Hyperresponsive cytosolic DNA-sensing pathway in monocytes from primary Sjögren's syndrome.

OBJECTIVES: Cytosolic DNA-sensing pathway stimulation prompts type I IFN (IFN-I) production, but its role in systemic IFN-I pathway activation in primary SS (pSS) is poorly studied. Here we investigate the responsiveness of pSS monocytes and plasmacytoid dendritic cells (pDCs) to stimulator of interferon genes (STING) activation in relation to systemic IFN-I pathway activation and compare this with SLE. METHODS: Expression of DNA-sensing receptors cGAS, IFI16, ZBP-1 and DDX41, signalling molecules STING, TBK1 and IRF3, positive and negative STING regulators, and IFN-I-stimulated genes MxA, IFI44, IFI44L, IFIT1 and IFIT3 was analysed in whole blood, CD14+ monocytes, pDCs, and salivary glands by RT-PCR, monocyte RNA sequencing data, flow cytometry and immunohistochemical staining. Peripheral blood mononuclear cells (PBMCs) from pSS, SLE and healthy controls (HCs) were stimulated with STING agonist 2'3'-cGAMP. STING phosphorylation (pSTING) and intracellular IFNα were evaluated using flow cytometry. RESULTS: STING activation induced a significantly higher proportion of IFNα-producing monocytes, but not pDCs, in both IFN-low and IFN-high pSS compared with HC PBMCs. Additionally, a trend towards more pSTING+ monocytes was observed in pSS and SLE, most pronounced in IFN-high patients. Positive STING regulators TRIM38, TRIM56, USP18 and SENP7 were significantly higher expression in pSS than HC monocytes, while the dual-function STING regulator RNF26 was downregulated in pSS monocytes. STING was expressed in mononuclear infiltrates and ductal epithelium in pSS salivary glands. STING stimulation induced pSTING and IFNα in pSS and SLE pDCs. CONCLUSION: pSS monocytes and pDCs are hyperresponsive to stimulation of the STING pathway, which was not restricted to patients with IFN-I pathway activation.

Innate immunity and interferons in the pathogenesis of Sjögren's syndrome.

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.

Hydroxychloroquine treatment downregulates systemic interferon activation in primary Sjögren's syndrome in the JOQUER randomized trial.

OBJECTIVE: HCQ 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. METHODS: Expression 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. RESULTS: HCQ 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. CONCLUSION: Treatment 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.

Associations of cigarette smoking with disease phenotype and type I interferon expression in primary Sjögren's syndrome.

Several studies have shown a negative association between smoking and primary Sjögren's syndrome (pSS), and smoking may interfere with the immune response. The purpose of this study was to investigate if smoking affects disease activity and disease phenotype in pSS. In this cross-sectional study, consecutive pSS patients filled out the EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI) form and a structured questionnaire regarding smoking habits. EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) scores were calculated and blood samples were analysed for type I interferon signature using RT-PCR. Of 90 patients (93% women, median age 66.5 years), 72% were type I IFN signature positive and 6, 42 and 53% were current, former and never smokers, respectively. No significant differences by smoking status were found regarding ESSDAI total score, activity in the ESSDAI domains or type I IFN signature. Patients with a higher cumulative cigarette consumption (≥ median) had higher scores in ESSPRI total [5.0 (3.0-6.3) vs 8.0 (6.0-8.3); p < 0.01] and ESSPRI sicca and pain domains. Comparing type I IFN signature negative and positive patients, the latter had significantly lower activity in ESSDAI articular domain (7/25 vs 3/64; p < 0.01) and lower scores in ESSPRI total [7.7 (5.2-8.2) vs 6.0 (4.0-7.7); p = 0.04]. Smoking was not associated with disease phenotype although patients with a higher cumulative cigarette consumption had worse symptoms in some disease domains. Current smokers were few making it difficult to draw any firm conclusions about associations to current smoking.

TBK1: A key regulator and potential treatment target for interferon positive Sjögren's syndrome, systemic lupus erythematosus and systemic sclerosis.

OBJECTIVE: Upregulation of type I interferons (IFN-I) is a hallmark of systemic autoimmune diseases like primary Sjögren's syndrome (pSS), systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). Expression of IFN-I is induced by three different receptor families: Toll-like receptors (TLRs), RIG-like receptors (RLRs) and DNA-sensing receptors (DSRs). TANK-binding kinase (TBK1) is an important signaling hub downstream of RLRs and DSRs. TBK1 activates IRF3 and IRF7, leading to IFN-I production and subsequent induction of interferon stimulated genes (ISGs). The objective of this study was to explore the potential of BX795, an inhibitor of TBK1, to downregulate IFN-I activation in pSS, SLE and SSc. METHODS: TBK1, IRF3, IRF7 and STAT1 were determined by RT-PCR in PAXgene samples and phosphorylated-TBK1 (pTBK1) was analyzed by flowcytometry in plasmacytoid dendritic cells (pDCs) from IFN-I positive (IFNpos) patients. Peripheral blood mononuclear cells (PBMCs) of pSS, SLE and SSc patients and TLR7 stimulated PBMCs of healthy controls (HCs) were cultured with the TBK1 inhibitor BX795, followed by analysis of ISGs. RESULTS: Increased gene expression of TBK1, IRF3, IRF7 and STAT1 in whole blood and pTBK1 in pDCs was observed in IFNpos pSS, SLE and SSc patients compared to HCs. Upon treatment with BX795, PBMCs from IFNpos pSS, SLE, SSc and TLR7-stimulated HCs downregulated the expression of the ISGs MxA, IFI44, IFI44L, IFIT1 and IFIT3. CONCLUSIONS: TBK1 inhibition reduced expression of ISGs in PBMCs from IFNpos patients with systemic autoimmune diseases indicating TBK1 as a potential treatment target.

Systemic interferon type I and type II signatures in primary Sjögren's syndrome reveal differences in biological disease activity.

Objective: To assess the relationships between systemic IFN type I (IFN-I) and II (IFN-II) activity and disease manifestations in primary SS (pSS). Methods: RT-PCR of multiple IFN-induced genes followed by principal component analysis of whole blood RNA of 50 pSS patients was used to identify indicator genes of systemic IFN-I and IFN-II activities. Systemic IFN activation levels were analysed in two independent European cohorts (n = 86 and 55, respectively) and their relationships with clinical features were analysed. Results: Three groups could be stratified according to systemic IFN activity: IFN inactive (19-47%), IFN-I (53-81%) and IFN-I + II (35-55%). No patient had isolated IFN-II activation. IgG levels were highest in patients with IFN-I + II, followed by IFN-I and IFN inactive patients. The prevalence of anti-SSA and anti-SSB was higher among those with IFN activation. There was no difference in total-EULAR SS Disease Activity Index (ESSDAI) or ClinESSDAI between the three subject groups. For individual ESSDAI domains, only the biological domain scores differed between the three groups (higher among the IFN active groups). For patient reported outcomes, there were no differences in EULAR Sjögren's syndrome patient reported index (ESSPRI), fatigue or dryness between groups, but pain scores were lower in the IFN active groups. Systemic IFN-I but not IFN-I + II activity appeared to be relatively stable over time. Conclusions: 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.

Genetic Variants of the BAFF Gene and Risk of Fatigue Among Patients With Primary Sjögren's Syndrome.

Background/Purpose: Primary Sjögren's Syndrome (SS) is characterized by B lymphocyte hyperactivity with B cell activating factor (BAFF) acting as an important regulator. Single Nucleotide Polymorphisms (SNPs) of the BAFF gene have been implicated in the pathogenesis of several autoimmune diseases characterized by heightened fatigue levels, including primary SS. We aimed to explore potential associations between BAFF SNPs and fatigue status of primary SS patients. Methods: Fatigue status was assessed in 199 consecutive primary SS patients (Greek cohort) using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) scale. Clinical, histological, laboratory, psychometric and personality data were also collected. DNA extracted from peripheral blood of all patients underwent evaluation for the presence of five BAFF SNPs (rs9514827, rs1041569, rs9514828, rs1224141, rs12583006) by PCR. To confirm our findings, an independent replicative cohort of 62 primary SS patients (Dutch cohort) was implemented. Finally, 52 multiple sclerosis (MS) patients were served as disease controls (MS cohort). Analysis of BAFF SNPs in association with fatigue levels was performed by the online platforms SNPStats and SHEsis and the SPSS 26 and Graph Pad Prism 8.00 software. Results: TT genotype of the rs9514828 BAFF polymorphism was significantly less frequent in the fatigued primary SS patients of the Greek cohort compared to the non-fatigued (14.1% vs 33.3%). The corresponding ORs [95%CI] in the dominant and overdominant models were 0.33 [0.15-0.72], p=0.003 and 0.42 [0.23-0.78], p=0.005 respectively. The association remained significant after adjustment for the variables contributing to fatigue in the univariate analysis (OR [95% CI]: 0.3 [0.1-0.9], p=0.026). Accordingly, in the Dutch cohort, there was a trend of lower mental fatigue among patients carrying the TT rs9514828 BAFF genotype compared to their CC counterparts (4.1 ± 2.4 vs 6.0 ± 2.2 respectively, p=0.06). The rs9514828 BAFF SNP was not significantly associated with fatigue in the MS cohort. Conclusions: We report a novel association between genetic makeup and primary SS-associated fatigue with the rs9514828 TT genotype decreasing the likelihood of fatigue development among these patients. These findings need validation in multi-center studies.

Fatigue in Sjögren's Syndrome: A Search for Biomarkers and Treatment Targets.

Background: Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease, where patients often suffer from fatigue. Biological pathways underlying fatigue are unknown. In this study aptamer-based SOMAscan technology is used to identify potential biomarkers and treatment targets for fatigue in pSS. Methods: SOMAscan® Assay 1.3k was performed on serum samples of healthy controls (HCs) and pSS patients characterized for interferon upregulation and fatigue. Differentially expressed proteins (DEPs) between pSS patients and HC or fatigued and non-fatigued pSS patients were validated and discriminatory capacity of markers was tested using independent technology. Results: Serum concentrations of over 1,300 proteins were compared between 63 pSS patients and 20 HCs resulting in 58 upregulated and 46 downregulated proteins. Additionally, serum concentrations of 30 interferon positive (IFNpos) and 30 interferon negative (IFNneg) pSS patients were compared resulting in 25 upregulated and 13 downregulated proteins. ELISAs were performed for several DEPs between pSS patients and HCs or IFNpos and IFNneg all showing a good correlation between protein levels measured by ELISA and relative fluorescence units (RFU) measured by the SOMAscan. Comparing 22 fatigued and 23 non-fatigued pSS patients, 16 serum proteins were differentially expressed, of which 14 were upregulated and 2 were downregulated. Top upregulated DEPs included neuroactive synaptosomal-associated protein 25 (SNAP-25), alpha-enolase (ENO1) and ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1). Furthermore, the proinflammatory mediator IL36a and several complement factors were upregulated in fatigued compared to non-fatigued pSS patients. ROC analysis indicated that DEPs showed good capacity to discriminate fatigued and non-fatigued pSS patients. Conclusion: In this study we validated the use of aptamer-based proteomics and identified a novel set of proteins which were able to distinguish fatigued from non-fatigued pSS patients and identified a so-called "fatigue signature."

Interferon activation in primary Sjögren's syndrome: recent insights and future perspective as novel treatment target.

INTRODUCTION: Primary Sjögren's syndrome (pSS) is one of the most common systemic autoimmune diseases. At the moment, there is no cure for this disease and its etiopathology is complex. Interferons (IFNs) play an important role in the pathogenesis of this disease and are a potential treatment target. Areas covered: Here we discuss the role of IFNs in pSS pathogenesis, complications encountered upon studying IFN-induced gene expression, and comment on the current knowledge on easy clinical applicable 'IFN signatures'. The current treatment options targeting IFNs in pSS are summarized and the perspective of potential new strategies discussed. Expert commentary: The authors provide their perspective on the role of IFNs in pSS and how this knowledge could be used to improve pSS diagnosis, provide new treatment targets, to monitor clinical trials and to stratify pSS patients in order to move toward precision medicine.

Type I IFN signature in childhood-onset systemic lupus erythematosus: a conspiracy of DNA- and RNA-sensing receptors?

BACKGROUND: Childhood-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. METHODS: The 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. RESULTS: The 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. CONCLUSIONS: IFN-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.