Ultrastructural characterization of cystic fibrosis sputum using atomic force and scanning electron microscopy

The Anti-Pseudomonal Peptide D-BMAP18 Is Active in Cystic Fibrosis Sputum and Displays Anti-Inflammatory In Vitro Activity

Most Cystic Fibrosis (CF) patients succumb to airway inflammation and pulmonary infections due to Pseudomonas aeruginosa. D-BMAP18, a membrane-permeabilizing antimicrobial peptide composed of D-amino acids, was evaluated as a possible antibacterial aimed to address this issue. The antipseudomonal activity of D-BMAP18 was tested in a pathophysiological context. The peptide displayed activity against CF isolates of Pseudomonas aeruginosa in the presence of CF sputum when combined with sodium chloride and DNase I. In combination with DNase I, D-BMAP18 discouraged the deposition of new biofilm and eradicated preformed biofilms of some P. aeruginosa strains. In addition, D-BMAP18 down regulated the production of TNF-α, IL1-β, and TGF-β in LPS-stimulated or IFN-γ macrophages derived from THP-1 cells indicating an anti-inflammatory activity. The biocompatibility of D-BMAP18 was assessed using four different cell lines, showing that residual cell-specific cytotoxicity at bactericidal concentrations could be abolished by the presence of CF sputum. Overall, this study suggests that D-BMAP18 may be an interesting molecule as a starting point to develop a novel therapeutic agent to simultaneously contrast lung infections and inflammation in CF patients.

On Neutrophil Extracellular Trap (NET) Removal: What We Know Thus Far and Why So Little

Although neutrophil extracellular traps (NETs) were discovered only 16 years ago, they have already taken us from heaven to hell as we learned that apart from beneficial trapping of pathogens, they cause, or contribute to, numerous disorders. The latter is connected to their persistent presence in the blood or tissue, and we hardly know how they are removed in mild pathophysiological conditions and why their removal is impaired in multiple severe pathological conditions. Herein, we bring together all data available up till now on how NETs are cleared—from engaged cells, their phenotypes, to involved enzymes and molecules. Moreover, we hypothesize on why NET removal is challenged in multiple disorders and propose further directions for studies on NET removal as well as possible therapeutic strategies to have them cleared.

Neutrophil Extracellular Traps and By-Products Play a Key Role in COVID-19: Pathogenesis, Risk Factors, and Therapy

Understanding of the pathogenesis of the coronavirus disease-2019 (COVID-19) remains incomplete, particularly in respect to the multi-organ dysfunction it may cause. We were the first to report the analogous biological and physiological features of COVID-19 pathogenesis and the harmful amplification loop between inflammation and tissue damage induced by the dysregulation of neutrophil extracellular traps (NETs) formation. Given the rapid evolution of this disease, the nature of its symptoms, and its potential lethality, we hypothesize that COVID-19 progresses under just such an amplifier loop, leading to a massive, uncontrolled inflammation process. Here, we describe in-depth the correlations of COVID-19 symptoms and biological features with those where uncontrolled NET formation is implicated in various sterile or infectious diseases. General clinical conditions, as well as numerous pathological and biological features, are analogous with NETs deleterious effects. Among NETs by-products implicated in COVID-19 pathogenesis, one of the most significant appears to be elastase, in accelerating virus entry and inducing hypertension, thrombosis and vasculitis. We postulate that severe acute respiratory syndrome-coronavirus 2 (SARS-CoV2) may evade innate immune response, causing uncontrolled NETs formation and multi-organ failure. In addition, we point to indicators that NETS-associated diseases are COVID-19 risk factors. Acknowledging that neutrophils are the principal origin of extracellular and circulating DNA release, we nonetheless, explain why targeting NETs rather than neutrophils themselves may in practice be a better strategy. This paper also offers an in-depth review of NET formation, function and pathogenic dysregulation, as well as of current and prospective future therapies to control NETopathies. As such, it enables us also to suggest new therapeutic strategies to fight COVID-19. In combination with or independent of the latest tested approaches, we propose the evaluation, in the short term, of treatments with DNase-1, with the anti-diabetic Metformin, or with drugs targeting elastase (i.e., Silvelestat). With a longer perspective, we also advocate a significant increase in research on the development of toll-like receptors (TLR) and C-type lectin-like receptors (CLEC) inhibitors, NET-inhibitory peptides, and on anti-IL-26 therapies.

Extracellular DNA in sputum is associated with pulmonary function and hospitalization in patients with cystic fibrosis

BACKGROUND

Elevated extracellular DNA levels are found in the sputum of patients with cystic fibrosis (CF). However, studies investigating the association of extracellular DNA with CF severity are scarce.

OBJECTIVE

To evaluate the association of extracellular DNA levels with pulmonary function, antibiotic use, and hospitalization in CF patients.

METHODS

This cross-sectional study included CF patients aged ≥5 years who were clinically stable and produced spontaneously expectorated sputum. Extracellular DNA in sputum was quantified, and extracellular DNA networks were seen with immunofluorescence microscopy. Also, cell death profile was assessed. Data on pulmonary function, airway colonization, antibiotic use, and hospitalization in the previous year were collected. Patients were divided into two groups based on median DNA level.

RESULTS

Thirty-three patients were included. Their mean age was 16.3 ± 6.2 years, mean forced expiratory volume in the first second (FEV₁) was 67.0 ± 26.7 (% of the predicted), and mean DNA level was 241.9 ± 147.2 μg/mL. There were significant correlations of DNA level with FEV₁ (r = -0.60; p < 0.001) and forced vital capacity (r = -0.59; p < 0.001). Moreover, patients with higher DNA level (>243.0 μg/mL) had lower FEV₁ (52.1 ± 27.8% vs. 81.1 ± 16.2%; p = 0.001) and required more hospitalizations (68.8% vs. 35.3%; p = 0.05). Additional findings were the presence of extracellular DNA networks and low rates of necrosis and apoptosis.

CONCLUSION

Elevated extracellular DNA levels in CF sputum are associated with reduced pulmonary function and increased hospitalizations.

Targeting Biofilms Therapy: Current Research Strategies and Development Hurdles

Biofilms are aggregate of microorganisms in which cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) and adhere to each other and/or to a surface. The development of biofilm affords pathogens significantly increased tolerances to antibiotics and antimicrobials. Up to 80% of human bacterial infections are biofilm-associated. Dispersal of biofilms can turn microbial cells into their more vulnerable planktonic phenotype and improve the therapeutic effect of antimicrobials. In this review, we focus on multiple therapeutic strategies that are currently being developed to target important structural and functional characteristics and drug resistance mechanisms of biofilms. We thoroughly discuss the current biofilm targeting strategies from four major aspects—targeting EPS, dispersal molecules, targeting quorum sensing, and targeting dormant cells. We explain each aspect with examples and discuss the main hurdles in the development of biofilm dispersal agents in order to provide a rationale for multi-targeted therapy strategies that target the complicated biofilms. Biofilm dispersal is a promising research direction to treat biofilm-associated infections in the future, and more in vivo experiments should be performed to ensure the efficacy of these therapeutic agents before being used in clinic.

COVID-19 and immunological regulations - from basic and translational aspects to clinical implications

The COVID‐19 pandemic caused by SARS‐CoV‐2 has far‐reaching direct and indirect medical consequences. These include both the course and treatment of diseases. It is becoming increasingly clear that infections with SARS‐CoV‐2 can cause considerable immunological alterations, which particularly also affect pathogenetically and/or therapeutically relevant factors.

Against this background we summarize here the current state of knowledge on the interaction of SARS‐CoV‐2/COVID‐19 with mediators of the acute phase of inflammation (TNF, IL‐1, IL‐6), type 1 and type 17 immune responses (IL‐12, IL‐23, IL‐17, IL‐36), type 2 immune reactions (IL‐4, IL‐13, IL‐5, IL‐31, IgE), B‐cell immunity, checkpoint regulators (PD‐1, PD‐L1, CTLA4), and orally druggable signaling pathways (JAK, PDE4, calcineurin). In addition, we discuss in this context non‐specific immune modulation by glucocorticosteroids, methotrexate, antimalarial drugs, azathioprine, dapsone, mycophenolate mofetil and fumaric acid esters, as well as neutrophil granulocyte‐mediated innate immune mechanisms.

From these recent findings we derive possible implications for the therapeutic modulation of said immunological mechanisms in connection with SARS‐CoV‐2/COVID‐19. Although, of course, the greatest care should be taken with patients with immunologically mediated diseases or immunomodulating therapies, it appears that many treatments can also be carried out during the COVID‐19 pandemic; some even appear to alleviate COVID‐19.

COVID‐19 und Immunregulation – von grundlegenden und translationalen Aspekten zu klinischen Implikationen

Die durch SARS‐CoV‐2 verursachte Pandemie COVID‐19 hat weitreichende direkte und indirekte medizinische Folgen. Dazu gehören sowohl der Verlauf als auch die Behandlung vieler Krankheiten. Es wird immer deutlicher, dass Infektionen mit SARS‐CoV‐2 erhebliche immunologische Veränderungen verursachen können, die insbesondere auch pathogenetisch und/oder therapeutisch relevante Faktoren betreffen.

Vor diesem Hintergrund fassen wir hier den aktuellen Wissensstand zur Interaktion von SARS‐CoV‐2/COVID‐19 mit Mediatoren der akuten Phase der Entzündung (TNF, IL‐1, IL‐6), der Typ‐1‐ und Typ‐17‐Immunantwort (IL‐12, IL‐23, IL‐17, IL‐36), Typ‐2‐Immunreaktionen (IL‐4, IL‐13, IL‐5, IL‐31, IgE), B‐Zell‐Immunität, Checkpoint‐Regulatoren (PD‐1, PD‐L1, CTLA4) und Signalwegen, die durch oral applizierte Medikamente moduliert werden (JAK, PDE4, Calcineurin), zusammen. Darüber hinaus diskutieren wir in diesem Zusammenhang die unspezifische Immunmodulation durch Glukokortikosteroide, Methotrexat, Malariamittel, Azathioprin, Dapson, Mycophenolsäure‐Derivate und Fumarsäureester sowie angeborene Immunmechanismen neutrophiler Granulozyten.

Aus diesen neueren Erkenntnissen leiten wir mögliche Implikationen für die therapeutische Modulation der genannten immunologischen Mechanismen im Zusammenhang mit SARS‐CoV‐2/COVID‐19 ab. Obwohl natürlich bei Patienten mit immunologisch vermittelten Krankheiten oder immunmodulierenden Therapien größte Vorsicht geboten ist, scheint es, dass viele Behandlungen auch während der COVID‐19‐Pandemie durchgeführt werden können; einige scheinen COVID‐19 sogar zu lindern.

Cytokine storm and leukocyte changes in mild versus severe SARS-CoV-2 infection: Review of 3939 COVID-19 patients in China and emerging pathogenesis and therapy concepts

Clinical evidence indicates that the fatal outcome observed with severe acute respiratory syndrome‐coronavirus‐2 infection often results from alveolar injury that impedes airway capacity and multi‐organ failure—both of which are associated with the hyperproduction of cytokines, also known as a cytokine storm or cytokine release syndrome. Clinical reports show that both mild and severe forms of disease result in changes in circulating leukocyte subsets and cytokine secretion, particularly IL‐6, IL‐1β, IL‐10, TNF, GM‐CSF, IP‐10 (IFN‐induced protein 10), IL‐17, MCP‐3, and IL‐1ra. Not surprising, therapies that target the immune response and curtail the cytokine storm in coronavirus 2019 (COVID‐19) patients have become a focus of recent clinical trials. Here we review reports on leukocyte and cytokine data associated with COVID‐19 disease in 3939 patients in China and describe emerging data on immunopathology. With an emphasis on immune modulation, we also look at ongoing clinical studies aimed at blocking proinflammatory cytokines; transfer of immunosuppressive mesenchymal stem cells; use of convalescent plasma transfusion; as well as immunoregulatory therapy and traditional Chinese medicine regimes. In examining leukocyte and cytokine activity in COVID‐19, we focus in particular on how these levels are altered as the disease progresses (neutrophil NETosis, macrophage, T cell response, etc.) and proposed consequences to organ pathology (coagulopathy, etc.). Viral and host interactions are described to gain further insight into leukocyte biology and how dysregulated cytokine responses lead to disease and/or organ damage. By better understanding the mechanisms that drive the intensity of a cytokine storm, we can tailor treatment strategies at specific disease stages and improve our response to this worldwide public health threat.

Targeting potential drivers of COVID-19: Neutrophil extracellular traps

Coronavirus disease 2019 (COVID-19) is a novel, viral-induced respiratory disease that in ∼10-15% of patients progresses to acute respiratory distress syndrome (ARDS) triggered by a cytokine storm. In this Perspective, autopsy results and literature are presented supporting the hypothesis that a little known yet powerful function of neutrophils-the ability to form neutrophil extracellular traps (NETs)-may contribute to organ damage and mortality in COVID-19. We show lung infiltration of neutrophils in an autopsy specimen from a patient who succumbed to COVID-19. We discuss prior reports linking aberrant NET formation to pulmonary diseases, thrombosis, mucous secretions in the airways, and cytokine production. If our hypothesis is correct, targeting NETs directly and/or indirectly with existing drugs may reduce the clinical severity of COVID-19.

Progress in Model Systems of Cystic Fibrosis Mucosal Inflammation to Understand Aberrant Neutrophil Activity

In response to recurrent infection in cystic fibrosis (CF), powerful innate immune signals trigger polymorphonuclear neutrophil recruitment into the airway lumen. Exaggerated neutrophil proteolytic activity results in sustained inflammation and scarring of the airways. Consequently, neutrophils and their secretions are reliable clinical biomarkers of lung disease progression. As neutrophils are required to clear infection and yet a direct cause of airway damage, modulating adverse neutrophil activity while preserving their pathogen fighting function remains a key area of CF research. The factors that drive their pathological behavior are still under investigation, especially in early disease when aberrant neutrophil behavior first becomes evident. Here we examine the latest findings of neutrophils in pediatric CF lung disease and proposed mechanisms of their pathogenicity. Highlighted in this review are current and emerging experimental methods for assessing CF mucosal immunity and human neutrophil function in the laboratory.

Extracellular DNA controls expression of Pseudomonas aeruginosa genes involved in nutrient utilization, metal homeostasis, acid pH tolerance and virulence

Introduction. Pseudomonas aeruginosa grows in extracellular DNA (eDNA)-enriched biofilms and infection sites. eDNA is generally considered to be a structural biofilm polymer required for aggregation and biofilm maturation. In addition, eDNA can sequester divalent metal cations, acidify growth media and serve as a nutrient source.Aim. We wanted to determine the genome-wide influence on the transcriptome of planktonic P. aeruginosa PAO1 grown in the presence of eDNA.Methodology. RNA-seq analysis was performed to determine the genome-wide effects on gene expression of PAO1 grown with eDNA. Transcriptional lux fusions were used to confirm eDNA regulation and to validate phenotypes associated with growth in eDNA.Results. The transcriptome of eDNA-regulated genes included 89 induced and 76 repressed genes (FDR<0.05). A large number of eDNA-induced genes appear to be involved in utilizing DNA as a nutrient. Several eDNA-induced genes are also induced by acidic pH 5.5, and eDNA/acidic pH promoted an acid tolerance response in P. aeruginosa. The cyoABCDE terminal oxidase is induced by both eDNA and pH 5.5, and contributed to the acid tolerance phenotype. Quantitative metal analysis confirmed that DNA binds to diverse metals, which helps explain why many genes involved in a general uptake of metals were controlled by eDNA. Growth in the presence of eDNA also promoted intracellular bacterial survival and influenced virulence in the acute infection model of fruit flies.Conclusion. The diverse functions of the eDNA-regulated genes underscore the important role of this extracellular polymer in promoting antibiotic resistance, virulence, acid tolerance and nutrient utilization; phenotypes that contribute to long-term survival.

Neutrophil extracellular traps activate IL-8 and IL-1 expression in human bronchial epithelia

Neutrophil extracellular traps (NETs) provide host defense but can contribute to the pathobiology of diverse human diseases. We sought to determine the extent and mechanism by which NETs contribute to human airway cell inflammation. Primary normal human bronchial epithelial cells (HBEs) grown at air-liquid interface and wild-type (wt)CFBE41o- cells (expressing wtCFTR) were exposed to cell-free NETs from unrelated healthy volunteers for 18 h in vitro. Cytokines were measured in the apical supernatant by Luminex, and the effect on the HBE transcriptome was assessed by RNA sequencing. NETs consistently stimulated IL-8, TNF-α, and IL-1α secretion by HBEs from multiple donors, with variable effects on other cytokines (IL-6, G-CSF, and GM-CSF). Expression of HBE RNAs encoding IL-1 family cytokines, particularly IL-36 subfamily members, was increased in response to NETs. NET exposure in the presence of anakinra [recombinant human IL-1 receptor antagonist (rhIL-1RA)] dampened NET-induced changes in IL-8 and TNF-α proteins as well as IL-36α RNA. rhIL-36RA limited the increase in expression of proinflammatory cytokine RNAs in HBEs exposed to NETs. NETs selectively upregulate an IL-1 family cytokine response in HBEs, which enhances IL-8 production and is limited by rhIL-1RA. The present findings describe a unique mechanism by which NETs may contribute to inflammation in human lung disease in vivo. NET-driven IL-1 signaling may represent a novel target for modulating inflammation in diseases characterized by a substantial NET burden.

High Nuclease Activity of Long Persisting Staphylococcus aureus Isolates Within the Airways of Cystic Fibrosis Patients Protects Against NET-Mediated Killing

Staphylococcus aureus is one of the first and most prevalent pathogens cultured from the airways of cystic fibrosis (CF) patients, which can persist there for extended periods. Airway infections in CF patients are characterized by a strong inflammatory response of highly recruited neutrophils. One killing mechanism of neutrophils is the formation of neutrophil extracellular traps (NETs), which capture and eradicate bacteria by extracellular fibers of neutrophil chromatin decorated with antimicrobial granule proteins. S. aureus secretes nuclease, which can degrade NETs. We hypothesized, that S. aureus adapts to the airways of CF patients during persistent infection by escaping from NET-mediated killing via an increase of nuclease activity. Sputum samples of CF patients with chronic S. aureus infection were visualized by confocal microscopy after immuno-fluorescence staining for NET-specific markers, S. aureus bacteria and overall DNA structures. Nuclease activity was analyzed in sequential isogenic long persisting S. aureus isolates, as confirmed by whole genome sequencing, from an individual CF patient using a FRET-based nuclease activity assay. Additionally, some of these isolates were selected and analyzed by qRT-PCR to determine the expression of nuc1 and regulators of interest. NET-killing assays were performed with clinical S. aureus isolates to evaluate killing and bacterial survival depending on nuclease activity. To confirm the role of nuclease during NET-mediated killing, a clinical isolate with low nuclease activity was transformed with a nuclease expression vector (pCM28nuc). Furthermore, two sputa from an individual CF patient were subjected to RNA-sequence analysis to evaluate the activity of nuclease in vivo. In sputa, S. aureus was associated to extracellular DNA structures. Nuclease activity in clinical S. aureus isolates increased in a time-and phenotype-dependent manner. In the clinical isolates, the expression of nuc1 was inversely correlated to the activity of agr and was independent of saeS. NET-mediated killing was significantly higher in S. aureus isolates with low compared to isolates with high nuclease activity. Importantly, transformation of the clinical isolate with low nuclease activity with pCM28nuc conferred protection against NET-mediated killing confirming the beneficial role of nuclease for protection against NETs. Also, nuclease expression in in vivo sputa was high, which underlines the important role of nuclease within the highly inflamed CF airways. In conclusion, our data show that S. aureus adapts to the neutrophil-rich environment of CF airways with increasing nuclease expression most likely to avoid NET-killing during long-term persistence.

Systemic levels of anti-PAD4 autoantibodies correlate with airway obstruction in cystic fibrosis

Cystic fibrosis (CF) airway disease is characterized by the long-term presence of neutrophil granulocytes. Formation of neutrophil extracellular traps (NETs) and/or autoantibodies directed against extracellular components of NETs are possible contributors to neutrophil-mediated lung damage in CF. The goal of this study was to measure their levels in CF adults compared to healthy controls and subjects with rheumatologic diseases known to develop NET-related autoantibodies and pathologies, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Sera were analyzed from the following number of subjects: 37 CF, 23 healthy controls (HC), 20 RA, and 21 SLE. CF had elevated serum myeloperoxidase (MPO) concentrations (347.5±56.1 ng/ml, mean+/-S.E.M., p = .0132) compared to HC (144.5±14.6 ng/ml) but not of neutrophil elastase (NE) complexed with alpha-1-antitrypsin, cell-free DNA or NE-DNA complexes. The peptidylarginine deiminase 4 (PAD4) enzyme is required for NET formation and associated DNA release in neutrophils. Serum levels of anti-PAD4 antibodies (Ab) were elevated in CF (p = .0147) compared to HC and showed an inverse correlation with a measure of lung function, FEV1% predicted (r = -0.5020, p = .015), as did MPO levels (r = -0.4801, p = .0026). Anti-PAD4 Ab levels in CF sera associated with lung infection by P. aeruginosa, but not that by S. aureus, age, sex, CF-related diabetes or the presence of musculoskeletal pain. Serum levels of anti-citrullinated protein Abs (ACPAs) and anti-nucleosome Abs were not elevated in CF compared to HC (p = .7498, p = .0678). In summary, adult CF subjects develop an autoimmune response against NET components that correlates with worsening lung disease.

Extracellular DNA NET-Works With Dire Consequences for Health

Neutrophils play a central role in innate immune defense. Advances in neutrophil biology have brought to light the capacity of neutrophils to release their decondensed chromatin and form large extracellular DNA networks called neutrophil extracellular traps (NETs). NETs are produced in response to many infectious and noninfectious stimuli and, together with fibrin, block the invasion of pathogens. However, their formation in inflamed blood vessels produces a scaffold that supports thrombosis, generates neo-antigens favoring autoimmunity, and aggravates damage in ischemia/reperfusion injury. NET formation can also be induced by cancer and promotes tumor progression. Formation of NETs within organs can be immediately detrimental, such as in lung alveoli, where they affect respiration, or they can be harmful over longer periods of time. For example, NETs initiate excessive deposition of collagen, resulting in fibrosis, thus likely contributing to heart failure. Here, we summarize the latest knowledge on NET generation and discuss how excessive NET formation mediates propagation of thrombosis and inflammation and, thereby, contributes to various diseases. There are many ways in which NET formation could be averted or NETs neutralized to prevent their detrimental consequences, and we will provide an overview of these possibilities.

A Flow Cytometric Method for Isolating Cystic Fibrosis Airway Macrophages from Expectorated Sputum

Research to understand the contribution of macrophages to nonresolving airway inflammation in cystic fibrosis (CF) and other chronic suppurative airways diseases has been hindered by a lack of methods for isolating and studying these cells. With the development of technologies that can characterize small numbers of cells or individual cells, there is an even greater need for methodologies to isolate rare cells in heterogeneous specimens. Here, we describe a method that overcomes the technical obstacles imposed by sputum debris and apoptotic cells, and allows isolation of pure populations of macrophages from CF sputum. In addition to enhancing our ability to study human CF airway macrophages, this protocol can be adapted to study cells in sputum from other chronic suppurative lung diseases (e.g., chronic obstructive pulmonary disease) and used for isolation of individual cells for single cell analyses.

The Emerging Role of Neutrophil Extracellular Traps in Respiratory Disease

Neutrophil extracellular traps (NETs) are extrusions of intracellular DNA and attached granular material that enable bacterial killing. NETs are increasingly recognized for their role in the pathogenesis of respiratory disease. NETs are composed of a complex mix of intracellularly derived material that neutrophils organize within the cytoplasm and then expel in a nondirected manner in the vicinity of invading organisms. Combined, these trap and destroy multiple genera of microbes including bacteria, fungi, viruses, and protozoans, limiting infection especially where phagocytosis is not possible. At first, NET formation was thought to be a terminal event for neutrophils; however, it is now apparent that some neutrophils survive this process, becoming anuclear, and may drive ongoing tissue damage. NETs are now known to be directly cytotoxic to lung epithelium and endothelium, and their excessive production is seen in pneumonia and acute lung injury as well as several chronic diseases, including COPD, asthma, and cystic fibrosis. NETs also appear to play a role in both tumor defense and dissemination, depending on the local microenvironment and the specific tumor subtype. It is becoming increasingly apparent that NET formation can exert a positive or negative influence on multiple respiratory pathologies and that simply globally reducing or increasing NET formation is unlikely to be a therapeutic success. Rather, as our understanding grows, it is likely that targeted NET up- or downregulation along with destruction or protection of already formed NETs may become an additional point of intervention for respiratory physicians.

Trapped Chromatin Fibers Damage Flowing Red Blood Cells

Neutrophils are the most abundant white blood cells in the circulation and serve antimicrobial functions. One of their antimicrobial mechanisms involves the release of neutrophil extracellular traps (NETs), long chromatin fibers decorated with antimicrobial granular proteins that contribute to the elimination of pathogens. However, the release of NETs has also been associated with disease processes. While recent research has focused on biochemical reactions catalyzed by NETs, significantly less is known about the mechanical effect of NETs in circulation. Here, microfluidic devices and biophysical models are employed to study the consequences of the interactions between NETs trapped in channels and red blood cells (RBCs) flowing in blood over the NETs. It has been found that the RBCs can be deformed and ruptured after interactions with NETs, generating RBC fragments. Significant increases in the number of RBC fragments have also been found in the circulation of patients with conditions in which NETs have been demonstrated to be present in circulation, including sepsis and kidney transplant. Further studies will probe the potential utility of RBC fragments in the diagnostic, monitoring, and treatment of diseases associated with the presence of NETs in circulation.

High-Content Screening Identifies Vanilloids as a Novel Class of Inhibitors of NET Formation

Neutrophils migrate to sites of infection where they phagocytose, degranulate, and/or, in the presence of appropriate stimuli, release decondensed chromatin strands (called neutrophil extracellular traps, NETs) for trapping and possibly killing microorganisms. NET formation is characterized by marked morphological cell changes, in particular within the nucleus. Lytic NET formation can be observed in neutrophils undergoing cell death, which is referred to as NETosis. Dysregulation of NET production and/or degradation can exert pathogenic effects, contributing to the pathogenesis of various diseases, including cystic fibrosis, autoimmune diseases and inflammatory conditions. By employing a phenotypic assay based on high-content imaging and analysis, we screened a library of biologically active compounds and identified vanilloids as a novel class of chemical compounds able to hinder NETosis induction and NET release. Vanilloids also markedly decrease cytosolic ROS production. The identification of novel vanilloid NET inhibitors, able to stop excessive or aberrant NET production might offer new therapeutic options for those disorders displaying NET overproduction.

"NETtling" the host: Breaking of tolerance in chronic inflammation and chronic infection

How and why we break tolerance to self-proteins still remains a largely unanswered question. Neutrophils have been identified as a rich source of autoantigens in a wide array of autoimmune diseases that arise as a consequence of different environmental and genetic factors, e.g. rheumatoid arthritis (RA), lupus, vasculitis, cystic fibrosis (CF) etc. Specifically, neutrophil extracellular trap (NET) formation has been identified as a link between innate and adaptive immune responses in autoimmunity. Autoantigens including neutrophil granular proteins (targeted by anti-neutrophil cytoplasmic antibodies, ANCA) as well as post-translationally modified proteins, i.e. citrullinated and carbamylated proteins targeted by anti-citrullinated protein antibodies (ACPA) and anti-carbamylated protein antibodies (ACarPA), respectively, localize to the NETs. Moreover, NETs provide stimuli to dendritic cells that potentiate adaptive autoimmune responses. However, while NETs promote inflammation and appear to induce humoral autoreactivity across autoimmune diseases, the antigen specificity of autoantibodies found in these disorders is striking. These unique autoantigen signatures suggest that not all NETs are created equal and that the environment in which NETs arise shapes their disease-specific character. In this review article, we discuss the effects of different stimuli on the mechanism of NET formation as well as how they contribute to antigen specificity in the breaking of immune tolerance. Specifically, we compare and contrast the autoreactive nature of NETs in two settings of chronic airway inflammation: one triggered by smoking, a recognized environmental NET stimulus in RA patients, and one mediated by Pseudomonas aeruginosa, the most prevalent lung pathogen in CF patients. Finally, we draw attention to novel findings that, together with the specific environmental/chemical stimuli, should be taken into account when investigating how and why antigen specificity arises in the context of NET formation.

Antimicrobial Microwebs of DNA-Histone Inspired from Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are decondensed chromatin networks released by neutrophils that can trap and kill pathogens but can also paradoxically promote biofilms. The mechanism of NET functions remains ambiguous, at least in part, due to their complex and variable compositions. To unravel the antimicrobial performance of NETs, a minimalistic NET-like synthetic structure, termed "microwebs," is produced by the sonochemical complexation of DNA and histone. The prepared microwebs have structural similarity to NETs at the nanometer to micrometer dimensions but with well-defined molecular compositions. Microwebs prepared with different DNA to histone ratios show that microwebs trap pathogenic Escherichia coli in a manner similar to NETs when the zeta potential of the microwebs is positive. The DNA nanofiber networks and the bactericidal histone constituting the microwebs inhibit the growth of E. coli. Moreover, microwebs work synergistically with colistin sulfate, a common and a last-resort antibiotic, by targeting the cell envelope of pathogenic bacteria. The synthesis of microwebs enables mechanistic studies not possible with NETs, and it opens new possibilities for constructing biomimetic bacterial microenvironments to better understand and predict physiological pathogen responses.

Biofilm Formations in Pediatric Respiratory Tract Infection : Part 1: Biofilm Structure, Role of Innate Immunity in Protection Against and Response to Biofilm, Methods of Biofilm Detection, Pediatric Respiratory Tract Diseases Associated with Mucosal Biofilm Formation

PURPOSE OF REVIEW

Biofilm represents an organized structure of microorganisms within an extracellular matrix attached to a surface. While the importance of biofilm in prosthetic heart valve and catheter-related infections has been known since the 1980s, the role of mucosal biofilm in human disease pathogenesis has only recently been elucidated. It is now clear that mucosal biofilm is present in both healthy and pathologic states. The purpose of this review is to examine the role of mucosal biofilm in pediatric respiratory infections.

RECENT FINDINGS

Mucosal biofilm has been implicated in relationship to several pediatric respiratory infections, including tonsillitis, adenoiditis, otitis media with effusion, chronic rhinosinusitis, persistent endobronchial infection, and bronchiectasis. In these conditions, core pathogens are detected in the biofilm, biofilm organisms are often detected by molecular techniques when conventional cultures are negative, and biofilm presence is more extensive in relation to disease than in healthy tissues. In chronic rhinosinusitis, the presence of polymicrobial biofilm is also a predictor of poorer outcome following sinus surgery. Biofilm in the tonsillar and adenoidal compartments plays a distinct role in contributing to disease in the middle ear and sinuses. Key observations regarding the relevance of biofilm to pediatric respiratory infections include (1) the association between the presence of biofilm and persistent/recurrent and more severe disease in these tissues despite antibiotic treatment, (2) linkage between biofilm core pathogens and acute infections, and (3) interrelationship between biofilm presence in one tissue and persistent or recurrent infection in an adjacent tissue. A greater understanding of the significance of mucosal biofilm will undoubtedly emerge with the development of effective means of eradicating mucosal biofilm.

Monocyte clearance of apoptotic neutrophils is unhindered in the presence of NETosis, but proteins of NET trigger ETosis in monocytes

Resolution of inflammation needs effective and timely removal of dead cells and other toxic products of neutrophils, monocytes, and macrophages. In this study, we evaluated the role of monocytes in the clearance of neutrophil extracellular trap (NET) and apoptotic neutrophils in the inflammation site. For this, monocytes were observed microscopically after exposing them with NETs and/or apoptotic bodies. A subset of monocytes exposed to NETs ejected extracellular traps and this was shown to be mediated by proteins like elastase and citrullinated histones present in NET supernatant. Monocytes showed a preference for the internalisation of the apoptotic body when both NET and apoptotic bodies were present in the medium. The study provides new insight into the role of monocytes in the clearance of NET and apoptotic neutrophils and this information may open up a way in formulating therapeutic strategies for accelerating resolution of inflammation.

Linear rheology as a potential monitoring tool for sputum in patients with Chronic Obstructive Pulmonary Disease (COPD)

BACKGROUND

The rheological properties of sputum may influence lung function and become modified in disease.

OBJECTIVE

This study aimed to correlate the viscoelastic properties of sputum with clinical data on the severity of disease in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Sputum samples from COPD patients were investigated using rheology, simple mathematical modelling and Scanning Electron Microscopy (SEM). The samples were all collected from patients within two days of their admission to Prince Philip Hospital due to an exacerbation of their COPD. Oscillatory and creep rheological techniques were used to measure changes in viscoelastic properties at different frequencies over time.

RESULTS

COPD sputum was observed to behave as a viscoelastic solid at all frequencies studied. Comparing the rheology of exacerbated COPD sputum with healthy sputum (not diagnosed with a respiratory disease) revealed significant differences in response to oscillatory shear and creep-recovery experiments, which highlights the potential clinical benefits of better understanding sputum viscoelasticity. A common power law model G(t)=G0(tτ0)-m was successfully fitted to experimental rheology data over the range of frequencies studied.

CONCLUSIONS

A comparison between clinical data and the power law index m obtained from rheology, suggested that an important possible future application of this parameter is as a potential biomarker for COPD severity.

Imaging and Manipulation of Extracellular Traps by Atomic Force Microscopy

Neutrophil extracellular traps (NETs) are part of an immunological response and one of the mechanisms by which neutrophils protect the host from pathogen invasion and proliferation. Notwithstanding their protective role, NETs have also been linked to the development of a variety of disorders, including cardiovascular and autoimmune diseases. Since the first reports on NETs in 2004 it has been possible to image NETs by a variety of imaging techniques. Despite this, such reports seldomly include contact probe methods, and therefore lack the unique insights such techniques typically provide. In fact, more than 10 years have passed since the discovery of NETs, and although their importance as part of a unique cellular response mechanism has become very clear, studies that attempt to address them by atomic force microscopy (AFM) remain very limited. Particularly striking is the almost absent information on the mechanical properties of NETs, and factors that may influence them. The fact that NETs are a particularly adhesive network of filaments poses a considerable technical challenge for contact probe methods and can limit advances involving either imaging or manipulation of NETs by AFM. The current set of protocols aims at aiding a knowledgeable AFM operator to obtain AFM images and to perform force spectroscopy experiments with such samples. A variety of different topics, including sample preparation and data analysis, are discussed.

Allergic Bronchopulmonary Aspergillosis-A Luminal Hypereosinophilic Disease With Extracellular Trap Cell Death

Allergic bronchopulmonary aspergillosis (ABPA) is characterized by an early allergic response and late-phase lung injury in response to repeated exposure to Aspergillus antigens, as a consequence of persistent fungal colonization of the airways. Here, we summarize the clinical and pathological features of ABPA, focusing on thick mucus plugging, a key observation in ABPA. Recent findings have indicated that luminal eosinophils undergo cytolytic extracellular trap cell death (ETosis) and release filamentous chromatin fibers (extracellular traps, ETs) by direct interaction with Aspergillus fumigatus. Production of ETs is considered to be an innate immune response against non-phagocytable pathogens using a "trap and kill" mechanism, although eosinophil ETs do not promote A. fumigatus damage or killing. Compared with neutrophils, eosinophil ETs are composed of stable and condensed chromatin fibers and thus might contribute to the higher viscosity of eosinophilic mucus. The major fate of massively accumulated eosinophils in the airways is ETosis, which potentially induces the release of toxic granule proteins and damage-associated molecular patterns, epithelial damage, and further decreases mucus clearance. This new perspective on ABPA as a luminal hypereosinophilic disease with ETosis/ETs could provide a better understanding of airway mucus plugging and contribute to future therapeutic strategies for this challenging disease.

Secreted Phosphatase and Deoxyribonuclease Are Required by Pseudomonas aeruginosa To Defend against Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are produced by neutrophils as an innate immune defense mechanism to trap and kill microbial pathogens. NETs are comprised of ejected chromatin that forms a lattice structure enmeshed with numerous antimicrobial proteins. In addition to forming the structural backbone of NETs, extracellular DNA (eDNA) has membrane-disrupting antimicrobial activity that contributes to NET killing. Many pathogens produce secreted extracellular DNases to evade the antimicrobial activity of NETs. Pseudomonas aeruginosa encodes an operon of two secreted enzymes, a predicted alkaline phosphatase and a DNase. The DNase (eddB) degrades eDNA to use as a nutrient source. Here we report that both eDNA and NETs are potent inducers of this DNase-phosphatase operon. Furthermore, the secreted DNase contributes to degrading NET DNA and defends P. aeruginosa against NET-mediated killing. We demonstrate that EddA has both alkaline phosphatase and phosphodiesterase (PDase) activities and also protects against the antimicrobial activity of NETs. Although the phosphatase does not cause DNA degradation similar to that of the DNase, its protective function is likely a result of removing the cation-chelating phosphates from the eDNA phosphodiester backbone. Therefore, both the DNase and PDase contribute to defense against NET killing of P. aeruginosa, highlighting the role of DNA-manipulating enzymes in targeting the eDNA in neutrophil extracellular traps.

Role of neutrophils in equine asthma

Neutrophilic bronchiolitis is the primary lesion in asthma-affected horses. Neutrophils are key actors in host defense, migrating toward sites of inflammation and infection, where they act as early responder cells toward external insults. However, neutrophils can also mediate tissue damage in various non-infectious inflammatory processes. Within the airways, these cells likely contribute to bronchoconstriction, mucus hypersecretion, and pulmonary remodeling by releasing pro-inflammatory mediators, including the cytokines interleukin (IL)-8 and IL-17, neutrophil elastase, reactive oxygen species (ROS), and neutrophil extracellular traps (NETs). The mechanisms that regulate neutrophil functions in the tissues are complex and incompletely understood. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task achieved through a complex network of mechanisms that regulates neutrophil survival. The discovery and development of compounds that can help regulate ROS, NET formation, cytokine release, and clearance would be highly beneficial in the design of therapies for this disease in horses. In this review, neutrophil functions during inflammation will be discussed followed by a discussion of their contribution to airway tissue injury in equine asthma.

Hypertonic Saline Suppresses NADPH Oxidase-Dependent Neutrophil Extracellular Trap Formation and Promotes Apoptosis

Tonicity of saline (NaCl) is important in regulating cellular functions and homeostasis. Hypertonic saline is administered to treat many inflammatory diseases, including cystic fibrosis. Excess neutrophil extracellular trap (NET) formation, or NETosis, is associated with many pathological conditions including chronic inflammation. Despite the known therapeutic benefits of hypertonic saline, its underlying mechanisms are not clearly understood. Therefore, we aimed to elucidate the effects of hypertonic saline in modulating NETosis. For this purpose, we purified human neutrophils and induced NETosis using agonists such as diacylglycerol mimetic phorbol myristate acetate (PMA), Gram-negative bacterial cell wall component lipopolysaccharide (LPS), calcium ionophores (A23187 and ionomycin from Streptomyces conglobatus), and bacteria (Pseudomonas aeruginosa and Staphylococcus aureus). We then analyzed neutrophils and NETs using Sytox green assay, immunostaining of NET components and apoptosis markers, confocal microscopy, and pH sensing reagents. This study found that hypertonic NaCl suppresses nicotinamide adenine dinucleotide phosphate oxidase (NADPH2 or NOX2)-dependent NETosis induced by agonists PMA, Escherichia coli LPS (0111:B4 and O128:B12), and P. aeruginosa. Hypertonic saline also suppresses LPS- and PMA- induced reactive oxygen species production. It was determined that supplementing H₂O₂ reverses the suppressive effect of hypertonic saline on NOX2-dependent NETosis. Many of the aforementioned suppressive effects were observed in the presence of equimolar concentrations of choline chloride and osmolytes (d-mannitol and d-sorbitol). This suggests that the mechanism by which hypertonic saline suppresses NOX2-dependent NETosis is via neutrophil dehydration. Hypertonic NaCl does not significantly alter the intracellular pH of neutrophils. We found that hypertonic NaCl induces apoptosis while suppressing NOX2-dependent NETosis. In contrast, hypertonic solutions do not suppress NOX2-independent NETosis. Although hypertonic saline partially suppresses ionomycin-induced NETosis, it enhances A23187-induced NETosis, and it does not alter S. aureus-induced NETosis. Overall, this study determined that hypertonic saline suppresses NOX2-dependent NETosis induced by several agonists; in contrast, it has variable effects on neutrophil death induced by NOX2-independent NETosis agonists. These findings are important in understanding the regulation of NETosis and apoptosis in neutrophils.

Development and Application of High-Content Biological Screening for Modulators of NET Production

Neutrophil extracellular traps (NETs) are DNA-based antimicrobial web-like structures whose release is predominantly mediated by reactive oxygen species (ROS); their purpose is to combat infections. However, unbalanced NET production and clearance is involved in tissue injury, circulation of auto-antibodies and development of several chronic diseases. Currently, there is lack of agreement regarding the high-throughput methods available for NET investigation. This study, therefore, aimed to develop and optimize a high-content analysis (HCA) approach, which can be applied for the assay of NET production and for the screening of compounds involved in the modulation of NET release. A suitable paraformaldehyde fixation protocol was established to enable HCA of neutrophils and NETs. Bespoke and in-built bioinformatics algorithms were validated by comparison with standard low-throughput approaches for application in HCA of NETs. Subsequently, the optimized protocol was applied to high-content screening (HCS) of a pharmaceutically derived compound library to identify modulators of NETosis. Of 56 compounds assessed, 8 were identified from HCS for further characterization of their effects on NET formation as being either inducers, inhibitors or biphasic modulators. The effects of these compounds on naïve neutrophils were evaluated by using specific assays for the induction of ROS and NET production, while their modulatory activity was validated in phorbol 12-myristate 13-acetate-stimulated neutrophils. Results indicated the involvement of glutathione reductase, Src family kinases, molecular-target-of-Rapamycin, and mitogen-activated-protein-kinase pathways in NET release. The compounds and pathways identified may provide targets for novel therapeutic approaches for treating NET-associated pathologies.

Neutrophils in tissue injury and repair

As one of the first defenders of innate immune response, neutrophils make a rapid and robust response against infection or harmful agents. While traditionally regarded as suicidal killers that cause collateral tissue damage, recent findings on neutrophil extracellular trap formation, heterogeneity and plasticity and novel reparative functions have expanded our understanding of their diverse roles in health and disease. This review summarizes our current understanding of neutrophil-associated tissue injury, highlighting the emerging roles of neutrophil extracellular traps. This review will also focus on scrutinizing the roles of neutrophils in tissue repair and regeneration and will examine data on unexpected aspects of involvement of neutrophils in regulating normal tissue homeostasis.

Neutrophil Fates in Bronchiectasis and Alpha-1 Antitrypsin Deficiency

The neutrophil is a powerful cellular defender of the vulnerable interface between the environment and pulmonary tissues. This cell's potent weapons are carefully calibrated in the healthy state to maximize effectiveness in fighting pathogens while minimizing tissue damage and allowing for repair of what damage does occur. The three related chronic airway disorders of cystic fibrosis, non-cystic fibrosis bronchiectasis, and alpha-1 antitrypsin deficiency all demonstrate significant derangements of this homeostatic system that result in their respective pathologies. An important shared feature among them is the inefficient resolution of chronic inflammation that serves as a central means for neutrophil-driven lung damage resulting in disease progression. Examining the commonalities and divergences between these diseases in the light of their immunopathology is informative and may help guide us toward future therapeutics designed to modulate the neutrophil's interplay with the pulmonary environment.

Targeting microbial biofilms: current and prospective therapeutic strategies

Biofilm formation is a key virulence factor for a wide range of microorganisms that cause chronic infections. The multifactorial nature of biofilm development and drug tolerance imposes great challenges for the use of conventional antimicrobials and indicates the need for multi-targeted or combinatorial therapies. In this Review, we focus on current therapeutic strategies and those under development that target vital structural and functional traits of microbial biofilms and drug tolerance mechanisms, including the extracellular matrix and dormant cells. We emphasize strategies that are supported by in vivo or ex vivo studies, highlight emerging biofilm-targeting technologies and provide a rationale for multi-targeted therapies aimed at disrupting the complex biofilm microenvironment.

Immunoregulation of Neutrophil Extracellular Trap Formation by Endothelial-Derived p33 (gC1q Receptor)

The formation of neutrophil extracellular traps (NETs) is a host defence mechanism, known to facilitate the entrapment and growth inhibition of many bacterial pathogens. It has been implicated that the translocation of myeloperoxidase (MPO) from neutrophilic granules to the nucleus is crucial to this process. Under disease conditions, however, excessive NET formation can trigger self-destructive complications by releasing pathologic levels of danger-associated molecular pattern molecules (DAMPs). To counteract such devastating immune reactions, the host has to rely on precautions that help circumvent these deleterious effects. Though the induction of DAMP responses has been intensively studied, the mechanisms that are used by the host to down-regulate them are still not understood. In this study, we show that p33 is an endothelial-derived protein that has the ability to annul NET formation. We found that the expression of human p33 is up-regulated in endothelial cells upon infections with Streptococcus pyogenes bacteria. Using tissue biopsies from a patient with streptococcal necrotising fasciitis, we monitored co-localisation of p33 with MPO. Further in vitro studies revealed that p33 is able to block the formation of DAMP-induced NET formation by inhibiting the enzymatic activity of MPO. Additionally, mice challenged with S. pyogenes bacteria demonstrated diminished MPO activity when treated with p33. Together, our results demonstrate that host-derived p33 has an important immunomodulating function that helps to counterbalance an overwhelming DAMP response.

Eosinophilic Otitis Media: the Aftermath of Eosinophil Extracellular Trap Cell Death

PURPOSE OF REVIEW

Eosinophilic otitis media (EOM) is a refractory disease characterized by the accumulation of eosinophils in middle ear effusion and mucosa. We summarize current knowledge regarding the clinical characteristics and management of EOM. Although eosinophil activation in inflamed foci is involved in the pathogenesis of EOM, little is known about the fate of the eosinophils and aftermath of their cell death. We discuss the possibility that eosinophils undergo non-apoptotic cell death that worsens tissue damage and increases effusion viscosity.

RECENT FINDINGS

Unlike chronic otitis media, EOM is strongly associated with an allergic background. Corticosteroids are currently the only effective pharmacological treatment, and surgical intervention is often required. Mucosal eosinophils infiltrate extensively into the middle ear cavity where they are stimulated by locally produced activators including interleukin-5 and eotaxin. The eosinophils undergo cytolysis in the effusion, which represents a major fate of activated eosinophils in vivo. Recent data revealed cytolysis could be renamed as extracellular trap cell death (ETosis). ETosis represents suicidal cell death involving total cell degranulation and development of sticky chromatin structures (extracellular traps (ETs)). The characteristics of eosinophil- and neutrophil-derived ET polymers might contribute to the difference in viscosity of secretions between EOM and common chronic otitis media. The extracellular products remaining after eosinophil ETosis are an important aspect of EOM pathology. The concept of ETosis also has novel implications for potential therapeutic modalities in various eosinophilic disorders.

Delayed neutrophil apoptosis enhances NET formation in cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) lung disease is defined by large numbers of neutrophils and associated damaging products in the airway. Delayed neutrophil apoptosis is described in CF although it is unclear whether this is a primary neutrophil defect or a response to chronic inflammation. Increased levels of neutrophil extracellular traps (NETs) have been measured in CF and we aimed to investigate the causal relationship between these phenomena and their potential to serve as a driver of inflammation. We hypothesised that the delay in apoptosis in CF is a primary defect and preferentially allows CF neutrophils to form NETs, contributing to inflammation.

METHODS

Blood neutrophils were isolated from patients with CF, CF pigs and appropriate controls. Neutrophils were also obtained from patients with CF before and after commencing ivacaftor. Apoptosis was assessed by morphology and flow cytometry. NET formation was determined by fluorescent microscopy and DNA release assays. NET interaction with macrophages was examined by measuring cytokine generation with ELISA and qRT-PCR.

RESULTS

CF neutrophils live longer due to decreased apoptosis. This was observed in both cystic fibrosis transmembrane conductance regulator (CFTR) null piglets and patients with CF, and furthermore was reversed by ivacaftor (CFTR potentiator) in patients with gating (G551D) mutations. CF neutrophils formed more NETs and this was reversed by cyclin-dependent kinase inhibitor exposure. NETs provided a proinflammatory stimulus to macrophages, which was enhanced in CF.

CONCLUSIONS

CF neutrophils have a prosurvival phenotype that is associated with an absence of CFTR function and allows increased NET production, which can in turn induce inflammation. Augmenting neutrophil apoptosis in CF may allow more appropriate neutrophil disposal, decreasing NET formation and thus inflammation.

Bacteria causing pyometra in bitch and queen induce neutrophil extracellular traps

Neutrophils are capable of releasing their DNA in response to infectious agents to form neutrophil extracellular traps (NETs) to destroy pathogens. Even though pyometra in queens and bitches is a common disease, its pathogenesis is not fully understood. The aim of this study was to assess the presence of NETs in the endometrium of queens and bitches suffering from pyometra. Pyometra and normal uteri were obtained after ovariohysterectomy from adult queens and bitches in diestrus. Uterine contents were evaluated for bacterial isolation and identification and for NETs presence. Escherichia coli were isolated in 5/5 queens and 4/5 bitches, and Streptococcus spp in one bitch. Sterile glass coverslips were placed on the endometrium surface to obtain material for NETs that were evaluated by immunocytochemistry (histone, neutrophil elastase or myeloperoxidase), fluorescence microscopy or scanning electron microscopy. NETs in endometrium content were positively stained by DNA histone DAPI, myeloperoxidase and by neutrophil elastase. NETs were spread in all observed queen and bitch endometria of pyometra cases. Ultrastructure images of NETs depicted clusters of globular material with fine filaments deposited on or around thick filaments and trapped bacteria. To the best of our knowledge these are the first findings confirming NETs endometrial presence in queen and bitch pyometra. Nevertheless, the precise role of NETs in pyometra in the bitch and queen, either to contribute to the defeat of infection or to its persistence remains to be unraveled.

Dysregulated Chemokine Signaling in Cystic Fibrosis Lung Disease: A Potential Therapeutic Target

CF lung disease is characterized by a chronic and non-resolving activation of the innate immune system with excessive release of chemokines/cytokines including IL-8 and persistent infiltration of immune cells, mainly neutrophils, into the airways. Chronic infection and impaired immune response eventually lead to pulmonary damage characterized by bronchiectasis, emphysema, and lung fibrosis. As a complete knowledge of the pathways responsible for the exaggerated inflammatory response in CF lung disease is lacking, understanding these pathways could reveal new therapeutic targets, and lead to novel treatments. Therefore, there is a strong rationale for the identification of mechanisms and pathways underlying the exaggerated inflammatory response in CF lung disease. This article reviews the role of inflammation in the pathogenesis of CF lung disease, with a focus on the dysregulated signaling involved in the overexpression of chemokine IL-8 and excessive recruitment of neutrophils in CF airways. The findings suggest that targeting the exaggerated IL-8/IL-8 receptor (mainly CXCR2) signaling pathway in immune cells (especially neutrophils) may represent a potential therapeutic strategy for CF lung disease.

Thermo-physical properties of synthetic mucus for the study of airway clearance

In this article, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al., Eur Respir J 1991; 4: 311-315 were experiementally determined. This simulant is mainly composed of a galactomannan gum and a scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of scleroglucan concentrations. More importantly and for some scleroglucan concentrations, the syntetic mucus, exhibits, somehow, comparable thermophysical properties to real bronchial mucus. An insight on the microstructure of this simulant is proposed and the different properties enounced previously have been measured for various scleroglucan concentrations and over a certain range of operating temperatures. This synthetic mucus is found to mimic well the rheological behavior and the surface tension of real mucus for different pathologies. Density and thermal properties have been measured for the first time. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3025-3033, 2017.

Harnessing Neutrophil Survival Mechanisms during Chronic Infection by Pseudomonas aeruginosa: Novel Therapeutic Targets to Dampen Inflammation in Cystic Fibrosis

More than two decades after cloning the cystic fibrosis transmembrane regulator (CFTR) gene, the defective gene in cystic fibrosis (CF), we still do not understand how dysfunction of this ion channel causes lung disease and the tremendous neutrophil burden which persists within the airways; nor why chronic colonization by Pseudomonas aeruginosa develops in CF patients who are thought to be immunocompetent. It appears that the microenvironment within the lung of CF patients provides favorable conditions for both P. aeruginosa colonization and neutrophil survival. In this context, the ability of bacteria to induce hypoxia, which in turn affects neutrophil survival is an additional level of complexity that needs to be accounted for when controlling neutrophil fate in CF. Recent studies have underscored the importance of neutrophils in innate immunity and their functions appear to extend far beyond their well-described role in antibacterial defense. Perhaps a disturbance in neutrophil reprogramming during the course of an infection severely modulates the inflammatory response in CF. Furthermore there is an emerging concept that the CFTR itself may be an immune modulator and stimulating CFTR function in CF patients could promote neutrophil and macrophages antimicrobial function. Fostering the resolution of inflammation by favoring neutrophil apoptosis could preserve their microbicidal activities but decrease their proinflammatory potential. In this context, triggering neutrophil apoptosis with roscovitine may be a potential therapeutic option and this is currently being evaluated in CF patients. In the present review we discuss how neutrophils functions are disturbed in CF and how this may relate to chronic infection with P. aeuginosa and we propose novel research directions aimed at modulating neutrophil survival, dampening lung inflammation and ultimately leading to an amelioration of the lung disease.

Diverse stimuli engage different neutrophil extracellular trap pathways

Neutrophils release neutrophil extracellular traps (NETs) which ensnare pathogens and have pathogenic functions in diverse diseases. We examined the NETosis pathways induced by five stimuli; PMA, the calcium ionophore A23187, nigericin, Candida albicans and Group B Streptococcus. We studied NET production in neutrophils from healthy donors with inhibitors of molecules crucial to PMA-induced NETs including protein kinase C, calcium, reactive oxygen species, the enzymes myeloperoxidase (MPO) and neutrophil elastase. Additionally, neutrophils from chronic granulomatous disease patients, carrying mutations in the NADPH oxidase complex or a MPO-deficient patient were examined. We show that PMA, C. albicans and GBS use a related pathway for NET induction, whereas ionophores require an alternative pathway but that NETs produced by all stimuli are proteolytically active, kill bacteria and composed mainly of chromosomal DNA. Thus, we demonstrate that NETosis occurs through several signalling mechanisms, suggesting that extrusion of NETs is important in host defence.

DOI:http://dx.doi.org/10.7554/eLife.24437.001

The immune system protects the body against microorganisms that can cause infections and diseases. Neutrophils are a type of immune cell that patrol the blood in search of germs. Once they encounter potentially harmful microbes, neutrophils eradicate them in different ways. One way to catch the germs is by using ‘neutrophil extracellular traps’, or NETs for short, to confine and kill the invaders.

NETs are web-like structures made up of anti-microbial proteins and the neutrophil’s own DNA. The process of making NETs kills the neutrophil, as it eventually explodes to release the NETs. NETs play a key role in disease prevention, but producing too many NETs or producing them at the wrong time or in the wrong place can actually make certain diseases worse. Therefore, it is important to fully understand the signaling pathways and molecules the neutrophils use to make NETs.

Kenny et al. exposed neutrophils from healthy people to five different compounds known to cause the cells to make NETs, including some harmful molecules, a fungus and a bacterium. Microscopy was then used to count how many neutrophils made NETs in response to each of the five stimuli. Further experiments showed that neutrophils from patients with an immune system disorder produced fewer NETs when stimulated with some of the compounds, while the other stimuli caused neutrophils to produce the same levels of NETs as healthy individuals.

Kenny et al. also revealed that neutrophils use several different ways to produce and release NETs, depending on the stimulus used. Some of the ways required reactive oxygen species, such as hydrogen peroxide and enzymes, while others produced NETs without the need for these molecules. Lastly, Kenny et al. showed that the way the cells die after the NET is released is unique from other pathways that are known to kill cells.

Future work will aim to identify a single molecule that can block neutrophils from releasing NETs at the wrong time and place, without affecting the important role NETs play in fighting germs. Such a molecule could be developed into a drug for people with diseases like lupus or rheumatoid arthritis, where the release of NETs makes the disease worse not better.

DOI:http://dx.doi.org/10.7554/eLife.24437.002

Neutrophil Extracellular Traps Stimulate Proinflammatory Responses in Human Airway Epithelial Cells

Tissue injury leads to the release of uric acid (UA). At high local concentrations, UA can form monosodium urate crystals (MSU). MSU and UA stimulate neutrophils to release extracellular traps (NET). Here, we investigated whether these NET could be involved in the development of inflammation by stimulating cytokine release by airway epithelial cells. We found that NET significantly increased the secretion of CXCL8/IL-8 and IL-6 by alveolar and bronchial epithelial cells. These effects were not observed when NETosis was inhibited by Diphenyleneiodonium, elastase inhibitor, or Cl-amidine. Similar findings were made with NET induced by cigarette smoke extract, suggesting that NET proinflammatory capacity is independent of the inducing stimulus. Furthermore, NET affected neither the viability and morphology of epithelial cells nor the barrier integrity of polarized cells. The epithelial stimulatory capacity of NET was not affected by degradation of DNA with micrococcal nuclease, treatment with heparin, or inhibition of the elastase immobilized to DNA, but it was significantly reduced by pretreatment with an anti-HMGB-1 blocking antibody. Altogether, our findings indicate that NET exert direct proinflammatory effects on airway epithelial cells that might contribute in vivo to the further recruitment of neutrophils and the perpetuation of inflammation upon lung tissue damage.

Understanding the Entanglement: Neutrophil Extracellular Traps (NETs) in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the gene that codes for the CF trans-membrane conductance regulator. These mutations result in abnormal secretions viscous airways of the lungs, favoring pulmonary infection and inflammation in the middle of neutrophil recruitment. Recently it was described that neutrophils can contribute with disease pathology by extruding large amounts of nuclear material through a mechanism of cell death known as Neutrophil Extracellular Traps (NETs) into the airways of patients with CF. Additionally, NETs production can contribute to airway colonization with bacteria, since they are the microorganisms most frequently found in these patients. In this review, we will discuss the implication of individual or mixed bacterial infections that most often colonize the lung of patients with CF, and the NETs role on the disease.

New Aspects of the Biology of Neutrophil Extracellular Traps

The formation and release of neutrophil extracellular traps (NETs) discovered in 2004 by Volker Brinkmann and Arturo Zychlinsky cast a new light on the role of neutrophils in the non-specific immune response of the body. This discovery has resulted in the rapid development of neutrophil studies in different bacterial and autoimmune diseases as well as neoplasms. Research is also being performed on the role of different signalling pathways engaged in the induction of NETosis, a unique form of a programmed cell death leading to the creation of NETs. The literature provides information on the structure and composition of neutrophil extracellular traps. This review presents the latest data on NET formation and the role of their key components, as well as describing the intracellular signalling pathways leading to the generation of NETs that have been discovered.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.

Dexamethasone Inhibits S. aureus-Induced Neutrophil Extracellular Pathogen-Killing Mechanism, Possibly through Toll-Like Receptor Regulation

Neutrophils release neutrophil extracellular traps (NETs) in a pathogen-killing process called NETosis. Excessive NETs formation, however, is implicated in disease pathogenesis. Therefore, to understand how NETosis is regulated, we examined the effect of dexamethasone (DXM), an anti-inflammatory drug, on this process and the role of toll-like receptors (TLRs). We stimulated human neutrophils with phorbol 12-myristate 13-acetate (PMA) or Staphylococcus aureus (S. aureus) and quantified NETs formation. We also examined the effect of DXM on the bactericidal effect of NETs and the role of reactive oxygen species (ROS) and nuclear factor (NF)-κB in DXM-regulated NETosis. DXM significantly inhibited S. aureus-induced NETosis and extracellular bacterial killing. ROS production and NF-κB activation were not involved in DXM-regulated NETosis. TLR2 and TLR4, but not TLR5 or TLR6, modified S. aureus-induced NETs formation. Neither DXM nor TLRs were involved in PMA-induced NETosis. Furthermore, TLR2 and TLR4 agonists rescued DXM-inhibited NETosis, and neither TLR2 nor TLR4 antagonists could further inhibit NETosis reduction induced by DXM, indicating that DXM may inhibit NETosis by regulating TLR2 and TLR4. In conclusion, the mechanisms of S. aureus- and PMA-induced NETosis are different. DXM decreases NETs formation independently of oxidant production and NF-κB phosphorylation and possibly via a TLR-dependent mechanism.

Neutrophil Extracellular Traps in Respiratory Disease: guided anti-microbial traps or toxic webs?

Neutrophil recruitment to the airways and lungs is a major hallmark of many respiratory diseases. One of the more recently discovered unique innate immune effector mechanisms of neutrophils is the formation of neutrophil extracellular traps (NETs), consisting of an extracellular network of DNA fibers studded with nuclear and granule proteins. Although in the respiratory system NETs contribute to capture and inactivation of bacteria, fungi and viruses, there is a delicate 'balance' between aid and damage to the host. Accumulating evidence now suggests that NETs can have direct cytotoxic effects to lung epithelial and endothelial cells and can contribute to airway obstruction. As such, NETs may play an important role in the pathogenesis of respiratory diseases. The purpose of this review is to give an up-to-date overview of the current status of NETs in respiratory diseases. We examine both experimental and clinical data concerning the role of NETs in host defence as well as immunopathology, with special attention paid to the literature relevant for the paediatric pulmonology community. Finally, we discuss future treatment strategies that may target the formation of NETs in the airways and lungs.