antigen presentation has been recognized (3) that involves small (30-100 nm) membrane vesicles, which are termed exosomes and are distinct from apoptotic bodies. These are different from the exosome protein complex, which is implicated in RNA processing and degradation processes. Exosomal vesicles are secreted following the fusion of multivesicular late endosome/lysosomes with the plasma membrane. Exosome production has been observed in a variety of cell types, including reticulocytes, platelets, cytotoxic T lymphocytes and B lymphocytes, dendritic cells, and neoplastic intestinal epithelial cells, whereas studies of non-neoplastic epithelial cells are lacking. Several physiologic roles have been assigned to exosomes, including the expulsion of obsolete membran...

Exosomes in the ascites of ovarian cancer patients: origin and effects on anti-tumor immunity

“…There are still many puzzles of ovarian cancer, including the relationship between the tumor and the host immune system, and the mechanisms of the development, invasion and metastasis of the tumor. Exosomes are a kind of microvesicles released by many types of cells such as tumor cell (1)(2)(3)(4), antigen presenting cells (APC) (5,6) and epithelial cells (7,8). Recent research revealed that exosomes purified from the ascites of patient with ovarian cancer contain some immunological-effect molecules (9).…”

The modulation of co-stimulatory molecules by circulating exosomes in primary biliary cirrhosis

“…[34][35][36][37] In autoimmunity, it has also been suggested that exosomes play a role in the chronic inflammatory response and that the cellular origin of exosomes will differentially influence the immune response in autoimmune disease. 6,38,39 Our data are important because they emphasize that co-stimulatory molecules play a pivotal role in APC-mediated immune responses, particularly T-cell activation and proliferation. [40][41][42][43][44][45] In the study herein, we demonstrate the ability of autologous exosomes to be taken up by peripheral monocytes and DCs.…”

“…For example, exosomes derived from salivary gland epithelial cells contain the autoantigenic ribonucleoproteins in Sjögren's syndrome. 6 We have previously demonstrated that apoptotic bodies from biliary epithelial cells contained the PBC-specific mitochondrial autoantigens. 26 Hence, within the liver, it is likely that biliary epithelial cells may produce exosomes that are critical for the homeostasis of biliary function 52,53 and we further hypothesize that exosomes released by damaged bile duct cells may augment this process.…”

“…47,48 Exosomes carry autoantigens as reflected in multiple autoimmune disease. 6,38 Once exosomes are internalized by DCs, autoantigens can be processed and further activated APCs via up-regulated co-stimulatory molecules. Indeed, we have found that exosomes harbor PDC-E2 (unpublished data), which is the major autoantigen in PBC.…”

“…However, the mechanism of how the exosomes participate in the induction and pathogenesis of autoimmune disease still remains unclear. [6][7][8] Primary biliary cirrhosis (PBC) is a progressive liver-specific autoimmune disease characterized by chronic non-suppurative destructive cholangitis. 9,10 The primary autoantigen of PBC has been identified as the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2).…”