Systemic IFN activation is associated with higher activity only in the ESSDAI biological domain but not in other domains or the total score. Our data raise the possibility that the ESSDAI biological domain score may be a more sensitive endpoint for trials targeting either IFN pathway.

Primary SS (pSS) is a rheumatic disease characterized by an immune-mediated exocrinopathy, resulting in severe dryness of eyes and mouth. Systemic symptoms include fatigue and joint pain and a subset of patients develop more severe disease with multi-organ involvement. Accumulating evidence points to involvement of innate immunity and aberrant activity of the type I IFN system in both the initiation and propagation of this disease. Analysis of the activity of IFN-inducible genes has evidenced that more than half of pSS patients present with a so-called ‘type I IFN signature’. In this review, we examine activation of the IFN system in pSS patients and how this may drive autoimmunity through various immune cells. We further discuss the clinical value of assessing IFN activity as a biomarker in pSS patients and review novel therapies targeting IFN signalling and their potential use in pSS.

ObjectiveHCQ is frequently used to treat primary SS (pSS), but evidence for its efficacy is limited. HCQ blocks IFN activation, which is present in half of the pSS patients. The effect of HCQ treatment on the expression of IFN-stimulated genes (ISGs) was studied in pSS. Furthermore, HCQ-treated patients were stratified based on IFN activation and differences in disease activity and clinical parameters were studied.MethodsExpression of ISGs and IFN scores was determined in 77 patients, who were previously enrolled in the placebo-controlled JOQUER trial. Patients were treated for 24 weeks with 400 mg/d HCQ or placebo.ResultsHCQ treatment reduced IFN scores and expression of ISGs compared with the placebo-treated group. HCQ reduced ESR, IgG and IgM levels independently of the patients' IFN activation status. No differences in EULAR SS disease activity index or EULAR SS patient reported index scores were observed after HCQ treatment, even after IFN stratification.ConclusionTreatment for 24 weeks with HCQ significantly reduced type I IFN scores and ISG-expression compared with the placebo-treated group. HCQ reduced several laboratory parameters, but failed to improve clinical response. This suggests that in pSS, type I IFN is associated to some laboratory parameters abnormalities, but not related to the clinical response.

BackgroundChildhood-onset systemic lupus erythematosus (cSLE) is an incurable multi-systemic autoimmune disease. Interferon type I (IFN-I) plays a pivotal role in the pathogenesis of SLE. The objective of this study was to assess the prevalence of the IFN-I signature and the contribution of cytosolic nucleic acid receptors to IFN-I activation in a cohort of primarily white cSLE patients.MethodsThe IFN-I score (positive or negative), as a measure of IFN-I activation, was assessed using real-time quantitative PCR (RT-PCR) expression values of IFN-I signature genes (IFI44, IFI44L, IFIT1, Ly6e, MxA, IFITM1) in CD14+ monocytes of cSLE patients and healthy controls (HCs). Innate immune receptor expression was determined by RT-PCR and flow cytometry. To clarify the contribution of RNA-binding RIG-like receptors (RLRs) and DNA-binding receptors (DBRs) to IFN-I activation, peripheral blood mononuclear cells (PBMCs) from patients were treated with BX795, a TANK-binding kinase 1 (TBK1) inhibitor blocking RLR and DBR pathways.ResultsThe IFN-I signature was positive in 57% of cSLE patients and 15% of the HCs. Upregulated gene expression of TLR7, RLRs (IFIH1, DDX58, DDX60, DHX58) and DBRs (ZBP-1, IFI16) was observed in CD14+ monocytes of the IFN-I-positive cSLE patients. Additionally, RIG-I and ZBP-1 protein expression was upregulated in these cells. Spontaneous IFN-I stimulated gene (ISG) expression in PBMCs from cSLE patients was inhibited by a TBK1-blocker.ConclusionsIFN-I activation, assessed as ISG expression, in cSLE is associated with increased expression of TLR7, and RNA and DNA binding receptors, and these receptors contribute to IFN-I activation via TBK1 signaling. TBK1-blockers may therefore be a promising treatment target for SLE.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-017-1501-z) contains supplementary material, which is available to authorized users.