Activated platelets present high mobility group box 1 to neutrophils, inducing autophagy and promoting the extrusion of neutrophil extracellular traps

Neutrophil extracellular traps mediate neuro-immunothrombosis

Neutrophil extracellular traps are primarily composed of DNA and histones and are released by neutrophils to promote inflammation and thrombosis when stimulated by various inflammatory reactions. Neutrophil extracellular trap formation occurs through lytic and non-lytic pathways that can be further classified by formation mechanisms. Histones, von Willebrand factor, fibrin, and many other factors participate in the interplay between inflammation and thrombosis. Neuro-immunothrombosis summarizes the intricate interplay between inflammation and thrombosis during neural development and the pathogenesis of neurological diseases, providing cutting-edge insights into post-neurotrauma thrombotic events. The blood-brain barrier defends the brain and spinal cord against external assaults, and neutrophil extracellular trap involvement in blood-brain barrier disruption and immunothrombosis contributes substantially to secondary injuries in neurological diseases. Further research is needed to understand how neutrophil extracellular traps promote blood-brain barrier disruption and immunothrombosis, but recent studies have demonstrated that neutrophil extracellular traps play a crucial role in immunothrombosis, and identified modulators of neuro-immunothrombosis. However, these neurological diseases occur in blood vessels, and the mechanisms are unclear by which neutrophil extracellular traps penetrate the blood-brain barrier to participate in immunothrombosis in traumatic brain injury. This review discusses the role of neutrophil extracellular traps in neuro-immunothrombosis and explores potential therapeutic interventions to modulate neutrophil extracellular traps that may reduce immunothrombosis and improve traumatic brain injury outcomes.

Relationship between thrombus vWF and NETs with clinical severity and peripheral blood immunocytes' indicators in patients with acute ischemic stroke

OBJECTIVE

To investigate the association between von Willebrand factor (vWF) and neutrophil extracellular traps (NETs) in thrombus with clinical severity and peripheral blood immunocytes' indicators in patients with early-stage acute ischemic stroke (AIS).

METHODS

A retrospective study was conducted using the clinical data of 66 patients with AIS who underwent endovascular mechanical thrombectomy and had their thrombus samples collected. The concentrations of vWF and NETs in the thrombus samples were quantitatively assessed. Peripheral blood samples taken in the early stages of the disease were analyzed for total white blood cell counts (WBC), ratios of neutrophils (NEU%), lymphocytes (LYM%), eosinophils (EOS%), and monocytes (MONO%). The severity of clinical symptoms in these patients was evaluated using the modified Rankin Scale (mRS), Essen Stroke Risk Score (ESRS), Barthel Index (BI), and National Institute of Health Stroke Scale (NIHSS).

RESULTS

Higher vWF levels in thrombus were associated with lower NIHSS scores, while higher NETs levels were associated with higher initial NIHSS scores. In the early stages of AIS, WBC count and vWF levels were negatively correlated, as well as NEU%. LYM% was positively correlated with vWF level; however, it was negatively correlated with NETs. EOS% was positively correlated with vWF levels.

CONCLUSION

In the early stages of AIS, a higher peripheral WBC count and NEU%, combined with decreased EOS% and LYM%, were significantly correlated with a lower vWF level in the thrombus, potentially indicating more severe symptoms. Consequently, the timely administration of vWF-targeted medications is recommended for such patients. Reduced LYM% is indicative of elevated NETs levels and correlated with more severe clinical symptoms. Therefore, the prompt initiation of NETs-targeted medication is warranted for these patients.

Platelets: Orchestrators of immunity in host defense and beyond

Platelets prevent blood loss during vascular injury and contribute to thrombus formation in cardiovascular disease. Beyond these classical roles, platelets are critical for the host immune response. They guard the vasculature against pathogens via specialized receptors, intracellular signaling cascades, and effector functions. Platelets also skew inflammatory responses by instructing innate immune cells, support adaptive immunosurveillance, and influence antibody production and T cell polarization. Concomitantly, platelets contribute to tissue reconstitution and maintain vascular function after inflammatory challenges. However, dysregulated activation of these multitalented cells exacerbates immunopathology with ensuing microvascular clotting, excessive inflammation, and elevated risk of macrovascular thrombosis. This dichotomy underscores the critical importance of precisely defining and potentially modulating platelet function in immunity.

HMGB1: A New Target for Ischemic Stroke and Hemorrhagic Transformation

Stroke in China is distinguished by its high rates of morbidity, recurrence, disability, and mortality. The ultra-early administration of rtPA is essential for restoring perfusion in acute ischemic stroke, though it concurrently elevates the risk of hemorrhagic transformation. High-mobility group box 1 (HMGB1) emerges as a pivotal player in neuroinflammation after brain ischemia and ischemia-reperfusion. Released passively by necrotic cells and actively secreted, including direct secretion of HMGB1 into the extracellular space and packaging of HMGB1 into intracellular vesicles by immune cells, glial cells, platelets, and endothelial cells, HMGB1 represents a prototypical damage-associated molecular pattern (DAMP). It is intricately involved in the pathogenesis of atherosclerosis, thromboembolism, and detrimental inflammation during the early phases of ischemic stroke. Moreover, HMGB1 significantly contributes to neurovascular remodeling and functional recovery in later stages. Significantly, HMGB1 mediates hemorrhagic transformation by facilitating neuroinflammation, directly compromising the integrity of the blood-brain barrier, and enhancing MMP9 secretion through its interaction with rtPA. As a systemic inflammatory factor, HMGB1 is also implicated in post-stroke depression and an elevated risk of stroke-associated pneumonia. The role of HMGB1 extends to influencing the pathogenesis of ischemia by polarizing various subtypes of immune and glial cells. This includes mediating excitotoxicity due to excitatory amino acids, autophagy, MMP9 release, NET formation, and autocrine trophic pathways. Given its multifaceted role, HMGB1 is recognized as a crucial therapeutic target and prognostic marker for ischemic stroke and hemorrhagic transformation. In this review, we summarize the structure and redox properties, secretion and pathways, regulation of immune cell activity, the role of pathophysiological mechanisms in stroke, and hemorrhage transformation for HMGB1, which will pave the way for developing new neuroprotective drugs, reduction of post-stroke neuroinflammation, and expansion of thrombolysis time window.

The role of platelets in central hubs of inflammation: A literature review

Platelets are increasingly recognized for their multifaceted roles in inflammation beyond their traditional involvement in haemostasis. This review consolidates knowledge on platelets as critical players in inflammatory responses. This study did an extensive search of electronic databases and identified studies on platelets in inflammation, focusing on molecular mechanisms, cell interactions, and clinical implications, emphasizing recent publications. Platelets contribute to inflammation via surface receptors, release of mediators, and participation in neutrophil extracellular trap formation. They are implicated in diseases like atherosclerosis, rheumatoid arthritis, and sepsis, highlighting their interaction with immune cells as pivotal in the onset and resolution of inflammation. Platelets are central to regulating inflammation, offering new therapeutic targets for inflammatory diseases. Future research should explore specific molecular pathways of platelets in inflammation for therapeutic intervention.

The role of neutrophil extracellular trap formation in kidney transplantation: Implications from donors to the recipient

Kidney transplantation remains the gold standard for patients with end-stage renal disease, but severe donor organ shortage has led to long waiting lists. The utilization of expanded criteria donor kidneys within the category of deceased donors has enlarged the pool of available kidneys for transplantation; however, these grafts often have an increased risk for delayed graft function or reduced graft survival following transplantation. During brain or circulatory death, neutrophils are recruited to the vascular beds of kidneys where a proinflammatory microenvironment might prime the formation of neutrophil extracellular traps (NETs), web-like structures, containing proteolytic enzymes, DNA, and histones. NETs are known to cause tissue damage and specifically endothelial damage while activating other systems such as coagulation and complement, contributing to tissue injury and an unfavorable prognosis in various diseases. In lung transplantation and kidney transplantation studies, NETs have also been associated with primary graft dysfunction or rejection. In this review, the role that NETs might play across the different phases of transplantation, already initiated in the donor, during preservation, and in the recipient, will be discussed. Based on current knowledge, NETs might be a promising therapeutic target to improve graft outcomes.

A2AR-mediated CXCL5 upregulation on macrophages promotes NSCLC progression via NETosis

Tumor-associated macrophages (TAMs) are abundant in tumors and interact with tumor cells, leading to the formation of an immunosuppressive microenvironment and tumor progression. Although many studies have explored the mechanisms underlying TAM polarization and its immunosuppressive functions, understanding of its progression remains limited. TAMs promote tumor progression by secreting cytokines, which subsequently recruit immunosuppressive cells to suppress the antitumor immunity. In this study, we established an in vitro model of macrophage and non-small cell lung cancer (NSCLC) cell co-culture to explore the mechanisms of cell-cell crosstalk. We observed that in NSCLC, the C-X-C motif chemokine ligand 5 (CXCL5) was upregulated in macrophages because of the stimulation of A2AR by adenosine. Adenosine was catalyzed by CD39 and CD73 in macrophages and tumor cells, respectively. Nuclear factor kappa B (NFκB) mediated the A2AR stimulation of CXCL5 upregulation in macrophages. Additionally, CXCL5 stimulated NETosis in neutrophils. Neutrophil extracellular traps (NETs)-treated CD8+ T cells exhibited upregulation of exhaustion-related and cytosolic DNA sensing pathways and downregulation of effector-related genes. However, A2AR inhibition significantly downregulated CXCL5 expression and reduced neutrophil infiltration, consequently alleviating CD8+ T cell dysfunction. Our findings suggest a complex interaction between tumor and immune cells and its potential as therapeutic target.

Neutrophil extracellular traps mediate cardiomyocyte ferroptosis via the Hippo-Yap pathway to exacerbate doxorubicin-induced cardiotoxicity

Doxorubicin-induced cardiotoxicity (DIC), which is a cardiovascular complication, has become the foremost determinant of decreased quality of life and mortality among survivors of malignant tumors, in addition to recurrence and metastasis. The limited ability to accurately predict the occurrence and severity of doxorubicin-induced injury has greatly hindered the prevention of DIC, but reducing the dose to mitigate side effects may compromise the effective treatment of primary malignancies. This has posed a longstanding clinical challenge for oncologists and cardiologists. Ferroptosis in cardiomyocytes has been shown to be a pivotal mechanism underlying cardiac dysfunction in DIC. Ferroptosis is influenced by multiple factors. The innate immune response, as exemplified by neutrophil extracellular traps (NETs), may play a significant role in the regulation of ferroptosis. Therefore, the objective of this study was to investigate the involvement of NETs in doxorubicin-induced cardiomyocyte ferroptosis and elucidate their regulatory role. This study confirmed the presence of NETs in DIC in vivo. Furthermore, we demonstrated that depleting neutrophils effectively reduced the occurrence of doxorubicin-induced ferroptosis and myocardial injury in DIC. Additionally, our findings showed the pivotal role of high mobility group box 1 (HMGB1) as a critical molecule implicated in DIC and emphasized its involvement in the modulation of ferroptosis subsequent to NETs inhibition. Mechanistically, we obtained preliminary evidence suggesting that doxorubicin-induced NETs could modulate yes-associated protein (YAP) activity by releasing HMGB1, which subsequently bound to toll like receptor 4 (TLR4) on the cardiomyocyte membrane, thereby influencing cardiomyocyte ferroptosis in vitro. Our findings suggest that doxorubicin-induced NETs modulate cardiomyocyte ferroptosis via the HMGB1/TLR4/YAP axis, thereby contributing to myocardial injury. This study offers a novel approach for preventing and alleviating DIC by targeting alterations in the immune microenvironment.

Mass production of iPSC-derived platelets toward the clinical application

The ex vivo production of platelets from induced pluripotent cells (iPSCs) may offer a safer and sustainable alternative for transfusions and drug delivery systems (DDS). However, the mass production of the clinically required number of iPSC-derived platelets (iPSC-PLTs) is challenging. Here, we introduce recent technologies for mass production and the first-in-human clinical trial using ex vivo iPSC-PLTs. To this end, we established immortalized megakaryocyte progenitor cell lines (imMKCLs) as an expandable master cell bank (MCB) through the overexpression of c-MYC, BMI1 and BCL-XL, which modulated megakaryopoiesis and thrombopoiesis. We also optimized a culture cocktail for maturation of the imMKCLs by mixing an aryl hydrocarbon receptor (AhR) antagonist, SR1/GNF-316; a Rho-associated protein kinase (ROCK) inhibitor, Y-27632/Y-39983; and a small-molecule compound replacing recombinant thrombopoietin (TPO), TA-316. Finally, we discovered the importance of turbulence on the manufacturing of intact iPSC-PLTs, allowing us to develop a turbulence-based bioreactor, VerMES. Combination of the MCB and VerMES enabled us to produce more than 100 billion iPSC-PLTs, leading to the first-in-human clinical trial. Despite these advancements, many challenges remain before expanding the clinical implementation of this strategy.

Platelets in Hemostasis, Thrombosis, and Inflammation After Major Trauma

Trauma currently accounts for 10% of the total global burden of disease and over 5 million deaths per year, making it a leading cause of morbidity and mortality worldwide. Although recent advances in early resuscitation have improved early survival from critical injury, the mortality rate in patients with major hemorrhage approaches 50% even in mature trauma systems. A major determinant of clinical outcomes from a major injury is a complex, dynamic hemostatic landscape. Critically injured patients frequently present to the emergency department with an acute traumatic coagulopathy that increases mortality from bleeding, yet, within 48 to 72 hours after injury will switch from a hypocoagulable to a hypercoagulable state with increased risk of venous thromboembolism and multiple organ dysfunction. This review will focus on the role of platelets in these processes. As effectors of hemostasis and thrombosis, they are central to each phase of recovery from injury, and our understanding of postinjury platelet biology has dramatically advanced over the past decade. This review describes our current knowledge of the changes in platelet behavior that occur following major trauma, the mechanisms by which these changes develop, and the implications for clinical outcomes. Importantly, supported by research in other disease settings, this review also reflects the emerging role of thromboinflammation in trauma including cross talk between platelets, innate immune cells, and coagulation. We also address the unresolved questions and significant knowledge gaps that remain, and finally highlight areas that with the further study will help deliver further improvements in trauma care.

Dying to Defend: Neutrophil Death Pathways and their Implications in Immunity

Neutrophils, accounting for ≈70% of human peripheral leukocytes, are key cells countering bacterial and fungal infections. Neutrophil homeostasis involves a balance between cell maturation, migration, aging, and eventual death. Neutrophils undergo different death pathways depending on their interactions with microbes and external environmental cues. Neutrophil death has significant physiological implications and leads to distinct immunological outcomes. This review discusses the multifarious neutrophil death pathways, including apoptosis, NETosis, pyroptosis, necroptosis, and ferroptosis, and outlines their effects on immune responses and disease progression. Understanding the multifaceted aspects of neutrophil death, the intersections among signaling pathways and ramifications of immunity will help facilitate the development of novel therapeutic methods.

Trauma-induced innate immune activation and disseminated intravascular coagulation

Dysregulated innate immunity participates in the pathomechanisms of disseminated intravascular coagulation (DIC) in trauma-induced coagulopathy. Accidental and regulated cell deaths and neutrophil extracellular traps release damage-associated molecular patterns (DAMPs), such as histones, nuclear and mitochondrial DNA, and high-mobility group box 1, into circulation immediately after trauma. DAMP-induced inflammation activation releases tissue factor-bearing procoagulant extracellular vesicles through gasdermin D-mediated pore formation and plasma membrane rupture by regulated cell death. DAMPs also evoke systemic inflammation, platelet, coagulation activation, and impaired fibrinolysis associated with endothelial injury, leading to the dysfunction of anticoagulation systems, which are the main pathophysiological mechanisms of DIC. All these processes induce systemic thrombin generation in vivo, not restricted to the injury sites immediately after trauma. Thrombin generation at the site of injury stops bleeding and maintains homeostasis. However, DIC associated with endothelial injury generates massive thrombin, enhancing protease-activated, receptor-mediated bidirectional interplays between inflammation and coagulation, aggravating the diverse actions of thrombin and disturbing homeostasis. Insufficiently regulated thrombin causes disseminated microvascular thrombosis, resulting in tissue hypoxia due to reduced oxygen delivery, and mitochondrial dysfunction due to DAMPs causes tissue dysoxia. In addition, DAMP-induced calcium influx and overload, as well as neutrophil activation, play a role in endothelial cell injury. Tissue hypoxia and cytotoxicity result in multiple organ dysfunction in DIC after trauma. Controls against dysregulated innate immunity evoking systemic inflammation, thrombin generation, and cytotoxicity are key issues in improving the prognosis of DIC in trauma-induced coagulopathy.

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) in label-free characterization of erythrocyte membranes and extracellular vesicles at the nano-scale and molecular level

The manuscript presents the potential of surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) for label-free characterization of extracellular microvesicles (EVs) and their isolated membranes derived from red blood cells (RBCs) at the nanoscale and at the single-molecule level, providing detection of a few individual amino acids, protein and lipid membrane compartments. The study shows future directions for research, such as investigating the use of the mentioned techniques for the detection and diagnosis of diseases. We demonstrate that SERS and TERS are powerful techniques for identifying the biochemical composition of EVs and their membranes, allowing the detection of small molecules, lipids, and proteins. Furthermore, extracellular vesicles released from red blood cells (REVs) can be broadly classified into exosomes, microvesicles, and apoptotic bodies, based on their size and biogenesis pathways. Our study specifically focuses on microvesicles that range from 100 to 1000 nanometres in diameter, as presented in AFM images. Using SERS and TERS spectra obtained for REVs and their membranes, we were able to characterize the chemical and structural properties of microvesicle membranes with high sensitivity and specificity. This information may help better distinguish and categorize different types of EVs, leading to a better understanding of their functions and potential biomedical applications.

Increased formation of neutrophil extracellular traps induced by autophagy and identification of autophagy-related biomarkers in systemic lupus erythematosus

Abnormal death of neutrophils and the subsequent ineffective clearance of cell fragments result in production of autoantigens that can lead to systemic lupus erythematosus (SLE). Excessive formation of neutrophil extracellular traps (NETs) can trigger the synthesis of pro-inflammatory cytokines such as type I interferons, leading to tissue damage and immune dysfunction in SLE patients. In this study, we found that a decrease in neutrophil counts in the peripheral blood was correlated with clinical parameters in SLE patients. Patients with low neutrophil counts had high renal activity index and chronicity index scores. NET formation and neutrophil autophagy in SLE patients were increased. The autophagy inhibitor hydroxychloroquine was shown to restrict NET formation. Using comprehensive bioinformatics analysis, we found that the expression of the autophagy-related gene, hypoxia-inducible factor 1A (HIF1A), was enhanced in peripheral neutrophils and in the renal glomeruli in SLE patients. Targeting HIF1A could be a potential therapeutic approach for SLE.

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.

What is the role of the neutrophil extracellular traps in the cardiovascular disease burden associated with hemodialysis bioincompatibility?

Despite significant progress in dialysis modalities, intermittent renal replacement therapy remains an "unphysiological" treatment that imperfectly corrects uremic disorders and may lead to low-grade chronic inflammation, neutrophil activation, and oxidative stress due to repetitive blood/membrane interactions contributing to the "remaining uremic syndrome" and cardiovascular disease burden of hemodialysis patients. Understanding dialysis bioincompatibility pathways still remains a clinical and biochemical challenge. Indeed, surrogate biomarkers of inflammation including C-reactive protein could not discriminate between all components involved in these complex pathways. A few examples may serve to illustrate the case. Cytokine release during dialysis sessions may be underestimated due to their removal using high-flux dialysis or hemodiafiltration modalities. Complement activation is recognized as a key event of bioincompatibility. However, it appears as an early and transient event with anaphylatoxin level normalization at the end of the dialysis session. Complement activation is generally assumed to trigger leukocyte stimulation leading to proinflammatory mediators' secretion and oxidative burst. In addition to being part of the innate immune response involved in eliminating physically and enzymatically microbes, the formation of Neutrophil Extracellular Traps (NETs), known as NETosis, has been recently identified as a major harmful component in a wide range of pathologies associated with inflammatory processes. NETs result from the neutrophil degranulation induced by reactive oxygen species overproduction via NADPH oxidase and consist of modified chromatin decorated with serine proteases, elastase, bactericidal proteins, and myeloperoxidase (MPO) that produces hypochlorite anion. Currently, NETosis remains poorly investigated as a sensitive and integrated marker of bioincompatibility in dialysis. Only scarce data could be found in the literature. Oxidative burst and NADPH oxidase activation are well-known events in the bioincompatibility phenomenon. NET byproducts such as elastase, MPO, and circulating DNA have been reported to be increased in dialysis patients more specifically during dialysis sessions, and were identified as predictors of poor outcomes. As NETs and MPO could be taken up by endothelium, NETs could be considered as a vascular memory of intermittent bioincompatibility phenomenon. In this working hypothesis article, we summarized the puzzle pieces showing the involvement of NET formation during hemodialysis and postulated that NETosis may act as a disease modifier and may contribute to the comorbid burden associated with dialysis bioincompatibility.

Interactions between neutrophils and T-helper 17 cells

Neutrophils comprise the majority of immune cells in human peripheral circulation, have potent antimicrobial activities, and are clinically significant in their abundance, heterogeneity, and subcellular localization. In the past few years, the role of neutrophils as components of the innate immune response has been studied in numerous ways, and these cells are crucial in fighting infections, autoimmune diseases, and cancer. T-helper 17 (Th17) cells that produce interleukin 17 (IL-17) are critical in fighting infections and maintaining mucosal immune homeostasis, whereas they mediate several autoimmune diseases. Neutrophils affect adaptive immune responses by interacting with adaptive immune cells. In this review, we describe the physiological roles of both Th17 cells and neutrophils and their interactions and briefly describe the pathological processes in which these two cell types participate. We provide a summary of relevant drugs targeting IL-17A and their clinical trials. Here, we highlight the interactions between Th17 cells and neutrophils in diverse pathophysiological situations.

Mannose binding lectin-associated serine protease-1 is a novel contributor to myocardial ischemia/reperfusion injury

BACKGROUND

The lectin pathway has been demonstrated to play a critical role in the pathological process of myocardial ischemia/reperfusion injury (IRI). Mannose-binding lectin (MBL)-associated serine protease-1 (MASP-1), especially different from other components of the lectin pathway, mediates proinflammatory and procoagulant reactions independent of complement cascades. However, the role of MASP-1 in myocardial IRI remains unknown so far.

METHODS

Myocardial IRI was established with 45 min ischemia and 24 h reperfusion in mice. C1 inhibitor, as the natural inhibitor of MASP-1, was administrated at 20 IU/Kg via tail vein 5 min before surgical operation. Cardiac function and myocardial infarct size were assessed. Myocardial histology and fibrosis were evaluated by H&E and Masson staining, respectively. Deposition of MASP-1, expression of PAR-1/4 and neutrophil extracellular traps (NET) were investigated on myocardium tissue by IHC staining. Cell apoptosis was detected by TUNEL assay. Levels of myocardial enzymes and proinflammatory cytokines were determined by ELISA.

RESULTS

Inhibition of MASP-1 with C1 INH improved cardiac function and alleviated myocardium tissue injury (infarct size, enzymes, histology and fibrosis) after myocardial IRI. Deposition of MASP-1 and expression PAR-1, as well as NET formation in myocardial tissue were suppressed by MASP-1 inhibitor, while PAR-4 was elevated. Levels of apoptosis, HMGB-1 and IL-6 were lower after blocking MASP-1. Yet, IL-8 and TNF-α remained unchanged.

CONCLUSIONS

MASP-1, as a new contributor, played a critical role in myocardial IRI. Inhibition of MASP-1 protected myocardial tissue from IRI probably via regulation of PARs/NET pathway. This may provide a novel target strategy against myocardial IRI.

Immune Thrombosis: Exploring the Significance of Immune Complexes and NETosis

Neutrophil extracellular traps (NETs) are major contributors to inflammation and autoimmunity, playing a key role in the development of thrombotic disorders. NETs, composed of DNA, histones, and numerous other proteins serve as scaffolds for thrombus formation and promote platelet activation, coagulation, and endothelial dysfunction. Accumulating evidence indicates that NETs mediate thrombosis in autoimmune diseases, viral and bacterial infections, cancer, and cardiovascular disease. This article reviews the role and mechanisms of immune complexes in NETs formation and their contribution to the generation of a prothrombotic state. Immune complexes are formed by interactions between antigens and antibodies and can induce NETosis by the direct activation of neutrophils via Fc receptors, via platelet activation, and through endothelial inflammation. We discuss the mechanisms by which NETs induced by immune complexes contribute to immune thrombotic processes and consider the potential development of therapeutic strategies. Targeting immune complexes and NETosis hold promise for mitigating thrombotic events and reducing the burden of immune thrombosis.

The intricate relationship between autoimmunity disease and neutrophils death patterns: a love-hate story

Autoimmune diseases are pathological conditions that result from the misidentification of self-antigens in immune system, leading to host tissue damage and destruction. These diseases can affect different organs and systems, including the blood, joints, skin, and muscles. Despite the significant progress made in comprehending the underlying pathogenesis, the complete mechanism of autoimmune disease is still not entirely understood. In autoimmune diseases, the innate immunocytes are not functioning properly: they are either abnormally activated or physically disabled. As a vital member of innate immunocyte, neutrophils and their modes of death are influenced by the microenvironment of different autoimmune diseases due to their short lifespan and diverse death modes. Related to neutrophil death pathways, apoptosis is the most frequent cell death form of neutrophil non-lytic morphology, delayed or aberrant apoptosis may contribute to the development anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). In addition, NETosis, necroptosis and pyroptosis which are parts of lytic morphology exacerbate disease progression through various mechanisms in autoimmune diseases. This review aims to summarize recent advancements in understanding neutrophil death modes in various autoimmune diseases and provide insights into the development of novel therapeutic approaches for autoimmune diseases.

Neutrophil extracellular traps and long COVID

Post-acute COVID-19 sequelae, commonly known as long COVID, encompasses a range of systemic symptoms experienced by a significant number of COVID-19 survivors. The underlying pathophysiology of long COVID has become a topic of intense research discussion. While chronic inflammation in long COVID has received considerable attention, the role of neutrophils, which are the most abundant of all immune cells and primary responders to inflammation, has been unfortunately overlooked, perhaps due to their short lifespan. In this review, we discuss the emerging role of neutrophil extracellular traps (NETs) in the persistent inflammatory response observed in long COVID patients. We present early evidence linking the persistence of NETs to pulmonary fibrosis, cardiovascular abnormalities, and neurological dysfunction in long COVID. Several uncertainties require investigation in future studies. These include the mechanisms by which SARS-CoV-2 brings about sustained neutrophil activation phenotypes after infection resolution; whether the heterogeneity of neutrophils seen in acute SARS-CoV-2 infection persists into the chronic phase; whether the presence of autoantibodies in long COVID can induce NETs and protect them from degradation; whether NETs exert differential, organ-specific effects; specifically which NET components contribute to organ-specific pathologies, such as pulmonary fibrosis; and whether senescent cells can drive NET formation through their pro-inflammatory secretome in long COVID. Answering these questions may pave the way for the development of clinically applicable strategies targeting NETs, providing relief for this emerging health crisis.

Platelets and the Atherosclerotic Process: An Overview of New Markers of Platelet Activation and Reactivity, and Their Implications in Primary and Secondary Prevention

The key role played by platelets in the atherosclerosis physiopathology, especially in the acute setting, is ascertained: they are the main actors during thrombus formation and, thus, one of the major investigated elements related to atherothrombotic process involving coronary arteries. Platelets have been studied from different points of view, according with the technology advances and the improvement in the hemostasis knowledge achieved in the last years. Morphology and reactivity constitute the first aspects investigated related to platelets with a significant body of evidence published linking a number of their values and markers to coronary artery disease and cardiovascular events. Recently, the impact of genetics on platelet activation has been explored with promising findings as additional instrument for patient risk stratification; however, this deserves further confirmations. Moreover, the interplay between immune system and platelets has been partially elucidated in the last years, providing intriguing elements that will be basic components for future research to better understand platelet regulation and improve cardiovascular outcome of patients.

Damage-associated molecular patterns and fibrinolysis perturbation are associated with lethal outcomes in traumatic injury

BACKGROUND

Upon cellular injury, damage-associated molecular patterns (DAMPs) are released into the extracellular space and evoke proinflammatory and prothrombotic responses in animal models of sterile inflammation. However, in clinical settings, the dynamics of DAMP levels after trauma and links between DAMPs and trauma-associated coagulopathy remain largely undetermined.

METHODS

Thirty-one patients with severe trauma, who were transferred to Kagoshima City Hospital between June 2018 and December 2019, were consecutively enrolled in this study. Blood samples were taken at the time of delivery, and 6 and 12 h after the injury, and once daily thereafter. The time-dependent changes of coagulation/fibrinolysis markers, including thrombin-antithrombin complex, α2-plasmin inhibitor (α2-PI), plasmin-α2-PI complex, and plasminogen activator inhibitor-1 (PAI-1), and DAMPs, including high mobility group box 1 and histone H3, were analyzed. The relationship between coagulation/fibrinolysis markers, DAMPs, Injury Severity Score, in-hospital death, and amount of blood transfusion were analyzed.

RESULTS

The activation of coagulation/fibrinolysis pathways was evident at the time of delivery. In contrast, PAI-1 levels remained low at the time of delivery, and then were elevated at 6-12 h after traumatic injury. Histone H3 and high mobility group box 1 levels were elevated at admission, and gradually subsided over time. PAI-1 levels at 6 h were associated with serum histone H3 levels at admission. Increased histone H3 levels and plasmin-α2-PI complex levels were associated with in-hospital mortality. α2-PI levels at admission showed the strongest negative correlation with the amount of blood transfusion.

CONCLUSION

The elevation of histone H3 levels and fibrinolysis perturbation are associated with fatal outcomes in patients with traumatic injury. Patients with low α2-PI levels at admission tend to require blood transfusion.

Neutrophil extracellular traps mediate deep vein thrombosis: from mechanism to therapy

Deep venous thrombosis (DVT) is a part of venous thromboembolism (VTE) that clinically manifests as swelling and pain in the lower limbs. The most serious clinical complication of DVT is pulmonary embolism (PE), which has a high mortality rate. To date, its underlying mechanisms are not fully understood, and patients usually present with clinical symptoms only after the formation of the thrombus. Thus, it is essential to understand the underlying mechanisms of deep vein thrombosis for an early diagnosis and treatment of DVT. In recent years, many studies have concluded that Neutrophil Extracellular Traps (NETs) are closely associated with DVT. These are released by neutrophils and, in addition to trapping pathogens, can mediate the formation of deep vein thrombi, thereby blocking blood vessels and leading to the development of disease. Therefore, this paper describes the occurrence and development of NETs and discusses the mechanism of action of NETs on deep vein thrombosis. It aims to provide a direction for improved diagnosis and treatment of deep vein thrombosis in the near future.

Pathophysiology of Disseminated Intravascular Coagulation in Sepsis: A Clinically Focused Overview

Sepsis is a major global health problem that results from a dysregulated and uncontrolled host response to infection, causing organ failure. Despite effective anti-infective therapy and supportive treatments, the mortality rate of sepsis remains high. Approximately 30-80% of patients with sepsis may develop disseminated intravascular coagulation (DIC), which can double the mortality rate. There is currently no definitive treatment approach for sepsis, with etiologic treatment being the cornerstone of therapy for sepsis-associated DIC. Early detection, diagnosis, and treatment are critical factors that impact the prognosis of sepsis-related DIC. Over the past several decades, researchers have made continuous efforts to better understand the mechanisms of DIC in sepsis, as well as improve its quantitative diagnosis and treatment. This article aims to provide a comprehensive overview of the current understanding of sepsis-related DIC, focusing on common causes and diagnoses, with the goal of guiding healthcare providers in the care of patients with sepsis.

Platelet-derived extracellular vesicles promote endothelial dysfunction in sepsis by enhancing neutrophil extracellular traps

BACKGROUND

The role of platelet-derived extracellular vesicles (PEVs) in the development of sepsis was investigated in this study.

METHODS

After collection of blood samples from sepsis patients and normal volunteers, the extracellular vesicles (EVs) were separated, followed by the isolation of PEVs from the blood of rats. Next, a sepsis rat model was constructed by cecal ligation and puncture (CLP), and rats received tail vein injection of PEVs to explore the role of PEVs in sepsis. Subsequently, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) were adopted to determine the diameter of EVs and observe the morphology of PEVs, respectively; flow cytometry to detect the percentage of CD41-and CD61-positive EVs in isolated EVs; and ELISA to assess neutrophil extracellular trap (NET) formation, endothelial function injury-related markers in clinical samples or rat blood and serum inflammatory factor level.

RESULTS

Compared with normal volunteers, the percentage of CD41- and CD61-positive EVs and the number of EVs were significantly elevated in sepsis patients. Moreover, sepsis patients also presented notably increased histone H3, myeloperoxidase (MPO), angiopoietin-2 and endocan levels in the blood, and such increase was positively correlated with the number of EVs. Also, animal experiments demonstrated that PEVs significantly promoted NET formation, mainly manifested as up-regulation of histone H3, high mobility group protein B1 (HMGB1), and MPO; promoted endothelial dysfunction (up-regulation of angiopoietin-2, endocan, and syndecan-1); and stimulated inflammatory response (up-regulation of interleukin (IL) -1β, IL-6, tumor necrosis factor (TNF)-α, and monocyte chemoattractant protein (MCP) -1) in the blood of sepsis rats.

CONCLUSION

PEVs aggravate endothelial function injury and inflammatory response in sepsis by promoting NET formation.

Neutrophil extracellular traps contributing to atherosclerosis: From pathophysiology to clinical implications

Neutrophil extracellular traps (NETs) are network-like structures of chromatin filaments decorated by histones, granules, and cytoplasmic-derived proteins expelled by activated neutrophils under multiple pathogenic conditions. NETs not only capture pathogens in innate immunity but also respond to sterile inflammatory stimuli in atherosclerosis, such as lipoproteins and inflammatory cytokines. Atherosclerosis is a lipid-driven chronic inflammatory disease characterized by the accumulation and transformation of inflammatory cells, and smooth muscle cells in the intimal space. NETs-derived extracellular components possess toxic and proinflammatory properties leading to cellular dysfunction and tissue damage, which may establish a link among lipid metabolism, inflammatory immunity, and atherosclerosis. In this review, we discuss recent advances regarding the role of NETs engaged in the pathogenesis of atherosclerosis, particularly focusing on the interaction with lipids and inflammasomes, crosstalk with smooth muscle cells and inflammatory cells, and the association with aging. We also evaluate the current knowledge on the potential of NETs as biomarkers and therapeutic targets for atherosclerosis and its related diseases in clinical practice.

Comprehensive bioinformatics analysis reveals the crosstalk genes and immune relationship between the systemic lupus erythematosus and venous thromboembolism

Background

It is well known that patients with systemic lupus erythematosus (SLE) had a high risk of venous thromboembolism (VTE). This study aimed to identify the crosstalk genes between SLE and VTE and explored their clinical value and molecular mechanism initially.

Methods

We downloaded microarray datasets of SLE and VTE from the Gene Expression Omnibus (GEO) dataset. Differential expression analysis was applied to identify the crosstalk genes (CGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed on the shared genes. The shared diagnostic biomarkers of the two diseases were further screened from CGs using least absolute shrinkage and selection operator (Lasso) regression. Two risk scores for SLE and VTE were constructed separately to predict the likelihood of illness according to the diagnostic biomarkers using a logical regression algorithm. The immune infiltration levels of SEL and VTE were estimated via the CIBERSORT algorithm and the relationship of CGs with immune cell infiltration was investigated. Finally, we explored potential phenotype subgroups in SLE and VTE based on the expression level of CGs through the consensus clustering method and studied immune cell infiltration in different subtypes.

Result

A total of 171 CGs were obtained by the intersection of differentially expressed genes (DEGs) between SLE and VTE cohorts. The functional enrichment shown these CGs were mainly related to immune pathways. After screening by lasso regression, we found that three hub CGs (RSAD2, HSP90AB1, and FPR2) were the optimal shared diagnostic biomarkers for SLE and VTE. Based on the expression level of RSAD2 and HSP90AB1, two risk prediction models for SLE and VTE were built by multifactor logistic regression and systemically validated in internal and external validation datasets. The immune infiltration results revealed that CGs were highly correlated with multiple infiltrated immunocytes. Consensus clustering was used to respectively regroup SLE and VTE patients into C1 and C2 clusters based on the CGs expression profile. The levels of immune cell infiltration and immune activation were higher in C1 than in C2 subtypes.

Conclusion

In our study, we further screen out diagnostic biomarkers from crosstalk genes SLE and VTE and built two risk scores. Our findings reveal a close relationship between CGs and the immune microenvironment of diseases. This provides clues for further exploring the common mechanism and interaction between the two diseases.

Platelet extracellular vesicles: Darkness and light of autoimmune diseases

Autoimmune diseases are characterized by a breakdown of immune tolerance, leading to inflammation and irreversible end-organ tissue damage. Platelet extracellular vesicles are cellular elements that are important in blood circulation and actively participate in inflammatory and immune responses through intercellular communication and interactions between inflammatory cells, immune cells, and their secreted factors. Therefore, platelet extracellular vesicles are the "accelerator" in the pathological process of autoimmune diseases; however, this robust set of functions of platelet extracellular vesicles has also prompted new advances in therapeutic strategies for autoimmune diseases. In this review, we update fundamental mechanisms based on platelet extracellular vesicles communication function in autoimmune diseases. We also focus on the potential role of platelet extracellular vesicles for the treatment of autoimmune diseases. Some recent studies have found that antiplatelet aggregation drugs, specific biological agents can reduce the release of platelet extracellular vesicles. Platelet extracellular vesicles can also serve as vehicles to deliver drugs to targeted cells. It seems that we can try to silence or inhibit microRNA carried by platelet extracellular vesicles transcription and regulate the target cells to treat autoimmune diseases as platelet extracellular vesicles can transfer microRNA to other cells to regulate immune-inflammatory responses. Hopefully, the information presented here will provide hope for patients with autoimmune diseases.

Mapping current status and emerging trends in NETosis: A bibliometric study

BACKGROUND

NETosis is a critical innate immune mechanism of neutrophils that contributes to the accelerated progression of autoimmune diseases, thrombosis, cancer, and coronavirus disease 2019 (COVID-19). This study qualitatively and quantitatively analyzed the relevant literature by bibliometric methods in order to provide a more comprehensive and objective view of the knowledge dynamics in the field.

METHODS

The literature on NETosis was downloaded from the Web of Science Core Collection, analyzed with VOSviewer, CiteSpace, and Microsoft for co-authorship, co-occurrence, and co-citation analysis.

RESULTS

In the field of NETosis, the United States was the most influential countries. Harvard University was the most active institutions. Mariana J. Kaplan and Brinkmann V were, respectively, the most prolific and most co-cited authors. Frontiers in Immunology, Journal of Immunology, Plos One, Blood, Science, Journal of Cell Biology, and Nature Medicine were the most influential journals. The top 15 keywords are associated with immunological and NETosis formation mechanisms. The keywords with the strongest burst detection were mainly related to COVID-19 (coronavirus, ACE2, SARS coronavirus, cytokine storm, pneumonia, neutrophil to lymphocyte ratio), and cancer (circulating tumor cell).

CONCLUSION

Research on NETosis is currently booming. The mechanism of NETosis and its role in innate immunity, autoimmune diseases, especially systemic lupus erythematosus and rheumatoid arthritis, and thrombosis are the focus of research in the field of NETosis. A future study will concentrate on the function of NETosis in COVID-19 and recurrent metastasis of cancer.

NET-(works) in arterial and venous thrombo-occlusive diseases

Formation of Neutrophil Extracellular Traps (NETosis), accompanied by the release of extracellular decondensed chromatin and pro-inflammatory as well as pro-thrombotic factors, is a pivotal element in the development and progression of thrombo-occlusive diseases. While the process of NETosis is based on complex intracellular signalling mechanisms, it impacts a wide variety of cells including platelets, leukocytes and endothelial cells. Consequently, although initially mainly associated with venous thromboembolism, NETs also affect and mediate atherothrombosis and its acute complications in the coronary, cerebral and peripheral arterial vasculature. In this context, besides deep vein thrombosis and pulmonary embolism, NETs in atherosclerosis and especially its acute complications such as myocardial infarction and ischemic stroke gained a lot of attention in the cardiovascular research field in the last decade. Thus, since the effect of NETosis on platelets and thrombosis in general is extensively discussed in other review articles, this review focusses on the translational and clinical relevance of NETosis research in cardiovascular thrombo-occlusive diseases. Consequently, after a brief summary of the neutrophil physiology and the cellular and molecular mechanisms underlying NETosis are presented, the role of NETosis in atherosclerotic and venous thrombo-occlusive diseases in chronic and acute settings are discussed. Finally, potential prevention and treatment strategies of NET-associated thrombo-occlusive diseases are considered.

Platelet-neutrophil interaction in COVID-19 and vaccine-induced thrombotic thrombocytopenia

Coronavirus disease 2019 (COVID-19) is known to commonly induce a thrombotic diathesis, particularly in severely affected individuals. So far, this COVID-19-associated coagulopathy (CAC) has been partially explained by hyperactivated platelets as well as by the prothrombotic effects of neutrophil extracellular traps (NETs) released from neutrophils. However, precise insight into the bidirectional relationship between platelets and neutrophils in the pathophysiology of CAC still lags behind. Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare autoimmune disorder caused by auto-antibody formation in response to immunization with adenoviral vector vaccines. VITT is associated with life-threatening thromboembolic events and thus, high fatality rates. Our concept of the thrombophilia observed in VITT is relatively new, hence a better understanding could help in the management of such patients with the potential to also prevent VITT. In this review we aim to summarize the current knowledge on platelet-neutrophil interplay in COVID-19 and VITT.

Amelioration of nephritis in receptor for advanced glycation end-products (RAGE)-deficient lupus-prone mice through neutrophil extracellular traps

The receptor for advanced glycation end-products (RAGE) is a pattern recognition receptor that regulates inflammation, cell migration, and cell fate. Systemic lupus erythematosus (SLE) is a chronic multiorgan autoimmune disease. To understand the function of RAGE in SLE, we generated RAGE-deficient (Ager-/-) lupus-prone mice by backcrossing MRL/MpJ-Faslpr/J (MRL-lpr) mice with Ager-/- C57BL/6 mice. In 18-week-old Ager-/- MRL-lpr, the weights of the spleen and lymph nodes, as well as the frequency of CD3+CD4-CD8- cells, were significantly decreased. Ager-/- MRL-lpr mice had significantly reduced urine albumin/creatinine ratios and markedly improved renal pathological scores. Moreover, neutrophil infiltration and neutrophil extracellular trap formation in the glomerulus were significantly reduced in Ager-/- MRL-lpr. Our study is the first to reveal that RAGE can have a pathologic role in immune cells, particularly neutrophils and T cells, in inflammatory tissues and suggests that the inhibition of RAGE may be a potential therapeutic strategy for SLE.

HMGB1, angel or devil, in ischemic stroke

INTRODUCTION

High-mobility group box 1 protein (HMGB1) is extensively involved in causing ischemic stroke, pathological damage of ischemic brain injury, and neural tissue repair after ischemic brain injury. However, the precise role of HMGB1 in ischemic stroke remains to be elucidated.

METHODS

Comprehensive literature search and narrative review to summarize the current field of HMGB1 in cerebral ischemic based on the basic structure, structural modification, and functional roles of HMGB1 described in the literature.

RESULTS

Studies have exhibited the crucial roles of HMGB1 in cell death, immunity and inflammation, thrombosis, and remodeling and repair. HMGB1 released after cerebral infarction is extensively involved in the pathological injury process in the early stage of cerebral infarction, whereas it is involved in the promotion of brain tissue repair and remodeling in the late stage of cerebral infarction. HMGB1 plays a neurotrophic role in acute white matter stroke, whereas it causes sustained activation of inflammation and plays a damaging role in chronic white matter ischemia.

CONCLUSIONS

HMGB1 plays a complex role in cerebral infarction, which is related to not only the modification of HMGB1 and bound receptors but also different stages and subtypes of cerebral infarction. future studies on HMGB1 should investigate the spatial and temporal dynamics of HMGB1 after cerebral infarction. Moreover, future studies on HMGB1 should attempt to integrate different stages and infarct subtypes of cerebral infarction.

Immobility-associated thromboprotection is conserved across mammalian species from bear to human

Venous thromboembolism (VTE) comprising deep venous thrombosis and pulmonary embolism is a major cause of morbidity and mortality. Short-term immobility-related conditions are a major risk factor for the development of VTE. Paradoxically, long-term immobilized free-ranging hibernating brown bears and paralyzed spinal cord injury (SCI) patients are protected from VTE. We aimed to identify mechanisms of immobility-associated VTE protection in a cross-species approach. Mass spectrometry-based proteomics revealed an antithrombotic signature in platelets of hibernating brown bears with heat shock protein 47 (HSP47) as the most substantially reduced protein. HSP47 down-regulation or ablation attenuated immune cell activation and neutrophil extracellular trap formation, contributing to thromboprotection in bears, SCI patients, and mice. This cross-species conserved platelet signature may give rise to antithrombotic therapeutics and prognostic markers beyond immobility-associated VTE.

Role of antimicrobial peptide cathelicidin in thrombosis and thromboinflammation

Thrombosis is a frequent cause of cardiovascular mortality and hospitalization. Current antithrombotic strategies, however, target both thrombosis and physiological hemostasis and thereby increase bleeding risk. In recent years the pathophysiological understanding of thrombus formation has significantly advanced and inflammation has become a crucial element. Neutrophils as most frequent immune cells in the blood and their released mediators play a key role herein. Neutrophil-derived cathelicidin next to its strong antimicrobial properties has also shown to modulates thrombosis and thus presents a potential therapeutic target. In this article we review direct and indirect (immune- and endothelial cell-mediated) effects of cathelicidin on platelets and the coagulation system. Further we discuss its implications for large vessel thrombosis and consecutive thromboinflammation as well as immunothrombosis in sepsis and COVID-19 and give an outlook for potential therapeutic prospects.

Endothelial dysfunction and immunothrombosis in sepsis

Sepsis is a life-threatening clinical syndrome characterized by multiorgan dysfunction caused by a dysregulated or over-reactive host response to infection. During sepsis, the coagulation cascade is triggered by activated cells of the innate immune system, such as neutrophils and monocytes, resulting in clot formation mainly in the microcirculation, a process known as immunothrombosis. Although this process aims to protect the host through inhibition of the pathogen’s dissemination and survival, endothelial dysfunction and microthrombotic complications can rapidly lead to multiple organ dysfunction. The development of treatments targeting endothelial innate immune responses and immunothrombosis could be of great significance for reducing morbidity and mortality in patients with sepsis. Medications modifying cell-specific immune responses or inhibiting platelet–endothelial interaction or platelet activation have been proposed. Herein, we discuss the underlying mechanisms of organ-specific endothelial dysfunction and immunothrombosis in sepsis and its complications, while highlighting the recent advances in the development of new therapeutic approaches aiming at improving the short- or long-term prognosis in sepsis.

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.

Low P-Selectin Glycoprotein Ligand-1 Expression in Neutrophils Associates with Disease Activity and Deregulated NET Formation in Systemic Lupus Erythematosus

Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by the generation of anti-DNA autoantibodies due to exposure of immune cells to excessive amounts of extracellular DNA. Lack of P-selectin in mice induces the development of a lupus-like syndrome and patients with cutaneous lupus have reduced P-selectin expression in skin vessels. Using flow cytometry we analyzed in healthy donors and patients the expression of P-selectin Glycoprotein Ligand-1 (PSGL-1) in circulating neutrophils and the implication of PSGL-1/P-selectin interaction in neutrophil extracellular traps (NETs) generation. We found a statistical significance that neutrophils from active SLE patients have a reduced expression of PSGL-1 and low levels of PSGL-1 in neutrophils from SLE patients associated with the presence of anti-dsDNA antibodies, clinical lung involvement, Raynaud's phenomenon, and positive lupus anticoagulant. PSGL-1 is present along the DNA in the NET. In healthy donors, neutrophil interaction with immobilized P-selectin triggers Syk activation, increases the NETs percentage and reduces the amount of DNA extruded in the NETs. In active SLE patients, neutrophil interaction with P-selectin does not activate Syk or reduce the amount of DNA extruded in the NETs, that might contribute to increase the extracellular level of DNA and hence, to disease pathogenesis.

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 primed intercellular communication in cancer progression as a promising therapeutic target

In addition to the anti-infection response, neutrophils are linked to tumor progression through the secretion of inflammation components and neutrophil extracellular traps (NETs) formation. NET is a web-like structure constituted by a chromatin scaffold coated with specific nuclear and cytoplasmic proteins, such as histone and granule peptides. Increasing evidence has demonstrated that NETs are favorable factors to promote tumor growth, invasion, migration, and immunosuppression. However, the cell-cell interaction between NETs and other cells (tumor cells and immune cells) is complicated and poorly studied. This work is the first review to focus on the intercellular communication mediated by NETs in cancer. We summarized the complex cell-cell interaction between NETs and other cells in the tumor microenvironment. We also address the significance of NETs as both prognostic/predictive biomarkers and molecular targets for cancer therapy. Moreover, we presented a comprehensive landscape of cancer immunity, improving the therapeutic efficacy for advanced cancer in the future.

The protective role of HMGB1 in affecting the balance between autophagy and pyroptosis to maintain neutrophils homeostasis during β-glucan-induced mice lung inflammation

Fungal contamination is omnipresent, and inhalation of fungi-contaminated organic dust leads to hypersensitivity pneumonitis (HP), in which neutrophils played a pivotal role. Existing studies have suggested that cell homeostasis is crucial for the pathogenesis of the inflammatory disease. Although HMGB1 has been shown to contribute to suppressing HP, there is a lack of studies on its mechanisms, especially the regulation of neutrophil homeostasis. This study aims to investigate how HMGB1 regulates neutrophil function by affecting neutrophil homeostasis, and then affects lung inflammation induced by β-glucan, the exposure marker of fungi. Our results showed that deficient HMGB1 led to neutrophil death by disrupting the balance between autophagy and pyroptosis after β-glucan treatment. And HMGB1 deficiency exacerbated the β-glucan-induced lung inflammation and neutrophil dysfunction both in vivo and in vitro. Furthermore, HMGB1 contributed to remodeling neutrophil function by restricting autophagy and aggravating pyroptosis β-glucan exposure. Our funding suggested that HMGB1 deficiency could break the balance between autophagy and pyroptosis towards pyroptosis to cause neutrophil dysfunction during the exacerbated inflammatory response, which provides insights into the pathogenesis of HP and the potential biological targets for its treatment. DATA AVAILABILITY: The datasets used during the current study are available from the corresponding author on reasonable request.

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.

Prognostic Value of the Systemic Immune Inflammation Index after Thoracic Endovascular Aortic Repair in Patients with Type B Aortic Dissection

The study aimed at investigating the association between postoperative inflammatory scores and aorta-related adverse events (AAEs) after thoracic endovascular aortic repair (TEVAR) for patients with type B aortic dissection (TBAD). This single-centre, retrospective cohort included all patients who underwent TEVAR for TBAD between November 2016 and November 2020 at a university hospital. The risk factors for AAEs were analyzed by Cox proportional hazards model regression. Prediction accuracy was assessed using the area under the receiver operating characteristic curves. This study included 186 patients with a mean age of 58.5 years and a median follow-up period of 26 months. A total of 68 patients developed AAEs. Age and postoperative systemic immune inflammation index (SII) (>2893) were associated with post-TEVAR AAEs (hazard ratio (HR) 1.03, p = 0.003; HR 1.88, p = 0.043, respectively). Increased postoperative SII and age are independent risk factors for AAE post-TEVAR in patients with TBAD.

Novel mechanisms of thrombo-inflammation during infection: spotlight on neutrophil extracellular trap-mediated platelet activation

A state-of-the-art lecture titled "novel mechanisms of thrombo-inflammation during infection" was presented at the ISTH Congress in 2022. Platelet, neutrophil, and endothelial cell activation coordinate the development, progression, and resolution of thrombo-inflammatory events during infection. Activated platelets and neutrophil extracellular traps (NETs) are frequently observed in patients with sepsis and COVID-19, and high levels of NET-derived damage-associated molecular patterns (DAMPs) correlate with thrombotic complications. NET-associated DAMPs induce direct and indirect platelet activation, which in return potentiates neutrophil activation and NET formation. These coordinated interactions involve multiple receptors and signaling pathways contributing to vascular and organ damage exacerbating disease severity. This state-of-the-art review describes the main mechanisms by which platelets support NETosis and the key mechanisms by which NET-derived DAMPs trigger platelet activation and the formation of procoagulant platelets leading to thrombosis. We report how these DAMPs act through multiple receptors and signaling pathways differentially regulating cell activation and disease outcome, focusing on histones and S100A8/A9 and their contribution to the pathogenesis of sepsis and COVID-19. We further discuss the complexity of platelet activation during NETosis and the potential benefit of targeting selective or multiple NET-associated DAMPs to limit thrombo-inflammation during infection. Finally, we summarize relevant new data on this topic presented during the 2022 ISTH Congress.

NET formation is independent of gasdermin D and pyroptotic cell death

Neutrophil extracellular traps (NETs) are DNA scaffolds coated with granule proteins that are released by neutrophils to ensnare and kill bacteria. NET formation occurs in response to many stimuli through independent molecular pathways. Although NET release has been equated to a form of lytic cell death, live neutrophils can rapidly release antimicrobial NETs. Gasdermin D (GSDMD), which causes pyroptotic death in macrophages, is thought to be required for NET formation by neutrophils. Through experiments with known physiological activators of NET formation and ligands that activate canonical and noncanonical inflammasome signaling pathways, we demonstrated that Gsdmd-deficient mouse neutrophils were as competent as wild-type mouse neutrophils in producing NETs. Furthermore, GSDMD was not cleaved in wild-type neutrophils during NET release in response to inflammatory mediators. We found that activation of both canonical and noncanonical inflammasome signaling pathways resulted in GSDMD cleavage in wild-type neutrophils but was not associated with cell death. Moreover, NET formation as a result of either pathway of inflammasome activation did not require GSDMD. Together, these data suggest that NETs can be formed by viable neutrophils after inflammasome activation and that this function does not require GSDMD.

Coagulation Disorders in Sepsis and COVID-19-Two Sides of the Same Coin? A Review of Inflammation-Coagulation Crosstalk in Bacterial Sepsis and COVID-19

Sepsis is a major cause of morbidity and mortality worldwide. Sepsis-associated coagulation disorders are involved in the pathogenesis of multiorgan failure and lead to a subsequently worsening prognosis. Alongside the global impact of the COVID-19 pandemic, a great number of research papers have focused on SARS-CoV-2 pathogenesis and treatment. Significant progress has been made in this regard and coagulation disturbances were once again found to underlie some of the most serious adverse outcomes of SARS-CoV-2 infection, such as acute lung injury and multiorgan dysfunction. In the attempt of untangling the mechanisms behind COVID-19-associated coagulopathy (CAC), a series of similarities with sepsis-induced coagulopathy (SIC) became apparent. Whether they are, in fact, the same disease has not been established yet. The clinical picture of CAC shows the unique feature of an initial phase of intravascular coagulation confined to the respiratory system. Only later on, patients can develop a clinically significant form of systemic coagulopathy, possibly with a consumptive pattern, but, unlike SIC, it is not a key feature. Deepening our understanding of CAC pathogenesis has to remain a major goal for the research community, in order to design and validate accurate definitions and classification criteria.

Beta 2 glycoprotein I and neutrophil extracellular traps: Potential bridge between innate and adaptive immunity in anti-phospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by recurrent vascular thrombosis and miscarriages in the absence of known causes. Antibodies against phospholipid-binding proteins (aPL) are pathogenic players in both clotting and pregnancy APS manifestations. There is sound evidence that antibodies specific for beta2 glycoprotein I (β2GPI) trigger thrombotic and pregnancy complications by interacting with the molecule on the membranes of different cell types of the coagulation cascade, and in placenta tissues. In addition to the humoral response against β2GPI, both peripheral and tissue CD4⁺ β2GPI-specific T cells have been reported in primary APS as well as in systemic lupus erythematosus (SLE)-associated APS. While adaptive immunity plays a clear role in APS, it is still debated whether innate immunity is involved as well. Acute systemic inflammation does not seem to be present in the syndrome, however, there is sound evidence that complement activation is crucial in animal models and can be found also in patients. Furthermore, neutrophil extracellular traps (NETs) have been documented in arterial and venous thrombi with different etiology, including clots in APS models. Keeping in mind that β2GPI is a pleiotropic glycoprotein, acting as scavenger molecule for infectious agents and apoptotic/damaged body constituents and that self-molecules externalized through NETs formation may become immunogenic autoantigens, we demonstrated β2GPI on NETs, and its ability to stimulate CD4⁺β2GPI-specific T cells. The aim of this review is to elucidate the role of β2GPI in the cross-talk between the innate and adaptive immunity in APS.

Platelet-Neutrophil Crosstalk in Thrombosis

Platelets are essential for the formation of a haemostatic plug to prevent bleeding, while neutrophils are the guardians of our immune defences against invading pathogens. The interplay between platelets and innate immunity, and subsequent triggering of the activation of coagulation is part of the host system to prevent systemic spread of pathogen in the blood stream. Aberrant immunothrombosis and excessive inflammation can however, contribute to the thrombotic burden observed in many cardiovascular diseases. In this review, we highlight how platelets and neutrophils interact with each other and how their crosstalk is central to both arterial and venous thrombosis and in COVID-19. While targeting platelets and coagulation enables efficient antithrombotic treatments, they are often accompanied with a bleeding risk. We also discuss how novel approaches to reduce platelet-mediated recruitment of neutrophils could represent promising therapies to treat thrombosis without affecting haemostasis.

The Role of Neutrophils in Lower Limb Peripheral Artery Disease: State of the Art and Future Perspectives

In recent years, increasing attention has been paid to the role of neutrophils in cardiovascular (CV) disease (CVD) with evidence supporting their role in the initiation, progression, and rupture of atherosclerotic plaque. Although these cells have long been considered as terminally differentiated cells with a relatively limited spectrum of action, recent research has revealed intriguing novel cellular functions, including neutrophil extracellular trap (NET) generation and inflammasome activation, which have been linked to several human diseases, including CVD. While most research to date has focused on the role of neutrophils in coronary artery and cerebrovascular diseases, much less information is available on lower limb peripheral artery disease (PAD). PAD is a widespread condition associated with great morbidity and mortality, though physician and patient awareness of the disease remains low. To date, several studies have produced some evidence on the role of certain biomarkers of neutrophil activation in this clinical setting. However, the etiopathogenetic role of neutrophils, and in particular of some of the newly discovered mechanisms, has yet to be fully elucidated. In the future, complementary assessment of neutrophil activity should improve CV risk stratification and provide personalized treatments to patients with PAD. This review aims to summarize the basic principles and recent advances in the understanding of neutrophil biology, current knowledge about the role of neutrophils in atherosclerosis, as well as available evidence on their role of PAD.