Defensins- and cathepsin G-ANCA in systemic lupus erythematosus

ANCA in patients with systemic lupus erythematosus. A cross sectional study in Brazilian patients and review of literature

BACKGROUND

Antineutrophil cytoplasmatic antibodies (ANCA) have been detected in patients with systemic lupus erythematosus (SLE). In this study, we investigated the presence of ANCA in a sample of Brazilian SLE patients and its possible associations with clinical and serological outcomes. Additionally, we reviewed the literature of on ANCA in SLE.

RESULTS

The presence of ANCA was detected in 130 patients using indirect immunofluorescence (IIF). The test was positive in 29.9% of the cases (17.6% pANCA and 11.5% cANCA). Male sex and peripheral vasculitis were more prevalent in the ANCA-positive sample. cANCA was associated with lupus anticoagulant and pANCA had a positive association with peripheral vasculitis and a negative association with anti- SSB/La antibodies. In the 22 studies included in the literature review, a wide range of ANCA positivity was found (13% to 81.1% by IIF and 0 to 22.2% by ELISA). ANCA was associated with renal damage in the Asian population. Although other associations have been found in isolated studies, they were not consistently reported.

CONCLUSIONS

The ANCA prevalence found in this Brazilian sample was within the range reported in the literature and these autoantibodies were more frequent in males and in patients with vasculitis. The literature showed controversial results on the association between ANCA and SLE disease activity or clinical characteristics.

Clinical features and outcomes of patients with antineutrophil cytoplasmic antibody-positive systemic lupus erythematosus

Purpose: To investigate the clinical characteristics, pathological features, and outcomes of patients with antineutrophil cytoplasmic antibody (ANCA)-positive systemic lupus erythematosus (SLE) in northwest China.Methods: This retrospective study included 491 patients with SLE tested for ANCA antibodies and 171 patients with ANCA-associated vasculitis (AAV) as controls. Subgroup analysis limited to those with renal involvement, and by ANCA antibody subtype (PR3 vs MPO). To compare the proteinuria remission rates between ANCA-positive and ANCA-negative lupus nephritis (LN) groups, a logistic regression model was used for propensity score matching based on age, hemoglobin, and baseline estimated glomerular filtration rate (eGFR).Results: Compared to ANCA-negative SLE (n = 442), ANCA-positive SLE (n = 46) occur in older patients; however, these patients were younger than those with AAV (n = 167). The eGFR of patients with ANCA-positive LN (n = 25) was higher than that of patients having AAV with renal involvement (n = 56) but lower than that of patients with ANCA-negative LN (n = 163). Patients with SLE who had MPO-ANCA (n = 16) had higher levels of serum creatinine compared to those with PR3-ANCA (n = 30) (156.5 µmol/L vs. 45.5 µmol/L, p = 0.005). During the follow-up period, the remission rate of proteinuria in patients with ANCA-positive LN was lower than that of patients with ANCA-negative LN (50% vs. 75%, p = 0.008).Conclusion: Patients with ANCA-positive LN may have worse baseline renal function and lower protein remission rates compared to patients with ANCA-negative LN. ANCA titers should be regularly monitored throughout the follow-up period in patients with SLE, especially in cases of renal involvement.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

Exploring the role of cathepsin in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease which is marked by leukocytes infiltration inside synovial tissue, joints and also inside synovial fluid which causes progressive destruction of joint cartilage. There are numerous genetical and lifestyle factors, responsible for rheumatoid arthritis. One such factor can be cysteine cathepsins, which act as proteolytic enzymes. These proteolytic enzyme gets activated at acidic pH and are found in lysosomes and are also termed as cysteine proteases. These proteases belong to papain family and have their elucidated role in musculoskeletal disorders. Numerous cathepsins have their targeted role in rheumatoid arthritis. These proteases are secreted through various cell types which includes matrix metalloproteases and papain like cysteine proteases. These proteases can potentially lead to bone and cartilage destruction which causes an immune response in case of inflammatory arthritis.

Linagliptin, A Xanthine-Based Dipeptidyl Peptidase-4 Inhibitor, Ameliorates Experimental Autoimmune Myocarditis

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Treatment with linagliptin, a DPP-4 inhibitor, alleviates not only EAM but also ICIM.

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DPP-4 physically interacts with cathepsin G and enhances its activity.

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Linagliptin promotes SerpinA3N activity, thereby suppressing cathepsin G activity.

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Cathepsin G aggravates EAM through upregulating angiotensin II.

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Linagliptin suppresses oxidative stress in EAM hearts.

This study sought to show the mechanism of how to ameliorate experimental autoimmune myocarditis (EAM) by administering dipeptidyl peptidase (DPP)-4 inhibitor linagliptin. The number of RAR-related orphan nuclear receptor gamma–positive Th17 cells infiltrated to the EAM myocardium was significantly attenuated by linagliptin treatment. Tandem mass spectrometry–based analysis demonstrated that DPP-4 binds to cathepsin G in EAM hearts, thereby protecting cathepsin G activity through inhibiting SerpinA3N activity. Linagliptin suppresses oxidative stress in EAM hearts as well. Thus, we found that DPP-4 plays a detrimental role in the progression of EAM by interacting with cathepsin G, which, in turn, suppresses SerpinA3N activity.

Serum defensin levels in patients with systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis of skin and lung as well as involvement of kidney, gastrointestinal system and heart. Aetiology and exact mechanism of disease is poorly understood. The association between antimicrobial peptides (AMPs) and other diseases such as idiopathic pulmonary fibrosis, diffuse panbronchiolitis, pulmoner alveolar proteinosis and psoriasis have been reported. A small number of studies have examined the role of AMPs on autoimmune diseases which has not been studied in scleroderma yet. We aimed to investigate AMP serum levels and their association with disease characteristics of SSc.

METHODS

Forty-two patients (40 female, mean age 42 years) and 38 healthy subjects (32 female, mean age 38 years) were enrolled. For SSc patients, the following data were recorded: disease subset (limited/diffuse), autoantibodies (antinuclear, anti-centromere (ACA), and anti-SCL-70), blood tests, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), modified Rodnan skin score, presence and history of digital ulcers, kidney, gastrointestinal disease and lung involvement assessed by computed tomography and pulmonary function tests. Association between serum AMPs and disease characteristics were analysed.

RESULTS

Twenty-nine of the patients had diffuse (69%) and 13 of the patients had limited (31%) systemic sclerosis. Average disease duration was 5.5 years. Pulmonary involvement was detected in 20 patients (47.6%). Serum concentration of alpha defensin was higher than healthy subjects (563 ± 415 vs 377 ± 269 ng/mL, p = 0.02). However, no difference was observed for beta-1 and beta-2 defensins in SSc patients and healthy controls. In sub-group analysis patients with interstitial lung disease had higher levels of alpha defensin than those without lung involvement (684 ± 473 vs 430 ± 299 ng/ml, p = 0.04). There was also correlation between alfa defensin serum concentrations and CRP (r = 0.34).

CONCLUSIONS

Alpha defensin levels are increased in scleroderma patients and correlated with lung involvement indicating a role in the pathogenesis of disease.

TRIAL REGISTRATION

This study is not a clinical trial study.

The significance of α-defensins 1-3 in Behcet’s disease: a case-control study among Egyptian patients

Background

Behcet’s disease (BD) is associated with uveitis, oral ulcers, genital ulcers and arthritis. Enhanced activity of innate immunity components, such as neutrophils, natural killer (NK) cells and endothelial cells, is a prominent feature of BD. The aim of this study was to clarify the significance of α-defensins 1-3 in BD and detect their correlation with disease activity, severity and oral ulcer activity.

Results

Significant differences were found between Behcet’s patients and controls as regards serum α-defensins 1-3 (median 10.1, IQR 4–45 μg/ml versus median 7.4, IQR 0.6–13.2 μg/ml, p = 0.001) and salivary α-defensins 1-3 (median 17.4, IQR 5.7–44 μg/ml versus median 8.6, IQR 3.3–11 μg/ml, p < 0.001). Receiver operating characteristic (ROC) showed a fair area under curve (AUC) (AUC = 0.743), with sensitivity of 40% and specificity 100% at cutoff value of 17.3 μg/ml for serum α-defensins 1-3, while salivary α-defensins 1-3 showed excellent AUC (AUC = 0.936), with sensitivity of 93.3% and specificity of 86.7% at cutoff value of 9.8 μg/ml. The levels of serum and salivary α-defensins 1-3 > cutoff value were significantly higher in active severe Behcet’s patients with active oral ulcers (p < 0.001).

Conclusion

α-Defensins 1-3 may be involved in the pathogenesis of BD and could be valuable markers in the determination of disease activity, severity and oral ulcer activity.

The Dual Role of Antimicrobial Peptides in Autoimmunity

Autoimmune diseases (AiDs) are characterized by the destruction of host tissues by the host immune system. The etiology of AiDs is complex, with the implication of multiple genetic defects and various environmental factors (pathogens, antibiotic use, pollutants, stress, and diet). The interaction between these two compartments results in the rupture of tolerance against self-antigens and the unwanted activation of the immune system. Thanks to animal models, the immunopathology of many AiDs is well described, with the implication of both the innate and adaptive immune systems. This progress toward the understanding of AiDs led to several therapies tested in patients. However, the results from these clinical trials have not been satisfactory, from reversing the course of AiDs to preventing them. The need for a cure has prompted many investigators to explore alternative aspects in the immunopathology of these diseases. Among these new aspects, the role of antimicrobial host defense peptides (AMPs) is growing. Indeed, beyond their antimicrobial activity, AMPs are potent immunomodulatory molecules and consequently are implicated in the development of numerous AiDs. Importantly, according to the disease considered, AMPs appear to play a dual role in autoimmunity with either anti- or pro-inflammatory abilities. Here, we aimed to summarize the current knowledge about the role of AMPs in the development of AiDs and attempt to provide some hypotheses explaining their dual role. Definitely, a complete understanding of this aspect is mandatory before the design of AMP-based therapies against AiDs.

Human antimicrobial peptides in autoimmunity

Antimicrobial peptides (AMPs) were firstly discovered as cytotoxic substances that killed bacteria. Later they were described as biologically active peptides that are able not only to kill invaders but also to modulate host immunity. In particular, it is shown that human antimicrobial peptides are able to influence the activity of different innate and adaptive immunity components, thus, obviously, they also participate in autoimmune processes. In this review we discuss the nature of human AMPs and analyze their role in such autoimmune disorders like type 1 diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosus, psoriasis, Crohn's disease and sarcoidosis. These peptides were shown to have a "double-sided" influence on the autoimmune disease pathogenesis. Thus, described facts should be taken into account for the development of new pharmaceutical agents to cure patients with autoimmune disorders. These agents could derive from natural antimicrobial peptides that in some cases modulate immune response. For example, it was shown that human AMPs are able to modulate complement system dysregulation of which is known to be one of the most dangerous pathogenic factors during autoimmune processes.

Lysosomes as a therapeutic target

Lysosomes are membrane-bound organelles with roles in processes involved in degrading and recycling cellular waste, cellular signalling and energy metabolism. Defects in genes encoding lysosomal proteins cause lysosomal storage disorders, in which enzyme replacement therapy has proved successful. Growing evidence also implicates roles for lysosomal dysfunction in more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. With a focus on lysosomal dysfunction in autoimmune disorders and neurodegenerative diseases - including lupus, rheumatoid arthritis, multiple sclerosis, Alzheimer disease and Parkinson disease - this Review critically analyses progress and opportunities for therapeutically targeting lysosomal proteins and processes, particularly with small molecules and peptide drugs.

Clinical Implications of Excessive Neutrophil Extracellular Trap Formation in Renal Autoimmune Diseases

Neutrophil extracellular traps (NETs) are extracellular DNA structures covered with antimicrobial peptides, danger molecules, and autoantigens that can be released by neutrophils. NETs are an important first-line defense mechanism against bacterial, viral, fungal, and parasitic infections, but they can also play a role in autoimmune diseases. NETs are immunogenic and toxic structures that are recognized by the autoantibodies of patients with antineutrophil cytoplasmic antibodies−associated vasculitis (AAV) (i.e., against myeloperoxidase or proteinase-3) and systemic lupus erythematosus (SLE) (i.e., against double-stranded DNA, histones, or nucleosomes). There is cumulating preclinical and clinical evidence that both excessive formation and impaired degradation of NETs are involved in the pathophysiology of AAV and SLE. These autoimmune diseases give rise to 2 clinically and pathologically distinct forms of glomerulonephritis (GN), respectively, crescentic pauci-immune GN and immune complex−mediated GN. Therefore, it is relevant to understand the different roles NET formation can play in the pathophysiology of these most prevalent renal autoimmune diseases. This review summarizes the current concepts on the role of NET formation in the pathophysiology of AAV and SLE, and provides a translational perspective on the clinical implications of NETs, such as potential therapeutic approaches that target NET formation in these renal autoimmune diseases.

Cathepsin G and Its Role in Inflammation and Autoimmune Diseases

Cathepsin G belongs to the neutrophil serine proteases family, known for its function in killing pathogens. Studies over the past several years indicate that cathepsin G has important effects on inflammation and immune reaction, and may be a key factor in the pathogenesis of some autoimmune diseases. In this article, we discuss the roles of cathepsin G in inflammation, immune reaction, and autoimmune diseases. To our knowledge, this is the first study providing important information about cathepsin G in the pathogenesis of autoimmune diseases and suggesting that cathepsin G may be a new biomarker or treatment target.

Clearance Deficiency and Cell Death Pathways: A Model for the Pathogenesis of SLE

Alterations of cell death pathways, including apoptosis and the neutrophil specific kind of death called NETosis, can represent a potential source of autoantigens. Defects in the clearance of apoptotic cells may be responsible for the initiation of systemic autoimmunity in several chronic inflammatory diseases, including systemic lupus erythematosus (SLE). Autoantigens are released mainly from secondary necrotic cells because of a defective clearance of apoptotic cells or an inefficient degradation of DNA-containing neutrophil extracellular traps (NETs). These modified autoantigens are presented by follicular dendritic cells to autoreactive B cells in germinal centers of secondary lymphoid organs. This results in the loss of self-tolerance and production of autoantibodies, a unifying feature of SLE. Immune complexes (IC) are formed from autoantibodies bound to uncleared cellular debris in blood or tissues. Clearance of IC by blood phagocytes, macrophages, and dendritic cells leads to proinflammatory cytokine secretion. In particular, plasmacytoid dendritic cells produce high amounts of interferon-α upon IC uptake, thereby contributing to the interferon signature of patients with SLE. The clearance of antinuclear IC via Fc-gamma receptors is considered a central event in amplifying inflammatory immune responses in SLE. Along with this, the accumulation of cell remnants represents an initiating event of the etiology, while the subsequent generation of autoantibodies against nuclear antigens (including NETs) results in the perpetuation of inflammation and tissue damage in patients with SLE. Here, we discuss the implications of defective clearance of apoptotic cells and NETs in the development of clinical manifestations in SLE.

Quantitative Proteomic Analysis of Peripheral Blood Mononuclear Cells in Ankylosing Spondylitis by iTRAQ

This study was designed to identify and quantify the different proteins expression levels in ankylosing spondylitis (AS) and to explore the pathogenesis of AS. We performed isobaric tags for relative and absolute quantitation (iTRAQ) coupled with multiple chromatographic fractionation and tandem mass spectrometry to detect the proteins profiling in peripheral blood mononuclear cells (PBMCs) from AS patients and healthy controls. Mascot software and the International Protein Index and the Gene Ontology (GO) database were used to conduct the bioinformatics analysis. The differentially expressed proteins were validated by enzyme-linked immunosorbent assay (ELISA). A total of 1,232 proteins were identified by iTRAQ, of which 183 showed differential expression and 18 differentially expressed proteins were acute phase reactants. Upon mapping of the differentially expressed proteins to GO database, we found four differentially expressed proteins involved in the biological process of cell killing, including up-regulated cathepsin G (CTSG), neutrophil defensin3 (DEFA3), protein tyrosine phosphatase receptor type C (PTPRC), and down-regulated peroxiredoxin-1(PRDX1),which were consistent with the verified results of ELISA. Our proteomic analyses suggested that the proteins involved in the biological process of cell killing might play an important role in the pathogenesis of AS.

Deimination of linker histones links neutrophil extracellular trap release with autoantibodies in systemic autoimmunity

Autoantibodies to nuclear antigens arise in human autoimmune diseases, but a unifying pathogenetic mechanism remains elusive. Recently we reported that exposure of neutrophils to inflammatory conditions induces the citrullination of core histones by peptidylarginine deiminase 4 (PAD4) and that patients with autoimmune disorders produce autoantibodies that recognize such citrullinated histones. Here we identify histone H1 as an additional substrate of PAD4, localize H1 within neutrophil extracellular traps, and detect autoantibodies to citrullinated H1 in 6% of sera from patients with systemic lupus erythematosus and Sjögren's syndrome. No preference for deiminated H1 was observed in healthy control sera and sera from patients with scleroderma or rheumatoid arthritis. We map binding to the winged helix of H1 and determine that citrulline 53 represents a key determinant of the autoantibody epitope. In addition, we quantitate RNA for H1 histone subtypes in mature human neutrophils and identify citrulline residues by liquid chromatography and tandem mass spectrometry. Our results indicate that deimination of linker histones generates new autoantibody epitopes with enhanced potential for stimulating autoreactive human B cells.-Dwivedi, N., Neeli, I., Schall, N., Wan, H., Desiderio, D. M., Csernok, E., Thompson, P. R., Dali, H., Briand, J.-P., Muller, S., Radic, M. Deimination of linker histones links neutrophil extracellular trap release with autoantibodies in systemic autoimmunity.

Cardiovascular disease in lupus: insights and updates

PURPOSE OF REVIEW

With improved management of the classical disease manifestations of systemic lupus erythematosus (SLE), cardiovascular disease (CVD) has emerged as one of the most important causes of morbidity and mortality. This review in particular focuses on progress over the past year in clinical and basic aspects of SLE-driven accelerated atherosclerosis.

RECENT FINDINGS

Both subclinical CVD and CV events continue to be recognized at increased frequency in previously unstudied lupus cohorts and populations. Novel associations have been identified between lupus CVD and cognitive impairment, depression, and low-income status. In terms of pathogenesis, there is an ever-increasing focus on the innate immune system and, in particular, type I interferons (IFNs). Recent studies have drawn connections in both human and murine models between neutrophils, plasmacytoid dendritic cells, type I IFNs, and endothelial dysfunction. Whether treatments such as mycophenolate mofetil or statins have a role in prevention of lupus CVD is an area of intensive study.

SUMMARY

CVD is a major complication of lupus and is now a leading cause of death among people living with this disease. As such, additional studies are needed in order to identify the most effective preventive strategies and most predictive vascular risk biomarkers. Type I IFNs may play a critical role in lupus CVD pathogenesis, and it is recommended that vascular outcomes be included in ongoing trials testing the efficacy of anti-IFN biologics.

Detection of SLE antigens in neutrophil extracellular traps (NETs)

Neutrophils are sentinel cells of the innate immune system with a primary role of clearing extracellular pathogens. The release of weblike structures decorated with granular proteins called neutrophil extracellular traps (NETs) has recently been implicated in the pathogenesis of inflammatory and autoimmune diseases. Indeed, NETs may represent an important source of autoantigens and immunostimulatory proteins in systemic lupus erythematosus (SLE). In this chapter, we describe protocols to isolate human peripheral neutrophils, to generate and isolate NETs, and to detect SLE antigens in NETs using immunofluorescence and immunoblot.

Citrullination of autoantigens implicates NETosis in the induction of autoimmunity

Tolerance blocks the expression of autoantibodies, whereas autoimmunity promotes it. How tolerance breaks and autoantibody production begins thus are crucial questions for understanding and treatment of autoimmune diseases. Evidence implicates cell death and autoantigen modifications in the initiation of autoimmune reactions. One form of neutrophil cell death called NETosis deserves attention because it requires the post-translational modification of histones and results in the extracellular release of chromatin. NETosis received its name from NET, the acronym given to Neutrophil Extracellular Trap. The extracellular chromatin incorporates histones in which arginines have been converted to citrullines by peptidylarginine deiminase IV (PAD4). The deiminated chromatin may function to capture or 'trap' bacterial pathogens, thus generating an extracellular complex of deiminated histones and bacterial cell adjuvants. The complex of bacterial antigens and deiminated chromatin may be internalised by host phagocytes during acute inflammatory conditions, as arise during bacterial infections or chronic autoinflammatory disorders. The uptake and processing of deiminated chromatin together with bacterial adjuvants by phagocytes may induce the presentation of modified histone epitopes and co-stimulation, thus yielding a powerful stimulus to break tolerance. Autoantibodies to deiminated histones are prevalent in Felty's syndrome patients and are present in systemic lupus erythematosus (SLE) and patients with rheumatoid arthritis (RA). These observations clearly implicate histone deimination as an epigenetic mark that can act as an autoantibody stimulant.

Alpha-defensin DEFA1A3 gene copy number variation in Asians and its genetic association study in Chinese systemic lupus erythematosus patients

Neutrophil extracellular traps (NETs) were closely associated with activation of type I interferon (IFN) pathway in systemic lupus erythematosus (SLE). We aimed to study the genetic basis of NETs-DEFA1A3 copy number variations (CNV) in SLE and HapMap CHB+JPT populations by quantitative real-time PCR and whole genome sequences data. DEFA1A3 CNs did not differ significantly between SLE patients and controls. DEFA1A3 CNs ranged from 3 to 11 in CHB and 4 to 16 in JPT. The median of DEFA1A3 CNV of CHB (6 copies) was significantly lower than that of JPT (9 copies). Associations of genotype of tag SNP rs2738113 with DEFA1A3 CNs and mRNA expression of IFNα were observed in CHB and JPT populations. Our data provided a genetic reference of DEFA1A3 CNV for further studies and suggested that the genetic pathogenesis of NETs, as well as DEFA1A3 in SLE should be further evaluated, specially in different populations.

Lupus neutrophils: 'NET' gain in understanding lupus pathogenesis

PURPOSE OF REVIEW

Historically, researchers have focused on the role of adaptive immunity in lupus pathogenesis; recently, however, there has been renewed interest in the contributions of a prototypical innate immune cell - the neutrophil.

RECENT FINDINGS

Neutrophil extracellular traps (NETs) are released via a novel form of cell death called NETosis. NETs, consisting of a chromatin meshwork decorated with antimicrobial peptides, play an important role in the innate response to microbial infections. Some lupus patients do not clear NETs normally, a phenotype that correlates with disease activity. Further, lupus neutrophils - and, in particular, an aberrant subset called low-density granulocytes - have an increased propensity to undergo NETosis. Both interferon alpha (IFNα) and immune complexes are potential triggers of enhanced NETosis in lupus patients.

SUMMARY

NETs are a potent stimulus for IFNα release by plasmacytoid dendritic cells, and, as such, may play an important role in propagation of the lupus phenotype. NETs can also directly damage tissues - including the endothelium - with implications for lupus nephritis and accelerated atherosclerosis. Whether aberrant NETosis is sufficient to trigger systemic lupus erythematosus, and whether inhibition of NETosis can ameliorate clinical manifestations of lupus, are open questions, and will be exciting topics of future research.

Proteins derived from neutrophil extracellular traps may serve as self-antigens and mediate organ damage in autoimmune diseases

Neutrophils are the most abundant leukocytes in circulation and represent one of the first lines of defense against invading pathogens. Neutrophils possess a vast arsenal of antimicrobial proteins, which can be released from the cell by a death program termed NETosis. Neutrophil extracellular traps (NETs) are web-like structures consisting of decondensed chromatin decorated with granular and cytosolic proteins. Both exuberant NETosis and impaired clearance of NETs have been implicated in the organ damage of autoimmune diseases, such as systemic lupus erythematosus (SLE), small vessel vasculitis (SVV), and psoriasis. NETs may also represent an important source of modified autoantigens in SLE and SVV. Here, we review the autoimmune diseases linked to NETosis, with a focus on how modified proteins externalized on NETs may trigger loss of immune tolerance and promote organ damage.

Functional single-nucleotide polymorphisms in the DEFB1 gene are associated with systemic lupus erythematosus in Southern Brazilians

Systemic lupus erythematosus (SLE) is an autoimmune disease that results in inflammation and tissue damage. The etiology of SLE remains unknown, but recent studies have shown that the innate immune system may have a role in SLE pathogenesis through the secretion of small cationic peptides named defensins. The aim of the study was to determine the possible involvement in SLE of three functional single nucleotide polymorphisms (SNPs) (c.−52G>A, c.−44C>G and c.−20G>A) in the 5’UTR region of DEFB1 gene, by analyzing them in a population of 139 SLE patients and 288 healthy controls. The c.−52G>A SNP showed significant differences in allele and genotype frequency distribution between SLE patients and controls ( p = 0.01 and p = 0.02 respectively) indicating protection against SLE (A allele, OR = 0.68, AA genotype OR = 0.51). Significant differences were also observed for c.−44C>G SNP, the C/G genotype being associated with susceptibility to SLE (OR = 1.60, p = 0.04). Moreover , statistically significant differences between patients and controls were found for two DEFB1 haplotypes (GCA and GGG, p = 0.01 and p = 0.02 respectively). When considering DEFB1 SNPs and SLE clinical and laboratory manifestations, significant association was found with neuropsychiatric disorders, immunological alterations and anti-DNA antibodies. In conclusion, our results evidence a possible role for the c.−52G>A and c.−44C>G DEFB1 polymorphisms in SLE pathogenesis, that can be considered as possible risk factors for development of disease and disease-related clinical manifestations. Additional studies are needed, to corroborate these results as well as functional studies to understand the biological role of these SNPs in the pathogenesis of SLE.

Felty's syndrome autoantibodies bind to deiminated histones and neutrophil extracellular chromatin traps

OBJECTIVE

To test the hypothesis that autoantigen modifications by peptidylarginine deiminase type 4 (PAD-4) increase immunoreactivity.

METHODS

We assembled sera from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Felty's syndrome (FS), and antineutrophil cytoplasmic antibody-associated vasculitides (AAVs), as well as sera from control subjects without autoimmune diseases. The sera were tested for binding to activated neutrophils, deiminated histones, and neutrophil extracellular chromatin traps (NETs). IgG binding to lipopolysaccharide-activated neutrophils was assessed with confocal microscopy, and binding to in vitro-deiminated histones was measured using enzyme-linked immunosorbent assay (ELISA) and Western blotting. In addition, we quantitated histone deimination in freshly isolated neutrophils from the blood of patients and control subjects.

RESULTS

Increased IgG reactivity with activated neutrophils, particularly binding to NETs, was paralleled by preferential binding to deiminated histones over nondeiminated histones by ELISA in a majority of sera from FS patients but only in a minority of sera from SLE and RA patients. Immunoblotting revealed autoantibody preference for deiminated histones H3, H4, and H2A in most FS patients and in a subset of SLE and RA patients. In patients with AAVs, serum IgG preferentially bound nondeiminated histones over deiminated histones. Increased levels of deiminated histones were detected in neutrophils from RA patients.

CONCLUSION

Circulating autoantibodies in FS are preferentially directed against PAD-4-deiminated histones and bind to activated neutrophils and NETs. Thus, increased reactivity with modified autoantigens in FS implies a direct contribution of neutrophil activation and the production of NET-associated nuclear autoantigens in the initiation or progression of FS.

Neutrophils activate plasmacytoid dendritic cells by releasing self-DNA-peptide complexes in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe and incurable autoimmune disease characterized by chronic activation of plasmacytoid dendritic cells (pDCs) and production of autoantibodies against nuclear self-antigens by hyperreactive B cells. Neutrophils are also implicated in disease pathogenesis; however, the mechanisms involved are unknown. Here, we identified in the sera of SLE patients immunogenic complexes composed of neutrophil-derived antimicrobial peptides and self-DNA. These complexes were produced by activated neutrophils in the form of web-like structures known as neutrophil extracellular traps (NETs) and efficiently triggered innate pDC activation via Toll-like receptor 9 (TLR9). SLE patients were found to develop autoantibodies to both the self-DNA and antimicrobial peptides in NETs, indicating that these complexes could also serve as autoantigens to trigger B cell activation. Circulating neutrophils from SLE patients released more NETs than those from healthy donors; this was further stimulated by the antimicrobial autoantibodies, suggesting a mechanism for the chronic release of immunogenic complexes in SLE. Our data establish a link between neutrophils, pDC activation, and autoimmunity in SLE, providing new potential targets for the treatment of this devastating disease.

Netting neutrophils induce endothelial damage, infiltrate tissues, and expose immunostimulatory molecules in systemic lupus erythematosus

An abnormal neutrophil subset has been identified in the PBMC fractions from lupus patients. We have proposed that these low-density granulocytes (LDGs) play an important role in lupus pathogenesis by damaging endothelial cells and synthesizing increased levels of proinflammatory cytokines and type I IFNs. To directly establish LDGs as a distinct neutrophil subset, their gene array profiles were compared with those of autologous normal-density neutrophils and control neutrophils. LDGs significantly overexpress mRNA of various immunostimulatory bactericidal proteins and alarmins, relative to lupus and control neutrophils. In contrast, gene profiles of lupus normal-density neutrophils do not differ from those of controls. LDGs have heightened capacity to synthesize neutrophils extracellular traps (NETs), which display increased externalization of bactericidal, immunostimulatory proteins, and autoantigens, including LL-37, IL-17, and dsDNA. Through NETosis, LDGs have increased capacity to kill endothelial cells and to stimulate IFN-α synthesis by plasmacytoid dendritic cells. Affected skin and kidneys from lupus patients are infiltrated by netting neutrophils, which expose LL-37 and dsDNA. Tissue NETosis is associated with increased anti-dsDNA in sera. These results expand the potential pathogenic roles of aberrant lupus neutrophils and suggest that dysregulation of NET formation and its subsequent responses may play a prominent deleterious role.

Expression of antimicrobial peptides in different subtypes of cutaneous lupus erythematosus

BACKGROUND

Antimicrobial peptides (AMPs) are small effector molecules of the innate immune system with well-known antimicrobial activity. Skin infections rarely occur in patients with cutaneous lupus erythematosus (CLE), and AMP expression in CLE has not been previously evaluated.

OBJECTIVES

We aimed to determine the expression of several important AMPs in 3 different subtypes of CLE.

METHODS

Skin lesions were analyzed for the gene and protein expression of human β-defensin (hBD)-1, -2, and -3; RNase-7; the cathelicidin LL-37; and psoriasin (S100A7) using real-time reverse transcriptase polymerase chain reaction and immunohistochemistry.

RESULTS

Skin biopsy specimens of 96 study participants including 47 patients with CLE (15 patients with discoid lupus erythematosus [LE], 11 patients with subacute CLE, and 21 patients with LE tumidus), 34 patients with psoriasis, and 15 healthy control subjects were evaluated in this study. HBD-2, hBD-3, LL-37, and psoriasin were significantly more highly expressed in CLE as compared with healthy controls, and most AMPs were significantly more highly induced in subacute CLE as compared with discoid LE and LE tumidus. AMP gene expression paralleled well with AMP protein expression in CLE and controls. Subacute CLE and discoid LE showed a similar correlation of AMP gene expression (significant correlations between hBD-1 and RNase-7, hBD-2 and hBD-3, hBD-2 and psoriasin, and hBD-3 and psoriasin).

LIMITATIONS

The relatively small number of samples and the lack of analysis of the lesional bacterial colonization are a limitation.

CONCLUSIONS

Several AMPs are increased in CLE at both gene and protein levels. This could explain the low prevalence of skin infections in CLE. It remains to be elucidated whether AMPs play a pathogenic role in CLE.

Elevated levels of human beta-defensin 2 and human neutrophil peptides in systemic lupus erythematosus

OBJECTIVE

Defensins are immunomodulatory peptides and components of the innate immune response. They have been shown to be modulated in various disease states and in response to inflammatory stimuli. Recently, alpha-defensins have been implicated in the pathogenesis of autoimmune diseases. In order to explore whether these defensins may have a role in the pathogenesis of systemic lupus erythematosus (SLE), we sought to determine whether altered expression can be found in SLE patients.

MATERIAL AND METHODS

Serum and EDTA-blood of 50 SLE patients who fulfilled the American College of Rheumatology (ACR) criteria (aged 41.4 ± 13.3 years) and 28 age- and sex-matched healthy controls were collected. Real-time polymerase chain reaction with gene-specific primers for human neutrophil peptides (HNPs), human beta-defensin 2 and 3 (hBD2, 3) in isolated polymorphonuclear cells and enzyme-linked immunosorbent assay (ELISA) in serum samples were performed. Results of SLE patients were compared with the control group and correlated to routine laboratory parameters, clinical data and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI).

RESULTS

SLE patients were predominantly female (90%) with a mean SLEDAI of 5.7 ± 6.1. In sera, patients displayed higher amounts of hBD2 and HNPs when compared with healthy controls. Furthermore, hBD2 correlated with levels of anti-dsDNA antibodies, erythrocyte count and the SLEDAI. Elevated values were observed in patients with myositis (n = 4). Serum HNPs on the other hand correlated with the neutrophil count and was elevated in patients with a rash (n = 7). Lupus patients suffering from transverse myelitis (n = 3) had raised serum-values of both HNPs and hBD2. While no mRNA of hBD2 or hBD3 was detected in polymorphonuclear cells, HNP mRNA was found in both healthy controls and patients without significant difference. Lupus nephritis and rash were associated with higher amounts of HNP mRNA, and the relative amount of copies correlated positively with the SLEDAI and negatively with C3 measurements.

CONCLUSIONS

Serum levels of hBD2 and HNPs are elevated in SLE. The correlations of hBD2 and HNPs to established disease activity parameters and distinct clinical situations suggest that innate immune mechanisms are activated. Defensins may be involved in SLE pathogenesis.

Defensins in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease, resulting in inflammation and tissue damage. The precise etiology for SLE is so far unknown. It has been shown that the innate immunity plays a role in SLE pathogenesis. The innate immune system confers broad protection against pathogens by the secretion of broad-spectrum antibacterial and immunomodulatory substances named defensins. Recently, alpha-defensin, the products of neutrophils have been found to be upregulated at the mRNA and protein levels in SLE patients. In addition, increased antidefensin antibodies were found in sera of patients with SLE, but these levels decreased after therapy with corticosteroids. These recent findings suggest a role for defensins in the pathogenesis of SLE. Thus, activation and degranulation of neutrophils leads to alpha-defensin secretion in SLE patients. Given their immunomodulatory role, alpha-defensin secretion might activate the adaptive immune system leading to the stimulation of the immune system, as is manifested in SLE.

High alpha-defensin levels in patients with systemic lupus erythematosus

Innate immunity plays a role in systemic lupus erythematosus (SLE). Our objective was to determine the levels of defensins, which are antimicrobial and immunomodulatory polypeptides, in SLE. Sera from SLE patients and healthy controls were tested for pro-inflammatory human beta-defensin 2 (hBD-2) and for alpha-defensin human neutrophil peptide 1 (HNP-1). hBD-2 could not be detected by enzyme-linked immunosorbent assay (ELISA) and its mRNA levels were low in SLE patients and similar to those found in controls. In contrast, the mean alpha-defensin level in the sera of all SLE patients (11.07 +/- 13.92 ng/microl) was significantly higher than that of controls (0.12 +/- 0.07 ng/microl). Moreover, 60% of patients demonstrated very high serum levels (18.5 +/- 13.36 ng/microl) and 50% showed elevated gene expression in polymorphonuclear cells. High alpha-defensin levels correlated with disease activity, but not with neutrophil count. Thus, activation and degranulation of neutrophils led to alpha-defensin secretion in SLE patients. Given the immunomodulatory role of alpha-defensins, it is possible that their secretion may activate the adaptive immune system leading to a systemic response.

Gene expression in systemic lupus erythematosus: bone marrow analysis differentiates active from inactive disease and reveals apoptosis and granulopoiesis signatures

OBJECTIVE

The cells of the immune system originate from the bone marrow, where many of them also mature. This study was undertaken to examine gene expression in the bone marrow of patients with systemic lupus erythematosus (SLE), in order to better understand the aberrant immune response in this disease.

METHODS

Bone marrow mononuclear cells (BMMCs) from 20 SLE patients (11 with active disease and 9 with inactive disease) and peripheral blood mononuclear cells (PBMCs) from 27 patients (16 with active disease and 11 with inactive disease) were studied; BMMCs and PBMCs from 7 healthy individuals and 3 osteoarthritis patients were studied as controls. Samples were analyzed on genome-scale DNA microarrays, with 21,329 genes represented.

RESULTS

We identified 102 genes involved in various biologic processes that were differentially expressed between patient and control BMMCs; 53 of them are genes that are involved in major networks, including cell death, growth, signaling, and proliferation. Comparative analysis revealed 88 genes that were differentially expressed between bone marrow and blood, the majority of which are involved in cell growth and differentiation, cellular movement and morphology, immune response, and other hematopoietic cell functions. Unsupervised clustering of highly expressed genes revealed 2 major SLE patient clusters (active disease and inactive disease) based on gene expression in bone marrow, but not in peripheral blood. The up-regulated genes in the bone marrow of patients with active disease included genes involved in cell death and granulopoiesis.

CONCLUSION

Microarray analysis of the bone marrow differentiated active from inactive SLE and provided further evidence of the role of apoptosis and granulocytes in the pathogenesis of the disease.