Quantification Of Neutrophil Extracellular Traps Research Articles

Association of Neutrophil extracellular traps burden with clinical and angiographic characteristics in patients with ST-elevation myocardial infarction

Abstract Background The precise triggers for arterial plaque rupture and the underlying pathophysiology of thrombogenesis remain elusive. Polymorphonuclear neutrophils (PMN), particularly their formation of Neutrophil Extracellular Traps (NETs), have garnered attention in the context of coronary atherothrombosis. This study sought to explore the association of NETs burden with clinical and angiographic characteristics in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (pPCI) and thrombus aspiration (TA). Methods This study included 336 consecutive STEMI patients undergoing pPCI and TA. Aspirated thrombi underwent histological analysis and NETs quantification via immunohistochemistry. Potential associations of clinical variables and angiographic outcomes with NETs burden were assessed. Results Manual TA was selectively performed in 72 cases with increased thrombotic burden and 60 thrombi were suitable for analysis. Most thrombi specimens displayed lytic features (63%) and almost three out of four specimens were identified as white thrombi. Increased NETs burden was significantly associated with prolonged pain-to-balloon time (>300 minutes) OR=10.29 (95% CI 2.11-42.22, p=0.001) and stress-induced hyperglycemia (SIH) OR=6.58 (95% CI 1.23-52.63, p=0.04) after multivariate regression analysis. Additionally, distal embolization (DE), a predictor of adverse outcomes, was more frequent among patients with an elevated NETs burden OR=16.9 (95% CI 4.23-44.52, p<0.001). Conversely, no significant association between NETs burden and final TIMI flow=3 was observed. Conclusion Elevated NETs burden in STEMI thrombi is linked to delayed reperfusion, SIH and increased risk of DE. Further research is needed to elucidate the role of NETs as a potential therapeutic target in acute atherothrombosis.

Real-Time, High-Throughput Microscopic Quantification of Human Neutrophil Extracellular Trap Release and Assessing the Pharmacology of Antagonists.

Neutrophils play an important role in innate immune defense by using several strategies, including the release of neutrophil extracellular traps (NETs) in a process referred to as NETosis. However, in the past two decades, it has become clear that the accumulation of NETs in tissues contributes to the pathophysiology of multiple inflammatory and autoimmune diseases. Therefore, interest in the development of NETosis antagonists has risen. Variable and non-standardized methods to detect and analyze NETosis were developed concomitantly, each with its own advantages and limitations. Here, we describe a real-time microscopy method for the quantification of human NET release, allowing to study NETosis as well as NET inhibition in a high-throughput manner. The surface area-based semi-automated analysis recognizes NETs and distinguishes them from non-netting activated neutrophils. We demonstrate that the non-physiological NETosis inducers, calcium ionophore and phorbol-12-myristate-13-acetate (PMA), trigger the release of NETs with different characteristics and kinetics. Furthermore, we show that this approach allows studying NET release in response to disease-relevant stimuli, including immune complexes, N-Formylmethionine-leucyl-phenylalanine (fMLF), monosodium urate crystals, and calcium pyrophosphate crystals. To exemplify the utility of this method to study NETosis antagonists, we used CIT-013, a first-in-class monoclonal antibody inhibitor of NET release. CIT-013 targets citrullinated histone H2A and H4 and efficiently inhibits NET release with an IC50 of 4.6 nM. Other anti-histone antibodies tested lacked this NETosis-inhibitory capacity. Altogether, we demonstrate that this protocol enables specific, reliable, and reproducible high-throughput quantification of NETs, enhancing the study of NET release characteristics, kinetics, and pharmacology of NETosis antagonists.

Association of neutrophil extracellular traps burden with clinical and angiographic characteristics in patients with ST-elevation myocardial infarction

BackgroundThe precise triggers for atherosclerotic plaque rupture and the underlying pathophysiology of coronary thrombogenesis remain elusive. Polymorphonuclear neutrophils, particularly their formation of neutrophil extracellular traps (NETs), have garnered attention in the context of coronary atherothrombosis. This study sought to explore the association of NETs burden with clinical and angiographic characteristics in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (pPCI) and thrombus aspiration (TA). MethodsFor this study, 336 consecutive STEMI patients undergoing pPCI were considered for TA. Aspirated thrombi underwent histological analysis and NETs quantification via immunohistochemistry. Potential associations of clinical variables and angiographic outcomes with NETs burden were assessed. ResultsManual TA was selectively performed in 72 cases with increased thrombotic burden, and 60 thrombi were suitable for analysis and included in the current study. Most thrombi specimens displayed lytic features (63%), and almost three out of four were identified as white thrombi. Increased NETs burden was significantly associated with prolonged pain-to-balloon time (>300 min), OR = 10.29 (95% CI 2.11–42.22, p = 0.001), and stress-induced hyperglycemia OR = 6.58 (95% CI 1.23–52.63, p < 0.01) after multivariate regression analysis. Additionally, distal embolization, and left ventricular ejection fraction ≤40% were more frequent among patients with an elevated NETs burden OR = 16.9 (95% CI 4.23–44.52, p < 0.01) and OR = 3.2 (95% CI 1.05–12.1, p = 0.05), respectively. ConclusionElevated NETs burden in STEMI thrombi may be due to delayed reperfusion and stress-induced hyperglycemia, and it is associated with an increased risk of distal embolization and lower left ventricular ejection fraction. Further research is needed to elucidate the role of NETs as a potential therapeutic target in acute atherothrombosis.

Fasciola hepatica soluble antigens (FhAg) induce ovine PMN innate immune reactions and NET formation in vitro and in vivo

Fasciola hepatica causes liver fluke disease, a worldwide neglected and re-emerging zoonotic disease, leading to hepatitis in humans and livestock. In the pathogenesis, flukes actively migrate through liver parenchyma provoking tissue damage. Here, parasites must confront leukocytes of the innate immune system in vivo. Polymorphonuclear neutrophils (PMN) are the most abundant granulocytes and first ones arriving at infection sites. PMN may display neutrophil extracellular traps (NETs), consisting of nuclear DNA, decorated with histones, enzymes, and antimicrobial peptides. We investigated for the first time whether F. hepatica soluble antigens (FhAg) can also trigger NETosis and innate immune reactions in exposed ovine PMN. Thus, isolated PMN were co-cultured with FhAg and NET formation was visualized by immunofluorescence and scanning electron microscopy analyses resulting in various phenotypes with spread NETs being the most detected in vitro. In line, NETs quantification via Picogreen®-fluorometric measurements revealed induction of anchored- and cell free NETs phenotypes. Live cell 3D-holotomographic microscopy revealed degranulation of stimulated PMN at 30 min exposure to FhAg. Functional PMN chemotaxis assays showed a significant increase of PMN migration (p = 0.010) and intracellular ROS production significantly increased throughout time (p = 0.028). Contrary, metabolic activities profiles of FhAg-exposed PMN did not significantly increase. Finally, in vivo histopathological analysis on F. hepatica-parasitized liver tissue sections of sheep showed multifocal infiltration of inflammatory cells within liver parenchyma, and further fluorescence microscopy analyses confirmed NETs formation in vivo. Overall, we hypothesized that NET-formation is a relevant host defence mechanism that might have a role in the pathogenesis of fasciolosis in vivo.

Trapalyzer: a computer program for quantitative analyses in fluorescent live-imaging studies of neutrophil extracellular trap formation.

Neutrophil extracellular traps (NETs), pathogen-ensnaring structures formed by neutrophils by expelling their DNA into the environment, are believed to play an important role in immunity and autoimmune diseases. In recent years, a growing attention has been put into developing software tools to quantify NETs in fluorescent microscopy images. However, current solutions require large, manually-prepared training data sets, are difficult to use for users without background in computer science, or have limited capabilities. To overcome these problems, we developed Trapalyzer, a computer program for automatic quantification of NETs. Trapalyzer analyzes fluorescent microscopy images of samples double-stained with a cell-permeable and a cell-impermeable dye, such as the popular combination of Hoechst 33342 and SYTOX™ Green. The program is designed with emphasis on software ergonomy and accompanied with step-by-step tutorials to make its use easy and intuitive. The installation and configuration of the software takes less than half an hour for an untrained user. In addition to NETs, Trapalyzer detects, classifies and counts neutrophils at different stages of NET formation, allowing for gaining a greater insight into this process. It is the first tool that makes this possible without large training data sets. At the same time, it attains a precision of classification on par with state-of-the-art machine learning algorithms. As an example application, we show how to use Trapalyzer to study NET release in a neutrophil-bacteria co-culture. Here, after configuration, Trapalyzer processed 121 images and detected and classified 16 000 ROIs in approximately three minutes on a personal computer. The software and usage tutorials are available at https://github.com/Czaki/Trapalyzer.

Saxitoxin induces the release of human neutrophil extracellular traps

Saxitoxin (STX) is a potent shellfish toxin found in freshwater and marine ecosystems which threatens human health by contaminating drinking water and shellfish. The formation of neutrophil extracellular traps (NETs) is a defense mechanism employed by polymorphonuclear leukocytes (PMNs) to destroy invading pathogens, and also plays a critical role in the pathogenesis of various diseases. In this study, we aimed to investigate the role of STX on human NET formation. Typical NETs-associated characteristics were detected from STX-stimulated PMNs using immunofluorescence microscopy. Moreover, NET quantification based on PicoGreen® fluorescent dye revealed that STX triggered NET formation in a concentration-dependent manner, and NET formation peaked at 120 min (with a total time of 180 min) after induction by STX. Intracellular reactive oxygen species (iROS) detection showed that iROS were significantly elevated in STX-challenged PMNs. These findings present insight into the effects of STX on human NET formation and serve as a basis for further investigations of STX immunotoxicity.

A New Methodology for the Quantification of Neutrophil Extracellular Traps in Patient Plasma.

Neutrophil extracellular traps (NETs) are web-like structures made up of decondensed chromatin fibers along with neutrophil granular proteins that are extruded by neutrophils after activation or in response to foreign microorganisms. NETs have been associated with autoimmune and inflammatory diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, coronavirus disease 2019 (COVID-19), and others. There are reliable methods available to quantitate NETs from neutrophils, but their accurate quantification in patient plasma or serum remains a challenge. We developed a highly sensitive ELISA to detect NETs in serum/plasma and designed a novel smear immunofluorescence assay to detect NETs in as little as 1 μL of serum/plasma. We further validated our technology on plasma samples from SLE patients and healthy donors that carry interferon regulatory factor 5 genetic risk. The multiplex ELISA combines the use of three antibodies against myeloperoxidase (MPO), citrullinated histone H3 (CitH3), and DNA to detect the NET complexes with higher specificities. The immunofluorescence smear assay can visually detect intact structures of NETs in 1 μL of serum/plasma and provide similar results that correlate with findings from the multiplex ELISA. Furthermore, the smear assay is a relatively simple, inexpensive, and quantifiable method of NET detection for small volumes.

Label-free virtual staining of neutrophil extracellular traps (NETs) in microfluidics.

Neutrophils are the most abundant circulating white blood cells and one of their critical functions to eliminate pathogenic threats includes the release of extracellular DNA, also known as neutrophil extracellular traps (NETs), which is dysregulated in many diseases including cancer, type 2 diabetes mellitus and infectious diseases. Currently, conventional methods to quantify the NET formation (NETosis) rely on fluorescence antibody-based NET labelling or circulating NET-associated protein detection by ELISA, which are expensive, laborious, and time-consuming. In this work, we employed a novel "virtual staining" using deep convolutional neural networks (CNNs) to facilitate label-free quantification of NETs trapped in a micropillar array in a microfluidic device. Virtual staining is constructed to establish relations between morphological features in phase contrast images and fluorescence features in Sytox-green (DNA dye) images. We first investigated the effect of different learning rates on model training and optimized the learning rate to achieve the best model which can provide outputs close to Sytox green staining based on various reconstruction metrics (e.g., structural similarity (SSIM) and pixel-wise error (MAE, MSE)). The virtual staining of different NET concentrations was investigated which showed a linear correlation with fluorescent staining. As a proof of concept for clinical testing, the model was used to characterize purified neutrophils treated with NETosis inducers, including lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), and calcium ionophore (CaI), and successfully detected different NET profiles for different treatments. Collectively, these results demonstrated the potential of using deep learning for enhanced label-free image analysis of NETs for clinical research, drug discovery and point-of-care testing of diseases.

Giardia duodenalis trophozoites triggered bovine neutrophil extracellular traps formation dependent on P2X1 receptor and PAD4 in vitro

Giardia duodenalis is an important intestinal protozoan parasite, infections of which are frequently seen in cattle and cause intermittent diarrhea and weight loss in young animals around the world. The release of neutrophil extracellular traps (NETs) is an effector mechanism of neutrophils to fight against invading pathogens including parasites. In this present study, we aimed to investigate the effect of Giardia duodenalis trophozoites on bovine NETs formation, and to further examine its basic characteristics and molecular mechanisms. Scanning electron microscopy analyses displayed that Giardia duodenalis trophozoites exposure triggered NET-like filamentary structures released by bovine polymorphonuclear leukocytes (PMNs), and many trophozoites were entrapped within these structures. Immunofluorescence analyses illustrated that these structures were mainly composed of DNA, histones, Myeloperoxidase (MPO) and neutrophil elastase (NE), which confirmed the classical characteristics of NETs. NETs quantification showed that Giardia duodenalis trophozoites significantly increased NETs formation, and it is in a dose-dependent manner from 4:1–1:2 ratio of PMN: trophozoites. Furthermore, pharmacological inhibitory experiment indicated that P2X1 receptor and PAD4 were essential for Giardia duodenalis trophozoites-triggered NETs formation. Additionally, LC3B-based immunostaining analyses revealed that autophagy and NETs formation occurred simultaneously in Giardia duodenalis trophozoites-exposed bovine PMN, imply that autophagy may play a key role in Giardia duodenalis trophozoites-triggered bovine NETs. In summary, these findings suggest that NETs formation might have a crucial role in innate host defense against Giardia duodenalis trophozoites. Hence, we call for future molecular investigations not only on Giardia duodenalis trophozoites-triggered NETs but also on its potential role in giardiasis-related pathology in vivo.

Quantification of Neutrophil Extracellular Traps (NETs) in Pediatric Patients with COVID-19 and Multisystem Inflammatory Syndrome (MIS-C) through Plasma and Peripheral Smear Analysis

Background: In response to inflammation, neutrophils expel NETs, decondensed chromatin coated with histones and granular proteins that capture pathogens. NET degradation products (NDPs), including cell free (cf) DNA, citrullinated histone 3 (citH3), and myeloperoxidase (MPO), are elevated in adults with COVID-19 and contribute to endothelial injury. However, NETs have not yet been quantified in pediatric patients with active SARS-CoV-2 infection, or children who develop the post-infection inflammatory syndrome MIS-C. Although NDPs can be measured in plasma samples in the research setting, it has been proposed that smudge cells (SC), leukocyte remnants composed of extracellular chromatin that are identified by automated digital morphology systems, represent circulating NETs. Automated quantification of SCs is attractive strategy to quantify systemic NET load because it is routinely performed on patient samples as part of a standardized clinical laboratory evaluation. Aims: The aims of this study are to measure NETs in the plasma of children with COVID-19 or MIS-C, and to determine if NDP and SC% elevation correlate with NET levels Methods: We analyzed plasma samples obtained from patients admitted to The Children's Hospital of Philadelphia (CHOP) with COVID-19 between April and October 2020, including children with mild (N=21) or severe (N=13) COVID-19, and MIS-C (N=23). Remnant plasma from healthy patients (N=13) was used as a control. Samples were analyzed with the Olink Explore 1536/384 protein biomarker platform, cfDNA was meauasred with a fluorescent plate assay, and citH3 was quantified wit a commercial ELISA (Cayman). Spearman rank correlation was used to quantify the association between cfDNA and citH3, protein biomarkers, and clinical data. We next reviewed 56 peripheral smears from patients with mild COVID-19(N=5), severe COVID-19 (N=8), and MIS-C (N=6), using the Cellavision® hematology autoanalyzer. Results were validated independently by two blinded observers, and Spearman rank correlation was used to measure the association between SC%, leukocyte counts, and clinical laboratory data. Results: cfDNA and citH3 were significantly elevated in pediatric patients with COVID-19 compared to healthy controls, with the highest levels observed in patients with severe COVID-19 and MIS-C (Figure 1). Correlative analysis with results of proteomic studies showed that citH3 was significantly associated with multiple markers of neutrophil activation including MPO, matrix metalloproteinase-9, and IL-8, demonstrating that citH3 is a specific marker of NET release. Although cfDNA does not exclusively originate from NETs, it was significantly correlated with the specific NET marker citH3 (r=0.7844, p<0.0001), suggesting that cfDNA is in part derived from NETs. Analysis of clinical data showed that citH3 was inversely correlated with sodium (r=-0.4289, p=0.011) and positive correlated with troponin levels (r=0.3587, p=0.0438). cfDNA significantly correlated with the complement membrane attack complex (r=0.2986, p=0.024) and LDH (r=0.5463, p=0.0015). Review of peripheral smears showed SC levels were elevated in pediatric patients with COVID-19 (Figure 2). SC% positively correlated with monocytes (r=0.4047, p=0.0018) and eosinophils (r=0.3420, p=0.0092) and inversely correlated with neutrophil counts (r=-0.4064, p=0.0017), suggesting that many SC originate from neutrophils. SC% was also inversely correlated with activated partial thromboplastin time (aPTT,r=-0.5153, p=0.04), a finding that may indicate activation of the contact coagulation pathway by increased plasma NETs. Conclusion: Plasma NET markers are elevated in the plasma of pediatric patients with COVID-19, with the highest levels observed in those with severe disease and MIS-C. Correlation of cfDNA and citH3 with proteins associated with neutrophil activation, complement fixation, and organ dysfunction adds support to our hypothesis that these markers originate from NETs and contribute to endothelial injury. SC% is elevated in children with COVID-19 infection and MIS-C. Further studies are underway to determine whether SCs originate from NETs. This work suggests there may be clinical utility in quantifying and reporting SC% in the hematology laboratory to identify increased NETs in children, a finding relevant to the study and treatment of COVID-19 and other viral infections. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Detection of neutrophil extracellular traps in patient plasma: method development and validation in systemic lupus erythematosus and healthy donors that carry IRF5 genetic risk.

Neutrophil extracellular traps (NETs) are web-like structures extruded by neutrophils after activation or in response to microorganisms. These extracellular structures are decondensed chromatin fibers loaded with antimicrobial granular proteins, peptides, and enzymes. NETs clear microorganisms, thus keeping a check on infections at an early stage, but if dysregulated, may be self-destructive to the body. Indeed, NETs have been associated with autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), antiphospholipid syndrome (APS), psoriasis, and gout. More recently, increased NETs associate with COVID-19 disease severity. While there are rigorous and reliable methods to quantify NETs from neutrophils via flow cytometry and immunofluorescence, the accurate quantification of NETs in patient plasma or serum remains a challenge. Here, we developed new methodologies for the quantification of NETs in patient plasma using multiplex ELISA and immunofluorescence methodology. Plasma from patients with SLE, non-genotyped healthy controls, and genotyped healthy controls that carry either the homozygous risk or non-risk IRF5-SLE haplotype were used in this study. The multiplex ELISA using antibodies detecting myeloperoxidase (MPO), citrullinated histone H3 (CitH3) and DNA provided reliable detection of NETs in plasma samples from SLE patients and healthy donors that carry IRF5 genetic risk. An immunofluorescence smear assay that utilizes only 1 µl of patient plasma provided similar results and data correlate to multiplex ELISA findings. The immunofluorescence smear assay is a relatively simple, inexpensive, and quantifiable method of NET detection for small volumes of patient plasma.

O-031 Activation of NLRP3 inflammasome enhances neutrophil extracellular traps in women with stage III/IV endometriosis: convergence of multiple signaling portray association between genetics and lesion type

Abstract Study question Do NOD-like receptor pyrin-containing 3 (NLRP3) signaling affect neutrophil extracellular traps (NET)-osis in women with stage III/IV endometriosis? Summary answer Inflammasome activation whether due to pathogen (disease itself) or damage-associated molecular pattern (through NET) might be one mechanism involved in establishing perturbed endometrium in endometriosis. What is known already Endometriosis is characterized by number of processes like vascularization, hypernociception, and fibrosis, cardinal cause being inflammation. Recently, expression of inflammasome components, including NLRP3 and apoptosis signal-regulating kinase has been demonstrated in human endometrium cueing involvement in uterine innate immunity. Moreover, a novel extracellular killing mechanism, NET, is documented to reflect an inflammatory status in deep infiltrating endometriosis. Since, endometriosis demonstrates similarities with chronic inflammatory and autoimmune disorders; we postulated inflammatory responses in endometriosis may become modulated through a feed-forward loop of NET-induced specific cytokine production thus providing insights against potentiality of endometriotic cells to limit progression of the disease. Study design, size, duration Twenty-two consented women (24-39 years) with endometriosis (Group A) (Stages III–IV) (based on ASRM-2018 guidelines) and age-matched counterpart/s of male sub-fertility (Group B; control), free of uterine abnormalities (n = 18) were recruited between January to December 2021 from Institute of Reproductive Medicine, Kolkata. Eutopic endometrium, were collected from women undergoing diagnostic laparoscopy (Group A) or by curettage from women undergoing endometrial ablation (Group B). Serum was collected during window-of-implantation (LH + 7) for both the group/s. Participants/materials, setting, methods Pro-(IFN-g, TNF-a, IL-6, TGF-b) and anti-inflammatory (IL-10, IL-13, IL-4, IL-5) cytokines was evaluated by western blot. Expression level of inflammasome-related proteins (NLRP3, ASC, CASPASE1, PYCARD, IL-1-b) and mRNA expression was estimated by western-blot and quantitative-real-time PCR (qRT-PCR) respectively from tissue biopsies in Group A and B. SYTOX® green assay by flow-cytometry and neutrophil-elastase activity by immunofluorescence was done to quantify and characterize NET production in blood monocytes. P &amp;lt; 0.05 was considered statistically significant. Main results and the role of chance The mean (±SD) age of study population was 31.6±5.2 years. Hyperestrogenic milieu possibly stimulated (p &amp;lt; 0.001) pro-inflammatory molecules (IFN-g, TNF-a, IL-6, TGF-b) in endometriosis as observed by western-blot and qRT-PCR. A significant up-regulation (p &amp;lt; 0.001) was observed in relative mRNA expression of NLRP3 and PYCARD gene in Group A. However, caspase 1 expression documented non-significant variation in biopsies from endometriosis patients. Western blot corroborated the finding/s. The outcome of NLRP3 activation was supported by increased (p &amp;lt; 0.002) mRNA expression of IL-1b. NETs were detected significantly higher (p &amp;lt; 0.01) in 54.54% (12/22) patients in group A compared to control (16.66%; (3/18)). Moreover, quantification of NETs showed a significantly higher amount in endometriosis compared to group B (0.097 vs. 0.02, p &amp;lt; 0.03). Spermann-rank correlation by SPSS version22 revealed positive correlation between IL-1b with NLRP3 (r = 0.56, p&amp;lt; 0.001), PYCARD (r = 0.11, p&amp;lt; 0.01); and caspase1 (r = 0.16, p&amp;lt; 0.01) and IL-1b (r = 0.47, p&amp;lt; 0.01) with NET-positive cell/s in endometriosis. Moreover, posterior cul-de-sac lesions correlated positively with NET-positive cell/s (r = 0.29; p &amp;lt; 0.01) cueing to possible prognostic marker/s. In summary, a coordinated-fashioned action of components of NLRP3 inflammasome machinery may regulate production of NET/s forming a complex network allowing communication between cell-types in order to maintain viability and development of endometrial lesion/s. Limitations, reasons for caution Our findings need to be replicated in larger study cohort/s, especially stratified by severity of endometriosis sub-groups and in women of different ethnicities. Another limitation is the missing information about NETs in normal functioning human endometrium throughout the menstrual cycle. Wider implications of the findings The proposed study aims to understand potential role of NLRP3 inflammasome complex as a “double-edged sword” in the development and pathophysiology of endometriosis. Therapeutic alternatives that aim to re-balance the pro- to anti-inflammatory milieu in the endometrium should consider the inflammasome as part of the equation. Trial registration number Not applicable

An Imaging and Computational Algorithm for Efficient Identification and Quantification of Neutrophil Extracellular Traps.

Neutrophil extracellular traps (NETs) are associated with multiple disease pathologies including sepsis, asthma, rheumatoid arthritis, cancer, systemic lupus erythematosus, acute respiratory distress syndrome, and COVID-19. NETs, being a disintegrated death form, suffered inconsistency in their identification, nomenclature, and quantifications that hindered therapeutic approaches using NETs as a target. Multiple strategies including microscopy, ELISA, immunoblotting, flow cytometry, and image-stream-based methods have exhibited drawbacks such as being subjective, non-specific, error-prone, and not being high throughput, and thus demand the development of innovative and efficient approaches for their analyses. Here, we established an imaging and computational algorithm using high content screening (HCS)—cellomics platform that aid in easy, rapid, and specific detection as well as analyses of NETs. This method employed membrane-permeable and impermeable DNA dyes in situ to identify NET-forming cells. Automated algorithm-driven single-cell analysis of change in nuclear morphology, increase in nuclear area, and change in intensities provided precise detection of NET-forming cells and eliminated user bias with other cell death modalities. Further combination with Annexin V staining in situ detected specific death pathway, e.g., apoptosis, and thus, discriminated between NETs, apoptosis, and necrosis. Our approach does not utilize fixation and permeabilization steps that disturb NETs, and thus, allows the time-dependent monitoring of NETs. Together, this specific imaging-based high throughput method for NETs analyses may provide a good platform for the discovery of potential inhibitors of NET formation and/or agents to modulate neutrophil death, e.g., NETosis-apoptosis switch, as an alternative strategy to enhance the resolution of inflammation.

Bongkrekic acid induced neutrophil extracellular traps via p38, ERK, PAD4, and P2X1-mediated signaling

Bongkrekic acid (BKA) produced by pseudomonas cocovenenans is a deadly toxin, and is mainly found in spoiled or fermented foods. However, less is known on its immunotoxicity. Neutrophil extracellular traps (NETs) are a novel effector mechanism of neutrophils against invading pathogens, but excessive NETs also contribute to tissue damage. This study aimed to investigate NET formation triggered by BKA in murine neutrophils, and describe its characteristics and potential mechanisms. Our results showed that BKA triggered NET formation via co-localization of DNA and histone or MPO by immunostaining. Moreover, BKA-triggered NET formation was dose- and time-dependent via NET quantification based on Picogreen-derived fluorescence intensities. Furthermore, BKA increased ROS production in neutrophils. Pharmacological inhibition indicated that BKA-triggered NET formation was associated with ROS-p38 and –ERK signaling pathways, but independent on NADPH oxidase. Besides, PAD4 and P2X1 receptor also mediated BKA-triggered NET formation. To our knowledge, all these findings provide for the first time an initial understanding of BKA on innate immunity, which might be helpful for further investigation on BKA immunotoxicity.

Histamine triggers the formation of neutrophil extracellular traps via NADPH oxidase, ERK and p38 pathways

Histamine plays a central role in various allergic diseases, such as allergic asthma and allergic rhinitis. Neutrophil extracellular traps (NETs) formation is a novel effector mechanism of neutrophils to defend against various stimuli. In this present study, we aimed to investigate the role of histamine on bovine NET formation, and examined its preliminary molecular mechanisms. Cell Counting Kit-8 (CCK8) and Lactate dehydrogenase assays showed that histamine had no significant influence on PMNs (polymorphonuclear leukocytes) viability. Confocal microscopy analyses identified NET structures by co-localizing the main components of NETs, and NET quantification revealed that histamine-triggered NETs were released in a dose-dependent manner. Furthermore, we found reactive oxygen species (ROS) production, phosphorylated extracellular signal-regulated kinase (ERK) and p38 proteins were significantly elevated in histamine-challenged PMNs. By applying functional inhibitors of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase), ERK and p38, histamine-triggered NETs were markedly reduced, indicating their importance in histamine-triggered NET formation. Our findings described histamine-triggered NET formation, and revealed its potential molecular mechanisms via NADPH oxidase, ERK and p38 pathways. This is the first study to depict histamine-triggered NET formation, which could provide a new insight into histamine-related diseases.

Neutrophil Extracellular Traps in SARS-CoV2 Related Pneumonia in ICU Patients: The NETCOV2 Study.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a poorly understood disease involving a high inflammatory status. Neutrophil extracellular traps (NETs) have been described as a new pathway to contain infectious diseases but can also participate in the imbalance of the inflammatory and the coagulation systems. NETs could be a therapeutic target in COVID-19 patients.Methods: Consecutive patients with SARS-CoV2 related pneumonia admitted to the intensive care unit were included in a prospective bicentric study. Neutrophil extracellular trap concentrations were quantified in whole blood samples at day-1 and day-3 by flow cytometry. The primary outcome was the association between the blood NET quantification at ICU admission and the number of days with refractory hypoxemia defined by a PaO2/FIO2 ratio ≤100 mmHg.Results: Among 181 patients admitted to the ICUs for acute respiratory failure related to SARS-CoV2 pneumonia, 58 were included in the analysis. Patients were 62 [54, 69] years old in median, mostly male (75.9%). The median number of days with severe hypoxemia was 4 [2, 6] days and day-28 mortality was 27.6% (n = 16). The blood level of NETs significantly decreased between day-1 and day-3 in patients who survived (59.5 [30.5, 116.6] to 47 [33.2, 62.4] p = 0.006; 8.6 [3.4, 18.0] to 4 [1.4, 10.7] p = 0.001 and 7.4 [4.0, 16.7] to 2.6 [1.0, 8.3] p = 0.001 for MPO+, Cit-H3+, and MPO+ Cit-H3+ NETs, respectively) while it remained stable in patients who died (38.4 [26.0, 54.8] to 44.5 [36.4, 77.7] p = 0.542; 4.9 [1.3, 13.0] to 5.5 [2.8, 6.9] p = 0.839 and 4 [1.3, 13.6] to 2.7 [1.4, 4.5] p = 0.421 for MPO+, Cit-H3+, and MPO+ Cit-H3+ NETs, respectively). In multivariable negative binomial regression, the blood level of MPO+ NETs was negatively associated with the number of days with severe hypoxemia within 7 days (0.84 [0.73, 0.97]), while neither Cit-H3+ NETs nor double-positive NETs were significantly associated with the primary outcome.Conclusion: The whole blood level of NETs at day-1 was negatively associated with the number of days with severe hypoxemia in patients admitted to the intensive care unit for SARS-CoV2 related pneumonia. The lack of decrease of the blood level of NETs between day-1 and day-3 discriminated patients who died within day-28.

Differentiation of HL-60 cells in serum-free hematopoietic cell media enhances the production of neutrophil extracellular traps.

Neutrophil extracellular traps (NETs) are web-like structures made of chromatin and have been identified to have a role in the host's immune defense. Differentiated human promyelocytic leukemia HL-60 cells (dHL-60) have been used to study the mechanisms of NETs formation, as neutrophils have a short lifespan that limits their use. However, dHL-60 cells are inefficient at generating NETs and therefore are not ideal replacements for neutrophils in studying of NET formation. In the present study, the optimal cell culture conditions and differentiation time that result in the most effective release of NETs from dHL-60 cells upon stimulation were determined. HL-60 cells were cultured in serum (FBS) or serum-free (X-VIVO) medium and differentiated using all-trans retinoic acid (ATRA) or dimethyl sulfoxide (DMSO). dHL-60 cells were stimulated with phorbol 12-myristate 13-acetate (PMA) or Ca2+ ionophore (CI). Cell differentiation and apoptosis, as well as the formation of reactive oxygen species (ROS) and citrullinated histone H3 (citH3) were analyzed using flow cytometry. NETs were visualized using fluorescence microscopy and NET quantification was performed using PicoGreen. Induction of HL-60 cells for five days produced the best results in terms of differentiation markers and cell viability. Both ATRA- and DMSO-induced dHL-60 cells were able to release NETs upon PMA and CI stimulation; dHL-60 cells in serum-free medium produced more NETs than those in serum-containing medium. DMSO-dHL-60 (X-VIVO) cells were most efficient at producing NETs and ROS upon stimulation with PMA, while ATRA-dHL-60 (X-VIVO) cells were most efficient at producing NETs and citH3 upon stimulation with CI. It was concluded that DMSO-dHL-60 (X-VIVO) may be a model for the study of ROS-high NETosis and ATRA-dHL-60 (X-VIVO) may be suitable for ROS-low NETosis.

Paracoccidioides brasiliensis Releases a DNase-Like Protein That Degrades NETs and Allows for Fungal Escape.

Paracoccidioidomycosis is a systemic fungal disease, considered endemic in Latin America. Its etiological agents, fungi of the Paracoccidioides complex, have restricted geographic habitat, conidia as infecting form, and thermo-dimorphic characteristics. Polymorphonuclear neutrophils (PMNs) are responsible for an important defense response against fungus, releasing Neutrophil Extracellular Traps (NETs), which can wrap and destroy the yeasts. However, it has been described that some pathogens are able to evade from these DNA structures by releasing DNase as an escape mechanism. As different NETs patterns have been identified in PMNs cultures challenged with different isolates of Paracoccidioides brasiliensis, the general objective of this study was to identify if different patterns of NETs released by human PMNs challenged with Pb18 (virulent) and Pb265 (avirulent) isolates would be correlated with fungal ability to produce a DNase-like protein. To this end, PMNs from healthy subjects were isolated and challenged in vitro with both fungal isolates. The production, release, and conformation of NETs in response to the fungi were evaluated by Confocal Microscopy, Scanning Microscopy, and NETs Quantification. The identification of fungal DNase production was assessed by DNase TEST Agar, and the relative gene expression for hypothetical proteins was investigated by RT-qPCR, whose genes had been identified in the fungal genome in the GenBank (PADG_11161 and PADG_08285). It was possible to verify the NETs release by PMNs, showing different NETs formation when in contact with different isolates of the fungus. The Pb18 isolate induced the release of looser, larger, and more looking like degraded NETs compared to the Pb265 isolate, which induced the release of denser and more compact NETs. DNase TEST Agar identified the production of a DNase-like protein, showing that only Pb18 showed the capacity to degrade DNA in these plates. Besides that, we were able to identify that both PADG_08528 and PADG_11161 genes were more expressed during interaction with neutrophil by the virulent isolate, being PADG_08528 highly expressed in these cultures, demonstrating that this gene could have a greater contribution to the production of the protein. Thus, we identified that the virulent isolate is inducing more scattered and loose NETs, probably by releasing a DNase-like protein. This factor could be an important escape mechanism used by the fungus to escape the NETs action.

Visualization and Quantification of Neutrophil Extracellular Traps.

Neutrophils are innate immune cells that play important roles in many physiological and pathological processes, including immune defense and cancer metastasis. In addition to the release of proinflammatory cytokines, chemokines, and cytoplasmic granules containing digestive proteins, in recent years, neutrophils have been observed to release neutrophil extracellular traps (NETs) that consist of extracellular DNA associated with antimicrobial proteins, such as histones and myeloperoxidase. These NETs are increasingly being recognized as an important mechanism of neutrophil host defense and function. This chapter will summarize the current literature on the known processes of NET formation and describe in detail an immunofluorescence approach that can be employed to visualize and quantify NETs in vitro.

Quantification of Citrullinated Histone H3 Bound DNA for Detection of Neutrophil Extracellular Traps.

Simple SummaryNeutrophil extracellular traps (NETs) are extracellular web-like structures comprised of proteins and DNA that have been associated with the development of cancer. Citrullination of histone H3 has been implicated in the formation of NETs. The aim of our study was to develop a quick and reliable method for NET quantitation. Here, we describe a novel protocol for the quantification of NETs based on the detection of citrullinated histone H3 bound to DNA (CitH3DNA binding assay). This assay was validated by comparing the ability of neutrophils from control tumor-free and myeloma-bearing mice to form NETs in response to stimuli. We demonstrated that neutrophils from tumor-bearing mice produced more NETs than those from tumor-free counterparts following stimulation with PMA. The increase in NET production as detected by microscopy correlated with significantly higher histone H3 citrullination levels and increased measurements of CitH3DNA in our novel binding assay.Formation of neutrophil extracellular traps (NETs) has been associated with multiple pathologies including cancer. While the visualization of NETs by microscopy is a routine technique, their quantification presents a number of challenges. Commonly, as citrullination of histone H3 is required for NET formation, the presence of this modified histone along with DNA is considered to be a hallmark of NETs. Here, we describe and validate a novel assay for the quantification of NETs based on the detection of citrullinated histone H3 bound to DNA (CitH3DNA binding assay). Using this assay, we investigated the effect of phorbol 12-myristate 13-acetate (PMA) on NET formation by neutrophils isolated from the bone marrow of control and myeloma-bearing mice. We found that PMA induced citrullination of histone H3, an increase in the level of CitH3DNA, and NET formation in neutrophils from both tumor-free and myeloma-bearing mice. The levels of CitH3DNA in the NET fractions, as measured by our assay directly correlated with the citrullination of histone H3 in neutrophils, as detected by Western blotting, and were significantly higher in PMA-stimulated compared to unstimulated neutrophils. Neutrophils from tumor-bearing mice produced more NETs than those from tumor-free counterparts following stimulation with PMA. The increase in NET production correlated with significantly higher histone H3 citrullination levels and increased measurements of CitH3DNA. Thus, our data indicate that bone marrow neutrophils from myeloma-bearing hosts are prone to NET formation.