Neutrophil elastase enhances sputum solubilization in cystic fibrosis patients receiving DNase therapy

Tumor metastasis and recurrence: The role of perioperative NETosis

Although surgical resection of tumor mass remains the mainstay of curative therapeutic management for solid tumors, accumulating studies suggest that these procedures promote tumor recurrence and metastasis. Regarded as the first immune cells to fight against infectious or inflammatory insults from surgery, neutrophils along with their ability of neutrophil extracellular traps (NETs) production has attracted much attention. A growing body of evidence suggests that NETs promote cancer metastasis by stimulating various stages, including local invasion, colonization, and growth. Therefore, we discussed the mechanism of NETosis induced by surgical stress and tumor cells, and the contribution of NETs on tumor metastasis: aid in the tumor cell migration and proliferation, evasion of immune surveillance, circulating tumor cell adhesion and establishment of a metastatic niche. Lastly, we summarized existing NET-targeting interventions, offering recent insights into potential targets for clinical intervention.

Turning Neutrophil Cell Death Deadly in the Context of Hypertensive Vascular Disease

Hypertensive vascular disease (HVD) is a major health burden globally and is a comorbidity commonly associated with other metabolic diseases. Many factors are associated with HVD including obesity, diabetes, smoking, chronic kidney disease, and sterile inflammation. Increasing evidence points to neutrophils as an important component of the chronic inflammatory response in HVD. Neutrophils are abundant in the circulation and can respond rapidly upon stimulation to deploy an armament of antimicrobial effector functions. One of the outcomes of neutrophil activation is the generation of neutrophil extracellular traps (NETs), a regulated extrusion of chromatin and proteases. Although neutrophils and NETs are well described as components of the innate immune response to infection, recent evidence implicates them in HVD. Endothelial cell activation can trigger neutrophil adhesion, activation, and production of NETs promoting vascular dysfunction, vessel remodelling, and loss of resistance. The regulated release of NETs can be controlled by the pore-forming activities of distinct cell death pathways. The best characterized pathways in this context are apoptosis, pyroptosis, and necroptosis. In this review, we discuss how inflammatory cell death signalling and NET formation contribute to hypertensive disease. We also examine novel therapeutic approaches to limit NET production and their future potential as therapeutic drugs for cardiovascular disorders.

The bacterial serine protease inhibitor ecotin inhibits neutrophil elastase enzymatic activity in cystic fibrosis sputa

Cystic Fibrosis (CF) airway disease is characterized by impaired mucociliary clearance, chronic, polymicrobial infections and robust, neutrophil-dominated inflammation. Pulmonary disease is the leading cause of morbidity and mortality in people with CF and is due to progressive airflow obstruction and ultimately respiratory failure. One of the earliest abnormalities in CF airway disease is the recruitment of neutrophils to the lungs. Neutrophil activation leads to the release of their intracellular content, including neutrophil elastase (NE), that damages lung tissues in CF. Our goal is to characterize a known bacterial NE inhibitor, ecotin, in the CF airway environment. Our results indicate that ecotins cloned from four Gram-negative bacterial species (Campylobacter rectus, Campylobacter showae, Escherichia coli and Pseudomonas aeruginosa) inhibit NE activity in CF sputum samples in a dose-dependent manner. Although we observed differences in the NE-inhibitory activity of the tested ecotins with the Campylobacter homologs being the most effective in NE inhibition in CF sputa, none of the ecotins impaired the ability of human neutrophils to kill major CF respiratory pathogens, P. aeruginosa or S. aureus, in vitro. Overall, we demonstrate that bacterial ecotins inhibit NE activity in CF sputa without compromising bacterial killing by neutrophils.

Neutrophil extracellular traps in homeostasis and disease

Neutrophil extracellular traps (NETs), crucial in immune defense mechanisms, are renowned for their propensity to expel decondensed chromatin embedded with inflammatory proteins. Our comprehension of NETs in pathogen clearance, immune regulation and disease pathogenesis, has grown significantly in recent years. NETs are not only pivotal in the context of infections but also exhibit significant involvement in sterile inflammation. Evidence suggests that excessive accumulation of NETs can result in vessel occlusion, tissue damage, and prolonged inflammatory responses, thereby contributing to the progression and exacerbation of various pathological states. Nevertheless, NETs exhibit dual functionalities in certain pathological contexts. While NETs may act as autoantigens, aggregated NET complexes can function as inflammatory mediators by degrading proinflammatory cytokines and chemokines. The delineation of molecules and signaling pathways governing NET formation aids in refining our appreciation of NETs' role in immune homeostasis, inflammation, autoimmune diseases, metabolic dysregulation, and cancer. In this comprehensive review, we delve into the multifaceted roles of NETs in both homeostasis and disease, whilst discussing their potential as therapeutic targets. Our aim is to enhance the understanding of the intricate functions of NETs across the spectrum from physiology to pathology.

Anti-inflammatory therapy with nebulized dornase alfa for severe COVID-19 pneumonia: a randomized unblinded trial

Background

Prinflammatory extracellular chromatin from neutrophil extracellular traps (NETs) and other cellular sources is found in COVID-19 patients and may promote pathology. We determined whether pulmonary administration of the endonuclease dornase alfa reduced systemic inflammation by clearing extracellular chromatin.

Methods

Eligible patients were randomized (3:1) to the best available care including dexamethasone (R-BAC) or to BAC with twice-daily nebulized dornase alfa (R-BAC + DA) for seven days or until discharge. A 2:1 ratio of matched contemporary controls (CC-BAC) provided additional comparators. The primary endpoint was the improvement in C-reactive protein (CRP) over time, analyzed using a repeated-measures mixed model, adjusted for baseline factors.

Results

We recruited 39 evaluable participants: 30 randomized to dornase alfa (R-BAC +DA), 9 randomized to BAC (R-BAC), and included 60 CC-BAC participants. Dornase alfa was well tolerated and reduced CRP by 33% compared to the combined BAC groups (T-BAC). Least squares (LS) mean post-dexamethasone CRP fell from 101.9 mg/L to 23.23 mg/L in R-BAC +DA participants versus a 99.5 mg/L to 34.82 mg/L reduction in the T-BAC group at 7 days; p=0.01. The anti-inflammatory effect of dornase alfa was further confirmed with subgroup and sensitivity analyses on randomised participants only, mitigating potential biases associated with the use of CC-BAC participants. Dornase alfa increased live discharge rates by 63% (HR 1.63, 95% CI 1.01-2.61, p=0.03), increased lymphocyte counts (LS mean: 1.08 vs 0.87, p=0.02) and reduced circulating cf-DNA and the coagulopathy marker D-dimer (LS mean: 570.78 vs 1656.96 μg/mL, p=0.004).

Conclusions

Dornase alfa reduces pathogenic inflammation in COVID-19 pneumonia, demonstrating the benefit of cost-effective therapies that target extracellular chromatin.

Funding

LifeArc, Breathing Matters, The Francis Crick Institute (CRUK, Medical Research Council, Wellcome Trust).

Clinical trial number

NCT04359654.

Eosinophilic mucus diseases

Eosinophilic inflammation is primarily characterized by type 2 immune responses against parasitic organisms. In the contemporary human being especially in developed countries, eosinophilic inflammation is strongly associated with allergic/sterile inflammation, and constitutes an undesired immune reaction. This situation is in stark contrast to neutrophilic inflammation, which is indispensable for the host defense against bacterial infections. Among eosinophilic inflammatory disorders, massive accumulation of eosinophils within mucus is observed in certain cases, and is often linked to the distinctive clinical finding of mucus with high viscosity. Eosinophilic mucus is found in a variety of diseases, including chronic allergic keratoconjunctivitis, chronic rhinosinusitis encompassing allergic fungal sinusitis, eosinophilic otitis media, eosinophilic sialodochitis, allergic bronchopulmonary aspergillosis/mycosis, eosinophilic plastic bronchitis, and eosinophilic asthma. In these pathological conditions, chronic inflammation and tissue remodeling coupled with irreversible organ damage due to persistent adhesion of toxic substances and luminal obstruction may impose a significant burden on the body. Eosinophils aggregate in the hyperconcentrated mucus together with cell-derived crystals, macromolecules, and polymers, thereby affecting the biophysical properties of the mucus. This review focuses on the clinically significant challenges of mucus and discusses the consequences of activated eosinophils on the mucosal surface that impact mucus and persistent inflammation.

Polymerized Salicylic Acid Microparticles Reduce the Progression and Formation of Human Neutrophil Extracellular Traps (NET)s

Neutrophils can contribute to inflammatory disease propagation via innate mechanisms intended for inflammation resolution. For example, neutrophil extracellular traps (NETs) are necessary for trapping pathogens but can contribute to clot formation and blood flow restriction, that is, ischemia. Currently, no therapeutics in the clinic directly target NETs despite the known involvement of NETs contributing to mortality and increased disease severity. Vascular-deployed particle-based therapeutics are a novel and robust alternative to traditional small-molecule drugs by enhancing drug delivery to cells of interest. This work designs a high-throughput assay to investigate the immunomodulatory behavior and functionality of salicylic acid-based polymer-based particle therapeutics against NETosis in human neutrophils. Briefly, this work finds that polymeric composition plays a role, and particle size can also influence rates of NETosis. Salicylate-based polymeric (Poly-SA) particles are found to functionally inhibit NETosis depending on the particle size and concentration exposed to neutrophils. This work demonstrates the high throughput method can help fast-track particle-based therapeutic optimization and design, more efficiently preparing this innovative therapeutics for the clinic.

The Bifunctional Effects of Lactoferrin (LFcinB11) in Inhibiting Neural Cell Adhesive Molecule (NCAM) Polysialylation and the Release of Neutrophil Extracellular Traps (NETs)

The expression of polysialic acid (polySia) on the neuronal cell adhesion molecule (NCAM) is called NCAM-polysialylation, which is strongly related to the migration and invasion of tumor cells and aggressive clinical status. Thus, it is important to select a proper drug to block tumor cell migration during clinical treatment. In this study, we proposed that lactoferrin (LFcinB11) may be a better candidate for inhibiting NCAM polysialylation when compared with CMP and low-molecular-weight heparin (LMWH), which were determined based on our NMR studies. Furthermore, neutrophil extracellular traps (NETs) represent the most dramatic stage in the cell death process, and the release of NETs is related to the pathogenesis of autoimmune and inflammatory disorders, with proposed involvement in glomerulonephritis, chronic lung disease, sepsis, and vascular disorders. In this study, the molecular mechanisms involved in the inhibition of NET release using LFcinB11 as an inhibitor were also determined. Based on these results, LFcinB11 is proposed as being a bifunctional inhibitor for inhibiting both NCAM polysialylation and the release of NETs.

Neutrophil Extracellular Traps and Respiratory Disease

Extracellular traps made by neutrophils (NETs) and other leukocytes such as macrophages and eosinophils have a key role in the initial immune response to infection but are highly inflammatory and may contribute to tissue damage. They are particularly relevant to lung disease, with the pulmonary anatomy facilitating their ability to fully extend into the airways/alveolar space. There has been a rapid expansion in the number of published studies demonstrating their role in a variety of important respiratory diseases including chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, asthma, pneumonia, COVID-19, rhinosinusitis, interstitial lung disease and lung cancer. The expression of NETs and other traps is a specific process, and diagnostic tests need to differentiate them from other inflammatory pathways/causes of cell death that are also characterised by the presence of extracellular DNA. The specific targeting of this pathway by relevant therapeutics may have significant clinical benefit; however, current clinical trials/evidence are at a very early stage. This review will provide a broad overview of the role of NETs and their possible treatment in respiratory disease.

A crucial role of neutrophil extracellular traps in pulmonary infectious diseases

Neutrophil extracellular traps (NETs), extrusions of intracellular DNA with attached granular material that exert an antibacterial effect through entangling, isolating, and immobilizing microorganisms, have been extensively studied in recent decades. The primary role of NETs is to entrap and facilitate the killing of bacteria, fungi, viruses, and parasites, preventing bacterial and fungal dissemination. NET formation has been described in many pulmonary diseases, including both infectious and non-infectious. NETs are considered a double-edged sword. As innate immune cells, neutrophils release NETs to kill pathogens and remove cellular debris. However, the deleterious effects of excessive NET release in lung disease are particularly important because NETs and by-products of NETosis can directly induce epithelial and endothelial cell death while simultaneously inducing inflammatory cytokine secretion and immune-mediated thrombosis. Thus, NET formation must be tightly regulated to preserve the anti-microbial capability of NETs while minimizing damage to the host. In this review, we summarized the recent updates on the mechanism of NETs formation and pathophysiology associated with excessive NETs, aiming to provide insights for research and treatment of pulmonary infectious diseases.

The Pseudomonas aeruginosa lectin LecB modulates intracellular reactive oxygen species production in human neutrophils

Pseudomonas aeruginosa is a Gram-negative bacterium and an opportunistic pathogen ubiquitously present throughout nature. LecB, a fucose-, and mannose-binding lectin, is a prominent virulence factor of P. aeruginosa, which can be expressed on the bacterial surface but also be secreted. However, the LecB interaction with human immune cells remains to be characterized. Neutrophils comprise the first line of defense against infections and their production of reactive oxygen species (ROS) and release of extracellular traps (NETs) are critical antimicrobial mechanisms. When profiling the neutrophil glycome we found several glycoconjugates on granule and plasma membranes that could potentially act as LecB receptors. In line with this, we here show that soluble LecB can activate primed neutrophils to produce high levels of intracellular ROS (icROS), an effect that was inhibited by methyl fucoside. On the other hand, soluble LecB inhibits P. aeruginosa-induced icROS production. In support of that, during phagocytosis of wild-type and LecB-deficient P. aeruginosa, bacteria with LecB induced less icROS production as compared with bacteria lacking the lectin. Hence, LecB can either induce or inhibit icROS production in neutrophils depending on the circumstances, demonstrating a novel and potential role for LecB as an immunomodulator of neutrophil functional responses.

Quantifying neutrophil extracellular trap release in a combined infection-inflammation NET-array device

Excessive release of neutrophil extracellular traps (NETs) has been reported in various human pathologies, including COVID-19 patients. Elevated NET levels serve as a biomarker, indicating increased coagulopathy and immunothrombosis risks in these patients. Traditional immunoassays employed to quantify NET release focus on bulk measurements of released chromatin in simplified microenvironments. In this study, we fabricated a novel NET-array device to quantify NET release from primary human neutrophils with single-cell resolution in the presence of the motile bacteria Pseudomonas aeruginosa PAO1 and inflammatory mediators. The device was engineered to have wide chambers and constricted loops to measure NET release in variably confined spaces. Our open NET-array device enabled immunofluorescent labeling of citrullinated histone H3, a NET release marker. We took time-lapse images of primary healthy human neutrophils releasing NETs in clinically relevant infection and inflammation-rich microenvironments. We then developed a computer-vision-based image processing method to automate the quantification of individual NETs. We showed a significant increase in NET release to Pseudomonas aeruginosa PAO1 when challenged with inflammatory mediators tumor necrosis factor-α [20 ng mL-1] and interleukin-6 [50 ng mL-1], but not leukotriene B4 [20 nM], compared to the infection alone. We also quantified the temporal dynamics of NET release and differences in the relative areas of NETs, showing a high percentage of variable size NET release with combined PAO1 - inflammatory mediator treatment, in the device chambers. Importantly, we demonstrated reduced NET release in the confined loops of our combined infection-inflammation microsystem. Ultimately, our NET-array device stands as a valuable tool, facilitating experiments that enhance our comprehension of the spatiotemporal dynamics of NET release in response to infection within a defined microenvironment. In the future, our system can be used for high throughput and cost-effective screening of novel immunotherapies on human neutrophils in view of the importance of fine-tuning NET release in controlling pathological neutrophil-driven inflammation.

Neutrophil extracellular traps and their implications in airway inflammatory diseases

Neutrophil extracellular traps (NETs) are essential for immune defense and have been increasingly recognized for their role in infection and inflammation. In the context of airway inflammatory diseases, there is growing evidence suggesting the involvement and significance of NETs. This review aims to provide an overview of the formation mechanisms and components of NETs and their impact on various airway inflammatory diseases, including acute lung injury/ARDS, asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. By understanding the role of NETs in airway inflammation, we can gain valuable insights into the underlying pathogenesis of these diseases and identify potential targets for future therapeutic strategies that either target NETs formation or modulate their harmful effects. Further research is warranted to elucidate the complex interactions between NETs and airway inflammation and to develop targeted therapies that can effectively mitigate their detrimental effects while preserving their beneficial functions in host defense.

Design and synthesis of pyrazole derivatives against neutrophilic inflammation

Neutrophils are the most abundant immune cells. However, neutrophil dysregulation leads to acute and chronic inflammation and is involved in various diseases. The aim of this study was to develop anti-inflammatory agents in human neutrophils. A drug screening was conducted on in-house compounds with the potential to inhibit the respiratory burst, which involves the generation of superoxide anions in human neutrophils. Bioisosteric replacement was then applied to design more active derivatives. The most potent inhibitors of superoxide anion generation activity were compounds 58 and 59, which had IC50 values of 13.30 and 9.06 nM, respectively. The inhibitory effects of 58 and 59 were reversed by H89, a PKA inhibitor. PDE selective screening indicated that the best inhibitory effects were PDE4B1 and PDE4D2, and the inhibitory activities were 83% and 85%, respectively, at a 10 μM concentration of 59. The final molecular simulation experiment highlighted the slightly different binding poses of 58 and 59 in the PDE4 active site. An in vivo pharmacokinetic study revealed that the half-life of 59 was approximately 79 min when using intravenous bolus administration. This work introduced a new class structure of PDE4 inhibitors resulting in potent neutrophil inactivation activity, with the aim of contributing to new anti-inflammatory drug discovery.

Fractional Exhalation Nitric Oxide (FeNO) changes in cystic fibrosis patients induced by compound honey syrup: a pretest-posttest clinical trial

OBJECTIVE

To evaluate the effect of Persian medicine Syrup 'compound honey syrup (CHS)' on fractional exhalation nitric oxide (FENO) changes in patients with cystic fibrosis (CF).

STUDY DESIGN

We conducted a before-after clinical trial on 70 CF patients. All patients received classical treatments for CF along with CHS (including honey, Ginger, cinnamon, saffron, cardamom and galangal), 5-10 cc (depending on the age and weight of patients) in 100 cc of warm boiled water twice a day, 30 min after meals. In this clinical trial, before and 12 weeks after the start of the CHS, FeNO test was evaluated.

RESULTS

From 70 patients were enrolled, 44 patients completed this 12-week course of treatment. At the end of the study, changes in FeNO was significantly different before and after treatment (P-value < 0.05). At the end of the study, no dangerous side effects of CHS was reported.

CONCLUSIONS

This study revealed that CHS can be effective as a complementary and safe drug in the medication of CF patients.

An Emerging Role of Extracellular Traps in Chronic Rhinosinusitis

PURPOSE OF REVIEW

Chronic rhinosinusitis (CRS) is a complicated, heterogeneous disease likely caused by inflammatory and infectious factors. There is clear evidence that innate immune cells, including neutrophils and eosinophils, play a significant role in CRS. Multiple immune cells, including neutrophils and eosinophils, have been shown to release chromatin and granular proteins into the extracellular space in response to triggering extracellular traps (ETs). The formation of ETs remains controversial due to their critical function during pathogen clearance while being associated with harmful inflammatory illnesses. This article summarizes recent research on neutrophil extracellular traps (NETs) and eosinophil extracellular traps (EETs) and their possible significance in the pathophysiology of CRS.

RECENT FINDINGS

A novel type of programmed cell death called ETosis, which releases ETs, has been proposed by recent study. Significantly more NETs are presented in nasal polyps, and its granule proteins LL-37 induce NETs production in CRS with nasal polyps (CRSwNP) patients. Similar to NETs, developed in the tissue of nasal polyps, primarily in subepithelial regions with epithelial barrier defects, and are associated with linked to elevated tissue levels of IL-5 and S. aureus colonization. This article provides a comprehensive overview of NETs and EETs, as well as an in-depth understanding of the functions of these ETs in CRS.

Recent advances in the role of neutrophils and neutrophil extracellular traps in acute pancreatitis

Pancreatitis is an inflammatory disease, which is triggered by adverse events in acinar cells of the pancreas. After the initial injury, infiltration of neutrophils in pancreas is observed. In the initial stages of pancreatitis, the inflammation is sterile. It has been shown that the presence of neutrophils at the injury site can modulate the disease. Their depletion in experimental animal models of the acute pancreatitis has been shown to be protective. But information on mechanism of contribution to inflammation by neutrophils at the injury site is not clear. Once at injury site, activated neutrophils release azurophilic granules containing proteolytic enzymes and generate hypochlorous acid which is a strong microbicidal agent. Additionally, emerging evidence shows that neutrophil extracellular traps (NETs) are formed which consist of decondensed DNA decorated with histones, proteases and granular and cytosolic proteins. NETs are considered mechanical traps for microbes, but there is preliminary evidence to indicate that NETs, which constitute a special mechanism of the neutrophil defence system, play an adverse role in pancreatitis by contributing to the pancreatic inflammation and distant organ injury. This review presents the overall current information about neutrophils and their role including NETs in acute pancreatitis (AP). It also highlights current gaps in knowledge which should be explored to fully elucidate the role of neutrophils in AP and for therapeutic gains.

Neutrophil extracellular traps in upper respiratory tract secretions: insights into infectious and allergic rhinitis

Introduction

Neutrophil extracellular traps (NETs) are structures released by neutrophils in response to various infections. NETs have a biocidal role and have been demonstrated to be effective against bacteria, fungi, viruses, and parasites. Depending on the situation, NETs can protect the host from pathogen invasion or contribute to the development of autoimmune diseases such as cystic fibrosis and rheumatoid arthritis. In this study, we aimed to investigate the occurrence of NET as one of the components in upper respiratory tract secretions in infectious and allergic diseases.

Methods

Nasal mucus was collected from donors diagnosed with infectious rhinitis or allergic rhinitis. The extracellular DNA content was determined using SytoxGreen staining, and the total protein pool was determined using the microBCA method. Micrococcal nuclease was used to digest the samples and ELISA was employed to identify the NET proteins. The enzymatic activity of elastase was determined.

Results

Our findings showed that nasal mucus collected from patients with infectious rhinosinusitis contained extracellular DNA that could come from a variety of sources, responsible for increasing the density and viscosity of secretions, as well as NETs proteins. The identified enzymatic activity of NET elastase indicates the possible irritation of nasal tissues. However, the DNA content was not identified in the samples from allergic patients. In addition, we have shown in preliminary studies that therapy using N-acetylcysteine can liquefy nasal secretions.

Discussion

The study suggests that the composition of nasal mucus varies according to the cause of mucosal irritation. The presence of DNA and NET proteins can have severe consequences for the therapeutic process prolonging treatment. The low viscosity of nasal mucus in allergic patients facilitates mucosal flushing and the removal of allergens. Understanding the occurrence and role of NETs in various respiratory diseases is critical for developing effective treatment strategies that consider the complex interaction between the immune system and pathogens. The results of this study suggest that NETs may be present in upper respiratory tract secretions with an infectious background, supporting basic defense mechanisms using eosinophils and EETs. Further research is needed to explore the potential of NETs as a therapeutic target in respiratory diseases.

Role of Neutrophil Extracellular Traps in Health and Disease Pathophysiology: Recent Insights and Advances

Neutrophils are the principal trouper of the innate immune system. Activated neutrophils undergo a noble cell death termed NETosis and release a mesh-like structure called neutrophil extracellular traps (NETs) as a part of their defensive strategy against microbial pathogen attack. This web-like architecture includes a DNA backbone embedded with antimicrobial proteins like myeloperoxidase (MPO), neutrophil elastase (NE), histones and deploys in the entrapment and clearance of encountered pathogens. Thus NETs play an inevitable beneficial role in the host's protection. However, recent accumulated evidence shows that dysregulated and enhanced NET formation has various pathological aspects including the promotion of sepsis, pulmonary, cardiovascular, hepatic, nephrological, thrombotic, autoimmune, pregnancy, and cancer diseases, and the list is increasing gradually. In this review, we summarize the NET-mediated pathophysiology of different diseases and focus on some updated potential therapeutic approaches against NETs.

Engineering in vitro models of cystic fibrosis lung disease using neutrophil extracellular trap inspired biomaterials

Cystic fibrosis (CF) is a muco-obstructive lung disease where inflammatory responses due to chronic infection result in the accumulation of neutrophil extracellular traps (NETs) in the airways. NETs are web-like complexes comprised mainly of decondensed chromatin that function to capture and kill bacteria. Prior studies have established excess release of NETs in CF airways increases viscoelasticity of mucus secretions and reduces mucociliary clearance. Despite the pivotal role of NETs in CF disease pathogenesis, current in vitro models of this disease do not account for their contribution. Motivated by this, we developed a new approach to study the pathobiological effects of NETs in CF by combining synthetic NET-like biomaterials, composed of DNA and histones, with an in vitro human airway epithelial cell culture model. To determine the impact of synthetic NETs on airway clearance function, we incorporated synthetic NETs into mucin hydrogels and cell culture derived airway mucus to assess their rheological and transport properties. We found that the addition of synthetic NETs significantly increases mucin hydrogel viscoelasticity. As a result, mucociliary transport in vitro was significantly reduced with the addition of mucus containing synthetic NETs. Given the prevalence of bacterial infection in the CF lung, we also evaluated the growth of Pseudomonas aeruginosa in mucus with or without synthetic NETs. We found mucus containing synthetic NETs promoted microcolony growth and prolonged bacterial survival. Together, this work establishes a new biomaterial enabled approach to study innate immunity mediated airway dysfunction in CF.

Roles of trained immunity in the pathogenesis of periodontitis

Periodontitis is a chronic, inflammatory, and destructive disease caused by the imbalance of host immune response and dental biofilm, and has strong epidemiological and pathogenesis correlations with systemic diseases. The immune response in periodontitis involves both innate and adaptive immunity, with numerous immune cells and inflammatory pathways participating in a complex network of interactions. In the past decade, the concept of "trained immunity" has emerged, which highlights the memory characteristics of innate immunity, thus opening up a new avenue of research. There is growing interest in exploring the role of trained immunity in chronic inflammatory and metabolic diseases such as atherosclerosis and diabetes mellitus. Evidence suggests that trained immunity may also regulate the onset and progression of periodontitis, serving as a bridge between periodontitis-related comorbidities. In this review, we summarize concepts related to trained immunity and its development. Furthermore, we present current evidence that endorses the notion of trained immunity in periodontitis and analyze possible roles it may assume regarding periodontitis-associated inflammatory reactions from a cellular perspective. Finally, we discuss various clinical therapeutic strategies for periodontitis and its associated comorbidities that target trained immunity. We hope that more researchers will pay attention to this emerging concept, thereby providing deeper insights into this novel field.

Neutrophil extracellular traps and long COVID

Post-acute COVID-19 sequelae, commonly known as long COVID, encompasses a range of systemic symptoms experienced by a significant number of COVID-19 survivors. The underlying pathophysiology of long COVID has become a topic of intense research discussion. While chronic inflammation in long COVID has received considerable attention, the role of neutrophils, which are the most abundant of all immune cells and primary responders to inflammation, has been unfortunately overlooked, perhaps due to their short lifespan. In this review, we discuss the emerging role of neutrophil extracellular traps (NETs) in the persistent inflammatory response observed in long COVID patients. We present early evidence linking the persistence of NETs to pulmonary fibrosis, cardiovascular abnormalities, and neurological dysfunction in long COVID. Several uncertainties require investigation in future studies. These include the mechanisms by which SARS-CoV-2 brings about sustained neutrophil activation phenotypes after infection resolution; whether the heterogeneity of neutrophils seen in acute SARS-CoV-2 infection persists into the chronic phase; whether the presence of autoantibodies in long COVID can induce NETs and protect them from degradation; whether NETs exert differential, organ-specific effects; specifically which NET components contribute to organ-specific pathologies, such as pulmonary fibrosis; and whether senescent cells can drive NET formation through their pro-inflammatory secretome in long COVID. Answering these questions may pave the way for the development of clinically applicable strategies targeting NETs, providing relief for this emerging health crisis.

Role of innate immunity and systemic inflammation in cystic fibrosis disease progression

Pathophysiological manifestations of cystic fibrosis (CF) result from a functional defect in the cystic fibrosis transmembrane conductance regulator (CFTR) paving way for mucus obstruction and pathogen colonization. The role of CFTR in modulating immune cell function and vascular integrity, irrespective of mucus thickening, in determining the host cell response to pathogens/allergens and causing systemic inflammation is least appreciated. Since CFTR plays a key role in the conductance of anions like Cl-, loss of CFTR function could affect various basic cellular processes, such as cellular homeostasis, lysosome acidification, and redox balance. CFTR aids in endotoxin tolerance by regulating Toll-like receptor-mediated signaling resulting in uncontrolled activation of innate immune cells. Although leukocytes of CF patients are hyperactivated, they exhibit compromised phagosome activity thus favouring the orchestration of sepsis from defective pathogen clearance. This review will emphasize the importance of innate immunity and systemic inflammatory response in the development of CF and other CFTR-associated pathologies.

Loss of TET2 in human hematopoietic stem cells alters the development and function of neutrophils

Somatic mutations commonly occur in hematopoietic stem cells (HSCs). Some mutant clones outgrow through clonal hematopoiesis (CH) and produce mutated immune progenies shaping host immunity. Individuals with CH are asymptomatic but have an increased risk of developing leukemia, cardiovascular and pulmonary inflammatory diseases, and severe infections. Using genetic engineering of human HSCs (hHSCs) and transplantation in immunodeficient mice, we describe how a commonly mutated gene in CH, TET2, affects human neutrophil development and function. TET2 loss in hHSCs produce a distinct neutrophil heterogeneity in bone marrow and peripheral tissues by increasing the repopulating capacity of neutrophil progenitors and giving rise to low-granule neutrophils. Human neutrophils that inherited TET2 mutations mount exacerbated inflammatory responses and have more condensed chromatin, which correlates with compact neutrophil extracellular trap (NET) production. We expose here physiological abnormalities that may inform future strategies to detect TET2-CH and prevent NET-mediated pathologies associated with CH.

Comparison of NET quantification methods based on immunofluorescence microscopy: Hand-counting, semi-automated and automated evaluations

Formation of neutrophil extracellular traps was first described in 2004, showing that NETs are composed of decondensed chromatin fibers and nuclear and granule components. Free DNA is often used to quantify NETs, but to differentiate NETosis from necrotic DNA-release, immunofluorescence microscopy with NET-specific markers is required. Although evaluation by hand is time-consuming and difficult to standardize, it is still widespread. Unfortunately, no standardized method and only limited software tools are available for NET evaluation. This study provides an overview of recent techniques in use and aims to compare two published computer-based methods with hand counting. We found that the selected semi-automated quantification method and fully automated quantification via NETQUANT differed significantly from results obtained by hand and exhibited problems in detection of complex NET structures with partially illogical results. In contrast to that, trained persons were able to adapt to varying settings. Future approaches aimed at developing deep-learning algorithms for fast and reproducible quantification of NETs are needed.

Synthetic neutrophil extracellular traps dissect bactericidal contribution of NETs under regulation of α-1-antitrypsin

Deciphering the complex interplay of neutrophil extracellular traps (NETs) with the surrounding environment is a challenge with notable clinical implications. To bridge the gap in knowledge, we report our findings on the antibacterial activity against Pseudomonas aeruginosa of synthetic NET-mimetic materials composed of nanofibrillated DNA-protein complexes. Our synthetic system makes component-by-component bottom-up analysis of NET protein effects possible. When the antimicrobial enzyme neutrophil elastase (NE) is incorporated into the bactericidal DNA-histone complexes, the resulting synthetic NET-like structure exhibits an unexpected reduction in antimicrobial activity. This critical immune function is rescued upon treatment with alpha-1-antitrypsin (AAT), a physiological tissue-protective protease inhibitor. This suggests a direct causal link between AAT inhibition of NE and preservation of histone-mediated antimicrobial activity. These results help better understand the complex and, at times, contradictory observations of in vivo antimicrobial effects of NETs and AAT by excluding neutrophil, cytokine, and chemoattractant contributions.

NETworking with cancer: The bidirectional interplay between cancer and neutrophil extracellular traps

Neutrophils are major effectors and regulators of the immune system. They play critical roles not only in the eradication of pathogens but also in cancer initiation and progression. Conversely, the presence of cancer affects neutrophil activity, maturation, and lifespan. By promoting or repressing key neutrophil functions, cancer cells co-opt neutrophil biology to their advantage. This co-opting includes hijacking one of neutrophils' most striking pathogen defense mechanisms: the formation of neutrophil extracellular traps (NETs). NETs are web-like filamentous extracellular structures of DNA, histones, and cytotoxic granule-derived proteins. Here, we discuss the bidirectional interplay by which cancer stimulates NET formation, and NETs in turn support disease progression. We review how vascular dysfunction and thrombosis caused by neutrophils and NETs underlie an elevated risk of death from cardiovascular events in cancer patients. Finally, we propose therapeutic strategies that may be effective in targeting NETs in the clinical setting.

Neutrophil Extracellular Traps in Airway Diseases: Pathological Roles and Therapeutic Implications

Neutrophils are important effector cells of the innate immune response that fight pathogens by phagocytosis and degranulation. Neutrophil extracellular traps (NETs) are released into the extracellular space to defend against invading pathogens. Although NETs play a defensive role against pathogens, excessive NETs can contribute to the pathogenesis of airway diseases. NETs are known to be directly cytotoxic to the lung epithelium and endothelium, highly involved in acute lung injury, and implicated in disease severity and exacerbation. This review describes the role of NET formation in airway diseases, including chronic rhinosinusitis, and suggests that targeting NETs could be a therapeutic strategy for airway diseases.

Neutrophils during SARS-CoV-2 infection: Friend or foe?

Coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has resulted in more than 6 million deaths worldwide. COVID-19 is a respiratory disease characterized by pulmonary dysfunction leading to acute respiratory distress syndrome (ARDs), as well as disseminated coagulation, and multi-organ dysfunction. Neutrophils and neutrophil extracellular traps (NETs) have been implicated in the pathogenesis of COVID-19. In this review, we highlight key gaps in knowledge, discuss the heterogeneity of neutrophils during the evolution of the disease, how they can contribute to COVID-19 pathogenesis, and potential therapeutic strategies that target neutrophil-mediated inflammatory responses.

Antibody-modified DNase I micelles specifically recognize the neutrophil extracellular traps (NETs) and promote their degradation

Neutrophil extracellular traps (NETs) are structures consisting of decondensed chromatin with associated proteins, including histones and antimicrobial peptides, released from activated neutrophils. They are believed to be one of the body's first lines of defense against infectious agents. Despite their beneficial effect on the immune response process, some studies indicate that their excessive formation and the associated accumulation of extracellular DNA (eDNA) together with other polyelectrolytes (F-actin) plays an important role in the pathogenesis of many diseases. Thus NETs formation and removal are clinically significant. The monoclonal antibody 2C5 has strong specificity for intact nucleohistones (NS) and targets NS in NETs as we previously confirmed. Creation of a nano preparation that can specifically recognize and destroy NETs represents the aim for treatment many diseases. 2C5 antibody functionalized micelles coated with DNase I were created to achieve this aim.

Functional proteomic profiling links deficient DNA clearance with increased mortality in individuals with severe COVID-19 pneumonia

The factors that influence survival during severe infection are unclear. Extracellular chromatin drives pathology, but the mechanisms enabling its accumulation remain elusive. Here, we show that in murine sepsis models, splenocyte death interferes with chromatin clearance through the release of the DNase I inhibitor actin. Actin-mediated inhibition was compensated by upregulation of DNase I or the actin scavenger gelsolin. Splenocyte death and neutrophil extracellular trap (NET) clearance deficiencies were prevalent in individuals with severe COVID-19 pneumonia or microbial sepsis. Activity tracing by plasma proteomic profiling uncovered an association between low NET clearance and increased COVID-19 pathology and mortality. Low NET clearance activity with comparable proteome associations was prevalent in healthy donors with low-grade inflammation, implicating defective chromatin clearance in the development of cardiovascular disease and linking COVID-19 susceptibility to pre-existing conditions. Hence, the combination of aberrant chromatin release with defects in protective clearance mechanisms lead to poor survival outcomes.

Effects of Neutrophil and Eosinophil Extracellular Trap Formation on Refractoriness in Chronic Rhinosinusitis With Nasal Polyps

PURPOSE

This study investigated the clinical implications of neutrophil extracellular trap (NET) formation (NETosis) and eosinophil extracellular trap (EET) formation (EETosis) regarding refractoriness in chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP).

METHODS

Nasal polyp specimens were obtained from 117 patients with CRSwNP who received endoscopic sinus surgery. Disease control status at postoperative 1 year was assessed. Refractory cases were defined as partly controlled or uncontrolled cases according to the EPOS 2020 guidelines. NETosis and EETosis were evaluated through immunofluorescence staining (citrullinated histone H3-human neutrophil elastase and citrullinated histone-galectin-10, respectively) followed by manual counting. The z-score of NET and EET counts was used to define the following four groups: low extracellular trap formation (ETosis), NETosis-predominant, EETosis-predominant, and high-ETosis.

RESULTS

The refractory and non-refractory groups showed significant differences in the tissue eosinophil count (P = 0.005) and EET count (P = 0.029). The tissue neutrophil count and the NET/neutrophil ratio were significantly different between the refractory and non-refractory groups of patients with neutrophilic CRS (P = 0.045, 0.031, respectively). Refractoriness significantly differed among the low-ETosis (30.77%), NETosis-predominant (47.83%), EETosis-predominant (56.67%), and high-ETosis (83.33%) groups (P = 0.005).

CONCLUSIONS

The results of this study suggest that tissue Eosinophilia and EETosis may play a prognostic role, primarily in CRSwNP and thattissue neutrophilia and NETosis can play as prognostic biomarkers in neutrophilic CRSwNP.

Genome Capture Sequencing Selectively Enriches Bacterial DNA and Enables Genome-Wide Measurement of Intrastrain Genetic Diversity in Human Infections

Within-host evolution produces genetic diversity in bacterial strains that cause chronic human infections. However, the lack of facile methods to measure bacterial allelic variation in clinical samples has limited understanding of intrastrain diversity's effects on disease. Here, we report a new method termed genome capture sequencing (GenCap-Seq) in which users inexpensively make hybridization probes from genomic DNA or PCR amplicons to selectively enrich and sequence targeted bacterial DNA from clinical samples containing abundant human or nontarget bacterial DNA. GenCap-Seq enables accurate measurement of allele frequencies over targeted regions and is scalable from specific genes to entire genomes, including the strain-specific accessory genome. The method is effective with samples in which target DNA is rare and inhibitory and DNA-degrading substances are abundant, including human sputum and feces. In proof-of-principle experiments, we used GenCap-Seq to investigate the responses of diversified Pseudomonas aeruginosa populations chronically infecting the lungs of people with cystic fibrosis to in vivo antibiotic exposure, and we found that treatment consistently reduced intrastrain genomic diversity. In addition, analysis of gene-level allele frequency changes suggested that some genes without conventional resistance functions may be important for bacterial fitness during in vivo antibiotic exposure. GenCap-Seq's ability to scalably enrich targeted bacterial DNA from complex samples will enable studies on the effects of intrastrain and intraspecies diversity in human infectious disease. IMPORTANCE Genetic diversity evolves in bacterial strains during human infections and could affect disease manifestations and treatment resistance. However, the extent of diversity present in vivo and its changes over time are difficult to measure by conventional methods. We developed a novel approach, GenCap-Seq, to enrich microbial DNA from complex human samples like sputum and feces for genome-wide measurements of bacterial allelic diversity. The approach is inexpensive, scalable to encompass entire targeted genomes, and works in the presence of abundant untargeted nucleic acids and inhibiting substances. We used GenCap-Seq to investigate in vivo responses of diversified bacterial strains to antibiotic treatment. This method will enable new ideas about the effects of intrastrain diversity on human infections to be tested.

Molecular mechanisms and therapeutic target of NETosis in diseases

Evidence shows that neutrophils can protect the host against pathogens in multiple ways, including the formation and release of neutrophil extracellular traps (NETs). NETs are web-like structures composed of fibers, DNA, histones, and various neutrophil granule proteins. NETs can capture and kill pathogens, including bacteria, viruses, fungi, and protozoa. The process of NET formation is called NETosis. According to whether they depend on nicotinamide adenine dinucleotide phosphate (NADPH), NETosis can be divided into two categories: "suicidal" NETosis and "vital" NETosis. However, NET components, including neutrophil elastase, myeloperoxidase, and cell-free DNA, cause a proinflammatory response and potentially severe diseases. Compelling evidence indicates a link between NETs and the pathogenesis of a number of diseases, including sepsis, systemic lupus erythematosus, rheumatoid arthritis, small-vessel vasculitis, inflammatory bowel disease, cancer, COVID-19, and others. Therefore, targeting the process and products of NETosis is critical for treating diseases linked with NETosis. Researchers have discovered that several NET inhibitors, such as toll-like receptor inhibitors and reactive oxygen species scavengers, can prevent uncontrolled NET development. This review summarizes the mechanism of NETosis, the receptors associated with NETosis, the pathology of NETosis-induced diseases, and NETosis-targeted therapy.

Bicarbonate Effects on Antibacterial Immunity and Mucus Glycobiology in the Cystic Fibrosis Lung: A Review With Selected Experimental Observations

The primary defect in cystic fibrosis (CF) is abnormal chloride and bicarbonate transport in the cystic fibrosis transmembrane conductance regulator (CFTR) epithelial ion channel. The apical surface of the respiratory tract is lined by an airway surface liquid layer (ASL) composed of mucin comprising mainly MUC5A and MUC5B glycoproteins. ASL homeostasis depends on sodium bicarbonate secretion into the airways and secretion deficits alter mucus properties leading to airway obstruction, inflammation, and infections. Downstream effects of abnormal ion transport in the lungs include altered intrinsic immune defenses. We observed that neutrophils killed Pseudomonas aeruginosa more efficiently when it had been exposed to sodium bicarbonate, and formation of neutrophil extracellular traps (NETs) by neutrophils was augmented in the presence of increasing bicarbonate concentrations. Physiological levels of bicarbonate sensitized P. aeruginosa to the antimicrobial peptide cathelicidin LL-37, which is present in both lung ASL and in NETs. Sodium bicarbonate has various uses in clinical medicine and in the care of CF patients, and could be further explored as a therapeutic adjunct against Pseudomonas infections.

Microbe capture by splenic macrophages triggers sepsis via T cell-death-dependent neutrophil lifespan shortening

The mechanisms linking systemic infection to hyperinflammation and immune dysfunction in sepsis are poorly understood. Extracellular histones promote sepsis pathology, but their source and mechanism of action remain unclear. Here, we show that by controlling fungi and bacteria captured by splenic macrophages, neutrophil-derived myeloperoxidase attenuates sepsis by suppressing histone release. In systemic candidiasis, microbial capture via the phagocytic receptor SIGNR1 neutralizes myeloperoxidase by facilitating marginal zone infiltration and T cell death-dependent histone release. Histones and hyphae induce cytokines in adjacent CD169 macrophages including G-CSF that selectively depletes mature Ly6G^high neutrophils by shortening their lifespan in favour of immature Ly6G^low neutrophils with a defective oxidative burst. In sepsis patient plasma, these mediators shorten mature neutrophil lifespan and correlate with neutrophil mortality markers. Consequently, high G-CSF levels and neutrophil lifespan shortening activity are associated with sepsis patient mortality. Hence, by exploiting phagocytic receptors, pathogens degrade innate and adaptive immunity through the detrimental impact of downstream effectors on neutrophil lifespan.

Hyperinflammation and immune dysfunction are key drivers of immunopathology in sepsis. Here the authors show microbial exploitation of phagocytic receptors is linked to triggering of sepsis and the immune cell mediated reduction in neutrophil life span.

The interplay between inflammation and thrombosis in COVID-19: Mechanisms, therapeutic strategies, and challenges

Coronavirus disease 2019 (COVID-19), caused by a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can cause life-threatening pathology characterized by a dysregulated immune response and coagulopathy. While respiratory failure induced by inflammation is the most common cause of death, micro-and macrovascular thrombosis leading to multiple organ failure are also causes of mortality. Dysregulation of systemic inflammation observed in severe COVID-19 patients is manifested by cytokine release syndrome (CRS) - the aberrant release of high levels of proinflammatory cytokines, such as IL-6, IL-1, TNFα, MP-1, as well as complement. CRS is often accompanied by activation of endothelial cells and platelets, coupled with perturbation of the balance between the pro-and antithrombotic mechanisms, resulting in thrombosis. Inflammation and thrombosis form a vicious circle, contributing to morbidity and mortality. Treatment of hyperinflammation has been shown to decrease thrombosis, while anti-thrombotic treatment also downregulates cytokine release. This review highlights the relationship between COVID-19-mediated systemic inflammation and thrombosis, the molecular pathways involved, the therapies targeting these processes, and the challenges currently encountered.

Neutrophil Extracellular Traps, Sepsis and COVID-19 - A Tripod Stand

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the current coronavirus disease 2019 (COVID-19) pandemic. Majority of COVID-19 patients have mild disease but about 20% of COVID-19 patients progress to severe disease. These patients end up in the intensive care unit (ICU) with clinical manifestations of acute respiratory distress syndrome (ARDS) and sepsis. The formation of neutrophil extracellular traps (NETs) has also been associated with severe COVID-19. Understanding of the immunopathology of COVID-19 is critical for the development of effective therapeutics. In this article, we discuss evidence indicating that severe COVID-19 has clinical presentations consistent with the definitions of viral sepsis. We highlight the role of neutrophils and NETs formation in the pathogenesis of severe COVID-19. Finally, we highlight the potential of therapies inhibiting NETs formation for the treatment of COVID-19.

Investigating neutrophil cell death in TB pathogenesis

Background: Neutrophils are one of the major early role players in antimycobacterial immunity. Upon infection, neutrophils can undergo NETosis, a cell death characterized by release of neutrophil extracellular traps (NETs). The role of NETosis in TB progression remains poorly characterized. We aim to characterize mechanisms underlying NETosis during TB pathogenesis by identifying genes that drive the cell death, and to determine their potential as markers of disease progression in high-risk individuals. Finally, we intend to evaluate neutrophil associated genes as targets for host directed therapy to reduce pathological damage caused by NETosis. Methods: Quantitative PCR will be used to quantify expression of specific genes identified in the blood of individuals with active lung disease (n=30), compared to those from healthy (n=30) and latently infected individuals (LTBI) (n=30). In addition, temporal events associated with NETosis will be measured using live microscopy in a neutrophil in vitro model of Mycobacterium tuberculosis (Mtb) infection. Candidate genes found to be associated with NETosis will be targeted with pharmaceutical inhibitors. Conclusion: Genes associated with neutrophil mediated cell death may serve as potential biomarkers of pathological damage and disease progression, as well as targets for host-directed therapy.

Liver ischaemia-reperfusion injury: a new understanding of the role of innate immunity

Liver ischaemia-reperfusion injury (LIRI), a local sterile inflammatory response driven by innate immunity, is one of the primary causes of early organ dysfunction and failure after liver transplantation. Cellular damage resulting from LIRI is an important risk factor not only for graft dysfunction but also for acute and even chronic rejection and exacerbates the shortage of donor organs for life-saving liver transplantation. Hepatocytes, liver sinusoidal endothelial cells and Kupffer cells, along with extrahepatic monocyte-derived macrophages, neutrophils and platelets, are all involved in LIRI. However, the mechanisms underlying the responses of these cells in the acute phase of LIRI and how these responses are orchestrated to control and resolve inflammation and achieve homeostatic tissue repair are not well understood. Technological advances allow the tracking of cells to better appreciate the role of hepatic macrophages and platelets (such as their origin and immunomodulatory and tissue-remodelling functions) and hepatic neutrophils (such as their selective recruitment, anti-inflammatory and tissue-repairing functions, and formation of extracellular traps and reverse migration) in LIRI. In this Review, we summarize the role of macrophages, platelets and neutrophils in LIRI, highlight unanswered questions, and discuss prospects for innovative therapeutic regimens against LIRI in transplant recipients.

Specific NLRP3 Inflammasome Assembling and Regulation in Neutrophils: Relevance in Inflammatory and Infectious Diseases

The NLRP3 inflammasome is a cytosolic multimeric protein platform that leads to the activation of the protease zymogen, caspase-1 (CASP1). Inflammasome activation mediates the proteolytic activation of pro-inflammatory cytokines (IL-1β and IL-18) and program cell death called pyroptosis. The pyroptosis is mediated by the protein executioner Gasdermin D (GSDMD), which forms pores at the plasma membrane to facilitate IL-1β/IL-18 secretion and causes pyroptosis. The NLRP3 inflammasome is activated in response to a large number of pathogenic and sterile insults. However, an uncontrolled inflammasome activation may drive inflammation-associated diseases. Initially, inflammasome-competent cells were believed to be limited to macrophages, dendritic cells (DC), and monocytes. However, emerging evidence indicates that neutrophils can assemble inflammasomes in response to various stimuli with functional relevance. Interestingly, the regulation of inflammasome in neutrophils appears to be unconventional. This review provides a broad overview of the role and regulation of inflammasomes—and more specifically NLRP3—in neutrophils.

Molecular Prerequisites for Neutrophil Extracellular Trap Formation and Evasion Mechanisms of Staphylococcus aureus

NETosis is a multi-facetted cellular process that promotes the formation of neutrophil extracellular traps (NETs). NETs as web-like structures consist of DNA fibers armed with granular proteins, histones, and microbicidal peptides, thereby exhibiting pathogen-immobilizing and antimicrobial attributes that maximize innate immune defenses against invading microbes. However, clinically relevant pathogens often tolerate entrapment and even take advantage of the remnants of NETs to cause persistent infections in mammalian hosts. Here, we briefly summarize how Staphylococcus aureus, a high-priority pathogen and causative agent of fatal diseases in humans as well as animals, catalyzes and concurrently exploits NETs during pathogenesis and recurrent infections. Specifically, we focus on toxigenic and immunomodulatory effector molecules produced by staphylococci that prime NET formation, and further highlight the molecular and underlying principles of suicidal NETosis compared to vital NET-formation by viable neutrophils in response to these stimuli. We also discuss the inflammatory potential of NET-controlled microenvironments, as excessive expulsion of NETs from activated neutrophils provokes local tissue injury and may therefore amplify staphylococcal disease severity in hospitalized or chronically ill patients. Combined with an overview of adaptation and counteracting strategies evolved by S. aureus to impede NET-mediated killing, these insights may stimulate biomedical research activities to uncover novel aspects of NET biology at the host-microbe interface.

Combining nanotechnology with the multifunctional roles of neutrophils against cancer and inflammatory disease

Neutrophils, the most abundant leukocytes in humans, play a crucial role in acute inflammation during infection and tumorigenesis. Neutrophils are the major types of cells recruited to the inflammation sites induced by pathogens, exhibiting great homing ability towards inflammatory disorders and tumor sites. Therefore, a neutrophil-based drug delivery system (NDDS) has become a promising platform for anti-cancer and anti-inflammatory treatment. Recent decades have witnessed the huge progress of applying nanomaterials in drug delivery. Nanomaterials are regarded as innovative components to enrich the field of neutrophil-based therapies due to their unique physiochemical characteristics. In this review, the latest advancement of combining diverse nanomaterials with an NDDS for cancer and inflammatory disease treatment will be summarized. It is discussed how nanomaterials empower the therapeutic area of an NDDS and how an NDDS circumvents the limitations of nanomaterials. Moreover, based on the finding that neutrophils are closely involved in the progression of cancer and inflammatory diseases, emerging therapeutic strategies that target neutrophils will be outlined. Finally, as neutrophils were demonstrated to play a central role in the immunopathology of COVID-19, which causes necroinflammation that is responsible for the cytokine storm and sepsis during coronavirus infections, novel therapeutic approaches that anchor neutrophils against the pathological consequences related to COVID-19 will be highlighted as well.

Tumor-Associated Neutrophil Extracellular Traps Regulating Nanocarrier-Enhanced Inhibition of Malignant Tumor Growth and Distant Metastasis

Tumor-associated neutrophil extracellular traps (NETs) play a critical role in promoting tumor growth and assisting tumor metastasis. Herein, a smart nanocarrier (designated as mP-NPs-DNase/PTX) based on regulating tumor-associated NETs has been developed, which consists of a paclitaxel (PTX) prodrug nanoparticle core and a poly-l-lysine (PLL) conjugated with the matrix metalloproteinase 9 (MMP-9)-cleavable Tat-peptide-coupled deoxyribonuclease I (DNase I) shell. After accumulating at the site of the tumor tissue, the nanocarrier can release DNase I in response to MMP-9 to degrade the structure of NETs. Then, the remaining moiety can uptake the tumor cells via the mediation of exposed cell penetrating peptide, and the PTX prodrug nanoparticles will lyse in response to the high intracellular concentration of reduced glutathione to release PTX to exert a cytotoxic effect of tumor cells. Through in vitro and in vivo evaluations, it has been proven that mP-NPs-DNase/PTX could serve as potential NET-regulated nanocarrier for enhanced inhibition of malignant tumor growth and distant metastasis.

Neutrophils and Platelets: Immune Soldiers Fighting Together in Stroke Pathophysiology

Neutrophils and platelets exhibit a diverse repertoire of functions in thromboinflammatory conditions such as stroke. Most cerebral ischemic events result from longstanding chronic inflammation secondary to underlying pathogenic conditions, e.g., hypertension, diabetes mellitus, obstructive sleep apnea, coronary artery disease, atrial fibrillation, morbid obesity, dyslipidemia, and sickle cell disease. Neutrophils can enable, as well as resolve, cerebrovascular inflammation via many effector functions including neutrophil extracellular traps, serine proteases and reactive oxygen species, and pro-resolving endogenous molecules such as Annexin A1. Like neutrophils, platelets also engage in pro- as well as anti-inflammatory roles in regulating cerebrovascular inflammation. These anucleated cells are at the core of stroke pathogenesis and can trigger an ischemic event via adherence to the hypoxic cerebral endothelial cells culminating in aggregation and clot formation. In this article, we review and highlight the evolving role of neutrophils and platelets in ischemic stroke and discuss ongoing preclinical and clinical strategies that may produce viable therapeutics for prevention and management of stroke.

Investigating neutrophil cell death in TB pathogenesis

Background: Neutrophils are one of the major early role players in antimycobacterial immunity. Upon infection, neutrophils can undergo NETosis, a cell death characterized by release of neutrophil extracellular traps (NETs). The role of NETosis in TB progression remains poorly characterized. We aim to characterize mechanisms underlying NETosis during TB pathogenesis by identifying genes that drive the cell death, and to determine their potential as markers of disease progression in high-risk individuals. Finally, we intend to evaluate neutrophil associated genes as targets for host directed therapy to reduce pathological damage caused by NETosis. Methods: Quantitative PCR will be used to quantify expression of specific genes identified in the blood of individuals with active lung disease (n=30), compared to those from healthy (n=30) and latently infected individuals (LTBI) (n=30). In addition, temporal events associated with NETosis will be measured using live microscopy in a neutrophil in vitro model of Mycobacterium tuberculosis (Mtb) infection. Candidate genes found to be associated with NETosis will be targeted with pharmaceutical inhibitors. Conclusion: Genes associated with neutrophil mediated cell death may serve as potential biomarkers of pathological damage and disease progression, as well as targets for host-directed therapy.

Clinical drug therapies and biologicals currently used or in clinical trial to treat COVID-19

The potential emergence of SARS-CoV-2 variants capable of escaping vaccine-generated immune responses poses a looming threat to vaccination efforts and will likely prolong the duration of the COVID-19 pandemic. Additionally, the prevalence of beta coronaviruses circulating in animals and the precedent they have set in jumping into human populations indicates that they pose a continuous threat for future pandemics. Currently, only one therapeutic is approved by the U.S. Food and Drug Administration (FDA) for use in treating COVID-19, remdesivir, although other therapies are authorized for emergency use due to this pandemic being a public health emergency. In this review, twenty-four different treatments are discussed regarding their use against COVID-19 and any potential future coronavirus-associated illnesses. Their traditional use, mechanism of action against COVID-19, and efficacy in clinical trials are assessed. Six treatments evaluated are shown to significantly decrease mortality in clinical trials, and ten treatments have shown some form of clinical efficacy.

Z-form extracellular DNA is a structural component of the bacterial biofilm matrix

Biofilms are community architectures adopted by bacteria inclusive of a self-formed extracellular matrix that protects resident bacteria from diverse environmental stresses and, in many species, incorporates extracellular DNA (eDNA) and DNABII proteins for structural integrity throughout biofilm development. Here, we present evidence that this eDNA-based architecture relies on the rare Z-form. Z-form DNA accumulates as biofilms mature and, through stabilization by the DNABII proteins, confers structural integrity to the biofilm matrix. Indeed, substances known to drive B-DNA into Z-DNA promoted biofilm formation whereas those that drive Z-DNA into B-DNA disrupted extant biofilms. Importantly, we demonstrated that the universal bacterial DNABII family of proteins stabilizes both bacterial- and host-eDNA in the Z-form in situ. A model is proposed that incorporates the role of Z-DNA in biofilm pathogenesis, innate immune response, and immune evasion.

Effects of neutrophil extracellular traps during human respiratory syncytial virus infection in vitro

The human respiratory syncytial virus (hRSV) is the most common cause of severe lower respiratory tract diseases in young children worldwide, leading to a high number of hospitalizations and significant expenditures for health systems. Neutrophils are massively recruited to the lung tissue of patients with acute respiratory diseases. At the infection site, they release neutrophil extracellular traps (NETs) that can capture and/or inactivate different types of microorganisms, including viruses. Evidence has shown that the accumulation of NETs results in direct cytotoxic effects on endothelial and epithelial cells. Neutrophils stimulated by the hRSV-F protein generate NETs that are able to capture hRSV particles, thus reducing their transmission. However, the massive production of NETs obstructs the airways and increases disease severity. Therefore, further knowledge about the effects of NETs during hRSV infections is essential for the development of new specific and effective treatments. This study evaluated the effects of NETs on the previous or posterior contact with hRSV-infected Hep-2 cells. Hep-2 cells were infected with different hRSV multiplicity of infection (MOI 0.5 or 1.0), either before or after incubation with NETs (0.5-16 μg/mL). Infected and untreated cells showed decreased cellular viability and intense staining with trypan blue, which was accompanied by the formation of many large syncytia. Previous contact between NETs and cells did not result in a protective effect. Cells in monolayers showed a reduced number and area of syncytia, but cell death was similar in infected and non-treated cells. The addition of NETs to infected tissues maintained a similar virus-induced cell death rate and an increased syncytial area, indicating cytotoxic and deleterious damages. Our results corroborate previously reported findings that NETs contribute to the immunopathology developed by patients infected with hRSV.

Emerging nanomaterials applied for tackling the COVID-19 cytokine storm

During the global outbreak of coronavirus disease 2019 (COVID-19), a hyperinflammatory state called the cytokine storm was recognized as a major contributor to multiple organ failure and mortality. However, to date, the diagnosis and treatment of the cytokine storm remain major challenges for the clinical prognosis of COVID-19. In this review, we outline various nanomaterial-based strategies for preventing the COVID-19 cytokine storm. We highlight the contribution of nanomaterials to directly inhibit cytokine release. We then discuss how nanomaterials can be used to deliver anti-inflammatory drugs to calm the cytokine storm. Nanomaterials also play crucial roles in diagnostics. Nanomaterial-based biosensors with improved sensitivity and specificity can be used to detect cytokines. In summary, emerging nanomaterials offer platforms and tools for the detection and treatment of the COVID-19 cytokine storm and future pandemic.