Cytokines induced neutrophil extracellular traps formation: implication for the inflammatory disease condition

Physical Mechanisms of Bacterial Killing by Histones

Antibiotic resistance is a global epidemic, becoming increasingly pressing due to its rapid spread. There is thus a critical need to develop new therapeutic approaches. In addition to searching for new antibiotics, looking into existing mechanisms of natural host defense may enable researchers to improve existing defense mechanisms, and to develop effective, synthetic drugs guided by natural principles. Histones, primarily known for their role in condensing mammalian DNA, are antimicrobial and share biochemical similarities with antimicrobial peptides (AMPs); however, the mechanism by which histones kill bacteria is largely unknown. Both AMPs and histones are similar in size, cationic, contain a high proportion of hydrophobic amino acids, and possess the ability to form alpha helices. AMPs, which mostly kill bacteria through permeabilization or disruption of the biological membrane, have recently garnered significant attention for playing a key role in host defenses. This chapter outlines the structure and function of histone proteins as they compare to AMPs and provides an overview of their role in innate immune responses, especially regarding the action of specific histones against microorganisms and their potential mechanism of action against microbial pathogens.

Therapeutic Myeloperoxidase Inhibition Attenuates Neutrophil Activation, ANCA-Mediated Endothelial Damage, and Crescentic GN

BACKGROUND

Myeloperoxidase released after neutrophil and monocyte activation can generate reactive oxygen species, leading to host tissue damage. Extracellular glomerular myeloperoxidase deposition, seen in ANCA-associated vasculitis, may enhance crescentic GN through antigen-specific T and B cell activation. Myeloperoxidase-deficient animals have attenuated GN early on, but augmented T cell responses. We investigated the effect of myeloperoxidase inhibition, using the myeloperoxidase inhibitor AZM198, to understand its potential role in treating crescentic GN.

METHODS

We evaluated renal biopsy samples from patients with various forms of crescentic GN for myeloperoxidase and neutrophils, measured serum myeloperoxidase concentration in patients with ANCA-associated vasculitis and controls, and assessed neutrophil extracellular trap formation, reactive oxygen species production, and neutrophil degranulation in ANCA-stimulated neutrophils in the absence and presence of AZM198. We also tested the effect of AZM198 on ANCA-stimulated neutrophil-mediated endothelial cell damage in vitro, as well as on crescentic GN severity and antigen-specific T cell reactivity in the murine model of nephrotoxic nephritis.

RESULTS

All biopsy specimens with crescentic GN had extracellular glomerular myeloperoxidase deposition that correlated significantly with eGFR and crescent formation. In vitro, AZM198 led to a significant reduction in neutrophil extracellular trap formation, reactive oxygen species production, and released human neutrophil peptide levels, and attenuated neutrophil-mediated endothelial cell damage. In vivo, delayed AZM198 treatment significantly reduced proteinuria, glomerular thrombosis, serum creatinine, and glomerular macrophage infiltration, without increasing adaptive T cell responses.

CONCLUSIONS

Myeloperoxidase inhibition reduced neutrophil degranulation and neutrophil-mediated endothelial cell damage in patients with ANCA-associated vasculitis. In preclinical crescentic GN, delayed myeloperoxidase inhibition suppressed kidney damage without augmenting adaptive immune responses, suggesting it might offer a novel adjunctive therapeutic approach in crescentic GN.

Neutrophil Extracellular Traps in Autoimmunity and Allergy: Immune Complexes at Work

Neutrophil extracellular traps (NETs) have been initially described as main actors in host defense owing to their ability to immobilize and sometimes kill microorganisms. Subsequent studies have demonstrated their implication in the pathophysiology of various diseases, due to the toxic effects of their main components on surrounding tissues. Several distinct NETosis pathways have been described in response to various triggers. Among these triggers, IgG immune complexes (IC) play an important role since they induce robust NET release upon binding to activating FcγRs on neutrophils. Few in vitro studies have documented the mechanisms of IC-induced NET release and evidence about the partners involved is controversial. In vivo, animal models and clinical studies have strongly suggested the importance of IgG IC-induced NET release for autoimmunity and anaphylaxis. In this review, we will focus on two autoimmune diseases in which NETs are undoubtedly major players, systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). We will also discuss anaphylaxis as another example of disease recently associated with IC-induced NET release. Understanding the role of IC-induced NETs in these settings will pave the way for new diagnostic tools and therapeutic strategies.

Interleukin-1β Mediates Arterial Thrombus Formation via NET-Associated Tissue Factor

CANTOS reported reduced secondary atherothrombotic events in patients with residual inflammatory risk treated with the inhibitory anti-IL-1β antibody, Canakinumab. Yet, mechanisms that underlie this benefit remain elusive. Recent work has implicated formation of neutrophil extracellular traps (NETosis) in arterial thrombosis. Hence, the present study explored the potential link between IL-1β, NETs, and tissue factor (TF)—the key trigger of the coagulation cascade—in atherothrombosis. To this end, ST-elevation myocardial infarction (STEMI) patients from the Swiss multicenter trial SPUM-ACS were retrospectively and randomly selected based on their CRP levels. In particular, 33 patients with STEMI and high C-reactive protein (CRP) levels (≥ 10 mg/L) and, 33 with STEMI and low CRP levels (≤ 4 mg/L) were investigated. High CRP patients displayed elevated circulating IL-1β, NETosis, and NET-associated TF plasma levels compared with low CRP ones. Additionally, analysis of patients stratified by circulating IL-1β levels yielded similar results. Moreover, NETosis and NET-associated TF plasma levels correlated positively in the whole population. In addition to the above, translational research experiments provided mechanistic confirmation for the clinical data identifying IL-1β as the initial trigger for the release of the pro-coagulant, NET-associated TF. In conclusion, blunted TF presentation by activated neutrophils undergoing NETosis may provide a mechanistic explanation to reduced secondary atherothrombotic events as observed in canakinumab-treated patients in CANTOS.

[Significance of neutrophil extracellular trap and its markers in the early diagnosis of community-acquired pneumonia in children]

OBJECTIVE

To study the significance of plasma neutrophil extracellular trap (NET) and its markers in the diagnosis of community-acquired pneumonia (CAP) in children.

METHODS

A total of 160 children with CAP were enrolled as the CAP group, and 50 healthy children were enrolled the control group. According to disease severity, the CAP group was further divided into a mild CAP subgroup with 137 children and a severe CAP subgroup with 23 children. According to the pathogen, the CAP group was further divided into a bacterial pneumonia subgroup with 78 children, a Mycoplasma pneumonia subgroup with 35 children, and a viral pneumonia subgroup with 47 children. The levels of plasma NET and its markers [antibacterial peptide (LL-37), extracellular free DNA (cfDNA), and deoxyribonuclease I (DNase I)] were measured. Receiver operating characteristic (ROC) curve was used to analyze the value of each index in diagnosing CAP and assessing its severity.

RESULTS

Compared with the control group, the CAP group had significant increases in the levels of NET, LL-37, and cfDNA and a significant reduction in the activity of DNase I (P<0.05). Compared with the mild CAP subgroup, the severe CAP subgroup had significantly higher levels of NET, LL-37 and cfDNA and a significantly lower activity of DNase I (P<0.05). There were no significant differences in the levels of NET, LL-37, and cfDNA and the activity of DNase I among the bacterial pneumonia, Mycoplasma pneumonia, and viral pneumonia subgroups (P>0.05). In the CAP group, plasma NET levels were positively correlated with white blood cell count (WBC), percentage of neutrophils, and serum levels of C-reactive protein (CRP), procalcitonin and tumor necrosis factor-α (r=0.166, 0.168, 0.275, 0.181 and 0.173 respectively, P<0.05); LL-37 and cfDNA levels were positively correlated with WBC (r=0.186 and 0.338 respectively, P<0.05) and CRP levels (r=0.309 and 0.274 respectively, P<0.05); the activity of DNase I was negatively correlated with CRP levels (r=-0.482, P<0.05). The ROC curve analysis showed that NET, LL-37, cfDNA, and DNase I had an area under the ROC curve (AUC) of 0.844, 0.648, 0.727, and 0.913 respectively in the diagnosis of CAP, with optimal cut-off values of 182.89, 46.26 ng/mL, 233.13 ng/mL, and 0.39 U/mL respectively, sensitivities of 88.12%, 35.63%, 54.37%, and 91.25% respectively, and specificities of 74.00%, 92.00%, 86.00%, and 76.00% respectively. In the assessment of the severity of CAP, NET, LL-37, cfDNA, and DNase I had an AUC of 0.873, 0.924, 0.820, and 0.778 respectively, with optimal cut-off values of 257.7, 49.11 ng/mL, 252.54 ng/mL, and 0.29 U/mL respectively, sensitivities of 83.21%, 86.96%, 78.26%, and 95.65% respectively, and specificities of 78.26%, 83.94%, 76.64%, and 56.93% respectively.

CONCLUSIONS

Plasma NET and its related markers have a certain value in diagnosing CAP and assessing its severity in children.

Neutrophil Extracellular Traps in the Establishment and Progression of Renal Diseases

Uncontrolled inflammatory and immune responses are often involved in the development of acute and chronic forms of renal injury. Neutrophils are innate immune cells recruited early to sites of inflammation, where they produce pro-inflammatory cytokines and release mesh-like structures comprised of DNA and granular proteins known as neutrophil extracellular traps (NETs). NETs are potentially toxic, contribute to glomerular injury, activate autoimmune processes, induce vascular damage, and promote kidney fibrosis. Evidence from multiple studies suggests that an imbalance between production and clearance of NETs is detrimental for renal health. Hence strategies aimed at modulating NET-associated processes could have a therapeutic impact on a myriad of inflammatory diseases that target the kidney. Here, we summarize the role of NETs in the pathogenesis of renal diseases and their mechanisms of tissue damage.

Neutrophil-Extracellular Traps, Cell-Free DNA, and Immunothrombosis in Companion Animals: A Review

Immunothrombosis is a potentially beneficial physiological process that aids innate immunity and host defense against pathogen invasion. However, this process can also be damaging when it occurs to excess or in critical blood vessels. Formation of extracellular traps by leukocytes, particularly neutrophils, is central to our understanding of immunothrombosis. In addition to degranulation and phagocytosis, extracellular traps are the third mechanism by which neutrophils combat potential pathogens. These traps consist of extracellular DNA decorated with bactericidal cellular proteins, including elastase, myeloperoxidase, and cathepsins. Neutrophils can release these structures as part of a controlled cell-death process or via a process termed vital NETosis that enables the cells to extrude DNA but remain viable. There is accumulating evidence that NETosis occurs in companion animals, including dogs, horses, and cats, and that it actively contributes to pathogenesis. Numerous studies have been published detailing various methods for identification and quantification of extracellular trap formation, including cell-free DNA, measurements of histones and proteins such as high-mobility group box-1, and techniques involving microscopy and flow cytometry. Here, we outline the present understanding of these phenomena and the mechanisms of extracellular trap formation. We critically review the data regarding measurement of NETosis in companion animals, summarize the existing literature on NETosis in veterinary species, and speculate on what therapeutic options these insights might present to clinicians in the future.

Neutrophil Extracellular Traps: Villains and Targets in Arterial, Venous, and Cancer-Associated Thrombosis

Recent studies have demonstrated a role of neutrophils in both venous and arterial thrombosis. A key prothrombotic feature of neutrophils is their ability to release web-like structures composed of DNA filaments coated with histones and granule proteins referred to as neutrophil extracellular traps (NETs). NETs were discovered over a decade ago as part of our first line of host defense against invading microorganisms. Although NETs have a protective role against pathogens, recent data suggest that an uncontrolled and excessive NET formation within the vasculature may contribute to pathological thrombotic disorders. In vitro studies suggest that NETs promote vessel occlusion by providing a scaffold for platelets, red blood cells, extracellular vesicles, and procoagulant molecules, such as von Willebrand factor and tissue factor. In addition, NET components enhance coagulation by both activating the intrinsic pathway and degrading an inhibitor of the extrinsic pathway (tissue factor pathway inhibitor). NET formation has, therefore, been proposed to contribute to thrombus formation and propagation in arterial, venous, and cancer-associated thrombosis. This review will describe animal and human studies suggesting a role of NETs in the pathogenesis of various thrombotic disorders. Targeting NETs may be a novel approach to reduce thrombosis without affecting hemostasis.

Lipopolysaccharide-Stimulated Human Fetal Membranes Induce Neutrophil Activation and Release of Vital Neutrophil Extracellular Traps

Preterm birth is a major contributor to neonatal mortality and morbidity, and infection is a major risk factor. Chorioamnionitis, inflammation of the placenta, and fetal membranes (FMs) are commonly observed in preterm birth and are characterized by neutrophil infiltration. However, interactions between FMs and neutrophils remain incompletely understood. The objectives of this study were to determine how FMs, with or without bacterial LPS stimulation, affect neutrophil recruitment, activation, and the formation of neutrophil extracellular traps (NETs) and to elucidate the signaling mechanisms involved. Using a combination of in vitro, ex vivo, and in vivo approaches, we show that human resting FMs can directly recruit neutrophils and induce them to produce proinflammatory factors. Furthermore, neutrophils release vital NETs in response to FM-derived factors. LPS-stimulated FMs further augmented neutrophil recruitment, inflammatory cytokine/chemokine secretion, and vital NET release and also induced reactive oxygen species production and degranulation. We demonstrate a role for FM-derived TNF-α in mediating these effects through activation of neutrophil p38 MAPK. We propose that, during infection, neutrophil recruitment and activation may neutralize pathogens, vital NET formation, and prolonged neutrophil viability, and in combination with degranulation, reactive oxygen species production and inflammatory chemokine/cytokine production may contribute to tissue injury at the maternal/fetal interface.

Neutrophil Extracellular Traps Sustain Inflammatory Signals in Ulcerative Colitis

BACKGROUND AND AIMS

In ulcerative colitis [UC], mucosal damage occurs in areas that are infiltrated with neutrophils. The antimicrobial function of neutrophils relies in part on the formation of extracellular web-like structures, named neutrophil extracellular traps [NETs]. The formation and/or clearance of aberrant NETs have been associated with several immune diseases. Here we investigated the role of NETs in UC-related inflammation.

METHODS

The expression of NET-associated proteins was evaluated in colonic biopsies of patients with Crohn's disease [CD], UC and in normal controls [NC] by Western blotting, immunofluorescence and immunohistochemistry. Colonic biopsies of UC patients were analysed before and after anti-tumour necrosis factor α [anti-TNF-α] treatment. The capacity of neutrophils to produce NETs upon activation was tested in vitro. UC lamina propria mononuclear cells [LPMCs] were cultured with NETs in the presence or absence of an extracellular signal-regulated kinase-1/2 [ERK1/2] inhibitor and inflammatory cytokine induction was assessed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. We also characterized the contribution of NETs in dextran sodium sulfate [DSS]-induced colitis.

RESULTS

NET-associated proteins were over-expressed in inflamed colon of UC patients as compared to CD patients and NC. Circulating neutrophils of UC patients produced NETs in response to TNF-α stimulation, and reduced expression of NET-related proteins and diminished NET formation were seen in patients receiving successful treatment with anti-TNF-α. Treatment of UC LPMCs with NETs activated ERK1/2, thus enhancing TNF-α and interleukin-1β [IL-1β] production. NETs were induced in mice with DSS-colitis and in vivo inhibition of NET release attenuated colitis.

CONCLUSIONS

Our data show that NET release occurs in UC and suggest a role for NETs in sustaining mucosal inflammation in this disorder.

Extracellular RNAs from lung cancer cells activate epithelial cells and induce neutrophil extracellular traps

Neutrophil infiltration is frequently observed in lung cancer tissues. Extracellular RNAs (exRNAs) may facilitate tumor progression. The present study investigated the cross-talk of tumor exRNAs and neutrophil extracellular traps (NETs) in lung cancer. Lewis lung carcinoma (LLC) cells were cultured with the deprived sera. And the cell culture supernatants (CCS) were analyzed in vitro and in vivo. The results revealed that exRNAs from lung cancer CCS promoted the inflammatory cytokine interleukin-1β and reduced the vascular cell adhesion molecule-1 expression in lung epithelial cells. Lung cancer CCS-treated epithelial cells induced the production of NETs. By contrast, NETs reduced the tight junction protein claudin-5 in epithelial cells. Furthermore, NETs caused the necrosis of epithelial cells, which resulted in the release of exRNAs. In mice, lung cancer cells instilled in the lung recruited neutrophils and initiated NETs. In patients with lung cancer, NETs were also observed. These results suggested that exRNAs in the cell culture supernatant may indirectly induce NETs and contribute to lung cancer oncogenesis.

Neutrophil extracellular traps enhance procoagulant activity in patients with oral squamous cell carcinoma

BACKGROUND

Hypercoagulability is a major cancer-associated complication linked to poor patient prognosis. The production of neutrophil extracellular traps (NETs) is increasingly found to be linked with the development and metastasis of cancer, as well as with thrombi formation in cancer patients. We hypothesized that the neutrophil NET release may be triggered by specific cytokines in oral squamous cell carcinoma (OSCC) patients, thereby predisposing them to a hypercoagulable state. Moreover, we have evaluated the interaction between NETs and endothelial cells (ECs).

METHODS

NET procoagulant activity was assessed based on fibrin and purified coagulation complex production assays, as well as by measuring coagulation time (CT). We further used confocal microscopy to quantify the exposure of phosphatidylserine (PS), fibrin strands, and cell FVa/Xa binding.

RESULTS

OSCC patients with stage III/IV exhibited elevated plasma NET levels compared to stage I/II or CTR (all P < 0.05). Neutrophils from OSCC patients are predisposed to amplified NET release compared to those from CTR. Furthermore, depleting IL-8, IL-6, and TNF-α led to a reduction in NET release in the plasma. OSCC NETs increased thrombin and fibrin generation and decreased CT significantly (P < 0.05). When NETs were isolated and used to treat ECs, these cells exhibited disrupted morphology by retracting from their cell-cell junctions and convert to a procoagulant phenotype. These effects could be attenuated by approximately 70% using DNase I.

CONCLUSIONS

Our findings are consistent with a model wherein OSCC drives a systemic inflammatory state, which, in turn, drives neutrophils to prime and release NETs, which drive the development of a hypercoagulable state. Intervening in this process may be a viable means of disrupting these undesirable coagulation dynamics in stage III/IV OSCC patients.

Traumatic Injury and Exposure to Mitochondrial-Derived Damage Associated Molecular Patterns Suppresses Neutrophil Extracellular Trap Formation

Major traumatic injury induces significant remodeling of the circulating neutrophil pool and loss of bactericidal function. Although a well-described phenomenon, research to date has only analyzed blood samples acquired post-hospital admission, and the mechanisms that initiate compromised neutrophil function post-injury are therefore poorly understood. Here, we analyzed pre-hospital blood samples acquired from 62 adult trauma patients (mean age 44 years, range 19-95 years) within 1 h of injury (mean time to sample 39 min, range 13-59 min). We found an immediate impairment in neutrophil extracellular trap (NET) generation in response to phorbol 12-myristate 13-acetate (PMA) stimulation, which persisted into the acute post-injury phase (4-72 h). Reduced NET generation was accompanied by reduced reactive oxygen species production, impaired activation of mitogen-activated protein kinases, and a reduction in neutrophil glucose uptake and metabolism to lactate. Pre-treating neutrophils from healthy subjects with mitochondrial-derived damage-associated molecular patterns (mtDAMPs), whose circulating levels were significantly increased in our trauma patients, reduced NET generation. This mtDAMP-induced impairment in NET formation was associated with an N-formyl peptide mediated activation of AMP-activated protein kinase (AMPK), a negative regulator of aerobic glycolysis and NET formation. Indeed, activation of AMPK via treatment with the AMP-mimetic AICAR significantly reduced neutrophil lactate production in response to PMA stimulation, a phenomenon that we also observed for neutrophils pre-treated with mtDAMPs. Furthermore, the impairment in NET generation induced by mtDAMPs was partially ameliorated by pre-treating neutrophils with the AMPK inhibitor compound C. Taken together, our data demonstrate an immediate trauma-induced impairment in neutrophil anti-microbial function and identify mtDAMP release as a potential initiator of acute post-injury neutrophil dysfunction.

Neutrophil Extracellular Traps Exert Potential Cytotoxic and Proinflammatory Effects in the Dental Pulp

INTRODUCTION

Neutrophil extracellular traps (NETs) are an important innate immune mechanism aimed at limiting the dissemination of bacteria within tissues and localizing antibacterial killing mechanisms. There is significant interest in the role of NETs in a range of infectious and inflammatory diseases; however, their role in diseased pulp has yet to be explored. Our aim was to determine their relevance to infected pulp and how their components affect human dental pulp cell (HDPC) responses.

METHODS

Diseased pulp tissue was stained for the presence of extracellular DNA and elastase to detect the presence of NETs. Bacteria known to infect pulp were also assayed to determine their ability to stimulate NETs. Coculture studies and NET component challenge were used to determine the effect of extracellular NET release on HDPC viability and inflammatory response. NET-stimulated HDPC secretomes were assessed for their chemotactic activity for lymphocytes and macrophages.

RESULTS

Data indicate that NETs are present in infected pulp tissue and whole NETs, and their histone components, particularly H2A, decreased HDPC viability and stimulated chemokine release, resulting in an attraction of lymphocyte populations.

CONCLUSIONS

NETs are likely important in pulpal pathogenesis with injurious and chronic inflammatory effects on HDPCs, which may contribute to disease progression. Macrophages are chemoattracted to NET-induced apoptotic HDPCs, facilitating cellular debris removal. NETs and histones may provide novel prognostic markers and/or therapeutic targets for pulpal diseases.

c-Abl kinase regulates neutrophil extracellular trap formation, inflammation, and tissue damage in severe acute pancreatitis

Neutrophil extracellular traps (NETs) are involved in acute pancreatitis (AP) but mechanisms controlling NET expulsion in AP are incompletely understood. Herein, we examined the role of c-Abelson (c-Abl) kinase in NET formation and tissue damage in severe AP. AP was induced by taurocholate infusion into pancreatic duct or intraperitoneal administration of l-arginine in mice. Pancreatic, lung, and blood samples were collected and levels of phosphorylated c-Abl kinase, citrullinated histone 3, DNA-histone complexes, myeloperoxidase, amylase, cytokines, and CXC chemokines were quantified. Citrullinated histone 3, reactive oxygen species (ROS), and NET formation were determined in bone marrow neutrophils. Taurocholate challenge increased phosphorylation of c-Abl kinase and levels of citrullinated histone 3 in the pancreas as well as DNA-histone complexes in the plasma. Administration of the c-Abl kinase inhibitor GZD824 not only abolished activation of c-Abl kinase but also decreased levels of citrullinated histone 3 in the pancreas and DNA-histone complexes in the plasma of animals with AP. Moreover, GZD824 decreased plasma levels of amylase, IL-6, and MMP-9 as well as edema, acinar cell necrosis, hemorrhage, CXC chemokine formation, and neutrophil infiltration in the inflamed pancreas. A beneficial effect of c-Abl kinase inhibition was confirmed in l-arginine-induced pancreatitis. In vitro, inhibition of c-Abl kinase reduced TNF-α-induced formation of ROS, histone 3 citrullination, and NETs in isolated bone marrow neutrophils. Our findings demonstrate that c-Abl kinase regulates NET formation in the inflamed pancreas. In addition, inhibition of c-Abl kinase reduced pancreatic tissue inflammation, and damage in AP. Thus, targeting c-Abl kinase might be a useful way to protect the pancreas in severe AP.

To NET or not to NET:current opinions and state of the science regarding the formation of neutrophil extracellular traps

Since the discovery and definition of neutrophil extracellular traps (NETs) 14 years ago, numerous characteristics and physiological functions of NETs have been uncovered. Nowadays, the field continues to expand and novel mechanisms that orchestrate formation of NETs, their previously unknown properties, and novel implications in disease continue to emerge. The abundance of available data has also led to some confusion in the NET research community due to contradictory results and divergent scientific concepts, such as pro- and anti-inflammatory roles in pathologic conditions, demarcation from other forms of cell death, or the origin of the DNA that forms the NET scaffold. Here, we present prevailing concepts and state of the science in NET-related research and elaborate on open questions and areas of dispute.

Progression of Cystic Fibrosis Lung Disease from Childhood to Adulthood: Neutrophils, Neutrophil Extracellular Trap (NET) Formation, and NET Degradation

Genetic defects in cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene cause CF. Infants with CFTR mutations show a peribronchial neutrophil infiltration prior to the establishment of infection in their lung. The inflammatory response progressively increases in children that include both upper and lower airways. Infectious and inflammatory response leads to an increase in mucus viscosity and mucus plugging of small and medium-size bronchioles. Eventually, neutrophils chronically infiltrate the airways with biofilm or chronic bacterial infection. Perpetual infection and airway inflammation destroy the lungs, which leads to increased morbidity and eventual mortality in most of the patients with CF. Studies have now established that neutrophil cytotoxins, extracellular DNA, and neutrophil extracellular traps (NETs) are associated with increased mucus clogging and lung injury in CF. In addition to opportunistic pathogens, various aspects of the CF airway milieux (e.g., airway pH, salt concentration, and neutrophil phenotypes) influence the NETotic capacity of neutrophils. CF airway milieu may promote the survival of neutrophils and eventual pro-inflammatory aberrant NETosis, rather than the anti-inflammatory apoptotic death in these cells. Degrading NETs helps to manage CF airway disease; since DNAse treatment release cytotoxins from the NETs, further improvements are needed to degrade NETs with maximal positive effects. Neutrophil-T cell interactions may be important in regulating viral infection-mediated pulmonary exacerbations in patients with bacterial infections. Therefore, clarifying the role of neutrophils and NETs in CF lung disease and identifying therapies that preserve the positive effects of neutrophils, while reducing the detrimental effects of NETs and cytotoxic components, are essential in achieving innovative therapeutic advances.

Neutrophil Activation and Early Features of NET Formation Are Associated With Dengue Virus Infection in Human

The involvement of the immune system in the protection and pathology of natural dengue virus (DENV) has been extensively studied. However, despite studies that have referred to activation of neutrophils in DENV infections, the exact roles of neutrophils remain elusive. Here, we explored the phenotypic and functional responses of neutrophils in a cohort of adult dengue patients. Results indicated that during an acute DENV infection, neutrophils up-regulate CD66b expression, and produce a more robust respiratory response as compared with that in convalescent or healthy individuals; this confirmed in vivo neutrophil activation during DENV infection. Spontaneous decondensation of nuclei, an early event of neutrophil extracellular trap (NET) formation, was also markedly increased in cells isolated from DENV-infected patients during the acute phase of the infection. In vitro incubation of NETs with DENV-2 virus significantly decreased DENV infectivity. Interestingly, increased levels of NET components were found in the serum of patients with more severe disease form-dengue hemorrhagic fever (DHF), but not uncomplicated dengue fever, during the acute phase of the infection. Levels of pro-inflammatory cytokines IL-8 and TNFα were also increased in DHF patients as compared with those in healthy and DF subjects. This suggested that NETs may play dual roles during DENV infection. The increased ability for NET formation during acute DENV infection appeared to be independent of PAD4-mediated histone H3 hyper-citrullination. Our study suggests that neutrophils are involved in immunological responses to DENV infection.

Neutrophil Function in an Inflammatory Milieu of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by the presence of autoantibodies against citrullinated protein antigens and proinflammatory cytokines which cause chronic synovitis, bone erosion, and eventual deformity; however, the precise etiology of RA is unclear. In the early stage of RA, neutrophils migrate into the articular cavity, become activated, and exert their function in an inflammatory process, suggesting an essential role of neutrophils in the initial events contributing to the pathogenesis of RA. Solid evidence exists that supports the contribution of neutrophil extracellular traps (NETs) to the production of autoantibodies against citrullinated proteins which can trigger the immune reaction in RA. Concurrently, proinflammatory cytokines regulate the neutrophil migration, apoptosis, and NET formation. As a result, the inflammatory neutrophils produce more cytokines and influence other immune cells thereby perpetuating the inflammatory condition in RA. In this review, we summarize the advances made in improving our understanding of neutrophil migration, apoptosis, and NET formation in the presence of an RA inflammatory milieu. We will also discuss the most recent strategies in modulating the inflammatory microenvironment that have an impact on neutrophil function which may provide alternative novel therapies for RA.

Computational Analysis Supports IL-17A as a Central Driver of Neutrophil Extracellular Trap-Mediated Injury in Liver Ischemia Reperfusion

Hepatic ischemia reperfusion (I/R) is a clinically relevant model of acute sterile inflammation leading to a reverberating, self-sustaining inflammatory response with resultant necrosis. We hypothesized that computerized dynamic network analysis (DyNA) of 20 inflammatory mediators could help dissect the sequence of post-I/R mediator interactions that induce injury. Although the majority of measured inflammatory mediators become elevated in the first 24 h, we predicted that only a few would be secreted early in the process and serve as organizational centers of downstream intermediator complexity. In support of this hypothesis, DyNA inferred a central organizing role for IL-17A during the first 3 h of reperfusion. After that, DyNA revealed connections among almost all the inflammatory mediators, representing an ongoing cytokine storm. Blocking IL-17A immediately after reperfusion disassembled the inflammatory networks and protected the liver from injury. Disassembly of the networks was not achieved if IL-17A blockage was delayed two or more hours postreperfusion. Network disassembly was accompanied by decrease in neutrophil infiltration and neutrophil extracellular trap (NET) formation. By contrast, administration of recombinant IL-17A increased neutrophil infiltration, NET formation, and liver necrosis. The administration of DNase, a NET inhibitor, significantly reduced hepatic damage despite prior administration of IL-17A, and DNase also disassembled the inflammatory networks. In vitro, IL-17A was a potent promoter of NET formation. Therefore, computational analysis identified IL-17A's early, central organizing role in the rapid evolution of a network of inflammatory mediators that induce neutrophil infiltration and NET formation responsible for hepatic damage after liver I/R.

A Comparative Review of Neutrophil Extracellular Traps in Sepsis

Sepsis is the leading cause of critical illness and mortality in human beings and animals. Neutrophils are the primary effector cells of innate immunity during sepsis. Besides degranulation and phagocytosis, neutrophils also release neutrophil extracellular traps (NETs), composed of cell-free DNA, histones, and antimicrobial proteins. Although NETs have protective roles in the initial stages of sepsis, excessive NET formation has been found to induce thrombosis and multiple organ failure in murine sepsis models. Since the discovery of NETs nearly a decade ago, many investigators have identified NETs in various species. However, many questions remain regarding the exact mechanisms and fate of neutrophils following NET formation. In humans and mice, platelet-neutrophil interactions via direct binding or soluble mediators seem to play an important role in mediating NET formation during sepsis. Preliminary data suggest that these interactions may be species dependent. Regardless of these differences, there is increasing evidence in human and veterinary medicine suggesting that NETs play a crucial role in the pathogenesis of intravascular thrombosis and multiple organ failure in sepsis. Because the outcome of sepsis is highly dependent on early recognition and intervention, detection of NETs or NET components can aid in the diagnosis of sepsis in humans and veterinary species. In addition, the use of novel therapies such as deoxyribonuclease and non-anticoagulant heparin to target NET components shows promising results in murine septic models. Much work is needed in translating these NET-targeting therapies to clinical practice.

Increased Neutrophil Activation and Plasma DNA Levels in Patients with Pre-Eclampsia

Pre-eclampsia (PE) is a chronic inflammatory disease in pregnancy, which is associated with enhanced blood coagulation and high thrombotic risk. To date, the mechanisms underlying such an association are not fully understood. Previous studies reported high levels of plasma deoxyribonucleic acid (DNA) in PE women, but the cellular source of the circulation DNA remains unknown. In this study, we tested the hypothesis that activated neutrophils undergoing cell death, also called NETosis, may be responsible for the elevated plasma DNA levels in PE women. We analysed plasma samples from non-pregnant, normal pregnant and PE women and found high levels of double-stranded DNA, myeloperoxidase (an abundant neutrophil granular enzyme) and histones (the major nucleosome proteins) in PE-derived samples, indicating increased NETosis in the maternal circulation. The high plasma DNA levels positively correlated with enhanced blood coagulation in PE women. When isolated neutrophils from normal individuals were incubated with PE-derived plasma, an elevated NETosis-stimulating activity was detected. Further experiments showed that endothelial micro-particles, but not soluble proteins, in the plasma were primarily responsible for the NETosis-stimulating activity in PE women. These results indicate that circulating micro-particles from damaged maternal endothelium are a potent stimulator for neutrophil activation and NETosis in PE women. Given the pro-coagulant and pro-thrombotic nature of granular and nuclear contents from neutrophils, enhanced systemic NETosis may represent an important mechanism underlying the hyper-coagulability and increased thrombotic risk in PE.

Immune mechanisms in the different phases of acute tubular necrosis

Acute kidney injury is a clinical syndrome that can be caused by numerous diseases including acute tubular necrosis (ATN). ATN evolves in several phases, all of which are accompanied by different immune mechanisms as an integral component of the disease process. In the early injury phase, regulated necrosis, damage-associated molecular patterns, danger sensing, and neutrophil-driven sterile inflammation enhance each other and contribute to the crescendo of necroinflammation and tissue injury. In the late injury phase, renal dysfunction becomes clinically apparent, and M1 macrophage-driven sterile inflammation contributes to ongoing necroinflammation and renal dysfunction. In the recovery phase, M2-macrophages and anti-inflammatory mediators counteract the inflammatory process, and compensatory remnant nephron and cell hypertrophy promote an early functional recovery of renal function, while some tubules are still badly injured and necrotic material is removed by phagocytes. The resolution of inflammation is required to promote the intrinsic regenerative capacity of tubules to replace at least some of the necrotic cells. Several immune mechanisms support this wound-healing-like re-epithelialization process. Similar to wound healing, this response is associated with mesenchymal healing, with a profound immune cell contribution in terms of collagen production and secretion of profibrotic mediators. These and numerous other factors determine whether, in the chronic phase, persistent loss of nephrons and hyperfunction of remnant nephrons will result in stable renal function or progress to decline of renal function such as progressive chronic kidney disease.

Neutrophil Extracellular Traps as an Adhesion Substrate for Different Tumor Cells Expressing RGD-Binding Integrins

Neutrophil extracellular traps (NETs), in addition to their function as a host defense mechanism, play a relevant role in thrombus formation and metastatic dissemination of cancer cells. Here we screened different cancer cell lines endogenously expressing a variety of integrins for their ability to bind to NETs. To this end, we used NETs isolated from neutrophil-like cells as a substrate for adhesion assays of HT1080, U-87 MG, H1975, DU 145, PC-3 and A-431 cells. Levels of α5, αIIb, αv, β1, β3 and β5 chains were determined by western blot analysis in all cell lines and levels of whole integrins on the plasma membrane were assessed by fluorescence-activated cell sorting (FACS) analysis. We found that high levels of α5β1, αvβ3 and αvβ5 enhance cell adhesion to NETs, whereas low expression of α5β1 prevents cell attachment to NETs. Excess of cyclic RGD peptide inhibited cell adhesion to NETs by competing with fibronectin within NETs. The maximal reduction of such adhesion was similar to that obtained by DNase 1 treatment causing DNA degradation. Our findings indicate that NETs from neutrophil-like cells may be used as a substrate for large screening of the adhesion properties of cancer cells expressing a variety of RGD-binding integrins.

Inflammation and Regeneration in the Dentin-pulp Complex: Net Gain or Net Loss?

The balance between the immune/inflammatory and regenerative responses in the diseased pulp is central to the clinical outcome, and this response is unique within the body because of its tissue site. Cariogenic bacteria invade the dentin and pulp tissues, triggering molecular and cellular events dependent on the disease stage. At the early onset, odontoblasts respond to bacterial components in an attempt to protect the tooth's hard and soft tissues and limit disease progression. However, as disease advances, the odontoblasts die, and cells central to the pulp core, including resident immune cells, pulpal fibroblasts, endothelial cells, and stem cells, respond to the bacterial challenge via their expression of a range of pattern recognition receptors that identify pathogen-associated molecular patterns. Subsequently, recruitment and activation occurs of a range of immune cell types, including neutrophils, macrophages, and T and B cells, which are attracted to the diseased site by cytokine/chemokine chemotactic gradients initially generated by resident pulpal cells. Although these cells aim to disinfect the tooth, their extravasation, migration, and antibacterial activity (eg, release of reactive oxygen species [ROS]) along with the bacterial toxins cause pulp damage and impede tissue regeneration processes. Recently, a novel bacterial killing mechanism termed neutrophil extracellular traps (NETs) has also been described that uses ROS signaling and results in cellular DNA extrusion. The NETs are decorated with antimicrobial peptides (AMPs), and their interaction with bacteria results in microbial entrapment and death. Recent data show that NETs can be stimulated by bacteria associated with endodontic infections, and they may be present in inflamed pulp tissue. Interestingly, some bacteria associated with pulpal infections express deoxyribonuclease enzymes, which may enable their evasion of NETs. Furthermore, although NETs aim to localize and kill invading bacteria using AMPs and histones, limiting the spread of the infection, data also indicate that NETs can exacerbate inflammation and their components are cytotoxic. This review considers the potential role of NETs within pulpal infections and how these structures may influence the pulp's vitality and regenerative responses.

Plasma myeloperoxidase-conjugated DNA level predicts outcomes and organ dysfunction in patients with septic shock

Background

Recent studies have suggested that excessive formation of neutrophil extracellular traps (NETs) plays a critical role in the pathogenesis of sepsis. Although elevation of the plasma level of cell-free DNA (cf-DNA) has been reported in sepsis patients, there has been little direct measurement of circulating free NETs such as myeloperoxidase-conjugated DNA (MPO-DNA). The objectives of this study were to detect NETs in the bloodstream of patients with septic shock, and to assess the correlations of circulating NET levels with organ dysfunction, disease severity, and mortality.

Methods

Fifty-five patients with septic shock admitted to the intensive care units (ICUs) of 35 Japanese hospitals were studied. Septic shock was diagnosed according to the 1997 definition of the American College of Chest Physicians/Society of Critical Care Medicine. To detect circulating NETs, plasma levels of MPO-DNA and cf-DNA were measured by sandwich enzyme-linked immunosorbent assay and by fluorometric assay on days 1, 3, and 7 after the onset of septic shock. Physiological and mortality data were collected from the clinical database.

Results

On days 1, 3, and 7, the patients showed a marked increase in plasma MPO-DNA levels compared with healthy volunteers, whereas the plasma cf-DNA level was only increased significantly on day 1 and then decreased rapidly. A high MPO-DNA level on days 3 and 7 were associated with 28-day mortality.

On days 3 and 7, the MPO-DNA levels were inversely correlated with both the mean arterial pressure and the PaO₂/F_IO₂ ratio, whereas the cf-DNA level was not correlated with either parameter. There was a positive correlation between the plasma MPO-DNA level and the sepsis-related organ failure assessment score on days 3 and 7. Neither cf-DNA nor MPO-DNA levels were correlated with the disseminated intravascular coagulation (DIC) score or the platelet count.

Conclusion

The increase in circulating MPO-DNA in patients with septic shock indicates acceleration of NET formation in the early stages of sepsis. High MPO-DNA levels are associated with the severity of organ dysfunction and 28-day mortality due to septic shock, but not with the DIC score. These results suggest that excessive NET formation contributes to the pathogenesis of septic shock.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2109-7) contains supplementary material, which is available to authorized users.

Neutrophil Extracellular Traps Formation and Aggregation Orchestrate Induction and Resolution of Sterile Crystal-Mediated Inflammation

The formation of neutrophil extracellular traps (NETs) to immobilize pathogens represents a novel antimicrobial strategy of the immune system. The microcrystals related to human diseases are classified into endogenous microcrystals, including monosodium urate (MSU), calcium pyrophosphate dihydrate, calcium carbonate, calcium phosphate, calcium oxalate, cholesterol, and exogenous material like crystals from silica. Although microcrystals possess distinct compositions and shapes, they have a common characteristic: they stimulate neutrophils to release NETs. In low and high densities, neutrophils form NETs and aggregated NETs (aggNETs) that reportedly orchestrate the initiation and resolution of sterile crystal-mediated inflammation, respectively. Here, we summarize the different roles of NETs and aggNETs stimulated by the crystals mentioned above in related inflammatory reactions. The NETosis-derived products may represent a potential therapeutic target in crystal-mediated diseases.

Novel Role of IL (Interleukin)-1β in Neutrophil Extracellular Trap Formation and Abdominal Aortic Aneurysms

OBJECTIVE

Neutrophils promote experimental abdominal aortic aneurysm (AAA) formation via a mechanism that is independent from MMPs (matrix metalloproteinases). Recently, we reported a dominant role of IL (interleukin)-1β in the formation of murine experimental AAAs. Here, the hypothesis that IL-1β-induced neutrophil extracellular trap formation (NETosis) promotes AAA was tested.

APPROACH AND RESULTS

NETs were identified through colocalized staining of neutrophil, Cit-H3 (citrullinated histone H3), and DNA, using immunohistochemistry. NETs were detected in human AAAs and were colocalized with IL-1β. In vitro, IL-1RA attenuated IL-1β-induced NETosis in human neutrophils. Mechanistically, IL-1β treatment of isolated neutrophils induced nuclear localization of ceramide synthase 6 and synthesis of C16-ceramide, which was inhibited by IL-1RA or fumonisin B1, an inhibitor of ceramide synthesis. Furthermore, IL-1RA or fumonisin B1 attenuated IL1-β-induced NETosis. In an experimental model of murine AAA, NETs were detected at a very early stage-day 3 of aneurysm induction. IL-1β-knockout mice demonstrated significantly lower infiltration of neutrophils to aorta and were protected from AAA. Adoptive transfer of wild-type neutrophils promoted AAA formation in IL-1β-knockout mice. Moreover, treatment of wild-type mice with Cl-amidine, an inhibitor NETosis, significantly attenuated AAA formation, whereas, treatment with deoxyribonuclease, a DNA digesting enzyme, had no effect on AAA formation.

CONCLUSIONS

Altogether, the results suggest a dominant role of IL-1β-induced NETosis in AAA formation.

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.

A High-Throughput Real-Time Imaging Technique To Quantify NETosis and Distinguish Mechanisms of Cell Death in Human Neutrophils

Neutrophils play a key role in host defenses and have recently been implicated in the pathogenesis of autoimmune diseases by various mechanisms, including formation of neutrophil extracellular traps through a recently described distinct form of programmed cell death called NETosis. Techniques to assess and quantitate NETosis in an unbiased, reproducible, and efficient way are lacking, considerably limiting the advancement of research in this field. We optimized and validated, a new method to automatically quantify the percentage of neutrophils undergoing NETosis in real time using the IncuCyte ZOOM imaging platform and the membrane-permeability properties of two DNA dyes. Neutrophils undergoing NETosis induced by various physiological stimuli showed distinct changes, with a loss of multilobulated nuclei, as well as nuclear decondensation followed by membrane compromise, and were accurately counted by applying filters based on fluorescence intensity and nuclear size. Findings were confirmed and validated with the established method of immunofluorescence microscopy. The platform was also validated to rapidly assess and quantify the dose-dependent effect of inhibitors of NETosis. In addition, this method was able to distinguish among neutrophils undergoing NETosis, apoptosis, or necrosis based on distinct changes in nuclear morphology and membrane integrity. The IncuCyte ZOOM platform is a novel real-time assay that quantifies NETosis in a rapid, automated, and reproducible way, significantly optimizing the study of neutrophils. This platform is a powerful tool to assess neutrophil physiology and NETosis, as well as to swiftly develop and test novel neutrophil targets.

Citrullinated histone H3 as a novel prognostic blood marker in patients with advanced cancer

Citrullinated histone H3 (H3Cit) is a central player in the neutrophil release of nuclear chromatin, known as neutrophil extracellular traps (NETs). NETs have been shown to elicit harmful effects on the host, and were recently proposed to promote tumor progression and spread. Here we report significant elevations of plasma H3Cit in patients with advanced cancer compared with age-matched healthy individuals. These elevations were specific to cancer patients as no increase was observed in severely ill and hospitalized patients with a higher non-malignant comorbidity. The analysis of neutrophils from cancer patients showed a higher proportion of neutrophils positive for intracellular H3Cit compared to severely ill patients. Moreover, the presence of plasma H3Cit in cancer patients strongly correlated with neutrophil activation markers neutrophil elastase (NE) and myeloperoxidase (MPO), and the inflammatory cytokines interleukin-6 and -8, known to induce NETosis. In addition, we show that high levels of circulating H3Cit strongly predicted poor clinical outcome in our cohort of cancer patients with a 2-fold increased risk for short-term mortality. Our results also corroborate the association of NE, interleukin-6 and -8 with poor clinical outcome. Taken together, our results are the first to unveil H3Cit as a potential diagnostic and prognostic blood marker associated with an exacerbated inflammatory response in patients with advanced cancer.

Recent advances in pathophysiology of disseminated intravascular coagulation: the role of circulating histones and neutrophil extracellular traps

Disseminated intravascular coagulation (DIC) is an acquired condition that develops as a complication of systemic and sustained cell injury in conditions such as sepsis and trauma. It represents major dysregulation and increased thrombin generation in vivo. A poor understanding and recognition of the complex interactions in the coagulation, fibrinolytic, inflammatory, and innate immune pathways have resulted in continued poor management and high mortality rates in DIC. This review focuses attention on significant recent advances in our understanding of DIC pathophysiology. In particular, circulating histones and neutrophil extracellular traps fulfil established criteria in DIC pathogenesis. Both are damaging to the vasculature and highly relevant to the cross talk between coagulation and inflammation processes, which can culminate in adverse clinical outcomes. These molecules have a strong potential to be novel biomarkers and therapeutic targets in DIC, which is still considered synonymous with 'death is coming'.

Possible involvement of NETosis in inflammatory processes in the eye: Evidence from a small cohort of patients

PURPOSE

To evaluate whether NETosis is involved in cytokine-induced ocular inflammation and to track neutrophil extracellular traps (NET) complexes in patients with proliferative diabetic retinopathy (PDR).

METHODS

For the animal model, the eyes of C57BL/6J mice were intravitreally injected with interleukin-8 (IL-8), tumor necrosis factor alpha (TNF-α), or saline. Histology and immunofluorescence staining for CD11b, neutrophil elastase (NE), myeloperoxidase (MPO), citrullinated histone 3 (H3Cit), and net-like structure were performed. Vitreous samples were collected from patients with PDR; the PDR1 group had no need for repeated surgical intervention, and the PDR2 group had repeated vitreous bleeding or other complication and controls. Levels of MPO, H3Cit-MPO, and NE-MPO complex were measured with enzyme-linked immunosorbent assay (ELISA).

RESULTS

Massive influx of CD11+ inflammatory cells, involving the anterior and posterior chambers, was observed in the murine eyes 24 h after the IL-8 or TNF-α injections. Cells excreted to their surroundings an extracellular net-like structure positive for NE, MPO, and H3Cit. H3Cit staining was abolished with the DNase I treatment, indicating the presence of extracellular DNA in the net-like structures. The vitreous samples of the patients with PDR2 contained statistically significantly higher levels of MPO (173±230) compared to those of the patients with PDR1 (12.0±33.0, p<0.05) or the controls (0.00, p<0.01). The levels of H3Cit-MPO and NE-MPO complexes were also statistically significantly higher in the patients with PDR2 (776.0±1274, 573.0±911.0, respectively) compared to those in the patients with PDR1 (0, p<0.05) and the controls (0, p<0.05).

CONCLUSIONS

This study showed the existence of NETosis in cytokine-induced ocular inflammation in a mouse model and human samples. Furthermore, the extent of NET complex formation was higher in a subset of patients who exhibited more complicated PDR.

cfDNA correlates with endothelial damage after cardiac surgery with prolonged cardiopulmonary bypass and amplifies NETosis in an intracellular TLR9-independent manner

Cardiopulmonary bypass (CPB) provokes inflammation culminating in organ dysfunction and increased mortality. Recently, neutrophil extracellular traps (NETs) have been found to be involved in a variety of cardiovascular diseases promoting tissue and organ injury. Here, we aimed to elaborate the proinflammatory potential of circulating cell-free (cf)DNA in patients undergoing cardiac surgery with CPB. Plasma was collected pre- and postoperatively as well as at d1, d3, d5 and d8 after surgery. At d1, we found circulating cfDNA levels to be significantly increased in patients with prolonged CPB duration (>100 min) when compared to those with shorter CPB times (CPB < 100 min). Increased CPB duration yielded in higher levels of circulating mitochondrial (mt)DNA, soluble thrombomodulin (sCD141) and ICAM-1, reflecting endothelial damage. Positive correlation between cfDNA and sCD141 was demonstrated at all time points. Plasma and cfDNA from patients with CPB > 100 min induced NETs release by neutrophils from healthy donors which was not suppressed by inhibitors of intracellular toll-like receptor (TLR)9. DNA binding to neutrophils’ surface (s)TLR9 has been evidenced. Altogether, we demonstrate that elevated plasma cfDNA might be useful to assess CPB-mediated detrimental effects, including endothelial damage, in cardiac surgical patients with prolonged CPB duration. cfDNA-triggered NETosis is independent of classical TLR9 signaling.

Chemoattractants and cytokines in primary ciliary dyskinesia and cystic fibrosis: key players in chronic respiratory diseases

Patients with primary ciliary dyskinesia (PCD) and cystic fibrosis (CF), two inherited disorders, suffer from recurrent airway infections characterized by persistent bacterial colonization and uncontrollable inflammation. Although present in high counts, neutrophils fail to clear infection in the airways. High levels of C-X-C motif chemokine ligand 8/interleukin-8 (CXCL8/IL-8), the most potent chemokine to attract neutrophils to sites of infection, are detected in the sputum of both patient groups and might cause the high neutrophil influx in the airways. Furthermore, in CF, airway neutrophils are highly activated because of the genetic defect and the high levels of proinflammatory chemoattractants and cytokines (e.g., CXCL8/IL-8, tumor necrosis factor-α and IL-17). The overactive state of neutrophils leads to lung damage and fuels the vicious circle of infection, excessive inflammation and tissue damage. The inflammatory process in CF airways is well characterized, whereas the lung pathology in PCD is far less studied. The knowledge of CF lung pathology could be useful to guide molecular investigations of the inflammatory processes in PCD lungs. Current available therapies can not completely remedy the chronic airway infections in these diseases. This review gives an overview of the role that chemoattractants and cytokines play in these neutrophil-dominated lung pathologies. Finally, the most frequently applied treatments in CF and PCD and new experimental therapies to reduce neutrophil-dominated airway inflammation are described.

In vivo induction of neutrophil extracellular traps by Mycobacterium tuberculosis in a guinea pig model

In 2004, a novel mechanism of cellular death, called 'NETosis', was described in neutrophils. This mechanism, different from necrosis and apoptosis, is characterized by the release of chromatin webs admixed with microbicidal granular proteins and peptides (NETs). NETs trap and kill a variety of microorganisms. Diverse microorganisms, including Mycobacterium tuberculosis, are NET inducers in vitro. The aim of this study was to examine whether M. tuberculosis can also induce NETs in vivo and if the NETs are bactericidal to the microorganism. Guinea pigs were intradermally inoculated with M. tuberculosis H37Rv, and the production of NETs was investigated at several time points thereafter. NETs were detected as early as 30 min post-inoculation and were clearly evident by 4 h post-inoculation. NETs produced in vivo contained DNA, myeloperoxidase, elastase, histones, ROS and acid-fast bacilli. Viable and heat-killed M. tuberculosis, as well as Mycobacterium bovis BCG were efficient NET inducers, as were unilamellar liposomes prepared with lipids from M. tuberculosis. In vitro, guinea pig neutrophils also produced NETs in response to M. tuberculosis. However, neither the in vivo nor the in vitro-produced NETs were able to kill M. tuberculosis. Nevertheless, in vivo, neutrophils might propitiate recruitment and activation of more efficient microbicidal cells.

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.

Nucleosomes and neutrophil extracellular traps in septic and burn patients

NETosis is a host defense mechanism associated with inflammation and tissue damage. Experimental models show that platelets and von Willebrand factor (VWF) are key elements for intravascular NETosis. We determined NETosis in septic and burn patients at 1 and 4days post-admission (dpa). Nucleosomes were elevated in patients. In septics, they correlated with Human Neutrophil Elastase (HNE)-DNA complexes and SOFA score at 1dpa, and were associated with mortality. Patient's neutrophils had spontaneous NETosis and were unresponsive to stimulation. Although platelet P-selectin and TNF-α were increased in both groups, higher platelet TLR-4 expression, VWF levels and IL-6 were found in septics at 1dpa. Neither platelet activation markers nor cytokines correlated with nucleosomes or HNE-DNA. Nucleosomes could be indicators of organ damage and predictors of mortality in septic but not in burn patients. Platelet activation, VWF and cytokines do not appear to be key mediators of NETosis in these patient groups.

Neutrophil-mediated anticancer drug delivery for suppression of postoperative malignant glioma recurrence

Cell-mediated drug-delivery systems have received considerable attention for their enhanced therapeutic specificity and efficacy in cancer treatment. Neutrophils (NEs), the most abundant type of immune cells, are known to penetrate inflamed brain tumours. Here we show that NEs carrying liposomes that contain paclitaxel (PTX) can penetrate the brain and suppress the recurrence of glioma in mice whose tumour has been resected surgically. Inflammatory factors released after tumour resection guide the movement of the NEs into the inflamed brain. The highly concentrated inflammatory signals in the brain trigger the release of liposomal PTX from the NEs, which allows delivery of PTX into the remaining invading tumour cells. We show that this NE-mediated delivery of drugs efficiently slows the recurrent growth of tumours, with significantly improved survival rates, but does not completely inhibit the regrowth of tumours.

Neutrophil-Derived Exosomes: A New Mechanism Contributing to Airway Smooth Muscle Remodeling

Neutrophils infiltrate the airways of patients with asthma of all severities, yet their role in the pathogenesis of asthma and their contribution to airway remodeling is largely unknown. We hypothesized that neutrophils modulate airway smooth muscle (ASM) proliferation in asthma by releasing bioactive exosomes. These newly discovered nano-sized vesicles have the capacity to modulate immune responses, cell migration, cell differentiation, and other aspects of cell-to-cell communication. The aim of the study is to determine whether bioactive exosomes are released by neutrophils, and, if so, characterize their proteomic profile and evaluate their capacity to modulate ASM cell proliferation. Exosomes were isolated from equine neutrophil supernatants by differential centrifugation and filtration methods, followed by size-exclusion chromatography. Nanovesicles were characterized using electron microscopy, particle size determination, and proteomic analyses. Exosomes were cocultured with ASM cells and analyzed for exosome internalization by confocal microscopy. ASM proliferation was measured using an impedance-based system. Neutrophils release exosomes that have characteristic size, morphology, and exosomal markers. We identified 271 proteins in exosomes from both LPS and unstimulated neutrophils, and 16 proteins that were differentially expressed, which carried proteins associated with immune response and positive regulation of cell communication. Furthermore, neutrophil-derived exosomes were rapidly internalized by ASM cells and altered their proliferative properties. Upon stimulation of LPS, neutrophil-derived exosomes can enhance the proliferation of ASM cells and could therefore play an important role in the progression of asthma and promoting airway remodeling in severe and corticosteroid-insensitive patients with asthma.

Role of Neutrophil Extracellular Traps in Asthma and Chronic Obstructive Pulmonary Disease

Objective:

Asthma and chronic obstructive pulmonary disease (COPD) are representative chronic inflammatory airway diseases responsible for a considerable burden of disease. In this article, we reviewed the relationship between neutrophil extracellular traps (NETs) and chronic inflammatory airway diseases.

Data Sources:

Articles published up to January 1, 2017, were selected from the PubMed, Ovid Medline, Embase databases, with the keywords of “asthma” or “pulmonary disease, chronic obstructive”, “neutrophils” and “extracellular traps.”

Study Selection:

Articles were obtained and reviewed to analyze the role of NETs in asthma and COPD.

Results:

NETs are composed of extracellular DNA, histones, and granular proteins, which are released from activated neutrophils. Multiple studies have indicated that there are a large amount of NETs in the airways of asthmatics and COPD patients. NETs can engulf and kill invading pathogens in the host. However, disordered regulation of NET formation has shown to be involved in the development of asthma and COPD. An overabundance of NETs in the airways or lung tissue could cause varying degrees of damage to lung tissues by inducing the death of human epithelial and endothelial cells, and thus resulting in impairing pulmonary function and accelerating the progress of the disease.

Conclusions:

Excessive NETs accumulate in the airways of asthmatics and COPD patients. Although NETs play an essential role in the innate immune system against infection, excessive components of NETs can cause lung tissue damage and accelerate disease progression in asthmatics and COPD patients. These findings suggest that administration of NETs could be a novel approach to treat asthma and COPD. Mechanism studies, clinical practice, and strategies to regulate neutrophil activation or directly interrupt NET function in asthmatics and COPD patients are desperately needed.

In vitro induction of NETosis: Comprehensive live imaging comparison and systematic review

BACKGROUND

Multiple inducers of in vitro Neutrophil Extracellular Trap (NET) formation (NETosis) have been described. Since there is much variation in study design and results, our aim was to create a systematic review of NETosis inducers and perform a standardized in vitro study of NETosis inducers important in (cardiac) wound healing.

METHODS

In vitro NETosis was studied by incubating neutrophils with PMA, living and dead bacteria (S. aureus and E. coli), LPS, (activated) platelets (supernatant), glucose and calcium ionophore Ionomycin using 3-hour periods of time-lapse confocal imaging.

RESULTS

PMA is a consistent and potent inducer of NETosis. Ionomycin also consistently resulted in extrusion of DNA, albeit with a process that differs from the NETosis process induced by PMA. In our standardized experiments, living bacteria were also potent inducers of NETosis, but dead bacteria, LPS, (activated) platelets (supernatant) and glucose did not induce NETosis.

CONCLUSION

Our systematic review confirms that there is much variation in study design and results of NETosis induction. Our experimental results confirm that under standardized conditions, PMA, living bacteria and Ionomycin all strongly induce NETosis, but real-time confocal imaging reveal different courses of events.

Anti-inflammatory effects of the petasin phyto drug Ze339 are mediated by inhibition of the STAT pathway

Ze339, an herbal extract from Petasites hybridus leaves is effective in treatment of allergic rhinitis by inhibition of a local production of IL-8 and eicosanoid LTB₄ in allergen-challenged patients. However, the mechanism of action and anti-inflammatory potential in virally induced exacerbation of the upper airways is unknown. This study investigates the anti-inflammatory mechanisms of Ze339 on primary human nasal epithelial cells (HNECs) upon viral, bacterial and pro-inflammatory triggers. To investigate the influence of viral and bacterial infections on the airways, HNECs were stimulated with viral mimics, bacterial toll-like-receptor (TLR)-ligands or cytokines, in presence or absence of Ze339. The study uncovers Ze339 modulated changes in pro-inflammatory mediators and decreased neutrophil chemotaxis as well as a reduction of the nuclear translocation and phosphorylation of STAT molecules. Taken together, this study suggests that phyto drug Ze339 specifically targets STAT-signalling pathways in HNECs and has high potential as a broad anti-inflammatory drug that exceeds current indication. © 2016 BioFactors, 43(3):388-399, 2017.