Nucleic acid-sensing toll-like receptors: Important players in Sjögren’s syndrome

A comprehensive review of Sjögren's syndrome: Classification criteria, risk factors, and signaling pathways

Sjögren's syndrome (SS) is a chronic autoimmune disease that affects the exocrine glands and may lead to a range of systemic symptoms that impact various organs. Both innate and adaptive immune pathways might trigger the disease. Studying the signaling pathways underlying SS is crucial for enhancing diagnostic and therapeutic effectiveness. SS poses an ongoing challenge for medical professionals owing to the limited therapeutic options available. This review offers a comprehensive understanding of the intricate nature of SS, encompassing disease classification criteria, risk factors, and signaling pathways in immunity and inflammation. The advancements summarized herein have the potential to spark new avenues of research into SS.

Elevated expression of Toll-like receptor 7 and its correlation with clinical features in patients with primary Sjögren's syndrome

BACKGROUND

The labial salivary glands (LSGs) are important for the diagnosis, evaluation of therapeutic efficacy, and genetic analyses of primary Sjögren's syndrome (pSS). In autoimmune diseases, the recognition of self nucleic acids and viral RNA and DNA through endogenous Toll-like receptor(TLR) triggers the production of type I IFN and pro-inflammatory cytokines, leading to the occurrence and progression of the disease. Here, we detected the expression of TLR7 in LSGs and analyse its correlation with clinical features and serum cytokines in pSS patients.

METHODS

LSGs and serum samples were obtained from 56 pSS patients and 19 non-SS patients (non-pSS patients). The expression of TLR7 in the LSGs was evaluated with immunohistochemistry. The serum levels of interferon-α (IFN-α) and interleukin-6 (IL-6) were quantified by ELISA. Laboratory parameters were measured by clinical standard laboratory techniques.

RESULTS

TLR7-positive cells in pSS were localized in the ductal epithelial cells and lymphocytes of LSGs. The expression of TLR7 was upregulated in pSS patients compared with controls. Patients with anti-Ro52 antibody positivity showed higher TLR7 levels than those who were negative but not those with anti-Ro60 and anti-SSB. TLR7 levels were positively associated with the levels of IgG, IgA, ANA, IL-6, IFN-α and serum globulin but were not associated with IgM, C3, C4, or rheumatoid factor (RF) in serum.

CONCLUSION

TLR7 may be involved in the inflammatory response and the production of antibodies in pSS and plays an important role in local and systemic pSS manifestations. This research showed that TLR7 is involved in pSS pathogenesis.

The Role of Regulatory T Cells in the Onset and Progression of Primary Sjögren's Syndrome

Regulatory T cells (Tregs) play a key role in maintaining immune balance and regulating the loss of self-tolerance mechanisms in various autoimmune diseases, including primary Sjögren's syndrome (pSS). With the development of pSS primarily in the exocrine glands, lymphocytic infiltration occurs in the early stages, mainly due to activated CD4⁺ T cells. Subsequently, in the absence of rational therapy, patients develop ectopic lymphoid structures and lymphomas. While the suppression of autoactivated CD4⁺ T cells is involved in the pathological process, the main role belongs to Tregs, making them a target for research and possible regenerative therapy. However, the available information about their role in the onset and progression of this disease seems unsystematized and, in certain aspects, controversial. In our review, we aimed to organize the data on the role of Tregs in the pathogenesis of pSS, as well as to discuss possible strategies of cell therapy for this disease. This review provides information on the differentiation, activation, and suppressive functions of Tregs and the role of the FoxP3 protein in these processes. It also highlights data on various subpopulations of Tregs in pSS, their proportion in the peripheral blood and minor salivary glands of patients as well as their role in the development of ectopic lymphoid structures. Our data emphasize the need for further research on Tregs and highlight their potential use as a cell-based therapy.

Recent Advances on Small-Molecule Antagonists Targeting TLR7

Toll-like receptor 7 (TLR7) is a class of pattern recognition receptors (PRRs) recognizing the pathogen-associated elements and damage and as such is a major player in the innate immune system. TLR7 triggers the release of pro-inflammatory cytokines or type-I interferons (IFN), which is essential for immunoregulation. Increasing reports also highlight that the abnormal activation of endosomal TLR7 is implicated in various immune-related diseases, carcinogenesis as well as the proliferation of human immunodeficiency virus (HIV). Hence, the design and development of potent and selective TLR7 antagonists based on small molecules or oligonucleotides may offer new tools for the prevention and management of such diseases. In this review, we offer an updated overview of the main structural features and therapeutic potential of small-molecule antagonists of TLR7. Various heterocyclic scaffolds targeting TLR7 binding sites are presented: pyrazoloquinoxaline, quinazoline, purine, imidazopyridine, pyridone, benzanilide, pyrazolopyrimidine/pyridine, benzoxazole, indazole, indole, and quinoline. Additionally, their structure-activity relationships (SAR) studies associated with biological activities and protein binding modes are introduced.