PAD4-mediated neutrophil extracellular trap formation is not required for immunity against influenza infection

A Web of Challenges: The Therapeutic Struggle to Target NETs in Disease

Neutrophil extracellular traps (NETs) play a crucial role in the pathophysiology of many debilitating conditions, including autoimmune diseases, inflammatory diseases, and cancer. As a result, NET-targeted therapies have been investigated in search of effective treatment strategies. Despite promising preclinical findings, clinical translation of NET inhibitors has had limited success. These preclinical studies have faced limitations such as mouse models that inaccurately reflect human disease dynamics, as well as by the complexity of NETs-including their diverse morphology and convoluted pathways to formation relative to pathology. The NET inhibitors themselves have several limitations, including off-target effects and bioavailability issues. The challenges facing NET-targeted therapies reported here may explain what is required to go from bench to bedside successfully.

Single Cell Transcriptomics Genomics Based on Machine Learning Algorithm: Constructing and Validating Neutrophil Extracellular Trap Gene Model in COPD

Background

Neutrophil trap (NET) is an important feature of chronic inflammatory diseases. At present, there are still few studies to explore the characteristics of NET in different chronic obstructive pulmonary disease (COPD) patients. This study aimed to identify NET signature genes in different COPD patients.

Methods

We analyzed single-cell RNA sequencing data from COPD and non-COPD individuals to identify differentially expressed neutrophil genes. Machine learning algorithms were applied to construct models A and B, specific to smoking and non-smoking COPD patients, respectively.

Results

Through single-cell cluster analysis, 165 neutrophil characteristic genes in COPD group were successfully identified. Model A, consisting of key genes CD63, RNASE2, ERAP2, and model B, consisting of GRIPAP1, NHS, EGFLAM, and GLUL, were validated internally and externally, showing significant risk scores and good diagnostic efficacy (AUC: 60.24-87.22). Alveolar lavage fluid in patients with COPD was studied and confirmed higher expression levels of RNASE2 and NHS in severe COPD patients.

Conclusion

The study successfully developed NET signature gene models for identifying smoking and non-smoking COPD respectively, with validated specificity and predictive power, offering a foundation for personalized treatment strategies.

Impact of peptidylarginine deiminase 4 (PAD4) deficiency in a fecal-induced peritonitis model of sepsis

BACKGROUND

Peptidylarginine deiminase 4 (PAD4) citrullinates histones, enabling the release of neutrophil extracellular traps. While neutrophil extracellular traps capture and kill pathogens, they also drive immunothrombosis, potentially worsening sepsis outcomes. However, it remains unclear whether PAD4 deficiency is beneficial or harmful in sepsis.

OBJECTIVES

To evaluate the impact of PAD4 deficiency in a fecal-induced peritonitis sepsis model, with and without antibiotic treatment, and incorporating fluid resuscitation in both sexes.

METHODS

Wild-type and PAD4 knockout (PAD4-/-) C57Bl/6 mice received intraperitoneal injections of fecal slurry (0.6 mg/g). Mice received buprenorphine every 8 hours and antibiotics/fluids every 12 hours. Survival studies were also conducted without antibiotics at a reduced fecal dose (0.4 mg/g). Mice were culled at 8 hours or 48 hours after infection. Organs, blood, and peritoneal cavity fluid were collected. Plasma levels of interleukin (IL)-6, IL-10, cell-free DNA, and thrombin-antithrombin were quantified, as well as bacterial loads in blood and peritoneal cavity fluid. Organ histology/immunohistochemistry was performed.

RESULTS

Female PAD4-/- mice had worsened survival compared with female wild-type mice. Male mice exhibited worse survival than females in both strains. Antibiotics eliminated survival differences between strains and sexes. Septic PAD4-/- mice had reduced IL-10 in the early phase of sepsis, increased lung myeloperoxidase, and exacerbated lung injury compared with septic wild-type mice.

CONCLUSION

PAD4 deficiency in female mice worsened survival in the fecal-induced peritonitis sepsis model. In both strains, male mice exhibited worse survival compared with their female counterparts. PAD4 deficiency is associated with reduced IL-10, increased neutrophil infiltration, and exacerbated lung injury. Antibiotics eliminated survival differences between strains and sexes.

A patent review of peptidylarginine deiminase 4 (PAD4) inhibitors (2014-present)

INTRODUCTION

PAD4 mediates the post-translational modification of arginine residues into citrulline which can have profound effects on protein structure, function and interactions. Protein citrullination and neutrophil extracellular trap (NET) formation associated with increased PAD4 activity have been implicated in the development of autoimmune conditions, cardiovascular diseases, neurodegenerative disorders, and cancer. PAD4 inhibitors have been shown to suppress citrullination and NETs formation.

AREAS COVERED

This review covers 10 years of industrial drug discovery campaigns reported in 28 patent applications from 10 companies. Cortellis, the World Intellectual Property Organization website, Scopus and SciFinder were used to search the patent literature using the keywords 'PAD4' and 'PAD4 inhibitor.' Most of the reported inhibitors share the same core scaffold with varied decoration of different complexity, including highly functionalized macrocycles, with some in vivo and pharmacokinetic (PK) data reported for selected examples.

EXPERT OPINION

Despite PAD4's clear involvement in multiple disease pathways, its detailed mechanism remains insufficiently understood. Selective and potent compounds with improved PK properties have been provided but most research on PAD4 is still at the experimental stage or preclinical development; the most promising is JBI-1044, at the IND stage, while some companies have turned to antibodies despite considerable previous investment in small molecules.

Sepsis-induced NET formation requires MYD88 but is independent of GSDMD and PAD4

Neutrophils are peripheral blood-circulating leukocytes that play a pivotal role in host defense against bacterial pathogens which upon activation, they release web-like chromatin structures called neutrophil extracellular traps (NETs). Here, we analyzed and compared the importance of myeloid differentiation factor 88 (MYD88), peptidyl arginine deiminase 4 (PAD4), and gasdermin D (GSDMD) for NET formation in vivo following sepsis and neutrophilia challenge. Injection of lipopolysaccharide (LPS)/E. coli or the transgenic expression of granulocyte colony-stimulating factor (G-CSF), each induced NET-mediated lethal vascular occlusions in mice with combined genetic deficiency in Dnase1 and Dnase1l3 (D1/D1l3-/-). In accordance with the signaling of toll-like receptors, Myd88/D1/D1l3-/- animals were protected from the formation of lethal intravascular NETs during septic conditions. However, this protection was not observed during neutrophilia. It was unexpected to find that both Gsdmd/D1/D1l3-/- and Pad4/D1/D1l3-/- mice were fully capable of forming NETs upon LPS/E.coli challenge. Sepsis equally triggered a similar inflammatory response in these mice characterized by formation of DNA-rich thrombi, vessel occlusions, and mortality from pulmonary embolism, compared to D1/D1l3-/- mice. Pharmacologic GSDMD inhibitors did not reduce PMA-stimulated NET formation in ex vivo models either. Similarly, neither Pad4 nor GSDMD deficiency affected intravascular occlusive NET formation upon neutrophilia challenge. The magnitude of NET production, multi-organ damage, and lethality were comparable to those observed in challenged control mice. In conclusion, our data indicate that NET formation during experimental sepsis and neutrophilia is regulated by distinct stimulus-dependent pathways that may be independent of canonical PAD4 and GSDMD.

Neutrophils drive sexual dimorphism in experimental periodontitis

The motivating premise of this study is to improve the treatment of periodontal disease by elucidating sex-specific mechanisms of periodontal disease progression. Men and women experience inflammation in fundamentally different ways and understanding the sex-specific biology leading to inflammation and bone loss in the periodontium will inevitably improve patient outcomes. We therefore examined clinical and immunological differences in the progression of periodontal disease using the ligature-induced periodontitis model. Periodontitis was induced in male and female C57BL/6j mice by tying a 5-0 silk suture around the left maxillary second molar. The ligature was left on for 7 or 21 days at which point maxillae were characterized for bone loss by μCT or immune infiltrate by flow cytometry. Neutrophil depletion was accomplished through systemic administration of a Ly6G antibody. Conditions were compared using two-way ANOVA with Tukey's multiple comparison correction from n≥5 animals. Ligature-induced periodontitis led to alveolar bone loss at both 7 and 21 days in both female and male mice. Males and females had approximately the same amount of linear bone loss 7 days post-ligature placement, while male mice had significantly more linear bone loss by day 21. Male mice had significantly more immune cells in their maxillae 7 days post ligature placement compared to female mice. Both male and female mice showed a shift in immune populations towards neutrophils, with no significant difference between males and females. Neutrophil counts were significantly elevated in male mice on day 7 but not day 21, while female mice did not have any statistically significant changes in neutrophil counts. Neutrophil depletion using a Ly6G antibody limited bone loss in male but not female mice relative to isotype antibody-treated controls. Analysis of single-cell sequencing data from human patients with periodontitis showed differences in neutrophil phenotypes that were also observed in a mouse model of periodontitis. Together, these data suggest a mechanistic role for neutrophil inflammation in sexual dimorphism in periodontitis.

Lupus-prone NZM2328 mice exhibit enhanced UV-induced myeloid cell recruitment and activation in a type I interferon dependent manner

Though the exact causes of systemic lupus erythematosus (SLE) remain unknown, exposure to ultraviolet (UV) light is one of the few well-known triggers of cutaneous inflammation in SLE. However, the precise cell types which contribute to the early cutaneous inflammatory response in lupus, and the ways that UV dosing and interferons modulate these findings, have not been thoroughly dissected. Here, we explore these questions using the NZM2328 spontaneous murine model of lupus. In addition, we use iNZM mice, which share the NZM2328 background but harbor a whole-body knockout of the type I interferon (IFN) receptor, and wild-type BALB/c mice. 10-13-week-old female mice of each strain were treated with acute (300 mJ/cm2 x1), chronic (100 mJ/cm2 daily x5 days), or no UVB, and skin was harvested and processed for bulk RNA sequencing and flow cytometry. We identify that inflammatory pathways and gene signatures related to myeloid cells - namely neutrophils and monocyte-derived dendritic cells - are a shared feature of the acute and chronic UVB response in NZM skin greater than iNZM and wild-type skin. We also verify recruitment and activation of these cells by flow cytometry in both acutely and chronically irradiated NZM and WT mice and demonstrate that these processes are dependent on type I IFN signaling. Taken together, these data indicate a skewed IFN-driven inflammatory response to both acute and chronic UVB exposure in lupus-prone skin dominated by myeloid cells, suggesting both the importance of type I IFNs and myeloid cells as therapeutic targets for photosensitive patients and highlighting the risks of even moderate UV exposure in this patient population.

Recent Advances in Immunological Landscape and Immunotherapeutic Agent of Nipah Virus Infection

Over the last two decades, the Nipah virus (NiV) emerged as a highly lethal zoonotic pathogen to humans. Outbreaks occurred occasionally in South and Southeast Asia. Therefore, a safe and effective vaccine against the virus is needed to fight against the deadly virus. Understanding the immunological landscape during this lethal virus infection is necessary in this direction. However, we found scattered information on the immunological landscape of the virus's reservoir, as well as hosts such as humans and livestock. The review provides a recent understanding of the immunological landscape of the virus's reservoir, human hosts, monoclonal antibodies, and vaccines for NiV infection. To describe the immunological landscape, we divided our review article into some points. Firstly, we illustrated bats' immune response as a reservoir during the NiV infection. Secondly, we illustrated an overview of the molecular mechanisms underlying the immune response to the NiV infection, various immune cells, humans' innate immune response, adaptive immunity, and the landscape of cytokines and chemokines. We also discussed INF escape, NET evasion, the T cell landscape, and the B cell landscape during virus infection. Thirdly, we also demonstrated the potential monoclonal antibody therapeutics, and vaccines. Finally, neutralizing antibodies (nAbs) of NiV and potentially other therapeutic strategies were discussed. The review will help researchers for better understanding the immunological landscape, mAbs, and vaccines, enabling them to develop their next-generation versions.

Emerging mechanisms of lipid peroxidation in regulated cell death and its physiological implications

Regulated cell death (RCD) refers to the form of cell death that can be regulated by various biomacromolecules. Each cell death modalities have their distinct morphological changes and molecular mechanisms. However, intense evidences suggest that lipid peroxidation can be the common feature that initiates and propagates the cell death. Excessive lipid peroxidation alters the property of membrane and further damage the proteins and nucleic acids, which is implicated in various human pathologies. Here, we firstly review the classical chain process of lipid peroxidation, and further clarify the current understanding of the myriad roles and molecular mechanisms of lipid peroxidation in various RCD types. We also discuss how lipid peroxidation involves in diseases and how such intimate association between lipid peroxidation-driven cell death and diseases can be leveraged to develop rational therapeutic strategies.

Role of Peptidyl Arginine Deiminase 4-Dependent Macrophage Extracellular Trap Formation in Type 1 Diabetes Pathogenesis

Excessive formation of macrophage extracellular trap (MET) has been implicated in several autoimmune disease pathogeneses; however, its impact on type 1 diabetes (T1D) and related mechanisms remains enigmatic. We demonstrated the pivotal role of peptidyl arginine deiminase 4 (PAD4) in driving profuse MET formation and macrophage M1 polarization in intestinal inflammation in NOD mice. Genetic knockout of PAD4 or adoptive transfer of METs altered the proportion of proinflammatory T cells in the intestine, subsequently influencing their migration to the pancreas. Combining RNA sequencing and CUT&Tag analysis, we found activated PAD4 transcriptionally regulated CXCL10 expression. This study comprehensively investigated how excessive PAD4-mediated MET formation in the colon increases the aggravation of intestinal inflammation and proinflammatory T-cell migration and finally is involved in T1D progression, suggesting that inhibition of MET formation may be a potential therapeutic target in T1D.

ARTICLE HIGHLIGHTS

Differential requirement of formyl peptide receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. Here, we investigate the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed in a murine TB model utilizing hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion had no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1-/- mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased Mtb persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1-/- neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

Neutrophils under the microscope: neutrophil dynamics in infection, inflammation, and cancer revealed using intravital imaging

Neutrophils rapidly respond to inflammation resulting from infection, injury, and cancer. Intravital microscopy (IVM) has significantly advanced our understanding of neutrophil behavior, enabling real-time visualization of their migration, interactions with pathogens, and coordination of immune responses. This review delves into the insights provided by IVM studies on neutrophil dynamics in various inflammatory contexts. We also examine the dual role of neutrophils in tumor microenvironments, where they can either facilitate or hinder cancer progression. Finally, we highlight how computational modeling techniques, especially agent-based modeling, complement experimental data by elucidating neutrophil kinetics at the level of individual cells as well as their collective behavior. Understanding the role of neutrophils in health and disease is essential for developing new strategies for combating infection, inflammation and cancer.

APOE Protects Against Severe Infection with Mycobacterium tuberculosis by Restraining Production of Neutrophil Extracellular Traps

While neutrophils are the predominant cell type in the lungs of humans with active tuberculosis (TB), they are relatively scarce in the lungs of most strains of mice that are used to study the disease. However, similar to humans, neutrophils account for approximately 45% of CD45+ cells in the lungs of Apoe -/- mice on a high-cholesterol (HC) diet following infection with Mycobacterium tuberculosis (Mtb). We hypothesized that the susceptibility of Apoe -/- HC mice might arise from an unrestrained feed-forward loop in which production of neutrophil extracellular traps (NETs) stimulates production of type I interferons by pDCs which in turn leads to the recruitment and activation of more neutrophils, and demonstrated that depleting neutrophils, depleting plasmacytoid dendritic cells (pDCs), or blocking type I interferon signaling, improved the outcome of infection. In concordance with these results, we found that Mtb-infected in Apoe -/- HC mice produce high levels of LTB4 and 12-HETE, two eicosanoids known to act as neutrophil chemoattractants and showed that blocking leukotriene B4 (LTB4) receptor signaling also improved the outcome of tuberculosis. While production of NETs has been associated with severe tuberculosis in other mouse models and in humans, a causative role for NETs in the pathology has not been directly established. We demonstrate that blocking the activation of peptidylarginine deiminase 4 (PAD4), an enzyme critical to NET formation, leads to fewer NETs in the lungs and, strikingly, completely reverses the hypersusceptibility of Apoe -/- HC mice to tuberculosis.

AAV-mouse DNase I sustains long-term DNase I expression in vivo and suppresses breast cancer metastasis

Neutrophil extracellular traps (NETs) have been implicated in the pathology of various inflammatory conditions. In cancer, NETs have been demonstrated to induce systemic inflammation, impair peripheral vessel and organ function and promote metastasis. Here we show that the plasma level of NETs is significantly higher in patients with metastatic breast cancer compared to those with local disease, or those that were considered cured at a 5-year follow-up, confirming NETs as interesting therapeutic targets in metastatic breast cancer. Administration of DNase I is one strategy to eliminate NETs but long-term treatment requires repeated injections and species-specific versions of the enzyme. To enhance administration and therapeutic efficacy, we have developed an adeno-associated virus (AAV) vector system for delivery of murine DNase I and addressed its potential to counteract cancer-associated pathology in the murine MMTV-PyMT model for metastatic mammary carcinoma. The AAV vector is comprised of capsid KP1 and an expression cassette encoding hyperactive murine DNase I (AAV-mDNase I) under the control of a liver-specific promotor. This AAV-mDNase I vector could support elevated expression and serum activity of murine DNase I over at least 8 months. Neutrophil Gelatinase-Associated Lipocalin (NGAL), a biomarker for kidney hypoperfusion that is upregulated in urine from MMTV-PyMT mice, was suppressed in mice receiving AAV-mDNase I compared to an AAV-null control group. Furthermore, the proportion of mice that developed lung metastasis was reduced in the AAV-mDNase I group. Altogether, our data indicate that AAV-mDNase I has the potential to reduce cancer-associated impairment of renal function and development of metastasis. We conclude that AAV-mDNase I could represent a promising therapeutic strategy in metastatic breast cancer.

Neutrophil extracellular traps promote immunopathogenesis of virus-induced COPD exacerbations

Respiratory viruses are a major trigger of exacerbations in chronic obstructive pulmonary disease (COPD). Airway neutrophilia is a hallmark feature of stable and exacerbated COPD but roles played by neutrophil extracellular traps (NETS) in driving disease pathogenesis are unclear. Here, using human studies of experimentally-induced and naturally-occurring exacerbations we identify that rhinovirus infection induces airway NET formation which is amplified in COPD and correlates with magnitude of inflammation and clinical exacerbation severity. We show that inhibiting NETosis protects mice from immunopathology in a model of virus-exacerbated COPD. NETs drive inflammation during exacerbations through release of double stranded DNA (dsDNA) and administration of DNAse in mice has similar protective effects. Thus, NETosis, through release of dsDNA, has a functional role in the pathogenesis of COPD exacerbations. These studies open up the potential for therapeutic targeting of NETs or dsDNA as a strategy for treating virus-exacerbated COPD.

Differential requirement of Formyl Peptide Receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. This study investigates the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed using a TB model of hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion showed no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1 -/- mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased bacterial persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1 -/- neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

Platelet factor 4 promotes deep venous thrombosis by regulating the formation of neutrophil extracellular traps

The presence of neutrophil extracellular traps (NETs) in thrombotic diseases has been extensively studied. The exact mechanism of NET formation in deep venous thrombosis (DVT) has not been largely studied. This study is aimed to explore the role of NETs and their interaction with platelet factor 4 (PF4) in DVT. In plasma samples from 51 healthy volunteers and 52 DVT patients, NET markers and PF4 were measured using enzyme-linked immunosorbent assays (ELISA). NET generation in blood samples from healthy subjects and DVT patients was analyzed by confocal microscopy and flow cytometry. The plasma levels of NETs were significantly elevated in DVT patients, and neutrophils from patients showed a stronger ability to generate NETs after treatment. PF4 was upregulated in plasma samples from DVT patients and mediated NET formation. NETs enhanced procoagulant (PCA) via tissue factor and activating platelets to induce procoagulant activity. In addition, we established an inferior vena cava ligation (IVC) model to examine the role of NETs in thrombogenicity in DVT. In conclusion, NET formation was mediated by PF4 and enhance the procoagulant activity in DVT.

Neutrophil extracellular trap induction through peptidylarginine deiminase 4 activity is involved in 2,4,6-trinitrobenzenesulfonic acid-induced colitis

Neutrophil extracellular traps (NETs) are induced in the innate immune response against infectious agents and are also implicated in the pathogenesis of various cancers and autoimmune diseases. Peptidylarginine deiminase 4 (PAD4), an enzyme that converts arginine to citrulline, is also involved in NET formation. In this study, we investigated the pathogenic effect of PAD4 on NETs in inflammatory bowel disease using a trinitrobenzene sulfonic acid (TNBS)-induced murine colitis model. PAD4-deficient (PAD4KO) mice were generated by CRISPR-Cas9-mediated genomic editing. NETs were triggered in peritoneal neutrophils obtained from wild-type mice by A23187 (a calcium ionophore), but these responses were completely abolished in the PAD4KO mice. Experimental colitis was induced in wild-type and PAD4KO mice via an intrarectal injection of TNBS. TNBS injection resulted in body weight loss, extensive colonic erosion, and ulceration in wildtype mice. However, these responses were significantly attenuated following the administration of Cl-amidine (an inhibitor of pan-PADs) and DNase I (an inhibitor of NET formation), in combination with PAD4KO in mice. TNBS-induced increases in myeloperoxidase activity, inflammatory cytokine expression, and NET formation in the colon were significantly reduced following the administration of Cl-amidine, DNase I injection, and PAD4KO. These findings suggest that NET formation contributes to the pathogenesis of TNBS-induced colitis via PAD4. Thus, PAD4 is a promising target for the treatment of inflammatory bowel disease.

Nanoparticles for stimulation of neutrophil extracellular trap-mediated immunity

Neutrophil extracellular traps (NETs) have been identified as triggers for a self-limited inflammatory reaction upon contact with nanoparticles within our bodies. This typically results in entrapping potentially harmful nano- or micro-objects following an immune burst. The demand for potent adjuvants has led to research on particulate-based adjuvants, particularly those that act via NET formation. Various particles, including hydrophobic nanoparticles, needle-like microparticles, and other natural and artificial crystals, have been shown to induce NET formation, eliciting a robust humoral and cellular immune response toward co-injected antigens. The NET formation was found to be the basis of the efficient use of alum as a vaccine adjuvant. Thus, nanoparticles with specific surface properties serve as NET-stimulating adjuvants. In this mini-review, we aim to summarize the current knowledge about the surface properties of particulate objects and the molecular pathways involved in inducing NET formation by neutrophils. Additionally, we discuss the potential use of nanoparticles for activating neutrophils in the tissues and the exploitation of such activation for enhancing vaccine adjuvants.

NETosis Secondary to the Use of Levamisole-Adulterated Cocaine: A Likely Underlying Mechanism of Vasculopathy

Background

Since 2010, several cases of a new vasculopathy induced by the use of levamisole-adulterated cocaine (LAC) have been reported. This vasculopathy is characterized by retiform purpura, earlobe necrosis, multisystem compromise, and multiple autoantibodies. Given its similarity to antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, LAC-associated vasculopathy is postulated to be mediated by pathophysiologic processes resulting from neutrophil cell death by NETosis, a phenomenon previously described in ANCA vasculitis. This study tries to establish the presence of NETosis induced by cocaine, levamisole, or both. Methodology. Neutrophils were isolated from the peripheral blood of healthy controls by Ficoll-Hystopaque density gradient centrifugation followed by dextran sedimentation. Cell viability and purity were evaluated by flow cytometry after staining with PI/DiOC6 and labeling with fluorescent anti-CD45/anti-CD3 monoclonal antibodies (mAbs), respectively. Neutrophils were exposed to levamisole, cocaine, a cocaine-levamisole mixture, and sera pools from healthy controls and patients with LAC-associated vasculopathy. NETosis was then assessed by flow cytometry after staining cells with Sytox Green, Hoechst-33342, and fluorescent antineutrophil elastase (NE) and antimyeloperoxidase (MPO) mAbs. In addition, NETosis was morphologically confirmed by fluorescence microscopy. Proinflammatory cytokine levels in culture supernatants and reactive oxygen species (ROS) synthesis were determined by flow cytometry. The involvement of calcium and muscarinic receptors in cell death induction was evaluated in parallel experiments carried out in the presence of 1,2-bis (o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid (BAPTA) and hyoscine butylbromide (HBB), their respective inhibitors.

Results

Cocaine, levamisole, and a cocaine-levamisole mixture induced neutrophil cell death. DNA/MPO extrusion and cell morphology patterns were consistent with NETosis. Neither proinflammatory cytokines nor ROS behaved as proNETotic factors. Preliminary results suggested that muscarinic receptors and calcium-dependent signals were involved in LAC-induced NETosis.

Conclusions

Cocaine, levamisole, and a cocaine-levamisole mixture can induce NETosis through mechanisms involving muscarinic receptors and calcium-dependent pathways.

Neutrophil extracellular traps induce persistent lung tissue damage via thromboinflammation without altering virus resolution in a mouse coronavirus model

BACKGROUND

During infection, neutrophil extracellular traps (NETs) are associated with severity of pulmonary diseases such as acute respiratory disease syndrome. NETs induce subsequent immune responses, are directly cytotoxic to pulmonary cells, and are highly procoagulant. Anticoagulation treatment was shown to reduce in-hospital mortality, indicating thromboinflammatory complications. However, data are sparsely available on the involvement of NETs in secondary events after virus clearance, which can lead to persistent lung damage and postacute sequelae with chronic fatigue and dyspnea.

OBJECTIVES

This study focuses on late-phase events using a murine model of viral lung infection with postacute sequelae after virus resolution.

METHODS

C57BL/6JRj mice were infected intranasally with the betacoronavirus murine coronavirus (MCoV, strain MHV-A95), and tissue samples were collected after 2, 4, and 10 days. For NET modulation, mice were pretreated with OM-85 or GSK484 and DNase I were administered intraperitoneally between days 2 to 5 and days 4 to 7, respectively.

RESULTS

Rapid, platelet-attributed thrombus formation was followed by a second, late phase of thromboinflammation. This phase was characterized by negligible virus titers but pronounced tissue damage, apoptosis, oxidative DNA damage, and presence of NETs. Inhibition of NETs during the acute phase did not impact virus burden but decreased lung cell apoptosis by 67% and oxidative stress by 94%. Prevention of neutrophil activation by immune training before virus infection reduced damage by 75%, NETs by 31%, and pulmonary thrombi by 93%.

CONCLUSION

NETs are detrimental inducers of tissue damage during respiratory virus infection but do not contribute to virus clearance.

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.

Cell death classification: A new insight based on molecular mechanisms

Cells tend to disintegrate themselves or are forced to undergo such destructive processes in critical circumstances. This complex cellular function necessitates various mechanisms and molecular pathways in order to be executed. The very nature of cell death is essentially important and vital for maintaining homeostasis, thus any type of disturbing occurrence might lead to different sorts of diseases and dysfunctions. Cell death has various modalities and yet, every now and then, a new type of this elegant procedure gets to be discovered. The diversity of cell death compels the need for a universal organizing system in order to facilitate further studies, therapeutic strategies and the invention of new methods of research. Considering all that, we attempted to review most of the known cell death mechanisms and sort them all into one arranging system that operates under a simple but subtle decision-making (If \ Else) order as a sorting algorithm, in which it decides to place and sort an input data (a type of cell death) into its proper set, then a subset and finally a group of cell death. By proposing this algorithm, the authors hope it may solve the problems regarding newer and/or undiscovered types of cell death and facilitate research and therapeutic applications of cell death.

DEL-1 deficiency aggravates pressure overload-induced heart failure by promoting neutrophil infiltration and neutrophil extracellular traps formation

Recent studies have shown that neutrophils play an important role in the development and progression of heart failure. Developmental endothelial locus-1 (DEL-1) is an anti-inflammatory glycoprotein that has been found to have protective effects in various cardiovascular diseases. However, the role of DEL-1 in chronic heart failure is not well understood. In a mouse model of pressure overload-induced non-ischemic cardiac failure, we found that neutrophil infiltration in the heart increased and DEL-1 levels decreased in the early stages of heart failure. DEL-1 deficiency worsened pressure overload-induced cardiac dysfunction and remodeling in mice. Mechanistically, DEL-1 deficiency promotes neutrophil infiltration and the formation of neutrophil extracellular traps (NETs) through the regulation of P38 signaling. In vitro experiments showed that DEL-1 can inhibit P38 signaling and NETs formation in mouse neutrophils in a MAC-1-dependent manner. Depleting neutrophils, inhibiting NETs formation, and inhibiting P38 signaling all reduced the exacerbation of heart failure caused by DEL-1 deletion. Overall, our findings suggest that DEL-1 deficiency worsens pressure overload-induced heart failure by promoting neutrophil infiltration and NETs formation.

Balancing the functions of DNA extracellular traps in intracellular parasite infections: implications for host defense, disease pathology and therapy

The release of DNA to the extracellular milieu is a biological process referred to as etosis, which is involved in both physiological and pathological functions. Although the release of DNA extracellular traps (ETs) was initially attributed to innate immune cells such as neutrophils, eosinophils, and macrophages, recent studies have shown that T cells, as well as non-immune cells, are capable of releasing ETs. These structures were described primarily for their potential to trap and kill pathogens, presenting an important strategy of host defense. Intriguingly, these functions have been associated with intracellular pathogens such as the parasites Leishmania sp. and Trypanosoma cruzi, causative agents of leishmaniasis and Chagas disease, respectively. These are two devastating tropical diseases that lead to thousands of deaths every year. In an apparent contradiction, ETs can also induce and amplify inflammation, which may lead to worsening disease pathology. This has prompted the concept of targeting ETs' release as a means of controlling tissue destruction to treat human diseases. What is the best approach to prevent disease severity: inducing ETs to kill pathogens or preventing their release? In this Perspective article, we will discuss the importance of understanding ETs released by different cell types and the need to balance their potentially complementary functions. In addition, we will explore other functions of ETs and their translational applications to benefit individuals infected with intracellular parasites and other pathogens. Ultimately, a better understanding of the role of ETs in disease pathogenesis will provide valuable insights into developing novel therapies for human diseases.

Immune Checkpoint Inhibitors, Small-Molecule Immunotherapies and the Emerging Role of Neutrophil Extracellular Traps in Therapeutic Strategies for Head and Neck Cancer

Immune checkpoint inhibitor (ICI) therapy has revolutionized the treatment of many cancer types, including head and neck cancers (HNC). When checkpoint and partner proteins bind, these send an "off" signal to T cells, which prevents the immune system from destroying tumor cells. However, in HNC, and indeed many other cancers, more people do not respond and/or suffer from toxic effects than those who do respond. Hence, newer, more effective approaches are needed. The challenge to durable therapy lies in a deeper understanding of the complex interactions between immune cells, tumor cells and the tumor microenvironment. This will help develop therapies that promote lasting tumorlysis by overcoming T-cell exhaustion. Here we explore the strengths and limitations of current ICI therapy in head and neck squamous cell carcinoma (HNSCC). We also review emerging small-molecule immunotherapies and the growing promise of neutrophil extracellular traps in controlling tumor progression and metastasis.

Role of phagocyte extracellular traps during Mycobacterium tuberculosis infections and tuberculosis disease processes

Mycobacterium tuberculosis (M.tb) infections remain one of the most significant causes of mortality worldwide. The current situation shows an emergence of new antibiotic-resistant strains making it difficult to control the tuberculosis (TB) disease. A large part of its success as a pathogen is due to its ability to persist for years or even decades without causing evident clinical manifestations. M.tb is highly successful in evading the host-defense by manipulating host-signalling pathways. Although macrophages are generally viewed as the key cell type involved in harboring M.tb, growing evidence shows that neutrophils also play a fundamental role. Both cells are known to act in multiple ways when encountering an invading pathogen, including phagocytosis, release of cytokines and chemokines, and oxidative burst. In addition, the formation of neutrophil extracellular traps (NETs) and macrophage extracellular traps (METs) has been described to contribute to M.tb infections. NETs/METs are extracellular DNA fibers with associated granule components, which are released upon activation of the cells by the pathogen or by pro-inflammatory mediators. On one hand, they can lead to a protective immune response by entrapment and killing of pathogens. However, on the other hand, they can also play a severe pathological role by inducing tissue damage. Extracellular traps (ETs) produced in the pulmonary alveoli can expand easily and expose tissue-damaging factors with detrimental effects. Since host-directed therapies offer a complementary strategy in TB, the knowledge of NET/MET formation is important for understanding potential protective versus detrimental pathways during innate immune signaling. In this review, we summarize the progress made in understanding the role of NETs/METs in the pathogenesis of TB.

Neutrophil extracellular traps in acute coronary syndrome

Acute coronary syndrome (ACS) is a group of clinical syndromes caused by acute myocardial ischemia, which can cause heart failure, arrhythmia and even sudden death. It is the major cause of disability and death worldwide. Neutrophil extracellular traps (NETs) are reticular structures released by neutrophils activation and have various biological functions. NETs are closely related to the occurrence and development of ACS and also the subsequent damage after myocardial infarction. The mechanisms are complex and interdependent on various pathways, which require further exploration. This article reviewed the role and mechanism of NETs in ACS, thereby providing a valuable reference for the diagnosis and clinical treatment of ACS.

The emerging role of neutrophil extracellular traps in endometritis

Endometritis is a kind of common obstetric disease in women, usually caused by various pathogenic bacteria. Neutrophil infiltration is one of the most important pathological features of endometritis. Neutrophils can reach the uterine cavity through the endometrium, and make early response to the infection caused by the pathogen. Neutrophil extracellular traps (NETs), a meshwork of chromatin fibers extruded by neutrophils, have a role in entrapping microbial pathogens. It has been confirmed that NETs have a strong antibacterial effect and play crucial roles in the occurrence and development of various diseases. However, while killing pathogenic bacteria, excessive NETs formation may cause immune damage to the body. NETs are present in endometrium of female domestic animals in different physiological periods, especially post-mating, postpartum and in the presence of lesions, especially in endometritis. Meanwhile, NETs and its products might contribute to a reduction in physical clearance and persistent endometritis. In brief, NETs is a double-edged sword and it may play a different role in the development of endometritis, which may be beneficial or harmful, and its specific mechanism needs further study. Here we provide an overview of the role of NETs in the development of endometritis and the regulatory role of selenium on NETs formation and endometritis.

Transient receptor potential melastatin 2 regulates neutrophil extracellular traps formation and delays resolution of neutrophil-driven sterile inflammation

The formation of neutrophil extracellular traps (NETs) is a process releasing into the extracellular space networks of chromatin fibers decorated with granular proteins. It is implicated in infection-related as well as sterile inflammation. Monosodium urate (MSU) crystals serve as damage-associated molecular pattern (DAMP) in various conditions of disease. Formation of NETs or aggregated NETs (aggNETs) orchestrates initiation and resolution of MSU crystals-triggered inflammation, respectively. Elevated intracellular calcium levels and the generation of reactive oxygen species (ROS) are crucial for the formation of MSU crystal-induced NETs. However, the exact signaling pathways involved are still elusive. Herein, we demonstrate that the ROS-sensing, non-selective calcium-permeable channel transient receptor potential cation channel subfamily M member 2 (TRPM2) is required for a full-blown MSU crystal-induced NET formation. Primary neutrophils from TRPM2^-/- mice showed reduced calcium influx and ROS production and, consequently a reduced formation of MSU crystal-induced NETs and aggNETs. Furthermore, in TRPM2^-/- mice the infiltration of inflammatory cells into infected tissues and their production of inflammatory mediators was suppressed. Taken together these results describe an inflammatory role of TRPM2 for neutrophil-driven inflammation and identify TRPM2 as potential target for therapeutic intervention.

Neutrophil inhibition improves acute inflammation in a murine model of viral myocarditis

AIMS

Viral myocarditis (VM) is an inflammatory pathology of the myocardium triggered by a viral infection that may cause sudden death or heart failure (HF), especially in the younger population. Current treatments only stabilize and improve cardiac function without resolving the underlying inflammatory cause. The factors that induce VM to progress to HF are still uncertain, but neutrophils have been increasingly associated with the negative evolution of cardiac pathologies. The present study investigates the contribution of neutrophils to VM disease progression in different ways.

METHODS AND RESULTS

In a coxsackievirus B3- (CVB3) induced mouse model of VM, neutrophils and neutrophil extracellular traps (NETs) were prominent in the acute phase of VM as revealed by enzyme-linked immunosorbent assay analysis and immunostaining. Anti-Ly6G-mediated neutrophil blockade starting at model induction decreased cardiac necrosis and leucocyte infiltration, preventing monocyte and Ly6CHigh pro-inflammatory macrophage recruitment. Furthermore, genetic peptidylarginine deiminase 4-dependent NET blockade reduced cardiac damage and leucocyte recruitment, significantly decreasing cardiac monocyte and macrophage presence. Depleting neutrophils with anti-Ly6G antibodies at 7 days post-infection, after the acute phase, did not decrease cardiac inflammation.

CONCLUSION

Collectively, these results indicate that the repression of neutrophils and the related NET response in the acute phase of VM improves the pathological phenotype by reducing cardiac inflammation.

Histones of Neutrophil Extracellular Traps Directly Disrupt the Permeability and Integrity of the Intestinal Epithelial Barrier

BACKGROUND

Increased neutrophil extracellular trap (NET) formation and abundant NET-associated proteins are frequently found in the inflamed colon of patients with inflammatory bowel disease. Peptidyl arginine deiminase 4 (PAD4) activation is essential for the generation of NET and NET-mediated pathogenesis. However, the role of PAD4-dependent NET formation in murine inflammatory bowel disease models and the molecular mechanisms responsible for the altered gut barrier function are unknown.

METHODS

Wild-type and Pad4 knockout (Pad4-/-) mice were administrated 3% dextran sulfate sodium (DSS) in their drinking water. Caco-2 monolayers were used to test the effect of NETs on intestinal barrier function and cytotoxicity. Histones were intrarectally administrated to wild-type mice to determine their effects on intestinal barrier function and cytotoxicity in vivo.

RESULTS

PAD4 deficiency reduced the severity of DSS-induced colitis with decreased intestinal NET formation and enhanced gut barrier function and integrity in mice. NETs disrupted the barrier function in intestinal epithelial Caco-2 monolayers through their protein, rather than DNA, components. Pretreatment of NETs with histone inhibitors abrogated the effects on epithelial permeability. Consistent with these observations, adding purified histone proteins to Caco-2 monolayers significantly damaged epithelial barrier function, which was associated with the abnormal distribution and integrity of tight junctions as well as with increased cell death. Furthermore, intrarectal administration of histones damaged the intestinal barrier integrity and induced cytotoxicity in the mouse colon epithelium.

CONCLUSIONS

PAD4-mediated NET formation has a detrimental role in acute colitis. NET-associated histones directly inhibit intestinal barrier function, resulting in cytotoxicity in vitro and in vivo.

Neutrophil extracellular traps: Modulation mechanisms by pathogens

Neutrophils, as innate effector cells, play an essential role in the containment and elimination of pathogens. Among the main neutrophil mechanisms use for these processes is the release of neutrophil extracellular traps (NETs), which consist of decondensed DNA decorated with various cytoplasmic proteins. NETs' principal role is the trapping and elimination of infectious agents; therefore, the formation of NETs is regulated by bacteria, fungi, parasites, and viruses through different mechanisms: the presence of virulence factors (adhered or secreted), microbial load, size of the microorganism, and even due to other immune cells activation (mainly platelets). This review summarizes the significant aspects that contribute to NETs modulation by pathogens and their components, and the effect NETs have on these pathogens as a cellular defense mechanism.

Neutrophils prevent rectal bleeding in ulcerative colitis by peptidyl-arginine deiminase-4-dependent immunothrombosis

OBJECTIVE

Bleeding ulcers and erosions are hallmarks of active ulcerative colitis (UC). However, the mechanisms controlling bleeding and mucosal haemostasis remain elusive.

DESIGN

We used high-resolution endoscopy and colon tissue samples of active UC (n = 36) as well as experimental models of physical and chemical mucosal damage in mice deficient for peptidyl-arginine deiminase-4 (PAD4), gnotobiotic mice and controls. We employed endoscopy, histochemistry, live-cell microscopy and flow cytometry to study eroded mucosal surfaces during mucosal haemostasis.

RESULTS

Erosions and ulcerations in UC were covered by fresh blood, haematin or fibrin visible by endoscopy. Fibrin layers rather than fresh blood or haematin on erosions were inversely correlated with rectal bleeding in UC. Fibrin layers contained ample amounts of neutrophils coaggregated with neutrophil extracellular traps (NETs) with detectable activity of PAD. Transcriptome analyses showed significantly elevated PAD4 expression in active UC. In experimentally inflicted wounds, we found that neutrophils underwent NET formation in a PAD4-dependent manner hours after formation of primary blood clots, and remodelled clots to immunothrombi containing citrullinated histones, even in the absence of microbiota. PAD4-deficient mice experienced an exacerbated course of dextrane sodium sulfate-induced colitis with markedly increased rectal bleeding (96 % vs 10 %) as compared with controls. PAD4-deficient mice failed to remodel blood clots on mucosal wounds eliciting impaired healing. Thus, NET-associated immunothrombi are protective in acute colitis, while insufficient immunothrombosis is associated with rectal bleeding.

CONCLUSION

Our findings uncover that neutrophils induce secondary immunothrombosis by PAD4-dependent mechanisms. Insufficient immunothrombosis may favour rectal bleeding in UC.

Changes in Tumor Necrosis Factor α (TNFα) and Peptidyl Arginine Deiminase 4 (PAD-4) Levels in Serum of General Treated Psoriatic Patients

Psoriasis is an autoimmune disease in which the disturbed dependencies between lymphocytes, dendritic cells, keratinocytes and neutrophils play the most important role. One of them is the overproduction of neutrophil extracellular traps (NETs). The release of NETs can be induced by pathogens, as well as antibodies and immune complexes, cytokines and chemokines, including TNFα. The first step of the NET creation is the activation of peptidyl arginine deiminase 4 (PAD-4). PAD-4 seems to be responsible for citrullination of histones and chromatin decondensation, but the data on PAD-4 in NETs is inconclusive. Thus, the current study aimed to determine PAD-4 and TNFα levels in the serum of psoriatic patients by ELISA and observe the response of these factors to systemic (anti-17a, anti-TNFα and methotrexate) therapies. Increased levels of both PAD-4 and its main stimulus factor TNFα in pre-treatment patients have been reported along with the concentrations of proteins correlated with disease severity (PASI, BSA). Before treatment, the irregularities in the case of anti-nuclear antibodies level (ANA) were also observed. All of the applied therapies led to a decrease in PAD-4 and TNFα levels after 12 weeks. The most significant changes, both in protein concentrations as well as in scale scores, were noted with anti-TNFα therapy (adalimumab and infliximab). This phenomenon may be associated with the inhibition of TNFα production at different stages of psoriasis development, including NET creation. The obtained data suggest the participation of PAD-4 in the activation of neutrophils to produce NETs in psoriasis, which may create opportunities for modern therapies with PAD inhibitors. However, further exploration of gene and protein expression in psoriatic skin is needed.

Revisiting Regulated Cell Death Responses in Viral Infections

The fate of a viral infection in the host begins with various types of cellular responses, such as abortive, productive, latent, and destructive infections. Apoptosis, necroptosis, and pyroptosis are the three major types of regulated cell death mechanisms that play critical roles in viral infection response. Cell shrinkage, nuclear condensation, bleb formation, and retained membrane integrity are all signs of osmotic imbalance-driven cytoplasmic swelling and early membrane damage in necroptosis and pyroptosis. Caspase-driven apoptotic cell demise is considered in many circumstances as an anti-inflammatory, and some pathogens hijack the cell death signaling routes to initiate a targeted attack against the host. In this review, the selected mechanisms by which viruses interfere with cell death were discussed in-depth and were illustrated by compiling the general principles and cellular signaling mechanisms of virus–host-specific molecule interactions.

Intrinsic function of the peptidylarginine deiminase PADI4 is dispensable for normal haematopoiesis

Peptidylarginine deiminases (PADIs) are strongly associated with the development of autoimmunity, neurodegeneration and cancer but their physiological roles are ill-defined. The nuclear deiminase PADI4 regulates pluripotency in the mammalian pre-implantation embryo but its function in tissue development is unknown. PADI4 is primarily expressed in the bone marrow, as part of a self-renewal-associated gene signature. It has been shown to regulate the proliferation of multipotent haematopoietic progenitors and proposed to impact on the differentiation of haematopoietic stem cells (HSCs), suggesting that it controls haematopoietic development or regeneration. Using conditional in vivo models of steady state and acute Padi4 ablation, we examined the role of PADI4 in the development and function of the haematopoietic system. We found that PADI4 loss does not significantly affect HSC self-renewal or differentiation potential upon injury or serial transplantation, nor does it lead to HSC exhaustion or premature ageing. Thus PADI4 is dispensable for cell-autonomous HSC maintenance, differentiation and haematopoietic regeneration. This work represents the first study of PADI4 in tissue development and indicates that pharmacological PADI4 inhibition may be tolerated without adverse effects.

Neutrophil phenotypes and functions in cancer: A consensus statement

Neutrophils are the first responders to infection and inflammation and are thus a critical component of innate immune defense. Understanding the behavior of neutrophils as they act within various inflammatory contexts has provided insights into their role in sterile and infectious diseases; however, the field of neutrophils in cancer is comparatively young. Here, we summarize key concepts and current knowledge gaps related to the diverse roles of neutrophils throughout cancer progression. We discuss sources of neutrophil heterogeneity in cancer and provide recommendations on nomenclature for neutrophil states that are distinct in maturation and activation. We address discrepancies in the literature that highlight a need for technical standards that ought to be considered between laboratories. Finally, we review emerging questions in neutrophil biology and innate immunity in cancer. Overall, we emphasize that neutrophils are a more diverse population than previously appreciated and that their role in cancer may present novel unexplored opportunities to treat cancer.

The Immunobiology of Nipah Virus

Nipah virus (NiV) is a highly lethal zoonotic paramyxovirus that emerged in Malaysia in 1998. It is a human pathogen capable of causing severe respiratory infection and encephalitis. The natural reservoir of NiV, Pteropus fruit bats, remains a continuous virus source for future outbreaks, although infection in the bats is largely asymptomatic. NiV provokes serious disease in various mammalian species. In the recent human NiV outbreaks in Bangladesh and India, both bats-to-human and human-to-human transmissions have been observed. NiV has been demonstrated to interfere with the innate immune response via interferon type I signaling, promoting viral dissemination and preventing antiviral response. Studies of humoral immunity in infected NiV patients and animal models have shown that NiV-specific antibodies were produced upon infection and were protective. Studies on cellular immunity response to NiV infection in human and animal models also found that the adaptive immune response, specifically CD4+ and CD8+ T cells, was stimulated upon NiV infection. The experimental vaccines and therapeutic strategies developed have provided insights into the immunological requirements for the development of successful medical countermeasures against NiV. This review summarizes the current understanding of NiV pathogenesis and innate and adaptive immune responses induced upon infection.

Autophagy-driven neutrophil extracellular traps: The dawn of sepsis

Sepsis is a systemic inflammatory syndrome caused by infection disorders. The core mechanism of sepsis is immune dysfunction. Neutrophils are the most abundant circulating white blood cells, which play a crucial role in mediating the innate immune response. Previous studies have shown that an effective way to treat sepsis is through the regulation of neutrophil functions. Autophagy, a highly conserved degradation process, is responsible for removing denatured proteins or damaged organelles within cells and protecting cells from external stimuli. It is a key homeostasis process that promotes neutrophil function and differentiation. Autophagy has been shown to be closely associated with inflammation and immunity. Neutrophils, the first line of innate immunity, migrate to inflammatory sites upon their activation. Neutrophil-mediated autophagy may participate in the clinical course of sepsis. In this review, we summarized and analyzed the latest research findings on the changes in neutrophil external traps during sepsis, the regulatory role of autophagy in neutrophil, and the potential application of autophagy-driven NETs in sepsis, so as to guide clinical treatment of sepsis.

Low density neutrophils are increased in patients with Behçet's disease but do not explain differences in neutrophil function

BACKGROUND

Behçet's disease (BD) is a multisystem autoinflammatory disease characterised by mucosal ulceration, ocular, neural, joint and skin inflammation. The cause of BD is not known but there is a strong genetic association with HLA-B*51, IL10 and IL23R. Neutrophils are a first line of defence against invading pathogens and have been described as activated in patients with BD. Neutrophils can now be separated into different subsets, such as low density (LDN) and normal density (NDN) that have diverse functional roles. We wished to address neutrophil heterogeneity in patients with BD.

METHODS

Peripheral blood neutrophils were obtained from 32 BD patients and 37 healthy aged-matched controls. Percoll isolation was used to isolate all neutrophils, while Ficol-Hypaque was used to obtain LDN and NDN. Phagocytic capacity and production of reactive oxygen species (ROS), and neutrophil extracellular traps (NET) stimulated with phorbol 12-myristate 13-acetate (PMA) and Escherichia coli (E.coli) were assessed in both groups.

RESULTS

We have demonstrated reduced phagocytic capacity and ROS production but greater NET production by total neutrophils stimulated with PMA or E.coli from BD patients in comparison with healthy controls. Patients with BD had elevated numbers of LDN and lower number of NDN compared with healthy controls. However, both neutrophil subsets showed the same reduced ROS production and phagocytic function as total neutrophils in both groups.

CONCLUSION

Our novel findings indicate that the neutrophil population in BD is heterogeneous and the increased number of LDN in combination with greater NET production may contribute to the inflammatory response and pathogenesis.

On the Origin of Neutrophil Extracellular Traps in COVID-19

Despite ongoing vaccination COVID-19 is a global healthcare problem because of the lack of an effective targeted therapy. In severe COVID-19 manifesting as acute respiratory distress syndrome, uncontrolled innate immune system activation results in cytokine deregulation, damage-associated molecular patterns release upon tissue damage and high occurrence of thrombotic events. These pathomechanisms are linked to neutrophil function and dysfunction, particularly increased formation of neutrophil extracellular traps (NETs). While the association of NETs and severity of COVID-19 has been shown and proved, the causes of NETs formation are unclear. The aim of this review is to summarize potential inducers of NETs formation in severe COVID-19 and to discuss potential treatment options targeting NETs formation of removal.

Application of Regulatory Cell Death in Cancer: Based on Targeted Therapy and Immunotherapy

The development of cancer treatment methods is constantly changing. For common cancers, our treatment methods are still based on conventional treatment methods, such as chemotherapy, radiotherapy, and targeted drug therapy. Nevertheless, the emergence of tumor resistance has a negative impact on treatment. Regulated cell death is a gene-regulated mode of programmed cell death. After receiving specific signal transduction, cells change their physical and chemical properties and the extracellular microenvironment, resulting in structural destruction and decomposition. As research accumulates, we now know that by precisely inducing specific cell death patterns, we can treat cancer with less collateral damage than other treatments. Many newly discovered types of RCD are thought to be useful for cancer treatment. However, some experimental results suggest that some RCDs are not sensitive to cancer cell death, and some may even promote cancer progression. This review summarizes the discovered types of RCDs, reviews their clinical efficacy in cancer treatment, explores their anticancer mechanisms, and discusses the feasibility of some newly discovered RCDs for cancer treatment in combination with the immune and tumor microenvironment.

Identification of Nifurtimox and Chrysin as Anti-Influenza Virus Agents by Clinical Transcriptome Signature Reversion

The rapid development in the field of transcriptomics provides remarkable biomedical insights for drug discovery. In this study, a transcriptome signature reversal approach was conducted to identify the agents against influenza A virus (IAV) infection through dissecting gene expression changes in response to disease or compounds’ perturbations. Two compounds, nifurtimox and chrysin, were identified by a modified Kolmogorov–Smirnov test statistic based on the transcriptional signatures from 81 IAV-infected patients and the gene expression profiles of 1309 compounds. Their activities were verified in vitro with half maximal effective concentrations (EC₅₀s) from 9.1 to 19.1 μM against H1N1 or H3N2. It also suggested that the two compounds interfered with multiple sessions in IAV infection by reversing the expression of 28 IAV informative genes. Through network-based analysis of the 28 reversed IAV informative genes, a strong synergistic effect of the two compounds was revealed, which was confirmed in vitro. By using the transcriptome signature reversion (TSR) on clinical datasets, this study provides an efficient scheme for the discovery of drugs targeting multiple host factors regarding clinical signs and symptoms, which may also confer an opportunity for decelerating drug-resistant variant emergence.

The prominent role of hematopoietic peptidyl arginine deiminase 4 in arthritis: collagen and G-CSF induced arthritis model in C57BL/6 mice

OBJECTIVES

Genome-wide association studies have connected PADI4, encoding peptidylarginine deiminase 4 (PAD4), with rheumatoid arthritis (RA). PAD4 promotes neutrophil extracellular trap (NET) formation. We studied Padi4 origin and NETs in an arthritis model in C57BL/6 mice.

METHODS

To permit the effective use of C57BL/6 mice in the collagen-induced arthritis (CIA) model, we introduced the administration of granulocyte colony-stimulating factor (G-CSF) for four consecutive days in conjunction with the booster immunization on day 21. The model evaluated global (Padi4^-/- ) and hematopoietic lineage-specific (Padi4^Vav1Cre/+ ) Padi4-deficient mice.

RESULTS

G-CSF significantly increased the incidence and severity of arthritis in CIA. G-CSF-treated mice showed elevated citrullinated histone H3 (H3Cit) in plasma while vehicle-treated mice did not. Immunofluorescent microscopy revealed deposition of H3Cit in synovial tissue in G-CSF-treated mice. Padi4^-/- mice developed less arthritis, demonstrating lower serum interleukin 6 and plasma H3Cit, less citrullinated histone H4 in synovial tissue, and less bone erosion observed by micro-computed tomography than Padi4^+/+ mice in the G-CSF-modified CIA model. Similarly, Padi4^Vav1Cre/+ mice developed less arthritis compared with Padi4^fl/fl mice, and presented the same phenotype as Padi4^-/- mice.

CONCLUSIONS

We succeeded in developing an arthritis model suitable for use in C57BL/6 mice that was fully compliant with high animal welfare standards. We observed an over 90% incidence of arthritis in male mice and detectable NET markers. This model, with some futures consistent with human RA, demonstrates that hematopoietic PAD4 is an important contributor to arthritis development and may prove useful in future RA research.

Peptidylarginine Deiminase 2 in Murine Antiviral and Autoimmune Antibody Responses

The peptidylarginine deiminases (PADs) and the citrullinated proteins that they generate have key roles in innate immunity and rheumatoid arthritis, an inflammatory arthritis with antibodies that target citrullinated proteins. However, the importance of PADs, particularly PAD2, in the adaptive immune response, both normal and pathogenic, is newly emerging. In this study, we evaluated a requirement for PAD2 in the antibody response in collagen-induced arthritis (CIA), a T and B cell-driven murine model of rheumatoid arthritis, and in the protective antibody response to murine influenza infection. Using PAD2-/- and PAD2+/+ mice on the DBA/1J background, we found that PAD2 is required for maximal anti-collagen antibody levels, but not collagen-specific plasma cell numbers, T cell activation or polarization, or arthritis severity in CIA. Also, we found that PAD2 is required not just for normal levels of persistent hemagglutination inhibiting antibodies but also for full protection from lethal influenza rechallenge. Together, these data provide evidence for a novel modest requirement for PAD2 in a normal antiviral antibody response and in an abnormal autoantibody response in inflammatory arthritis.

A Hairy Cituation - PADIs in Regeneration and Alopecia

In this Review article, we focus on delineating the expression and function of Peptidyl Arginine Delminases (PADIs) in the hair follicle stem cell lineage and in inflammatory alopecia. We outline our current understanding of cellular processes influenced by protein citrullination, the PADI mediated posttranslational enzymatic conversion of arginine to citrulline, by exploring citrullinomes from normal and inflamed tissues. Drawing from other stem cell lineages, we detail the potential function of PADIs and specific citrullinated protein residues in hair follicle stem cell activation, lineage specification and differentiation. We highlight PADI3 as a mediator of hair shaft differentiation and display why mutations in PADI3 are linked to human alopecia. Furthermore, we propose mechanisms of PADI4 dependent fine-tuning of the hair follicle lineage progression. Finally, we discuss citrullination in the context of inflammatory alopecia. We present how infiltrating neutrophils establish a citrullination-driven self-perpetuating proinflammatory circuitry resulting in T-cell recruitment and activation contributing to hair follicle degeneration. In summary, we aim to provide a comprehensive perspective on how citrullination modulates hair follicle regeneration and contributes to inflammatory alopecia.