Sjögren's Syndrome: Concerted Triggering of Sicca Conditions

Making Sense of Intracellular Nucleic Acid Sensing in Type I Interferon Activation in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a systemic autoimmune rheumatic disease characterized by dryness of the eyes and mucous membranes, which can be accompanied by various extraglandular autoimmune manifestations. The majority of patients exhibit persistent systemic activation of the type I interferon (IFN) system, a feature that is shared with other systemic autoimmune diseases. Type I IFNs are integral to anti-viral immunity and are produced in response to stimulation of pattern recognition receptors, among which nucleic acid (NA) receptors. Dysregulated detection of endogenous NAs has been widely implicated in the pathogenesis of systemic autoimmune diseases. Stimulation of endosomal Toll-like receptors by NA-containing immune complexes are considered to contribute to the systemic type I IFN activation. Accumulating evidence suggest additional roles for cytosolic NA-sensing pathways in the pathogenesis of systemic autoimmune rheumatic diseases. In this review, we will provide an overview of the functions and signaling of intracellular RNA- and DNA-sensing receptors and summarize the evidence for a potential role of these receptors in the pathogenesis of pSS and the sustained systemic type I IFN activation.

The dark side of Sjögren's syndrome: the possible pathogenic role of infections

PURPOSE OF REVIEW

To highlight recent findings on pathogenic mechanisms and clinical associations which characterize the role of infectious agents as triggers for Sjögren's syndrome development.

RECENT FINDINGS

Several candidate infectious agents have been identified to induce the autoimmune and inflammatory pathways leading to Sjögren's syndrome clinical appearance in the setting of a genetic background. This is reinforced by the demonstration that Sjögren's syndrome patients are characterized by higher prevalence of seropositivity to virus and bacterial agents in comparison with general population. Moreover, these agents may infect salivary gland epithelial cells. Stronger evidence confirmed the role of some viruses, like Epstein-Barr, as triggers of the disease and different mechanisms have been demonstrated to interplay. Recent experimental and clinical studies supported the adjunctive role of an altered buccal and intestinal microbial composition and chronic inflammatory response to Helicobacter pylori in disease induction. Finally, latent viral infections and immune system chronic stimulation induced by persistent infections may participate in disease lymphoproliferative evolution.

SUMMARY

Different viral and bacterial agents have been identified as triggers in Sjögren's syndrome induction and contributors to the chronic immune system stimulation underlying lymphoproliferative complication. Deeper knowledge of involved microbial agents and pathogenic mechanisms linking Sjögren's syndrome and infections may help the identification of preventive therapeutic strategy.