Activation of the type I interferon pathway in primary Sjögren's syndrome: an update

Single-cell transcriptomic analysis uncovers heterogeneity in the labial gland microenvironment of primary Sjögren's syndrome

Objective

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disorder with an unclear pathogenetic mechanism in the labial gland. This study aims to investigate the cellular and molecular mechanisms contributing to the development of this disease.

Methods

Single-cell RNA sequencing (scRNA-seq) was performed on 32,337 cells of labial glands from three pSS patients and three healthy individuals. We analyzed all cell subsets implicated in pSS pathogenesis.

Results

Our research revealed diminished differentiation among epithelial cells, concomitant with an enhancement of interferons (IFNs)-mediated signaling pathways. This indicates a cellular functional shift in reaction to inflammatory triggers. Moreover, we observed an augmentation in the population of myofibroblasts and endothelial cells, likely due to the intensified IFNs signaling, suggesting a possible reconfiguration of tissue structure and vascular networks in the impacted regions. Within the immune landscape, there was an apparent increase in immunosuppressive macrophages and dendritic cells (DCs), pointing to an adaptive immune mechanism aimed at modulating inflammation and averting excessive tissue harm. Elevated activation levels of CD4+T cells, along with a rise in regulatory T (Treg) cells, were noted, indicating a nuanced immune interplay designed to manage the inflammatory response. In the CD8+T cell subsests, we detected a notable increase in cells expressing granzyme K (GZMK), signaling an intensified cytotoxic activity. Additionally, the escalated presence of T cells with high levels of heat shock proteins (HSPs) suggests a cellular stress condition, possibly associated with persistent low-grade inflammation, mirroring the chronic aspect of the condition.

Conclusions

Our research identified distinct stromal and immune cell populations linked to pSS, revealing new potential targets for its management. The activation of myeloid, B, and T cells could contribute to pSS pathogenesis, providing important guidance for therapeutic approaches.

Oral Administration of Vitamin D3 Prevents Corneal Damage in a Knock-Out Mouse Model of Sjögren's Syndrome

BACKGROUND

Vitamin D deficiency has been associated with dry eye development during Sjögren's syndrome (SS). Here, we investigated whether repeated oral vitamin D3 supplementation could prevent the corneal epithelium damage in an SS mouse model.

METHODS

30 female mouse knock-out for the thrombospondin 1 gene were randomized (six per group) in untreated mice euthanized at 6 weeks as negative control (C-) or at 12 weeks as the positive control for dry eye (C+). Other mice were sacrificed after 6 weeks of oral vitamin D3 supplementation in the drinking water (1000, 8000, and 20,000 IU/kg/week, respectively).

RESULTS

The C+ mice showed alterations in their corneal epithelial morphologies and thicknesses (p < 0.01 vs. C-), while the mice receiving 8000 (M) and 20,000 (H) IU/kg/week of vitamin D3 showed preservation of the corneal epithelium morphology and thickness (p < 0.01 vs. C+). Moreover, while the C+ mice exhibited high levels and activity of corneal tumor necrosis factor alpha converting enzyme (TACE), neovascularization and fibrosis markers; these were all reduced in the M and H mice.

CONCLUSIONS

Oral vitamin D3 supplementation appeared to counteract the negative effect of TACE on corneal epithelium in a mouse model of SS-associated dry eye.

Targeting type I interferons in systemic lupus erythematous

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with systemic clinical manifestations including, but not limited to, rash, inflammatory arthritis, serositis, glomerulonephritis, and cerebritis. Treatment options for SLE are expanding and the increase in our understanding of the immune pathogenesis is leading to the development of new therapeutics. Autoantibody formation and immune complex formation are important mediators in lupus pathogenesis, but an important role of the type I interferon (IFN) pathway has been identified in SLE patients and mouse models of lupus. These studies have led to the development of therapeutics targeting type I IFN and related pathways for the treatment of certain manifestations of SLE. In the current narrative review, we will discuss the role of type I IFN in SLE pathogenesis and the potential translation of these data into strategies using type I IFN as a biomarker and therapeutic target for patients with SLE.

Identification of key interferon-stimulated genes for indicating the condition of patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with highly heterogeneous clinical symptoms and severity. There is complex pathogenesis of SLE, one of which is IFNs overproduction and downstream IFN-stimulated genes (ISGs) upregulation. Identifying the key ISGs differentially expressed in peripheral blood mononuclear cells (PBMCs) of patients with SLE and healthy people could help to further understand the role of the IFN pathway in SLE and discover potential diagnostic biomarkers.

The differentially expressed ISGs (DEISG) in PBMCs of SLE patients and healthy persons were screened from two datasets of the Gene Expression Omnibus (GEO) database. A total of 67 DEISGs, including 6 long noncoding RNAs (lncRNAs) and 61 messenger RNAs (mRNAs) were identified by the “DESeq2” R package. According to Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, those DEISGs were mainly concentrated in the response to virus and immune system processes. Protein-protein interaction (PPI) network showed that most of these DEISGs could interact strongly with each other. Then, IFIT1, RSAD2, IFIT3, USP18, ISG15, OASL, MX1, OAS2, OAS3, and IFI44 were considered to be hub ISGs in SLE by “MCODE” and “Cytohubba” plugins of Cytoscape, Moreover, the results of expression correlation suggested that 3 lncRNAs (NRIR, FAM225A, and LY6E-DT) were closely related to the IFN pathway.

The lncRNA NRIR and mRNAs (RSAD2, USP18, IFI44, and ISG15) were selected as candidate ISGs for verification. RT-qPCR results showed that PBMCs from SLE patients had substantially higher expression levels of 5 ISGs compared to healthy controls (HCs). Additionally, statistical analyses revealed that the expression levels of these ISGs were strongly associated to various clinical symptoms, including thrombocytopenia and facial erythema, as well as laboratory indications, including the white blood cell (WBC) count and levels of autoantibodies. The Receiver Operating Characteristic (ROC) curve demonstrated that the IFI44, USP18, RSAD2, and IFN score had good diagnostic capabilities of SLE.

According to our study, SLE was associated with ISGs including NRIR, RSAD2, USP18, IFI44, and ISG15, which may contribute to the future diagnosis and new personalized targeted therapies.

Association between Anti-Hepatitis C Viral Intervention Therapy and Risk of Sjögren’s Syndrome: A National Retrospective Analysis

Hepatitis C virus (HCV) infection is a potential risk factor for Sjögren’s syndrome (SS). However, it is unclear whether anti-HCV intervention therapy could decrease SS risk. A retrospective cohort analysis from 1997–2012 comprising 17,166 eligible HCV-infected adults was conducted. By 1:2 propensity score matching, a total of 2123 treated patients and 4246 untreated patients were subjected to analysis. The incidence rates and risks of SS and death were evaluated through to the end of 2012. In a total follow-up of 36,906 person-years, 177 (2.8%) patients developed SS, and 522 (8.2%) died during the study period. The incidence rates of SS for the treated and untreated cohorts were 5.3 vs. 4.7/1000 person-years, and those of death for the treated and untreated cohorts were 10.0 vs. 14.8/1000 person-years. A lower risk of death (adjusted hazard ratio, 0.68; 95% CI, 0.53–0.87) was present in HCV-infected patients receiving anti-HCV therapy in multivariable Cox regression, and this remained consistent in multivariable stratified analysis. However, there were no relationships between anti-HCV therapy and its therapeutic duration, and SS risk in multivariable Cox regression. In conclusion, anti-HCV intervention therapy was not associated with lower SS risk in HCV-infected patients, but associated with lower death risk.

Management of Sjögren's Syndrome: Present Issues and Future Perspectives

In view of the new possibilities for the treatment of primary Sjögren's syndrome (pSS) given by the availability of new biotechnological agents targeting the various molecular and cellular actors of the pathological process of the disease, classification criteria aimed at selecting patients to be enrolled in therapeutic trials, and validated outcome measures to be used as response criteria to these new therapies, have been developed and validated in the last decades. Unfortunately, the therapeutic trials so far completed with these new treatments have yielded unsatisfactory or only partially positive results. The main issues that have been evoked to justify the poor results of the new therapeutic attempts are: (i) the extreme variability of the disease phenotypes of the patients enrolled in the trials, which are dependent on different underlying patterns of biological mechanisms, (ii) the fact that the disease has a long indolent course, and that most of the enrolled patients might already have irreversible clinical features. The advances in the research of new disease biomarkers that can better distinguish the different clinical phenotypes of patients and diagnose the disease in an earlier phase are also discussed.

Characterization of Type I Interferon-Associated Chemokines and Cytokines in Lacrimal Glands of Nonobese Diabetic Mice

Type I interferons (IFNs) are required for spontaneous lacrimal gland inflammation in the nonobese diabetic (NOD) mouse model of Sjögren’s disease, but the consequences of type I IFN signaling are not well-defined. Here, we use RNA sequencing to define cytokine and chemokine genes upregulated in lacrimal glands of NOD mice in a type I IFN-dependent manner. Interleukin (IL)-21 was the highest differentially expressed cytokine gene, and Il21 knockout NOD mice were relatively protected from lacrimal gland inflammation. We defined a set of chemokines upregulated early in disease including Cxcl9 and Cxcl10, which share a receptor, CXCR3. CXCR3⁺ T cells were enriched in lacrimal glands with a dominant proportion of CXCR3⁺ regulatory T cells. Together these data define the early cytokine and chemokine signals associated with type I IFN-signaling in the development of lacrimal gland inflammation in NOD mice providing insight into the role of type I IFN in autoimmunity development.

Genome-wide DNA methylation patterns in monocytes derived from patients with primary Sjogren syndrome

Background:

Epigenetics, especially DNA methylation, plays an important role in the pathogenesis of primary Sjogren syndrome (pSS). Our study aimed to reveal the role of DNA methylation in peripheral monocytes of pSS patients.

Methods:

A total of 11 pSS patients and five age-matched healthy controls (HCs) were included in this study. Monocytes were isolated from peripheral blood mononuclear cells using magnetic microbeads. DNA methylation profiles were generated using Human Methylation 850K BeadChips.

Results:

In monocytes from pSS patients, we identified 2819 differentially methylated positions (DMPs), comprising 1977 hypomethylated- and 842 hypermethylated-DMPs, corresponding to 1313 unique genes when compared with HCs. IFI44L, MX1, PAARP9, and IFITM1, which influence the interferon (IFN) signaling pathway, were among the genes hypomethylated in pSS. Functional analysis of genes with a minimum of two DMPs showed involvement in antigen binding, transcriptional regulation, cell adhesion, IFN-γ pathway, type I IFN pathway, antigen presentation, Epstein-Barr virus infection, human T-lymphotropic virus type 1 virus infection, and metabolic disease-related pathways. In addition, patients with higher serum IgG levels exhibited enrichment in Notch signaling and metabolic-related pathways. Upon comparing monocytes with salivary gland epithelial cells, an important overlap was observed in the cell cycle, cell senescence, and interleukin-17 signaling pathways. The differentially methylated genes were more enriched in the ribosome- and AMP-activated protein kinase signaling pathway in anti-Ro/SSA and anti-La/SSB autoantibodies double-positive patients.

Conclusion:

Genome-wide DNA methylation profiling revealed significant differences in DNA methylation in monocytes isolated from patients with pSS.

Role of the Innate Immunity Signaling Pathway in the Pathogenesis of Sjögren's Syndrome

Sjögren’s syndrome (SS) is a systemic autoimmune disease characterized by chronic inflammation of the salivary and lacrimal glands and extra-glandular lesions. Adaptive immune response including T- and B-cell activation contributes to the development of SS. However, its pathogenesis has not yet been elucidated. In addition, several patients with SS present with the type I interferon (IFN) signature, which is the upregulation of the IFN-stimulated genes induced by type I IFN. Thus, innate immune responses including type I IFN activity are associated with SS pathogenesis. Recent studies have revealed the presence of activation pattern recognition receptors (PRRs) including Toll-like receptors, RNA sensor retinoic acid-inducible gene I and melanoma differentiation-associated gene 5, and inflammasomes in infiltrating and epithelial cells of the salivary glands among patients with SS. In addition, the activation of PRRs via the downstream pathway such as the type I IFN signature and nuclear factor kappa B can directly cause organ inflammation, and it is correlated with the activation of adaptive immune responses. Therefore, this study assessed the role of the innate immune signal pathway in the development of inflammation and immune abnormalities in SS.

The Involvement of Innate and Adaptive Immunity in the Initiation and Perpetuation of Sjögren's Syndrome

Sjogren’s syndrome (SS) is a chronic autoimmune disease characterized by the infiltration of exocrine glands including salivary and lachrymal glands responsible for the classical dry eyes and mouth symptoms (sicca syndrome). The spectrum of disease manifestations stretches beyond the classical sicca syndrome with systemic manifestations including arthritis, interstitial lung involvement, and neurological involvement. The pathophysiology underlying SS is not well deciphered, but several converging lines of evidence have supported the conjuncture of different factors interplaying together to foster the initiation and perpetuation of the disease. The innate and adaptive immune system play a cardinal role in this process. In this review, we discuss the inherent parts played by both the innate and adaptive immune system in the pathogenesis of SS.

Innate Immunity and Biological Therapies for the Treatment of Sjögren's Syndrome

Sjögren's syndrome (SS) is a systemic autoimmune disorder affecting approximately 3% of the population in the United States. This disease has a female predilection and affects exocrine glands, including lacrimal and salivary glands. Dry eyes and dry mouths are the most common symptoms due to the loss of salivary and lacrimal gland function. Symptoms become more severe in secondary SS, where SS is present along with other autoimmune diseases like systemic lupus erythematosus, systemic sclerosis, or rheumatoid arthritis. It is known that aberrant activation of immune cells plays an important role in disease progression, however, the mechanism for these pathological changes in the immune system remains largely unknown. This review highlights the role of different immune cells in disease development, therapeutic treatments, and future strategies that are available to target various immune cells to cure the disease.

LncRNA and mRNA expression profile of peripheral blood mononuclear cells in primary Sjögren's syndrome patients

The aim of this study was to elucidate the expression profile and the potential role of long non-coding RNA (LncRNA) in the peripheral blood mononuclear cells of primary Sjögren’s syndrome (pSS) patients. RNA-seq technology was used to detect the differentially expressed LncRNAs and mRNAs between five age-and sex-matched paired pSS patients and healthy control PBMCs. The selected LncRNAs were detected in the validation study by RT-qPCR in 16 paired pSS patients and healthy controls. The GO, KEGG, co-localization, and co-expression analysis were performed to enrich the potential gene functions and pathways. In this study, 44 out of 1772 LncRNAs and 1034 out of 15,424 mRNAs were expressed differentially in the PBMCs of pSS patients. LINC00426, TPTEP1-202, CYTOR, NRIR, and BISPR were validated as aberrantly expressed, and these LncRNAs strongly correlated with disease activity of pSS. GO and KEGG pathway analysis revealed the significant enrichment of biological processes, cellular components, and molecular function of the up and down-regulated mRNAs, which were mainly concentrated in the immune response and immune system processes. Co-localization and co-expression analysis also revealed that differentially expressed LncRNAs in the PBMCs of pSS were strongly correlated to the mRNA functioning associated with immune response and cell metastasis. Numerous LncRNAs and mRNAs were found differentially expressed in the PBMCs of pSS patients, especially NRIR and BISPR; they interacted with the co-localized and co-expressed mRNAs, which might participate in the pathogenesis of pSS through the NF-κB, JAK-STAT, and other signaling pathways that regulate cell metastasis.

Recent Advances in Mouse Models of Sjögren's Syndrome

Sjögren's syndrome (SS) is a complex rheumatoid disease that mainly affects exocrine glands, resulting in xerostomia (dry mouth) and xerophthalmia (dry eye). SS is characterized by autoantibodies, infiltration into exocrine glands, and ectopic expression of MHC II molecules on glandular epithelial cells. In contrast to the well-characterized clinical and immunological features, the etiology and pathogenesis of SS remain largely unknown. Animal models are powerful research tools for elucidating the pathogenesis of human diseases. To date, many mouse models of SS, including induced models, in which disease is induced in mice, and genetic models, in which mice spontaneously develop SS-like disease, have been established. These mouse models have provided new insight into the pathogenesis of SS. In this review, we aim to provide a comprehensive overview of recent advances in the field of experimental SS.

Primary Sjogren Syndrome: Focus on Innate Immune Cells and Inflammation

Primary Sjogren Syndrome (pSS) is a complex, multifactorial rheumatic disease that mainly targets salivary and lacrimal glands, inducing epithelitis. The cause behind the autoimmunity outbreak in pSS is still elusive; however, it seems related to an aberrant reaction to exogenous triggers such as viruses, combined with individual genetic pre-disposition. For a long time, autoantibodies were considered as the hallmarks of this disease; however, more recently the complex interplay between innate and adaptive immunity as well as the consequent inflammatory process have emerged as the main mechanisms of pSS pathogenesis. The present review will focus on innate cells and on the principal mechanisms of inflammation connected. In the first part, an overview of innate cells involved in pSS pathogenesis is provided, stressing in particular the role of Innate Lymphoid Cells (ILCs). Subsequently we have highlighted the main inflammatory pathways, including intra- and extra-cellular players. A better knowledge of such processes could determine the detection of new therapeutic targets that are a major need for pSS.

Poly(ADP-Ribose) Polymerase Enhances Infiltration of Mononuclear Cells in Primary Sjögren's Syndrome Through Interferon-Induced Protein With Tetratricopeptide Repeats 1-Mediated Up-Regulation of CXCL10

OBJECTIVE

Mononuclear cell infiltration and type I interferon (IFN) system activation play an important role in primary Sjögren's syndrome (SS). We undertook this study to investigate the mechanism of poly(ADP-ribose) polymerase family member 9 (PARP-9) on mononuclear cell infiltration triggered by type I IFN.

METHODS

A proteomic study was conducted in peripheral blood mononuclear cells from patients with primary SS (n = 30) and healthy controls (n = 30) to determine differentially expressed proteins (DEPs) (P < 0.05; fold change >1.20). Labial salivary glands (LSGs) were isolated for hematoxylin and eosin staining and immunohistochemical analysis. CD19+ B cells were purified by magnetic cell sorting for immunofluorescence staining, lentivirus-PARP-9 transfection, and IFNα treatment experiments. PARP-9 small interfering RNA (siRNA) and DTX3L siRNA were delivered into female NOD/LtJ female mice to determine their effect.

RESULTS

The overexpression of PARP-9 and CXCL10 as well as their colocalization was confirmed in primary SS. PARP-9 levels in LSGs rose with increased Chisholm scores in patients with primary SS. PARP-9 and DTX3L were present in the infiltrating mononuclear cells from salivary glands in female NOD/LtJ mouse models. Additionally, Ingenuity Pathway Analysis networks of DEPs demonstrated that PARP-9, STAT1, and IFN-induced protein with tetratricopeptide repeats 1 (IFIT-1) participated in the IFN-related pathway. Furthermore, PARP-9 could up-regulate the expression of IFIT1 and CXCL10 in B cells. Moreover, PARP-9 and CXCL10 could be induced by IFNα in B cells.

CONCLUSION

This study is the first to implicate PARP-9 as a regulator of infiltration of mononuclear cells in primary SS progression and to reveal that PARP-9 increases CXCL10 expression through up-regulating IFIT-1, which is mediated by the phosphorylation of STAT1. PARP-9 might therefore be a novel therapeutic target for primary SS.

Sjögren's syndrome: Old and new therapeutic targets

Sjögren's syndrome (SS) is a prototype autoimmune disease characterized by oral and ocular mucosal dryness following chronic inflammation of salivary and lachrymal glands, respectively. Profound B cell hyperactivity along with systemic manifestations including fatigue, musculoskeletal complaints, features related to hepatic, pulmonary, renal and nervous system involvement, as well as lymphoma development can be also present. Despite that activation of both innate and adaptive immune pathways has been long well documented in SS pathogenesis, systemic immunosuppression in SS, in contrast to other autoimmune diseases, has been largely inefficacious. Biological agents previously implemented in successful therapeutic outcomes in rheumatoid arthritis (RA), such as anti-TNF agents, anakinra, tocilizumab and rituximab failed to reach primary outcomes in randomized double-blind controlled trials in the context of SS. Abatacept and belimumab, already licensed for the treatment of RA and lupus respectively, as well combination regimens of both rituximab and belimumab hold some promise in alleviation of SS-specific complaints, but data from large controlled trials are awaited. Recent advances in dissecting the molecular pathways underlying SS pathogenesis led to an expanding number of novel biological compounds directed towards type I interferon system, antigen presentation, costimulatory pathways, B and T cell activation, as well as germinal center formation. While targeting of cathepsin-S (Petesicatib), inducible costimulator of T cells ligand (prezalumab), and lymphotoxin beta receptor (baminercept) failed to fulfil the primary outcome measures, preliminary results from two randomized placebo controlled trials on CD40 blockade (Iscalimab) and B-cell activating factor receptor (Ianalumab) inhibition resulted in significant reduction of SS disease activity, with a favorable so far safety profile. Results from administration of other kinase inhibitors, a transmembrane activator and calcium-modulator and cytophilin ligand interactor TACI fusion protein (RC18), as well as low dose recombinant interleukin-2 to expand T-regulatory cells are currently awaited.

Identifying Key Genes and Functionally Enriched Pathways in Sjögren's Syndrome by Weighted Gene Co-Expression Network Analysis

Purpose: Sjögren’s syndrome (SS) is an autoimmune disease characterized by dry mouth and eyes. To date, the exact molecular mechanisms of its etiology are still largely unknown. The aim of this study was to identify SS related key genes and functionally enriched pathways using the weighted gene co-expression network analysis (WGCNA).

Materials and Methods: We downloaded the microarray data of 190 SS patients and 32 controls from Gene Expression Omnibus (GEO). Gene network was constructed and genes were classified into different modules using WGCNA. In addition, for the hub genes in the most related module to SS, gene ontology analysis was applied. The expression profile and diagnostic capacity (ROC curve) of interested hub genes were verified using a dataset from the GEO. Moreover, gene set enrichment analysis (GSEA) was also performed.

Results: A total of 1483 differentially expressed genes were filtered. Weighted gene coexpression network was constructed and genes were classified into 17 modules. Among them, the turquoise module was most closely associated with SS, which contained 278 genes. These genes were significantly enriched in 10 Gene Ontology terms, such as response to virus, immune response, defense response, response to cytokine stimulus, and the inflammatory response. A total of 19 hub genes (GBP1, PARP9, EPSTI1, LOC400759, STAT1, STAT2, IFIH1, EIF2AK2, TDRD7, IFI44, PARP12, FLJ20035, PARP14, ISGF3G, XAF1, RSAD2,LY6E, IFI44L, and DDX58) were identified. The expression levels of the five interested genes including EIF2AK2, GBP1, PARP12, PARP14, and TDRD7 were also confirmed. ROC curve analysis determined that the above five genes’ expression can distinguish SS from controls (the area under the curve is all greater than 0.7). GSEA suggests that the SS samples with highly expressed EIF2AK2 or TDRD7 genes are correlated with inflammatory response, interferon α response, and interferon γ response.

Conclusion: The present study applied WGCNA to generate a holistic view of SS and provide a basis for the identification of potential pathways and hub genes that may be involved in the development of SS.

Activation of Toll-like receptor 7 signaling in labial salivary glands of primary Sjögren's syndrome patients

The aim of this study was to determine the expressions of Toll-like receptors (TLRs) 7-9 and type I interferon (IFN) signal in labial salivary glands (LSGs) and cultured salivary gland epithelial cells (SGECs) from primary Sjögren's syndrome (pSS) patients. We performed an immunohistochemistry analysis of LSGs from 11 patients with pSS as defined by American-European Consensus Group classification criteria and five healthy subjects. The pSS patients' SGECs were analyzed by immunofluorescence and western blotting. IFN-α expression was examined by immunosorbent assay and flow cytometry. Mononuclear cells (MNCs) from pSS patients' LSGs showed TLR-7-dominant expression. B cells, plasma cells and plasmacytoid dendritic cells (pDCs) co-expressed with TLR-7. Myeloid differentiation primary response gene 88 (MyD88), tumor necrosis factor receptor-associated factor 6 (TRAF6) and interferon regulatory factor 7 (IRF7) co-expressed with the pDC marker CD303 in LSGs. Ducts from pSS patients dominantly expressed TLR-7, and TLR-7 in the ducts co-expressed with MyD88, TRAF6 and IRF7. Type I IFNs including IFN-α and IFN-β were detected in MNCs and ducts in pSS patients' LSGs. Increased TRAF6 expression and the nuclear translocation of IRF7 in SGECs were detected by immunofluorescence following loxoribine (a TLR-7 ligand) stimulation despite IFN-β pretreatment. Western blotting showed increased TRAF6 expression in SGECs following IFN-β and loxoribine stimulation. Although no increase in IFN-α was detected in supernatant from stimulated SGECs, the IFN-α in supernatant from stimulated peripheral blood pDCs from pSS patients was significantly increased. Our findings suggest that TLR-7 is dominantly expressed in both MNCs and ducts with downstream signals for type I IFNs, indicating that TLR7-dominant innate immunity is related to the development of sialadenitis in pSS.

Biomarkers for Sjögren's syndrome

Sjögren's syndrome (pSS) is a complex and heterogeneous disorder characterized by different clinical subsets. Recently, great efforts have been made searching for reliable biomarkers able to ameliorate the diagnostic algorithm and the prognostic stratification of pSS patients and ultimately allowing the scientific community to address some of the unmet needs for the disease. In this review, we have summarized the state of the art of 'traditional' widely acknowledged clinical, serological and histologic biomarkers for pSS with the aim of highlighting their relevance and limitations in clinical practice. We have also explored some of the novel potential biomarkers that have been proposed more recently, potentially able to open new ways in the assessment of the disease.

Activation of plasmacytoid dendritic cells by apoptotic particles - mechanism for the loss of immunological tolerance in Sjögren's syndrome

Sjögren's syndrome (SS) is a common autoimmune disease targeting salivary and lacrimal glands. It is strongly female-dominant, characterized by low oestrogen levels combined with a local intracrine dihydrotestosterone defect. We hypothesized that these hormonal deficits lead to increased apoptosis of the epithelial cells and plasmacytoid dendritic cell (pDC)-mediated proinflammatory host responses. Expression of Toll-like receptors (TLRs)-7 and -9 and cytokine profiles was studied in pDCs treated with apoptotic particles collected in consecutive centrifugation steps of media from apoptotic cells. Expression and localization of SS autoantigens in these particles was also analysed. Furthermore, the effects of sex steroids were studied in pDCs cultured with several concentrations of dihydrotestosterone and 17-β-oestradiol, and in saliva of patient treated with dehydroepiandrosterone. Apoptosis of the epithelial cells led to cleavage and translocation of SS-autoantigens, α-fodrin and SS-A, into apoptotic particles. The apoptosis-induced apoptotic particles also contained another SS-autoantigen, hy1-RNA. These particles were internalized by pDCs in a size-dependent manner and affected TLR-7 and -9 expression and the production of proinflammatory cytokines. The analysed androgens protected cells from apoptosis, influenced redistribution of autoantigens and diminished the apoptotic particle-stimulated increase of the TLRs in pDCs. Our findings suggest that the formation of apoptotic particles may play a role in loss of immune tolerance, manifested by production of autoantibodies and the onset of autoinflammation in SS.

Transcriptomic Segregation of Human Autoantigens Useful for the Diagnosis of Autoimmune Diseases

The measurement of autoantibodies in the clinical care of autoimmune patients allows for diagnosis, monitoring, and even disease prediction. Despite their clinical utility, the functional significance of autoantibody target proteins in many autoimmune diseases remains unclear. Here we present a comprehensive review of 52 autoantigens commonly employed for the serological diagnosis of 24 autoimmune diseases. We discuss their function, whether they have extracellular-exposed epitopes, and whether antibodies to these proteins are known to be pathogenic. Transcriptomics (RNA-Seq) datasets were mined to display messenger RNA (mRNA) expression of the autoantigens across 32 tissues and organs. This analysis revealed that autoantigens cluster into one of three groups: expression in the tissue most strongly affected in the disease (Group I), ubiquitous expression with enrichment in immune tissues (Group II), or expression in other tissues not typically associated with the clinical presentation (Group III). Clustering demonstrated that the autoantigens within Group I were often proteins containing extracellular epitopes, many of which are targets of pathogenic autoantibodies. Group II autoantigens were targets for several rheumatological diseases, including Sjögren syndrome, systemic lupus erythematosus, myositis, and systemic sclerosis, and were ubiquitously expressed with enrichment in immune-rich tissues. This raises the possibility that immune cells in Group II disorders may be the source of autoimmunization and/or targets of immune cell responses. Since tissues showing enriched autoantigen gene expression may contribute to the development of autoantibodies and subsequent autoimmunity, the emergent patterns arising from the autoantigen transcriptomic profiles may provide a new heuristic framework to deconvolute these complex disorders.

Hepatitis Delta Virus Detected in Salivary Glands of Sjögren's Syndrome Patients and Recapitulates a Sjögren's Syndrome-Like Phenotype in Vivo

Background:

Low-level, chronic viral infections have been suspect in the development of select autoimmune diseases, including primary Sjögren's syndrome (pSS). Multiple studies have shown stimulation of antiviral response pathways in pSS tissues suggestive of a viral infection. Yet, with this data in hand, a causal link between a viral infection and development of pSS had not been identified. Therefore, a study was designed to further define the viral landscape within pSS-affected salivary gland tissue to identify potential viral-mediated triggers in the pathogenesis of this autoimmune disease.

Methods:

A viral microarray was utilized to measure viral transcripts present in salivary gland tissue from patients diagnosed with pSS compared to healthy controls. Murine models of salivary gland localized HDV antigen expression were developed to evaluate the capacity of a chronic HDV signature to trigger the development of a pSS-like phenotype.

Results:

Through this analysis, two distinct viral profiles were identified, including the increased presence of hepatitis delta virus (HDV) in 50% of pSS patients evaluated. Presence of HDV antigen and sequence were confirmed in minor salivary gland tissue. Patients with elevated HDV levels in salivary gland tissue were negative for detectible hepatitis B virus (HBV) surface antigen and antibodies to HBV or HDV. Expression of HDV antigens in vivo resulted in reduced stimulated saliva flow, increase in focal lymphocytic infiltrates, and development of autoantibodies.

Conclusion:

Identification of HDV in pSS patients and induction of a complete pSS-like phenotype in vivo provides further support of a viral-mediated etiopathology in the development of pSS.

Role of Toll-like receptors and retinoic acid inducible gene I in endogenous production of type I interferon in dermatomyositis

To explore the possible mechanisms implicated in the endogenous production of type I interferons within the muscle tissue of dermatomyositis (DM) patients. We detected the co-localization of plasmacytoid dendritic cells (pDCs) with Toll-like receptors (TLRs) and retinoic acid inducible gene (RIG)-I by immunohistochemistry and immunofluorescence. Western blotting confirmed the expression of TLRs and RIG-I. TLR-3 and RIG-I was preferentially expressed in the perifascicular atrophy fibers of DM. TLR-7 was only in inflammatory infiltrates of a few DM patients. TLR-4 and TLR-9 was expressed mainly in inflammatory infiltrates. Immunofluorescence showed extensive co-localization of BDCA-2 with TLR-9 and little co-localization with TLR-7. Western blotting showed upregulation of expression of TLRs and RIG-I in DM compared with the controls. Our findings indicate that endogenous production of type I IFN in DM is generated by pDCs, mainly through the TLR-9 pathway and in part by TLR-7. TLR-3 and RIG-I are implicated in the formation of perifascicular atrophy in DM.

Type I and II interferon signatures in Sjogren's syndrome pathogenesis: Contributions in distinct clinical phenotypes and Sjogren's related lymphomagenesis

Both type I and II interferons (IFNs) have been implicated in the pathogenesis of Sjogren's syndrome (SS). We aimed to explore the contribution of type I and II IFN signatures in the generation of distinct SS clinical phenotypes including lymphoma development. Peripheral blood (PB) from SS patients (n = 31), SS patients complicated by lymphoma (n = 13) and healthy controls (HC, n = 30) were subjected to real-time PCR for 3 interferon inducible genes (IFIGs) preferentially induced by type I IFN, 2 IFIGs preferentially induced by IFNγ as well as for IFNα and IFNγ genes. The same analysis was performed in minor salivary gland tissues (MSG) derived from 31 SS patients, 10 SS-lymphoma patients and 17 sicca controls (SC). In PB and MSG tissues, overexpression of both type I and type II IFIGs was observed in SS patients versus HC and SC, respectively, with a predominance of type I IFN signature in PB and a type II IFN signature in MSG tissues. In SS-lymphoma MSG tissues, lower IFNα, but higher IFNγ and type II IFIG transcripts compared to both SS and SC were observed. In receiver operating characteristic curve analysis, IFNγ/IFNα mRNA ratio in MSG tissues showed the best discrimination for lymphoma development. Discrete expression patterns of type I and II IFN signatures might be related to distinct SS clinical phenotypes. Additionally, IFNγ/IFNα mRNA ratio in diagnostic salivary gland biopsies is proposed as a novel histopathological biomarker for the prediction of in situ lymphoma development in the setting of SS.

TLR2 and TLR4 in autoimmune diseases: a comprehensive review

Autoimmune diseases are immune disorders characterized by T cell hyperactivity and B cell overstimulation leading to overproduction of autoantibodies. Although the pathogenesis of various autoimmune diseases remains to be elucidated, environmental factors have been thought to contribute to the initiation and maintenance of auto-respond inflammation. Toll-like receptors (TLRs) are pattern recognition receptors belonging to innate immunity that recognize and defend invading microorganisms. Besides these exogenous pathogen-associated molecular patterns, TLRs can also bind with damage-associated molecular patterns produced under strike or by tissue damage or cells apoptosis. It is believed that TLRs build a bridge between innate immunity and autoimmunity. There are five adaptors to TLRs including MyD88, TRIF, TIRAP/MAL, TRAM, and SARM. Upon activation, TLRs recruit specific adaptors to initiate the downstream signaling pathways leading to the production of inflammatory cytokines and chemokines. Under certain circumstances, ligation of TLRs drives to aberrant activation and unrestricted inflammatory responses, thereby contributing to the perpetuation of inflammation in autoimmune diseases. In the past, most studies focused on the intracellular TLRs, such as TLR3, TLR7, and TLR9, but recent studies reveal that cell surface TLRs, especially TLR2 and TLR4, also play an essential role in the development of autoimmune diseases and afford multiple therapeutic targets. In this review, we summarized the biological characteristics, signaling mechanisms of TLR2/4, the negative regulators of TLR2/4 pathway, and the pivotal function of TLR2/4 in the pathogenesis of autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, Sjogren's syndrome, psoriasis, multiple sclerosis, and autoimmune diabetes.

Identification of interferon-inducible genes as diagnostic biomarker for systemic lupus erythematosus

The identification of biomarkers helps to perform early diagnosis, thus benefits the outcome of patients with systemic lupus erythematosus (SLE), in which delayed treatment has been proposed as an independent adverse prognostic factor. In this study, we assessed the values of expression levels of five type I interferon (IFN)-inducible genes (LY6E, OAS1, OASL, MX1, and ISG15) and total IFN score for the diagnosis of SLE. Quantitative real-time PCR was applied to determine gene expressions at transcription level in peripheral blood from 69 SLE patients, 42 patients with other connective tissue diseases, and 26 normal controls. Expressions of five genes and IFN score, calculated according to the expressions of IFN-inducible genes, were all significantly increased in SLE patients compared to those in normal subjects and disease controls. IFN score was not related to age, gender, and the dose of steroids, but weakly correlated with SLE disease activity index. None of the gene expression was associated with concomitant infection status or elevated antibodies against Epstein-Barr (EB) virus in SLE. Both modified IFN score (calculated by the expression of three major IFN-inducible genes) and LY6E level showed good diagnostic accuracy in discriminating between SLE patients and disease controls as well as normal subjects (area under the receiver operating characteristic curve was 0.812 and 0.815, respectively), with 70-80 % specificity and 70-80 % sensitivity at the cutoff of 2.37 and 3.23. In conclusion, high IFN-inducible gene expression is constitutional for SLE patients. The modified IFN score or the LY6E level alone may serve as good biomarkers for SLE diagnosis.

New advances in the classification, pathogenesis and treatment of Sjogren's syndrome

PURPOSE OF REVIEW

In the current review, we summarize the newly proposed classification criteria for Sjogren's syndrome, recent findings of Sjogren's syndrome pathogenesis and the latest achievements in disease management.

RECENT FINDINGS

A new set of Sjogren's syndrome classification criteria has been recently proposed by an expert consensus panel of the American College of Rheumatology-Sjögren's International Collaborative Clinical Alliance. Recent findings reveal new aspects in the activation of innate and adaptive immune pathways and novel animal models - highly reminiscent of human Sjogren's syndrome-are described. Of particular note, apoptosis of epithelial cells as a result of deficient IκBζ, previously shown to be a modulator of NFκB activity, has been suggested as a central pathogenetic event. Mechanistic data on anti-B-cell therapies, gene transfer approaches aimed to restore secretory function, as well mesenchymal stem cell transplantation in mice and humans are also discussed.

SUMMARY

Over the last year, a new set of classification criteria for Sjogren's syndrome has been suggested, new Sjogren's syndrome-like animal models have been described and significant progress has been made in understanding the activation of innate and adaptive immune responses. New therapeutic approaches have been also implemented with variable success.

Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disorder that typically affects exocrine glands--mainly labial and lacrimal--leading to complaints of dry mouth and eyes. Given that periepithelial mononuclear cell infiltrates, both in exocrine glands and in other parenchymal organs (kidney, lung, and liver), are the histopathological disease hallmark, the term autoimmune epithelitis has been proposed. B cell hyperactivity is another cardinal SS feature manifested by the presence of autoantibodies and hypergammaglobulinemia, as well as clinical/serological phenotypes mediated by immune complexes, such as peripheral neuropathy, vasculitic lesions, and hypocomplementemia. These have been designated adverse predictors for lymphoma development in approximately 5% to 10% of patients. Activation of the type I interferon/B cell-activating factor axis in SS has recently attracted particular attention. Inappropriate overexpression of endogenous nucleic acids in a genetically susceptible individual might provide a plausible scenario for the immune activation observed in SS.

Type I interferon receptor deficiency prevents murine Sjogren's syndrome

In Sjögren's Syndrome (SS), inherent glandular defects, autoimmunity, and mononuclear cell infiltration within the salivary glands cause reduced salivation leading to xerostomia. Excessive production of type I interferons (IFN), triggered by environmental and genetic factors, is considered pathogenic in this disorder. However, whether type I IFN production is causative or an outcome of the disease process is not known. To address this question, we introduced a deficiency of interferon alpha receptor 1 (Ifnar1) into B6.Aec1Aec2 mice, which are known to have the genetic loci necessary for developing a SS-like disorder. This new mouse strain, B6.Aec1Aec2Ifnar1 (-/-), lacking type I IFN-mediated signaling, was characterized for pilocarpine-induced salivation, the presence of serum autoantibodies, sialoadenitis, and dacryoadenitis. Compared with the B6.Aec1Aec2Ifnar1 (+/+) (wild-type) mice, the B6.Aec1Aec2Ifnar1 (-/-) (knockout) mice had significantly lower mononuclear cell infiltration in the salivary and lacrimal glands. The knockout mice were completely protected from salivary gland dysfunction. Surprisingly, they had a robust autoantibody response comparable with that of the wild-type mice. These findings demonstrate that, in the absence of type I IFN-mediated signaling, systemic autoantibody responses can be dissociated from glandular pathology. Our study suggests that, in genetically susceptible individuals, the type I IFN pathway can instigate certain features of SS.

Sjögren's syndrome, the old and the new

Sjögren's syndrome is a chronic autoimmune disease characterised by progressive injury to exocrine glands accompanied by diverse extra-glandular manifestations. The spectrum of Sjögren's manifestations expanded in recent years to include new symptoms and signs such as small fibre neuropathy, and also well-defined activity and prognostic indexes. Similar to other non-organ-specific autoimmune diseases, a mosaic of factors have been linked with the development and appearances of Sjögren's syndrome. Progress has been made unravelling those factors, including susceptibility genes, immunological parameters and various environmental factors in the last decade, some of which may enable targeted therapies, biological and non-biological ones, for patients suffering from this disease. Thus, herein we review the postulated aetiologies, pathogenesis and new insights related to Sjögren's syndrome.

Brief report: adrenal autoimmunity in primary Sjögren's syndrome

OBJECTIVE

To evaluate the prevalence of antibodies to 21-hydroxylase (anti-21[OH]), a marker of autoimmune adrenal disease, in a cohort of patients with primary Sjögren's syndrome (SS) and to investigate whether the presence of anti-21(OH) correlates with clinical, serologic, and salivary gland features of the disease.

METHODS

Sera from 63 consecutive patients with primary SS, 32 patients with autoimmune thyroid disease (AITD), and 20 healthy controls were obtained and anti-21(OH) levels were determined by radioimmunoassay. Clinical, serologic, and histopathologic features were recorded, and a short Synacthen test was used to assess adrenal function reserve. Seven available minor salivary gland (MSG) tissue specimens from patients in the primary SS cohort were also assessed for interferon-α (IFNα), BAFF, and interleukin-21 (IL-21) cytokine transcripts, which are all implicated in B cell activation.

RESULTS

Anti-21(OH) positivity was detected in 17.5% and 28.1% of primary SS and AITD patients, respectively, and in none of the healthy controls. While no evidence of adrenal insufficiency was detected in any of the patients studied, a blunted rate of increase in cortisol levels was observed in patients with detectable serum autoantibodies against 21(OH), compared to their anti-21(OH)-negative counterparts. A strong correlation between the serum titer of anti-21(OH) antibodies and expression of IFNα, BAFF, and IL-21 messenger RNA in MSG tissues was also detected.

CONCLUSION

Adrenal autoimmunity occurs in almost 20% of patients with primary SS in association with markers of B cell activation. Although the presence of adrenal autoantibodies was not associated with adrenal insufficiency in the present study, there was a blunted adrenal response, suggesting the need for further followup and monitoring of adrenal function in patients with primary SS who are positive for the autoantibodies.

Transcriptome analysis of the interferon-signature defining the autoimmune process of Sjögren's syndrome

Sjögren's syndrome (SS) of humans and SS-like (SjS-like) diseases in mouse models are characterized by chronic immune attacks against the salivary and lacrimal glands leading to exocrine dysfunction. One characteristic of SS and SjS-like diseases repeatedly observed is a strong upregulated expression of both the type I (α/β) and type II (γ) interferons (IFNs). In addition, recent global transcriptome studies have identified a variety of IFN-stimulated gene (ISG) transcripts differentially expressed in tissues of SS patients and mouse models exhibiting SjS-like disease. Analyses of these transcriptome databases indicate that the sets of differentially expressed genes are highly restricted, suggesting that there is a unique specificity in ISGs activated (or suppressed) during development and onset of disease. As a result, these observations have led to both SS and SjS-like diseases being designated as 'interferon-signature' diseases. While SS and SjS-like diseases may be designated as such, very little effort has been made to determine what an interferon-signature might signify relative to autoinflammation and whether it might point directly to an underlying etiopathological mechanism. Here, we review these limited data and provide a model of how the products of these genes interact molecularly and biologically to define critical details of SS pathology.

Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observations.