Abstract
Sjögren’s syndrome (SS) is a systemic autoimmune disease characterized by chronic inflammation of the salivary and lacrimal glands and extra-glandular lesions. Adaptive immune response including T- and B-cell activation contributes to the development of SS. However, its pathogenesis has not yet been elucidated. In addition, several patients with SS present with the type I interferon (IFN) signature, which is the upregulation of the IFN-stimulated genes induced by type I IFN. Thus, innate immune responses including type I IFN activity are associated with SS pathogenesis. Recent studies have revealed the presence of activation pattern recognition receptors (PRRs) including Toll-like receptors, RNA sensor retinoic acid-inducible gene I and melanoma differentiation-associated gene 5, and inflammasomes in infiltrating and epithelial cells of the salivary glands among patients with SS. In addition, the activation of PRRs via the downstream pathway such as the type I IFN signature and nuclear factor kappa B can directly cause organ inflammation, and it is correlated with the activation of adaptive immune responses. Therefore, this study assessed the role of the innate immune signal pathway in the development of inflammation and immune abnormalities in SS.
Highlights
Sjögren’s syndrome (SS) is an autoimmune disease that mainly causes chronic inflammation of the exocrine glands, resulting in formation of glandular lesions along with ocular and oral dryness and extra-glandular lesions that spread to systemic organs [1]
A higher level of IL-17 and activation of Th17 cells that produce IL-17 were observed in the salivary glands and peripheral blood, indicating that TLR2 signaling promotes the differentiation of T cells into Th17 cells and enhances IL-17 production in patients with SS [45]
TLR4 was expressed by infiltrating mononuclear cells and acinar and ductal epithelial cells in the salivary glands in patients with SS, and this phenomenon was correlated with salivary gland inflammation [45,46]
Summary
Sjögren’s syndrome (SS) is an autoimmune disease that mainly causes chronic inflammation of the exocrine glands, resulting in formation of glandular lesions along with ocular and oral dryness and extra-glandular lesions that spread to systemic organs [1]. Activated T cells produce cytokines such as interleukin (IL)-2, and further proliferation of T cells promotes the production of inflammatory cytokines such as interferon gamma (IFN-γ), IL-17, and tumor necrosis factor-α These cytokines act on acinar and ductal epithelial cells and enhance the expression of costimulatory and adhesion molecules such as CD40, CD80, CD86, and ICAM-1 on the cell surface, thereby enhancing inflammatory response. Adaptive immune abnormalities, which are caused by activated T and B cells, play an essential role in tissue disorders and chronic inflammation in SS. The innate immune response, which is a reaction to tissue destruction triggered by microbes, is activated by multiple signaling cascades, which do present antigens and cause direct inflammation and tissue damage. This review article evaluated the role of innate immune signaling in SS pathogenesis
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