DNA Area and NETosis Analysis (DANA): a High-Throughput Method to Quantify Neutrophil Extracellular Traps in Fluorescent Microscope Images

Protein Citrullination by Peptidyl Arginine Deiminase/Arginine Deiminase Homologs in Members of the Human Microbiota and Its Recognition by Anti-Citrullinated Protein Antibodies

The human microbiome exists throughout the body, and it is essential for maintaining various physiological processes, including immunity, and dysbiotic events, which are associated with autoimmunity. Peptidylarginine deiminase (PAD) enzymes can citrullinate self-proteins related to rheumatoid arthritis (RA) that induce the production of anti-citrullinated protein antibodies (ACPAs) and lead to inflammation and joint damage. The present investigation was carried out to demonstrate the expression of homologs of PADs or arginine deiminases (ADs) and citrullinated proteins in members of the human microbiota. To achieve the objective, we used 17 microbial strains and specific polyclonal antibodies (pAbs) of the synthetic peptide derived from residues 100-200 of human PAD2 (anti-PAD2 pAb), and the recombinant fragment of amino acids 326 and 611 of human PAD4 (anti-PAD4 pAb), a human anti-citrulline pAb, and affinity ACPAs of an RA patient. Western blot (WB), enzyme-linked immunosorbent assay (ELISA), elution, and a test with Griess reagent were used. This is a cross-sectional case-control study on patients diagnosed with RA and control subjects. Inferential statistics were applied using the non-parametric Kruskal-Wallis test and Mann-Whitney U test generated in the SPSS program. Some members of phyla Firmicutes and Proteobacteria harbor homologs of PADs/ADs and citrullinated antigens that are reactive to the ACPAs of RA patients. Microbial citrullinome and homolog enzymes of PADs/ADs are extensive in the human microbiome and are involved in the production of ACPAs. Our findings suggest a molecular link between microorganisms of a dysbiotic microbiota and RA pathogenesis.

Primary sarcopenia is associated with elevated spontaneous NET formation

Introduction: Sarcopenia is a frequent complication of liver cirrhosis, but it can also occur independently as a result of any underlying cause. The immune system plays an important role in the pathogenesis of both liver cirrhosis and sarcopenia. Neutrophil function, including neutrophil extracellular trap (NET) formation, is linked to chronic inflammation; however, it has not been extensively studied in patients with sarcopenia. Here, we aim to study if main neutrophil functions, such as phagocytosis, reactive oxygen species (ROS) production, and NET formation, are altered in patients with sarcopenia with or without liver cirrhosis. Methods: Neutrophils from 92 patients (52 patients with liver cirrhosis and sarcopenia, 25 patients with liver cirrhosis without sarcopenia, and 15 patients with sarcopenia without liver cirrhosis) and 10 healthy controls were isolated and stimulated with heat-inactivated E. coli (250 bacteria/cell), phorbol 12-myristate 13-acetate (PMA) (100 nM), or incubation medium in duplicates for 2 h at 37°C. Cells were fixed with paraformaldehyde and stained with 4',6-diamidino-2-phenylindole (DAPI). Pictures of 10 random fields of vision per slide were taken with an Olympus BX51 fluorescence microscope (Olympus, Shinjuku, Tokyo, Japan) at 600x total magnification. The DNA Area and NETosis Analysis (DANA) algorithm was used to quantify the percentage of NET formation per patient. Phagocytosis and ROS production were assessed with the PhagotestTM kit and PhagoburstTM kit (Glycotope, Heidelberg, Germany) in 92 patients and 21 healthy controls, respectively. Results: Spontaneous NET formation was significantly elevated in patients with only sarcopenia compared to patients with cirrhosis and sarcopenia (p = 0.008) and healthy controls (p = 0.039). NET formation in response to PMA was significantly decreased in patients with cirrhosis (p = 0.007), cirrhosis and sarcopenia (p < 0.001), and sarcopenia (p = 0.002) compared to healthy controls. There was no significant difference in NET formation in response to E. coli between the groups. The DANA algorithm was successfully optimized and validated for assessment of clinical samples. There were no significant changes in neutrophil phagocytosis between patients' groups compared to healthy controls. A significantly lower percentage of neutrophils produced ROS in response to N-formylmethionine-leucyl-phenylalanine (fMLF) in patients compared to healthy controls. Discussion: Spontaneous NET formation might contribute to chronic inflammation and sarcopenia pathogenesis. This, however, does not result in the impairment of the NET formation function of neutrophils in response to a bacterial stimulus and, therefore, cannot be not linked with the increased risk of bacterial infections neither in sarcopenia nor in cirrhosis. The semi-automated NET formation analysis can be successfully implemented to analyze the vast amount of data generated within clinical studies. This approach opens up the possibilities to develop an NET formation-based biomarker in different diseases including sarcopenia and implement NET formation analysis into clinical settings. Phagocytosis and ROS production were not affected in patients with sarcopenia. Further research is needed to explore the mechanism of NET formation in patients with sarcopenia and its potential as a biomarker in sarcopenia.

Macrophage extracellular traps require peptidylarginine deiminase 2 and 4 and are a source of citrullinated antigens bound by rheumatoid arthritis autoantibodies

Introduction

Anti-citrullinated protein antibodies (ACPAs) are a hallmark of rheumatoid arthritis, but the sources of citrullinated antigens as well as which peptidylarginine deiminases (PADs) are required for their production remain incompletely defined. Here, we investigated if macrophage extracellular traps (METs) could be a source of citrullinated proteins bound by APCAs, and if their formation requires PAD2 or PAD4.

Methods

Thioglycolate-induced peritoneal macrophages from wild-type, PAD2-/-, and PAD4-/- mice or human peripheral blood-derived M1 macrophages were activated with a variety of stimulants, then fixed and stained with DAPI and either anti-citrullinated histone H4 (citH4) antibody or sera from ACPA+ or ACPA- rheumatoid arthritis subjects. METs were visualized by immunofluorescence, confirmed to be extracellular using DNase, and quantified.

Results

We found that ionomycin and monosodium urate crystals reliably induced murine citH4+ METs, which were reduced in the absence of PAD2 and lost in the absence of PAD4. Also, IgG from ACPA+, but not ACPA-, rheumatoid arthritis sera bound to murine METs, and in the absence of PAD2 or PAD4, ACPA-bound METs were lost. Finally, ionomycin induced human METs that are citH4+ and ACPA-bound.

Discussion

Thus, METs may contribute to the pool of citrullinated antigens bound by ACPAs in a PAD2- and PAD4-dependent manner, providing new insights into the targets of immune tolerance loss in rheumatoid arthritis.

Neutrophil extracellular traps - a potential trigger for the development of thrombocytopenia during extracorporeal membrane oxygenation

Neutrophil extracellular traps (NETs) have recently emerged as a potential link between inflammation, immunity, and thrombosis, as well as other coagulation disorders which present a major challenge in the context of extracorporeal membrane oxygenation (ECMO). By examining blood from ECMO patients for NETs and their precursors and correlating them with clinical and laboratory biomarkers of coagulation and inflammation, this study aims to evaluate the association between the presence of NETs in the bloodstream of ECMO patients and the development of potentially severe coagulation disorders during ECMO therapy. Therefore, blood samples were collected from healthy volunteers (n=13) and patients receiving veno-venous (VV) ECMO therapy (n=10). To identify NETs and their precursors, DNA and myeloperoxidase as well as granulocyte marker CD66b were visualized simultaneously by immunofluorescence staining in serial blood smears. Differentiation of DNA-containing objects and identification of NETs and their precursors was performed semiautomatically by a specific algorithm using the shape and size of DNA staining and the intensity of MPO and CD66b signal. Neutrophil extracellular traps and their precursors could be detected in blood smears from patients requiring VV ECMO. Compared to volunteers, ECMO patients presented significantly higher rates of NETs and NET precursors as well as an increased proportion of neutrophil granulocytes in all detected nucleated cells. A high NET rate prior to the initiation of ECMO therapy was associated with both increased IL-6 and TNF-α levels as an expression of a high cytokine burden. These patients with increased NET release also presented an earlier and significantly more pronounced decrease in platelet counts and ATIII activity following initiation of therapy compared with patients with less elevated NETs. These findings provide further indications for the development of immune-mediated acquired thrombocytopenia in ECMO patients.

Visualizing neutrophil extracellular traps in septic equine synovial and peritoneal fluid samples using immunofluorescence microscopy

Septic synovitis and peritonitis are routinely diagnosed in horses based on clinical examination findings and laboratory assessment of synoviocentesis and abdominocentesis samples, respectively. Diagnosis is difficult in some cases because of an overlap in laboratory results for septic and non-septic inflammation. Neutrophil extracellular trap (NET) formation is part of the innate immune response against pathogens. Identifying and quantifying NETs, which have not been explored in clinical samples from horses with septic synovitis and peritonitis, to our knowledge, may be helpful in detecting infectious processes. Our main objective was to determine whether NETs could be visualized in septic equine synovial and peritoneal fluid cytology samples using immunofluorescence with antibodies against citrullinated histone H3 (Cit-H3) and myeloperoxidase (MPO). We analyzed 9 synovial and 4 peritoneal fluid samples. NET percentages were quantified using a simple counting technique, which is suitable for high-quality, well-preserved, and stained cytospin smears. NETs were evident in all septic samples and were absent in a non-septic sample; NETs were better visualized with Cit-H3 than with MPO immunolabeling. Overall, we believe that there is the potential for NETs and associated markers to be used to investigate and understand septic inflammation in horses.

Evaluation of the innate immune response of caprine neutrophils against Mycobacterium avium subspecies paratuberculosis in vitro

Neutrophils constitute an essential component of the innate immune response, readily killing most bacteria through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs) among other mechanisms. These cells play an unclear role in mycobacterial infections such as Mycobacterium avium subspecies paratuberculosis (Map), the etiological agent of paratuberculosis, and its response is particularly understudied in ruminants. Herein, a wide set of techniques were adapted, or newly developed, to study the in vitro response of caprine neutrophils after Map infection. Immunofluorescence was used to demonstrate, simultaneously, chemotaxis, phagocytosis, degranulation, and NETs. The quantification of neutrophil phagocytic activity against Map at a 1:10 multiplicity of infection (MOI), through flow cytometry, showed values that varied from 4.54 to 5.63% of phagocyting neutrophils. By immunofluorescence, a 73.3 ± 14.5% of the fields showed NETs, and the mean release of DNA, attributable to NETosis, calculated through a fluorometric method, was 16.2 ± 3.5%. In addition, the RNA expression of TGF-β, TNF and IL-1β cytokines, measured through reverse transcription qPCR, was significantly higher in the two latter. Overall, neutrophil response was proportional to the number of bacteria. This work confirms that the simultaneous study of several neutrophil mechanisms, and the combination of different methodologies, are essential to reach a comprehensive understanding of neutrophil response against pathogens, demonstrates that, in vitro, caprine neutrophils display a strong innate response against Map, using their entire repertoire of effector functions, and sets the basis for further in vitro and in vivo studies on the role of neutrophils in paratuberculosis.

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.

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.

d-lactate-induced ETosis in cattle polymorphonuclear leucocytes is dependent on the release of mitochondrial reactive oxygen species and the PI3K/Akt/HIF-1 and GSK-3β pathways

d-lactate is a metabolite originating from bacterial metabolism that accumulates as a result of dietary disturbances in cattle, leading to ruminal acidosis. d-lactate exerts functions as a metabolic signal inducing metabolic reprogramming and extracellular trap (ET) release in polymorphonuclear leucocytes (PMNs). We previously demonstrated that d-lactate induces metabolic reprogramming via hypoxia-induced factor 1 alpha (HIF-1α) stabilization in bovine fibroblast-like synoviocytes (FLSs). In the present study, the role of HIF-1 in ET formation induced by d-lactate was assessed. HIF-1α stabilization in PMNs was controlled by mitochondrial reactive oxygen species (_mtROS) release. Furthermore, inhibition of mitochondrial complex I and scavenging of _mtROS decreased d-lactate-triggered ETosis. d-lactate-enhanced HIF-1α accumulation was dependent on the PI3K/Akt pathway but independent of GSK-3β activity. Pharmacological blockade of the PI3K/Akt/HIF-1 and GSK-3β axes inhibited d-lactate-triggered ETosis and downregulated PDK1 and LDHA expression. However, only GSK-3β inhibition decreased the expression of glycogen metabolism enzymes and prevented the decline in glycogen stores induced by d-lactate exposure. The results of this study suggest that _mtROS, PI3K/Akt/HIF-1 and GSK-3β axes regulate carbohydrate metabolism adaptations that support d-lactate-induced ET formation in cattle.

Anti-DNA-IgM Favors the Detection of NET-Associated Extracellular DNA

During inflammatory responses, neutrophils enter the sites of attack where they execute various defense mechanisms. They (I) phagocytose microorganisms, (II) degranulate to release cytokines, (III) recruit various immune cells by cell-type specific chemokines, (IV) secrete anti-microbials including lactoferrin, lysozyme, defensins and reactive oxygen species, and (V) release DNA as neutrophil extracellular traps (NETs). The latter originates from mitochondria as well as from decondensed nuclei. This is easily detected in cultured cells by staining of DNA with specific dyes. However, in tissues sections the very high fluorescence signals emitted from the condensed nuclear DNA hamper the detection of the widespread, extranuclear DNA of the NETs. In contrast, when we employ anti-DNA-IgM antibodies, they are unable to penetrate deep into the tightly packed DNA of the nucleus, and we observe a robust signal for the extended DNA patches of the NETs. To validate anti-DNA-IgM, we additionally stained the sections for the NET-markers histone H2B, myeloperoxidase, citrullinated histone H3, and neutrophil elastase. Altogether, we have described a fast one-step procedure for the detection of NETs in tissue sections, which provides new perspectives to characterize neutrophil-associated immune reactions in disease.

Tamoxifen triggers the in vitro release of neutrophil extracellular traps in healthy horses

Neutrophils display an array of biological functions including the formation of neutrophil extracellular traps (NETs), web-like structures specialized in trapping, neutralizing, killing and preventing microbial dissemination within the host. However, NETs contribute to a number of inflammatory pathologies, including severe equine asthma. Tamoxifen (TX) is a selective estrogen receptor modulator which belongs to the triphenylethyllenes group of molecules, and which is used as a treatment in all stages of estrogen-positive human breast cancer. Our previous results suggest that tamoxifen can modulate neutrophil functionality and promote resolution of inflammation; this would partly explain the clinical beneficial effect of this drug in horses with airway inflammation. Enhanced NETs production has been reported with tamoxifen use in humans, but minimal data exists regarding the drug's effect on NETs in horses. The aim of this study is to assess the in vitro effect of TX on NETs formation from peripheral blood of healthy horses. Five clinically healthy mixed-breed adult horses were enrolled in the study. For this, cellular free DNA quantification, immunofluorescence for the visualization of NETs, assessment of different types of NETs, and detection of mitochondrial superoxide. TX induced NETs formation at a concentration of 10 uM. Our results show that only two types of NETs were induced by TX: 95% spread NETs (sprNETs) and 5% aggregated NETs (aggNETs). Furthermore, induction of these NETs could be influenced by mitochondrial ROS. Future research should involve an In vivo study of horses with severe asthma and TX treatment, to evaluate BALF neutrophil NET formation. In conclusion, this in vitro study suggests that the resolution of inflammation by TX in horses with airway inflammation is due to inhibition of other neutrophilic functions but not to NET formation.

Emerging Role of Neutrophil Extracellular Traps in Gastrointestinal Tumors: A Narrative Review

Neutrophil extracellular traps (NETs) are extracellular fibrous networks consisting of depolymerized chromatin DNA skeletons with a variety of antimicrobial proteins. They are secreted by activated neutrophils and play key roles in host defense and immune responses. Gastrointestinal (GI) malignancies are globally known for their high mortality and morbidity. Increasing research suggests that NETs contribute to the progression and metastasis of digestive tract tumors, among them gastric, colon, liver, and pancreatic cancers. This article explores the formation of NETs and reviews the role that NETs play in the gastrointestinal oncologic microenvironment, tumor proliferation and metastasis, tumor-related thrombosis, and surgical stress. At the same time, we analyze the qualitative and quantitative detection methods of NETs in recent years and found that NETs are specific markers of coronavirus disease 2019 (COVID-19). Then, we explore the possibility of NET inhibitors for the treatment of digestive tract tumor diseases to provide a new, efficient, and safe solution for the future therapy of gastrointestinal tumors.

d-lactate-triggered extracellular trap formation in cattle polymorphonuclear leucocytes is glucose metabolism dependent

D-lactic acidosis is a metabolic disease of cattle caused by the digestive overgrowth of bacteria that are highly producers of d-lactate, a metabolite that then reaches and accumulates in the bloodstream. d-lactate is a proinflammatory agent in cattle that induces the formation of extracellular traps (ETs) in polymorphonuclear leucocytes (PMN), although information on PMN metabolic requirements for this response mechanism is insufficient. In the present study, metabolic pathways involved in ET formation induced by d-lactate were studied. We show that d-lactate but not l-lactate induced ET formation in cattle PMN. We analyzed the metabolomic changes induced by d-lactate in bovine PMN using gas chromatography-mass spectrometry (GC-MS). Several metabolic pathways were altered, including glycolysis/gluconeogenesis, amino sugar and nucleotide sugar metabolism, galactose metabolism, starch and sucrose metabolism, fructose and mannose metabolism, and pentose phosphate pathway. d-lactate increased intracellular levels of glucose and glucose-6-phosphate, and increased uptake of the fluorescent glucose analog 2-NBDG, suggesting improved glycolytic activity. In addition, using an enzymatic assay and transmission electron microscopy (TEM), we observed that d-lactate was able to decrease intracellular glycogen levels and the presence of glycogen granules. Relatedly, d-lactate increased the expression of enzymes of glycolysis, gluconeogenesis and glycogen metabolism. In addition, 2DG (a hexokinase inhibitor), 3PO (a 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 inhibitor), MB05032 (inhibitor of fructose-1,6-bisphosphatase) and CP-91149 (inhibitor of glycogen phosphorylase) reduced d-lactate-triggered ETosis. Taken together, these results suggest that d-lactate induces a metabolic rewiring that increases glycolysis, gluconeogenesis and glycogenolysis, all of which are required for d-lactate-induced ET release in cattle PMN.

Tumor ENPP1(CD203a)/Haptoglobin Axis Exploits Myeloid-Derived Suppressor Cells to Promote Post-Radiotherapy Local Recurrence in Breast Cancer

Locoregional failure (LRF) in breast cancer patients post-surgery and post-irradiation (IR) is linked to a dismal prognosis. In a refined new model, we identified Enpp1 (Ectonucleotide pyrophosphatase /phosphodiesterase 1/CD203a) to be closely associated with LRF. Enpp1high circulating tumor cells (CTC) contribute to relapse by a self-seeding mechanism. This process requires the infiltration of PMN-MDSC and neutrophil extracellular traps (NET) formation. Genetic and pharmacological Enpp1 inhibition or NET blockade extend relapse-free survival. Furthermore, in combination with fractionated irradiation (FD), Enpp1 abrogation obliterates LRF. Mechanistically, Enpp1-generated adenosinergic metabolites enhance Haptoglobin (Hp) expression. This inflammatory mediator elicits myeloid invasiveness and promotes NET formation. Accordingly, a significant increase in ENPP1 and NET formation is detected in relapsed human breast cancer tumors. Moreover, high ENPP1 or HP levels are associated with poor prognosis. These findings unveil the ENPP1/HP axis as an unanticipated mechanism exploited by tumor cells linking inflammation to immune remodeling favoring local relapse.

Rheumatoid factor and anti-modified protein antibody reactivities converge on IgG epitopes

OBJECTIVE

Rheumatoid arthritis (RA) patients often develop rheumatoid factors (RFs), antibodies that bind IgG Fc, and anti-modified protein antibodies (AMPAs), multi-reactive autoantibodies that commonly bind citrullinated, homocitrullinated, and acetylated antigens. Recently, antibodies that bind citrulline-containing IgG epitopes were discovered in RA, suggesting that additional undiscovered IgG epitopes could exist and that IgG could be a shared antigen for RFs and AMPAs. The objective of this study was to reveal new IgG epitopes in rheumatic disease and to determine if multi-reactive AMPAs bind IgG.

METHODS

Using RA, systemic lupus erythematosus, Sjögren's disease, and spondyloarthropathy sera, IgG binding to native, citrulline-containing, and homocitrulline-containing linear epitopes of the IgG constant region were evaluated by peptide array with highly bound epitopes further evaluated by ELISA. Monoclonal AMPA binding to IgG-derived peptides and IgG Fc was evaluated by ELISA.

RESULTS

Seropositive RA sera had high IgG binding to multiple citrulline- and homocitrulline-containing IgG-derived peptides, whereas anti-SSA+ Sjögren's disease sera had consistent binding to a single linear native epitope of IgG in the hinge region. Monoclonal AMPAs bound citrulline- and homocitrulline-containing IgG peptides and modified IgG Fc.

CONCLUSION

The repertoire of epitopes bound by AMPAs includes modified IgG epitopes, positioning IgG as a common antigen that connects the otherwise divergent reactivities of RFs and AMPAs.

Macrophage Extracellular Traps: Current Opinions and the State of Research regarding Various Diseases

Macrophages are an important component of the human immune system and play a key role in the immune response, which can protect the body against infection and regulate the development of tissue inflammation. Some studies found that macrophages can produce extracellular traps (ETs) under various conditions of stimulation. ETs are web-like structures that consist of proteins and DNA. ETs are thought to immobilize and kill microorganisms, as well as play an important role in tissue damage, inflammatory progression, and autoimmune diseases. In this review, the structure, identification, mechanism, and research progress of macrophage extracellular traps (METs) in related diseases are reviewed.

Methods for Quantifying Neutrophil Extracellular Traps on Biomaterials

Neutrophils rapidly accumulate at sites of inflammation, including biomaterial implantation sites, where they can modulate the microenvironment toward repair through a variety of functions, including superoxide generation, granule release, and extrusion of neutrophil extracellular traps (NETs). NETs are becoming increasing implicated as a central player in the host response to a biomaterial, and as such, there is a need for reliable in vitro methods to evaluate the relative degree of NETs and quantify NETs on the surface of biomaterials. Such methods should be relatively high throughput and minimize sampling bias. In this chapter, we describe two procedures, (1) fluorescent image analysis and (2) a NETs-based ELISA, both of which have been specifically optimized to quantify NETs generated from human neutrophils on electrospun polydioxanone templates. Both methods are valid and also compatible with tissue culture plastic, but have a variety of advantages and disadvantages. Therefore, both methods can be used to concomitantly study NETs on the surface of a biomaterial. Finally, while these methods were developed for electrospun templates in a 96-well cell culture plate, they may be easily adapted to a large scale and for other biomaterials, including but not limited to metallics, ceramics, and natural and synthetic polymers.

Complement C5a induces the formation of neutrophil extracellular traps by myeloid-derived suppressor cells to promote metastasis

Myeloid-derived suppressor cells (MDSCs) play a major role in cancer progression. In this study, we investigated the mechanisms by which complement C5a increases the capacity of polymorphonuclear MDSCs (PMN-MDSCs) to promote tumor growth and metastatic spread. Stimulation of PMN-MDSCs with C5a favored the invasion of cancer cells via a process dependent on the formation of neutrophil extracellular traps (NETs). NETosis was dependent on the production of high mobility group box 1 (HMGB1) by cancer cells. Moreover, C5a induced the surface expression of the HMGB1 receptors TLR4 and RAGE in PMN-MDSCs. In a mouse lung metastasis model, inhibition of C5a, C5a receptor-1 (C5aR1) or NETosis reduced the number of circulating-tumor cells (CTCs) and the metastatic burden. In support of the translational relevance of these findings, C5a was able to stimulate migration and NETosis in PMN-MDSCs obtained from lung cancer patients. Furthermore, myeloperoxidase (MPO)-DNA complexes, as markers of NETosis, were elevated in lung cancer patients and significantly correlated with C5a levels. In conclusion, C5a induces the formation of NETs from PMN-MDSCs in the presence of cancer cells, which may facilitate cancer cell dissemination and metastasis.

PADI4 Polymorphisms Confer Risk of Anti-CCP-Positive Rheumatoid Arthritis in Synergy With HLA-DRB1*04 and Smoking

Peptidylarginine deiminases (PADs) catalyze citrullination, a post-translational modification playing a pathogenic role in anti-citrullinated protein antibody (ACPA)-positive rheumatoid arthritis (RA). The interplay between single nucleotide polymorphisms (SNPs) in the PADI genes and known risk factors for ACPA-positive RA, including smoking, HLA-DR4 and -1, and the PTPN22 R620W polymorphism, was investigated. We typed four PADI2 SNPs, four PADI4 SNPs, and the PTPN22 R620W SNP in 445 Danish RA patients and 533 age-matched healthy controls, as well as in 200 North American RA patients and 100 age- and sex-matched controls. The HLA-DRB1 locus was typed in the Danish cohort. Logistic regression analyses, adjusted for age, sex, smoking status, and PTPN22 R620W, revealed increased risk of anti-CCP-positive RA in carriers of rs11203367(T) (OR: 1.22, p=0.03) and reduced risk in carriers of rs2240335(A) in PADI4 (OR: 0.82, p=0.04). rs74058715(T) in PADI4 conferred reduced risk of anti-CCP-negative RA (OR: 0.38, p=0.003). In HLA-DRB1*04-positive individuals, specifically, the risk of anti-CCP-positive RA was increased by carriage of PADI4 rs1748033(T) (OR: 1.54, p=0.007) and decreased by carriage of PADI4 rs74058715(T) (OR: 0.44, p=0.01), and we observed an interaction between these SNPs and HLA-DRB1*04 (p=0.004 and p=0.008, respectively) Thus, PADI4 polymorphisms associate with ACPA-positive RA, particularly in HLA-DRB1*04-positive individuals, and with ACPA-negative RA independently of HLA-DRB1*04.

The FcγRIII Engagement Augments PMA-Stimulated Neutrophil Extracellular Traps (NETs) Formation by Granulocytes Partially via Cross-Talk between Syk-ERK-NF-κB and PKC-ROS Signaling Pathways

Polymorphonuclear neutrophils (PMNs) are the most abundant white blood cell in the circulation capable of neutrophil extracellular traps (NETs) formation after stimulation. Both NADPH oxidase-dependent and -independent pathways are involved in NET formation. The IgG is the most abundant immunoglobulin in human serum. However, the impact of the circulating IgG on NET formation is totally unexplored. In this study, the all-trans retinoic acid (ATRA)-induced mature granulocytes (dHL-60) were pre-treated with monomeric human IgG, papain-digested Fab fragment, crystallizable IgG Fc portion, rituximab (a human IgG1), or IgG2. The NET formation of the dHL-60 in the presence/absence of phorbol 12-myristate 13-acetate (PMA) stimulation was then measured by the fluorescent area after SYTOX green nucleic acid stain. The intracellular reactive oxygen species (ROS) generation was measured by flow cytometry. Total and phosphorylated Syk, SHP-1, and ERK were detected by immunoblot. We found that human monomeric IgG and its subclasses IgG1 and IgG2 per se induced negligible NET formation of dHL-60, but the FcγRIII engagement by these IgG subclasses and Fc portion augment PMA-stimulated dHL-60 NET formation in a dose-dependent manner. Furthermore, we found that increased Syk and ERK phosphorylation, intracellular ROS generation, and pro-inflammatory cytokines, IL-8 and TNF-α, production could be induced after FcγRIII engagement. Blocking FcγRIII engagement by a specific antibody diminished the augmented NET formation. In conclusion, we discovered that cross-talk between FcγRIII engagement-induced Syk-ERK and PMA-induced PKC signaling pathways augment NET formation of dHL-60 via increased ROS generation and pro-inflammatory cytokines, IL-8 and TNF-α, production.

A Review of the Neutrophil Extracellular Traps (NETs) from Cow, Sheep and Goat Models

This review provides insight into the importance of understanding NETosis in cows, sheep, and goats in light of the importance to their health, welfare and use as animal models. Neutrophils are essential to innate immunity, pathogen infection, and inflammatory diseases. The relevance of NETosis as a conserved innate immune response mechanism and the translational implications for public health are presented. Increased understanding of NETosis in ruminants will contribute to the prediction of pathologies and design of strategic interventions targeting NETs. This will help to control pathogens such as coronaviruses and inflammatory diseases such as mastitis that impact all mammals, including humans. Definition of unique attributes of NETosis in ruminants, in comparison to what has been observed in humans, has significant translational implications for one health and global food security, and thus warrants further study.

Canine Angiostrongylus vasorum-Induced Early Innate Immune Reactions Based on NETs Formation and Canine Vascular Endothelial Cell Activation In Vitro

Simple Summary

Angiostrongylus vasorum is a cardiopulmonary nematode that affects canids, residing in the pulmonary artery and right atrium/ventricle. Due to its location, the parasite will have a close interaction with the different components of the innate immune system, including endothelial cells and polymorphonuclear neutrophils (PMN). Here we evaluated the expression of adhesion molecules of canine aortic endothelial cells (CAEC), and NETs formation by co-culture of freshly isolated canine PMN with A. vasorum L3. Overall, we found distinct inter-donor variations in adhesion molecule expression among CAEC isolates. Additionally, PMN and A. vasorum co-culture induced NETs release without affecting larval viability.

Abstract

Due to its localization in the canine blood stream, Angiostrongylus vasorum is exposed to circulating polymorphonuclear neutrophils (PMN) and the endothelial cells of vessels. NETs release of canine PMN exposed to A. vasorum infective stages (third stage larvae, L3) and early pro-inflammatory immune reactions of primary canine aortic endothelial cells (CAEC) stimulated with A. vasorum L3-derived soluble antigens (AvAg) were analyzed. Expression profiles of the pro-inflammatory adhesion molecules ICAM-1, VCAM-1, P-selectin and E-selectin were analyzed in AvAg-stimulated CAEC. Immunofluorescence analyses demonstrated that motile A. vasorum L3 triggered different NETs phenotypes, with spread NETs (sprNETs) as the most abundant. Scanning electron microscopy confirmed that the co-culture of canine PMN with A. vasorum L3 resulted in significant larval entanglement. Distinct inter-donor variations of P-selectin, E-selectin, ICAM-1 and VCAM-1 gene transcription and protein expression were observed in CAEC isolates which might contribute to the high individual variability of pathological findings in severe canine angiostrongylosis. Even though canine NETs did not result in larval killing, the entanglement of L3 might facilitate further leukocyte attraction to their surface. Since NETs have already been documented as involved in both thrombosis and endothelium damage events, we speculate that A. vasorum-triggered NETs might play a critical role in disease outcome in vivo.

Cathepsin C promotes breast cancer lung metastasis by modulating neutrophil infiltration and neutrophil extracellular trap formation

Lung metastasis is the major cause of breast cancer-related mortality. The neutrophil-associated inflammatory microenvironment aids tumor cells in metastatic colonization in lungs. Here, we show that tumor-secreted protease cathepsin C (CTSC) promotes breast-to-lung metastasis by regulating recruitment of neutrophils and formation of neutrophil extracellular traps (NETs). CTSC enzymatically activates neutrophil membrane-bound proteinase 3 (PR3) to facilitate interleukin-1β (IL-1β) processing and nuclear factor κB activation, thus upregulating IL-6 and CCL3 for neutrophil recruitment. In addition, the CTSC-PR3-IL-1β axis induces neutrophil reactive oxygen species production and formation of NETs, which degrade thrombospondin-1 and support metastatic growth of cancer cells in the lungs. CTSC expression and secretion are associated with NET formation and lung metastasis in human breast tumors. Importantly, targeting CTSC with compound AZD7986 effectively suppresses lung metastasis of breast cancer in a mouse model. Overall, our findings reveal a mechanism of how tumor cells regulate neutrophils in metastatic niches and support CTSC-targeting approaches for cancer treatment.

Neutrophil Extracellular Traps Tied to Rheumatoid Arthritis: Points to Ponder

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

Mitochondria-derived ATP participates in the formation of neutrophil extracellular traps induced by platelet-activating factor through purinergic signaling in cows

Neutrophil extracellular trap (NET) formation eliminates/prevents the spread of infectious agents. Platelet activating factor (PAF) is involved in infectious diseases of cattle because it recruits and activates neutrophils. However, its ability to induce NET release and the role of metabolism in this process is not known. We investigated if inhibition of glycolysis, mitochondrial-derived adenosine triphosphate (ATP) synthesis and purinergic signaling though P2X₁ purinoceptors interfered with NET formation induced by PAF. We inhibited bovine neutrophils with 2-deoxy-d-glucose, rotenone, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and NF449 to evaluate PAF-mediated NET extrusion. PAF induced mitochondrial hyperpolarization and triggered extracellular ATP release via pannexin-1. Inhibition of mitochondrial metabolism prevented extracellular ATP release. Inhibition of glycolysis, complex-I activity and oxidative phosphorylation prevented NET formation induced by PAF. Inhibition of P2X₁ purinergic receptors inhibited mitochondrial hyperpolarization and NET formation. We concluded that PAF-induced NET release is dependent upon glycolysis, mitochondrial ATP synthesis and purinergic signaling.

Staphylococcus aureus Panton-Valentine Leukocidin triggers an alternative NETosis process targeting mitochondria

Panton-Valentine Leukocidin (PVL) is a bicomponent leukotoxin produced by 3%-10% of clinical Staphylococcus aureus (SA) strains involved in the severity of hospital and community-acquired infections. Although PVL was long known as a pore-forming toxin, recent studies have challenged the formation of a pore at the plasma membrane, while its endocytosis and the exact mode of action remain to be defined. In vitro immunolabeling of human neutrophils shows that Neutrophil Extracellular Traps (NETosis) is triggered by the action of purified PVL, but not by Gamma hemolysin CB (HlgCB), a structurally similar SA leukotoxin. PVL causes the ejection of chromatin fibers (NETs) decorated with antibacterial peptides independently of the NADPH oxidase oxidative burst. Leukotoxin partially colocalizes with mitochondria and enhances the production of reactive oxygen species from these organelles, while showing an increased autophagy, which results unnecessary for NETs ejection. PVL NETosis is elicited through Ca²⁺ -activated SK channels and Myeloperoxidase activity but is abolished by Allopurinol pretreatment of neutrophils. Moreover, massive citrullination of the histone H3 is performed by peptidyl arginine deiminases. Inhibition of this latter enzymes fails to abolish NET extrusion. Unexpectedly, PVL NETosis does not seem to involve Src kinases, which is the main kinase family activated downstream the binding of PVL F subunit to CD45 receptor, while the specific kinase pathway differs from the NADPH oxidase-dependent NETosis. PVL alone causes a different and specific form of NETosis that may rather represent a bacterial strategy conceived to disarm and disrupt the immune response, eventually allowing SA to spread.

Trypanosoma brucei brucei Induces Polymorphonuclear Neutrophil Activation and Neutrophil Extracellular Traps Release

Trypanosoma brucei brucei trypomastigotes are classical blood parasites of cattle, these stages might become potential targets for circulating polymorphonuclear neutrophils (PMN). We here investigated NETs extrusion and related oxygen consumption in bovine PMN exposed to motile T. b. brucei trypomastigotes in vitro. Parasite exposure induced PMN activation as detected by enhanced oxygen consumption rates (OCR), extracellular acidification rates (ECAR), and production of total and extracellular reactive oxygen species (ROS). Scanning electron microscopy (SEM) showed that co-cultivation of bovine PMN with motile trypomastigotes resulted in NETs formation within 120 min of exposure. T. b. brucei-induced NETs were confirmed by confocal microscopy demonstrating co-localization of extruded DNA with neutrophil elastase (NE) and nuclear histones. Immunofluorescence analyses demonstrated that trypomastigotes induced different phenotypes of NETs in bovine PMN, such as aggregated NETs (aggNETs), spread NETs (sprNETs), and diffuse NETs (diffNETs) with aggNETs being the most abundant ones. Furthermore, live cell 3D-holotomographic microscopy unveiled detailed morphological changes during the NETotic process. Quantification of T. b. brucei-induced NETs formation was estimated by DNA and nuclear area analysis (DANA) and confirmed enhanced NETs formation in response to trypomastigote stages. Formation of NETs does not result in a decrease of T. b. brucei viability, but a decrease of 26% in the number of motile parasites. Referring the involved signaling pathways, trypomastigote-induced NETs formation seems to be purinergic-dependent, since inhibition via NF449 treatment resulted in a significant reduction of T. b. brucei-triggered DNA extrusion. Overall, future studies will have to analyze whether the formation of aggNETs indeed plays a role in the outcome of clinical disease and bovine African trypanosomiasis-related immunopathological disorders, such as increased intravascular coagulopathy and vascular permeability, often reported to occur in this disease.

Neutrophil Extracellular Traps Generation Relates with Early Stage and Vascular Complications in Systemic Sclerosis

Systemic sclerosis (SSc) is a systemic disease characterized by a great clinical and immunological heterogeneity whose pathophysiology is still being unraveled. Recently, innate immunity has been proposed to participate to the pathogenesis of SSc. In this study, we investigated the release of neutrophil extracellular traps (NETs) according to patient phenotype. Polymorphonuclear neutrophils (PMN) from 34 SSc patients and 26 healthy controls were stimulated by serum from SSc or healthy subject. NETs were visualized using epifluorescence microscope after DNA, myeloperoxidase, and Histone H3 tagging. Area of NETs were quantified using an original macro running in ImageJ^® software. PMN from SSc patients were significantly more prone to releasing NETs than control PMN after autologous stimulation. PMN from patients with severe vascular complications (pulmonary arterial hypertension, digital ulcers) produced more NETs than PMN from other SSc patients and their aberrant NET production appeared to be sustained over time. In patients with pulmonary interstitial disease or extensive cutaneous fibrosis, NET production was high at an early stage of the disease before progressively decreasing. Both serum factors and PMN activation status were involved in the enhanced production of NETs in SSc. Consequently, neutrophils and especially NETosis represent new physiopathological and therapeutic fields in SSc.

A novel cell-based assay for dynamically detecting neutrophil extracellular traps-induced lung epithelial injuries

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS) are common lung disorders characterized by alveolar-capillary barrier disruption and dyspnea, which can cause substantial morbidity and mortality. Currently, a cluster of acute respiratory illnesses, known as novel coronavirus (2019-nCoV)-infected pneumonia (NCIP), which allegedly originally occurred in Wuhan, China, has increased rapidly worldwide. The critically ill patients with ARDS have high mortality in subjects with comorbidities. Previously, the excessive recruitment and activation of neutrophils (polymorphonuclear leukocytes [PMNs]), accompanied by neutrophil extracellular traps (NETs) formation were reported being implicated in the pathogenesis of ALI/ARDS. However, the direct visualization of lung epithelial injuries caused by NETs, and the qualitative and quantitative evaluations of this damage are still lacking. Additionally, those already reported methods are limited for their neglect of the pathological role exerted by NETs and focusing only on the morphological features of NETosis. Therefore, we established a cell-based assay for detecting NETs during lung epithelial cells-neutrophils co-culture using the xCELLigence system, a recognized real-time, dynamic, label-free, sensitive, and high-throughput apparatus. Our results demonstrated that lung epithelial injuries, reflected by declines in cell index (CI) values, could be induced by lipopolysaccharide (LPS)-activated PMNs, or NETs in a time and dose-dependent manner. NETs generation was verified to be the major contributor to the cytotoxicity of activated PMNs; protein components of NETs were the prevailing cytotoxic mediators. Moreover, this cell-based assay identified that PMNs from severe pneumonia patients had a high NETs formative potential. Additionally, acetylsalicylic acid (ASA) and acetaminophen (APAP) were discovered alleviating NETs formation. Thus, this study not only presents a new methodology for detecting the pathophysiologic role of NETs but also lays down a foundation for exploring therapeutic interventions in an effort to cure ALI/ARDS in the clinical setting of severe pneumonia, including the emerging of NCIP.

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A real-time, dynamical and label-free assay for detecting NETs is established using the xCELLigence system.

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This establishment relies on the co-culture of lung epithelia and neutrophils, focusing on evaluating NETs’ effects.

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This cell-based assay has feasibility and practicality in clinical applications.

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This methodology builds a solid foundation for exploring therapies for ALI/ARDS, including the emerging NCIP.

Convolutional Neural Networks-Based Image Analysis for the Detection and Quantification of Neutrophil Extracellular Traps

Over a decade ago, the formation of neutrophil extracellular traps (NETs) was described as a novel mechanism employed by neutrophils to tackle infections. Currently applied methods for NETs release quantification are often limited by the use of unspecific dyes and technical difficulties. Therefore, we aimed to develop a fully automatic image processing method for the detection and quantification of NETs based on live imaging with the use of DNA-staining dyes. For this purpose, we adopted a recently proposed Convolutional Neural Network (CNN) model called Mask R-CNN. The adopted model detected objects with quality comparable to manual counting—Over 90% of detected cells were classified in the same manner as in manual labelling. Furthermore, the inhibitory effect of GW 311616A (neutrophil elastase inhibitor) on NETs release, observed microscopically, was confirmed with the use of the CNN model but not by extracellular DNA release measurement. We have demonstrated that a modern CNN model outperforms a widely used quantification method based on the measurement of DNA release and can be a valuable tool to quantitate the formation process of NETs.

Detection, Visualization, and Quantification of Neutrophil Extracellular Traps (NETs) and NET Markers

Neutrophil extracellular traps (NETs) have been identified as a key player in the pathogenesis of infection and inflammation in human and animals. On the one hand, NETs have been characterized as fundamental to the innate immune defense against different pathogens since they are able to entrap and immobilize invading pathogens. On the other hand, NETs have been shown to contribute to several diseases, based on their detrimental consequences. This chapter describes methods to detect NETs and NET markers in blood-derived isolated neutrophils of human, pigs, and horses in vitro, as well as NETs and NET marker detection in body fluids from in vivo studies. To avoid nonspecific background in NET-formation, a well-established isolation method for the neutrophils from fresh blood is needed. After stimulation of neutrophils to release NETs, NETs are stained with different antibodies to confirm the presence of extracellular DNA extrusion consisting of histone-DNA complexes, as well as granule components (e.g., myeloperoxidase or elastase). Furthermore, specific methods to quantify NETs and NET markers in the cerebrospinal fluid (CSF) and bronchoalveolar lavage fluid (BALF) are described in detail. In addition to immunofluorescence microscopy, quantification of NET markers from in vivo experiments in various body fluids is described (e.g., nuclease activity, free extracellular DNA, or cationic host defense peptides, such as the porcine PR-39 in BALF and CSF).

Disordered Antigens and Epitope Overlap Between Anti-Citrullinated Protein Antibodies and Rheumatoid Factor in Rheumatoid Arthritis

OBJECTIVE

Anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF) are commonly present in rheumatoid arthritis (RA) without a clear rationale for their coexistence. Moreover, autoantibodies develop against proteins with different posttranslational modifications and native proteins without obvious unifying characteristics of the antigens. We undertook this study to broadly evaluate autoantibody binding in seronegative and seropositive RA to identify novel features of reactivity.

METHODS

An array was created using a total of 172,828 native peptides, citrulline-containing peptides, and homocitrulline-containing peptides derived primarily from proteins citrullinated in the rheumatoid joint. IgG and IgM binding to peptides were compared between cyclic citrullinated peptide (CCP)-positive RF+, CCP+RF-, CCP-RF+, and CCP-RF- serum from RA patients (n = 48) and controls (n = 12). IgG-bound and endogenously citrullinated peptides were analyzed for amino acid patterns and predictors of intrinsic disorder, i.e., unstable 3-dimensional structure. Binding to IgG-derived peptides was specifically evaluated. Enzyme-linked immunosorbent assay confirmed key results.

RESULTS

Broadly, CCP+RF+ patients had high citrulline-specific IgG binding to array peptides and CCP+RF- and CCP-RF+ patients had modest citrulline-specific IgG binding (median Z scores 3.02, 1.42, and 0.75, respectively; P < 0.0001). All RA groups had low homocitrulline-specific binding. CCP+RF+ patients had moderate IgG binding to native peptides (median Z score 2.38; P < 0.0001). The highest IgG binding was to citrulline-containing peptides, irrespective of protein identity, especially if citrulline was adjacent to glycine or serine, motifs also seen in endogenous citrullination in the rheumatoid joint. Highly bound peptides had multiple features predictive of disorder. IgG from CCP+RF+ patients targeted citrulline-containing IgG-derived peptides.

CONCLUSION

Disordered antigens, which are frequently citrullinated, and common epitopes for ACPAs and RF are potentially unifying features for RA autoantibodies.

Machine Learning to Quantitate Neutrophil NETosis

We introduce machine learning (ML) to perform classification and quantitation of images of nuclei from human blood neutrophils. Here we assessed the use of convolutional neural networks (CNNs) using free, open source software to accurately quantitate neutrophil NETosis, a recently discovered process involved in multiple human diseases. CNNs achieved >94% in performance accuracy in differentiating NETotic from non-NETotic cells and vastly facilitated dose-response analysis and screening of the NETotic response in neutrophils from patients. Using only features learned from nuclear morphology, CNNs can distinguish between NETosis and necrosis and between distinct NETosis signaling pathways, making them a precise tool for NETosis detection. Furthermore, by using CNNs and tools to determine object dispersion, we uncovered differences in NETotic nuclei clustering between major NETosis pathways that is useful in understanding NETosis signaling events. Our study also shows that neutrophils from patients with sickle cell disease were unresponsive to one of two major NETosis pathways. Thus, we demonstrate the design, performance, and implementation of ML tools for rapid quantitative and qualitative cell analysis in basic science.

Neutrophil Extracellular Traps Induce Tissue-Invasive Monocytes in Granulomatosis With Polyangiitis

Objective: Granulomatosis with polyangiitis (GPA) is a multi-organ vasculitic syndrome typically associated with neutrophil extracellular trap (NET) formation and aggressive tissue inflammation. Manifestations in head and neck (H&N) GPA include septal perforations, saddle-nose deformities, bony erosions of the orbital and sinus walls, middle ear damage and epiglottitis, indicative of bone, cartilage, and connective tissue destruction. Whether H&N-centric lesions engage disease pathways distinctive from the ischemic tissue damage in the lungs, kidneys, skin, and peripheral nerves is unknown. We have compared inflammatory responses triggered by neutrophilic NETs in patients with H&N GPA and systemic GPA (sGPA). Methods: Neutrophils and monocytes were isolated from the peripheral blood of patients with H&N GPA, sGPA, and age/gender matched healthy individuals. Neutrophil NETosis was induced. NETs were isolated and cocultured with monocytes. Gene induction was quantified by RT-PCR, protein upregulation by flow cytometry. Tissue invasiveness of monocytes was measured in a 3D collagen matrix system. Expression of MMP-9 in tissue-residing macrophages was assessed by immunohistochemistry in tissue biopsies. Results: Neutrophils from H&N GPA patients showed more intense NETosis with higher frequencies of netting neutrophils (P < 0.001) and release of higher amounts of NETs (P < 0.001). Isolated NETs from H&N GPA functioned as an inducer of danger-associated molecular patterns in monocytes; specifically, alarmin S100A9. NET-induced upregulation of monocyte S100A9 required recognition of DNA. S100A9 release resulted in the induction of metalloproteinases, including MMP-9, and enabled monocytes to invade into extracellular matrix. Anti-MMP-9 treatment attenuated the tissue invasiveness of monocytes primed with NETs from H&N GPA patients. MMP-9-producing macrophages dominated the tissue infiltrates in naso-sinal biopsies from H&N GPA patients. Conclusion: Distinct disease patterns in GPA are associated with differences in NET formation and NET content. H&N GPA patients with midline cartilaginous and bony lesions are highly efficient in generating NETs. H&N GPA neutrophils trigger the induction of the alarmin S100A9, followed by production of MMP-9, endowing monocytes with tissue-invasive capabilities.

Computational Methodologies for the in vitro and in situ Quantification of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are a neutrophil defensive mechanism where chromatin is expelled together with antimicrobial proteins in response to a number of stimuli. Even though beneficial in many cases, their dysfunction has been implicated in many diseases, such as rheumatoid arthritis and cancer. Accurate quantification of NETs is of utmost importance for correctly studying their role in various diseases, especially when considering them as therapeutic targets. Unfortunately, NET quantification has a number of limitations. However, recent developments in computational methodologies for quantifying NETs have vastly improved the ability to study NETs. Methods range from using ImageJ to user friendly applications and to more sophisticated machine-learning approaches. These various methods are reviewed and discussed in this review.

Reduced Anti-Histone Antibodies and Increased Risk of Rheumatoid Arthritis Associated with a Single Nucleotide Polymorphism in PADI4 in North Americans

Autoantibodies against citrullinated proteins are a hallmark of rheumatoid arthritis, a destructive inflammatory arthritis. Peptidylarginine deiminase 4 (PAD4) has been hypothesized to contribute to rheumatoid arthritis by citrullinating histones to induce neutrophil extracellular traps (NETs), which display citrullinated proteins that are targeted by autoantibodies to drive inflammation and arthritis. Consistent with this theory, PAD4-deficient mice have reduced NETs, autoantibodies, and arthritis. However, PAD4′s role in human rheumatoid arthritis is less clear. Here, we determine if single nucleotide polymorphism rs2240335 in PADI4, whose G allele is associated with reduced PAD4 in neutrophils, correlates with NETs, anti-histone antibodies, and rheumatoid arthritis susceptibility in North Americans. Control and rheumatoid arthritis subjects, divided into anti-cyclic citrullinated peptide (CCP) antibody positive and negative groups, were genotyped at rs2240335. In homozygotes, in vitro NETosis was quantified in immunofluorescent images and circulating NET and anti-histone antibody levels by enzyme linked immunosorbent assay (ELISA). Results were compared by t-test and correlation of rheumatoid arthritis diagnosis with rs2240335 by Armitage trend test. NET levels did not significantly correlate with genotype. G allele homozygotes in the CCP⁻ rheumatoid arthritis group had reduced anti-native and anti-citrullinated histone antibodies. However, the G allele conferred increased risk for rheumatoid arthritis diagnosis, suggesting a complex role for PAD4 in human rheumatoid arthritis.

Reduced IgG titers against pertussis in rheumatoid arthritis: Evidence for a citrulline-biased immune response and medication effects

BACKGROUND

The antibody response to pertussis vaccination in rheumatoid arthritis is unknown, a concerning omission given the relatively low efficacy of the pertussis vaccine, a rise in pertussis infections, and a general increased susceptibility to infection in rheumatoid arthritis. Additionally, the contributions from an intrinsically dysregulated immune system in rheumatoid arthritis and immune-suppressing medications to the response to pertussis vaccination is poorly defined. This study examines antibody titers against pertussis in vaccinated rheumatoid arthritis patients and controls as well as evaluates potential contributions from demographic factors, immune suppressing medications, and reactivity against citrullinated pertussis.

METHODS

Serum IgG titers against native and citrullinated pertussis and tetanus were quantified by enzyme-linked immunosorbent assay in rheumatoid arthritis subjects and controls who were vaccinated within 10 years. Titers were compared by t-test and percent immunity by Fisher's exact test. Multivariable logistic regression was used to identify clinical factors that correlate with native pertussis titers.

RESULTS

Compared to controls, rheumatoid arthritis subjects had lower titers against pertussis, but not tetanus, and reduced immunity to pertussis. These results were even more prominent at 5-10 years post-vaccination, when rheumatoid arthritis patients had 50% lower titers than controls and 2.5x more rheumatoid arthritis subjects were not considered immune to pertussis. Multiple logistic regression demonstrated that female sex and methotrexate use, but not TNF inhibiting medications, correlated with reduced immunity to pertussis. Finally, rheumatoid arthritis patients had higher IgG titers against citrullinated pertussis than native pertussis.

CONCLUSIONS

Pertussis titers are lower in vaccinated rheumatoid arthritis patients with evidence for contributions from female sex, a citrulline-biased immune response, and methotrexate use.

Mast Cell Cytonemes as a Defense Mechanism against Coxiella burnetii

Mast cells (MCs) are found in tissues that are in close contact with external environment, such as skin, lungs, or intestinal mucosa but also in the placenta during pregnancy. If their role in mediating allergic conditions is established, several studies now highlight their importance during infection with extracellular pathogens. This study showed a new and effective antimicrobial mechanism of MCs against Coxiella burnetii, an intracellular bacterium whose infection during pregnancy is associated with abortion, preterm labor, and stillbirth. The data reveal that in response to C. burnetii, MCs release extracellular actin filaments that contain antimicrobial agents and are capable to trap and kill bacteria. We show that this mechanism is dependent on the cooperation of two membrane receptors, CD36 and Toll-like receptor 4, and may occur in the placenta during pregnancy by using ex vivo placental MCs. Overall, this study reports an unexpected role for MCs during infection with intracellular bacteria and suggests that MC response to C. burnetii infection is a protective defense mechanism during pregnancy.

Mast cells (MCs) are critical mediators of inflammation; however, their microbicidal activity against invading pathogens remains largely unknown. Here, we describe a nonpreviously reported antibacterial mechanism used by MCs against Coxiella burnetii, the agent of Q fever. We show that C. burnetii interaction with MCs does not result in bacterial uptake but rather induces the formation of extracellular actin filaments named cytonemes. MC cytonemes express cathelicidin and neutrophil elastase and mediate the capture and destruction of entrapped bacteria. We provide evidence that MC cytoneme formation and microbicidal activity are dependent on the cooperation of the scavenger receptor CD36 and Toll-like receptor 4. Taken together, our results suggest that MCs use an extracellular sophisticated mechanism of defense to eliminate intracellular pathogens, such as C. burnetii, before their entry into host cells.

Rapid Quantification of NETs In Vitro and in Whole Blood Samples by Imaging Flow Cytometry

Neutrophil extracellular trap (NET) formation involves the release of DNA outside the cell to neutralize pathogens. Techniques such as live microscopy, flow cytometry, and intravital imaging allow the characterization of NETs, but these either cannot be applied in vivo, lack specificity or require invasive procedures. We developed an automated analysis method to rapidly acquire and characterize cells as NETs or NET precursors, as opposed to cells undergoing other forms of cell death, using imaging flow cytometry. NETs were maintained in solution using a novel three-dimensional cell culture system in which cells are suspended at the interface of two liquids of different density. Critically, we identify NETs using an image analysis algorithm based on morphological data showing the extrusion of DNA beyond the cell boundaries. In vitro, we used this technique to demonstrate different requirements for NET formation in human and mouse neutrophils. We also measured NETs in whole blood during infection of mice with the malaria parasite Plasmodium yoelii. We expect this technique will provide a valuable approach to better understand the process of NET formation and its importance in disease. © 2019 International Society for Advancement of Cytometry.

NET Formation in Bullous Pemphigoid Patients With Relapse Is Modulated by IL-17 and IL-23 Interplay

Background: DNA extracellular traps (ETs), released by neutrophils (NETs), or eosinophils (EETs), play a pathogenic role in several autoimmune disorders. However, to date, NETs have never been investigated in bullous pemphigoid (BP) with respect to clinical and immunological activities, both at baseline and at time of relapse which have been characterized with specific IL-17 and IL-23 patterns. Objective: We sought to assess whether ETs were associated with BP as well as the relative contribution of IL-17 axis cytokines to NET induction. Methods: Skin biopsy specimens were obtained from 11 patients with BP. Immuno-detection of neutrophils and eosinophils combined to DNA staining allowed us to investigate the in-situ presence of NETs and EETs using confocal scanning microscopy. NETs release was evaluated ex vivo by stimulating polymorphonuclear cells from BP patients with BP biological fluids in presence of IL-17A and IL-23 or of glucocorticoids. Results: At baseline, ETs were observed in BP lesions at the site of dermal-epidermal cleavage. Despite an important infiltrate of eosinophils, ETs were essentially associated with neutrophils in situ and were not related to BP clinical activity at diagnosis. In situ observation of NETs was associated in 6 among 8 patients with serum capacity of NET induction. Notably both blister fluid and sera from BP patients at diagnosis and at time of relapse could induce NET formation ex vivo. In contrast, a longitudinal investigation showed a decrease of NET formation with time of treatment in patients undergoing remission. Mimicking relapse, complementation of sera from BP patients with ongoing remission with either IL-17A or IL-23 increased NET formation. Conversely, IL-17A inhibited NET formation induced by serum from BP patients with relapse supplemented or not with IL-23. Finally, glucocorticoids also inhibited NET formation ex vivo in BP. Conclusion: NET formation is an associated phenomenon with BP. Furthermore, we showed that IL-23 favored NET formation, whereas the effects of IL-17A are environment dependent. Indeed, IL-17A displayed a protective effect on NET formation when associated with IL-23, showing for the first-time differential effects of these two cytokines in BP.

IL-4 receptor engagement in human neutrophils impairs their migration and extracellular trap formation

BACKGROUND

Type 2 immunity serves to resist parasitic helminths, venoms, and toxins, but the role and regulation of neutrophils during type 2 immune responses are controversial. Helminth models suggested a contribution of neutrophils to type 2 immunity, whereas neutrophils are associated with increased disease severity during type 2 inflammatory disorders, such as asthma.

OBJECTIVE

We sought to evaluate the effect of the prototypic type 2 cytokines IL-4 and IL-13 on human neutrophils.

METHODS

Human neutrophils from peripheral blood were assessed without or with IL-4 or IL-13 for (1) expression of IL-4 receptor subunits, (2) neutrophil extracellular trap (NET) formation, (3) migration toward CXCL8 in vitro and in humanized mice, and (4) CXCR1, CXCR2, and CXCR4 expression, as well as (5) in nonallergic versus allergic subjects.

RESULTS

Human neutrophils expressed both types of IL-4 receptors, and their stimulation through IL-4 or IL-13 diminished their ability to form NETs and migrate toward CXCL8 in vitro. Likewise, in vivo chemotaxis in NOD-scid-Il2rg^-/- mice was reduced in IL-4-stimulated human neutrophils compared with control values. These effects were accompanied by downregulation of the CXCL8-binding chemokine receptors CXCR1 and CXCR2 on human neutrophils on IL-4 or IL-13 stimulation in vitro. Ex vivo analysis of neutrophils from allergic patients or exposure of neutrophils from nonallergic subjects to allergic donor serum in vitro impaired their NET formation and migration toward CXCL8, thereby mirroring IL-4/IL-13-stimulated neutrophils.

CONCLUSION

IL-4 receptor signaling in human neutrophils affects several neutrophil effector functions, which bears important implications for immunity in type 2 inflammatory disorders.