An immunohistochemical study of immunological phenomena in minor salivary glands in patients with Sjögren's syndrome

Immunobiology of T Cells in Sjögren's Syndrome

Sjögren's syndrome (SjS) is a systemic autoimmune disease marked by xerostomia (dry mouth), keratoconjunctivitis sicca (eye dryness), and other systematic disorders. Its pathogenesis involves an inflammatory process that is characterized by lymphocytic infiltration into exocrine glands and other tissues. Although the development of ectopic lymphoid tissue and overproduction of autoantibodies by hyperactive B cells suggest that they may promote SjS development, treatment directed towards them fails to induce significant laboratory or clinical improvement. T cells are overwhelming infiltrators in most phases of the disease, and the involvement of multiple T cell subsets of suggests the extraordinary complexity of SjS pathogenesis. The factors, including various cellular subtypes and molecules, regulate the activation and suppression of T cells. T cell activation induces inflammatory cell infiltration, B cell activation, tissue damage, and metabolic changes in SjS. Knowledge of the pathways that link these T cell subtypes and regulation of their activities are not completely understood. This review comprehensively summarizes the research progress and our understanding of T cells in SjS, including CD4⁺ T cells, CD8⁺ T_RM cells, and innate T cells, to provide insights into for clinical treatment.

Salivary dysbiosis in Sjögren's syndrome and a commensal-mediated immunomodulatory effect of salivary gland epithelial cells

Salivary gland epithelial cells (SGECs) have been implicated in the pathogenesis of Sjögren's syndrome due to aberrant antigen-presentation function. This study examined the hypothesis that oral dysbiosis modulates the antigen-presentation function of SGECs, which regulates CD4 T cell proliferation in primary Sjögren's syndrome (pSS). Saliva samples from 8 pSS patients and 16 healthy subjects were analyzed for bacterial 16S ribosomal DNA. As a result, 39 differentially abundant taxa were identified. Among them, the phylum Proteobacteria comprised 21 taxa, and this phylum was mostly enriched in the healthy controls. The proteobacterium Haemophilus parainfluenzae was enriched in the healthy controls, with the greatest effect size at the species level. Treatment of A253 cells in vitro with H. parainfluenzae upregulated PD-L1 expression, and H. parainfluenzae-pretreated A253 cells suppressed CD4 T cell proliferation. The suppression was partially reversed by PD-L1 blockade. Among low-grade xerostomia patients, salivary abundance of H. parainfluenzae decreased in pSS patients compared to that in non-pSS sicca patients. Our findings suggest that H. parainfluenzae may be an immunomodulatory commensal bacterium in pSS.

Activation of epithelial and myoepithelial cells in the salivary glands of patients with Sjögren's syndrome: high expression of intercellular adhesion molecule-1 (ICAM.1) in biopsy specimens and cultured cells

ICAM.1 (CD54) is a surface protein expressed on epithelial and other nonhematopoietic cells upon activation and is known to play an important role in the stimulation of T cells by the provision of cellular adhesion and costimulatory support. Sjogren's syndrome (SS) is an autoimmune exocrinopathy, which is characterized by chronic lymphocytic infiltration of exocrine glands and aberrant activation of epithelial tissues. To address the contribution of ICAM.1 in the pathogenesis of SS, the expression of this protein was studied by immunohistochemistry and flow cytometry in minor salivary gland (SG) biopsies as well as in cultured SG epithelial cell (SGEC) lines obtained from 18 SS patients and 16 controls. In biopsies from SS patients (but not controls), strong ICAM.1 was expressed by infiltrating mononuclear cells (52%) and by a significant proportion of periacinar myoepithelial cells (18%). In addition, a patchy pattern of moderate ICAM.1 expression was detected in 31% of ductal epithelia of SS patients. These ICAM.1-expressing epithelial and myoepithelial cells were observed throughout glandular tissues and were not confined in areas proximal to lymphoid infiltrates. In support to an intrinsic activation profile of SGEC in SS, long-term cultured non-neoplastic SGEC lines derived from SS patients displayed significantly upregulated spontaneous expression of ICAM.1, compared to controls (P < 0.05). The high expression of ICAM.1 protein by the salivary epithelium of SS patients is likely suggestive of its important role in the pathogenesis of the disorder. Further, our results support a model of intrinsic activation of salivary epithelial and myoepithelial cells in SS, whereby these cells actively participate in the induction and maintenance of lymphocytic infiltrates of patients.