Experimental autoallergic sialadenitis in mice. Histopathological and ultrastructural studies

Recent Advances in Mouse Models of Sjögren's Syndrome

Sjögren's syndrome (SS) is a complex rheumatoid disease that mainly affects exocrine glands, resulting in xerostomia (dry mouth) and xerophthalmia (dry eye). SS is characterized by autoantibodies, infiltration into exocrine glands, and ectopic expression of MHC II molecules on glandular epithelial cells. In contrast to the well-characterized clinical and immunological features, the etiology and pathogenesis of SS remain largely unknown. Animal models are powerful research tools for elucidating the pathogenesis of human diseases. To date, many mouse models of SS, including induced models, in which disease is induced in mice, and genetic models, in which mice spontaneously develop SS-like disease, have been established. These mouse models have provided new insight into the pathogenesis of SS. In this review, we aim to provide a comprehensive overview of recent advances in the field of experimental SS.

Usefulness of mouse models to study the pathogenesis of Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disorder characterized by ocular and oral dryness as well as systemic manifestations. The immunopathogenesis of SS is complex with different intricate factors. Because of the delay in the appearance of symptoms and due to ethical issues it is very difficult to study the wide array of factors intervening in the pathogenesis of SS in human patients. To circumvent this problem, different animal models have been elaborated for studying the different subsets of the aspects of the physiopathology of this disease. In this review, we focus on the mouse models that have been established to deepen our insight into the immunopathogenesis of SS.

Presence of B7-2+ dendritic cells and expression of Th1 cytokines in the early development of sialodacryoadenitis in the IqI/Jic mouse model of primary Sjörgren's syndrome

Subpopulations of infiltrating lymphocytes, professional antigen-presenting cells (APCs), and Th1/Th2 cytokines that could initiate an autoimmune sialodacryoadenitis were studied in the IQI/Jic mouse model of primary Sjögren's syndrome. Although lymphocytic infiltrations were first seen in submandibular glands (SMGs) of females and in lacrimal glands (LGs) of males at 8 weeks of age, clusters of MHC class II+, CD11c+, B7-2+ dendritic cells (DCs) were already localized in these tissues at 4 weeks. At 8 weeks, the infiltrating lymphocytes consisted of almost equal numbers of B cells and CD4+ T cells. In the inflammatory foci, MHC class II+, CD11c+, B7-2+ DCs formed network-like structures. Duct cells in the lesions showed immunoreactivities for MHC class II and ALCAM (a costimulatory adhesion molecule). IL-12 and IFN-gamma transcripts were detected by RT-PCR in SMGs of females and in LGs of males at 8-12 weeks. These results suggest that the clustered DCs might play an important role in the initiation of the adenitis, and further suggest that the DCs and epithelial cells may participate in the activation of CD4+ T cells. It is also likely that Th1 cytokines mediate the functional interactions between the APCs and CD4+ T cells in the early lesions.

Production of experimental autoimmune sialadenitis in mice immunized with homologous salivary gland extract and Klebsiella O3 lipopolysaccharide

An experimental murine model for autoimmune sialadenitis was produced by repeated immunization of homologous salivary gland extract together with Klebsiella O3 lipopolysaccharides as an immunological adjuvant. The cell infiltration was observed in the salivary glands of mice immunized more than twice. Inflammatory cells consisting mainly of CD4+ T cells and CD8+ T cells accumulated at the perivascular regions. There was hyperplasia and enlargement of ductal epithelial cells in the secretory acinar units in salivary glands of repeatedly immunized mice. The repeated immunization developed delayed-type hypersensitivity and autoantibody production to the homologous salivary gland extract. The immunohistochemical analysis showed positive staining on the cuboidal cells in the intercalated ducts, and the columnar pseudostratified cells in the striated ducts. Organ-specific antigens with molecular weights ranging from 20 to 90 kDa were recognized by the sera from immunized mice. Therefore, it was suggested that the sialadenitis was produced by the autoimmune mechanism and might be a new experimental model for characterization of the pathogenesis of autoimmune sialadenitis.

Salivary gland cytokine expression in NOD and normal BALB/c mice

The autoimmune diabetes-prone nonobese diabetic (NOD) mouse develops a chronic lymphocytic infiltration of endocrine and exocrine glands. The objectives of this study were to characterize the salivary immune infiltration and cytokine expression of NOD mice and compare these findings to those of normal BALB/c mice. A decline in salivary flow rates in NOD mice began between 8 and 12 weeks of age. At this same time lymphocytic foci are detectable in the salivary glands. Lymphocytic infiltration in the salivary glands of NOD mice increased with age and simultaneously salivary function declined. No lymphocytic infiltration was seen in BALB/c salivary tissues. Messenger RNA expression of several inflammatory cytokines, including interleukin-1beta (IL-1beta), IL-2, IL-10, interferon-gamma, and tumor necrosis factor-alpha was detected in the submandibular glands of both NOD and BALB/c mice by the reverse transcription polymerase chain reaction. IL-4 synthesis was also present in some tissues. Immunohistochemical analysis demonstrated the intense expression of inflammatory cytokines within lymphocytic infiltrates and epithelial cells of all NOD mice. Minimal expression of the same cytokines was detected only occasionally in BALB/c tissues stained in parallel. These results demonstrate cytokine expression in the salivary glands of normal mice and suggest that the overexpression of these inflammatory cytokines is likely involved in the development and progression of the organ-localized autoimmunity in the salivary glands of NOD mice.

Nodular hyperplasia of oncocytes in mouse submandibular glands

Multinodular hyperplastic foci of oncocytes found in mouse submandibular glands were examined ultrastructurally, and their morphogenesis discussed. The oncocytic foci showed lobular architecture surrounded by myoepithelial cells, and tubular formations were frequently present. The cytoplasm of the oncocytes was distended by tightly-packed and non-oriented mitochondria which varied in size and shape. Furthermore, varying numbers of electron-dense fine granules, which were remnants of secretory granules of granular duct cells, were scattered in the cytoplasm. Within the salivary gland parenchyma neighboring the hyperplastic foci of oncocytes, intermediate-type cells between oncocytes and normal salivary gland epithelia were found. The result of the present study shows that the oncocytic change has a tendency to be more frequent in the granular ducts and less in the striated ducts, and that some oncocyte-transformed cells proliferate to form nodular hyperplastic foci.