Molecular Subsetting of Interferon Pathways in Sjögren's Syndrome.

Primary Sjogren’s Syndrome (SS) is a chronic, autoimmune inflammatory disease which is characterized by lymphocytic infiltration of the salivary and lacrimal glands, resulting in abnormal tear and saliva secretion (1–3). Although all SS patients have abnormal secretory function and inflammatory infiltration of their salivary glands, there is significant heterogeneity in disease features, pathology and clinical course (4, 5). This heterogeneity is a feature of all rheumatic autoimmune diseases and likely reflects distinct patient subsets within a primary disease phenotype, driven by unique pathophysiologic mechanisms. While substantial evidence indicates that interferons (IFNs) play significant roles in the pathogenesis of rheumatic diseases including SS (6–13), there is striking heterogeneity in IFN activity amongst different individuals and diseases. Indeed, it still remains to be determined whether type I or type II IFNs are the primary drivers of the IFN signature seen in patients with SS and other rheumatic diseases (14) and whether IFN expression in target tissue is associated with disease activity. In recent studies (12), we defined and validated specific markers of type I and II IFN activity, and used these probes in a small study to investigate the distinct IFN pathways active in patient tissues. We examined relevant target tissues in patients with SS and dermatomyositis and determined that different patterns of IFN activity were apparent between rheumatic diseases and the magnitude of the IFN effects varied significantly amongst patients. While heterogeneity in the IFN signatures exists in SS, the frequency and clinical associations of the different patterns are unclear. To better understand this, we investigated the IFN expression patterns in labial salivary glands (LSG) from a large cohort of well-characterized SS participants and controls. All subjects were enrolled in the Sjogren’s International Collaborative Clinical Alliance (SICCA) registry, which systematically collected extensive phenotypic data and biospecimens across 9 sites internationally between 2003 and 2013 (15). Based on our recent findings (12), we selected to use interferon-induced protein with tetratricopeptide repeats (IFIT3) to readout type I IFN, and interferon inducible guanylate binding proteins 1 and 2 (GBP1 and GBP2), as markers of type II IFN activity (for immunoblotting and immunohistochemistry, respectively) in the current study. We show that high levels of IFN activity are associated with a more severe disease phenotype, and that distinct IFN patterns are apparent in the group with high IFN activity. Although SS participants in this group are clinically indistinguishable, those with type II IFN activity have higher LSG focus scores, and the presence of inflammatory infiltrates correlates well with type II IFN activity, but not with type I IFN. As therapies targeting immune effector pathways become increasingly available, it will be helpful to develop approaches which quantitatively define inflammatory pathway activity in patient tissues to assess their activity prior to initiating treatment. These studies demonstrate that analysis of patient-derived target tissues can identify distinct molecular subgroups. These analyses provide opportunities to identify optimal candidates for participation in clinical trials, monitor therapeutic responses, and to determine the efficacy of novel agents in SS and possibly other autoimmune rheumatic diseases.