Molecular subsetting of interferon pathways in Sjögren's syndrome

Objective Sjögren's syndrome (SS) is an autoimmune disease that targets the salivary and lacrimal glands. While all patients demonstrate inflammatory infiltration and abnormal secretory function in the target tissues, the disease features, pathology, and clinical course can vary. Activation of distinct inflammatory pathways may drive disease heterogeneity. The purpose of this study was to investigate whether activation of the interferon (IFN) pathway correlates with key phenotypic features. Methods Clinical data and 1 labial salivary gland (stored frozen) were obtained from each of 82 participants (53 patients with primary SS and 29 control subjects) in the Sjögren's International Collaborative Clinical Alliance (SICCA) registry. Salivary gland lysates were immunoblotted with markers of type I or type II IFN, and patterns of IFN activity were determined by hierarchical clustering. Correlations between SS phenotypic features and IFN activity in the salivary gland were performed. Results A total of 58% of the SS participants had high IFN activity and differed significantly from those with low IFN activity (higher prevalence of abnormal findings on sialometry, leukopenia, hyperglobulinemia, high-titer antinuclear antibody, anti-SSA, and high focus score on labial salivary gland [LSG] biopsy). Three distinct patterns of IFN were evident: type I-predominant, type II-predominant, and type I/II mixed IFN. These groups were clinically indistinguishable except for the LSG focus score, which was highest in those with type II-predominant IFN. Conclusion The SS phenotype includes distinct molecular subtypes, which are segregated by the magnitude and pattern of IFN responses. Associations between IFN pathways and disease activity suggest that IFNs are relevant therapeutic targets in SS. Patients with distinct patterns of high IFN activity are clinically similar, demonstrating that IFN-targeting therapies must be selected according to the specific pathway(s) that is active in vivo in the individual patient.