Neutrophil extracellular traps (NET) induced by different stimuli: A comparative proteomic analysis

Mouse Bone Marrow Neutrophil Extracellular Trap Proteomics by Microbial Stimuli

Neutrophils, the most abundant white blood cells in human circulation, play a crucial role in innate immunity. One of their key defense mechanisms is the formation of neutrophil extracellular traps (NETs), web-like structures composed of chromatin and antimicrobial proteins that help capture and neutralize pathogens. While previous studies have identified a limited set of NET-associated proteins, the comprehensive proteomic landscape of NETs induced by different stimuli remains largely unexplored. In this study, we used data-independent acquisition mass spectrometry to analyze the proteomic composition of NETs induced by five distinct stimuli: β-glucan, lipopolysaccharide, polyinosinic-polycytidylic acid sodium, resiquimod, and severe fever with thrombocytopenia syndrome bunyavirus. Across all conditions, we identified 5,868 NET-associated proteins, revealing significant stimulus-dependent differences in protein composition. Notably, differentially expressed proteins were detected in each condition, highlighting unique proteomic signatures that may reflect distinct immune responses. This dataset offers key insights into the proteomic diversity of NETs and their role in immune regulation, providing a foundation for future research on NET-mediated immunity in infectious and inflammatory diseases.

Anti-TFAM antibodies link mitochondrial damage with antiphospholipid syndrome and thrombosis in SLE

OBJECTIVES

Mitochondria are a source of autoantigens and damage-associated molecular patterns (DAMPs) in systemic lupus erythematosus (SLE). Nucleoids carrying TFAM (transcription factor A, mitochondrial) and mitochondrial DNA (mtDNA) are important DAMPs in SLE. While mtDNA has been associated with anti-double-stranded (ds)DNA antibodies and type I interferon (IFN-I), the immunogenic role of TFAM in SLE pathogenesis is unknown. Here, we characterised the clinical and transcriptional phenotypes linked to anti-TFAM antibodies in SLE.

METHODS

Anti-TFAM antibodies were discovered in an exploratory sample of 22 SLE patients and 9 healthy controls. To define the prevalence, clinical significance, and associations with transcriptional profiles and IFN levels, anti-TFAM antibodies were detected using enzyme-linked immunosorbent assay (ELISA) in 98 healthy controls and 158 SLE patients. Sera from patients with dermatomyositis, rheumatoid arthritis, and primary antiphospholipid syndrome (PAPS) were also tested.

RESULTS

Anti-TFAM antibodies were discovered in patients with SLE while analysing neutrophil autoantigens and confirmed by ELISA and immunoblotting. One-third of SLE patients (48/158) were positive for anti-TFAM antibodies. Unlike anti-dsDNA antibodies, anti-TFAM antibodies were not associated with disease activity or the IFN signature. Instead, anti-TFAM antibodies were associated with thrombosis, antiphospholipid syndrome (APS) (odds ratio [OR], 2.9 and 5.4, respectively), thrombosis-associated transcriptional profiles, and elevated IFN-III. Anti-TFAM antibodies were also found in PAPS, supporting their role in APS but not SLE pathogenesis. Lupus anticoagulant increased the risk of thrombosis associated with anti-TFAM antibodies (OR, 8.71), indicating they are markers of independent prothrombotic pathways.

CONCLUSIONS

Anti-TFAM antibodies identify a distinct clinical and transcriptional disease subset associated with mitochondrial damage, thrombosis, and APS in SLE.

Targeting neutrophil extracellular traps in cancer progression and metastasis

Neutrophils serve as pivotal effectors and regulators of the intricate immune system. Their contributions are indispensable, encompassing the obliteration of pathogens and a significant role in both cancer initiation and progression. Conversely, malignancies profoundly affect neutrophil activity, maturation, and lifespans. Cancer cells manipulate their biology to enhance or suppress the key functions of neutrophils. This manipulation is one of the most remarkable defensive mechanisms used by neutrophils, including the formation of neutrophil extracellular traps (NETs). NETs are filamentous structures comprising DNA, histones, and proteins derived from cytotoxic granules. In this review, we discuss the bidirectional interplay in which cancer elicits NET formation, and NETs concurrently facilitate cancer progression. Here, we discuss how vascular dysfunction and thrombosis induced by neutrophils and NETs contribute to an elevated risk of mortality from cardiovascular complications in patients with cancer. Ultimately, we propose a series of therapeutic strategies that hold promise for effectively targeting NETs in clinical settings.

A Mimetic Assay of Neutrophil Extracellular Trap Degradation Using YOYO-1-Stained DNA-Histone Surface Webs

Neutrophil extracellular traps (NETs) are not only promising biomarkers of disease, but also potential therapeutic targets. Overproduction or the improper clearance of NETs has been linked to disease severity. In vitro NET degradation assays can reveal mechanisms and degradation efficiency differences in diseased serum samples. There is a need for more convenient assays to increase the speed of NET degradation studies. This paper describes a simplified, lower variability mimetic assay with DNA-histone structures, referred to as surface webs, that performs functionally similarly to traditional NET degradation assays with increased scalability, ease of use, shorter preparation time, and lowered costs. The surface webs are created and dehydrated in a 96-well microplate that is shelf-stable, transportable, and viable for 30 days of storage at room temperature. The surface webs, compared to NETs, have similar shapes and distribution but lower intraplate variability while degrading with healthy serum and DNase I within the same timeframe. The assay can identify patient serum with reduced degradation capabilities. This assay opens new opportunities for NET-targeted drug discovery and studies on the role of NETs as modulators of disease.

Gasdermin D-dependent neutrophil extracellular traps exacerbate cytokine storm contributing to pyoderma gangrenosum pathogenesis

Pyoderma gangrenosum (PG) is characterized by the agonizing necrotizing ulcers with non-infectious neutrophil infiltration. Neutrophil extracellular traps (NETs) represent one of the mechanisms of neutrophils activation, and gasdermin D (GSDMD) plays a regulatory role in NETs. In this study, we discovered that the serum levels of NETs were elevated in PG patients compared to healthy controls. Injection of serum from PG patients into the dorsal skin of wild-type mice led to the formation of localized cutaneous ulcers. Furthermore, subsequent modeling demonstrated a significant increase of NETs and GSDMD in skin lesions and peripheral blood serum of wild-type mice. In GSDMD -/- mice, the severity of skin ulcers after modeling was significantly diminished. Overall, our findings shed light on the role of GSDMD in regulating the production of NETs by neutrophils and the release of inflammatory factors in the pathogenesis of PG and establish an animal model for studying PG.

[Research Progress of Neutrophil Extracellular Traps in Lung Cancer]

Neutrophil extracellular traps (NETs), intricate reticular structures released by activated neutrophils, play a pivotal regulatory role in the pathogenesis of malignant tumors. Lung cancer is one of the most prevalent malignancies globally, with persistently high incidence and mortality rates. Recent studies have revealed that NETs dynamically modulate the tumor microenvironment through unique pathological mechanisms, exhibiting complex immunoregulatory characteristics during the progression of lung cancer, and this discovery has increasingly become a focal point in tumor immunology research. This paper provides a comprehensive review of the latest advancements in NETs research related to lung cancer, offering an in-depth analysis of their impact on lung cancer progression, their potential diagnostic value, and the current state of research on targeting NETs for lung cancer prevention and treatment. The aim is to propose novel strategies to enhance therapeutic outcomes and improve the prognosis for lung cancer patients.
.

Novel Methods for the Analysis of Serum NET Remnants: Evaluation in Patients with Severe COVID-19

Neutrophil extracellular traps (NETs) are web-like structures composed of chromatin and proteins from neutrophil granules. Several studies highlight the heterogeneity of NETs, underscoring the challenges associated with their detection. In patients with COVID-19, high levels of NET fragments, called NET remnants, are detected in the circulation but also in alveoli and bronchioles. NET remnants are usually measured as complexes of DNA and myeloperoxidase (DNA-MPO). Taking advantage of proteomic data on NET composition, we developed new solid-phase assays to detect NET remnants, measuring complexes of DNA with alpha enolase (DNA-eno) or calprotectin (DNA-cal). The two assays were compared with the DNA-MPO test for the detection of in vitro-generated NET and serum NET remnants; all of them showed similar sensitivity in the detection of in vitro-generated NET. In an analysis of 40 patients with severe COVID-19 and 25 healthy subjects, the results of the three assays were highly correlated, and all detected significantly higher levels of NET remnants in patient sera. Moreover, the level of NET remnants correlated with impaired gas exchange and increased with the progressive decline of pulmonary function. The proposed assays thus represent a novel tool with which to evaluate NETosis; using antibodies to different NET constituents may allow their fingerprinting in different disorders.

Staphylococcus aureus in Inflammation and Pain: Update on Pathologic Mechanisms

Staphylococcus aureus (S. aureus) is a Gram-positive bacterium of significant clinical importance, known for its versatility and ability to cause a wide array of infections, such as osteoarticular, pulmonary, cardiovascular, device-related, and hospital-acquired infections. This review describes the most recent evidence of the pathogenic potential of S. aureus, which is commonly part of the human microbiota but can lead to severe infections. The prevalence of pathogenic S. aureus in hospital and community settings contributes to substantial morbidity and mortality, particularly in individuals with compromised immune systems. The immunopathogenesis of S. aureus infections involves intricate interactions with the host immune and non-immune cells, characterized by various virulence factors that facilitate adherence, invasion, and evasion of the host's defenses. This review highlights the complexity of S. aureus infections, ranging from mild to life-threatening conditions, and underscores the growing public health concern posed by multidrug-resistant strains, including methicillin-resistant S. aureus (MRSA). This article aims to provide an updated perspective on S. aureus-related infections, highlighting the main diseases linked to this pathogen, how the different cell types, virulence factors, and signaling molecules are involved in the immunopathogenesis, and the future perspectives to overcome the current challenges to treat the affected individuals.

Cytokine signalling in formation of neutrophil extracellular traps: Implications for health and diseases

Neutrophils, as essential component of the innate immune response, form a crucial part in the defence mechanisms through the release of extracellular traps (NETs). These web-like structures, composed of chromatin and antimicrobial proteins, are essential for the entrapment and inactivation of pathogens. However, either constitutive formation or inefficient clearance of NETs leads to adverse effects such as fibrosis, thrombosis, delayed wound healing and tissue damage in multiple diseases associated with sterile inflammation. This dichotomy casts NETs as both protective agents and harmful factors in several diseases such as autoimmune diseases, metabolic syndromes, systemic infections, and malignancies. Besides microbes and their products, variety of stimulants including pro-inflammatory cytokines induce NETs. The complex interactions and cross talk among the pro-inflammatory cytokines including IL-8, IL-6, GM-CSF, TNF-α, IFNs, and IL-1β activate neutrophils to form NETs and also contributes to a vicious circle of inflammatory cascade, leading to increased inflammation, oxidative stress, and thrombotic events. Emerging evidence indicates that the dysregulated cytokine milieus in diseases, such as diabetes mellitus, obesity, atherosclerosis, stroke, rheumatoid arthritis, and systemic lupus erythematosus, potentiate NETs release, thereby promoting disease development. Thus, neutrophils represent both critical effectors and potential therapeutic targets, underscoring their importance in the context of cytokine-mediated therapies for a spectrum of diseases. In the present review, we describe various cytokines and associated signalling pathways activating NETs formation in different human pathologies. Further, the review identifies potential strategies to pharmacologically modulate cytokine pathways to reduce NETs.

Nitric oxide synthase inhibitors reduce the formation of neutrophil extracellular traps and alleviate airway inflammation in the mice model of asthma

Asthma, a widespread chronic inflammatory disease can contribute to different degrees of lung function damage. The objective of this study is to explore the potential effects of nitric oxide synthase (NOS) inhibitors in asthma using mice model induced by ovalbumin (OVA). BALB/c mice were treated with OVA to establish an asthma model. Mice were intranasally challenged with different NOS inhibitors and analyzed the impact of NOS inhibitors on the lung tissues and bronchoalveolar lavage fluid (BALF). Histopathological analysis was performed by Periodic Acid-Schiff (PAS) staining. Airway reactivity was assessed using methacholine challenge testing. The concentrations of nitric oxide (NO), Neutrophil extracellular traps (NETs), and cytokines were determined by enzyme-linked immunosorbent assay (ELISA) assay. NOS inhibitors effectively improved airway inflammation and reduced airway hyperresponsiveness. In addition, NOS inhibitors decreased the concentrations of NO, NETs, and inflammation in the airway and BALF. The decreased NO production and reduced NET formation in the lung indicate that NOS inhibitors inhibit the process of NET release to alleviate asthma.

Factor XIII-A Transglutaminase Contributes to Neutrophil Extracellular Trap (NET)-mediated Fibrin(ogen) Network Formation and Crosslinking

BACKGROUND

 Neutrophil extracellular traps can contribute to thrombosis via stabilization of fibrin network, which is normally conducted by plasma transglutaminase, Factor XIII-A as part of coagulation cascade. The possible presence and activity of FXIII-A in neutrophils or during NETosis are unknown. Here, we investigated potential presence of FXIII-A in neutrophils and participation in NET-fibrin(ogen) interaction in vitro. METHODS:  Data mining of human and mouse F13A1/F13a1 mRNA expression in whole-body scRNA sequence atlases was conducted. F13a1 mRNA and protein expression was assessed in isolated mouse bone marrow neutrophils. NETosis was induced using 12-phorbol 13-myristate acetate (PMA), and the transglutaminase activity was assessed with 5-(biotinamido)pentylamine incorporation to plasma fibronectin and a fluorescence-fibrin(ogen)-based activity assay using ATTO488-Cadaverine. Externalization of FXIII-A and its interaction with neutrophil extracellular trap (NET) markers, namely, decondensed DNA, CitH3, and MPO, were examined with immunofluorescence microscopy. NET-fibrin(ogen) interaction was investigated with and without serum and/or transglutaminase inhibitor, NC9. Effect of soluble fibrinogen and fibrin(ogen) network on NETosis was also assessed.

RESULTS

 Data mining of RNAseq atlases showed F13A1/F13a1 expression in adipose tissue, blood, and bone marrow neutrophils. mRNA expression and protein production were confirmed in isolated neutrophils where expression was comparable to that of macrophages and monocytes. FXIII-A was externalized and active as a transglutaminase and colocalized with NET markers during NETosis. FXIII-A transglutaminase activity promoted NET-fibrin(ogen) interaction and entrapment of neutrophils within fibrin(ogen) matrix. Soluble fibrinogen or fibrin(ogen) network did not induce NETosis.

CONCLUSION

 This study identifies neutrophils as a source of FXIII-A and suggests its role in stabilizing NET-fibrin(ogen) matrix structures.

Neutrophil extracellular traps promote pre-metastatic niche formation in the omentum by expanding innate-like B cells that express IL-10

Disseminated cancer cells in the peritoneal fluid often colonize omental fat-associated lymphoid clusters but the mechanisms are unclear. Here, we identify that innate-like B cells accumulate in the omentum of mice and women with early-stage ovarian cancer concomitantly with the extrusion of chromatin fibers by neutrophils called neutrophil extracellular traps (NETs). Studies using genetically modified NET-deficient mice, pharmacologic inhibition of NETs, and adoptive B cell transfer show that NETs induce expression of the chemoattractant CXCL13 in the pre-metastatic omentum, stimulating recruitment of peritoneal innate-like B cells that in turn promote expansion of regulatory T cells and omental metastasis through producing interleukin (IL)-10. Ex vivo studies show that NETs elicit IL-10 production in innate-like B cells by inactivating SHP-1, a phosphatase that inhibits B cell activation pathways, and by generating reactive oxygen species. These findings reveal that NETs alter immune cell dynamics in the pre-metastatic omentum, rendering this niche conducive for colonization.

Tamm-Horsfall protein augments neutrophil NETosis during urinary tract infection

Urinary neutrophils are a hallmark of urinary tract infection (UTI), yet the mechanisms governing their activation, function, and efficacy in controlling infection remain incompletely understood. Tamm-Horsfall glycoprotein (THP), the most abundant protein in urine, uses terminal sialic acids to bind an inhibitory receptor and dampen neutrophil inflammatory responses. We hypothesized that neutrophil modulation is an integral part of THP-mediated host protection. In a UTI model, THP-deficient mice showed elevated urinary tract bacterial burdens, increased neutrophil recruitment, and more severe tissue histopathological changes compared with WT mice. Furthermore, THP-deficient mice displayed impaired urinary NETosis during UTI. To investigate the effect of THP on NETosis, we coupled in vitro fluorescence-based NET assays, proteomic analyses, and standard and imaging flow cytometry with peripheral human neutrophils. We found that THP increases proteins involved in respiratory chain, neutrophil granules, and chromatin remodeling pathways; enhances NETosis in an ROS-dependent manner; and drives NET-associated morphologic features including nuclear decondensation. These effects were observed only in the presence of a NETosis stimulus and could not be solely replicated with equivalent levels of sialic acid alone. We conclude that THP is a critical regulator of NETosis in the urinary tract, playing a key role in host defense against UTI.

Neutrophil Extracellular Traps (NETs) as a Potential Target for Anti-Aging: Role of Therapeutic Apheresis

Neutrophil extracellular traps (NETs) are large structures composed of chromatin, histones and granule-derived proteins released extracellularly by neutrophils. They are generally considered to be a part of the antimicrobial defense strategy, preventing the dissemination of pathogens. However, overproduction of NETs or their ineffective clearance can drive various pathologies, many of which are associated with advanced age and involve uncontrolled inflammation, oxidative, cardiovascular and neurodegenerative stress as underlying mechanisms. Targeting NETs in the elderly as an anti-aging therapy seems to be a very attractive therapeutic approach. Therapeutic apheresis with a specific filter to remove NETs could be a promising strategy worth considering.

Neutrophil Extracellular Traps Participate in the Pathogenesis of Lupus Through S100A10-Mediated Regulatory T-Cell Differentiation and Functional Abnormalities

In systemic lupus erythematosus (SLE), neutrophil dysregulation and neutrophil extracellular traps (NETs) formation contribute to disease pathogenesis, potentially worsening the autoimmune response. Although research indicates NETs' involvement in various autoimmune conditions, their relationship with regulatory T cells (Tregs) in SLE remains elusive. In this study, in vivo experiments were involved in administering NET injections to C57BL/6 and MRL/Ipr mice. In vitro, a co-culture system facilitated interaction between Tregs and NETs. Proteomic analysis elucidated NET composition, while RNA sequencing delineated their impact on Treg differentiation. We demonstrated that increased NET levels correlate inversely with Treg abundance in SLE patients, influencing both their proportion and functionality. NET administration reduced Treg levels and induced lupus-like symptoms in C57BL/6 mice, exacerbating symptoms in MRL/Ipr mice. DNase I treatment mitigated NET effects, restoring Treg levels and alleviating symptoms. RNA sequencing revealed altered gene expression in naïve CD4+ T cells exposed to NETs. Additionally, proteomic analysis showed S100A10 protein changes between SLE patients and healthy controls, hindering Treg differentiation. NETs influence TLR-4 of naïve CD4+ T cells via S100A10, thereby modulating Treg proportion and functionality. These findings highlight the critical role of NETs in Treg differentiation in SLE, suggesting that targeting NETs may provide a novel therapeutic approach.

Effect of neutrophils on tumor immunity and immunotherapy resistance with underlying mechanisms

Neutrophils are key mediators of the immune response and play essential roles in the development of tumors and immune evasion. Emerging studies indicate that neutrophils also play a critical role in the immunotherapy resistance in cancer. In this review, firstly, we summarize the novel classification and phenotypes of neutrophils and describe the regulatory relationships between neutrophils and tumor metabolism, flora microecology, neuroendocrine and tumor therapy from a new perspective. Secondly, we review the mechanisms by which neutrophils affect drug resistance in tumor immunotherapy from the aspects of the immune microenvironment, tumor antigens, and epigenetics. Finally, we propose several promising strategies for overcoming tumor immunotherapy resistance by targeting neutrophils and provide new research ideas in this area.

Leishmania amazonensis-derived extracellular vesicles (EVs) induce neutrophil extracellular traps (NETs)

Neutrophils interact with Leishmania when the sandfly vector inoculates these parasites in the host with saliva and promastigotes-derived extracellular vesicles (EVs). It has been shown that this co-injection induces inflammation and exacerbates leishmaniasis lesions. EVs are a heterogeneous group of vesicles released by cells that play a crucial role in intercellular communication. Neutrophils are among the first cells to interact with the parasites and release neutrophil extracellular traps (NETs) that ensnare and kill the promastigotes. Here, we show that Leishmania amazonensis EVs induce NET formation and identify molecular mechanisms involved. We showed the requirement of neutrophils' toll-like receptors for EVs-induced NET. EVs carrying the virulence factors lipophosphoglycan and the zinc metalloproteases were endocytosed by some neutrophils and snared by NETs. EVs-induced NET formation required reactive oxygen species, myeloperoxidase, elastase, peptidyl arginine deiminase, and Ca++. The proteomic analysis of the EVs cargo revealed 1,189 proteins; the 100 most abundant identified comprised some known Leishmania virulent factors. Importantly, L. amazonensis EVs-induced NETs lead to the killing of promastigotes and could participate in the exacerbated inflammatory response induced by the EVs, which may play a role in the pathogenesis process.

Fantastic proteins and where to find them - histones, in the nucleus and beyond

Animal genomes are packaged into chromatin, a highly dynamic macromolecular structure of DNA and histone proteins organised into nucleosomes. This accommodates packaging of lengthy genomic sequences within the physical confines of the nucleus while also enabling precise regulation of access to genetic information. However, histones existed before chromatin and have lesser-known functions beyond genome regulation. Most notably, histones are potent antimicrobial agents, and the release of chromatin to the extracellular space is a defence mechanism nearly as ancient and widespread as chromatin itself. Histone sequences have changed very little throughout evolution, suggesting the possibility that some of their 'non-canonical' functions are at play in parallel or in concert with their genome regulatory functions. In this Review, we take an evolutionary perspective of histone, nuclear chromatin and extracellular chromatin biology and describe the known extranuclear and extracellular functions of histones. We detail molecular mechanisms of chromatin release and extracellular chromatin sensing, and we discuss their roles in physiology and disease. Finally, we present evidence and give a perspective on the potential of extracellular histones to act as bioactive, cell modulatory factors.

The Janus-faced nature of complement in hemodialysis: interplay between complement, inflammation, and bioincompatibility unveiling a self-amplifying loop contributing to organ damage

In hemodialysis (HD), complement activation, bioincompatibility, and inflammation are intricately intertwined. In the 1970s, as HD became a routine therapy, the observation of complement pathway activation and transient leukopenia by cellulosic dialysis membranes triggered the bioincompatibility debate and its clinical relevance. Extensive deliberations have covered definitions, assessment markers, scope, and long-term clinical consequences of membrane-dependent bioincompatibility reactions. While complement pathways' interplay with coagulation and inflammation has been delineated, HD's focus has primarily been on developing more biocompatible membranes using advanced technologies. Recent advances and understanding of the current HD delivery mode (4-hour sessions, thrice weekly) suggest that factors beyond membrane characteristics play a significant role, and a more complex, multifactorial picture of bioincompatibility is emerging. Chronic activation of the complement system and persistent low-grade "uremic inflammation" in chronic kidney disease (CKD) and HD lead to premature inflammaging of the kidney, resembling aging in the general population. Cellular senescence, modulated by complement activation and the uremic milieu, contributes to chronic inflammaging. Additionally, the formation of neutrophil extracellular traps (NETs, process of NETosis) during HD and their biological activity in the interdialytic period can lead to dialysis-induced systemic stress. Thus, complement-inflammation manifestations in HD therapies extend beyond traditional membrane-related bioincompatibility consequences. Recent scientific knowledge is reshaping strategies to mitigate detrimental consequences of bioincompatibility, both technologically and in HD therapy delivery modes, to improve dialysis patient outcomes.

Entamoeba histolytica-induced NETs are highly cytotoxic on hepatic and colonic cells due to serine proteases and myeloperoxidase activities

During intestinal and liver invasion by the protozoan parasite Entamoeba histolytica, extensive tissue destruction linked to large neutrophil infiltrates is observed. It has been proposed that microbicidal components of neutrophils are responsible for the damage, however, the mechanism by which they are released and act in the extracellular space remains unknown. In previous studies, we have shown that E. histolytica trophozoites induce NET formation, leading to the release of neutrophil granule content into extruded DNA. In this work, we evaluate the possible participation of NETs in the development of amoeba-associated pathology and analyze the contribution of anti-microbial components of the associated granules. E. histolytica-induced NETs were isolated and their effect on the viability and integrity of HCT 116 colonic and Hep G2 liver cultures were evaluated. The results showed that simple incubation of cell monolayers with purified NETs for 24 h resulted in cell detachment and death in a dose-dependent manner. The effect was thermolabile and correlated with the amount of DNA and protein present in NETs. Pretreatment of NETs with specific inhibitors of some microbicidal components suggested that serine proteases, are mostly responsible for the damage caused by NETs on HCT 116 cells, while the MPO activity was the most related to Hep G2 cells damage. Our study also points to a very important role of DNA as a scaffold for the activity of these proteins. We show evidence of the development of NETs in amoebic liver abscesses in hamsters as a preamble to evaluate their participation in tissue damage. In conclusion, these studies demonstrate that amoebic-induced NETs have potent cytotoxic effects on target cells and, therefore, may be responsible for the intense damage associated with tissue invasion by this parasite.

Regulation of neutrophil associated RNASET2 expression in rheumatoid arthritis

Neutrophils (PMNs) are key players of innate immune responses through the release of cytoplasmic granule content and the formation of neutrophil extracellular traps (NETs). RNASET2 is an acidic ribonuclease, recently proposed as an alarmin signal associated with inflammatory responses. Here we show that, along the neutrophil maturation cascade, RNASET2 is expressed in segmented and mature PMNs. In human PMNs, RNASET2 colocalized with primary and tertiary granules and was found to be associated with NETs following PMA or Nigericin stimulation. Similarly, activation of PMNs by soluble immune complexes, a hallmark of several autoimmune diseases, also induced RNASET2-associated NETs. Genome-wide association studies recently identified RNASET2 among a cluster of genes associated with increased susceptibility to develop autoimmune diseases, including rheumatoid arthritis (RA). RNASET2 was found expressed by PMNs and macrophages infiltrating inflamed joints in a murine model of RA (K/BxN Serum-Transfer-Induced Arthritis, STIA), by immunostaining. Similar results were found in synovial biopsies of RA patients with active disease. In addition, we demonstrate that RNASET2 circulating levels correlated with the onset and the severity of disease in two mouse models of inflammatory arthritis, STIA and CIA (Collagen-Induced Arthritis) and in serum of RA patients. These results show that PMNs are an important source of RNASET2 and that its circulating levels are associated with RA development suggesting a role for RNASET2 in the pathogenesis of immune-mediated diseases.

Peptidyl arginine deiminase-4 inhibitor ameliorates pulmonary fibrosis through positive regulation of developmental endothelial locus-1

Recurring lung injury, chronic inflammation, aberrant tissue repair and impaired tissue remodelling contribute to the pathogenesis of pulmonary fibrosis (PF). Neutrophil extracellular traps (NETs) are released by activated neutrophils to trap, immobilise and kill invading pathogen and is facilitated by peptidyl arginine deiminase-4 (PAD-4). Dysregulated NETs release and abnormal PAD-4 activation plays a crucial role in activating pro-fibrotic events in PF. Developmental endothelial locus-1 (Del-1), expressed by the endothelial cells of lungs and brain acts as an endogenous inhibitor of inflammation and fibrosis. We have hypothesised that PAD-4 inhibitor exerts anti-inflammatory and anti-fibrotic effects in mice model of PF. We have also hypothesised by PAD-4 regulated the transcription of Del-1 through co-repression and its inhibition potentiates anti-fibrotic effects of Del-1. In our study, the PAD-4 inhibitor chloro-amidine (CLA) demonstrated anti-NETotic and anti-inflammatory effects in vitro in differentiated HL-60 cells. In a bleomycin-induced PF mice model, CLA administration in two doses (3 mg/kg, I.P and 10 mg/kg, I.P) improved lung function, normalized bronchoalveolar lavage fluid parameters, and attenuated fibrotic events, including markers of extracellular matrix and epithelial-mesenchymal transition. Histological analyses confirmed the restoration of lung architecture and collagen deposition with CLA treatment. ELISA, IHC, IF, RT-PCR, and immunoblot analysis supported the anti-NETotic effects of CLA. Furthermore, BLM-induced PF reduced Del-1 and p53 expression, which was normalized by CLA treatment. These findings suggest that inhibition of PAD-4 results in amelioration of PF in animal model and may involve modulation of Del-1 and p53 pathways, warranting further investigation.

Cytoplasmic DNA and AIM2 inflammasome in RA: where they come from and where they go?

Rheumatoid arthritis is a chronic autoimmune disease of undetermined etiology characterized by symmetric synovitis with predominantly destructive and multiple joint inflammation. Cytoplasmic DNA sensors that recognize protein molecules that are not themselves or abnormal dsDNA fragments play an integral role in the generation and perpetuation of autoimmune diseases by activating different signaling pathways and triggering innate immune signaling pathways and host defenses. Among them, melanoma deficiency factor 2 (AIM2) recognizes damaged DNA and double-stranded DNA and binds to them to further assemble inflammasome, initiating the innate immune response and participating in the pathophysiological process of rheumatoid arthritis. In this article, we review the research progress on the source of cytoplasmic DNA, the mechanism of assembly and activation of AIM2 inflammasome, and the related roles of other cytoplasmic DNA sensors in rheumatoid arthritis.

Canto F, Fraga-Junior VDS, Eustáquio Lopes M, Gomes Vaz L, Pessenda G, Paun A, Freitas-Mesquita AL, Meyer-Fernandes JR, Boroni M, Bellio M, Batista Menezes G, Brzostowski J, Mottram J, Sacks D, Lima APCA, Saraiva EM. Functional plasticity shapes neutrophil response to Leishmania major infection in susceptible and resistant strains of mice

Neutrophils rapidly infiltrate sites of infection and possess several microbicidal strategies, such as neutrophil extracellular traps release and phagocytosis. Enhanced neutrophil infiltration is associated with higher susceptibility to Leishmania infection, but neutrophil effector response contribution to this phenotype is uncertain. Here, we show that neutrophils from susceptible BALB/c mice (B/c) produce more NETs in response to Leishmania major than those from resistant C57BL/6 mice (B6), which are more phagocytic. The absence of neutrophil elastase contributes to phagocytosis regulation. Microarray analysis shows enrichment of genes involved in NET formation (mpo, pi3kcg, il1b) in B/c, while B6 shows upregulation of genes involved in phagocytosis and cell death (Arhgap12, casp9, mlkl, FasL). scRNA-seq in L. major-infected B6 showed heterogeneity in the pool of intralesional neutrophils, and we identified the N1 subset as the putative subpopulation involved with phagocytosis. In vivo, imaging validates NET formation in infected B/c ears where NETing neutrophils were mainly uninfected cells. NET digestion in vivo augmented parasite lymphatic drainage. Hence, a balance between NET formation and phagocytosis in neutrophils may contribute to the divergent phenotype observed in these mice.

Identification and validation of diagnostic genes associated with neutrophil extracellular traps of type 2 diabetes mellitus

Background

Neutrophil extracellular traps (NETs) cause delayed wound closed up in type 2 diabetes mellitus (T2DM), but the specific regulatory mechanism of NETs-related genes (NETs-RGs) in T2DM is unclear.

Methods

We acquired GSE21321 and GSE15932 datasets from gene expression omnibus (GEO) database. First, differentially expressed genes (DEGs) between T2DM and control samples of GSE21321 dataset were sifted out by differential expression analysis. NETs scores were calculated for all samples in GSE21321 dataset, and key module genes associated with NETs scores were screened by constructing co-expression network. Then, DEGs and key module genes were intersected to yield intersection genes, and candidate genes were identified by constructing a protein protein interaction (PPI) network. Least absolute shrinkage and selection operator (LASSO) regression analysis was implemented on candidate genes to screen out diagnostic genes, and they were subjected to single sample gene set enrichment analysis (ssGSEA). Finally, immune characteristic analysis was carried out, and we constructed the gene-drug and transcription factor (TF)-miRNA-mRNA networks. Besides, we validated the expression of diagnostic genes by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

In total, 23 candidate genes were gained by PPI analysis. The 5 diagnostic genes, namely, inter-trypsin inhibitor heavy chain 3 (ITIH3), fibroblast growth factor 1 (FGF1), neuron cell adhesion molecule (NRCAM), advanced glycosylation end-product-specific receptor (AGER), and calcium voltage-gated channel subunit alpha1 C (CACNA1C), were identified via LASSO analysis, and they were involved in carboxylic acid transport, axonogenesis, etc. M2 Macrophage, Monocyte, Natural killer (NK) cell, and Myeloid dendritic cells (DC) were remarkably different between T2DM and control samples. Diagnostic genes had the strongest and the most significant positive correlation with B cells. The gene-drug network included CACNA1C-Isradipine, CACNA1C-Benidipine and other relationship pairs. Totally 76 nodes and 44 edges constituted the TF-miRNA-mRNA network, including signal transducer and activator of transcription 1(STAT1) -hsa-miR-3170-AGER, CCCTC-binding factor (CTCF)-hsa-miR-455-5p-CACNA1C, etc. Moreover, qRT-PCR suggested that the expression trends of FGF1 and AGER were in keeping with the results of bioinformatic analysis. FGF1 and AGER were markedly regulated downwards in the T2DM group.

Conclusion

Through bioinformatic analysis, we identified NETs-related diagnostic genes (ITIH3, FGF1, NRCAM, AGER, CACNA1C) in T2DM, and explored their mechanism of action from different aspects, providing new ideas for the studies related to diagnosis and treatment of T2DM.

Zinc Supplementation Reduces the Formation of Neutrophil Extracellular Traps by Decreasing the Expression of Peptidyl Arginine Deiminase 4

SCOPE

Neutrophils play a decisive role during the immediate defense against infections. However, as observed during rheumatoid arthritis, activated neutrophils can also cause tissue damage. Previous studies indicate that zinc supplementation may alter certain neutrophil functions. However, precise underlying mechanisms and possible effects of zinc deficiency remain incompletely understood. The objective of this study is to investigate the effects of changes in zinc status on formation of neutrophil extracellular traps (NETs) and other fundamental neutrophil functions.

METHODS AND RESULTS

Interleukin (IL)-17 and tumor necrosis factor (TNF)-α are used to simulate the inflammatory environment observed in autoimmune diseases. The study analyzes the impact of the zinc status on NETs release, using a fluorescence plate reader, and on the expression of peptidylarginine deiminase 4 (PAD4), S100A8/A9, and certain cytokines by PCR and western blot. These results show that zinc supplementation significantly reduces NETs formation and downregulates PAD4 protein expression. Zinc supplementation results in increased protein expression of interleukin-1 receptor antagonist (IL-1RA) and IL-8 in stimulated cells.

CONCLUSION

The results suggest that changes in extracellular zinc availability may influence the functions of neutrophils. Therefore, maintaining an appropriate zinc level is advisable for preserving innate immunity and to prevent hyper-activation of neutrophils.

Sex Differences of Neutrophil Extracellular Traps on Lipopolysaccharide-Stimulated Human Neutrophils

Objective: Sex differences exist in sepsis, but the commitment of neutrophils to these differences remains unclear. Neutrophil extracellular traps (NETs) function to remove pathogens, yet excessive NETs release can contribute to organ damage. This study explores effects of the gender hormones on endotoxin-induced NETs using neutrophils from both male and female sources. Methods: Blood samples were collected from healthy volunteers. Isolated neutrophils were seeded in collagen-coated cell culture plates, and NETs were induced by lipopolysaccharide (LPS) treatment. After 15 minutes of LPS treatment, 17β-estradiol (0.03-272.4 ng/mL), testosterone enanthate (0.01-10 ng/mL), dimethyl sulfoxide, or ethanol (vehicle control) was added to the plates. These were incubated for three hours at 37°C with 5% CO2. Neutrophil extracellular traps formation was assessed using immunofluorescence staining. Results: Lipopolysaccharide-induced NETs formation was significantly greater in females than in males. In male-derived neutrophils, 17β-estradiol at above the blood concentrations significantly suppressed LPS-induced NETs. No effect was seen while using testosterone enanthate to NETs at any concentration. In female-derived neutrophils, 17β-estradiol, which was near to the highest concentration of non-pregnant women's blood, tended to increase NETs. Testosterone enanthate, which was near to female blood concentration, significantly promoted NETs. Conclusions: Sex differences existed in LPS-induced NETs of human neutrophil. In males, high concentrations of 17β-estradiol administration may have a suppressive effect on excessive NETs during infection. In females, endogenous gender hormones may promote NETs during infection. Sex differences in neutrophils may need to be considered in organ damage owing to NETs excess such as sepsis.

Neutrophils and extracellular traps in crystal-associated diseases

Crystalline material can cause a multitude of acute and chronic inflammatory diseases, such as gouty arthritis, silicosis, kidney disease, and atherosclerosis. Crystals of various types are thought to cause similar inflammatory responses, including the release of proinflammatory mediators and formation of neutrophil extracellular traps (NETs), processes that further promote necroinflammation and tissue damage. It has become apparent that the intensity of inflammation and the related mechanisms of NET formation and neutrophil death in crystal-associated diseases can vary depending on the crystal type, amount, and site of deposition. This review details new mechanistic insights into crystal biology, highlights the differential effects of various crystals on neutrophils and extracellular trap (ET) formation, and discusses treatment strategies and potential future approaches for crystal-associated disorders.

HL-60 cells as a valuable model to study LPS-induced neutrophil extracellular traps release

Neutrophil Extracellular Traps (NETs) present a paradoxical role in infectious diseases, contributing to both immunity and pathogenesis. The complex nature of this process necessitates further characterization to elucidate its clinical implications. However, studying NETs faces challenges with primary neutrophils due to their heterogeneity, short lifespan, and lack of adequate cryopreservation. Researchers often turn to alternative models, such as differentiated HL-60 cells (dHL-60). This study explored LPS-induced NETs formation in dHL-60 cells, revealing significant responses to LPS from Pseudomonas aeruginosa, although significantly lower than primary neutrophils. Moreover, Spleen Tyrosine Kinase (SYK) inhibition with R406, the active metabolite of the drug Fostamatinib, previously demonstrated to suppress NETs in primary neutrophils, effectively reduced NETs release in dHL-60 cells. dHL-60 cells, offering easier manipulation, consistent availability, and no donor variability in functional responses, possess characteristics suitable for high-throughput studies evaluating NETosis. Overall, dHL-60 cells may be a valuable in vitro model for deciphering the molecular mechanisms of NETosis in response to LPS, contributing to our available tools for understanding this complex immune process.

NETosis of psoriasis: a critical step in amplifying the inflammatory response

NETosis, a regulated form of neutrophil death, is crucial for host defense against pathogens. However, the release of neutrophil extracellular traps (NETs) during NETosis can have detrimental effects on surrounding tissues and contribute to the pro-inflammatory response, in addition to their role in controlling microbes. Although it is well-established that the IL-23-Th17 axis plays a key role in the pathogenesis of psoriasis, emerging evidence suggests that psoriasis, as an autoinflammatory disease, is also associated with NETosis. The purpose of this review is to provide a comprehensive understanding of the mechanisms underlying NETosis in psoriasis. It will cover topics such as the formation of NETs, immune cells involved in NETosis, and potential biomarkers as prognostic/predicting factors in psoriasis. By analyzing the intricate relationship between NETosis and psoriasis, this review also aims to identify novel possibilities targeting NETosis for the treatment of psoriasis.

The role of P-selectin/PSGL-1 in regulating NETs as a novel mechanism in cerebral ischemic injury

In recent years, substantial advancements have been made in understanding the pathophysiology of ischemic stroke. Despite these developments, therapeutic options for cerebral ischemia remain limited due to stringent time windows and various contraindications. Consequently, there has been a concentrated effort to elucidate the underlying mechanisms of cerebral ischemic injury. Emerging research indicates that neutrophil extracellular traps (NETs) exacerbate inflammation and damage in ischemic brain tissue, contributing to neuronal cell death. The inhibition of NETs has shown potential in preventing thrombosis and the infiltration of immune cells. Central to the formation of NETs are P-selectin and its ligand, P-selectin glycoprotein ligand-1 (PSGL-1), which represent promising therapeutic targets. This review explores the detrimental impact of P-selectin, PSGL-1, and NETs on cerebral ischemia. Additionally, it delineates the processes by which P-selectin and PSGL-1 stimulate NETs production and provides evidence that blocking these molecules reduces NETs formation. This novel insight highlights a potential therapeutic avenue that warrants further investigation by researchers in the field.

SzM protein of Streptococcus equi ssp. zooepidemicus triggers the release of neutrophil extracellular traps depending on GSDMD

Streptococcus equissp.zooepidemicus (SEZ) is a crucial pathogen and contributes to various infections in numerous animal species. Swine streptococcicosis outbreak caused by SEZ has been reported in several countries in recent years. SzM protein is a cell membrane-anchored protein, which exhibits as an important virulence factor of SEZ. Effects of SzM protein on host innate immune need further study. Here, recombinant SzM (rSzM) protein of the SEZ was obtained, and mice were intraperitoneally injected with rSzM protein. We discovered that rSzM protein can recruit neutrophils into the injected site. In further study, neutrophils were isolated and treated with rSzM protein, NETs release were triggered by rSzM protein independently, and GSDMD protein was promoted-expressed and activated. In order to investigate the role of GSDMD in NETs formation, neutrophils isolated from WT mice and GSDMD-/- mice were treated with rSzM protein. The results showed that GSDMD deficiency suppressed the NETs release. In conclusion, SzM protein of SEZ can trigger the NETs release in a GSDMD-depending manner.

Reorganization of the actin cytoskeleton during the formation of neutrophil extracellular traps (NETs)

We analyzed actin cytoskeleton alterations during NET extrusion by neutrophil-like dHL-60 cells and human neutrophils in the absence of DNase1 containing serum to avoid chromatin degradation and microfilament disassembly. NET-formation by dHL-60 cells and neutrophils was induced by Ionomycin or phorbol-12-myristat-13-acetate (PMA). Subsequent staining with anti-actin and TRITC-phalloidin showed depolymerization of the cortical F-actin at spatially confined areas, the NET extrusion sites, effected by transient activation of the monooxygenase MICAL-1 supported by the G-actin binding proteins cofilin, profilin, thymosin ß4 and probably the F-actin fragmenting activity of gelsolin and/or its fragments, which also decorated the formed NETs. MICAL-1 itself appeared to be proteolyzed by neutrophil elastase possibly to confine its activity to the NET-extrusion area. The F-actin oxidization activity of MICAL-1 is inhibited by Levosimendan leading to reduced NET-formation. Anti-gasdermin-D immunohistochemistry showed a cytoplasmic distribution in non-stimulated cells. After stimulation the NET-extrusion pore displayed reduced anti-gasdermin-D staining but accumulated underneath the plasma membrane of the remaining cell body. A similar distribution was observed for myosin that concentrated together with cortical F-actin along the periphery of the remaining cell body suggesting force production by acto-myosin interactions supporting NET expulsion as indicated by the inhibitory action of the myosin ATPase inhibitor blebbistatin. Isolated human neutrophils displayed differences in their content of certain cytoskeletal proteins. After stimulation neutrophils with high gelsolin content preferentially formed "cloud"-like NETs, whereas those with low or no gelsolin formed long "filamentous" NETs.

Neutrophils display distinct post-translational modifications in response to varied pathological stimuli

Neutrophils play a vital role in the innate immunity by perform effector functions through phagocytosis, degranulation, and forming extracellular traps. However, over-functioning of neutrophils has been associated with sterile inflammation such as Type 2 Diabetes, atherosclerosis, cancer and autoimmune disorders. Neutrophils exhibiting phenotypical and functional heterogeneity in both homeostatic and pathological conditions suggests distinct signaling pathways are activated in disease-specific stimuli and alter neutrophil functions. Hence, we examined mass spectrometry based post-translational modifications (PTM) of neutrophil proteins in response to pathologically significant stimuli, including high glucose, homocysteine and bacterial lipopolysaccharides representing diabetes-indicator, an activator of thrombosis and pathogen-associated molecule, respectively. Our data revealed that these aforesaid stimulators differentially deamidate, citrullinate, acetylate and methylate neutrophil proteins and align to distinct biological functions associated with degranulation, platelet activation, innate immune responses and metabolic alterations. The PTM patterns in response to high glucose showed an association with neutrophils extracellular traps (NETs) formation, homocysteine induced proteins PTM associated with signaling of systemic lupus erythematosus and lipopolysaccharides induced PTMs were involved in pathways related to cardiomyopathies. Our study provides novel insights into neutrophil PTM patterns and functions in response to varied pathological stimuli, which may serve as a resource to design therapeutic strategies for the management of neutrophil-centred diseases.

Association of neutrophil extracellular trap levels with Raynaud's phenomenon, glomerulonephritis and disease index score in SLE patients from Brazil

Neutrophil extracellular traps (NETs) are cell-extruded DNA strands coated with neutrophils' nuclear proteins and enzymes from cytotoxic granules, produced by NETosis, a cell death pathway. They perform an important defensive role in innate immunity, but their increased production and/or inefficient degradation expose new antigens, such as DNA or citrullinated histone peptides, triggering autoimmunity. This study aimed to access possible associations between serum NETs levels with epidemiological, clinical, and serological data from a well-characterized SLE Brazilian patients' cohort. NET levels were evaluated in one hundred seventy serum samples of patients with Systemic Lupus Erythematosus (SLE) using an Immunoassay. Univariate and multivariate binary logistic regression used clinical patients' data as independent variables. Parametric and non-parametric tests compared log10 base serum NET levels transformed between patients' groups. SLE patients were also dichotomized into "High serum NET levels" and "Low serum NET levels" groups. All analyses were performed in R language 4.1.2, and p < 0.05 were considered significant. Increased susceptibility for high serum NET levels was observed in SLE patients with Raynaud's phenomenon (OR = 2.30, 95 % CI = 1.06-5.21 and p = 0.039), independently of any other risk factor. Also, SLE patients with Raynaud's phenomenon presented higher mean NET serum levels (mean = -0.13 vs. -0.51, p = 0.01). In addition, higher mean NET serum levels were associated with glomerulonephritis (mean = -0.45 vs. -0.12, p = 0.03). Ultimately, the SLEDAI index scored higher in the high NETs serum levels group (median = 2.0 vs. 0.0, p = 6 × 10-3). The formation of NETs might be implicated in Raynaud's phenomenon, glomerulonephritis, and disease index score in SLE patients. Our results highlight the importance of serum NET levels as a possible therapeutical target to modulate the clinical course of SLE.

Lidocaine effects on neutrophil extracellular trapping and angiogenesis biomarkers in postoperative breast cancer patients with different anesthesia methods: a prospective, randomized trial

BACKGROUND

Anesthesia techniques and drug selection may influence tumor recurrence and metastasis. Neutrophil extracellular trapping (NETosis), an immunological process, has been linked to an increased susceptibility to metastasis in individuals with tumors. Furthermore, recurrence may be associated with vascular endothelial growth factor A (VEGF-A), a mediator of angiogenesis. This study investigates the impact of lidocaine (combined with sevoflurane or propofol anesthesia ) during breast cancer surgery inhibits the expression of biomarkers associated with metastasis and recurrence (specifically H3Cit, NE, MPO, MMP-9 and VEGF-A).

METHODS

We randomly assigned 120 women undergoing primary or invasive breast tumor resection to receive one of four anesthetics: sevoflurane (S), sevoflurane plus i.v. lidocaine (SL), propofol (P), and propofol plus i.v. lidocaine (PL). Blood samples were collected before induction and 3 h after the operation. Biomarkers associated with NETosis (citrullinated histone H3 [H3Cit], myeloperoxidase [MPO], and neutrophil elastase [NE]) and angiogenesis were quantified using enzyme-linked immunosorbent assays.

RESULTS

Patient and breast tumor characteristics, along with perioperative management, did not differ between study groups. In intra-group comparisons, S and P groups demonstrated a statistically significant increase in post-operative MPO (S group: 10.39[6.89-17.22] vs. 14.31[8.55-20.87] ng ml-1, P = 0.032; P group: 9.45[6.73-17.37] vs. 14.34[9.87-19.75] ng ml-1, P = 0.035)and NE(S group: 182.70[85.66-285.85] vs. 226.20[91.85-391.65] ng ml-1, P = 0.045; P group: 154.22[97.31-325.30] vs. 308.66[132.36-483.57] ng ml-1, P = 0.037) concentrations compared to pre-operative measurements, whereas SL and PL groups did not display a similar increase. H3Cit, MMP-9, and VEGF-A concentrations were not significantly influenced by the anesthesia techniques and drugs.

CONCLUSIONS

Regardless of the specific technique employed for general anesthesia, there was no increase in the postoperative serum concentrations of MPO and NE after perioperative lidocaine infusion compared to preoperative serum concentrations. This supports the hypothesis that intravenous lidocaine during cancer surgery aimed at achieving a cure may potentially decrease the likelihood of recurrence. Further interpretation and discussion of clinical implications are warranted, emphasizing the significance of these findings in the context of cancer surgery and recurrence prevention.

CLINICAL TRIAL REGISTRATION

ChiCTR2300068563.

Neutrophil Extracellular Traps and Respiratory Disease

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

Composition and Function of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are intricate fibrous structures released by neutrophils in response to specific stimuli. These structures are composed of depolymerized chromatin adorned with histones, granule proteins, and cytosolic proteins. NETs are formed via two distinct pathways known as suicidal NETosis, which involves NADPH oxidase (NOX), and vital NETosis, which is independent of NOX. Certain proteins found within NETs exhibit strong cytotoxic effects against both pathogens and nearby host cells. While NETs play a defensive role against pathogens, they can also contribute to tissue damage and worsen inflammation. Despite extensive research on the pathophysiological role of NETs, less attention has been paid to their components, which form a unique structure containing various proteins that have significant implications in a wide range of diseases. This review aims to elucidate the components of NETs and provide an overview of their impact on host defense against invasive pathogens, autoimmune diseases, and cancer.

The Dual Role of Neutrophil Extracellular Traps (NETs) in Sepsis and Ischemia-Reperfusion Injury: Comparative Analysis across Murine Models

A better understanding of the function of neutrophil extracellular traps (NETs) may facilitate the development of interventions for sepsis. The study aims to investigate the formation and degradation of NETs in three murine sepsis models and to analyze the production of reactive oxygen species (ROS) during NET formation. Murine sepsis was induced by midgut volvulus (720° for 15 min), cecal ligation and puncture (CLP), or the application of lipopolysaccharide (LPS) (10 mg/kg body weight i.p.). NET formation and degradation was modulated using mice that were genetically deficient for peptidyl arginine deiminase-4 (PAD4-KO) or DNase1 and 1L3 (DNase1/1L3-DKO). After 48 h, mice were killed. Plasma levels of circulating free DNA (cfDNA) and neutrophil elastase (NE) were quantified to assess NET formation and degradation. Plasma deoxyribonuclease1 (DNase1) protein levels, as well as tissue malondialdehyde (MDA) activity and glutathione peroxidase (GPx) activity, were quantified. DNase1 and DNase1L3 in liver, intestine, spleen, and lung tissues were assessed. The applied sepsis models resulted in a simultaneous increase in NET formation and oxidative stress. NET formation and survival differed in the three models. In contrast to LPS and Volvulus, CLP-induced sepsis showed a decreased and increased 48 h survival in PAD4-KO and DNase1/1L3-DKO mice, when compared to WT mice, respectively. PAD4-KO mice showed decreased formation of NETs and ROS, while DNase1/1L3-DKO mice with impaired NET degradation accumulated ROS and chronicled the septic state. The findings indicate a dual role for NET formation and degradation in sepsis and ischemia-reperfusion (I/R) injury: NETs seem to exhibit a protective capacity in certain sepsis paradigms (CLP model), whereas, collectively, they seem to contribute adversely to scenarios where sepsis is combined with ischemia-reperfusion (volvulus).

Bovine neutrophils stimulated with Streptococcus uberis induce neutrophil extracellular traps, and cause cytotoxicity and transcriptional upregulation of inflammatory cytokine genes in bovine mammary epithelial cells

This study aimed to understand the response of neutrophils stimulated by Streptococcus uberis, a major cause of mastitis. It was found that the production of neutrophil extracellular traps (NETs) was induced in milk clots from mastitic milk produced by S. uberis-infected bovine udders. The release of NETs from neutrophils stimulated by S. uberis was investigated. Bovine neutrophils cocultured with S. uberis in vitro released the components of NETs, which contained extracellular DNA and elastase. Bovine mammary epithelial cells (BMECs) incubated in coculture supernatants containing components of NETs, caused cytotoxicity and transcriptional upregulation of inflammatory cytokines, including of interleukin (IL) -1β, tumor necrosis factor (TNF)-α, IL-6, and IL-8, in BMECs. These findings suggest that bovine neutrophils stimulated by S. uberis induce responses that cause exacerbated inflammation, such as NET formation, cytotoxicity against BMECs, and increased production of inflammatory cytokines. Bovine neutrophil responses stimulated by S. uberis could be involved in the progression of S. uberis-induced mastitis.

Tamm-Horsfall protein augments neutrophil NETosis during urinary tract infection

Urinary neutrophils are a hallmark of urinary tract infection (UTI), yet the mechanisms governing their activation, function, and efficacy in controlling infection remain incompletely understood. Tamm-Horsfall glycoprotein (THP), the most abundant protein in urine, uses terminal sialic acids to bind an inhibitory receptor and dampen neutrophil inflammatory responses. We hypothesized that neutrophil modulation is an integral part of THP-mediated host protection. In a UTI model, THP-deficient mice showed elevated urinary tract bacterial burdens, increased neutrophil recruitment, and more severe tissue histopathological changes compared to WT mice. Furthermore, THP-deficient mice displayed impaired urinary NETosis during UTI. To investigate the impact of THP on NETosis, we coupled in vitro fluorescence-based NET assays, proteomic analyses, and standard and imaging flow cytometry with peripheral human neutrophils. We found that THP increases proteins involved in respiratory chain, neutrophil granules, and chromatin remodeling pathways, enhances NETosis in an ROS-dependent manner, and drives NET-associated morphologic features including nuclear decondensation. These effects were observed only in the presence of a NETosis stimulus and could not be solely replicated with equivalent levels of sialic acid alone. We conclude that THP is a critical regulator of NETosis in the urinary tract, playing a key role in host defense against UTI.

Stroke emboli from patients with atrial fibrillation enriched with neutrophil extracellular traps

Background

Recent literature has demonstrated remarkable heterogeneity in the composition of acute ischemic stroke (AIS) emboli, which may impact susceptibility to therapy.

Objectives

In this study, we explored differences in proteomic composition of retrieved embolic material from patients with stroke with and without atrial fibrillation (AF) (AF+ and AF-, respectively).

Methods

The full proteome of retrieved thromboembolic material from 24 patients with AIS was obtained by mass spectrometry. Known marker proteins were assigned groups representing broad classes of embolus components: red blood cells, platelets, neutrophils, eosinophils, histones, complement, and other clotting-associated proteins (eg, fibrinogen). Relative protein abundances were compared between AF+ and AF- samples. Functional implications of differences were explored with gene set enrichment analysis and Gene Ontology enrichment analysis and visualization tool.

Results

One hundred sixty-six proteins were differentially expressed between AF+ and AF- specimens. Eight out of the 15 neutrophil proteins (P < .05; fold change, >2) and 4 of the 14 histone proteins were significantly enriched in AF+ emboli (P < .05; fold change, >2). Gene set enrichment analysis revealed a significant representation of proteins from published neutrophil extracellular trap (NET) proteomic gene sets. The most significantly represented functional Gene Ontology pathways in patients with AF involved neutrophil activation and degranulation (P < 1 × 10-7).

Conclusion

The present analysis suggests enrichment of NETs in emboli of patients with stroke and AF. NETs are a significant though understudied structural component of thrombi. This work suggests not only unique stroke biology in AF but also potential therapeutic targets for AIS in this population.

LPS-TLR4 pathway exaggerates alcoholic hepatitis via provoking NETs formation

BACKGROUND

Intrahepatic infiltration of neutrophils is a character of alcoholic hepatitis (AH) and neutrophil extracellular traps (NETs) are an important strategy for neutrophils to fix and kill invading microorganisms. The gut-liver axis has been thought to play a critical role in many liver diseases also including AH. However, whether NETs appear in AH and play role in AH is still unsure.

METHODS

Serum samples from AH patients were collected and LPS and MPO-DNA were detected. WT, NE KO, and TLR4 KO mice were used to build the AH model, and the intestinal bacteria were eliminated at the same time and LPS was given. Then the formation of NETs and AH-related markers were detected.

RESULTS

The serum MPO-DNA and LPS concentration was increased in AH patients and a correlation was revealed between these two indexes. More intrahepatic NETs formed in AH mice. NETs formation decreased with antibiotic intervention and restored with antibiotic intervention plus LPS supplement. While NETs formation failed to change with gut microbiome or combine LPS supplement in TLR4 KO mice. As we tested AH-related characters, liver injury, intrahepatic fat deposition, inflammation, and fibrosis alleviated with depletion of NE. These related marks were also attenuated with gut sterilization by antibiotics and recovered with a combined treatment with antibiotics plus LPS. But the AH-related markers did show a difference in TLR4 KO mice when they received the same treatment.

CONCLUSION

Intestinal-derived LPS promotes NETs formation in AH through the TLR4 pathway and further accelerates the AH process by NETs.

Panton-Valentine leukocidin-induced neutrophil extracellular traps lack antimicrobial activity and are readily induced in patients with recurrent PVL + -Staphylococcus aureus infections

Staphylococcus aureus strains that produce the toxin Panton-Valentine leukocidin (PVL-SA) frequently cause recurrent skin and soft tissue infections. PVL binds to and kills human neutrophils, resulting in the formation of neutrophil extracellular traps (NETs), but the pathomechanism has not been extensively studied. Furthermore, it is unclear why some individuals colonized with PVL-SA experience recurring infections whereas others are asymptomatic. We thus aimed to (1) investigate how PVL exerts its pathogenicity on neutrophils and (2) identify factors that could help to explain the predisposition of patients with recurring infections. We provide genetic and pharmacological evidence that PVL-induced NET formation is independent of NADPH oxidase and reactive oxygen species production. Moreover, through NET proteome analysis we identified that the protein content of PVL-induced NETs is different from NETs induced by mitogen or the microbial toxin nigericin. The abundance of the proteins cathelicidin (CAMP), elastase (NE), and proteinase 3 (PRTN3) was lower on PVL-induced NETs, and as such they were unable to kill S. aureus. Furthermore, we found that neutrophils from affected patients express higher levels of CD45, one of the PVL receptors, and are more susceptible to be killed at a low PVL concentration than control neutrophils. Neutrophils from patients that experience recurring PVL-positive infections may thus be more sensitive to PVL-induced NET formation, which might impair their ability to combat the infection.

Unveiling the Web: Exploring the Multifaceted Role of Neutrophil Extracellular Traps in Ocular Health and Disease

Neutrophil extracellular traps (NETs) play an essential role in antimicrobial defense. However, NETs have also been shown to promote and mediate a wide spectrum of diseases, including cancer, diabetes mellitus, cardiovascular diseases, and ocular diseases. Data regarding NETs in ocular diseases remain limited. In physiological conditions, NETs protect the eye from debris and cleave proinflammatory cytokines, including several interleukins. On the other hand, NETs play a role in corneal diseases, such as dry eye disease and ocular graft-versus-host disease, where they promote acinar atrophy and delayed wound healing. Additionally, NET levels positively correlate with increased severity of uveitis. NETs have also been described in the context of diabetic retinopathy. Although increased NET biomarkers are associated with an increased risk of the disease, NETs also assist in the elimination of pathological blood vessels and the regeneration of normal vessels. Targeting NET pathways for the treatment of ocular diseases has shown promising outcomes; however, more studies are still needed in this regard. In this article, we summarize the literature on the protective roles of NETs in the eye. Then, we describe their pathogenetic effects in ocular diseases, including those of the cornea, uvea, and retinal blood vessels. Finally, we describe the therapeutic implications of targeting NETs in such conditions.

Proteomics: Unraveling the Cross Talk Between Innate Immunity and Disease Pathophysiology, Diagnostics, and Treatment Options

Inflammation is crucial in diseases, and proteins play a key role in the interplay between innate immunity and pathology. This review explores how proteomics helps understanding this relationship, focusing on diagnosis and treatment. We explore the dynamic innate response and the significance of proteomic techniques in deciphering the complex network of proteins involved in prevalent diseases, including infections, cancer, autoimmune and neurodegenerative disorders. Proteomics identifies key proteins in host-pathogen interactions, shedding light on infection mechanisms and inflammation. These discoveries hold promise for diagnostic tools, therapies, and vaccines. In cancer research, proteomics reveals innate signatures associated with tumor development, immune evasion, and therapeutic response. Additionally, proteomic analysis has unveiled autoantigens and dysregulation of the innate immune system in autoimmunity, offering opportunities for early diagnosis, disease monitoring, and new therapeutic targets. Moreover, proteomic analysis has identified altered protein expression patterns in neurodegenerative diseases like Alzheimer's and Parkinson's, providing insights into potential therapeutic strategies. Proteomics of the innate immune system provides a comprehensive understanding of disease mechanisms, identifies biomarkers, and enables effective interventions in various diseases. Despite still in its early stages, this approach holds great promise to revolutionize innate immunity research and significantly improve patient outcomes across a wide range of diseases.

A variety of death modes of neutrophils and their role in the etiology of autoimmune diseases

Neutrophils are important in the context of innate immunity and actively contribute to the progression of diverse autoimmune disorders. Distinct death mechanisms of neutrophils may exhibit specific and pivotal roles in autoimmune diseases and disease pathogenesis through the orchestration of immune homeostasis, the facilitation of autoantibody production, the induction of tissue and organ damage, and the incitement of pathological alterations. In recent years, more studies have provided in-depth examination of various neutrophil death modes, revealing nuances that challenge conventional understanding and underscoring their potential clinical utility in diagnosis and treatment. This review explores the multifaceted processes and characteristics of neutrophil death, with a focus on tailored investigations within various autoimmune diseases. It also highlights the potential interplay between neutrophil death and the landscape of autoimmune disorders. The review encapsulates the pertinent pathways implicated in various neutrophil death mechanisms across diverse autoimmune diseases while also charts possible avenues for future research.