Neutrophil extracellular traps and their role in the development of chronic inflammation and autoimmunity

Angiopoietin 1 release from human neutrophils is independent from neutrophil extracellular traps (NETs)

Background

Neutrophils induce the synthesis and release of angiopoietin 1 (Ang1), a cytosolic growth factor involved in angiogenesis and capable of inducing several pro-inflammatory activities in neutrophils. Neutrophils also synthesize and release neutrophil extracellular traps (NETs), comprised from decondensed nuclear DNA filaments carrying proteins such as neutrophil elastase (NE), myeloperoxidase (MPO), proteinase 3 (PR3) and calprotectin (S100A8/S100A9), which together, contribute to the innate immune response against pathogens (e.g., bacteria). NETs are involved in various pathological conditions through pro-inflammatory, pro-thrombotic and endothelial dysfunction effects and have recently been found in heart failure (HF) and type 2 diabetes (T2DM) patients. The aim of the present study was to investigate the role of NETs on the synthesis and release of Ang1 by the neutrophils in patients with T2DM and HF with preserved ejection fraction (HFpEF) (stable or acute decompensated; ADHFpEF) with or without T2DM.

Results

Our data show that at basal level (PBS) and upon treatment with LPS, levels of NETs are slightly increased in patients suffering from T2DM, HFpEF ± T2DM and ADHF without (w/o) T2DM, whereas this increase was significant in ADHFpEF + T2DM patients compared to healthy control (HC) volunteers and ADHFpEF w/o T2DM. We also observed that treatments with PMA or A23187 increase the synthesis of Ang1 (from 150 to 250%) in HC and this effect is amplified in T2DM and in all cohorts of HF patients. Ang1 is completely released (100%) by neutrophils of all groups and does not bind to NETs as opposed to calprotectin.

Conclusions

Our study suggests that severely ill patients with HFpEF and diabetes synthesize and release a greater abundance of NETs while Ang1 exocytosis is independent of NETs synthesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00442-8.

Diacerein Alone and in Combination with Infliximab Suppresses the Combined Proinflammatory Effects of IL-17A, IL-22, Oncostatin M, IL-1A, and TNF-alpha in Keratinocytes: A Potential Therapeutic Option in Psoriasis

Psoriasis is a chronic disorder characterized by a complex interplay between keratinocytes and inflammatory mediators. In a previous study, we evaluated diacerein's ability to diminish interleukin (IL)-1's proinflammatory effects on cultured primary human keratinocytes. In this study, we evaluated diacerein's ability to diminish the inflammatory effects of a cytokine mixture (CM) consisting of IL-17A, IL-22, oncostatin M, IL-1A, and tumor necrosis factor (TNF)-alpha on cultured primary human keratinocytes. These five cytokines have been previously shown to induce an in vivo-equivalent cell culture psoriasis model. We also evaluated diacerein's anti-inflammatory effects in comparison to and in combination with infliximab, a TNF-alpha inhibitor currently used in the treatment of psoriasis. We found 81 genes that were significantly (P < 0.05) dysregulated by CM compared to medium control. All three treatment groups (diacerein alone, infliximab alone, and diacerein plus infliximab) diminished the effects of CM on these genes, with the greatest effect seen with diacerein plus infliximab. Using enzyme-linked immunosorbent assay method on cell culture supernatant, we determined the protein concentration for five genes (IL-19, IL-6, CSF3, S100A8, and NAP-2) significantly (P < 0.05) upregulated by CM at the gene level. Diacerein alone diminished the effect of CM on the protein concentration of two genes, whereas diacerein plus infliximab diminished the effect of CM on the protein concentration of all the five genes. Based on these results, we conclude that diacerein alone or in combination with infliximab may have a therapeutic role in psoriasis by downregulating key inflammatory mediators.

Dysfunctional mitochondria as critical players in the inflammation of autoimmune diseases: Potential role in Sjögren's syndrome

Relevant reviews highlight the association between dysfunctional mitochondria and inflammation, but few studies address the contribution of mitochondria and mitochondria-endoplasmic reticulum (ER) contact sites (MERCs) to cellular homeostasis and inflammatory signaling. The present review outlines the important role of mitochondria in cellular homeostasis and how dysfunctional mitochondrion can release and misplace mitochondrial components (cardiolipin, mitochondrial DNA (mtDNA), and mitochondrial formylated peptides) through multiple mechanisms. These components can act as damage-associated molecular patterns (DAMPs) and induce an inflammatory response via pattern recognition receptors (PRRs). Accumulation of damaged ROS-generating mitochondria, accompanied by the release of mitochondrial DAMPs, can activate PRRs such as the NLRP3 inflammasome, TLR9, cGAS/STING, and ZBP1. This process would explain the chronic inflammation that is observed in autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), type I diabetes (T1D), and Sjögren's syndrome. This review also provides a comprehensive overview of the importance of MERCs to mitochondrial function and morphology, cellular homeostasis, and the inflammatory response. MERCs play an important role in calcium homeostasis by mediating the transfer of calcium from the ER to the mitochondria and thereby facilitating the production of ATP. They also contribute to the synthesis and transfer of phospholipids, protein folding in the ER, mitochondrial fission, mitochondrial fusion, initiation of autophagosome formation, regulation of cell death/survival signaling, and regulation of immune responses. Therefore, alterations within MERCs could increase inflammatory signaling, modulate ER stress responses, cell homeostasis, and ultimately, the cell fate. This study shows severe ultrastructural alterations of mitochondria in salivary gland cells from Sjögren's syndrome patients for the first time, which could trigger alterations in cellular bioenergetics. This finding could explain symptoms such as fatigue and malfunction of the salivary glands in Sjögren's syndrome patients, which would contribute to the chronic inflammatory pathology of the disease. However, this is only a first step in solving this complex puzzle, and several other important factors such as changes in mitochondrial morphology, functionality, and their important contacts with other organelles require further in-depth study. Future work should focus on detecting the key milestones that are related to inflammation in patients with autoimmune diseases, such as Sjögren´s syndrome.

Role of neutrophil extracellular traps in radiation resistance of invasive bladder cancer

Radiation therapy (RT) is used in the management of several cancers; however, tumor radioresistance remains a challenge. Polymorphonuclear neutrophils (PMNs) are recruited to the tumor immune microenvironment (TIME) post-RT and can facilitate tumor progression by forming neutrophil extracellular traps (NETs). Here, we demonstrate a role for NETs as players in tumor radioresistance. Using a syngeneic bladder cancer model, increased NET deposition is observed in the TIME of mice treated with RT and inhibition of NETs improves overall radiation response. In vitro, the protein HMGB1 promotes NET formation through a TLR4-dependent manner and in vivo, inhibition of both HMGB1 and NETs significantly delays tumor growth. Finally, NETs are observed in bladder tumors of patients who did not respond to RT and had persistent disease post-RT, wherein a high tumoral PMN-to-CD8 ratio is associated with worse overall survival. Together, these findings identify NETs as a potential therapeutic target to increase radiation efficacy.

Radioresistance remains a challenge in the treatment of bladder cancer. In this study, the authors show in mice that radiation increases deposits of neutrophil extracellular traps (NETs) via a TLR4-dependent mechanism and that NETs-targeting strategies can improve the response to radiotherapy.

Neutrophil Extracellular Traps: New Aspects

Neutrophils are the "first line" of defense against pathogens in the locus of inflammation, where they use effector functions such as phagocytosis, degranulation, and formation of reactive oxygen species (ROS). In 2004, Artuto Zychlinsky characterized one more neutrophil effector function-the release of neutrophil extracellular traps (or NETs). NETs are a modified chromatin "decorated" by bactericidal proteins of granules, nucleus, and cytoplasm. The release of NETs can be activated by diverse physiological and pharmacological stimuli and depends on ROS, for which NADPH oxidase is the main source. In the process of NET formation, the release of bactericidal components of granules into the cytoplasm, modification of histones leading to chromatin decondensation, destruction of the nuclear envelope and cytoplasmic membrane with the involvement of gasdermin D protein, and, finally, the release of chromatin outside the cell occurs. At the same time, uncontrolled formation of NETs is a provoking factor in the development of many inflammatory and autoimmune diseases. NETs were found at autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, psoriasis, and vasculitis; NETs are involved in the pathogenesis of cardiovascular, pulmonary, and oncological diseases. In this review, the main ideas about the mechanisms of NET formation, as well as their role in physiological processes and pathogenesis of a number of diseases (including COVID-19), are discussed.

Neutrophil Extracellular Traps Tied to Rheumatoid Arthritis: Points to Ponder

In recent years, neutrophil extracellular traps at the forefront of neutrophil biology have proven to help capture and kill pathogens involved in the inflammatory process. There is growing evidence that persistent neutrophil extracellular traps drive the pathogenesis of autoimmune diseases. In this paper, we summarize the potential of neutrophil extracellular traps to drive the pathogenesis of rheumatoid arthritis and experimental animal models. We also describe the diagnosis and treatment of rheumatoid arthritis in association with neutrophil extracellular traps.

NETosis in Rheumatic Diseases

PURPOSE OF REVIEW

Neutrophils are the most numerous and the first responder cells of the innate immune system. Evidence suggests that neutrophils may play an essential role in the pathogenesis of multiple systemic diseases. A novel mechanism of neutrophil extracellular traps (NETs) leading to breaking of self-tolerance and generation of autoimmune responses in predisposed individuals has been described in various autoimmune conditions. The purpose of the review is to identify these important mechanisms of NETs leading to autoimmunity in various rheumatic diseases.

RECENT FINDINGS

NETs contain histone and chromatin, which contain important autoantigens. Many autoimmune conditions are associated with increased NET-generating capacity, unique low-density granulocyte population, and impaired NET degradation leading to persistent inflammation and tissue damage. NETs can also activate other immune cells, and their components may amplify the inflammatory response by activation of complement pathways and inflammasomes. NETs can also contribute to autoantibody formation in disorders such as rheumatoid arthritis, ANCA-associated vasculitis, and systemic lupus erythematosus by providing a constant source of autoantigens. NETs can also serve as biomarkers providing insights into disease diagnosis and therapeutics. NETs seem to play a primary role in inflammatory disease pathogenesis. Identification of different NET pathogenic pathways in various rheumatic conditions could provide new insights into disease pathogenesis and therapeutic targets could be developed towards the future treatment of inflammatory autoimmune diseases.

NETosis: Molecular Mechanisms, Role in Physiology and Pathology

NETosis is a program for formation of neutrophil extracellular traps (NETs), which consist of modified chromatin decorated with bactericidal proteins from granules and cytoplasm. Various pathogens, antibodies and immune complexes, cytokines, microcrystals, and other physiological stimuli can cause NETosis. Induction of NETosis depends on reactive oxygen species (ROS), the main source of which is NADPH oxidase. Activation of NADPH oxidase depends on increase in the concentration of Ca²⁺ in the cytoplasm and in some cases on the generation of ROS in mitochondria. NETosis includes release of the granule components into the cytosol, modification of histones leading to chromatin decondensation, destruction of the nuclear envelope, as well as formation of pores in the plasma membrane. In this review, basic mechanisms of NETosis, as well as its role in the pathogenesis of some diseases including COVID-19 are discussed.

The role of neutrophils in innate immunity-driven nonalcoholic steatohepatitis: lessons learned and future promise

The enrichment of innate immune cells and the enhanced inflammation represent the hallmark of non-alcoholic steatohepatitis (NASH), the advanced subtype with a significantly increased risk of progression to end-stage liver diseases within the spectrum of non-alcoholic fatty liver disease. Neutrophils are traditionally recognized as key components in the innate immune system to defend against pathogens. Recently, a growing body of evidence supports neutrophils as emerging key player in mediating the transition from steatosis to NASH, which is largely inspired by the histological findings in human liver biopsy indicating the enhanced infiltration of neutrophils as one of the key histological features of NASH. In this review, we discuss data regarding histological perspectives of hepatic infiltration of neutrophils in NASH. We also highlight the pathophysiological role of neutrophils in promoting metabolic inflammation in the liver through the release of a vast array of granule proteins, the interaction with other pro-inflammatory immune cells, and the formation of neutrophil extracellular traps. Neutrophil granule proteins possess pleiotropic effects on regulating neutrophil biology and functions. A variety of granule proteins (including lipocalin-2, myeloperoxidase, proteinase 3, neutrophil elastase, etc.) produced by neutrophils enhance liver metabolic inflammation, thereby promoting NASH progression by mediating neutrophil-macrophage interaction. Therapeutically, pharmacological inhibitors targeting neutrophil granule proteins hold promise to combat NASH. In addition, this article also summarizes potentials of neutrophils and its derived various granule proteins for the accurate, even non-invasive diagnosis of NASH.

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.

Role of Neutrophils in Psoriasis

Psoriasis is a common inflammatory disease that can involve the skin, joints, or both. The abnormalities of innate immunity play crucial roles in the pathogenesis of psoriasis. Neutrophils are the most abundant leukocytes in the circulation. Emerging evidences have demonstrated that neutrophils may play a role in autoimmune diseases. The neutrophil-to-lymphocyte ratio (NLR), the activity of neutrophils, and the number of NETotic cells were significantly higher in psoriasis patients compared to healthy controls. The number of low-density granulocytes (LDGs) in the blood of psoriasis patients was significantly higher than those in the control blood. Furthermore, neutrophils may play important roles in the cardiovascular risk in psoriasis. However, the exact role of neutrophils in psoriasis remains unclear. In this review, we highlight the role of neutrophils in the pathogenesis of psoriasis.

Neutrophil extracellular traps generation and degradation in patients with granulomatosis with polyangiitis and systemic lupus erythematosus

Neutrophils are one of the first cells to arrive at the site of infection, where they apply several strategies to kill pathogens: degranulation, respiratory burst, phagocytosis, and release of neutrophil extracellular traps (NETs). Recent discoveries try to connect NETs formation with autoimmune diseases, like systemic lupus erythematosus (SLE) or granulomatosis with polyangiitis (GPA) and place them among one of the factors responsible for disease pathogenesis. The aim of the study was to assess the NETotic capabilities of neutrophils obtained from freshly diagnosed autoimmune patients versus healthy controls. Further investigation involved assessing NETs production among treated patients. In the latter step, NETs degradation potency of collected sera from non-treated patients was checked. Lastly, the polymorphisms of the DNASE I gene among tested subjects were checked. NETs formation was measured in a neutrophil culture by fluorometry, while degradation assessment was performed with patients' sera and extracellular source of DNA. Additionally, Sanger sequencing was used to check potential SNP mutations between patients. About 121 subjects were enrolled into this study, 54 of them with a diagnosed autoimmune disorder. Neutrophils stimulated with NETosis inducers were able to release NETs in all cases. We have found that disease affected patients produce NETs more rapidly and in larger quantities than control groups, with up to 82.5% more released. Most importantly, we showed a difference between the diseases themselves. NETs release was 68.5% higher in GPA samples when compared to SLE ones while stimulated with Calcium Ionophore. Serum nucleases were less effective at degrading NETs in both autoimmune diseases, with a reduction in degradation of 20.9% observed for GPA and 18.2% for SLE when compared with the controls. Potential therapies targeting neutrophils and NETs should be specifically tailored to the type of the disease. Since there are significant differences between NETs release and disease type, a standard neutrophil targeted therapy could prevent over-generation of traps in some cases, while in others it would deplete the cells, leaving the immune system unresponsive to primary infections.

Activation of plasmacytoid dendritic cells and B cells with two structurally different Toll-like receptor 7 agonists

Synthetic Toll-like receptor (TLR) 7 agonists have been suggested as immune modulators in a range of conditions. In contrast, self-derived TLR7 activators, such as RNA-containing immune complexes (RNA-IC), can contribute to autoimmune diseases due to endogenous immune activation. The exact difference in immune cell response between synthetic and endogenous TLR7 triggers is only partly known. An understanding of these differences could aid in the development of new therapeutic agents and provide insights into autoimmune disease mechanisms. We therefore compared the stimulatory capacity of two TLR7 agonists, RNA-IC and a synthetic small molecule DSR-6434, on blood leucocytes, plasmacytoid dendritic cells (pDCs) and B cells from healthy individuals. IFN-α, IL-6, IL-8 and TNF levels were measured by immunoassays, and gene expression in pDCs was analysed by an expression array. DSR-6434 triggered 20-fold lower levels of IFN-α by pDCs, but higher production of IL-6, IL-8 and TNF, compared to RNA-IC. Furthermore, IFN-α and TNF production were increased with exogenous IFN-α2b priming, whereas IL-8 synthesis by B cells was reduced for both stimuli. Cocultivation of pDCs and B cells increased the RNA-IC-stimulated IFN-α and TNF levels, while only IL-6 production was enhanced in the DSR-6434-stimulated cocultures. When comparing pDCs stimulated with RNA-IC and DSR-6434, twelve genes were differentially expressed (log₂ fold change >2, adjusted P-value <.05). In conclusion, RNA-IC, which mimics an endogenous TLR7 stimulator, and the synthetic TLR7 agonist DSR-6434 trigger distinct inflammatory profiles in immune cells. This demonstrates the importance of using relevant stimuli when targeting the TLR7 pathway for therapeutic purposes.

Cytonemes Versus Neutrophil Extracellular Traps in the Fight of Neutrophils with Microbes

Neutrophils can phagocytose microorganisms and destroy them intracellularly using special bactericides located in intracellular granules. Recent evidence suggests that neutrophils can catch and kill pathogens extracellularly using the same bactericidal agents. For this, live neutrophils create a cytoneme network, and dead neutrophils provide chromatin and proteins to form neutrophil extracellular traps (NETs). Cytonemes are filamentous tubulovesicular secretory protrusions of living neutrophils with intact nuclei. Granular bactericides are localized in membrane vesicles and tubules of which cytonemes are composed. NETs are strands of decondensed DNA associated with histones released by died neutrophils. In NETs, bactericidal neutrophilic agents are adsorbed onto DNA strands and are not covered with a membrane. Cytonemes and NETs occupy different places in protecting the body against infections. Cytonemes can develop within a few minutes at the site of infection through the action of nitric oxide or actin-depolymerizing alkaloids of invading microbes. The formation of NET in vitro occurs due to chromatin decondensation resulting from prolonged activation of neutrophils with PMA (phorbol 12-myristate 13-acetate) or other stimuli, or in vivo due to citrullination of histones with peptidylarginine deiminase 4. In addition to antibacterial activity, cytonemes are involved in cell adhesion and communications. NETs play a role in autoimmunity and thrombosis.

Mitochondrial permeability transition pore is involved in oxidative burst and NETosis of human neutrophils

Neutrophils release neutrophil extracellular traps (NETs) in response to numerous pathogenic microbes as the last suicidal resource (NETosis) in the fight against infection. Apart from the host defense function, NETs play an essential role in the pathogenesis of various autoimmune and inflammatory diseases. Therefore, understanding the molecular mechanisms of NETosis is important for regulating aberrant NET release. The initiation of NETosis after the recognition of pathogens by specific receptors is mediated by an increase in intracellular Ca²⁺ concentration, therefore, the use of Ca²⁺ ionophore A23187 can be considered a semi-physiological model of NETosis. Induction of NETosis by various stimuli depends on reactive oxygen species (ROS) produced by NADPH oxidase, however, NETosis induced by Ca²⁺ ionophores was suggested to be mediated by ROS produced in mitochondria (mtROS). Using the mitochondria-targeted antioxidant SkQ1 and specific inhibitors of NADPH oxidase, we showed that both sources of ROS, mitochondria and NADPH oxidase, are involved in NETosis induced by A23187 in human neutrophils. In support of the critical role of mtROS, SkQ1-sensitive NETosis was demonstrated to be induced by A23187 in neutrophils from patients with chronic granulomatous disease (CGD). We assume that Ca²⁺-triggered mtROS production contributes to NETosis either directly (CGD neutrophils) or by stimulating NADPH oxidase. The opening of the mitochondrial permeability transition pore (mPTP) in neutrophils treated by A23187 was revealed using the electron transmission microscopy as a swelling of the mitochondrial matrix. Using specific inhibitors, we demonstrated that the mPTP is involved in mtROS production, NETosis, and the oxidative burst induced by A23187.

Neutrophil Elastase and Neutrophil Extracellular Traps in the Tumor Microenvironment

Tumor-associated neutrophils (TANs) play a major role during cancer development and progression in the tumor microenvironment. Neutrophil elastase (NE) is a serine protease normally expressed in neutrophil primary granules. Formation of neutrophil extracellular traps (NETs), a mechanism used by neutrophils, has been traditionally associated with the capture and killing of bacteria. However, there are recent discoveries suggesting that NE secretion and NETs formation are also involved in the tumor microenvironment. Here, we focus on how NE and NETs play a key regulatory function in the tumor microenvironment, such as tumor proliferation, distant metastasis, tumor-associated thrombosis, and antitumor activity. Additionally, the potential use of NETs, NE, or associated molecules as potential disease activity biomarkers or therapeutic targets will be introduced.

Neutrophil extracellular traps activate lung fibroblast to induce polymyositis-related interstitial lung diseases via TLR9-miR-7-Smad2 pathway

Excessive neutrophil extracellular trap (NET) formation may contribute to polymyositis (PM)‐associated interstitial lung diseases (ILD), but the underlying mechanism is not fully revealed. In this study, we found that NET accelerated the progression of ILD and promoted pulmonary fibrosis (PF) in vivo. miR‐7 expression was down‐regulated in lung tissue of PM group than control group, and NETs further decreased miR‐7 expression. TLR9 and Smad2 were up‐regulated in lung tissue of PM group than control group, and NETs further increased TLR9 and Smad2 expressions. In vitro experiments showed that PMA‐treated NETs accelerated the proliferation of LF and their differentiation into myofibroblast (MF), whereas DNase I decreased the promotion effect of NETs. Neutrophil extracellular trap components myeloperoxidase (MPO) and histone 3 also promoted the proliferation and differentiation of LF. In addition, we demonstrated that TLR9 involved in the regulation of NETs on LF proliferation and differentiation, and confirmed the interaction between miR‐7 and Smad2 in LF. Finally, miR‐7‐Smad2 pathway was confirmed to be involved in the regulation of TLR9 on LF proliferation and differentiation. Therefore, NETs promote PM‐related ILD, and TLR9‐miR‐7‐Smad2 signalling pathway is involved in the proliferation of LFs and their differentiation into MFs.

Lymphopenia and neutropenia are associated with subsequent incident proteinuria in Danish patients with systemic lupus erythematosus

Objective: The aim of this study was to investigate whether incident proteinuria in patients with systemic lupus erythematosus (SLE) was preceded by changes in blood lymphocytes and neutrophil counts and/or neutrophil-lymphocyte ratio (NLR).Method: SLE patients with no proteinuria before or at the time of classification were included. Longitudinal data on SLE manifestations, vital status, and SLE-associated medications were collected during clinical visits and chart review. Laboratory data were collected through a nationwide database. Lymphopenia, severe lymphopenia, and neutropenia were defined as values below 0.8 × 10⁹, 0.5 × 10⁹, and 2.0 × 10⁹ cells/L, respectively. High NLR was defined as values above the median. Proteinuria was defined by at least two measurements of elevated urine protein excretion (> 0.5 g/day). Hazard ratios (HRs) were calculated by Cox modelling using time-dependent continuous and binary covariates based on multiple laboratory measurements adjusted for use of immunosuppressants.Results: In total, 260 SLE patients were available for the analysis, of whom 30 (12%) developed incident proteinuria following the diagnosis of SLE. Median follow-up time was 73.5 months. Lymphocyte and neutrophil counts, but not NLR, were associated with incident proteinuria. HRs for incident proteinuria were 2.71 for lymphopenia [95% confidence interval (CI) 1.20-6.11], 4.73 for severe lymphopenia (95% CI 1.93-11.59), and 2.54 for neutropenia (95% CI 1.14-5.65).Conclusion: Lymphopenia and neutropenia predicted the risk of first-time proteinuria independently of immunosuppressants.

Neutrophils in Psoriasis

Neutrophils are the most abundant innate immune cells. The pathogenic roles of neutrophils are related to chronic inflammation and autoimmune diseases. Psoriasis is a chronic systemic inflammatory disease affecting ~2–3% of the world population. The abundant presence of neutrophils in the psoriatic skin lesions serves as a typical histopathologic hallmark of psoriasis. Recent reports indicated that oxidative stress, granular components, and neutrophil extracellular traps from psoriatic neutrophils are related to the initial and maintenance phases of psoriasis. This review provides an overview on the recent (up to 2019) advances in understanding the role of neutrophils in the pathophysiology of psoriasis, including the effects of respiratory burst, degranulation, and neutrophil extracellular trap formation on psoriatic immunity and the clinical relationships.

Effects of Neutrophil Extracellular Traps on Bovine Mammary Epithelial Cells in vitro

Bovine mastitis is a common infectious disease which causes huge economic losses in dairy cattle. Bovine mammary epithelial cell (BMEC) damage usually directly causes the decrease of milk production, which is one of the most important causes of economic loss. NETs, novel effector mechanisms, are reported to exacerbate the pathogenesis of several inflammatory diseases. NETs formation has also been observed in the milk and mammary glands of sheep. However, the effects and detailed mechanisms of NETs on BMEC damage remain unclear. Thus, we aim to examine the effects of NETs on BMECs in vitro, and further to investigate the detail mechanism. In this study, the cytotoxicity of NETs on BMECs was determined using lactic dehydrogenase (LDH) levels in culture supernatants. Histone-induced BMEC damage was examined by flow cytometry and immunofluorescence analysis. The activities of caspase 1, caspase 3, caspase 11, and NLRP3 was detected using western blotting and immunohistochemical analysis. The results showed that NETs and their component histone significantly increased cytotoxicity to BMECs, suggesting the critical role of NETs, and their component histone in BMEC damage. In addition, histone could also induce necrosis, pyroptosis, and apoptosis of BMECs, and the mechanisms by which histone leads to BMEC damage occurred via activating caspase 1, caspase 3, and NLRP3. Altogether, NETs formation regulates inflammation and BMEC damage in mastitis. Inhibiting excess NETs formation may be useful to ameliorate mammary gland damage associated with mastitis.

Rheumatoid arthritis (RA) and cardiovascular disease

Patients with rheumatoid arthritis (RA) suffer cardiovascular events 1.5-2 fold than the general population, and cardiovascular (CV) events are leading cause of death in patients with RA. It is known that patients with RA have endothelial dysfunction, related with impaired function of endothelial progenitor cells (EPCs). The mechanistic pathways leading to endothelial function are complicated, but understanding these mechanisms may open new frontiers of management and therapies to patients suffering from atherosclerosis. Inflammation is a key factor in atherosclerosis, including endothelial function, plaque stabilization and post infarct remodeling; thus, inhibition of TNF-α may affect the inflammatory burden and plaque vulnerability leading to less cardiovascular events and myocardial infarctions. An aggressive management of inflammation may lead to a significant improvement in the clinical cardiovascular outcome of patients with RA. The clinical evidence that showed a reduced risk of CV events following treatment with anti-inflammatory agents may suggest a new approach to treat atherosclerosis, i.e., inhibition of inflammation using biological medications that were primarily aimed to treat the high scale inflammation of RA and other autoimmune-inflammatory diseases, but may be useful also to prevent progression of atherosclerosis.

Human host defence peptide LL37 and anti-cyclic citrullinated peptide antibody in early inflammatory arthritis

Objective

Antibodies to citrullinated peptides (anti-CCP) develop in individuals predisposed to rheumatoid arthritis (RA). Neutrophil extracellular traps are a major source of citrullinated antigens and the immunomodulatory host defence peptide LL-37. Vitamin D regulates LL-37 expression. This study assessed the associations of LL-37 and anti-CCP, vitamin D metabolites and vitamin D receptor (VDR) polymorphisms in early inflammatory arthritis (EIA).

Methods

Serum LL-37, 25-hydroxy-vitamin D (25OHvitD) and anti-CCP were measured by ELISA in treatment naïve EIA (n = 181). VDR single nucleotide polymorphisms (Fok1, Bsm1, Apa1, Taq1, Cdx-2) and HLADRB1 shared epitope (SE) alleles were detected by DNA amplification. Associations were tested in multivariable models. Median (25%, 75%) or percentiles are reported.

Results

Participants (70 % female, age 56 [45, 66] years, disease activity score [DAS28ESR3var] 3.7 [2.8, 4.8], 41 % anti-CCP positive, 68 % RA) had low serum 25OHvitD; 20.5 nmol/L (13.9, 29.0). In multivariable models, controlling for age, sex, SE, smoking and vitamin D deficiency, LL37 level (top quartile) associated with anti-CCP seropositivity (OR 22; 95% CI 4 to 104).

Conclusions

Levels of circulating LL-37 are associated with anti-CCP seropositivity. LL37 activity may be one mechanism linking infection and toxin exposure to anti-CCP generation.

Neutrophil hyperactivation correlates with Alzheimer's disease progression

OBJECTIVE

Recent studies have underlined the effect of systemic inflammation on the pathophysiology of Alzheimer's disease (AD). Neutrophils are key components of early innate immunity and contribute to uncontrolled systemic inflammation if not tightly regulated. The aim of our study was to fully characterize human circulating neutrophils at different disease stages in AD.

METHODS

We analyzed neutrophil phenotypes and functions in 42 patients with AD (16 with mild cognitive impairment and 26 with dementia), and compared them to 22 age-matched healthy subjects. This study was performed directly in whole blood to avoid issues with data interpretation related to cell isolation procedures.

RESULTS

Blood samples from AD patients with dementia revealed neutrophil hyperactivation associated with increased reactive oxygen species production and increased levels of intravascular neutrophil extravascular traps. The homeostasis of circulating neutrophils in these patients also changed: The ratio between the harmful hyperreactive CXCR4^high /CD62L^low senescent and the CD16^bright /CD62L^dim immunosuppressive neutrophil subsets rose in the later stage of the disease. These abnormalities were greater in fast-decliner than in slow-decliner patients.

INTERPRETATION

Our results indicate that the inflammatory properties of circulating neutrophils shift as the percentage of aged neutrophils expands in patients with AD-changes that may play an instrumental role in establishing systemic chronic inflammation. Most important, our data strongly suggest that the neutrophil phenotype may be associated with the rate of cognitive decline and may thus constitute an innovative and prognostic blood biomarker in patients with AD. Ann Neurol 2018;83:387-405.

Bovine neutrophils form extracellular traps in response to the gastrointestinal parasite Ostertagia ostertagi

Ostertagia ostertagi (OO) is a widespread parasite that causes chronic infection in cattle and leads to annual losses of billions of dollars in the cattle industry. It remains unclear why cattle are unable to mount an effective immune response despite a large influx of immune cells to the infected abomasal mucosa and draining lymph nodes. Neutrophils, the immune system’s first responders, have the capacity to release neutrophil extracellular traps (NETs) to contain various pathogens, including some parasites. In the present study, the mechanisms by which O. ostertagi influences bovine NET formation were investigated. O. ostertagi larval soluble extract (OO extract) was able to induce typical NETs by purified neutrophils in vitro, confirmed by co-localization of extracellular DNA with typical NET-associated proteins histone and neutrophil elastase (NE). Consistent with existing literature, inhibition assays demonstrated that these OO extract-induced NETs were dependent upon the enzymes NADPH oxidase and myeloperoxidase (MPO). Live OO stage 4 larvae (L4) stimulated neutrophils to form NETs similar to those induced by OO extract. Bovine neutrophils also released NETs in response to Caenorhabditis elegans, a free-living soil nematode, suggesting that bovine NET production may be a conserved mechanism against a broad range of nematodes. This is the first report demonstrating O. ostertagi-induced NET formation by bovine neutrophils, a potentially underappreciated mechanism in the early immune response against nematode infections.

Sulforaphane as anticancer agent: A double-edged sword? Tricky balance between effects on tumor cells and immune cells

Sulforaphane (SFN) is a naturally occurring isothiocyanate derived from cruciferous vegetables such as broccoli. It has been reported to inhibit the growth of a variety of cancers, such as breast, prostate, colon, skin, lung, gastric or bladder cancer. SFN is supposed to act primarily as an antioxidant due to the activation of the Nrf2-Keap1 signaling pathway. This enhances the activity of phase II detoxifying enzymes and the trapping of free radicals. Finally, SFN induces cell cycle arrest or apoptosis of tumor cells. Here, we discuss effects of SFN on the immune defense system. In contrast to the situation in tumor cells, SFN acts pro-oxidatively in primary human T cells. It increases intracellular ROS levels and decreases GSH, resulting in inhibition of T cell activation and T cell effector functions. Regarding the use of SFN as an "anticancer agent" we conclude that SFN could act as a double-edged sword. On the one hand it reduces carcinogenesis, on the other hand it blocks the T cell-mediated immune response, the latter being important for immune surveillance of tumors. Thus, SFN could also interfere with the successful application of immunotherapy by immune checkpoint inhibitors (e.g. CTLA-4 antibodies and PD-1/PD-L1 antibodies) or CAR T cells. Therefore, a combination of SFN with T cell-mediated cancer immunotherapies does not seem advisable.

Polydatin effectively attenuates disease activity in lupus-prone mouse models by blocking ROS-mediated NET formation

Background

Neutrophil extracellular trap (NET) formation has been described to be closely involved in the pathogenesis of systemic lupus erythematosus (SLE). In this study, we aimed to investigate the effect of polydatin (PD) on NET formation and its effects on disease activity in lupus-prone mouse models.

Methods

In vitro, neutrophils from SLE patients and healthy people stimulated with phorbol 12-myristate 13-acetate (PMA) or phosphate-buffered saline (PBS) were treated with PD, and reactive oxygen species (ROS) production and NET formation examined. In vivo, pristane-induced lupus (PIL) mice were treated with vehicle, PD, mycophenolate mofetil (MMF) or cyclophosphamide (CYC) while MRL/lpr mice were treated with vehicle or PD. Proteinuria, serum autoantibodies, ROS production, NET formation and kidney histopathology were tested.

Results

Consistent with previous findings, blood neutrophils from SLE patients showed increased spontaneous NET formation. Both in vivo and in vitro, PD treatment significantly inhibited ROS production and NET release by neutrophils. In MRL/lpr mouse model, PD administration reduced the proteinuria, circulating autoantibody levels, and deposition of NETs and immune complex in the kidneys. In addition, PD treatment ameliorated lupus-like features in PIL mice as MMF or CYC did.

Conclusions

PD treatment inhibited ROS-mediated NET formation and ameliorated lupus manifestations in both PIL mice and MRL/lpr mice. These results highlight the involvement of NETosis in SLE pathogenesis and reveal that PD might be a potential therapeutic agent for SLE or other autoimmune diseases.

Gut Microbiota-Stimulated Innate Lymphoid Cells Support β-Defensin 14 Expression in Pancreatic Endocrine Cells, Preventing Autoimmune Diabetes

The gut microbiota is essential for the normal function of the gut immune system, and microbiota alterations are associated with autoimmune disorders. However, how the gut microbiota prevents autoimmunity in distant organs remains poorly defined. Here we reveal that gut microbiota conditioned innate lymphoid cells (ILCs) induce the expression of mouse β-defensin 14 (mBD14) by pancreatic endocrine cells, preventing autoimmune diabetes in the non-obese diabetic (NOD) mice. MBD14 stimulates, via Toll-like receptor 2, interleukin-4 (IL-4)-secreting B cells that induce regulatory macrophages, which in turn induce protective regulatory T cells. The gut microbiota-derived molecules, aryl hydrocarbon receptor (AHR) ligands and butyrate, promote IL-22 secretion by pancreatic ILCs, which induce expression of mBD14 by endocrine cells. Dysbiotic microbiota and low-affinity AHR allele explain the defective pancreatic expression of mBD14 observed in NOD mice. Our study reveals a yet unidentified crosstalk between ILCs and endocrine cells in the pancreas that is essential for the prevention of autoimmune diabetes development.

Platelet communication with the vascular wall: role of platelet-derived microparticles and non-coding RNAs

Platelets play an important role in vascular homeostasis through their interaction with circulating blood cells as well as the vascular wall. Platelet-mediated communication with other cells can take the form of direct cell-cell interactions via membrane receptors or indirectly through the release of different soluble factors stored in their granules as well as through the release of microparticles. The latter carry different proteins and RNAs which are transferred to the target cells. The aim of this review is to discuss the role of platelet-derived factors, adhesion molecules as well as RNAs as mediators of the cross-talk between platelets and the vessel wall.

Neutrophil elastase and myeloperoxidase mRNA expression in overweight and obese subjects

Neutrophil elastase and myeloperoxidase enzymes have been implicated in high-fat diet-induced obesity, insulin resistance (IR) and atherosclerosis in animal models. The aim of the present study was to explore neutrophil elastase and myeloperoxidase mRNA expressions in the peripheral blood leukocytes (PBL) in overweight and obese subjects, and to correlate those mRNA expressions with BMI, IR and cardiovascular biomarkers. In this cross-sectional study, 74 apparently healthy subjects including 22 lean, 27 overweight and 25 obese subjects were recruited. Cardiovascular and metabolic biomarkers were evaluated from fasting blood samples. The mRNA levels of neutrophil elastase and myeloperoxidase genes in the PBL were quantified by real-time PCR. Compared to lean group, the overweight and obese groups showed significant upregulation of both neutrophil elastase (p < 0.001) and myeloperoxidase (p < 0.03) mRNA expressions in the PBL. But no difference was found between overweight and obese groups. The neutrophil elastase and myeloperoxidase mRNA levels showed significant positive correlation with BMI, serum triglyceride, atherogenic index of plasma and 10-year risk of developing cardiovascular disease. But no correlation was found with glucose, insulin or IR. It was concluded that the neutrophil elastase and myeloperoxidase genes are up-regulated in both overweight and obese subjects and are associated with BMI and markers of cardiovascular disease.

Regulation and function of interleukin-36 cytokines

The interleukin (IL)-36 cytokines include 3 agonists, IL-36α, IL-36β, and IL-36γ that bind to a common receptor composed of IL-36R and IL-1RAcP to stimulate inflammatory responses. IL-36Ra is a natural antagonist that binds to IL-36R, but does not recruit the co-receptor IL-1RAcP and does not stimulate any intracellular responses. The IL-36 cytokines are expressed predominantly by epithelial cells and act on a number of cells including immune cells, epithelial cells, and fibroblasts. Processing of the N-terminus is required for full agonist or antagonist activity for all IL-36 members. The role of IL-36 has been extensively demonstrated in the skin where it can act on keratinocytes and immune cells to induce a robust inflammatory response that has been implicated in psoriatic disorders. Emerging data also suggest a role for this cytokine family in pulmonary and intestinal physiology and pathology.

β2 -Adrenoceptors inhibit neutrophil extracellular traps in human polymorphonuclear leukocytes

This study tests the hypothesis that in isolated human polymorphonuclear leukocytes (PMN) adrenergic ligands can affect neutrophil extracellular trap (NET) formation. We have previously shown that, in PMN, adrenaline (A), through the activation of adrenergic receptors (AR), reduces stimulus-dependent cell activation; we have, therefore, planned to investigate if AR are involved in NET production. PMN were obtained from venous blood of healthy subject. The ability of adrenergic ligands to affect reactive oxygen species (ROS) production, NET production, and cell migration was investigated in cells cultured under resting conditions or after activation with N-formyl-methionyl-leucyl-phenylalanine (fMLP), LPS, or IL-8. Stimuli-induced NET production measured as ROS, microscopic evaluation, and elastase production was reverted by A and this effect was blocked by the selective β₂ -AR antagonist ICI-118,551. The stimulus-induced ROS generation and migration was prevented by A and by isoprenaline (ISO), and these effects were counteracted only by ICI-118,551 and not by the other two selective ligands for the β₁ and β₃ -AR. Finally, the presence of the β-ARs on PMN was confirmed, by means of microscopy and flow cytometry. The data of the present study suggest that adrenergic compounds, through the interaction of mainly β₂ -AR, are able to affect neutrophil functions. These data are suggestive of a possible therapeutic role of β₂ -AR ligands (in addition to their classical use), promoting the possible therapeutic relevance of adrenergic system in the modulation of innate immunity proposing their possible use as anti-inflammatory drugs.

NETosis, complement, and coagulation: a triangular relationship

NETosis is a regulated form of neutrophil cell death that contributes to the host defense against pathogens and was linked to various diseases soon after its first description in 2004. During NETosis, neutrophils release neutrophil extracellular traps (NETs), which can capture and kill bacteria and other pathogens to prevent them from spreading. Although substantial progress has been made in our understanding of NETosis, the precise mechanism underlying NETosis is still a matter of debate. Research continues to elucidate the molecular pathways involved in NETosis. In recent years, interactions with the complement and coagulation systems have become increasingly apparent. Activated complement proteins can stimulate NET formation, and NETs, in turn, can serve as a platform for complement activation. In addition, NETs can act as a scaffold for thrombus formation during coagulation. While crosstalk between the coagulation and complement systems has been previously described, NETosis appears to be a third important player in this consortium to protect the host against pathogens. This review summarizes our current knowledge on the mutual interactions between NETosis, the complement system and the coagulation system, with an emerging description of their complex triangular relationship.

Circulating Neutrophil Extracellular Traps Are Elevated in Patients With Deep Infiltrating Endometriosis

Neutrophil extracellular traps (NETs) have been described to be related to the pathogenesis of inflammatory and autoimmune conditions. Endometriosis is currently considered a chronic inflammatory condition. Therefore, we performed a preliminary case-control study to compare the circulating plasma NET levels in patients with surgically confirmed endometriosis (E group, n = 82) and those of patients without surgical findings of endometriosis (C group, n = 35). Venous blood samples were obtained at the time of surgery. Circulating plasma NET levels were assessed as histone-DNA complexes (ie, nucleosomes) by a quantitative sandwich enzyme-linked immunosorbent assay. The results were expressed in arbitrary units. Circulating plasma NET levels were significantly higher in the E group compared with the C group (median [25th; 75th percentiles]): E group: 0.734 [0.484; 1.363]; C group: 0.541 [0.411; 0.653]; P = .005). The subanalysis of E group patients with deep infiltrating endometriosis (DIE group) or without DIE (non-DIE group) showed that plasma NET levels were higher in the DIE group ( P = .02). No differences were observed in NET levels among patients with and without severe pelvic pain or in patients with and without infertility, regardless of the presence of endometriotic lesions. Therefore, our study shows significantly higher NET levels in patients with endometriosis, which seem to be attributed to increased levels in the subgroup of patients with DIE, suggesting that the presence of elevated circulating plasma NET levels may reflect an inflammatory status in this gynecological condition. Further research is warranted to confirm our findings and to assess the exact role of NETs in the pathophysiological mechanisms of endometriosis.

Role of interferons in SLE

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease that affects many different organ systems, with excessive production of type I interferons (IFNs) and autoantibodies against nucleic acids as hallmarks. Activation of the type I IFN system in SLE is due to continuous stimulation of plasmacytoid dendritic cells by endogenous nucleic acids, leading to sustained type I IFN production. This is reflected by an overexpression of type I IFN-regulated genes or an IFN signature. Type I IFNs have effects on both the innate and adaptive immune systems, which contribute to both loss of tolerance and the autoimmune disease process. In this review, we discuss the current understanding of IFNs in SLE, focusing on their regulation, the influence of genetic background, and environmental factors and therapies that are under development aiming to inhibit the type I IFN system in SLE.

Redox Regulation of Inflammatory Processes Is Enzymatically Controlled

Redox regulation depends on the enzymatically controlled production and decay of redox active molecules. NADPH oxidases, superoxide dismutases, nitric oxide synthases, and others produce the redox active molecules superoxide, hydrogen peroxide, nitric oxide, and hydrogen sulfide. These react with target proteins inducing spatiotemporal modifications of cysteine residues within different signaling cascades. Thioredoxin family proteins are key regulators of the redox state of proteins. They regulate the formation and removal of oxidative modifications by specific thiol reduction and oxidation. All of these redox enzymes affect inflammatory processes and the innate and adaptive immune response. Interestingly, this regulation involves different mechanisms in different biological compartments and specialized cell types. The localization and activity of distinct proteins including, for instance, the transcription factor NFκB and the immune mediator HMGB1 are redox-regulated. The transmembrane protein ADAM17 releases proinflammatory mediators, such as TNFα, and is itself regulated by a thiol switch. Moreover, extracellular redox enzymes were shown to modulate the activity and migration behavior of various types of immune cells by acting as cytokines and/or chemokines. Within this review article, we will address the concept of redox signaling and the functions of both redox enzymes and redox active molecules in innate and adaptive immune responses.

Neutrophil extracellular traps (NETs) in autoimmune diseases: A comprehensive review

Neutrophil extracellular traps (NETs) are fibrous networks which protrude from the membranes of activated neutrophils. NETs are found in a variety of conditions such as infection, malignancy, atherosclerosis, and autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV), psoriasis, and gout. Studies suggest that an imbalance between "NETosis," which is a process by which NETs are formed, and NET degradation may be associated with autoimmune diseases. Neutrophils, interleukin-8, ANCA and other inflammatory molecules are considered to play a key role in NET formation. Prolonged exposure to NETs-related cascades is associated with autoimmunity and increases the chance of systemic organ damage. In this review, we discuss the roles of various inflammatory molecules in relation to NETs. We also describe the role of NETs in the pathogenesis of autoimmune diseases and discuss the possibility of using targeted therapies directed to NETs and associated molecules to treat autoimmune diseases.

Update on systemic vasculitides

Management of systemic vasculitis has been revolutionised over the last decade with the introduction of targeted biological agents. With an increase in both the prevalence and the recognition of vasculitis as well as the high cost of these agents, it is important to ensure their most optimal utilisation. The goals of vasculitis therapy include the induction and maintenance of remissions, preventing relapses, reducing the toxicity of therapy with the aim of reducing morbidity and mortality as well as improving the quality of life of those afflicted. This review focuses on the recent advances in the diagnosis, surveillance and treatment of these conditions.

Neutrophil Extracellular Traps in Atherosclerosis and Atherothrombosis

Neutrophil extracellular traps expelled from suicidal neutrophils comprise a complex structure of nuclear chromatin and proteins of nuclear, granular, and cytosolic origin. These net-like structures have also been detected in atherosclerotic lesions and arterial thrombi in humans and mice. Functionally, neutrophil extracellular traps have been shown to induce activation of endothelial cells, antigen-presenting cells, and platelets, resulting in a proinflammatory immune response. Overall, this suggests that they are not only present in plaques and thrombi but also they may play a causative role in triggering atherosclerotic plaque formation and arterial thrombosis. This review will focus on current findings of the involvement of neutrophil extracellular traps in atherogenesis and atherothrombosis.

Increased Neutrophil Extracellular Trap Formation in Uremia Is Associated with Chronic Inflammation and Prevalent Coronary Artery Disease

Background. Neutrophils are involved in the pathogenesis of atherosclerosis by neutrophil extracellular trap (NET) formation. We hypothesized that the NET formation of neutrophils might be changed in end-stage renal disease (ESRD) patients, explaining their higher incidence of coronary artery diseases (CAD). Method. A cross-sectional study was performed in 60 maintenance hemodialysis (MHD) patients, 30 age- and sex-matched healthy individuals (HV, negative control), and 30 patients with acute infection (positive control). Neutrophil activation and function were measured with reactive oxygen species (ROS) activity, degranulation, NET formation, and phenotypical changes. Result. Compared with HV, neutrophils extracted from MHD patients displayed significantly increased levels of basal NET formation, ROS production, and degranulation, suggesting spontaneous activation in uremia. Also, an increase in citrullinated histone H3 was detected in this group compared to the HV. And neutrophils from HV were normal CD16^bright/CD62L^bright cells; however, neutrophils from MHD were CD16^bright/CD62L^dim, similar to those from patients with acute infections. Interestingly, multivariate analyses identified the prevalent CAD and neutrophil counts as independent determinants of baseline NET formation (β = 0.323, p = 0.016 and β = 0.369, p = 0.006, resp.). Conclusions. Uremia-associated-increased NET formation may be a sign of increased burden of atherosclerosis.

Neutrophil Extracellular Traps, Antiphospholipid Antibodies and Treatment

Neutrophil extracellular traps (NETs) are a network of extracellular fibers, compounds of chromatin, neutrophil DNA and histones, which are covered with antimicrobial enzymes with granular components. Autophagy and the production of reactive oxygen species (ROS) by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are essential in the formation of NETs. There is increasing evidence that suggests that autoantibodies against beta-2-glycoprotein-1 (B2GP1) induce NETs and enhance thrombosis. Past research on new mechanisms of thrombosis formation in antiphospholipid syndrome (APS) has elucidated the pharmacokinetics of the most common medication in the treatment of the disease.

Nucleic acids as cofactors for factor XI and prekallikrein activation: Different roles for high-molecular-weight kininogen

The plasma zymogens factor XI (fXI) and prekallikrein (PK) are activated by factor XIIa (fXIIa) during contact activation. Polyanions such as DNA and RNA may contribute to thrombosis and inflammation partly by enhancing PK and fXI activation. We examined PK and fXI activation in the presence of nucleic acids, and determine the effects of the cofactor high molecular weight kininogen (HK) on the reactions. In the absence of HK, DNA and RNA induced fXI autoactivation. Proteases known to activate fXI (fXIIa and thrombin) did not enhance this process appreciably. Nucleic acids had little effect on PK activation by fXIIa in the absence of HK. HK had significant but opposite effects on PK and fXI activation. HK enhanced fXIIa activation of PK in the presence of nucleic acids, but blocked fXI autoactivation. Thrombin and fXIIa could overcome the HK inhibitory effect on autoactivation, indicating these proteases are necessary for nucleic acid-induced fXI activation in an HK-rich environment such as plasma. In contrast to PK, which requires HK for optimal activation, fXI activation in the presence of nucleic acids depends on anion binding sites on the fXI molecule. The corresponding sites on PK are not necessary for PK activation. Our results indicate that HK functions as a cofactor for PK activation in the presence of nucleic acids in a manner consistent with classic models of contact activation. However, HK has, on balance, an inhibitory effect on nucleic acid-supported fXI activation and may function as a negative regulator of fXI activation.

The Dual Role of Neutrophils in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are characterised by aberrant immunological responses leading to chronic inflammation without tissue regeneration. These two diseases are considered distinct entities, and there is some evidence that neutrophil behaviour, above all other aspects of immunity, clearly separate them. Neutrophils are the first immune cells recruited to the site of inflammation, and their action is crucial to limit invasion by microorganisms. Furthermore, they play an essential role in proper resolution of inflammation. When these processes are not tightly regulated, they can trigger positive feedback amplification loops that promote neutrophil activation, leading to significant tissue damage and evolution toward chronic disease. Defective chemotaxis, as observed in Crohn’s disease, can also contribute to the disease through impaired microbe elimination. In addition, through NET production, neutrophils may be involved in thrombo-embolic events frequently observed in IBD patients. While the role of neutrophils has been studied in different animal models of IBD for many years, their contribution to the pathogenesis of IBD remains poorly understood, and no molecules targeting neutrophils are used and validated for the treatment of these pathologies. Therefore, it is crucial to improve our understanding of their mode of action in these particular conditions in order to provide new therapeutic avenues for IBD.

Understanding the molecular mechanisms of NETs and their role in antiviral innate immunity

Polymorphonuclear neutrophils (PMNs) are the most abundant cells in the context of innate immunity; they are one of the first cells to arrive at the site of viral infection constituting the first line of defense in response to invading pathogens. Indeed, neutrophils are provided with several defense mechanisms including release of cytokines, cytotoxic granules and the last recently described neutrophil extracellular traps (NETs). The main components of NETs are DNA, granular antimicrobial peptides, and nuclear and cytoplasmic proteins, that together play an important role in the innate immune response. While NETs were first described as a mechanism against bacteria and fungi, recently, several studies are beginning to elucidate how NETs are involved in the host antiviral response and the prominent characteristics of this new mechanism are discussed in the present review.

NETosis provides the link between activation of neutrophils on hemodialysis membrane and comorbidities in dialyzed patients

INTRODUCTION

Neutrophil extracellular traps (NETs) are formed by activated neutrophils during the process of NETosis in which the nuclear material is released into extracellular space, including DNA molecules, citrullinated histones, and neutrophil granule enzymes, such as elastase. This material forms networks that are able not only to physically entrap bacteria but also to provide elevated concentration of bactericidal components. Over the last years, it has become clear that NETs can also be formed under numerous sterile inflammatory conditions, i.e., thrombosis, cancer, SLE, atherosclerosis, and diabetes.

METHOD

We reviewed studies published until July 2016 to find possible associations between elevated cell-free DNA levels in dialyzed patients and the process of NETosis and its consequences.

RESULTS

The process of NETosis, its elevated activation, or impaired clearance provides the link between clinical conditions and elevated levels of cell-free DNA found in plasma after the hemodialytic procedure which itself is able to activate neutrophils via platelets and ROS formation. NETs stimulate thrombosis and endothelial damage, and their formation may contribute to the development of spectrum of comorbidities described in dialyzed patients.

CONCLUSION

The study of plasma cell-free DNA levels together with markers of NETosis could contribute to the evaluation of the influence of hemodialysis on the immune system of patients.

Immune complexes and complexity: investigating mechanisms of renal disease

The deposition of immune complexes is the causal factor in distinct renal pathologies, e.g., lupus nephritis and membranous nephritis. The location of these deposits within a tissue biopsy is often the key to establishing a diagnosis. However, how immune complexes come to be deposited below the vascular endothelium was, until now, a mystery, as was their contribution to inducing inflammation. A recent paper in Cell by Stamatiades et al. (Cell 164(4):991-1003, 2016) demonstrates the active transport of immune complexes by the vascular endothelial cells and an Fc receptor-dependent uptake by tissue-resident macrophages. This leads to the activation of these macrophages and the release of pro-inflammatory cytokines, which in turn recruits immune cells from the blood into the kidney. The identification of these mechanisms should lead to a better stratification of kidney diseases and hopefully to the development of specific therapies.

Elevated homocysteine levels in type 2 diabetes induce constitutive neutrophil extracellular traps

Constitutively active neutrophil extracellular traps (NETs) and elevated plasma homocysteine are independent risk factors for Type 2 Diabetes (T2D) associated vascular diseases. Here, we show robust NETosis due to elevated plasma homocysteine levels in T2D subjects and increased components of NETs such as neutrophil elastase and cell free DNA. Cooperative NETs formation was observed in neutrophils exposed to homocysteine, IL-6 and high glucose suggesting acute temporal changes tightly regulate constitutive NETosis. Homocysteine induced NETs by NADPH oxidase dependent and independent mechanisms. Constitutively higher levels of calcium and mitochondrial superoxides under hyperglycemic conditions were further elevated in response to homocysteine leading to accelerated NETosis. Homocysteine showed robust interaction between neutrophils and platelets by inducing platelet aggregation and NETosis in an interdependent manner. Our data demonstrates that homocysteine can alter innate immune function by promoting NETs formation and disturbs homeostasis between platelets and neutrophils which may lead to T2D associated vascular diseases.

The important roles of type I interferon and interferon-inducible genes in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that causes multiple-organ dysfunction mainly affecting women in their childbearing years. Type I IFN synthesis is usually triggered by viruses, and its production is tightly regulated and limited in time in health individuals. However, many patients with systemic autoimmune diseases including SLE have signs of aberrant production of type I interferon (IFN) and display an increased expression of IFN-inducible genes. Continuous type I IFNs derived from activated plasmacytoid dendritic cells (pDCs) by interferogenic immune complexes (ICs) and migration of these cells to tissues both break immune tolerance and promote an on-going autoimmune reaction in human body. By the means of detecting type I IFNs and IFN-inducible genes, it can help with diagnosis and evaluation of SLE in early stage and more efficiently. Anti-IFN-α monoclonal antibodies in SLE patients were recently reported and is now being investigated in phase II clinical trails. In this review, we focus on recent research progress in type I IFN and IFN-inducible genes. Possible mechanisms behind the dysregulated type I IFN system in SLE and how they contribute to the development of an autoimmune process, and act as a biomarker and therapeutic target will be reviewed.

Antiinflammatory Activities of Crebanine by Inhibition of NF-κB and AP-1 Activation through Suppressing MAPKs and Akt Signaling in LPS-Induced RAW264.7 Macrophages

Crebanine, an aporphine alkaloid, displays various biological activities such as anticancer and antimicrobial activities. In this study, we further investigated the suppressive effect of crebanine on lipopolysaccharide (LPS)-induced expression of proinflammatory mediators and the molecular mechanisms underlying these activities in RAW264.7 macrophages. Crebanine inhibited the production of proinflammatory cytokines including interleukin-6 (IL-6) and tumor necrosis factor-alpha in LPS-induced RAW264.7 cells. Moreover, crebanine suppressed LPS-induced inducible nitric oxide (iNO) and prostaglandin E2 and reduced the expression of iNO synthase and cyclooxygenase-2 in RAW264.7 cells. Crebanine suppressed LPS-induced phosphorylation of Akt and mitogen-activated protein kinases (MAPKs), including extracellular signaling-regulated kinase 1/2, c-Jun NH2-terminal kinase, and p38 MAPK signaling. In addition, the specific inhibitor of MAPKs and Akt reduced the expression of IL-6 and NO production in LPS-induced macrophages. Furthermore, crebanine inhibited LPS-induced nuclear factor kappa B (NF-κB) activation by reducing the phosphorylation of p65 at Ser536 but not the p65 translocation to the nucleus and inhibitory factor kappa B alpha degradation. Crebanine also suppressed phosphorylation and nucleus translocation of activator protein-1 (AP-1). These observations suggest that the antiinflammatory properties of crebanine may stem from the inhibition of proinflammatory mediators via suppression of the NF-κB, AP-1, MAPKs, and Akt signaling pathways.