Neutrophils sense microbe size and selectively release neutrophil extracellular traps in response to large pathogens. Nat Immunol. 2014;15:1017-1025. [PMID: 25217981 PMCID: PMC4236687 DOI: 10.1038/ni.2987]

Interactions between the lung microbiome and host immunity in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common chronic respiratory disease and the third leading cause of death worldwide. Developments in next-generation sequencing technology have improved microbiome analysis, which is increasingly recognized as an important component of disease management. Similar to the gut, the lung is a biosphere containing billions of microbial communities. The lung microbiome plays an important role in regulating and maintaining the host immune system. The microbiome composition, metabolites of microorganisms, and the interactions between the lung microbiome and the host immunity profoundly affect the occurrence, development, treatment, and prognosis of COPD. In this review, we drew comparisons between the lung microbiome of healthy individuals and that of patients with COPD. Furthermore, we summarize the intrinsic interactions between the host and the overall lung microbiome, focusing on the underlying mechanisms linking the microbiome to the host innate and adaptive immune response pathways. Finally, we discuss the possibility of using the microbiome as a biomarker to determine the stage and prognosis of COPD and the feasibility of developing a novel, safe, and effective therapeutic target.

NETosis in Parasitic Infections: A Puzzle That Remains Unsolved

Neutrophils are the key players in the innate immune system, being weaponized with numerous strategies to eliminate pathogens. The production of extracellular traps is one of the effector mechanisms operated by neutrophils in a process called NETosis. Neutrophil extracellular traps (NETs) are complex webs of extracellular DNA studded with histones and cytoplasmic granular proteins. Since their first description in 2004, NETs have been widely investigated in different infectious processes. Bacteria, viruses, and fungi have been shown to induce the generation of NETs. Knowledge is only beginning to emerge about the participation of DNA webs in the host's battle against parasitic infections. Referring to helminthic infections, we ought to look beyond the scope of confining the roles of NETs solely to parasitic ensnarement or immobilization. Hence, this review provides detailed insights into the less-explored activities of NETs against invading helminths. In addition, most of the studies that have addressed the implications of NETs in protozoan infections have chiefly focused on their protective side, either through trapping or killing. Challenging this belief, we propose several limitations regarding protozoan-NETs interaction. One of many is the duality in the functional responses of NETs, in which both the positive and pathological aspects seem to be closely intertwined.

Dysregulated MicroRNAs in the Pathogenesis of Systemic Lupus Erythematosus: A Comprehensive Review

Systemic lupus erythematosus is a chronic autoimmune disease of which clinical presentation is vastly heterogeneous, ranging from mild skin rashes to severe renal diseases. Treatment goal of this illness is to minimize disease activity and prevent further organ damage. In recent years, much research has been done on the epigenetic aspects of SLE pathogenesis, for among the various factors known to contribute to the pathogenic process, epigenetic factors, especially microRNAs, bear the most therapeutic potential that can be altered unlike congenital genetic factors. This article reviews and updates what has been discovered so far about the pathogenesis of lupus, while focusing on the dysregulation of microRNAs in lupus patients in comparison to healthy controls along with the potentially pathogenic roles of the microRNAs commonly reported to be either upregulated or downregulated. Furthermore, this review includes microRNAs of which results are controversial, suggesting possible explanations for such discrepancies and directions for future research. Moreover, we aimed to emphasize the point that had been overlooked so far in studies regarding microRNA expression levels; that is, which specimen was used to assess the dysregulation of microRNAs. To our surprise, a vast number of studies have not considered this factor and have analyzed the potential role of microRNAs in general. Despite extensive investigations done on microRNA levels, their significance and potential role remain a mystery, which calls for further studies on this particular subject in regard of which specimen is used for assessment.

Curdione ameliorates sepsis-induced lung injury by inhibiting platelet-mediated neutrophil extracellular trap formation

Sepsis-associated acute lung injury remains to be a major cause of morbidity and mortality worldwide, and there is a lack of effective therapeutic drugs. Curdione, an activeingredient of Curcuma zedoary, a traditional Chinese medicine (TCM), possesses a variety of pharmacological actions, such as anti-inflammatory, antioxidant and inhibition of platelet aggregation. However, whether curdione protects against sepsis-induced lung injury is still undetermined. In this study, we investigated the effects of curdione on sepsis-induced lung injury. Cecal ligation and puncture (CLP) surgery was performed in mice to establish a model of sepsis. Twenty-four hours after CLP, bronchoalveolar lavage fluid (BALF) and lung tissue samples were harvested for investigation. The protective effects of curdione on acute lung injury and potential mechanisms were explored by detecting pathological sections, exudative proteins, oxidative responses, inflammatory factors, platelet activation, neutrophil infiltration, and neutrophil extracellular trap (NET) formation in the lung and were further verified in vitro. We showed that treatment with curdione clearly relieved histopathological changes, reduced inflammatory cytokine elevation and total protein concentrations in BALF, and decreased oxidative stress responses in lung tissues. In addition, curdione inhibited platelet activation, further blocking the interaction between platelets and neutrophils. Finally, neutrophil infiltration and NET formation was also reduced in mice treated with curdione. In conclusion, curdione alleviates sepsis-induced lung injury by inhibiting platelet-mediated neutrophil recruitment, infiltration, and NET formation as well as its anti-inflammatory and antioxidant properties. Curdione has great therapeutic potential in sepsis.

Tuning Bacterial Morphology to Enhance Anticancer Vaccination

Morphology tuning is a potent strategy to modulate physiological effects of synthetic biomaterials, but it is rarely explored in microbe-based biochemicals due to the lack of artificial adjustability. Inspired by the interesting phenomenon of microbial transformation, Escherichia coli is rationally adjusted into filamentous morphology-adjusted bacteria (MABac) via chemical stimulation to prepare a bacteria-based vaccine adjuvant/carrier. Inactivated MABac display stronger immunogenicity and special delivery patterns (phagosome escape and cytoplasmic retention) that are sharply distinct from the short rod-shaped bacteria parent (Bac). Transcriptomic study further offers solid evidence for deeply understanding the in vivo activity of MABac-based vaccine, which more effectively motivates multiple cytosolic immune pathways (such as NOD-like receptors and STING) and induces pleiotropic immune responses in comparison with Bac. Harnessing the special functions caused by morphology tuning, the MABac-based adjuvant/carrier significantly improves the immunogenicity and delivery profile of cancer antigens in vivo, thus boosting cancer-specific immunity against the melanoma challenge. This study validates the feasibility of tuning bacterial morphology to improve their biological effects, establishing a facile engineering strategy that upgrades bacterial properties and functions without complex procedures like gene editing.

Update of cellular responses to the efferocytosis of necroptosis and pyroptosis

Cell death is a basic physiological process that occurs in all living organisms. A few key players in these mechanisms, as well as various forms of cell death programming, have been identified. Apoptotic cell phagocytosis, also known as apoptotic cell clearance, is a well-established process regulated by a number of molecular components, including 'find-me', 'eat-me' and engulfment signals. Efferocytosis, or the rapid phagocytic clearance of cell death, is a critical mechanism for tissue homeostasis. Despite having similar mechanism to phagocytic clearance of infections, efferocytosis differs from phagocytosis in that it induces a tissue-healing response and is immunologically inert. However, as field of cell death has rapid expanded, much attention has recently been drawn to the efferocytosis of additional necrotic-like cell types, such as necroptosis and pyroptosis. Unlike apoptosis, this method of cell suicide allows the release of immunogenic cellular material and causes inflammation. Regardless of the cause of cell death, the clearance of dead cells is a necessary function to avoid uncontrolled synthesis of pro-inflammatory molecules and inflammatory disorder. We compare and contrast apoptosis, necroptosis and pyroptosis, as well as the various molecular mechanisms of efferocytosis in each type of cell death, and investigate how these may have functional effects on different intracellular organelles and signalling networks. Understanding how efferocytic cells react to necroptotic and pyroptotic cell uptake can help us understand how to modulate these cell death processes for therapeutic purposes.

Moonlighting chromatin: when DNA escapes nuclear control

Extracellular chromatin, for example in the form of neutrophil extracellular traps (NETs), is an important element that propels the pathological progression of a plethora of diseases. DNA drives the interferon system, serves as autoantigen, and forms the extracellular scaffold for proteins of the innate immune system. An insufficient clearance of extruded chromatin after the release of DNA from the nucleus into the extracellular milieu can perform a secret task of moonlighting in immune-inflammatory and occlusive disorders. Here, we discuss (I) the cellular events involved in the extracellular release of chromatin and NET formation, (II) the devastating consequence of a dysregulated NET formation, and (III) the imbalance between NET formation and clearance. We include the role of NET formation in the occlusion of vessels and ducts, in lung disease, in autoimmune diseases, in chronic oral disorders, in cancer, in the formation of adhesions, and in traumatic spinal cord injury. To develop effective therapies, it is of utmost importance to target pathways that cause decondensation of chromatin during exaggerated NET formation and aggregation. Alternatively, therapies that support the clearance of extracellular chromatin are conceivable.

The effect of herbal medicine in innate immunity to Candida albicans

Candida albicans (C. albicans) is an opportunistic pathogenic fungus that often causes mucosal and systemic infections. Several pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs) and C-type lectin receptors (CLRs), have been implicated in the host recognition of C. albicans. These PRRs recognize the pathogen-associated molecular patterns (PAMPs) of C. albicans to activate innate immune cells, thereby rapidly inducing various inflammatory responses by activating intracellular signaling cascades. Herbal medicine and its active components deserve priority development due to their low toxicity and high antibacterial, antiviral and antifungal activities. This review discussed the activities of herbal compounds against C. albicans and their related mechanisms, especially their regulatory role on innate immune cells such as neutrophils, macrophages, and dendritic cells (DCs) implicated in C. albicans infections. Our work aims to find new therapeutic drugs and targets to prevent and treat diseases caused by C. albicans infection with the mechanisms by which this fungus interacts with the innate immune response.

Secreted protease PRSS35 suppresses hepatocellular carcinoma by disabling CXCL2-mediated neutrophil extracellular traps

Hepatocytes function largely through the secretion of proteins that regulate cell proliferation, metabolism, and intercellular communications. During the progression of hepatocellular carcinoma (HCC), the hepatocyte secretome changes dynamically as both a consequence and a causative factor in tumorigenesis, although the full scope of secreted protein function in this process remains unclear. Here, we show that the secreted pseudo serine protease PRSS35 functions as a tumor suppressor in HCC. Mechanistically, we demonstrate that active PRSS35 is processed via cleavage by proprotein convertases. Active PRSS35 then suppresses protein levels of CXCL2 through targeted cleavage of tandem lysine (KK) recognition motif. Consequently, CXCL2 degradation attenuates neutrophil recruitment to tumors and formation of neutrophil extracellular traps, ultimately suppressing HCC progression. These findings expand our understanding of the hepatocyte secretome's role in cancer development while providing a basis for the clinical translation of PRRS35 as a therapeutic target or diagnostic biomarker.

HIF: a master regulator of nutrient availability and metabolic cross-talk in the tumor microenvironment

A role for hypoxia-inducible factors (HIFs) in hypoxia-dependent regulation of tumor cell metabolism has been thoroughly investigated and covered in reviews. However, there is limited information available regarding HIF-dependent regulation of nutrient fates in tumor and stromal cells. Tumor and stromal cells may generate nutrients necessary for function (metabolic symbiosis) or deplete nutrients resulting in possible competition between tumor cells and immune cells, a result of altered nutrient fates. HIF and nutrients in the tumor microenvironment (TME) affect stromal and immune cell metabolism in addition to intrinsic tumor cell metabolism. HIF-dependent metabolic regulation will inevitably result in the accumulation or depletion of essential metabolites in the TME. In response, various cell types in the TME will respond to these hypoxia-dependent alterations by activating HIF-dependent transcription to alter nutrient import, export, and utilization. In recent years, the concept of metabolic competition has been proposed for critical substrates, including glucose, lactate, glutamine, arginine, and tryptophan. In this review, we discuss how HIF-mediated mechanisms control nutrient sensing and availability in the TME, the competition for nutrients, and the metabolic cross-talk between tumor and stromal cells.

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

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

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

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

Virus-associated fungal infections and lost immune resistance

Invasive fungal infections are an increasing threat to human health. Of recent concern is the emergence of influenza- or SARS-CoV-2-virus-associated invasive fungal infections. Understanding acquired susceptibilities to fungi requires consideration of the collective and newly explored roles of adaptive, innate, and natural immunity. Neutrophils are known to provide host resistance, but new concepts are emerging that implicate innate antibodies, the actions of specialized B1 B cell subsets, and B cell-neutrophil crosstalk in mediating antifungal host resistance. Based on emerging evidence, we propose that virus infections impact on neutrophil and innate B cell resistance against fungi, leading to invasive infections. These concepts provide novel approaches to developing candidate therapeutics with the aim of restoring natural and humoral immunity and boosting neutrophil resistance against fungi.

Neutrophils in host defense, healing, and hypersensitivity: Dynamic cells within a dynamic host

Neutrophils are cells of the innate immune system that are extremely abundant in vivo and respond quickly to infection, injury, and inflammation. Their constant circulation throughout the body makes them some of the first responders to infection, and indeed they play a critical role in host defense against bacterial and fungal pathogens. It is now appreciated that neutrophils also play an important role in tissue healing after injury. Their short life cycle, rapid response kinetics, and vast numbers make neutrophils a highly dynamic and potentially extremely influential cell population. It has become clear that they are highly integrated with other cells of the immune system and can thus exert critical effects on the course of an inflammatory response; they can further impact tissue homeostasis and recovery after challenge. In this review, we discuss the fundamentals of neutrophils in host defense and healing; we explore the relationship between neutrophils and the dynamic host environment, including circadian cycles and the microbiome; we survey the field of neutrophils in asthma and allergy; and we consider the question of neutrophil heterogeneity-namely, whether there could be specific subsets of neutrophils that perform different functions in vivo.

Immunity to fungi in the lung

The respiratory tree maintains sterilizing immunity against human fungal pathogens. Humans inhale ubiquitous filamentous molds and geographically restricted dimorphic fungal pathogens that form small airborne conidia. In addition, pathogenic yeasts, exemplified by encapsulated Cryptococcus species, and Pneumocystis pose significant fungal threats to the lung. Classically, fungal pneumonia occurs in immune compromised individuals, specifically in patients with HIV/AIDS, in patients with hematologic malignancies, in organ transplant recipients, and in patients treated with corticosteroids and targeted biologics that impair fungal immune surveillance in the lung. The emergence of fungal co-infections during severe influenza and COVID-19 underscores the impairment of fungus-specific host defense pathways in the lung by respiratory viruses and by medical therapies to treat viral infections. Beyond life-threatening invasive syndromes, fungal antigen exposure can exacerbate allergenic disease in the lung. In this review, we discuss emerging principles of lung-specific antifungal immunity, integrate the contributions and cooperation of lung epithelial, innate immune, and adaptive immune cells to mucosal barrier immunity, and highlight the pathogenesis of fungal-associated allergenic disease. Improved understanding of fungus-specific immunity in the respiratory tree has paved the way to develop improved diagnostic, pre-emptive, therapeutic, and vaccine approaches for fungal diseases of the lung.

The formation and function of the neutrophil phagosome

Neutrophils are the most abundant circulating leukocyte and are crucial to the initial innate immune response to infection. One of their key pathogen-eliminating mechanisms is phagocytosis, the process of particle engulfment into a vacuole-like structure called the phagosome. The antimicrobial activity of the phagocytic process results from a collaboration of multiple systems and mechanisms within this organelle, where a complex interplay of ion fluxes, pH, reactive oxygen species, and antimicrobial proteins creates a dynamic antimicrobial environment. This complexity, combined with the difficulties of studying neutrophils ex vivo, has led to gaps in our knowledge of how the neutrophil phagosome optimizes pathogen killing. In particular, controversy has arisen regarding the relative contribution and integration of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived antimicrobial agents and granule-delivered antimicrobial proteins. Clinical syndromes arising from dysfunction in these systems in humans allow useful insight into these mechanisms, but their redundancy and synergy add to the complexity. In this article, we review the current knowledge regarding the formation and function of the neutrophil phagosome, examine new insights into the phagosomal environment that have been permitted by technological advances in recent years, and discuss aspects of the phagocytic process that are still under debate.

Neutrophil intrinsic and extrinsic regulation of NETosis in health and disease

Neutrophil extracellular traps (NETs) evolved to protect the host against microbial infections and are formed by a web-like structure of DNA that is decorated with antimicrobial effectors. Due to their potent inflammatory functions, NETs also cause tissue damage and can favor and/or aggravate inflammatory diseases. This multipronged activity of NETs requires that the induction, release, and degradation of NETs are tightly regulated. Here we describe the key pathways that are intrinsic to neutrophils and regulate NETosis, and we review the most recent findings on how neutrophil extrinsic factors participate in the formation of NETs. In particular, we emphasize how bystander cells contribute to modifying the capacity of neutrophils to undergo NETosis. Finally, we discuss how these neutrophil extrinsic processes can be harnessed to protect the host against the excessive inflammation elicited by uncontrolled NET release.

Association between Microorganisms and Microplastics: How Does It Change the Host-Pathogen Interaction and Subsequent Immune Response?

Plastic pollution is a significant problem worldwide because of the risks it poses to the equilibrium and health of the environment as well as to human beings. Discarded plastic released into the environment can degrade into microplastics (MPs) due to various factors, such as sunlight, seawater flow, and temperature. MP surfaces can act as solid scaffolds for microorganisms, viruses, and various biomolecules (such as LPS, allergens, and antibiotics), depending on the MP characteristics of size/surface area, chemical composition, and surface charge. The immune system has efficient recognition and elimination mechanisms for pathogens, foreign agents, and anomalous molecules, including pattern recognition receptors and phagocytosis. However, associations with MPs can modify the physical, structural, and functional characteristics of microbes and biomolecules, thereby changing their interactions with the host immune system (in particular with innate immune cells) and, most likely, the features of the subsequent innate/inflammatory response. Thus, exploring differences in the immune response to microbial agents that have been modified by interactions with MPs is meaningful in terms of identifying new possible risks to human health posed by anomalous stimulation of immune reactivities.

Antioxidant Strategies to Modulate NETosis and the Release of Neutrophil Extracellular Traps during Chronic Inflammation

Extracellular traps are released by neutrophils and other immune cells as part of the innate immune response to combat pathogens. Neutrophil extracellular traps (NETs) consist of a mesh of DNA and histone proteins decorated with various anti-microbial granule proteins, such as elastase and myeloperoxidase (MPO). In addition to their role in innate immunity, NETs are also strongly linked with numerous pathological conditions, including atherosclerosis, sepsis and COVID-19. This has led to significant interest in developing strategies to inhibit NET release. In this study, we have examined the efficacy of different antioxidant approaches to selectively modulate the inflammatory release of NETs. PLB-985 neutrophil-like cells were shown to release NETs on exposure to phorbol myristate acetate (PMA), hypochlorous acid or nigericin, a bacterial peptide derived from Streptomyces hygroscopicus. Studies with the probe R19-S indicated that treatment of the PLB-985 cells with PMA, but not nigericin, resulted in the production of HOCl. Therefore, studies were extended to examine the efficacy of a range of antioxidant compounds that modulate HOCl production by MPO to prevent NETosis. It was shown that thiocyanate, selenocyanate and various nitroxides could prevent NETosis in PLB-985 neutrophils exposed to PMA and HOCl, but not nigericin. These results were confirmed in analogous experiments with freshly isolated primary human neutrophils. Taken together, these data provide new information regarding the utility of supplementation with MPO inhibitors and/or HOCl scavengers to prevent NET release, which could be important to more specifically target pathological NETosis in vivo.

C-type lectin receptors in antifungal immunity: Current knowledge and future developments

C-type lectin receptors (CLRs) constitute a category of innate immune receptors that play an essential role in the antifungal immune response. For over two decades, scientists have uncovered what are the fungal ligands recognized by CLRs and how these receptors initiate the immune response. Such studies have allowed the identification of genetic polymorphisms in genes encoding for CLRs or for proteins involved in the signalisation cascade they trigger. Nevertheless, our understanding of how these receptors functions and the full extent of their function during the antifungal immune response is still at its infancy. In this review, we summarize some of the main findings about CLRs in antifungal immunity and discuss what the future might hold for the field.

Novel determinants of cell size homeostasis in the opportunistic yeast Candida albicans

The basis for commitment to cell division in late G1 phase, called Start in yeast, is a critical but still poorly understood aspect of eukaryotic cell proliferation. Most dividing cells accumulate mass and grow to a critical cell size before traversing the cell cycle. This size threshold couples cell growth to division and thereby establishes long-term size homeostasis. At present, mechanisms involved in cell size homeostasis in fungal pathogens are not well described. Our previous survey of the size phenome in Candida albicans focused on 279 unique mutants enriched mainly in kinases and transcription factors (Sellam et al. PLoS Genet 15:e1008052, 2019). To uncover novel size regulators in C. albicans and highlight potential innovation within cell size control in pathogenic fungi, we expanded our genetic survey of cell size to include 1301 strains from the GRACE (Gene Replacement and Conditional Expression) collection. The current investigation uncovered both known and novel biological processes required for cell size homeostasis in C. albicans. We also confirmed the plasticity of the size control network as few C. albicans size genes overlapped with those of the budding yeast Saccharomyces cerevisiae. Many new size genes of C. albicans were associated with biological processes that were not previously linked to cell size control and offer an opportunity for future investigation. Additional work is needed to understand if mitochondrial activity is a critical element of the metric that dictates cell size in C. albicans and whether modulation of the onset of actomyosin ring constriction is an additional size checkpoint.

Neutrophil Extracellular Traps and NLRP3 Inflammasome: A Disturbing Duo in Atherosclerosis, Inflammation and Atherothrombosis

Atherosclerosis is the formation of plaque within arteries due to overt assemblage of fats, cholesterol and fibrous material causing a blockage of the free flow of blood leading to ischemia. It is harshly impinging on health statistics worldwide because of being principal cause of high morbidity and mortality for several diseases including rheumatological, heart and brain disorders. Atherosclerosis is perpetuated by pro-inflammatory and exacerbated by pro-coagulatory mediators. Besides several other pathways, the formation of neutrophil extracellular traps (NETs) and the activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome contribute significantly to the initiation and propagation of atherosclerotic plaque for its worst outcomes. The present review highlights the contribution of these two disturbing processes in atherosclerosis, inflammation and atherothrombosis in their individual as well as collaborative manner.

The role of tumor-platelet interplay and micro tumor thrombi during hematogenous tumor metastasis

BACKGROUND

In addition to their pivotal roles in coagulation and thrombosis, platelets are crucial in tumor progression, with plenty of clinical and experimental data demonstrating that the interplay of platelets and tumor cells is essential for hematogenous tumor metastasis. After detach from primary sites, tumor cells intravasate into the blood circulation becoming circulating tumor cells and induce platelet activation, aggregation and encasement around tumor cells to form micro tumor thrombi, which create a permissive tumor microenvironment for metastasis. Platelets in micro tumor thrombi protect tumor cells from immune surveillance and anoikis (detachment-triggered apoptosis) through various pathways, which are significant for tumor cell survival in the bloodstream. Moreover, platelets can facilitate tumor metastasis by expediting epithelial-mesenchymal transition (EMT), adhesion to the endothelium, angiogenesis, tumor proliferation processes and platelet-derived microvesicle (PMV) formation.

CONCLUSIONS

Here, we provide a synopsis of the current understanding of the formation of micro tumor thrombi and the role of micro tumor thrombi in tumor hematogenous metastasis based on the tumor-platelet interplay. We also highlight potential therapeutic strategies targeting platelets for tumor treatment, including cancer-associated platelet-targeted nanomedicines.

Effects and mechanisms of Celastrol on the formation of neutrophil extracellular traps (NETs)

Background

To investigate the effect and mechanism of Celastrol on the formation of neutrophil extracellular traps (NETs), and to provide a theoretical basis for the clinical application of Tripterygium wilfordii.

Methods

First, we isolated neutrophils from the peripheral blood of healthy volunteers, and then observed the effect of Celastrol on Phorbol Myristate Acetate (PMA)-induced neutrophil release of NETs. The level of NETs was detected by using the membrane-impermeable nucleic acid dye, SytoxGreens. In addition, the levels of reactive oxygen species (ROS) were also examined to determine whether Celastrol affects ROS production during PMA-induced NETs.

Results

Celastrol produced significant cytotoxicity at a concentration of 5 µM (213.2±75.07), and the effect of stimulant PMA (25 nM) treatment was not statistically different (197.3±25.15) (P=0.9167). Celastrol (1.25, 0.625, and 0.3125 µM) did not exhibit cytotoxicity when treating neutrophils. Compared with the PMA (25 nM) + Celastrol (1.25, 0.625, and 0.3125 µM) group and the PMA (25 nM) monotherapy group, SytoxGreen showed a statistically significant reduction in fluorescence at 528 µM under 485 µM light excitation. Also, under the co-localization marker of Hochest and SytoxGreen double staining, we observed that the release of NETs in the PMA-treated group was higher than that in the control group. The PMA-induced neutrophil release of NETs was markedly reduced compared to the PMA-treated group. The NET release was substantially decreased under double staining with the Hochest and SytoxGreen co-localization markers. The fluorescence intensity of the Celastrol plus PMA group was significantly lower than that of the PMA treatment group alone, indicating a decrease in the level of intracellular ROS. Interestingly, the level of ROS in the treatment group who received Celastrol alone was lower than that in the control group, indicating that Tripterygium wilfordii could inhibit the spontaneous production of ROS by neutrophils in the absence of stimulation.

Conclusions

The molecular mechanism of Celastrol involves inhibition of PMA-stimulated neutrophil NETs formation in vitro, which is possibly related to the reduction of ROS levels. This indicates that Celastrol, the main component in Tripterygium wilfordii, can inhibit the formation of NETs, which provides a theoretical basis for the study of NETs-related diseases.

Progress of polymer-based strategies in fungal disease management: Designed for different roles

Fungal diseases have posed a great challenge to global health, but have fewer solutions compared to bacterial and viral infections. Development and application of new treatment modalities for fungi are limited by their inherent essential properties as eukaryotes. The microorganism identification and drug sensitivity analyze are limited by their proliferation rates. Moreover, there are currently no vaccines for prevention. Polymer science and related interdisciplinary technologies have revolutionized the field of fungal disease management. To date, numerous advanced polymer-based systems have been developed for management of fungal diseases, including prevention, diagnosis, treatment and monitoring. In this review, we provide an overview of current needs and advances in polymer-based strategies against fungal diseases. We high light various treatment modalities. Delivery systems of antifungal drugs, systems based on polymers' innate antifungal activities, and photodynamic therapies each follow their own mechanisms and unique design clues. We also discuss various prevention strategies including immunization and antifungal medical devices, and further describe point-of-care testing platforms as futuristic diagnostic and monitoring tools. The broad application of polymer-based strategies for both public and personal health management is prospected and integrated systems have become a promising direction. However, there is a gap between experimental studies and clinical translation. In future, well-designed in vivo trials should be conducted to reveal the underlying mechanisms and explore the efficacy as well as biosafety of polymer-based products.

Emerging mechanisms and functions of inflammasome complexes in teleost fish

Inflammasomes are multiprotein complexes, which are assembled in response to a diverse range of exogenous pathogens and endogenous danger signals, leading to produce pro-inflammatory cytokines and induce pyroptotic cell death. Inflammasome components have been identified in teleost fish. Previous reviews have highlighted the conservation of inflammasome components in evolution, inflammasome function in zebrafish infectious and non-infectious models, and the mechanism that induce pyroptosis in fish. The activation of inflammasome involves the canonical and noncanonical pathways, which can play critical roles in the control of various inflammatory and metabolic diseases. The canonical inflammasomes activate caspase-1, and their signaling is initiated by cytosolic pattern recognition receptors. However the noncanonical inflammasomes activate inflammatory caspase upon sensing of cytosolic lipopolysaccharide from Gram-negative bacteria. In this review, we summarize the mechanisms of activation of canonical and noncanonical inflammasomes in teleost fish, with a particular focus on inflammasome complexes in response to bacterial infection. Furthermore, the functions of inflammasome-associated effectors, specific regulatory mechanisms of teleost inflammasomes and functional roles of inflammasomes in innate immune responses are also reviewed. The knowledge of inflammasome activation and pathogen clearance in teleost fish will shed new light on new molecular targets for treatment of inflammatory and infectious diseases.

They shall not grow mold: Soldiers of innate and adaptive immunity to fungi

Fungi are ubiquitous commensals, seasoned predators, and important agents of emerging infectious diseases [1 ]. The immune system assumes the essential responsibility for responding intelligently to the presence of known and novel fungi to maintain host health. In this Review, we describe the immune responses to pathogenic fungi and the varied array of fungal agents confronting the vertebrate host within the broader context of fungal and animal evolution. We provide an overview of the mechanistic details of innate and adaptive antifungal immune responses, as well as ways in which these basic mechanisms support the development of vaccines and immunotherapies.

Inflammation-mediated tissue damage in pulmonary tuberculosis and host-directed therapeutic strategies

Treatment of tuberculosis (TB) involves the administration of anti-mycobacterial drugs for several months. The emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb, the causative agent) together with increased disease severity in people with co-morbidities such as diabetes mellitus and HIV have hampered efforts to reduce case fatality. In severe disease, TB pathology is largely attributable to over-exuberant host immune responses targeted at controlling bacterial replication. Non-resolving inflammation driven by host pro-inflammatory mediators in response to high bacterial load leads to pulmonary pathology including cavitation and fibrosis. The need to improve clinical outcomes and reduce treatment times has led to a two-pronged approach involving the development of novel antimicrobials as well as host-directed therapies (HDT) that favourably modulate immune responses to Mtb. HDT strategies incorporate aspects of immune modulation aimed at downregulating non-productive inflammatory responses and augmenting antimicrobial effector mechanisms to minimise pulmonary pathology and accelerate symptom resolution. HDT in combination with existing antimycobacterial agents offers a potentially promising strategy to improve the long-term outcome for TB patients. In this review, we describe components of the host immune response that contribute to inflammation and tissue damage in pulmonary TB, including cytokines, matrix metalloproteinases, lipid mediators, and neutrophil extracellular traps. We then proceed to review HDT directed at these pathways.

Neutrophil extracellular traps and phagocytosis in Pythium insidiosum

Neutrophils are innate immune cells that play crucial roles in response to extracellular pathogens, including bacteria and fungi. Pythium insidiosum (P insidiosum) is a fungus-like pathogen that causes "pythiosis" in mammals. This study investigated in vitro function of human neutrophils against P. insidiosum. We demonstrated the killing mechanism of neutrophils when incubated with P. insidiosum zoospores (infective stage), such as phagocytosis and neutrophil extracellular traps (NETs). Healthy human neutrophils significantly reduced six strains of live zoospores isolated from different sources compared to the condition without neutrophils (p < 0.001), observed by colony count and trypan blue staining. As our results showed the killing ability of neutrophils, we further investigated the neutrophil killing mechanism when incubating with zoospores. Our study found that only two strains of heat-killed zoospores significantly induced phagocytosis (p < 0.01). Co-culture of heat-killed zoospores and neutrophils demonstrated NET formation, which was detected by immunofluorescence staining using DAPI, anti-myeloperoxidase, and anti-neutrophil elastase and quantitated under the fluorescence microscope. In addition, the level of cell-free DNA released from neutrophils (as a marker of NET production) after incubation with zoospores showed significantly increased levels when compared with unstimulated neutrophils (p < 0.001). Our findings demonstrate that neutrophils revealed the NET formation in response to P. insidiosum zoospores. This study is the first observation of the neutrophil mechanism against P. insidiosum, which could provide a better understanding of some parts of the innate immune response during pythiosis.

Inhibition of neutrophil elastase prevents cigarette smoke exposure-induced formation of neutrophil extracellular traps and improves lung function in a mouse model of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is an important public health challenge worldwide, and is usually caused by significant exposure to noxious agents, particularly cigarette smoke. Recent studies have revealed that excessive production of neutrophil extracellular traps (NETs) in the airways is associated with disease severity in COPD patients. NETs are extracellular neutrophil-derived structures composed of chromatin fibers decorated with histones and granule proteases including neutrophil elastase (NE). However, the effective prevention of NET formation in COPD remains elusive. Here, we demonstrated that treatment with GW311616A, a potent and selective inhibitor of NE, prevented cigarette smoke extract (CSE)-induced NET formation in human neutrophils by blocking NE nuclear translocation and subsequent chromatin decondensation. Inhibition of NE also abrogated CSE-induced ROS production and migration impairment of neutrophils. Administration of GW311616A in vivo substantially reduced pulmonary generation of NETs while attenuating the key pathological changes in COPD, including airway leukocyte infiltration, mucus-secreting goblet cell hyperplasia, and emphysema-like alveolar destruction in a mouse model of COPD induced by chronic cigarette smoke exposure. Mice treated with GW311616A also showed significant attenuation of neutrophil numbers and percentages and the levels of neutrophil chemotactic factors (LTB4, KC, and CXCL5) and proinflammatory cytokines (IL-1β, and TNF-α) in bronchoalveolar lavage fluid compared to mice treated with cigarette smoke exposure only. Furthermore, GW311616A treatment considerably improved lung function in the COPD mouse model, including preventing the decline of FEV₁₀₀/FVC and delta PEF as well as inhibiting the increase in FRC, TLC, and FRC/TLC. Overall, our study suggests that NE plays a critical role in cigarette smoke-induced NET formation by neutrophils and that inhibition of NE is a promising strategy to suppress NET-mediated pathophysiological changes in COPD.

Microbial exopolysaccharides-β-glucans-as promising postbiotic candidates in vaccine adjuvants

The urgent task of creating new, enhanced adjuvants is closely related to our comprehension of their mechanisms of action. A few adjuvants have shown sufficient efficacy and low toxicity to be allowed for use in human vaccines, despite the fact that they have a long history and an important function. Adjuvants have long been used without a clear understanding of how precisely they augment the immune response. The rational production of stronger and safer adjuvants has been impeded by this lack of information, which necessitates more mechanistic research to support the development of vaccines. Carbohydrate structures-polygalactans, fructans, β-D-glucans, α-D-glucans, D-galactose, and D-glucose-are desirable candidates for the creation of vaccine adjuvants and immunomodulators because they serve important functions in nature and are often biocompatible, safe, and well tolerated. In this review, we have discussed recent advances in microbial-derived carbohydrate-based adjuvants, their immunostimulatory activity, and the implications of this for vaccine development, along with the critical view on the microbial sources, chemical composition, and biosynthetic pathways.

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

Non-albicans Candida Species: Immune Response, Evasion Mechanisms, and New Plant-Derived Alternative Therapies

Fungal infections caused by Candida species have become a constant threat to public health, especially for immunocompromised patients, who are considered susceptible to this type of opportunistic infections. Candida albicans is known as the most common etiological agent of candidiasis; however, other species, such as Candida tropicalis, Candida parapsilosis, Nakaseomyces glabrata (previously known as Candida glabrata), Candida auris, Candida guilliermondii, and Pichia kudriavzevii (previously named as Candida krusei), have also gained great importance in recent years. The increasing frequency of the isolation of this non-albicans Candida species is associated with different factors, such as constant exposure to antifungal drugs, the use of catheters in hospitalized patients, cancer, age, and geographic distribution. The main concerns for the control of these pathogens include their ability to evade the mechanisms of action of different drugs, thus developing resistance to antifungal drugs, and it has also been shown that some of these species also manage to evade the host's immunity. These biological traits make candidiasis treatment a challenging task. In this review manuscript, a detailed update of the recent literature on the six most relevant non-albicans Candida species is provided, focusing on the immune response, evasion mechanisms, and new plant-derived compounds with antifungal properties.

Immunomodulatory biomaterials for implant-associated infections: from conventional to advanced therapeutic strategies

Implant-associated infection (IAI) is increasingly emerging as a serious threat with the massive application of biomaterials. Bacteria attached to the surface of implants are often difficult to remove and exhibit high resistance to bactericides. In the quest for novel antimicrobial strategies, conventional antimicrobial materials often fail to exert their function because they tend to focus on direct bactericidal activity while neglecting the modulation of immune systems. The inflammatory response induced by host immune cells was thought to be a detrimental force impeding wound healing. However, the immune system has recently received increasing attention as a vital player in the host's defense against infection. Anti-infective strategies based on the modulation of host immune defenses are emerging as a field of interest. This review explains the importance of the immune system in combating infections and describes current advanced immune-enhanced anti-infection strategies. First, the characteristics of traditional/conventional implant biomaterials and the reasons for the difficulty of bacterial clearance in IAI were reviewed. Second, the importance of immune cells in the battle against bacteria is elucidated. Then, we discuss how to design biomaterials that activate the defense function of immune cells to enhance the antimicrobial potential. Based on the key premise of restoring proper host-protective immunity, varying advanced immune-enhanced antimicrobial strategies were discussed. Finally, current issues and perspectives in this field were offered. This review will provide scientific guidance to enhance the development of advanced anti-infective biomaterials.

Role of neutrophil extracellular traps in inflammatory evolution in severe acute pancreatitis

ABSTRACT

Severe acute pancreatitis (SAP) is a life-threatening acute abdominal disease with two peaks of death: the first in the early stage, characterized by systemic inflammatory response-associated organ failure; and the second in the late stage, characterized by infectious complications. Neutrophils are the main immune cells participating in the whole process of SAP. In addition to the traditional recognition of neutrophils as the origination of chemokine and cytokine cascades or phagocytosis and degranulation of pathogens, neutrophil extracellular traps (NETs) also play an important roles in inflammatory reactions. We reviewed the role of NETs in the occurrence and development of SAP and its fatal complications, including multiple organs injury, infected pancreatic necrosis, and thrombosis. This review provides novel insights into the involvement of NETs throughout the entire process of SAP, showing that targeting NETs might be a promising strategy in SAP treatment. However, precision therapeutic options targeting NETs in different situations require further investigation.

Rituximab induces a flare-up of activated neutrophil extracellular traps under in vitro conditions

Purpose: During neutrophil extracellular traps (NET) formation granulocytes release a decondensed chromatin web that is studded with antimicrobial proteins. These NET engulf and kill pathogens like bacteria and fungi. NET formation is part of the innate immune response but can also contribute to the aggravation of autoimmune diseases, thrombosis, and cancer metastasis. Anti-NET therapeutics to prevent potentially harmful consequences of excessive NET formation are warranted.Materials and methods: Therefore, we stimulated NET formation with ionomycin in the peripheral blood of 25 healthy individuals and quantified NET with flow cytometry and fluorescence microscopy after exposure to five different anti-inflammatory and cytostatic drugs. NET were identified by their expression of myeloperoxidase, citrullinated histone H3, and (extracellular) DNA release.Results: The preliminary in vitro drug screening indicated that acetylsalicylic acid (ASA) might suppress (-3.82%), and rituximab might enhance (+10.52%) NET formation. To consolidate the screening results, we quantified NET after exposure to rituximab and ASA in the blood of nine additional healthy subjects. Rituximab showed a significant increased NET formation compared to the neutrophils treated with ASA (a mean of differences 3.96%; 95% CI 1.90-6.03%; p < .01) or compared to neutrophils without treatment (a mean of differences 4.39%; 95% CI 1.17-7.61%; p = .01). Contrary to the screening results ASA showed no significant suppression of NET formation in the consolidation experiments (a mean of differences 0.43%; 95% CI -1.27 to 2.12%; p = .58).Conclusions: We conclude that rituximab therapy might further trigger activated NET formation and should be applied with caution in patients with pro-inflammatory state and underlying autoimmune disease, thrombosis, or cancer.

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.

Epigallocatechin-3-gallate reduces neutrophil extracellular trap formation and tissue injury in severe acute pancreatitis

Neutrophil extracellular traps (NETs) promote intra-acinar trypsin activation and tissue damage. Therefore, reducing NET formation can reduce tissue damage in severe acute pancreatitis (SAP). However, NET formation pathways may differ among disease models. In this study, we evaluated the role of the myeloperoxidase-neutrophil elastase (NE) pathway in NET formation in SAP. SAP was induced by intraperitoneal injection of cerulein and LPSs in mice, and NE activity was inhibited by GW311616. Pancreatic tissues were collected for multiplex immunofluorescence, scanning electron microscopy, and western blotting to detect NET formation and the effect of NE on citrullinated histone H3, followed by analyses of serum amylase and cytokine levels. Pretreatment with GW311616 significantly reduced NET formation, pancreatic tissue damage, and systemic inflammatory responses in SAP. Network pharmacology analyses using NE as the target revealed the monomeric compound epigallocatechin-3-gallate (EGCG). Binding between EGCG and NE was validated using molecular docking, and the ability of EGCG to inhibit NE activity was verified experimentally. NET formation by PMA-stimulated neutrophils was significantly reduced in vitro when the cells were pretreated with 40 μM EGCG. Pretreatment with EGCG significantly reduced NET formation, pancreatic tissue damage, and systemic inflammatory responses in vivo. These results reveal that NET formation requires the myeloperoxidase-NE pathway, and citrullination of histone H3 is affected by NE activity in SAP. EGCG shows therapeutic potential for affecting NE activity, NET formation, and systemic inflammation in SAP.

Trichinella spiralis excretory-secretory antigens selectively inhibit the release of extracellular traps from neutrophils without affecting their additional antimicrobial functions

Neutrophil extracellular traps (NETs) are fiber structures composed of chromatin and granular proteins that capture and eliminate microorganisms. The NETs formation is induced in response to pathogens and physiological stimuli; however, some pathogens have developed strategies to evade NETs activity. Trichinella spiralis excretory-secretory (ES) antigens are proteins that allow the establishment of the parasite in the host, facilitating penetration, migration, nutrition, and survival. In this paper we described that ES antigens inhibit NETs release, since neutrophils incubated with these antigens maintains a delobulated nucleus, without the release fibers structures indicative of NETs. We also found that other antimicrobial functions of neutrophils, such as phagocytic activity, degranulation, and ROS production, remain unchanged after incubation with ES antigens. This is relevant since it could constitute a novel strategy for the treatment of autoimmune pathologies in which the formation of NETs performs an important role.

Mechanisms regulating neutrophil responses in immunity, allergy, and autoimmunity

Neutrophil granulocytes, or neutrophils, are the most abundant circulating leukocytes in humans and indispensable for antimicrobial immunity, as exemplified in patients with inborn and acquired defects of neutrophils. Neutrophils were long regarded as the foot soldiers of the immune system, solely destined to execute a set of effector functions against invading pathogens before undergoing apoptosis, the latter of which was ascribed to their short life span. This simplistic understanding of neutrophils has now been revised on the basis of insights gained from the use of mouse models and single-cell high-throughput techniques, revealing tissue- and context-specific roles of neutrophils in guiding immune responses. These studies also demonstrated that neutrophil responses were controlled by sophisticated feedback mechanisms, including directed chemotaxis of neutrophils to tissue-draining lymph nodes resulting in modulation of antimicrobial immunity and inflammation. Moreover, findings in mice and humans showed that neutrophil responses adapted to different deterministic cytokine signals, which controlled their migration and effector function as well as, notably, their biologic clock by affecting the kinetics of their aging. These mechanistic insights have important implications for health and disease in humans, particularly, in allergic diseases, such as atopic dermatitis and allergic asthma bronchiale, as well as in autoinflammatory and autoimmune diseases. Hence, our improved understanding of neutrophils sheds light on novel therapeutic avenues, focusing on molecularly defined biologic agents.

Neutrophils as emerging protagonists and targets in chronic inflammatory diseases

INTRODUCTION

Neutrophils are the key cells of our innate immune system with a primary role in host defense. They rapidly arrive at the site of infection and display a range of effector functions including phagocytosis, degranulation, and NETosis to eliminate the invading pathogens. However, in recent years, studies focusing on neutrophil biology have revealed the highly adaptable nature and versatile functions of these cells which extend beyond host defense. Neutrophils are now referred to as powerful mediators of chronic inflammation. In several chronic inflammatory diseases, their untoward actions, such as immense infiltration, hyper-activation, dysregulation of effector functions, and extended survival, eventually contribute to disease pathogenesis. Therefore, a better understanding of neutrophils and their effector functions in prevalent chronic diseases will not only shed light on their role in disease pathogenesis but will also reveal them as novel therapeutic targets.

METHODS

We performed a computer-based online search using the databases, PubMed.gov and Clinical trials.gov for published research and review articles.

RESULTS AND CONCLUSIONS

This review provides an assessment of neutrophils and their crucial involvement in various chronic inflammatory disorders ranging from respiratory, neurodegenerative, autoimmune, and cardiovascular diseases. In addition, we also discuss the therapeutic approach for targeting neutrophils in disease settings that will pave the way forward for future research.

Pathogenesis and virulence of Candida albicans

Candida albicans is a commensal yeast fungus of the human oral, gastrointestinal, and genital mucosal surfaces, and skin. Antibiotic-induced dysbiosis, iatrogenic immunosuppression, and/or medical interventions that impair the integrity of the mucocutaneous barrier and/or perturb protective host defense mechanisms enable C. albicans to become an opportunistic pathogen and cause debilitating mucocutaneous disease and/or life-threatening systemic infections. In this review, we synthesize our current knowledge of the tissue-specific determinants of C. albicans pathogenicity and host immune defense mechanisms.

Neutrophil extracellular traps and complications of liver transplantation

Many end-stage liver disease etiologies are attributed to robust inflammatory cell recruitment. Neutrophils play an important role in inflammatory infiltration and neutrophil phagocytosis, oxidative burst, and degranulation. It has also been suggested that neutrophils may release neutrophil extracellular traps (NETs) to kill pathogens. It has been proven that neutrophil infiltration within the liver contributes to an inflammatory microenvironment and immune cell activation. Growing evidence implies that NETs are involved in the progression of numerous complications of liver transplantation, including ischemia-reperfusion injury, acute rejection, thrombosis, and hepatocellular carcinoma recurrence. NETs are discussed in this comprehensive review, focusing on their effects on liver transplantation complications. Furthermore, we discuss NETs as potential targets for liver transplantation therapy.

NETome: A model to Decode the Human Genome and Proteome of Neutrophil Extracellular Traps

Neutrophils are the most abundant type of white blood cells in humans with biological roles relevant to inflammation, and fighting off infections. Neutrophil Extracellular Traps (NETs) act as enxogenous agents controlling invasion by bacteria, viruses, fungi, metabolic, and traumatic agents. Traditionally, studies have focused on elucidating molecular and cellular pathways preceding NET formation. Here, we developed a model to decode the human genome and proteome of developted NETs. Via in vitro system to differentiate HL-60 human myeloid cell line into neutrophil extracellular trap (ecTrap) producing cells, we isolated and captured ectrap derived DNA and proteins for shotgun sequencing. The genomic sequences revealed accurate delineation of gene composition including immune response genes and mitochondrial enrichment, while providing a reference database for future interrogation. Shotgun proteomics showed global proteins in differentiated cells with specific immune pathways when compared to undifferentiated counterparts. Coupled with omics’ approaches, we validated our system by functional assays and began to dissect host-microbial interactions. Our work provides a new understanding of the genomic and proteomic sequences, establishing the first human database deposition of neutrophil extracellular traps.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

NETosis is critical in patients with severe community-acquired pneumonia

Pneumonia is the fourth leading cause of death globally, and the reason for the high mortality rate of patients with severe community-acquired pneumonia (SCAP) remains elusive. Corticosteroid treatment reduces mortality in adults with SCAP but can cause numerous adverse events. Therefore, novel therapeutic targets need to be explored and new adjunctive immune drugs are urgently required. We analyzed the transcriptome data of peripheral blood leukocytes from patients with SCAP and healthy controls from three perspectives: differentially expressed genes, predicted functions of differentially expressed long non-coding RNAs, and transcriptional read-through. We discovered that the NETosis pathway was top-ranked in patients with SCAP caused by diverse kinds of pathogens. This provides a potential therapeutic strategy for treating patients. Furthermore, we calculated the correlation between the expression of genes involved in NETosis and the ratio of arterial oxygen partial pressure to fractional inspired oxygen. We identified four novel potential therapeutic targets for NETosis in patients with SCAP, including H4C15, H3-5, DNASE1, and PRKCB. In addition, a higher occurrence of transcriptional read-through is associated with a worse outcome in patients with SCAP, which probably can explain the high mortality rate of patients with SCAP.

Reverse effects of Streptococcus mutans physiological states on neutrophil extracellular traps formation as a strategy to escape neutrophil killing

Bacteria in nature are present in different lifestyles with distinct characteristics. Streptococcus mutans is the etiologic pathogen of dental caries and could easily gain access into the bloodstream after oral surgery and adopt a biofilm lifestyle, resulting in infective endocarditis. A growing amount of evidence have revealed that the large web-like structure composed of extracellular DNA and antimicrobial proteins released by neutrophils, named Neutrophil Extracellular Traps (NETs), play an active role in the defense against bacterial invasion. The present study demonstrated that NETs formation was discriminatively affected by S. mutans biofilm and its planktonic counterpart. The free-floating planktonic S. mutans exhibited an active NETs response, whereas the biofilm community exhibited a reverse negative NETs response. Besides, impaired biofilm killing correlated with the decrease in NETs production. Unlike planktonic cells, biofilm avoided the burst of reactive oxygen species (ROS) when co-culture with neutrophils, and the NADPH-oxidase pathway was partially involved. A mice infection model also supported the distinguishing response of neutrophils challenged by different lifestyles of S. mutans. In conclusion, different bacterial physiological states can affect the distinct response of the host-microbe interaction, thus contributing to the anti-pathogen immune response activation and immune surveillance survival.

PAD4 and Its Inhibitors in Cancer Progression and Prognosis

The systemic spread of malignancies and the risk of cancer-associated thrombosis are major clinical challenges in cancer therapy worldwide. As an important post-translational modification enzyme, peptidyl arginine deiminase 4 (PAD4) could mediate the citrullination of protein in different components (including nucleus and cytoplasm, etc.) of a variety of cells (tumor cells, neutrophils, macrophages, etc.), thus participating in gene regulation, neutrophil extracellular trap (NET) and macrophage extracellular trap (MET). Thereby, PAD4 plays an important role in enhancing the growth of primary tumors and facilitating the distant metastasis of cancer cells. In addition, it is related to the formation of cancer-associated thrombosis. Therefore, the development of PAD4-specific inhibitors may be a promising strategy for treating cancer, and it may improve patient prognosis. In this review, we describe PAD4 involvement in gene regulation, protein citrullination, and NET formation. We also discuss its potential role in cancer and cancer-associated thrombosis, and we summarize the development and application of PAD4 inhibitors.

Neutrophil Extracellular Traps, Local IL-8 Expression, and Cytotoxic T-Lymphocyte Response in the Lungs of Patients With Fatal COVID-19

BACKGROUND

Excessive inflammation is pathogenic in the pneumonitis associated with severe COVID-19. Neutrophils are among the most abundantly present leukocytes in the inflammatory infiltrates and may form neutrophil extracellular traps (NETs) under the local influence of cytokines. NETs constitute a defense mechanism against bacteria, but have also been shown to mediate tissue damage in a number of diseases.

RESEARCH QUESTION

Could NETs and their tissue-damaging properties inherent to neutrophil-associated functions play a role in the respiratory failure seen in patients with severe COVID-19, and how does this relate to the SARS-CoV-2 viral loads, IL-8 (CXCL8) chemokine expression, and cytotoxic T-lymphocyte infiltrates?

STUDY DESIGN AND METHODS

Sixteen lung biopsy samples obtained immediately after death were analyzed methodically as exploratory and validation cohorts. NETs were analyzed quantitatively by multiplexed immunofluorescence and were correlated with local levels of IL-8 messenger RNA (mRNA) and the density of CD8+ T-cell infiltration. SARS-CoV-2 presence in tissue was quantified by reverse-transcriptase polymerase chain reaction and immunohistochemistry analysis.

RESULTS

NETs were found in the lung interstitium and surrounding the bronchiolar epithelium with interindividual and spatial heterogeneity. NET density did not correlate with SARS-CoV-2 tissue viral load. NETs were associated with local IL-8 mRNA levels. NETs were also detected in pulmonary thrombi and in only one of eight liver tissues. NET focal presence correlated negatively with CD8+ T-cell infiltration in the lungs.

INTERPRETATION

Abundant neutrophils undergoing NETosis are found in the lungs of patients with fatal COVID-19, but no correlation was found with viral loads. The strong association between NETs and IL-8 points to this chemokine as a potentially causative factor. The function of cytotoxic T-lymphocytes in the immune responses against SARS-CoV-2 may be interfered with by the presence of NETs.

Emerging roles of neutrophils in immune homeostasis

Neutrophils, the most abundant innate immune cells, play essential roles in the innate immune system. As key innate immune cells, neutrophils detect intrusion of pathogens and initiate immune cascades with their functions; swarming (arresting), cytokine production, degranulation, phagocytosis, and projection of neutrophil extracellular trap. Because of their short lifespan and consumption during immune response, neutrophils need to be generated consistently, and generation of newborn neutrophils (granulopoiesis) should fulfill the environmental/systemic demands for training in cases of infection. Accumulating evidence suggests that neutrophils also play important roles in the regulation of adaptive immunity. Neutrophil-mediated immune responses end with apoptosis of the cells, and proper phagocytosis of the apoptotic body (efferocytosis) is crucial for initial and post resolution by producing tolerogenic innate/adaptive immune cells. However, inflammatory cues can impair these cascades, resulting in systemic immune activation; necrotic/pyroptotic neutrophil bodies can aggravate the excessive inflammation, increasing inflammatory macrophage and dendritic cell activation and subsequent T_H1/T_H17 responses contributing to the regulation of the pathogenesis of autoimmune disease. In this review, we briefly introduce recent studies of neutrophil function as players of immune response.