Increased circulating levels and salivary gland expression of interleukin-18 in patients with Sjögren's syndrome: relationship with autoantibody production and lymphoid organization of the periductal inflammatory infiltrate

Advances in cellular and molecular pathways of salivary gland damage in Sjögren's syndrome

Sjögren's Syndrome (SS) is an autoimmune disorder characterized by dysfunction of exocrine glands. Primarily affected are the salivary glands, which exhibit the most frequent pathological changes. The pathogenesis involves susceptibility genes, non-genetic factors such as infections, immune cells-including T and B cells, macrophage, dendritic cells, and salivary gland epithelial cells. Inflammatory mediators such as autoantibodies, cytokines, and chemokines also play a critical role. Key signaling pathways activated include IFN, TLR, BAFF/BAFF-R, PI3K/Akt/mTOR, among others. Comprehensive understanding of these mechanisms is crucial for developing targeted therapeutic interventions. Thus, this study explores the cellular and molecular mechanisms underlying SS-related salivary gland damage, aiming to propose novel targeted therapeutic approaches.

Diagnostic Evaluation Using Salivary Gland Ultrasonography in Primary Sjögren's Syndrome

The purpose of this study is to investigate the clinical manifestations in patients with early primary Sjögren's syndrome (pSS) based on the severity score found by salivary gland ultrasonography. Thirty-five newly diagnosed patients with early pSS were enrolled and divided into mild (score 0-1) and severe (score 2-3) groups according to the salivary gland ultrasonography grade (SGUS) scores at baseline. Clinical evaluation, ESSPRI and ESSDAI index values, sicca symptoms of the mouth, salivary capacity, and serum autoantibodies and cytokines were investigated. The mean age of pSS patients at diagnosis was 49.9 ± 11.9 years, and the mean duration of sicca symptoms was 0.58 years. ESSPRI (EULAR Sjögren's syndrome patient report index) and ESSDAI (EULAR Sjögren's syndrome disease index) scores were 15.97 and 4.77, respectively. Clinical manifestations, including the low production of saliva and autoantibody production, such as antinuclear antibodies, rheumatoid factor, and anti-SSA antibody, were found. A higher prevalence of rheumatoid factor (p = 0.0365) and antinuclear antibody (p = 0.0063) and a higher elevation of total IgG (p = 0.0365) were found in the severe group than in the mild group. In addition, the elevated titer of IL-25 was detected in the severe group than in the mild group. This observation indicated that salivary gland ultrasonography grade (SGUS) scans may help physicians diagnose pSS and the elevated titer of IL-25 in patients may be implicated in the pathogenesis of pSS.

Salivary gland epithelial cell in Sjögren's syndrome: Metabolic shift and altered mitochondrial morphology toward an innate immune cell function

Salivary gland epithelial cells (SGEC) are the main targets of the autoimmune reactivity in Sjögren's syndrome (SS). This study aimed to investigate the core proteomic differences between SS and Control- (Ct) -derived SGEC. Proteome analysis of cultured SGEC from five SS patients and four Ct was performed in a label-free quantitation format (LFQ). Electron microscopy was applied for analysis of the mitochondrial ultrastructure of SGEC in minor salivary gland sections from six SS patients and four Ct. Four hundred seventy-four proteins were identified differentially abundant in SS- compared to Ct-SGEC. After proteomic analysis, two distinct protein expression patterns were revealed. Gene ontology (GO) pathway analysis of each protein block revealed that the cluster with highly abundant proteins in SS-SGEC showed enrichment in pathways associated with membrane trafficking, exosome-mediated transport and exocytosis as well as innate immunity related mainly to neutrophil degranulation. In contrast, the low abundance protein cluster in SS-SGEC was enriched for proteins regulating the translational process of proteins related to metabolic pathways associated to mitochondria. Electron microscopy showed decreased total number of mitochondria in SS-SGEC, which appeared elongated and swollen with less and abnormal cristae compared to Ct-SGEC mitochondria. This study defines, for the first time, the core proteomic differences of SGEC between SS and Ct, substantiates the metamorphosis of SGEC into an innate immune cell and reveals that these cells are translationally shifted towards metabolism rewiring. These metabolic alterations are related mainly to mitochondria and are mirrored in situ with heavy morphological changes.

In patients with primary Sjögren's syndrome innate-like MAIT cells display upregulated IL-7R, IFN-γ, and IL-21 expression and have increased proportions of CCR9 and CXCR5-expressing cells

Introduction

Mucosal-associated invariant T (MAIT) cells might play a role in B cell hyperactivity and local inflammation in primary Sjögren's syndrome (pSS), just like previously studied mucosa-associated CCR9+ and CXCR5+ T helper cells. Here, we investigated expression of CCR9, CXCR5, IL-18R and IL-7R on MAIT cells in pSS, and assessed the capacity of DMARDs to inhibit the activity of MAIT cells.

Methods

Circulating CD161+ and IL-18Rα+ TCRVα7.2+ MAIT cells from pSS patients and healthy controls (HC) were assessed using flow cytometry, and expression of CCR9, CXCR5, and IL-7R on MAIT cells was studied. Production of IFN-γ and IL-21 by MAIT cells was measured upon IL-7 stimulation in the presence of leflunomide (LEF) and hydroxychloroquine (HCQ).

Results

The numbers of CD161+ and IL-18Rα+ MAIT cells were decreased in pSS patients compared to HC. Relative increased percentages of CD4 MAIT cells in pSS patients caused significantly higher CD4/CD8 ratios in MAIT cells. The numbers of CCR9 and CXCR5-expressing MAIT cells were significantly higher in pSS patients. IL-7R expression was higher in CD8 MAIT cells as compared to all CD8 T cells, and changes in IL-7R expression correlated to several clinical parameters. The elevated production of IL-21 by MAIT cells was significantly inhibited by LEF/HCQ treatment.

Conclusion

Circulating CD161+ and IL-18Rα+ MAIT cell numbers are decreased in pSS patients. Given their enriched CCR9/CXCR5 expression this may facilitate migration to inflamed salivary glands known to overexpress CCL25/CXCL13. Given the pivotal role of IL-7 and IL-21 in inflammation in pSS this indicates a potential role for MAIT cells in driving pSS immunopathology.

GABA Administration Ameliorates Sjogren’s Syndrome in Two Different Mouse Models

Sjögren’s syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltrates in the salivary and lachrymal glands resulting in oral and ocular dryness. There are no clinically approved therapies to slow the progression of SS. Immune cells possess receptors for the neurotransmitter GABA (GABA-Rs) and their activation has immunoregulatory actions. We tested whether GABA administration has potential for amelioration of SS in NOD.B10-H2^b and C57BL/6.NOD-Aec1Aec2 mice, two spontaneous SS models. Oral GABA treatment was initiated (1) after the development of sialadenitis but before the onset of overt symptoms, or (2) after the appearance of overt symptoms. When assessed weeks later, GABA-treated mice had greater saliva and tear production, as well as quicker times to salvia flow, in both SS mouse models. This was especially evident when GABA treatment was initiated after the onset of overt disease. This preservation of exocrine function was not accompanied by significant changes in the number or area of lymphocytic foci in the salivary or lachrymal glands of GABA-treated mice and we discuss the possible reasons for these observations. Given that GABA-treatment preserved saliva and tear production which are the most salient symptoms of SS and is safe for consumption, it may provide a new approach to help ameliorate SS.

The Transcriptome of Paired Major and Minor Salivary Gland Tissue in Patients With Primary Sjögren's Syndrome

Background

While all salivary glands (SGs) can be involved in primary Sjögren’s syndrome (pSS), their respective role in pathogenesis remains unclear. Our objective was to assess immunopathway activation in paired parotid and labial gland tissue from biopsy-positive and biopsy-negative pSS and non-SS sicca patients.

Methods

Paraffin-embedded, paired parotid and labial salivary gland tissue and peripheral blood mononuclear cells were obtained from 39 pSS and 20 non-SS sicca patients. RNA was extracted, complementary DNA libraries were prepared and sequenced. For analysis of differentially expressed genes (DEGs), patients were subdivided based on fulfillment of ACR-EULAR criteria and histopathology.

Results

With principal component analysis, only biopsy-positive pSS could be separated from non-SS sicca patients based on SG gene expression. When comparing the transcriptome of biopsy-positive pSS and biopsy-negative non-SS sicca patients, 1235 and 624 DEGs (FDR<0.05, log2FC<-1 or >1) were identified for parotid and labial glands, respectively. The number of DEGs between biopsy-negative pSS and non-SS sicca patients was scarce. Overall, transcript expression levels correlated strongly between parotid and labial glands (R² = 0.86, p-value<0.0001). Gene signatures present in both glands of biopsy-positive pSS patients included IFN-α signaling, IL-12/IL-18 signaling, CD3/CD28 T-cell activation, CD40 signaling in B-cells, DN2 B-cells, and FcRL4+ B-cells. Signature scores varied considerably amongst pSS patients.

Conclusion

Transcriptomes of paired major and minor SGs in pSS were overall comparable, although significant inter-individual heterogeneity in immunopathway activation existed. The SG transcriptome of biopsy-negative pSS was indistinguishable from non-SS sicca patients. Different patterns of SG immunopathway activation in pSS argue for personalized treatment approaches.

Lymphomagenesis predictors and related pathogenesis

Sjögren's syndrome (SS) is a systemic autoimmune disease characterised by a wide range of clinical manifestations and complications, including B-cell lymphoma. This study aims to describe the predictors associated with lymphomagenesis in patients with Sjögren's syndrome, emphasising the pathophysiological bases that support this association. We performed a review of the literature published through a comprehensive search strategy in PubMed/MEDLINE, Scopus, and Web of science. Forty publications describing a total of 45,208 patients with SS were retrieved. The predictors were grouped according to their pathophysiological role in the lymphoproliferation process. Also, some new biomarkers such as MicroRNAs, P2X7 receptor-NLRP3 inflammasome, Thymic stromal lymphopoietin, and Three-prime repair exonuclease 1 (TREX1) were identified. The knowledge of the pathophysiology allows the discrimination of markers that participate in the initial stages. Considering that the lymphoproliferation process includes the progression of lymphoma towards more aggressive subtypes, it is essential to recognise biomarkers associated with a worse prognosis.

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.

Contributions of Major Cell Populations to Sjögren's Syndrome

Sjögren’s syndrome (SS) is a female dominated autoimmune disease characterized by lymphocytic infiltration into salivary and lacrimal glands and subsequent exocrine glandular dysfunction. SS also may exhibit a broad array of extraglandular manifestations including an elevated incidence of non-Hodgkin’s B cell lymphoma. The etiology of SS remains poorly understood, yet progress has been made in identifying progressive stages of disease using preclinical mouse models. The roles played by immune cell subtypes within these stages of disease are becoming increasingly well understood, though significant gaps in knowledge still remain. There is evidence for distinct involvement from both innate and adaptive immune cells, where cells of the innate immune system establish a proinflammatory environment characterized by a type I interferon (IFN) signature that facilitates propagation of the disease by further activating T and B cell subsets to generate autoantibodies and participate in glandular destruction. This review will discuss the evidence for participation in disease pathogenesis by various classes of immune cells and glandular epithelial cells based upon data from both preclinical mouse models and human patients. Further examination of the contributions of glandular and immune cell subtypes to SS will be necessary to identify additional therapeutic targets that may lead to better management of the disease.

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.

Activation of Myd88-Dependent TLRs Mediates Local and Systemic Inflammation in a Mouse Model of Primary Sjögren's Syndrome

Toll-like receptors (TLRs) are important mediators of chronic inflammation in numerous autoimmune diseases, although the role of these receptors in primary Sjögren's syndrome (pSS) remains incompletely understood. Previous studies in our laboratory established Myd88 as a crucial mediator of pSS, although the disease-relevant ligands and the upstream signaling events that culminate in Myd88 activation have yet to be established. The objective of this study was to identify specific Myd88-dependent TLR-related pathways that are dysregulated both locally and systemically in a mouse model of pSS [NOD.B10Sn-H2^b/J (NOD.B10)]. We performed RNA-sequencing on spleens derived from NOD.B10 mice. We then harvested salivary tissue and spleens from Myd88-sufficient and deficient C57BL/10 (BL/10) and NOD.B10 mice and performed flow cytometry to determine expression of Myd88-dependent TLRs. We cultured splenocytes with TLR2 and TLR4 agonists and measured production of inflammatory mediators by ELISA. Next, we evaluated spontaneous and TLR4-mediated inflammatory cytokine secretion in NOD.B10 salivary tissue. Finally, we assessed spontaneous Myd88-dependent cytokine secretion by NOD.B10 salivary cells. We identified dysregulation of numerous TLR-related networks in pSS splenocytes, particularly those employed by TLR2 and TLR4. We found upregulation of TLRs in both the splenic and salivary tissue from pSS mice. In NOD.B10 splenic tissue, robust expression of B cell TLR1 and TLR2 required Myd88. Splenocytes from NOD.B10 mice were hyper-responsive to TLR2 ligation and the endogenous molecule decorin modulated inflammation via TLR4. Finally, we observed spontaneous secretion of numerous inflammatory cytokines and this was enhanced following TLR4 ligation in female NOD.B10 salivary tissue as compared to males. The spontaneous production of salivary IL-6, MCP-1 and TNFα required Myd88 in pSS salivary tissue. Thus, our data demonstrate that Myd88-dependent TLR pathways contribute to the inflammatory landscape in pSS, and inhibition of such will likely have therapeutic utility.

Cell-autonomous epithelial activation of AIM2 (absent in melanoma-2) inflammasome by cytoplasmic DNA accumulations in primary Sjögren's syndrome

Primary Sjögren's syndrome (SS) is characterized by chronic periductal inflammatory infiltrates in the salivary glands. Several previous studies have indicated that the ductal epithelia of SS patients play a pro-inflammatory role and manifest an intrinsically activated status, as demonstrated in cultured non-neoplastic ductal salivary gland epithelial cell (SGEC) lines. Herein, we investigated the activation of inflammasomes in the salivary epithelia of SS patients and non-SS controls, using salivary biopsy tissues and SGEC lines. The ductal epithelial cells of SS patients were found to display significant activation of the AIM2 (absent in melanoma-2) inflammasome. Such activation occurred in a cell-autonomous manner, as it was illustrated by the constitutively high expression of AIM2 activation-related genes, the presence of cytoplasmic ASC specks and the increased spontaneous IL-1β production observed in patients' SGEC lines. Since AIM2 activation is known to occur in response to cytoplasmic DNA, we further searched for the presence of undegraded extranuclear DNA in the SGEC lines and SG tissues of patients and controls. This investigation revealed marked cytoplasmic accumulations of damaged genomic DNA that co-localized with AIM2 in the specimens of SS patients (but not controls). The SGEC lines and the ductal tissues of SS patients were also found to manifest impaired DNase1 expression and activity, which possibly denotes defective cytoplasmic DNA degradation in patients' cells and AIM2 triggering thereof. In corroboration, DNase1-silencing in normal SGEC was shown to lead to high AIM2-related gene expression and IL-1β production. Our findings indicate that the cell-intrinsic activation status of ductal epithelia in SS patients owes to persistent epithelial AIM2 activation by aberrant cytoplasmic DNA build-up.

Expression of interleukin-18 in muscle tissue of patients with polymyositis or dermatomyositis and effects of conventional immunosuppressive treatment

Objectives

To investigate the expression of IL-18 in symptomatic and asymptomatic muscle tissues of patients with PM and DM and the effects of conventional immunosuppressive treatment on such expression.

Methods

Two cohorts of patients were included in this study. The first cohort consisted of 10 new-onset myositis patients. IL-18 expression was compared between symptomatic and asymptomatic muscle biopsies that were taken prior to treatment. The second cohort consisted of another 10 patients with repeated muscle biopsies before and after 8 months with conventional immunosuppressive treatment. Using immunohistochemistry, IL-18 expression in muscle tissues was compared before and after treatment. Biopsies from seven healthy individuals were included as controls.

Results

IL-18 expression was predominantly localized to inflammatory cells and capillaries in patients and mostly to capillaries in healthy controls. Total IL-18 expression in muscle tissues from the new-onset patients, at both symptomatic and asymptomatic sites, was significantly higher compared with healthy controls (P = 0.007 and P = 0.002) with no statistical difference in appearances between symptomatic and asymptomatic sites. The number of IL-18 positive capillaries was not different among symptomatic, asymptomatic and healthy muscles. Total IL-18 expression appeared lower in biopsies from patients receiving and improving with immunosuppressive treatment, particularly the number of IL-18 positive inflammatory cells but not the number of IL-18 positive capillaries, which was consistent with significantly decreased expression of CD68+ macrophages (P = 0.04).

Conclusion

IL-18 is highly expressed in muscle tissue in the context of inflammatory myopathies and based on its plausible effector functions could provide a novel therapeutic target in future.

Ablation of the Chaperone Protein ERdj5 Results in a Sjögren's Syndrome-Like Phenotype in Mice, Consistent With an Upregulated Unfolded Protein Response in Human Patients

Objective: Sjögren's syndrome (SS) is a chronic autoimmune disorder that affects mainly the exocrine glands. Endoplasmic reticulum (ER) stress proteins have been suggested to participate in autoimmune and inflammatory responses, either acting as autoantigens, or by modulating factors of inflammation. The chaperone protein ERdj5 is an ER-resident disulfide reductase, required for the translocation of misfolded proteins during ER-associated protein degradation. In this study we investigated the role of ERdj5 in the salivary glands (SGs), in association with inflammation and autoimmunity.

Methods:In situ expression of ERdj5 and XBP1 activation were studied immunohistochemically in minor SG tissues from primary SS patients and non-SS sicca-complaining controls. We used the mouse model of ERdj5 ablation and characterized its features: Histopathological, serological (antinuclear antibodies and cytokine levels), and functional (saliva flow rate).

Results: ERdj5 was highly expressed in the minor SGs of SS patients, with stain intensity correlated to inflammatory lesion severity and anti-SSA/Ro positivity. Moreover, SS patients demonstrated higher XBP1 activation within the SGs. Remarkably, ablation of ERdj5 in mice conveyed many of the cardinal features of SS, like spontaneous inflammation in SGs with infiltrating T and B lymphocytes, distinct cytokine signature, excessive cell death, reduced saliva flow, and production of anti-SSA/Ro and anti-SSB/La autoantibodies. Notably, these features were more pronounced in female mice.

Conclusions: Our findings suggest a critical connection between the function of the ER chaperone protein ERdj5 and autoimmune inflammatory responses in the SGs and provide evidence for a new, potent animal model of SS.

Emerging roles for chemokines and cytokines as orchestrators of immunopathology in Sjögren's syndrome

In primary SS (pSS), chemokines and cytokines orchestrate immunopathology driven by a complex network of interacting inflammatory cells. In recent years, the importance of chemotactic and non-chemotactic cytokines that control function, movement and placing of all cells within the inflamed exocrine glands and directing immunopathology has become increasingly clear. This paper reviews the current knowledge on chemokines and focuses on the emerging roles of novel chemotactic and non-chemotactic mediators in pSS. It highlights their contribution to pathogenic processes such as B cell hyperactivity and the formation of ectopic lymphoid structures. To this end, the role of acquired (CXCR5/CCR9 Th-cell-mediated) and innate (inflammasome/IL-1/IL-18-mediated) pathways in steering immunopathology is discussed.

Molecular Evidence for Precursors of Sjögren's Foci in Histologically Normal Lacrimal Glands

Understanding the formation of Sjogren’s lymphocytic infiltrates could permit earlier diagnosis and better outcomes. We submitted gene transcript abundances in histologically normal rabbit lacrimal glands to principal component analysis. The analysis identified a cluster of transcripts associated with Sjögren’s foci, including messenger RNAs (mRNAs) for C–X–C motif chemokine ligand 13 (CXCL13) and B-cell activating factor (BAFF), which dominated the major principal component. We interpreted the transcript cluster as the signature of a cluster of integrally functioning cells. Pregnancy and dryness increased the likelihood that the cluster would develop to high levels, but responses were subject to high levels of stochasticity. Analyzing microdissected samples from high- and low-cluster-level glands, we found that certain transcripts, including mRNAs for C–C motif chemokine ligand 21 (CCL21), CXCL13, cluster of differentiation 4 (CD4), CD28, CD25, BAFF, and interleukin 18 (IL-18) were significantly more abundant in immune cell clusters (ICs) from the high-cluster-level gland; mRNAs for CCL2, CD25, and IL-1RA were significantly more abundant in acinus-duct axis samples; mRNAs for CCL4, BAFF, IL-6, and IL-10 were more abundant in some acinus-duct samples; cells with high prolactin immunoreactivity were more frequent in interacinar spaces. In conclusion, integrated functional networks comprising Sjögren’s infiltrates, such as ICs, acinar cells, ductal cells, and interacinar cells, can form in histologically normal glands, and it is feasible to detect their molecular signatures.

Update on Pathogenesis of Sjogren's Syndrome

Sjogren's syndrome is a common autoimmune disease that presents with sicca symptoms and extraglandular features. Sjogren's syndrome is presumably as common as RA; yet it is poorly understood, underdiagnosed and undertreated. From the usual identity as an autoimmune exocrinopathy to its most recent designate as an autoimmune epithelitis - the journey of SS is complex. We herein review some of the most important milestones that have shed light on different aspects of pathogenesis of this enigmatic disease. This includes role of salivary gland epithelial cells, and their interaction with cells of the innate and adaptive immune system. Non-immune factors acting in concert or in parallel with immune factors may also be important. The risk genes identified so far have only weak association, nevertheless advances in genetics have enhanced understanding of disease mechanisms. Role of epigenetic and environmental role factors is also being explored. SS has also some unique features such as congenital heart block and high incidence of lymphoma; disease mechanisms accounting for these manifestations are also reviewed.

Smoking, disease characteristics and serum cytokine levels in patients with primary Sjögren's syndrome

Smoking affects several disease processes. Epidemiological studies have previously found a negative association between primary Sjögren’s syndrome (pSS) and smoking. The aim of this study was to examine whether markers of disease activity and cytokine expression in pSS patients differ between ever and never smokers. Fifty-one consecutive pSS patients and 33 population controls were included in the study. Clinical and standard laboratory parameters were registered. Serum cytokines (IL-1β, IL-2, IL-3, IL-4, IL-6, IL-8, IL-10, IL-12, IL-17, IL-18, IL-33, IFN-α, IFN-γ, TNF-α, EGF, BAFF, Fas-ligand, RANTES, TGF-β1) were assessed. A positive lip biopsy was less prevalent among ever smoking patients compared to never smokers (81 vs 100%; p = 0.03). However, except for TNF-α, which was higher in ever smokers, no differences in cytokine levels were found when comparing ever and never smoking pSS patients. Furthermore, no significant differences were found between ever and never smoking patients in the ESSDAI total score, IgG levels, or complement levels. However, IL-6, IL-12, IL-17 and IL-18 were significantly increased in pSS patients compared to controls. In this study, a negative association between ever smoking and positive lip biopsy was found, confirming previous reports. Expected differences in cytokine levels compared to controls were noted, but no major differences were found between ever and never smoking pSS patients. Taking into account the negative association between pSS diagnosis and smoking in epidemiological studies, possible explanations include a local effect of smoking on salivary glands rather than systemic effects by cigarette smoke.

Role of inflammasomes in inflammatory autoimmune rheumatic diseases

Inflammasomes are intracellular multiprotein complexes that coordinate anti-pathogenic host defense during inflammatory responses in myeloid cells, especially macrophages. Inflammasome activation leads to activation of caspase-1, resulting in the induction of pyroptosis and the secretion of pro-inflammatory cytokines including interleukin (IL)-1β and IL-18. Although the inflammatory response is an innate host defense mechanism, chronic inflammation is the main cause of rheumatic diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), and Sjögren's syndrome (SS). Since rheumatic diseases are inflammatory/autoimmune disorders, it is reasonable to hypothesize that inflammasomes activated during the inflammatory response play a pivotal role in development and progression of these diseases. Indeed, previous studies have provided important observations that inflammasomes are actively involved in the pathogenesis of inflammatory/autoimmune rheumatic diseases. In this review, we summarize the current knowledge on several types of inflammasomes during macrophage-mediated inflammatory responses and discuss recent research regarding the role of inflammasomes in the pathogenesis of inflammatory/autoimmune rheumatic diseases. This avenue of research could provide new insights for the development of promising therapeutics to treat inflammatory/autoimmune rheumatic diseases.

Cytokines as therapeutic targets in primary Sjögren syndrome

Primary Sjögren syndrome (SjS) is a systemic autoimmune disease that may affect 1 in 1000 people (overwhelmingly women) and that can be a serious disease with excess mortality due to severe organ-specific involvements and the development of B cell lymphoma; systemic involvement clearly marks the disease prognosis, and strongly suggests the need for closer follow-up and more robust therapeutic management. Therapy is established according to the organ involved and severity. As a rule, the management of systemic SjS should be organ-specific, with glucocorticoids and immunosuppressive agents limited to potentially-severe involvements; unfortunately, the limited evidence available for these drugs, together with the potential development of serious adverse events, makes solid therapeutic recommendations difficult. The emergence of biological therapies has increased the therapeutic armamentarium available to treat primary SjS. Biologics currently used in SjS patients are used off-label and are overwhelmingly agents targeting B cells, but the most recent studies are moving on into the evaluation of targeting specific cytokines involved in the SjS pathogenesis. The most recent etiopathogenic advances in SjS are shedding some light in the search for new highly-selective biological therapies without the adverse effects of the standard drugs currently used (corticosteroids and immunosuppressant drugs). This review summarizes the potential pharmacotherapeutic options targeting the main cytokine families involved in the etiopathogenesis of primary SjS and analyzes potential insights for developing new therapies.

Myd88 is required for disease development in a primary Sjögren's syndrome mouse model

Sjögren's syndrome (SS) is an autoimmune disease that often results in diminished exocrine gland function. SS patients also experience systemic disease manifestations, including hypergammaglobulinemia and pulmonary and renal pathoses. MyD88 is a ubiquitously expressed adaptor molecule used by all immune cells that is required for IL-1 receptor (IL-1R), IL-18R, and most TLR signaling. The precise role of MyD88 in SS has not been evaluated, although this adaptor is critical for development of lupus, a related autoimmune disease. This study tested the hypothesis that Myd88-mediated signaling is required for local and systemic SS manifestations. To this end, we generated NOD.B10Sn-H2^b /J (NOD.B10) mice that are deficient in Myd88 (NOD.B10 ^Myd88-/- ). We found that NOD.B10 animals that lack Myd88 show reduced exocrine and extraglandular inflammation. Moreover, these animals are protected from loss of salivary flow. Splenocytes from NOD.B10 ^Myd88-/- mice did not up-regulate activation markers or secrete IL-6 in response to a Myd88-dependent agonist, although BCR signaling remained intact. Finally, IgM, IgG, and anti-nuclear autoantibodies were reduced in NOD.B10 ^Myd88-/- mice compared with the parental strain. These data demonstrate that Myd88 is a crucial mediator of local and systemic SS disease manifestations.

Innate immunity in Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disease of exocrine tissue that primarily affects women. Although patients typically experience xerostomia and xerophthalmia, numerous systemic disease manifestations are seen. Innate immune hyperactivity is integral to many autoimmune diseases, including SS. Results from SS mouse models suggest that innate immune dysregulation drives disease and this is a seminal event in SS pathogenesis. Findings in SS patients corroborate those in mouse models, as innate immune cells and pathways are dysregulated both in exocrine tissue and in peripheral blood. We will review the role of the innate immune system in SS pathogenesis. We will discuss the etiology of SS with an emphasis on innate immune dysfunction. Moreover, we will review the innate cells that mediate inflammation in SS, the pathways implicated in disease, and the potential mechanisms governing their dysregulation. Finally, we will discuss emerging therapeutic approaches to target dysregulated innate immune signaling in SS.

IL-18 associated with lung lymphoid aggregates drives IFNγ production in severe COPD

Background

Increased interferon gamma (IFNγ) release occurs in Chronic Obstructive Pulmonary Disease (COPD) lungs. IFNγ supports optimal viral clearance, but if dysregulated could increase lung tissue destruction.

Methods

The present study investigates which mediators most closely correlate with IFNγ in sputum in stable and exacerbating disease, and seeks to shed light on the spatial requirements for innate production of IFNγ, as reported in mouse lymph nodes, to observe whether such microenvironmental cellular organisation is relevant to IFNγ production in COPD lung.

Results

We show tertiary follicle formation in severe disease alters the dominant mechanistic drivers of IFNγ production, because cells producing interleukin-18, a key regulator of IFNγ, are highly associated with such structures. Interleukin-1 family cytokines correlated with IFNγ in COPD sputum. We observed that the primary source of IL-18 in COPD lungs was myeloid cells within lymphoid aggregates and IL-18 was increased in severe disease. IL-18 released from infected epithelium or from activated myeloid cells, was more dominant in driving IFNγ when IL-18-producing and responder cells were in close proximity.

Conclusions

Unlike tight regulation to control infection spread in lymphoid organs, this local interface between IL-18-expressing and responder cell is increasingly supported in lung as disease progresses, increasing its potential to increase tissue damage via IFNγ.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0641-7) contains supplementary material, which is available to authorized users.

The P2X7 receptor-NLRP3 inflammasome complex predicts the development of non-Hodgkin's lymphoma in Sjogren's syndrome: a prospective, observational, single-centre study

BACKGROUND

P2X7 receptor (P2X7R), trigger of acute inflammatory responses via the NLRP3 inflammasome, is hyperfunctioning in patients with Sjögren's syndrome (SS), where it stimulates IL-18 production. Some patients with SS develop a mucosa-associated lymphoid tissue non-Hodgkin's lymphoma (MALT-NHL).

OBJECTIVES

To prospectively evaluate the involvement and the putative prognostic role of this inflammatory pathway in the development of MALT-NHL.

METHODS

A total of 147 women with SS have been prospectively followed for a mean of 52 months, relating the expression and function of the P2X7R-inflammasome axis in salivary glands and circulating lymphomonocytes to the prognosis and the degree of the disease.

RESULTS

At baseline, gene expression of P2X7R and of the inflammasome components NLRP3, caspase-1 and IL-18 increased according to the presence of germinative centres and was higher in autoantibody-positive individuals and strongly higher in those developing a MALT-NHL over the follow-up. Glandular expression of IL-18 was threefold higher in MALT-NHL than in controls or in the other patients with SS. P2X7R did not colocalize with generic markers of inflammatory infiltrate, like CD20, being selectively expressed by epithelial cells. P2X4R, sharing functional characteristics with P2X7R, did not differ in SS and controls. The increased P2X7R gene and protein expression was tissue specific, no difference being observed in peripheral lymphomonocytes between SS with MALT-NHL and SS not developing MALT-NHL.

CONCLUSION

We propose the P2X7R-inflammasome axis as a novel potential pathway involved in both SS exocrinopathy and lymphomagenesis, reinforcing the hypothesis of a key role of IL-18, via its increased P2X7R-mediated production, in the pathogenesis of lymphoproliferative malignancies, and opening novel opportunities for the early diagnosis of lymphoproliferative complications and the development of potential targeted therapies.

Insight into pathogenesis of Sjögren's syndrome: Dissection on autoimmune infiltrates and epithelial cells

Sjögren's syndrome (SS) is a chronic autoimmune disease with broad clinical spectrum, extending from benign exocrinopathy to severe systemic disease and lymphoma development. The glandular and extraglandular dysfunction of SS is associated with lymphocytic infiltrates that invade the epithelial structures of affected organs. The in-depth study of autoimmune lesions in the minor salivary glands (MSG), which are the major target-organ of SS responses, revealed that the lymphocytic infiltrates vary in severity and composition among SS-patients, are full-blown at diagnosis and remain unchanged thereafter. Although the pathogenetic pathways underlying SS have not yet elucidated, it is well-established that glandular epithelial cells are central regulators of local autoimmune responses. Moreover, chronic inflammation affects epithelial function and phenotype, which strengthens or weakens their immunoregulatory/secretory function, leading to deterioration of autoimmune phenomena. Herein, the current findings regarding the autoimmune lesions, the role of epithelial cells and their interaction with infiltrating lymphocytic cells are discussed.

Is it Sjögren's syndrome or burning mouth syndrome? Distinct pathoses with similar oral symptoms

Sjögren's syndrome (SS) and burning mouth syndrome (BMS) typically occur in postmenopausal women. Although these conditions have significantly different etiopathogeneses, patients with SS or BMS often present with analogous oral complaints. The similarities between the two conditions have led to considerable confusion on the part of medical and dental practitioners, and those with BMS or SS often wait years to receive a diagnosis. Therefore, it is imperative for clinicians to understand the characteristic subjective and objective features of each disease and how these can be used to distinguish them. This review will discuss the proposed etiology, clinical manifestations, histopathology, diagnostic criteria, and patient management of SS and BMS. We also identify key differences between the two pathoses that aid in establishing the correct diagnosis. Recognition of the defining features of each condition will lead to reduced time to diagnosis and improved patient management for these poorly understood conditions.

Elevated IL-37, IL-18 and IL-18BP serum concentrations in patients with primary Sjögren's syndrome

The objectives of this study were to examine the serum levels of interleukin (IL)-37 and its clinical association in patients with primary Sjögren's syndrome (pSS) and to investigate whether or not IL-37 participates in the regulation of the pathogenesis of pSS. ELISA was used to analyse the serum levels of IL-37, total IL-18 and IL-18 binding protein (IL-18BP). The level of free IL-18 was calculated based on the mass action law. The correlations between the IL-37 serum levels with the laboratory values and the total IL-18 and IL-18BP serum levels were analyzed by a Spearman's correlation test. The serum levels of IL-37 in the patients with pSS were significantly increased compared with the healthy controls (HCs). The levels were especially elevated in the patients with pSS with positive anti-Ro/SSA and/or anti-La/SSB antibodies. Furthermore, the patients with pSS showed high serum levels of total IL-18, free IL-18 and IL-18BP compared with the HCs. Strikingly, the IL-37 levels were significantly positively correlated with the antibody levels in the patients with pSS, including rheumatoid factor, anti-Ro/SSA, and anti-La/SSB and the total IL-18 and IL-18BP serum levels. The serum levels of IL-37, which were correlated with antibody production and the serum levels of total IL-18 and IL-18BP, were elevated in the patients with pSS. IL-37, an important anti-inflammatory cytokine, may participate in the regulation of the pathogenesis of pSS.

Analysis of the cell populations composing the mononuclear cell infiltrates in the labial minor salivary glands from patients with rheumatoid arthritis and sicca syndrome

OBJECTIVES

Sicca symptoms occur in around 30% of rheumatoid arthritis (RA) patients. Herein, we examined the characteristics of RA patients bearing sicca symptomatology (RA-sicca) with a special focus on the immunohistopathological features of their labial minor salivary gland (LMSG) biopsies.

METHODS

Our cohort included 100 consecutive RA patients which were interrogated using a sicca symptoms questionnaire. Positive responders were evaluated for ocular and oral dryness and underwent an LMSG biopsy. All samples were immunohistochemically evaluated for the presence and distribution of specific leukocyte subsets using appropriate markers and for the expression of certain immunoregulatory molecules by salivary gland epithelial cells. Positively stained and total mononuclear cells (MNC) were counted in the entire section. Counts were expressed as cell frequency (percentage of cell type number/total infiltrating MNC number).

RESULTS

In the majority (86.1%) of the 44 RA-sicca cases, periductal infiltrates were observed in LMSG biopsies. The frequencies of infiltrating cell subtypes and their correlation with lesion severity were different from that previously described in primary Sjögren's syndrome (pSS). Moreover, DCs and ΜΦs frequencies were increased in RA-sicca patients who had a biopsy focus score <1 and absence of anti-Ro/anti-La autoantibodies, in contrast to what was observed for B cells. In about half of the biopsies, salivary gland epithelial cells expressed CD80/B7.1 molecules, most commonly in patients with a positive biopsy or anti-Ro/anti-La autoantibodies.

CONCLUSION

LMSG infiltrates composition in RA-sicca patients is distinct from that described in pSS. These differences, further attest to diverse pathophysiologic processes operating in these two entities.

Salivary Gland Pathology in Sjögren's Syndrome

Primary Sjögren syndrome (pSS) can be considered a systemic autoimmune disease with a strong organ bias. The involvement of the exocrine glands is prevalent and drives the pathognomonic manifestations of dryness that define the sicca syndrome. The salivary glands also represent the hub of pSS pathology. Elements belonging to both innate and acquired immune responses have been described at this site that contribute to disease establishment and progression. The interaction between those elements and their relative contributions to the clinical manifestations and lymphoma progression largely remain to be addressed.

Ectopic expression of CXCL13, BAFF, APRIL and LT-β is associated with artery tertiary lymphoid organs in giant cell arteritis

OBJECTIVES

To investigate whether artery tertiary lymphoid organs (ATLOs) are present in giant cell arteritis (GCA) and that their formation is associated with the ectopic expression of constitutive lymphoid tissue-homing chemokines.

METHODS

Reverse transcriptase PCR, immunohistochemical and immunofluorescence analysis were used to determine the presence of ectopic ATLOs in GCA and the expression of chemokines/chemokine receptors and cytokines involved in lymphoneogenesis in the temporal artery samples obtained from 50 patients with GCA and 30 controls. The presence of lymphatic conduits, of follicular dendritic cells (FDCs) precursors and lymphoid tissue inducer cells was also investigated. Finally, expression of CXCL13, B cell activating factor (BAFF), a proliferation-inducing ligand (APRIL) and CCL21 by isolated myofibroblasts was evaluated before and after stimulation with Toll-like receptors (TLRs) agonists and cytokines.

RESULTS

ATLOs were observed in the media layer of 60% of patients with GCA in close proximity to high endothelial venules and independently by the age of patients and the presence of atherosclerosis. ATLO formation was also accompanied by the expression of CXCL13, BAFF, a proliferation-inducing ligand (APRIL), lymphotoxin (LT)-β, interleukin (IL)-17 and IL-7, the presence of FDC precursors and of lymphoid conduits. Stimulation of myofibroblasts with TLR agonists and cytokines resulted in the upregulation of BAFF and CXCL13.

CONCLUSIONS

ATLOs occur in the inflamed arteries of patients with GCA possibly representing the immune sites where immune responses towards unknown arterial wall-derived antigens may be organised.

Sex differences in Sjögren's syndrome: a comprehensive review of immune mechanisms

Autoimmune diseases (ADs) are estimated to affect between 5 and 8 % of the US population, and approximately 80 % of these patients are women. Sjögren’s syndrome (SS) is an AD that occurs predominately in women over men (16:1). The hallmark characteristic of SS is diminished secretory production from the primary exocrine gland and the lacrimal or salivary glands resulting in symptoms of dry eye and mouth. The disease is believed to be mediated by an inflammatory and autoantibody response directed against salivary and lacrimal gland tissues. This review will examine the literature on sex differences in the immune response of patients and animal models of Sjögren’s syndrome in order to gain a better understanding of disease pathogenesis.

Interleukin (IL)-22 receptor 1 is over-expressed in primary Sjogren's syndrome and Sjögren-associated non-Hodgkin lymphomas and is regulated by IL-18

The aim of this study was to elucidate more clearly the role of interleukin (IL)-18 in modulating the IL-22 pathway in primary Sjögren's syndrome (pSS) patients and in pSS-associated lymphomas. Minor salivary glands (MSGs) from patients with pSS and non-specific chronic sialoadenitis (nSCS), parotid glands biopsies from non-Hodgkin lymphomas (NHL) developed in pSS patients, were evaluated for IL-18, IL-22, IL-22 receptor 1 (IL-22R1), IL-22 binding protein (IL-22BP) and signal transducer and activator of transcription-3 (STAT-3) expression. MSGs IL-22R1-expressing cells were characterized by confocal microscopy and flow cytometry in pSS, nSCS and healthy controls . The effect of recombinant IL-18 and IL-22 on peripheral blood mononuclear cells (PBMCs) from pSS and nSCS was studied by flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR). MSGs of pSS and NHL were characterized by an imbalance between IL-22 and IL-22BP protein expression, with IL-18 and IL-22BP being expressed in a mutually exclusive manner and IL-18 and IL-22R1 being correlated directly. Aberrant expression of IL-22R1, induced by IL-18, was observed only among tissue and circulating myeloid cells of pSS patients and macrophages of NHL tissues of pSS patients, but not nSCS. IL-22R1 expression on PBMC of pSS was functional, as its stimulation with recombinant IL-22 significantly up-regulated the expression of STAT-3, IL-17 and IL-22. An IL-18-dependent aberrant expression of IL-22R1 on cells of haematopoietic origin seems to be a specific immunological signature of patients with pSS and pSS-associated lymphomas.

MicroRNA-146a: A Dominant, Negative Regulator of the Innate Immune Response

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules that can play critical roles as regulators of numerous pathways and biological processes including the immune response. Emerging as one of the most important miRNAs to orchestrate immune and inflammatory signaling, often through its recognized target genes, IRAK1 and TRAF6, is microRNA-146a (miR-146a). MiR-146a is one, of a small number of miRNAs, whose expression is strongly induced following challenge of cells with bacterial endotoxin, and prolonged expression has been linked to immune tolerance, implying that it acts as a fine-tuning mechanism to prevent an overstimulation of the inflammatory response. In other cells, miR-146a has been shown to play a role in the control of the differentiation of megakaryocytic and monocytic lineages, adaptive immunity, and cancer. In this review, we discuss the central role prescribed to miR-146a in innate immunity. We particularly focus on the role played by miR-146a in the regulation and signaling mediated by one of the main pattern recognition receptors, toll/IL-1 receptors (TLRs). Additionally, we also discuss the role of miR-146a in several classes of autoimmune pathologies where this miRNA has been shown to be dysregulated, as well as its potential role in the pathobiology of neurodegenerative diseases.

The role of innate and lymphoid IL-22-producing cells in the immunopathology of primary Sjögren's syndrome

In primary Sjögren's syndrome (pSS) a complex of interconnections between epithelial barrier, innate and adaptive immunity occurs. IL-22 is a pleiotropic cytokine that in pSS may be placed at the intersection of the adaptive and innate branches of immunity. Some evidence suggests that, in pSS, IL-22 may play a prominent pro-inflammatory role driving the early phase of tissue and systemic inflammation and participating in the self-perpetuation of disease. Despite contradictory data in literature about the role of NK cells in pSS, recent data also suggest an important contribution of this subset of cells of the innate immune system in the development and perpetuation of inflammation. Here, we discuss the role of IL-22 in the pathogenesis of pSS and in epithelial barrier function.

The value of animal models to study immunopathology of primary human Sjögren's syndrome symptoms

Sjögren's syndrome (SjS) is a complex chronic autoimmune disease of multifactorial etiology that results in eventual loss of secretory function in the exocrine glands. The challenges towards finding a therapeutic prevention or treatment for SjS are due primarily to a lack of understanding in the pathophysiological and clinical progression of the disease. In order to circumnavigate this problem, there is a need for appropriate animal models that resemble the major phenotypes of human SjS and deliver a clear underlying biological or molecular mechanism capable of defining various aspects for the disease. Here, we present an overview of SjS mouse models that are providing insight into the autoimmune process of SjS and advance our focus on potential diagnostic and therapeutic targets.

Alum, an aluminum-based adjuvant, induces Sjögren's syndrome-like disorder in mice

OBJECTIVES

Adjuvant-induced innate immune responses have been suspected to play a role in the initiation of certain autoimmune disorders. This study investigates the role of alum, an aluminum-based adjuvant in the induction of Sjögren's syndrome-like disorder in mice.

METHODS

Inbred, female New Zealand Mixed (NZM) 2758 strain of mice were injected with alum. Control mice were treated similarly with PBS. The mice were monitored for salivary gland dysfunction by measuring pilocarpine-induced salivation. Presence of lymphocytic infiltrates within the submandibular glands was studied by histopathology. Autoantibodies to Ro and La proteins were analysed by ELISA and the presence of anti-nuclear antibodies (ANA) was analysed by indirect immunofluorescence.

RESULTS

By eight weeks after treatment, the saliva production in the alum-treated mice was significantly decreased in comparison to the PBS-treated mice. This functional loss persisted till the termination of experiments at 20 wks. The incidence and severity of sialoadenitis was significantly higher in the alum-treated mice. Although there were no differences in the levels of anti-Ro/La autoantibodies in sera of alum and PBS-treated groups, the alum group showed higher ANA reactivity.

CONCLUSIONS

In the NZM2758 mice, alum induces a Sjögren's syndrome-like disorder that is characterised by chronic salivary gland dysfunction and the presence of lymphocytic infiltrates within the salivary glands. Thus, the potential of aluminum-based adjuvants for induction of autoimmunity should be closely monitored in individuals genetically susceptible to developing autoimmune disorders.

CX3CL1 and CX3CR1 expression in tertiary lymphoid structures in salivary gland infiltrates: fractalkine contribution to lymphoid neogenesis in Sjogren's syndrome

OBJECTIVES

Primary SS is an autoimmune disease characterized by chronic lymphocytic inflammation and ectopic germinal centre (GC) formation within salivary glands. Fractalkine (CX3CL1), associated with the pathogenesis of RA, is the sole member of the CX3C chemokine (CK) family and acts as an adhesion and chemotactic molecule. The objectives of this work are to determine to what extent CX3CL1 and its receptor CX3CR1 expression might be altered in salivary glands obtained from patients and to establish whether these CKs might be involved in SS ectopic lymphoneogenesis.

METHODS

We assessed the presence of CX3CL1 protein in sera by ELISA in 21 patients with primary SS, 11 patients with Sicca syndrome (Sicca), 20 RA patients and 10 blood donors. Histological evaluation was performed on sequential sections of salivary gland tissue. Using TaqMan RT-PCR we studied CX3CL1 and CX3CR1 mRNA expression in salivary gland tissues from a molecular point of view.

RESULTS

Increased serum levels of CX3CL1 protein were observed in SS patients compared with controls (P < 0.0001) and in RA patients compared with controls (P < 0.0001), but no difference was found between Sicca patients and controls (P = 0.22). We identified histologically the cells expressing CX3CL1 and CX3CR1 in salivary glands of SS patients and we localized the molecule within tertiary lymphoid structures. Finally, the mRNA levels of the CK and its receptor were up-regulated in SS salivary glands.

CONCLUSION

We believe that our findings point to the need for future studies on CX3CL1 and CX3CR1 proteins as contributors to the formation of ectopic GCs and possibly as a new tool in the evaluation and diagnosis of SS.

The P2X7 receptor-inflammasome complex has a role in modulating the inflammatory response in primary Sjögren's syndrome

OBJECTIVE

Innate and adaptive immunity may contribute to gland dysfunction in patients with primary Sjögren's syndrome (pSS). The P2X7 receptor (P2X7 R)-NLRP3 inflammasome complex modulates the release of the inflammatory cytokines IL-1β and IL-18. The presence of P2X7 R in salivary glands suggests an interesting scenario for the initiation and amplification of the innate immune response in pSS. Therefore, the aim of this study was to assess the role of the P2X7 R-NLRP3 inflammasome in pSS.

SUBJECTS AND METHODS

Twenty-one consecutive patients with pSS according to the American-European Consensus Group criteria and 15 patients with sicca syndrome (i.e. without Sjögren's syndrome, non-SS) were enrolled in this study, together with six control (CTL) subjects. Expression of the P2X7R-NLRP3 platform and IL-18 was determined by real-time PCR and western blotting in gland specimens and peripheral lymphomonocytes; data were related to patients\x92 clinical, serological and histopathological characteristics. The presence of IL-18 was determined in gland and saliva samples.

RESULTS

P2X7 R expression was significantly higher in salivary glands from individuals with pSS than in those from non-SS and CTL subjects. Accordingly, the gene expression levels of the inflammasome components NLRP3, ASC and caspase-1 were significantly higher in pSS gland specimens, and this was paralleled by an increased expression of mature IL-18 in pSS saliva samples. The expression of both the P2X7 R and the inflammasome components was a marker of disease-related glandular involvement, being increased in patients with anti-Ro/SSA positivity and correlated with focus score.

CONCLUSION

The results of this study suggest an involvement of the P2X7 R-inflammasome-caspase-1-IL-18 axis in the development of pSS exocrinopathy. This finding provides the basis for studying the complex mechanisms underlying pSS, as well as for developing novel potential therapeutic strategies.

Reciprocal relation between GADD153 and Del-1 in regulation of salivary gland inflammation in Sjögren syndrome

Endoplasmic reticulum (ER) stress response is a pivotal regulator of inflammation and cell death. An integral component of ER stress-induced apoptosis is expression of growth arrest- and DNA damage-inducible protein 153 (GADD153). Further, ER stress response is implicated in leukocyte adhesion and recent studies have discovered endogenous inhibitors of leukocyte adhesion including the developmental endothelial locus-1 (Del-1). Accordingly, we tested the hypothesis that Sjögren's syndrome (SS) is associated with increased salivary gland expression of GADD153 and increased leukocyte infiltration in association with decreased Del-1 thereby contributing to inflammation and cell death. We utilized the non-obese diabetic (NOD) mice, a model of SS-like disease, in association with immunostaining and flow cytometry-based studies. Salivary glands of 14-week-old NOD mice displayed a) increased GADD153 expression, b) marked reduction in Del-1, c) inflammatory cell infiltrates including CD3+ T and CD19+ B lymphocytes as well as M1 and M2 macrophages and d) increased pro-inflammatory interleukin (IL)-17 but reduced anti-inflammatory cytokine, IL-10. These changes were accompanied with disruption of mitochondrial membrane potential and significant increase in apoptosis and necrosis of salivary gland cells of NOD than control mice. Our collective observations suggested that GADD153 directly and/or indirectly through downregulation of Del-1 contributes importantly to salivary gland inflammation and cell death. To establish the relevance of GADD153 and Del-1 for the human condition, lower lip biopsy samples of non-SS subjects and those with a diagnosis of SS were subjected to immunohistochemistry. The results show intense GADD153 immunostaining but marked reduction in Del-1 expression in biopsy samples of SS compared to non-SS subjects. Collectively, the results indicate that GADD153 regulates inflammation and cell death in salivary gland in SS. Further, Del-1 expression likely provides a mechanistic link between increased GADD153 and leukocyte infiltration and accompanying inflammation of salivary gland tissue in this condition.

The important role of T cells and receptor expression in Sjögren's syndrome

Sjögren's syndrome (SjS), an autoimmune disease characterized by exocrine gland dysfunction leading to dry mouth and dry eye diseases, is typified by progressive leucocyte infiltrations of the salivary and lacrimal glands. Histologically, these leucocyte infiltrations generally establish periductal aggregates, referred to as lymphocytic foci (LF), which occasionally appear as germinal centre (GC)-like structures. The formation and organization of these LF suggest an important and dynamic role for helper T cells (TH), specifically TH1, TH2 and the recently discovered TH17, in development and onset of clinical SjS, considered a B cell-mediated hypersensitivity type 2 disease. Despite an ever-increasing focus on identifying the underlying aetiology of SjS, defining factors that initiate this autoimmune disease remain a mystery. Thus, determining interactions between infiltrating TH cells and exocrine gland tissue (auto-)antigens represents a fertile research endeavour. This review discusses pathological functions of TH cells in SjS, the current status of TH cell receptor gene rearrangements associated with human and mouse models of SjS and potential future prospects for identifying receptor-autoantigen interactions.

Epistasis with HLA DR3 implicates the P2X7 receptor in the pathogenesis of primary Sjögren's syndrome

INTRODUCTION

The aim of this study was to examine the association between functional polymorphisms in the pro-inflammatory P2X7 receptor and the Ro/La autoantibody response in primary Sjögren's syndrome (pSS).

METHODS

Twelve functional P2RX7 polymorphisms were genotyped in 114 pSS patients fulfilling the Revised American-European Consensus Criteria for pSS, and 136 controls. Genotyping of the A1405G (rs2230912) polymorphism was performed on a replication cohort consisting of 281 pSS patients and 534 controls. P2X7 receptor function in lymphocytes and monocytes was assessed by measurement of ATP-induced ethidium+ uptake. Serum IL-18 levels were determined by ELISA.

RESULTS

The minor allele of P2RX7 A1405G is a tag for a common haplotype associated with gain in receptor function, as assessed by ATP-induced ethidium+ uptake. A positive association between 1405G and anti-Ro±La seropositive pSS patients was observed in Cohort 1. Although not replicated in Cohort 2, there was a consistent, significant, negative epistatic interaction effect with HLA-DR3 in seropositive pSS patients from both cohorts, thereby implicating this gain of function variant in the pathogenesis of pSS. Serum IL-18 was elevated in seropositive pSS patients, but was not influenced by P2RX7 A1405G.

CONCLUSIONS

The P2RX7 1405G gain-of-function haplotype may be a risk factor for seropositive pSS in a subset of subjects who do not carry HLA risk alleles, but has no effect in subjects who do (epistasis). Potential mechanisms relate to autoantigen exposure and inflammatory cytokine expression. The observed elevation of IL-18 levels is consistent with P2X7 receptor activation in seropositive pSS patients. Collectively these findings implicate P2X7 receptor function in the pathogenesis of pSS.

Association of MicroRNA-146a with autoimmune diseases

MicroRNAs (miRNAs) are a group of approximately 20-22-nucleotide-long non-coding RNAs that repress target gene expression through mRNA degradation and translation inhibition. MiRNA (miR)-146a, located in the second exon of the LOC285628 gene on human chromosome 5, is a negative regulator in immune and inflammatory responses. Studies have indicated that miR-146a is associated with the pathogenesis of several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome. In this review, emphasis will be laid on the recent progress in the functional roles of miR-146a in these autoimmune diseases.

Emerging avenues linking inflammation, angiogenesis and Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disease characterized by an inflammatory mononuclear infiltration and the destruction of epithelial cells of the lachrymal and salivary glands. The aetiology is unknown. The expression "autoimmune epithelitis" has been proposed as an alternative to SS, in view of the emerging central role of the epithelial cells in the disease pathogenesis. At the biomolecular level, the epithelial cells play an important role in triggering the autoimmune condition via antigen presentation, apoptosis, and chemokine and cytokines release. Inflammation and angiogenesis are frequently coupled in the pathological conditions associated to autoimmune diseases, and an angiogenic imbalance contributes to the pathogenesis of a number of inflammatory disorders. This work reviews the current knowledge of the molecular and cellular mechanisms underlying the pathogenesis of the inflammatory reactions that characterize SS. The literature and our data on the role of angiogenesis in the pathophysiology of the disease are discussed.

Role of lymphoid chemokines in the development of functional ectopic lymphoid structures in rheumatic autoimmune diseases

A sizeable subset of patients with the two most common organ-specific rheumatic autoimmune diseases, rheumatoid arthritis (RA) and Sjögren's syndrome (SS) develop ectopic lymphoid structures (ELS) in the synovial tissue and salivary glands, respectively. These structures are characterized by perivascular (RA) and periductal (SS) clusters of T and B lymphocytes, differentiation of high endothelial venules and networks of stromal follicular dendritic cells (FDC). Accumulated evidence from other and our group demonstrated that the formation and maintenance of ELS in these chronic inflammatory conditions is critically dependent on the ectopic expression of lymphotoxins (LT) and lymphoid chemokines CXCL13, CCL19, CCL21 and CXCL12. In this review we discuss recent advances highlighting the cellular and molecular mechanisms, which regulate the formation of ELS in RA and SS, with particular emphasis on the role of lymphoid chemokines. In particular, we shall focus on the evidence that in the inflammatory microenvironment of the RA synovium and SS salivary glands, several cell types, including resident epithelial, stromal and endothelial cells as well as different subsets of infiltrating immune cells, have been shown to be capable of producing lymphoid chemokines. Finally, we summarize accumulating data supporting the conclusion that ELS in RA and SS represent functional niches for B cells to undergo affinity maturation, clonal selection and differentiation into plasma cells autoreactive against disease-specific antigens, thus contributing to humoral autoimmunity over and above that of secondary lymphoid organs.

Inducible tertiary lymphoid structures, autoimmunity, and exocrine dysfunction in a novel model of salivary gland inflammation in C57BL/6 mice

Salivary glands in patients with Sjögren's syndrome (SS) develop ectopic lymphoid structures (ELS) characterized by B/T cell compartmentalization, the formation of high endothelial venules, follicular dendritic cell networks, functional B cell activation with expression of activation-induced cytidine deaminase, as well as local differentiation of autoreactive plasma cells. The mechanisms that trigger ELS formation, autoimmunity, and exocrine dysfunction in SS are largely unknown. In this article, we present a novel model of inducible ectopic lymphoid tissue formation, breach of humoral self-tolerance, and salivary hypofunction after delivery of a replication-deficient adenovirus-5 in submandibular glands of C57BL/6 mice through retrograde excretory duct cannulation. In this model, inflammation rapidly and consistently evolves from diffuse infiltration toward the development of SS-like periductal lymphoid aggregates within 2 wk from AdV delivery. These infiltrates progressively acquire ELS features and support functional GL7(+)/activation-induced cytidine deaminase(+) germinal centers. Formation of ELS is preceded by ectopic expression of lymphoid chemokines CXCL13, CCL19, and lymphotoxin-β, and is associated with development of anti-nuclear Abs in up to 75% of mice. Finally, reduction in salivary flow was observed over 3 wk post-AdV infection, consistent with exocrine gland dysfunction as a consequence of the inflammatory response. This novel model has the potential to unravel the cellular and molecular mechanisms that regulate ELS formation and their role in exocrine dysfunction and autoimmunity in SS.

The role of ectopic germinal centers in the immunopathology of primary Sjögren's syndrome: a systematic review

OBJECTIVES

To determine whether the presence of germinal centers (GCs) in salivary glands of patients with primary Sjögren's syndrome (pSS) is related to the severity of disease course and distinct immunopathology features.

METHODS

A systematic search was performed in September 2011 for terms and synonyms of Sjögren's syndrome and germinal centers. A total of 80 articles were retrieved, of which 16 were included for (meta-) analysis.

RESULTS

GC morphology was present in a mean ± SD 25.1 ± 5.0% of pSS patients. Mean lymphocyte focus scores were 1.25 points higher in patients with GCs as compared to those without GCs. Saliva production was reduced in patients with GCs, although this did not reach statistical significance. Percentages of patients positive for rheumatoid factor, anti-Sjögren's syndrome A (SSA), and anti-Sjögren's syndrome B (SSB) antibodies were significantly higher in patients with GCs (mean increase, 15%, 18%, and 18%, respectively). Additionally, patients with GCs were characterized by enhanced levels of local and systemic proinflammatory mediators. Importantly, these patients have a higher risk of lymphoma development (14% versus 1%).

CONCLUSIONS

Patients with GCs are characterized by more severe disease, although the small number of studies and their design hamper generalizability of results. The precise mechanisms that contribute to the development and persistence of germinal centers in pSS are largely unknown. This and the strongly increased risk of lymphoma development warrant intensive studies for the role of germinal centers in the immunopathology of pSS.