Neutrophil apoptosis pathways and their modifications in inflammation

Advances and Challenges in Sepsis Management: Modern Tools and Future Directions

Sepsis, a critical condition marked by systemic inflammation, profoundly impacts both innate and adaptive immunity, often resulting in lymphopenia. This immune alteration can spare regulatory T cells (Tregs) but significantly affects other lymphocyte subsets, leading to diminished effector functions, altered cytokine profiles, and metabolic changes. The complexity of sepsis stems not only from its pathophysiology but also from the heterogeneity of patient responses, posing significant challenges in developing universally effective therapies. This review emphasizes the importance of phenotyping in sepsis to enhance patient-specific diagnostic and therapeutic strategies. Phenotyping immune cells, which categorizes patients based on clinical and immunological characteristics, is pivotal for tailoring treatment approaches. Flow cytometry emerges as a crucial tool in this endeavor, offering rapid, low cost and detailed analysis of immune cell populations and their functional states. Indeed, this technology facilitates the understanding of immune dysfunctions in sepsis and contributes to the identification of novel biomarkers. Our review underscores the potential of integrating flow cytometry with omics data, machine learning and clinical observations to refine sepsis management, highlighting the shift towards personalized medicine in critical care. This approach could lead to more precise interventions, improving outcomes in this heterogeneously affected patient population.

Development and characterization of DIA 12.3, a fully human intact anti-CEACAM1 monoclonal antibody

Carcinoembryonic antigen cell adhesion molecule-1 (CEACAM1), a homotypic cell adhesion molecule glycoprotein with apical expression on normal epithelial cells and activated lymphocytes, is overexpressed on many tumors and acts as an inhibitory receptor on NK cells, preventing their killing of CEACAM1 positive tumors. Production of humanized anti-CEACAM1 antibodies to block the inhibitory activity of CEACAM1 for immunotherapy and immunoimaging. Starting from a scFv, a fully human intact anti-CEACAM1 (DIA 12.3) that recognizes the N-terminal domain of CEACAM1 was developed and shown to bind CEACAM1 positive tumor cells and enhanced NK cell killing of CEACAM1 positive targets. DIA 12.3 bound to human neutrophils without activation, indicating they would be safe for human use. DIA 12.3 exhibited some cross-reactivity to CEACAM5, a tumor marker with high sequence homology to the N-terminal domain of CEACAM1. CEACAM1 PET imaging with 64Cu-COTA-DIA 12.3 showed excellent imaging of CEACAM1 positive tumors with reduced binding to CEACAM5 tumors. Based on its immunoinhibitory an immunoimaging activities, DIA 12.3 shows promise for therapeutic studies in man.

Bcl-xL targeting eliminates ageing tumor-promoting neutrophils and inhibits lung tumor growth

Elevated peripheral blood and tumor-infiltrating neutrophils are often associated with a poor patient prognosis. However, therapeutic strategies to target these cells are difficult to implement due to the life-threatening risk of neutropenia. In a genetically engineered mouse model of lung adenocarcinoma, tumor-associated neutrophils (TAN) demonstrate tumor-supportive capacities and have a prolonged lifespan compared to circulating neutrophils. Here, we show that tumor cell-derived GM-CSF triggers the expression of the anti-apoptotic Bcl-xL protein and enhances neutrophil survival through JAK/STAT signaling. Targeting Bcl-xL activity with a specific BH3 mimetic, A-1331852, blocked the induced neutrophil survival without impacting their normal lifespan. Specifically, oral administration with A-1331852 decreased TAN survival and abundance, and reduced tumor growth without causing neutropenia. We also show that G-CSF, a drug used to combat neutropenia in patients receiving chemotherapy, increased the proportion of young TANs and augmented the anti-tumor effect resulting from Bcl-xL blockade. Finally, our human tumor data indicate the same role for Bcl-xL on pro-tumoral neutrophil survival. These results altogether provide preclinical evidence for safe neutrophil targeting based on their aberrant intra-tumor longevity.

Neutrophil-to-lymphocyte ratio an inflammatory biomarker, and prognostic marker in heart failure, cardiovascular disease and chronic inflammatory diseases: New insights for a potential predictor of anti-cytokine therapy responsiveness

In the 20th century, research focused on cholesterol and lipoproteins as the key mechanism in establishing atherosclerotic cardiovascular disease (ASCVD). Given that some studies demonstrated subclinical atherosclerosis in subjects without conventional cardiovascular risk factors, the elevated low-density lipoprotein (LDL) levels alone cannot account for the entire burden of atherosclerosis. Hence, large-scale clinical trials demonstrated the operation of immune and inflammatory pathways in ASCVD. In this regard, the evidence establishes that cells of the immune system, both the innate (neutrophils, macrophages) and adaptive (T cell and other lymphocytes) limbs, contribute to atherosclerosis and atherothrombosis. Besides, basic science studies have identified proatherogenic cytokines such as interleukin (IL)-1, IL-12, and IL-18. In this regard, some studies showed that antiinflammatory therapy targeting the immune system by modulating or blocking interleukins, also known as anti-cytokine therapy, can reduce the risk of major cardiovascular adverse events. The neutrophils play a key role in the innate immune system, representing the acute phase of an inflammatory response. In contrast, lymphocytes represent the adaptive immune system and promote the induction of autoimmune inflammation, especially in the chronic inflammatory response. Through the literature review, we will highlight the inflammatory pathway for the physiopathology of ASCVD, HF, and COVID-19. In this regard, the neutrophil-to-lymphocyte ratio (NLR) integrates the innate immune and adaptive immune systems, making the NLR a biomarker of inflammation. In addition, we provided an update on the evidence showing that high NLR is associated with worse prognosis in heart failure (HF), ASCVD, and COVID-19, as well as their clinical applications showing that the normalization of NLR after anti-cytokine therapy is a potential predictor of therapy responsiveness and is associated with reduction of major adverse cardiovascular events.

Regulated cell death in neutrophils: From apoptosis to NETosis and pyroptosis

Neutrophils are among the most abundant immune cells, representing about 50%- 70% of all circulating leukocytes in humans. Neutrophils rapidly infiltrate inflamed tissues and play an essential role in host defense against infections. They exert microbicidal activity through a variety of specialized effector mechanisms, including phagocytosis, production of reactive oxygen species, degranulation and release of secretory vesicles containing broad-spectrum antimicrobial factors. In addition to their homeostatic turnover by apoptosis, recent studies have revealed the mechanisms by which neutrophils undergo various forms of regulated cell death. In this review, we will discuss the different modes of regulated cell death that have been described in neutrophils, with a particular emphasis on the current understanding of neutrophil pyroptosis and its role in infections and autoinflammation.

Ductular reaction-associated neutrophils promote biliary epithelium proliferation in chronic liver disease

BACKGROUND & AIMS

Ductular reaction expansion is associated with poor prognosis in patients with advanced liver disease. However, the mechanisms promoting biliary cell proliferation are largely unknown. Here, we identify neutrophils as drivers of biliary cell proliferation and the defective wound-healing response.

METHODS

The intrahepatic localization of neutrophils was evaluated in patients with chronic liver disease. Neutrophil dynamics were analyzed by intravital microscopy and neutrophil-labeling assays in DDC-treated mice. Neutrophil depletion or inhibition of recruitment was achieved using a Ly6g antibody or a CXCR1/2 inhibitor, respectively. Mice deficient in PAD4 (peptidyl arginine deiminase 4) and ELANE/NE (neutrophil elastase) were used to investigate the mechanisms underlying ductular reaction expansion.

RESULTS

In this study we describe a population of ductular reaction-associated neutrophils (DRANs), which are in direct contact with biliary epithelial cells in chronic liver diseases and whose numbers increased in parallel with disease progression. We show that DRANs are immobilized at the site of ductular reaction for a prolonged period of time. In addition, liver neutrophils display a unique phenotypic and transcriptomic profile, showing a decreased phagocytic capacity and increased oxidative burst. Depletion of neutrophils or inhibition of their recruitment reduces DRANs and the expansion of ductular reaction, while mitigating liver fibrosis and angiogenesis. Mechanistically, neutrophils deficient in PAD4 and ELANE abrogate neutrophil-induced biliary cell proliferation, thus indicating the role of neutrophil extracellular traps and elastase release in ductular reaction expansion.

CONCLUSIONS

Overall, our study reveals the accumulation of DRANs as a hallmark of advanced liver disease and a potential therapeutic target to mitigate ductular reaction and the maladaptive wound-healing response.

IMPACT AND IMPLICATIONS

Our results indicate that neutrophils are highly plastic and can have an extended lifespan. Moreover, we identify a new role of neutrophils as triggers of expansion of the biliary epithelium. Overall, the results of this study indicate that ductular reaction-associated neutrophils (or DRANs) are new players in the maladaptive tissue-healing response in chronic liver injury and may be a potential target for therapeutic interventions to reduce ductular reaction expansion and promote tissue repair in advanced liver disease.

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Early immune system alterations in patients with septic shock

This study aims to investigate the early changes in the immune systems of patients with septic shock. A total of 243 patients with septic shock were included in this study. The patients were classified as survivors (n = 101) or nonsurvivors (n = 142). Clinical laboratories perform tests of the immune system's function. Each indicator was studied alongside healthy controls (n = 20) of the same age and gender as the patients. A comparative analysis of every two groups was conducted. Univariate and multivariate logistic regression analyses were performed to identify mortality risk factors that are independent of one another. In septic shock patients, neutrophil counts, infection biomarkers (C-reactive protein, ferritin, and procalcitonin levels), and cytokines (IL-1β, IL-2R, IL-6, IL-8, IL-10, and TNF-α) increased significantly. Lymphocyte and their subset counts (T, CD4+ T, CD8+ T, B, and natural killer cell counts), lymphocyte subset functions (the proportions of PMA/ionomycin-stimulated IFN-γ positive cells in CD4+ T cells), immunoglobulin levels (IgA, IgG, and IgM), and complement protein levels (C3 and C4) decreased significantly. Compared to survivors, nonsurvivors had higher levels of cytokines (IL-6, IL-8, and IL-10) but lower levels of IgM, complement C3 and C4, and lymphocyte, CD4+, and CD8+ T cell counts. Low IgM or C3 concentrations and low lymphocyte or CD4+ T cell counts were independent risk factors for mortality. These alterations should be considered in the future development of immunotherapies aimed at treating septic shock.

Pharmacological Induction of Granulocyte Cell Death as Therapeutic Strategy

Apoptosis is central for the maintenance of health. In the immune system, apoptosis guarantees proper development of immune cells and shutdown of immune reactions by the coordinated elimination of activated immune cells. Limitation of the life span of granulocytes is important, as overactivation of these cells is associated with chronic inflammation and collateral tissue damage. Consequently, targeted induction of granulocyte apoptosis may be beneficial in the course of respective immune disorders. Anti-inflammatory drugs such as glucocorticoids and monoclonal antibodies against IL-5Rα exert their function in part by triggering eosinophil apoptosis. Agonistic antibodies targeting Siglec-8 or death receptors are tested (pre)clinically. Moreover, a new class of inhibitors targeting antiapoptotic BCL-2 proteins shows great promise for anticancer treatments. Because of their specificity and tolerable side effects, these so-called BH3 mimetics may be worthwhile to evaluate in inflammatory disorders. Here, we review past and recent data on pharmacological apoptosis induction of granulocytes and highlight respective therapeutic potential.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

Molecular Basis for Paradoxical Activities of Polymorphonuclear Neutrophils in Inflammation/Anti-Inflammation, Bactericide/Autoimmunity, Pro-Cancer/Anticancer, and Antiviral Infection/SARS-CoV-II-Induced Immunothrombotic Dysregulation

Polymorphonuclear neutrophils (PMNs) are the most abundant white blood cells in the circulation. These cells act as the fast and powerful defenders against environmental pathogenic microbes to protect the body. In addition, these innate inflammatory cells can produce a number of cytokines/chemokines/growth factors for actively participating in the immune network and immune homeostasis. Many novel biological functions including mitogen-induced cell-mediated cytotoxicity (MICC) and antibody-dependent cell-mediated cytotoxicity (ADCC), exocytosis of microvesicles (ectosomes and exosomes), trogocytosis (plasma membrane exchange) and release of neutrophil extracellular traps (NETs) have been successively discovered. Furthermore, recent investigations unveiled that PMNs act as a double-edged sword to exhibit paradoxical activities on pro-inflammation/anti-inflammation, antibacteria/autoimmunity, pro-cancer/anticancer, antiviral infection/COVID-19-induced immunothrombotic dysregulation. The NETs released from PMNs are believed to play a pivotal role in these paradoxical activities, especially in the cytokine storm and immunothrombotic dysregulation in the recent SARS-CoV-2 pandemic. In this review, we would like to discuss in detail the molecular basis for these strange activities of PMNs.

Neutrophil Death in Myeloproliferative Neoplasms: Shedding More Light on Neutrophils as a Pathogenic Link to Chronic Inflammation

Neutrophils are an essential component of the innate immune response, but their prolonged activation can lead to chronic inflammation. Consequently, neutrophil homeostasis is tightly regulated through balance between granulopoiesis and clearance of dying cells. The bone marrow is both a site of neutrophil production and the place they return to and die. Myeloproliferative neoplasms (MPN) are clonal hematopoietic disorders characterized by the mutations in three types of molecular markers, with emphasis on Janus kinase 2 gene mutation (JAK2V617F). The MPN bone marrow stem cell niche is a site of chronic inflammation, with commonly increased cells of myeloid lineage, including neutrophils. The MPN neutrophils are characterized by the upregulation of JAK target genes. Additionally, MPN neutrophils display malignant nature, they are in a state of activation, and with deregulated apoptotic machinery. In other words, neutrophils deserve to be placed in the midst of major events in MPN. Our crucial interest in this review is better understanding of how neutrophils die in MPN mirrored by defects in apoptosis and to what possible extent they can contribute to MPN pathophysiology. We tend to expect that reduced neutrophil apoptosis will establish a pathogenic link to chronic inflammation in MPN.

Dichotomous roles of neutrophils in modulating pathogenic and repair processes of inflammatory bowel diseases

Neutrophils are considered as complex innate immune cells and play a critical role in maintaining intestinal mucosal homeostasis. They exert robust pro-inflammatory effects and recruit other immune cells in the acute phase of pathogen infection and intestinal inflammation, but paradoxically, they also limit exogenous microbial invasion and facilitate mucosal restoration. Hyperactivation or dysfunction of neutrophils results in abnormal immune responses, leading to multiple autoimmune and inflammatory diseases including systemic lupus erythematosus, rheumatoid arthritis, and inflammatory bowel diseases (IBD). As a refractory intestinal inflammatory disease, the pathogenesis and progression of IBD are associated with complicated immune response processes in which neutrophils are profoundly involved. However, the consensus on potential roles of neutrophils in modulating pathogenic and repair processes of IBD remains not fully understood. Accumulated infiltrating neutrophils cross the epithelial barrier and contribute to microbial dysbiosis, aggravated intestinal architectural damage, compromised resolution of intestinal inflammation and increased risk of thrombosis during IBD. Paradoxically, activated neutrophils are also associated with effective elimination of invaded microbiota, promoted angiogenesis and tissue restoration of gut mucosa in IBD. Here, we discuss the beneficial and detrimental roles of neutrophils in the onset and resolution of intestinal mucosal inflammation, hoping to provide a precise overview of neutrophil functions in the pathogenesis of IBD.

Neutrophil-derived heparin binding protein triggers vascular leakage and synergizes with myeloperoxidase at the early stage of severe burns (With video)

Background

Burn shock caused by vascular leakage is one of the main causes of high mortality in severe burn injury. However, the pathophysiological mechanism of vascular leakage is still unclear. The purpose of this study was to explore the molecular mechanism of vascular leakage in the early stage of severe burn and provide a new target for the treatment of severe burns.

Methods

Neutrophils were isolated from human peripheral blood by magnetic beads sorting. ELISA was used to detect neutrophil-derived granule proteins and glycocalyx injury products in plasma. The vascular leakage and neutrophil movement were assessed by in vivo laser confocal imaging in mice, and high-quality video were provided.. Adhesion-related molecules were investigated by qRT-PCR. The damage to glycocalyx of mice vascular endothelial cells was observed by transmission electron microscope and scanning electron microscope. Proteomic analysis, flow cytometry and immunofluorescence were used to further study the relationship between human peripheral blood neutrophil-derived hypochlorite (HOCl) and CD44 of human vascular endothelial cells.

Results

In this study, we found that rapidly increasing activated neutrophils secrete heparin binding protein (HBP) and myeloperoxidase (MPO) after severe burn injury. Increased HBP triggers vascular leakage with synergy of MPO, results in systemic edema and burn shock. Furthermore, we found that the MPO catalytic product HOCl but not MPO triggers CD44 extracellular domain shedding from vascular endothelial cells to damage the glycocalyx. Damage to the glycocalyx results in firm adhesion of neutrophils and increases vascular leakage. However, MPO inhibitors partially protect the glycocalyx of vascular endothelial cells. The combination of HBP and MPO inhibitors markedly reduces vascular leakage and systemic edema in the early stage of severe burns.

Conclusions

Taken together, these data reveal that neutrophil-derived HBP and MPO play an important synergies role in triggering vascular leakage at the early stage of severe burns. Targeted intervention in these two biomolecules may introduce new strategies for helping to reduce large amount of fluid loss and subsequent burn shock.

Tocilizumab in COVID-19: a study of adverse drug events reported in the WHO database

BACKGROUND

Elevated inflammatory cytokines in Coronavirus disease 2019 (COVID-19) affect the lungs leading to pneumonitis with a poor prognosis. Tocilizumab, a type of humanized monoclonal antibody antagonizing interleukin-6 receptors, is currently utilized to treat COVID-19. The present study reviews tocilizumab adverse drug events (ADEs) reported in the World Health Organization (WHO) pharmacovigilance database.

RESEARCH DESIGN AND METHODS

All suspected ADEs associated with tocilizumab between April to August 2020 were analyzed based on COVID-19 patients' demographic and clinical variables, and severity of involvement of organ system.

RESULTS

A total of 1005 ADEs were reported among 513 recipients. The majority of the ADEs (46.26%) were reported from 18-64 years, were males and reported spontaneously. Around 80%, 20%, and 64% were serious, fatal, and administered intravenously, respectively. 'Injury, Poisoning, and Procedural Complications' remain as highest (35%) among categorized ADEs. Neutropenia, hypofibrinogenemia were common hematological ADEs. The above 64 years was found to have significantly lower odds than of below 45 years. In comparison, those in the European Region have substantially higher odds compared to the Region of Americas.

CONCLUSION

Neutropenia, superinfections, reactivation of latent infections, hepatitis, and cardiac abnormalities were common ADEs observed that necessitate proper monitoring and reporting.

A cross-sectional cohort study of the activity and turnover of neutrophil granulocytes in juvenile idiopathic arthritis

BACKGROUND

The inflammatory process in juvenile idiopathic arthritis (JIA) involves both the innate and the adaptive immune system. The turnover and activity of neutrophil granulocytes may be reflected by proteins secreted from primary or secondary granules and from the cytoplasm of sequestered cells. Our primary aim was to compare the levels of the secondary neutrophil granule protein human neutrophil lipocalin (HNL), in JIA patients and controls, and to explore a possible priming of neutrophils through parallel analyses in plasma and serum. A secondary aim was to relate the levels of HNL to two other well-studied leukocyte proteins, S100A8/A9 and myeloperoxidase (MPO), as well as to clinical aspects of JIA.

METHODS

The concentrations of the three biomarkers in serum, two of them also in plasma, were measured using enzyme-linked immunosorbent assay in 37 children with JIA without medical treatment, in high disease activity based on juvenile arthritis disease activity score 27 (JADAS27), 32 children on medical treatment, mainly in lower disease activity, and 16 healthy children. We assessed for differences between two groups using the Mann-Whitney U test, and used the Kruskal-Wallis test for multiple group comparisons. Spearman rank correlation, linear and multiple regression analyses were used for evaluation of associations between biomarker concentrations and clinical scores.

RESULTS

The concentrations of HNL and MPO in serum were significantly increased in children with JIA (p < 0.001, p = 0.002) compared with healthy children, but we found no difference in the plasma levels of HNL and MPO between children with JIA and controls. The serum concentrations of MPO and HNL were unaffected by medical treatment, but S100A8/A9 was reduced by medical treatment and correlated with JADAS27 in both univariate (r = 0.58, p < 0.001) and multivariate (r = 0.59, p < 0.001) analyses.

CONCLUSIONS

Neutrophil granulocytes in children with JIA are primed to release primary and secondary granule proteins, without relation to medical treatment, whereas signs of increased turnover and sequestration of neutrophil granulocytes are reduced by treatment. Levels of neutrophil-originating proteins in serum most likely reflect underlying disease activities of JIA.

BCL-XL antagonism selectively reduces neutrophil life span within inflamed tissues without causing neutropenia

Neutrophils help to clear pathogens and cellular debris, but can also cause collateral damage within inflamed tissues. Prolonged neutrophil residency within an inflammatory niche can exacerbate tissue pathology. Using both genetic and pharmacological approaches, we show that BCL-XL is required for the persistence of neutrophils within inflammatory sites in mice. We demonstrate that a selective BCL-XL inhibitor (A-1331852) has therapeutic potential by causing apoptosis in inflammatory human neutrophils ex vivo. Moreover, in murine models of acute and chronic inflammatory disease, it reduced inflammatory neutrophil numbers and ameliorated tissue pathology. In contrast, there was minimal effect on circulating neutrophils. Thus, we show a differential survival requirement in activated neutrophils for BCL-XL and reveal a new therapeutic approach to neutrophil-mediated diseases.

Neutrophils: Many Ways to Die

Neutrophils or polymorphonuclear leukocytes (PMN) are key participants in the innate immune response for their ability to execute different effector functions. These cells express a vast array of membrane receptors that allow them to recognize and eliminate infectious agents effectively and respond appropriately to microenvironmental stimuli that regulate neutrophil functions, such as activation, migration, generation of reactive oxygen species, formation of neutrophil extracellular traps, and mediator secretion, among others. Currently, it has been realized that activated neutrophils can accomplish their effector functions and simultaneously activate mechanisms of cell death in response to different intracellular or extracellular factors. Although several studies have revealed similarities between the mechanisms of cell death of neutrophils and other cell types, neutrophils have distinctive properties, such as a high production of reactive oxygen species (ROS) and nitrogen species (RNS), that are important for their effector function in infections and pathologies such as cancer, autoimmune diseases, and immunodeficiencies, influencing their cell death mechanisms. The present work offers a synthesis of the conditions and molecules implicated in the regulation and activation of the processes of neutrophil death: apoptosis, autophagy, pyroptosis, necroptosis, NETosis, and necrosis. This information allows to understand the duality encountered by PMNs upon activation. The effector functions are carried out to eliminate invading pathogens, but in several instances, these functions involve activation of signaling cascades that culminate in the death of the neutrophil. This process guarantees the correct elimination of pathogenic agents, damaged or senescent cells, and the timely resolution of the inflammation that is essential for the maintenance of homeostasis in the organism. In addition, they alert the organism when the immunological system is being deregulated, promoting the activation of other cells of the immune system, such as B and T lymphocytes, which produce cytokines that potentiate the microbicide functions.

Magnetic fields as a potential therapy for diabetic wounds based on animal experiments and clinical trials

Diabetes mellitus (DM) is a chronic metabolic disorder with various complications that poses a huge worldwide healthcare burden. Wounds in diabetes, especially diabetic foot ulcers (DFUs), are difficult to manage, often leading to prolonged wound repair and even amputation. Wound management in people with diabetes is an extremely clinical and social concern. Nowadays, physical interventions gain much attention and have been widely developed in the fields of tissue regeneration and wound healing. Magnetic fields (MFs)-based devices are translated into clinical practice for the treatment of bone diseases and neurodegenerative disorder. This review attempts to give insight into the mechanisms and applications of MFs in wound care, especially in improving the healing outcomes of diabetic wounds. First, we discuss the pathological conditions associated with chronic diabetic wounds. Next, the mechanisms involved in MFs' effects on wounds are explored. At last, studies and reports regarding the effects of MFs on diabetic wounds from both animal experiments and clinical trials are reviewed. MFs exhibit great potential in promoting wound healing and have been practised in the management of diabetic wounds. Further studies on the exact mechanism of MFs on diabetic wounds and the development of suitable MF-based devices could lead to their increased applications into clinical practice.

A Putative Serine Protease is Required to Initiate the RIPK3-MLKL-Mediated Necroptotic Death Pathway in Neutrophils

Adhesion receptors, such as CD44, have been shown to activate receptor interacting protein kinase-3 (RIPK3)—mixed lineage kinase-like (MLKL) signaling, leading to a non-apoptotic cell death in human granulocyte/macrophage colony-stimulating factor (GM-CSF) – primed neutrophils. The signaling events of this necroptotic pathway, however, remain to be investigated. In the present study, we report the design, synthesis, and characterization of a series of novel serine protease inhibitors. Two of these inhibitors, compounds 1 and 3, were able to block CD44-triggered necroptosis in GM-CSF-primed neutrophils. Both inhibitors prevented the activation of MLKL, p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3’—kinase (PI3K), hence blocking the increased levels of reactive oxygen species (ROS) required for cell death. Although compounds one and three partially inhibited isolated human neutrophil elastase (HNE) activity, we obtained no pharmacological evidence that HNE is involved in the initiation of this death pathway within a cellular context. Interestingly, neither serine protease inhibitor had any effect on FAS receptor-mediated apoptosis. Taken together, these results suggest that a serine protease is involved in non-apoptotic CD44-triggered RIPK3-MLKL-dependent neutrophil cell death, but not FAS receptor-mediated caspase-dependent apoptosis. Thus, a pharmacological block on serine proteases might be beneficial for preventing exacerbation of disease in neutrophilic inflammatory responses.

The Dual Role of Myeloperoxidase in Immune Response

The heme protein myeloperoxidase (MPO) is a major constituent of neutrophils. As a key mediator of the innate immune system, neutrophils are rapidly recruited to inflammatory sites, where they recognize, phagocytose, and inactivate foreign microorganisms. In the newly formed phagosomes, MPO is involved in the creation and maintenance of an alkaline milieu, which is optimal in combatting microbes. Myeloperoxidase is also a key component in neutrophil extracellular traps. These helpful properties are contrasted by the release of MPO and other neutrophil constituents from necrotic cells or as a result of frustrated phagocytosis. Although MPO is inactivated by the plasma protein ceruloplasmin, it can interact with negatively charged components of serum and the extracellular matrix. In cardiovascular diseases and many other disease scenarios, active MPO and MPO-modified targets are present in atherosclerotic lesions and other disease-specific locations. This implies an involvement of neutrophils, MPO, and other neutrophil products in pathogenesis mechanisms. This review critically reflects on the beneficial and harmful functions of MPO against the background of immune response.

The Role of Neutrophils in Brucellosis

Brucellosis is a bacterial disease of domestic animals and humans. The pathogenic ability of Brucella organisms relies on their stealthy strategy and their capacity to replicate within host cells and to induce long-lasting infections. Brucella organisms barely induce neutrophil activation and survive within these leukocytes by resisting microbicidal mechanisms. Very few Brucella-infected neutrophils are found in the target organs, except for the bone marrow, early in infection. Still, Brucella induces a mild reactive oxygen species formation and, through its lipopolysaccharide, promotes the premature death of neutrophils, which release chemokines and express "eat me" signals. This effect drives the phagocytosis of infected neutrophils by mononuclear cells that become thoroughly susceptible to Brucella replication and vehicles for bacterial dispersion. The premature death of the infected neutrophils proceeds without NETosis, necrosis/oncosis, or classical apoptosis morphology. In the absence of neutrophils, the Th1 response exacerbates and promotes bacterial removal, indicating that Brucella-infected neutrophils dampen adaptive immunity. This modulatory effect opens a window for bacterial dispersion in host tissues before adaptive immunity becomes fully activated. However, the hyperactivation of immunity is not without a price, since neutropenic Brucella-infected animals develop cachexia in the early phases of the disease. The delay in the immunological response seems a sine qua non requirement for the development of long-lasting brucellosis. This property may be shared with other pathogenic alphaproteobacteria closely related to Brucella We propose a model in which Brucella-infected polymorphonuclear neutrophils (PMNs) function as "Trojan horse" vehicles for bacterial dispersal and as modulators of the Th1 adaptive immunity in infection.

IgA Triggers Cell Death of Neutrophils When Primed by Inflammatory Mediators

IVIG preparations consisting of pooled IgG are increasingly used for the treatment of autoimmune diseases. IVIG is known to regulate the viability of immune cells, including neutrophils. We report that plasma-derived IgA efficiently triggers death of neutrophils primed by cytokines or TLR agonists. IgA-mediated programmed neutrophil death was PI3K-, p38 MAPK-, and JNK-dependent and evoked anti-inflammatory cytokines in macrophage cocultures. Neutrophils from patients with acute Crohn's disease, rheumatoid arthritis, or sepsis were susceptible to both IgA- and IVIG-mediated death. In contrast to IVIG, IgA did not promote cell death of quiescent neutrophils. Our findings suggest that plasma-derived IgA might provide a therapeutic option for the treatment of neutrophil-associated inflammatory disorders.

Characterization of the cathepsin D in Procambarus clarkii and its biological role in innate immune responses

Cathepsin D belongs to aspartic protease family, produced in the rough endoplasmic reticulum, and then transported to lysosomes, where it participates in various physiological processes. Despite its importance, only a few reports available on the functional role of cathepsin D in crustaceans. Herein, we cloned a cDNA fragment of cathepsin D from the hepatopancreas of the red swamp crayfish, Procambarus clarkii (Pc-cathepsin D) for the first time. It included 1158 base pairs open reading frame, encoding a protein of 385 amino acids. Multiple alignment analysis confirmed the presence of aspartic proteinase active sites and N glycosylation sites. Pc-cathepsin D mRNA expression was high in the gills followed by gut, heart, hepatopancreas of P. clarkii. At different time points post-infection with lipopolysaccharides, peptidoglycan, or polyinosinic polycytidylic acid, Pc-cathepsin D mRNA expression significantly enhanced compared with the control group. Knockdown of the Pc-cathepsin D by double-stranded RNA, strikingly, changed the expression of all the tested P. clarkii immune-associated genes, including Pc-Toll, Pc-lectin, Pc-cactus, Pc-anti-lipopolysaccharide factor, Pc-phospholipase, and Pc-sptzale. Altogether, these results suggest that Pc-cathepsin D is needed to confer innate immunity against microbial pathogens by modulating the expression of crucial transcripts that encode immune-associated genes.

The Septic Neutrophil-Friend or Foe

ABSTRACT

Neutrophils play a critical role in the eradication of pathogenic organisms, particularly bacteria. However, in the septic patient the prolonged activation and accumulation of neutrophils may augment tissue and organ injury. This review discusses the different activation states and chemotaxis of neutrophils in septic patients. Neutrophil killing of bacteria and the formation of neutrophil extracellular traps represent important components of the innate immune response and they become dysregulated during sepsis, possibly through changes in their metabolism. Delayed neutrophil apoptosis may contribute to organ injury, or allow better clearance of pathogens. Neutrophils provide a friendly immune response to clear infections, but excessive activation and recruitment has the potential to turn them into potent foes.

Biomaterial-Driven Immunomodulation: Cell Biology-Based Strategies to Mitigate Severe Inflammation and Sepsis

Inflammation is an essential component of a wide variety of disease processes and oftentimes can increase the deleterious effects of a disease. Finding ways to modulate this essential immune process is the basis for many therapeutics under development and is a burgeoning area of research for both basic and translational immunology. In addition to developing therapeutics for cellular and molecular targets, the use of biomaterials to modify innate and adaptive immune responses is an area that has recently sparked significant interest. In particular, immunomodulatory activity can be engineered into biomaterials to elicit heightened or dampened immune responses for use in vaccines, immune tolerance, or anti-inflammatory applications. Importantly, the inherent physicochemical properties of the biomaterials play a significant role in determining the observed effects. Properties including composition, molecular weight, size, surface charge, and others affect interactions with immune cells (i.e., nano-bio interactions) and allow for differential biological responses such as activation or inhibition of inflammatory signaling pathways, surface molecule expression, and antigen presentation to be encoded. Numerous opportunities to open new avenues of research to understand the ways in which immune cells interact with and integrate information from their environment may provide critical solutions needed to treat a variety of disorders and diseases where immune dysregulation is a key inciting event. However, to elicit predictable immune responses there is a great need for a thorough understanding of how the biomaterial properties can be tuned to harness a designed immunological outcome. This review aims to systematically describe the biological effects of nanoparticle properties-separate from additional small molecule or biologic delivery-on modulating innate immune cell responses in the context of severe inflammation and sepsis. We propose that nanoparticles represent a potential polypharmacological strategy to simultaneously modify multiple aspects of dysregulated immune responses where single target therapies have fallen short for these applications. This review intends to serve as a resource for immunology labs and other associated fields that would like to apply the growing field of rationally designed biomaterials into their work.

Reactive Oxygen Species and Antitumor Immunity-From Surveillance to Evasion

The immune system is a crucial regulator of tumor biology with the capacity to support or inhibit cancer development, growth, invasion and metastasis. Emerging evidence show that reactive oxygen species (ROS) are not only mediators of oxidative stress but also players of immune regulation in tumor development. This review intends to discuss the mechanism by which ROS can affect the anti-tumor immune response, with particular emphasis on their role on cancer antigenicity, immunogenicity and shaping of the tumor immune microenvironment. Given the complex role that ROS play in the dynamics of cancer-immune cell interaction, further investigation is needed for the development of effective strategies combining ROS manipulation and immunotherapies for cancer treatment.

Tanshinone IIA alleviates brain damage in a mouse model of neuromyelitis optica spectrum disorder by inducing neutrophil apoptosis

Background

Neuromyelitis optica spectrum disorder (NMOSD), an autoimmune astrocytopathic disease associated with the anti-aquaporin-4 (AQP4) antibody, is characterized by extensive necrotic lesions primarily located on the optic nerves and spinal cord. Tanshinone IIA (TSA), an active natural compound extracted from Salvia miltiorrhiza Bunge, has profound immunosuppressive effects on neutrophils.

Objective

The present study aimed to evaluate the effect of TSA on NMOSD mice and explore the underlying mechanisms. Mice were initially administered TSA (pre-TSA group, n = 20) or vehicle (vehicle group, n = 20) every 8 h for 3 days, and then NMOSD model was induced by intracerebral injection of NMOSD-immunoglobulin G (NMO-IgG) and human complement (hC). In addition, post-TSA mice (n = 10) were administered equal dose of TSA at 8 h and 16 h after model induction. At 24 h after intracerebral injection, histological analysis was performed to assess the inhibitory effects of TSA on astrocyte damage, demyelination, and neuroinflammation in NMOSD mice, and western blotting was conducted to clarify the effect of TSA on the NF-κB and MAPK signaling pathways. Furthermore, flow cytometry and western blotting were conducted to verify the proapoptotic effects of TSA on neutrophils in vitro.

Results

There was a profound reduction in astrocyte damage and demyelination in the pre-TSA group and post-TSA group. However, prophylactic administration of TSA induced a better effect than therapeutic treatment. The number of infiltrated neutrophils was also decreased in the lesions of NMOSD mice that were pretreated with TSA. We confirmed that prophylactic administration of TSA significantly promoted neutrophil apoptosis in NMOSD lesions in vivo, and this proapoptotic effect was mediated by modulating the caspase pathway in the presence of inflammatory stimuli in vitro. In addition, TSA restricted activation of the NF-κB signaling pathway in vivo.

Conclusion

Our data provide evidence that TSA can act as a prophylactic agent that reduces NMO-IgG-induced damage in the mouse brain by enhancing the resolution of inflammation by inducing neutrophil apoptosis, and TSA may serve as a promising therapeutic agent for neutrophil-associated inflammatory disorders, such as NMOSD.

Organosulfur Compounds: A Review of Their Anti-inflammatory Effects in Human Health

Phytonutrients are widely recognized for providing protective human health benefits. Among the phytonutrients, epidemiological and experimental studies show that dietary organosulfur compounds (OSC) play a significant role in preventing various human pathological progressions, including chronic inflammation, by decreasing inflammatory mediators such as nitric oxide (NO), prostaglandin (PG)E₂, interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and IL-17, which are all typical hallmarks of inflammation. Evidence supports OSC in reducing the expression of these markers, thereby attenuating chronic inflammatory processes. Nuclear factor-kappa B (NF-κB) is a key regulating factor during inflammation, and novel evidence shows that OSC downregulates this transcriptional factor, thus contributing to the anti-inflammatory response. In vitro and in vivo studies show that inflammation is mechanistically linked with acute and chronic pathological conditions including cancer, diabetes, obesity, neural dysfunction, etc. Furthermore, a considerable number of experiments have demonstrated that the anti-inflammatory properties of OSC occur in a dose-dependent manner. These experiments also highlight indirect mechanisms as well as potent co-functions for protective roles as antioxidants, and in providing chemoprotection and neuroprotection. In this brief review, we provided an overview of the anti-inflammatory effects of OSC and elucidated probable mechanisms that are associated with inflammation and chronic disorders.

Suppressive effects of S100A8 and S100A9 on neutrophil apoptosis by cytokine release of human bronchial epithelial cells in asthma

S100A8 and S100A9 are important proteins in the pathogenesis of allergy. Asthma is an allergic lung disease, characterized by bronchial inflammation due to leukocytes, bronchoconstriction, and allergen-specific IgE. In this study, we examined the role of S100A8 and S100A9 in the interaction of cytokine release from bronchial epithelial cells, with constitutive apoptosis of neutrophils. S100A8 and S100A9 induce increased secretion of neutrophil survival cytokines such as MCP-1, IL-6 and IL-8. This secretion is suppressed by TLR4 inhibitor), LY294002, AKT inhibitor, PD98059, SB202190, SP600125, and BAY-11-7085. S100A8 and S100A9 also induce the phosphorylation of AKT, ERK, p38 MAPK and JNK, and activation of NF-κB, which were blocked after exposure to TLR4i, LY294002, AKTi, PD98059, SB202190 or SP600125. Furthermore, supernatants collected from bronchial epithelial cells after S100A8 and S100A9 stimulation suppressed the apoptosis of normal and asthmatic neutrophils. These inhibitory mechanisms are involved in suppression of caspase 9 and caspase 3 activation, and BAX expression. The degradation of MCL-1 and BCL-2 was also blocked by S100A8 and S100A9 stimulation. Essentially, neutrophil apoptosis was blocked by co-culture of normal and asthmatic neutrophils with BEAS-2B cells in the presence of S100A8 and S100A9. These findings will enable elucidation of asthma pathogenesis.

Identification of key protein-coding genes and lncRNAs in spontaneous neutrophil apoptosis

Polymorphonuclear leukocytes (PMNs) are the most abundant cells of the innate immune system in humans, and spontaneous PMN apoptosis plays crucial roles in maintaining neutrophil homeostasis and resolving inflammation. However, the detailed mechanisms of spontaneous PMN apoptosis remain to be elucidated. By analysis of the public microarray dataset GSE37416, we identified a total of 3050 mRNAs and 220 long non-coding RNAs (lncRNAs) specifically expressed during PMN apoptosis in a time-dependent manner. By short time-series expression miner (STEM) analysis, Gene Ontology analysis, and lncRNA-mRNA co-expression network analyses, we identified some key molecules specifically related to PMN apoptosis. STEM analysis identified 12 gene profiles with statistically significance, including 2 associated with apoptosis. Protein-protein interaction (PPI) network analysis of the genes from 2 profiles and lncRNA-mRNA co-expression network analysis identified a 12-gene hub (including NFκB1 and BIRC3) associated with apoptosis, as well as 2 highly correlated lncRNAs (THAP9-AS1, and AL021707.6). We experimentally examined the expression profiles of two mRNA (NFκB1 and BIRC3) and two lncRNAs (THAP9-AS1 andAL021707.6) by quantitative real-time polymerase chain reaction to confirm their time-dependent expressions. These data altogether demonstrated that these genes are involved in the regulation of spontaneous neutrophil apoptosis and the corresponding gene products could also serve as potential key regulatory molecules for PMN apoptosis and/or therapeutic targets for over-reactive inflammatory response caused by the abnormality in PMN apoptosis.

Ameliorative effect of docosahexaenoic acid on hepatocyte apoptosis and inflammation induced by oleic acid in grass carp, Ctenopharyngodon idella

Our previous study has shown that overload of lipid accumulation results in cell apoptosis and inflammation in grass carp (Ctenopharyngodon idella). In this study, we investigated the potential protective effects of docosahexaenoic acid (DHA) on inhibiting oleic acid (OA)-induced apoptosis and inflammation in grass carp hepatocytes. Firstly, the hepatocyte of grass carp were treated with OA (800 μM) and different concentration (0, 50, 100 and 200 μM) of DHA for 24 h, the apoptotic ratio, gene expression levels of apoptosis such as caspase 3, caspase 8, and caspase 9, protein levels of Caspase3, and mRNA levels of inflammation genes such as nf-kb, tnf-α, and il-8 were detected. Furthermore, the mRNA levels of lipogenesis genes srebp1c, fas, acc, and scd and a key enzyme of lipolysis Atgl were also detected. These results showed that the cell apoptosis and the inflammation increased by OA were significantly attenuated by DHA (P < 0.05). Furthermore, DHA could significantly decrease fatty acid synthesis gene expression levels which were induced by OA (P < 0.05). However, the hepatocytes exposed with DHA had no significant influence on the expression of Atgl. Taken together, the study indicated that DHA protects the hepatocytes against apoptosis and inflammation induced by OA might via inhibiting fatty acid synthesis, instead of promoting lipolysis. These results call for further studies to assess the effectiveness of DHA.

The role of platelets in mediating a response to human influenza infection

Influenza infection increases the incidence of myocardial infarction but the reason is unknown. Platelets mediate vascular occlusion through thrombotic functions but are also recognized to have immunomodulatory activity. To determine if platelet processes are activated during influenza infection, we collected blood from 18 patients with acute influenza infection. Microscopy reveals activated platelets, many containing viral particles and extracellular-DNA associated with platelets. To understand the mechanism, we isolate human platelets and treat them with influenza A virus. Viral-engulfment leads to C3 release from platelets as a function of TLR7 and C3 leads to neutrophil-DNA release and aggregation. TLR7 specificity is confirmed in murine models lacking the receptor, and platelet depletion models support platelet-mediated C3 and neutrophil-DNA release post-influenza infection. These findings demonstrate that the initial intrinsic defense against influenza is mediated by platelet–neutrophil cross-communication that tightly regulates host immune and complement responses but can also lead to thrombotic vascular occlusion.

Influenza viremia is rare in human blood and not well studied. Here, the authors show that influenza can be found in human platelets and that platelet engulfment of influenza A results in TLR7-dependent C3 release, which in turn promotes neutrophil-DNA release and formation of platelet-DNA aggregates.

Anti-inflammatory effect of a novel synthetic compound 1-((4-fluorophenyl)thio)isoquinoline in RAW264.7 macrophages and a zebrafish model

The compound, 1-((4-fluorophenyl)thio)isoquinoline (FPTQ), is a synthetic isoquinoline derivative. To test the anti-inflammatory effect of FPTQ, we used neutrophil-specific transgenic zebrafish Tg(mpx::EGFP)ⁱ¹¹⁴ line and lipopolysaccharide (LPS)-stimulated RAW264.7 cells. We also used two different methods, involving tail transection and LPS stimulation in the zebrafish model. Neutrophils translocation in the zebrafish tail-transected model was inhibited by FPTQ. Neutrophil aggregation was also inhibited by FPTQ in the LPS-stimulated zebrafish model. Decreased mRNA expression of the pro-inflammatory cytokine genes, interleukin-1β (il-1β) and interleukin-6 (il-6), was found in zebrafish larvae injected with FPTQ. Additionally, production of nitric oxide was inhibited by FPTQ in RAW264.7 macrophage cells treated with LPS. Moreover, the mRNA expression of Il-1β and Il-6 suppressed by FPTQ treatment in RAW264.7 macrophage cells, and an enzyme immunoassay showed that FPTQ suppressed the secretion of IL-1β and IL-6 in RAW264.7 cells. These results demonstrate that FPTQ reduced inflammatory responses and, therefore, suggest that it may be effective as an anti-inflammatory agent.

Identification of Specific miRNAs in Neutrophils of Type 2 Diabetic Mice: Overexpression of miRNA-129-2-3p Accelerates Diabetic Wound Healing

Neutrophils are involved in the first stage of acute inflammation. After injury, they are mobilized and recruited to the injured tissue. In diabetes, wound healing is delayed and aberrant, leading to excessive recruitment and retention of neutrophils that fail to promote angiogenesis and prolong inflammation. However, the exact pathological mechanisms of diabetic-derived neutrophils in chronic inflammation remain unclear. Here, miRNA profiling of neutrophils from bone marrow in type 2 diabetic mice was performed using a microarray. miRNAs regulate the posttranscriptional expression of target mRNAs and are important in countering inflammation-related diseases. Our study revealed that miRNAs exhibit differential expression in diabetic-derived neutrophils compared with non-diabetic-derived neutrophils, especially miR-129 family members. miR-129-2-3p directly regulated the translation of Casp6 and Ccr2, which are involved in inflammatory responses and apoptosis. Furthermore, miR-129-2-3p overexpression at the wound site of type 2 diabetic mice accelerated wound healing. These results suggest possible involvement of miR-129-2-3p in diabetic-derived neutrophil dysfunction and that retention kinetics of neutrophils and chronic inflammation may be initiated through miR-129-2-3p-regulated genes. This study characterizes changes in global miRNA expression in diabetic-derived neutrophils and systematically identifies critical target genes involved in certain biological processes related to the pathology of diabetic wound healing.

Neutrophils: Innate Effectors of TB Resistance?

Certain individuals are able to resist Mycobacterium tuberculosis infection despite persistent and intense exposure. These persons do not exhibit adaptive immune priming as measured by tuberculin skin test (TST) and interferon-γ (IFN-γ) release assay (IGRA) responses, nor do they develop active tuberculosis (TB). Genetic investigation of individuals who are able to resist M. tuberculosis infection shows there are likely a combination of genetic variants that contribute to the phenotype. The contribution of the innate immune system and the exact cells involved in this phenotype remain incompletely elucidated. Neutrophils are prominent candidates for possible involvement as primers for microbial clearance. Significant variability is observed in neutrophil gene expression and DNA methylation. Furthermore, inter-individual variability is seen between the mycobactericidal capacities of donor neutrophils. Clearance of M. tuberculosis infection is favored by the mycobactericidal activity of neutrophils, apoptosis, effective clearance of cells by macrophages, and resolution of inflammation. In this review we will discuss the different mechanisms neutrophils utilize to clear M. tuberculosis infection. We discuss the duality between neutrophils' ability to clear infection and how increasing numbers of neutrophils contribute to active TB severity and mortality. Further investigation into the potential role of neutrophils in innate immune-mediated M. tuberculosis infection resistance is warranted since it may reveal clinically important activities for prevention as well as vaccine and treatment development.

A comprehensive three-dimensional assay to assess neutrophil defense against bacteria

Neutrophil antibacterial capacity is measured in animal models and in vitro as an important indicator of neutrophil function. To be able to extrapolate their conclusions, in vitro experiments should mimic the in vivo situation. In vivo, antibacterial capacity depends on multiple steps of bacterial sensing, priming, chemotaxis, phagocytosis and intracellular killing. Therefore, we developed a simply executed assay that involves multiple steps in one assay. The neutrophils were incorporated into a three-dimensional matrix of fibrin fibers, in which they could freely migrate. The fibrin matrix provided a more physiological representation of tissue structure than a shaken suspension and extended ex vivo survival of neutrophils. Staphylococci endogenously producing GFP (Green Fluorescent Protein) provided a real-time quantification of the bacterial load without the need for lysing the fibrin matrix or counting of colony forming units on agar plates. The delay in bacterial outgrowth serves as a measure for the relative antibacterial capacity of the neutrophils. Additionally, neutrophil capacity could easily be measured high-throughput in a 96-wells format. In this new assay we study neutrophil behavior in a physiologically relevant setting and explore many functions of the neutrophil in a single test. The functional capacity of neutrophils from different in vitro treatments or different donors can directly be compared.

Characterization of cathepsin D from Eriocheir sinensis involved in Spiroplasma eriocheiris infection

Cathepsin D (catD) belongs to a lysosomal aspartic protease superfamily. The full-length catD cDNA from the Chinese mitten crab Eriocheir sinensis (EscatD) was 2748 bp and contained a 1158-bp ORF encoding a protein of 385 amino acids, including a signal peptide and two N-glycosylation sites. Phylogenetic analysis showed that EscatD was clustered into a single group, together with other catD for crustaceans. Quantitative real-time PCR revealed that EscatD was expressed mainly in the eyes, hemocytes, intestine and nerve and was expressed weakly in heart, muscle and gills. After challenge with Spiroplasma eriocheiris, the expression of EscatD was significantly up-regulated from 1 d to 9 d. The copy number of S. eriocheiris in a silencing EscatD group was significantly higher than those in the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in an EscatD-dsRNA group. We further found that knockdown of EscatD by RNA interference resulted in a downward trend of expression levels of JNK, ERK, relish and p38 during the early stage, as well as a reduction in the expression of five antimicrobial peptides genes, namely, crusrin1, crustin2, ALF1, ALF2 and ALF3. The subcellular localization experiment suggested that recombinant EscatD was mainly located in the cytoplasm. The over-expression in Drosophila S2 cells indicated that EscatD could decrease the copy number of S. eriocheiris and increase cell viability. The above results demonstrated that EscatD plays an important immune role in E. sinensis to S. eriocheiris challenge.

Multilateral Functional Alterations of Human Neutrophils in Sepsis: From the Point of Diagnosis to the Seventh Day

Neutrophil functional changes caused by sepsis itself and their time-course variation have not been fully elucidated because previous studies targeted patients who had received therapeutic interventions. We explored the multilateral functions of circulating neutrophils in patients with severe sepsis or septic shock who had not yet undergone interventions, and followed their changes. Patients were treated based on the Surviving Sepsis Campaign Guidelines 2012. Neutrophil functions were evaluated on days 0 (before therapeutic intervention), 3, and 7 in 59 septic patients. The clinical severity score (APACHE II and SOFA) and serum pro-/anti-inflammatory cytokine concentrations of the patients were significantly increased on day 0 and normalized on day 3. However, neutrophil priming state, estimated by measuring the fMLP-stimulated reactive oxygen species, was significantly elevated on day 0, further augmented on day 3, and then returned to day 0 levels on day 7 despite general resolution of the inflammatory response. The expression of CXC chemokine receptor 2 and paired immunoglobulin-like receptor α, assessed as surrogate markers of transmigration and adhesion potency, was suppressed most strongly on day 0 and gradually recovered. To conclude, contrary to the patient's clinical course, neutrophil priming state was augmented most strongly at 3 days after diagnosis of sepsis. Impaired transmigration and excessive adhesion potency were observed most prominently at diagnosis. These observations would partially explain the mechanism of development of multiple organ dysfunction of the host who is subjected to a secondary insult, and may provide an important perspective for the implementation of additional immune-modulating therapy in sepsis.

Coxiella burnetii Inhibits Neutrophil Apoptosis by Exploiting Survival Pathways and Antiapoptotic Protein Mcl-1

Our previous study demonstrated that neutrophils play an important role in host defense against Coxiella burnetii infection in mice. In this study, avirulent strain C. burnetii Nine Mile phase II (NMII) was used to examine if C. burnetii can modulate mouse bone marrow-derived neutrophil apoptosis. The results indicated that NMII can inhibit neutrophil apoptosis. Western blotting demonstrated that caspase-3 cleavage was decreased in NMII-infected neutrophils, while phosphorylated mitogen-activated protein kinase (MAPK) p38 and extracellular signal-regulated kinase 1 (Erk1) were increased. Additionally, p38, Erk1/2, phosphoinositide 3-kinase (PI3K), or NF-κB inhibitors reduced the ability of NMII to inhibit neutrophil apoptosis. These results suggest that NMII-mediated inhibition of neutrophil apoptosis depends on its ability to activate neutrophil MAPK pathways. Antiapoptotic protein myeloid cell leukemia-1 (Mcl-1) was significantly increased in NMII-infected neutrophils, and an Mcl-1 inhibitor significantly reduced the ability of NMII to inhibit neutrophil apoptosis. Mcl-1 protein stability was enhanced by phosphorylation at Thr-163 by Erk, and the protein levels were regulated by p38, Erk, PI3K, and NF-κB. Furthermore, the observation that a type IV secretion system (T4SS)-deficient dotA mutant showed a significantly reduced ability to inhibit neutrophil apoptosis compared to wild-type (WT) NMII suggests that T4SS-secreted factors may be involved in NMII-induced inhibition of neutrophil apoptosis. Collectively, these results demonstrate that NMII inhibits neutrophil apoptosis through inhibition of caspase-3 cleavage and activation of MAPK survival pathways with subsequent expression and stabilization of antiapoptotic protein Mcl-1, a process that may partially require the T4SS.

Janus face of complement-driven neutrophil activation during sepsis

During local and systemic inflammation, the complement system and neutrophil granulocytes are activated not only by pathogens, but also by released endogenous danger signals. It is recognized increasingly that complement-mediated neutrophil activation plays an ambivalent role in sepsis pathophysiology. According to the current definition, the onset of organ dysfunction is a hallmark of sepsis. The preceding organ damage can be caused by excessive complement activation and neutrophil actions against the host, resulting in bystander injury of healthy tissue. However, in contrast, persistent and overwhelming inflammation also leads to a reduction in neutrophil responsiveness as well as complement components and thus may render patients at enhanced risk of spreading infection. This review provides an overview on the molecular and cellular processes that link complement with the two-faced functional alterations of neutrophils in sepsis. Finally, we describe novel tools to modulate this interplay beneficially in order to improve outcome.

Necroptosis and neutrophil-associated disorders

Necroptosis is a form of regulated necrosis and is dependent on a signaling pathway involving receptor interacting protein kinase-3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Necroptosis is considered to have important functions in inflammation and, based on studies with animal disease models, is believed likely to be involved in the pathogenesis of many human inflammatory diseases. In neutrophils, necroptosis has recently been reported to be triggered by tumor necrosis factor (TNF) stimulation, ligation of adhesion receptors, exposure to monosodium urate (MSU) crystals, or phagocytosis of Staphylococcus aureus (S. aureus). Because neutrophils are involved in many kinds of tissue inflammation and disease, neutrophil necroptosis probably plays a vital role in such processes. Dissecting the signaling pathway of neutrophil necroptotic death may help to identify novel drug targets for inflammatory or autoimmune diseases. In this review, we discuss different mechanisms which regulate neutrophil necroptosis and are thus potentially important in neutrophil-associated disorders.

Mechanisms regulating immune surveillance of cellular stress in cancer

The purpose of this review is to explore immune-mediated mechanisms of stress surveillance in cancer, with particular emphasis on the idea that all cancers have classical hallmarks (Hanahan and Weinberg in Cell 100:57-70, 67; Cell 144:646-674, 68) that could be interrelated. We postulate that hallmarks of cancer associated with cellular stress pathways (Luo et al. in Cell 136:823-837, 101) including oxidative stress, proteotoxic stress, mitotic stress, DNA damage, and metabolic stress could define and modulate the inflammatory component of cancer. As such, the overarching goal of this review is to define the types of cellular stress that cancer cells undergo, and then to explore mechanisms by which immune cells recognize, respond to, and are affected by each stress response.

Age is the work of art? Impact of neutrophil and organism age on neutrophil extracellular trap formation

Neutrophil extracellular traps or NETs are released by highly activated neutrophils in response to infectious agents, sterile inflammation, autoimmune stimuli and cancer. In the cells, the nuclear envelop disintegrates and decondensation of chromatin occurs that depends on peptidylarginine deiminase 4 (PAD4) and neutrophil elastase (NE). Subsequently, proteins from neutrophil granules (e.g., NE, lactoferrin and myeloperoxidase) and the nucleus (histones) bind to decondensed DNA and the whole structure is ejected from the cell. The DNA decorated with potent antimicrobials and proteases can act to contain dissemination of infection and in sterile inflammation NETs were shown to degrade cytokines and chemokines via serine proteases. On the other hand, overproduction of NETs, or their inadequate removal and prolonged presence in vasculature or tissues, can lead to bystander damage or even initiation of diseases. Considering the pros and cons of NET formation, it is of relevance if the stage of neutrophil maturation (immature, mature and senescent cells) affects the capacity to produce NETs as the cells of different age-related phenotypes dominate in given (pathological) conditions. Moreover, the immune system of neonates and elderly individuals is weaker than in adulthood. Is the same pattern followed when it comes to NETs? The overall importance of individual and neutrophil age on the capacity to release NETs is reviewed in detail and the significance of these facts is discussed.

Granulocytes: New Members of the Antigen-Presenting Cell Family

Granulocytes, the most abundant types of leukocytes, are the first line of defense against pathogen invasion. However, the plasticity and diversity of granulocytes have been increasingly revealed, especially with regard to their versatile functions in orchestrating adaptive immune responses. A substantial body of recent evidence demonstrates that granulocytes can acquire the function as antigen-presenting cells under pathological or inflammatory conditions. In addition, they can acquire surface expression of MHC class II and costimulatory molecules as well as T cell stimulatory behavior when cultured with selected cytokines. The classic view of granulocytes as terminally differentiated, short-lived phagocytes is therefore changing to phenotypically and functionally heterogeneous cells that are engaged in cross-talk with other leukocyte populations and provide an additional link between innate and adaptive immunity. In this brief review, we summarize the current knowledge on the antigen-presenting capacity of granulocyte subsets (neutrophils, eosinophils, and basophils). Underlying mechanisms, relevant physiological significance and potential controversies are also discussed.

Neither eosinophils nor neutrophils require ATG5-dependent autophagy for extracellular DNA trap formation

The importance of extracellular traps (ETs) in innate immunity is well established, but the molecular mechanisms responsible for their formation remain unclear and in scientific dispute. ETs have been defined as extracellular DNA scaffolds associated with the granule proteins of eosinophils or neutrophils. They are capable of killing bacteria extracellularly. Based mainly on results with phosphoinositide 3-kinase (PI3K) inhibitors such as 3-methyladenine (3-MA) and wortmannin, which are commonly used to inhibit autophagy, several groups have reported that autophagy is required for neutrophil extracellular trap (NET) formation. We decided to investigate this apparent dependence on autophagy for ET release and generated genetically modified mice that lack, specifically in eosinophils or neutrophils, autophagy-related 5 (Atg5), a gene encoding a protein essential for autophagosome formation. Interestingly, neither eosinophils nor neutrophils from Atg5-deficient mice exhibited abnormalities in ET formation upon physiological activation or exposure to low concentrations of PMA, although we could confirm that human and mouse eosinophils and neutrophils, after pre-treatment with inhibitors of class III PI3K, show a block both in reactive oxygen species (ROS) production and in ET formation. The so-called late autophagy inhibitors bafilomycin A1 and chloroquine, on the other hand, were without effect. These data indicate that ET formation occurs independently of autophagy and that the inhibition of ROS production and ET formation in the presence of 3-MA and wortmannin is probably owing to their additional ability to block the class I PI3Ks, which are involved in signalling cascades initiated by triggers of ET formation.