Impaired degradation and aberrant phagocytosis of necrotic cell debris in the peripheral blood of patients with primary Sjögren's syndrome

Immunologic basis for development of keratoconjunctivitis sicca in systemic autoimmune diseases: Role of innate immune sensors

The literature is filled with citations reporting an increased incidence of chronic dry eye disease, also known as keratoconjunctivitis sicca, in patients with systemic autoimmune diseases such as rheumatoid arthritis, Sjögren's Syndrome, systemic sclerosis and lupus. As the most environmentally exposed mucosal surface of the body, the conjunctiva constantly responds to environmental challenges which are typically self limited, but when persistent and unresolved may provoke pathogenic innate and adaptive immune reactions. Our understanding of the pathophysiological mechanisms by which systemic autoimmune diseases cause dry eye inducing ocular surface inflammation continues to evolve. Conjunctival immune tone responds to self or foreign danger signals (including desiccating stress) on the ocular surface with an initial non-specific innate inflammatory response. If unchecked, this can lead to activation of dendritic cells that present antigen and prime T and B cells resulting in an adaptive immune reaction. These reactions generally resolve, but dysfunctional, hyper-responsive immune cells found in systemic autoimmune diseases that are recruited to the ocular surface can amplify inflammatory stress responses in the ocular surface and glandular tissues and result in autoimmune reactions that disrupt tear stability and lead to chronic dry eye disease. We here propose that unique features of the ocular surface immune system and the impact of systemic immune dysregulation in autoimmune diseases, can predispose to development of dry eye disease, and exacerbate severity of existing dry eye.

Unraveling the Role of the NLRP3 Inflammasome in Lymphoma: Implications in Pathogenesis and Therapeutic Strategies

Inflammasomes are multimeric protein complexes, sensors of intracellular danger signals, and crucial components of the innate immune system, with the NLRP3 inflammasome being the best characterized among them. The increasing scientific interest in the mechanisms interconnecting inflammation and tumorigenesis has led to the study of the NLRP3 inflammasome in the setting of various neoplasms. Despite a plethora of data regarding solid tumors, NLRP3 inflammasome's implication in the pathogenesis of hematological malignancies only recently gained attention. In this review, we investigate its role in normal lymphopoiesis and lymphomagenesis. Considering that lymphomas comprise a heterogeneous group of hematologic neoplasms, both tumor-promoting and tumor-suppressing properties were attributed to the NLRP3 inflammasome, affecting neoplastic cells and immune cells in the tumor microenvironment. NLRP3 inflammasome-related proteins were associated with disease characteristics, response to treatment, and prognosis. Few studies assess the efficacy of NLRP3 inflammasome therapeutic targeting with encouraging results, though most are still at the preclinical level. Further understanding of the mechanisms regulating NLRP3 inflammasome activation during lymphoma development and progression can contribute to the investigation of novel treatment approaches to cover unmet needs in lymphoma therapeutics.

Inflammasomes: Mechanisms of Action and Involvement in Human Diseases

Inflammasome complexes and their integral receptor proteins have essential roles in regulating the innate immune response and inflammation at the post-translational level. Yet despite their protective role, aberrant activation of inflammasome proteins and gain of function mutations in inflammasome component genes seem to contribute to the development and progression of human autoimmune and autoinflammatory diseases. In the past decade, our understanding of inflammasome biology and activation mechanisms has greatly progressed. We therefore provide an up-to-date overview of the various inflammasomes and their known mechanisms of action. In addition, we highlight the involvement of various inflammasomes and their pathogenic mechanisms in common autoinflammatory, autoimmune and neurodegenerative diseases, including atherosclerosis, rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, Alzheimer's disease, Parkinson's disease, and multiple sclerosis. We conclude by speculating on the future avenues of research needed to better understand the roles of inflammasomes in health and disease.

Defining the Role of Monocytes in Sjögren's Syndrome

Sjögren's syndrome is one of the most prevalent autoimmune diseases after rheumatoid arthritis, with a preference for middle age, and is characterised by exocrine glandular involvement leading to xerostomia and xerophthalmia. It can have systemic implications with vascular, neurological, renal, and pulmonary involvement, and in some cases, it may evolve to non-Hodgkin's lymphoma. For a long time, B- and T-lymphocytes have been the focus of research and have been considered key players in Sjögren's syndrome pathogenesis and evolution. With the development of new technologies, including omics, more insights have been found on the different signalling pathways that lead to inflammation and activation of the immune system. New evidence indicates that a third actor linking innate and adaptive immunity plays a leading role in the Sjögren's syndrome play: the monocyte. This review summarises the recent insights from transcriptomic, proteomic, and epigenetic studies that help us to understand more about the Sjögren's syndrome pathophysiology and redefine the involvement of monocytes in this disease.

Proteomics Analysis of Tears and Saliva From Sjogren's Syndrome Patients

Sjogren's syndrome (SS) is characterized by dysfunctional mucous membranes and dysregulated moisture-secreting glands resulting in various symptoms, including dry mouth and dry eyes. Here, we wanted to profile and compare the tear and saliva proteomes of SS patients to healthy controls. Tear and saliva samples were collected and subjected to an isotopic dimethylation labeling shotgun proteomics workflow to identify alterations in protein levels. In tear samples, we identified 83 upregulated and 112 downregulated proteins. Pathway enrichment analysis of the changing proteins by Metascape identified leukocyte transendothelial migration, neutrophil degranulation, and post-translation protein phosphorylation in tears of SS patients. In healthy controls' tears, an enrichment for proteins related to glycolysis, amino acid metabolism and apoptotic signaling pathway were identified. In saliva, we identified 108 upregulated and 45 downregulated proteins. Altered pathways in SS patients' saliva included cornification, sensory perception to taste and neutrophil degranulation. In healthy controls' saliva, an enrichment for proteins related to JAK-STAT signaling after interleukin-12 stimulation, phagocytosis and glycolysis in senescence were identified. Dysregulated protease activity is implicated in the initiation of inflammation and immune cell recruitment in SS. We identified 20 proteases and protease inhibitors in tears and 18 in saliva which are differentially expressed between SS patients and healthy controls. Next, we quantified endogenous proteoglycan 4 (PRG4), a mucin-like glycoprotein, in tear wash and saliva samples via a bead-based immune assay. We identified decreased levels of PRG4 in SS patients' tear wash compared to normal samples. Conversely, in saliva, we found elevated levels of PRG4 concentration and visualized PRG4 expression in human parotid gland via immunohistological staining. These findings will improve our mechanistic understanding of the disease and changes in SS patients' protein expression will help identify new potential drug targets. PRG4 is among the promising targets, which we identified here, in saliva, for the first time.

Adding Insult on Injury: Immunogenic Role for Donor-derived Cell-free DNA?

Donor-derived cell-free DNA (dd-cfDNA) in the blood circulation is an early marker of injury in solid organ transplantation. Here, we review recent evidence that indicates that dd-cfDNA may itself be a trigger of inflammation, thereby adding insult on injury. Early unresolving molecular allograft injury measured via changes in dd-cfDNA may be an early warning sign and may therefore enable stratification of patients who are at risk of subsequent allograft injury. Considering dd-cfDNA as a continuous and clinically significant biomarker opens up the potential for new management strategies, therapeutics, and ways to quantify interventions by considering the immunological potential of dd-cfDNA.

Making Sense of Intracellular Nucleic Acid Sensing in Type I Interferon Activation in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a systemic autoimmune rheumatic disease characterized by dryness of the eyes and mucous membranes, which can be accompanied by various extraglandular autoimmune manifestations. The majority of patients exhibit persistent systemic activation of the type I interferon (IFN) system, a feature that is shared with other systemic autoimmune diseases. Type I IFNs are integral to anti-viral immunity and are produced in response to stimulation of pattern recognition receptors, among which nucleic acid (NA) receptors. Dysregulated detection of endogenous NAs has been widely implicated in the pathogenesis of systemic autoimmune diseases. Stimulation of endosomal Toll-like receptors by NA-containing immune complexes are considered to contribute to the systemic type I IFN activation. Accumulating evidence suggest additional roles for cytosolic NA-sensing pathways in the pathogenesis of systemic autoimmune rheumatic diseases. In this review, we will provide an overview of the functions and signaling of intracellular RNA- and DNA-sensing receptors and summarize the evidence for a potential role of these receptors in the pathogenesis of pSS and the sustained systemic type I IFN activation.

Anti-DNase I Antibody: A New Serological Reactivity in Primary Sjögren Syndrome

BACKGROUND AND OBJECTIVE

Primary Sjögren syndrome (pSS) is a systemic autoimmune rheumatic disease that particularly affects exocrine glands. Dry eye is one of the most important features of this syndrome, and a recent study reported reduced deoxyribonuclease I (DNase I) activity in the tear of patients with dry eye. We therefore postulated that patients with pSS might have antibodies targeting DNAse I.

METHODS

We have evaluated in a cross-sectional study 85 patients with pSS (2002 American-European Consensus Group Criteria), 50 rheumatoid arthritis (RA) patients (1987 American College of Rheumatology Criteria) without sicca symptoms, and 88 healthy volunteers. IgG anti-DNase I was detected by enzyme-linked immunosorbent assay using as antigen bovine pancreas enzyme and confirmed by immunoblotting.

RESULTS

Age and sex were alike in the 3 groups (p > 0.05). Anti-DNase I was detected in 43.5% of the pSS patients. In contrast, this reactivity was absent in all RA patients (p = 0.0001). Additional comparison of pSS patients with (n = 37) or without (n = 48) anti-DNase I showed that the former group had higher IgG serum levels (2293.2 ± 666.2 vs 1483.9 ± 384.6 mg/dL, p = 0.0001) and greater rate of non-drug-induced leukopenia (43% vs 19%, p = 0.02). A multivariate logistic regression analysis identified that only IgG levels were independently associated with anti-DNase I.

CONCLUSIONS

We describe a high frequency of anti-DNase I antibodies in pSS patients associated with higher serum IgG levels. The lack of this reactivity in RA patients without sicca symptoms suggests that this antibody may be helpful in the differential diagnosis of these diseases.

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.

Sjögren's syndrome and systemic lupus erythematosus: links and risks

Systemic lupus erythematosus (SLE) and Sjögren’s syndrome (SS) may coexist, and they are chronic complex disorders, with an autoimmune background, multifactorial etiology, multiple circulating autoantibodies, and variable prognosis. The prominent feature of SS is the impairment of the lacrimal and salivary glands leading to sicca symptoms. This disease may be classified as primary Sjögren’s syndrome (pSS), or secondary Sjögren’s syndrome (sSS) since it is often associated to other autoimmune disorders, principally SLE, rheumatoid arthritis, and systemic sclerosis. Systematic reviews and meta-analyses show an sSS prevalence in SLE patients of about 14%–17.8%. Herein, we updated important aspects of the clinical association between SLE and sSS through a narrative review of the PubMed database in the last 5 years (from July 2013 to October 2018) with the terms “Sjogren syndrome and systemic lupus erythematosus”. The following aspects are addressed: the classification criteria for sSS; differences and similarities between SLE and pSS regarding demographic, clinical, and serological characteristics (including new autoantibodies), as well as comorbidities; the etiopathogenic links between SLE and pSS (including genetic and environmental factors, B-cell activation, and autoantibodies); the predictive factors for sSS onset in SLE patients; the ocular and oral involvements due to sSS in SLE; and the main distinctive demographic, clinical, and serological features of SLE with and without associated SS.

Cutaneous and Mucosal Manifestations of Sjögren's Syndrome

Sjögren's syndrome is currently considered an "autoimmune epithelitis," as exocrine glands, especially salivary and lacrimal, are progressively destructed by an immune-mediated process associated with specific serum autoantibodies and local lymphocyte infiltrate. Xerostomia remains a key complain in patients with Sjögren's syndrome but should be evaluated also for other causes such as xerogenic medications, followed by radiation and chemotherapy for head and neck cancers, hormone disorders, infections, or other connective tissue diseases. Further, xerophtalmia (also known as dry eye) frequently associated with keratoconjunctivitis sicca cumulatively affects approximately 10-30% of the general population with increasing incidence with age and is more frequently secondary to non-autoimmune diseases. On the other hand, numerous patients with Sjögren's syndrome manifest signs of systemic dryness involving the nose, the trachea, the vagina, and the skin, suggesting that other glands are also affected beyond the exocrine epithelia. Skin involvement in Sjögren's syndrome is relatively common, and various manifestations may be present, in particular xeroderma, eyelid dermatitis, annular erythema, and cutaneous vasculitis. Additional skin non-vasculitic manifestations include livedo reticularis which may occur in the absence of vasculitis, and localized nodular cutaneous amyloidosis possibly representing lymphoproliferative diseases related to Sjögren's syndrome. The treatment of skin and mucosal manifestations in Sjögren's syndrome is similar regardless of the cause, starting from patient education to avoid alcohol and tobacco smoking and to pursue dental hygiene. In conclusion, a strict collaboration between the dermatologist and the rheumatologist is essential in the adequate management of Sjögren's syndrome skin and mucosal manifestations.

Pulmonary manifestations of Sjögren's syndrome

In 9-20% of cases, Sjögren's syndrome is associated with various respiratory symptoms. The most typical manifestations are chronic interstitial lung disease (ILD) and tracheobronchial disease. The most common manifestation of ILD is nonspecific interstitial pneumonia in its fibrosing variant. Other types of ILD, such as organising pneumonia, usual interstitial pneumonia and lymphocytic interstitial pneumonitis, are rare. Their radiological presentation is less distinctive, and definitive diagnosis may require the use of transbronchial or surgical lung biopsy. Corticosteroid therapy is the mainstay of ILD treatment in Sjögren's syndrome, but the use of other immunosuppressive drugs needs to be determined. ILD is a significant cause of death in Sjögren's syndrome. Tracheobronchial disease is common in Sjögren's syndrome, characterised by diffuse lymphocytic infiltration of the airway. It is sometimes responsible for a crippling chronic cough. It can also present in the form of bronchial hyperresponsiveness, bronchiectasis, bronchiolitis or recurrent respiratory infections. The management of these manifestations may require treatment for dryness and/or inflammation of the airways. Airway disease has little effect on respiratory function and is rarely the cause of death in Sjögren's syndrome patients. Rare respiratory complications such as amyloidosis, lymphoma or pulmonary hypertension should not be disregarded in Sjögren's syndrome patients.

The association of Tyro3/Axl/Mer signaling with inflammatory response, disease activity in patients with primary Sjögren's syndrome

OBJECTIVES

Defects in Tyro3/Axl/Mer signaling may lead to impaired phagocytosis of apoptotic cells, eventually contributing to the development of autoimmune disease. The association of TAM signaling with several autoimmune disease has been investigated, but it remains unclear in primary Sjögren's syndrome. Therefore, the aim of this study was to evaluate the level of TAM signaling in primary Sjögren's syndrome with its clinical significance.

METHODS

Real-Time Polymerase Chain Reaction was used to determine the mRNA expression of Mer, Tyro-3, Axl, Gas6, and Protein S in Peripheral Blood Mononuclear Cell from 43 pSS and 46 control. The Enzyme-Linked Immunosorbent Assay method was used to test plasma levels of soluble TAM signaling from those individuals, and the relationship of their levels with clinical characteristic was evaluated.

RESULTS

The mRNA expression levels of Tyro-3, Axl were decreased in pSS patients. When considering the plasma level, increased levels of soluble Mer was observed with statistically significant difference. Soluble Mer levels were positively correlated with IgG levels (r=0.53, P<0.01), Erythrocyte Sedimentation Rate levels (r=0.44, P<0.01) and Sjögren's Syndrome Disease Activity Index (r=0.48, P<0.01). And the levels of soluble Mer in patients with the presence of SSA/SSB were higher than those without SSA/SSB.

CONCLUSIONS

The plasma levels of sMer were increased in pSS patients, which was associated with inflammatory response and disease activity.

Impaired clearance of early apoptotic cells mediated by inhibitory IgG antibodies in patients with primary Sjögren's syndrome

Objectives

Deficient efferocytosis (i.e. phagocytic clearance of apoptotic cells) has been frequently reported in systemic lupus erythematosus (SLE). Todate, patients with primary Sjögren's syndrome (SS) have not been assessed for phagocytosis of apoptotic cells (ApoCell-phagocytosis) and of particulate targets (microbeads, MB-phagocytosis).

Design

ApoCell-phagocytosis and MB-phagocytosis were comparatively assessed by flow cytometry in peripheral blood specimens and monocyte-derived macrophage (MDM) preparations from healthy blood donors (HBD) and consecutive SS, SLE and rheumatoid arthritis (RA) patients. Cross-admixture ApoCell-phagocytosis experiments were also performed using phagocytes from HBD or patients, and apoptotic cells pretreated with whole sera or purified serum IgG derived from patients or HBD.

Results

Compared to HBD, approximately half of SS and SLE patients studied (but not RA) manifested significantly reduced ApoCell-phagocytosis (p<0.001) and MB-phagocytosis (p<0.003) by blood-borne phagocytes that correlated inversely with disease activity (p≤0.004). In cross-admixture assays, healthy monocytes showed significantly reduced ApoCell-phagocytosis when fed with apoptotic cells that were pretreated with sera or purified serum IgG preparations from SS and SLE patients (p<0.0001, compared to those from HBD or RA). Such aberrant effect of the SS and SLE sera and IgG preparations correlated linearly with their content of IgG antibodies against apoptotic cells (p≤0.0001). Phagocytic dysfunction maybe also present in certain SS and SLE patients, as supported by deficient capacity of MDM for ApoCell-phagocytosis and MB-phagocytosis under patients' serum-free conditions.

Conclusion

Similarly to SLE, efferocytosis is frequently impaired in SS and is primarily due to the presence of inhibitory IgG anti-ApoCell antibodies and secondarily to phagocytes' dysfunction.