Neutrophil apoptosis and the resolution of infection

Gelatin methacryloyl @MP196/exos hydrogel induced neutrophil apoptosis and macrophage M2 polarization to inhibit periodontal bone loss

OBJECTIVES

Periodontitis is an inflammatory and destructive disease caused by dental plaque, which can result in the immune microenvironment disorders and loss of periodontal support tissue. In order to promote the restoration of local microenvironment stability, a functional biomaterial Gelatin methacryloyl @MP196/exos based on characteristics of disease occurrence is designed.

METHODS

Transmission electron microscopy, nanosight particle tracking analysis and western blot analysis were applied to prove the presence of exos in GelMA@MP196/exos. The swelling and degradation rates of GelMA@MP196/exos were evaluated. Cell proliferation, antibacterial ability and cellular uptake and intracellular internalization of exos were assessed in the study. Efferocytosis and M2 polarization of macrophages was estimated and the effects of GelMA@MP196/exos were proved in vivo.

RESULTS

GelMA@MP196/exos upregulated the expression of genes and proteins related to neutrophil apoptosis and promoted neutrophil apoptosis, macrophage M2 polarization, and efferocytosis. Furthermore, GelMA@MP196/exos exhibited significant antibacterial activity against Streptococcus gordonii, Fusobacterium nucleatum, and Porphyromonas gingivalis. GelMA@MP196/exos alleviated periodontitis and reduced alveolar bone loss in vivo in rat models.

CONCLUSIONS

GelMA@MP196/exos can serve as a potential strategy for the treatment of periodontitis.

CLINICAL SIGNIFICANCE

The main aim of periodontal therapy is to remove dental plaque and eliminate inflammation. However, some patients with low plaque scores and insufficient neutrophil clearance, resulting in poor responsiveness to periodontal therapy. Under the circumstances, local Application of drug that regulate the immune microenvironment had significance in controlling the progression of inflammation.

DNA methylation patterns contribute to changes of cellular differentiation pathways in leukocytes with LOY from patients with Alzheimer´s disease

Alzheimer's disease (AD) is a common and increasing societal problem due to the extending human lifespan. In males, loss of chromosome Y (LOY) in leukocytes is strongly associated with AD. We studied here DNA methylation and RNA expression in sorted monocytes and granulocytes with and without LOY from male AD patients. Through multi-omic analysis, we identified new candidate genes along with those previously associated with AD. Global analyses of DNA methylation in samples with LOY vs. normal state showed that hypomethylation dominated both in granulocytes and monocytes. Our findings highlight LOY-related differences in DNA methylation that occur in gene regulatory regions. Specifically, we observed alterations in key genes involved in leukocyte differentiation: FLI1, involved in early hematopoiesis; RUNX1, essential for blood cell development; RARA, regulating gene expression in response to retinoic acid; CANX, crucial for protein folding; CEBPB, a transcription factor important for immune responses; and MYADM, implicated in cell adhesion and migration. Moreover, protein-protein interaction analysis in granulocytes identified that products of two of these genes, CANX and CEBPB, are key hub proteins. This research underscores the potential of multi-omic approach in pure hematopoietic cell populations to uncover the molecular underpinnings of AD. Finally, our results link previous analysis showing impact of LOY on leukocyte differentiation, LOY-associated transcriptional dysregulation and GWAS studies of LOY.

Effects of the pan-caspase inhibitor Q-VD-OPh on human neutrophil lifespan and function

Human neutrophils are abundant, short-lived leukocytes that turn over at a rate of approximately 1011 cells/day via a constitutive apoptosis program. Certain growth factors, inflammatory mediators and infectious agents can delay apoptosis or induce neutrophils to die by other mechanisms. Nonetheless, a large body of data demonstrates that apoptosis of untreated neutrophils typically ensues within 24 hours of cell isolation and in vitro culture. At the molecular level apoptosis is driven by executioner caspase-3, and during this process cell proinflammatory capacity and host defense functions are downregulated. We undertook the current study to determine the extent to which human neutrophil viability and function could be prolonged by treatment with the non-toxic, irreversible, pan-caspase inhibitor Q-VD-OPh. Our data demonstrate that a single 10 μM dose of this drug was sufficient to markedly prolong cell lifespan. Specifically, we show that apoptosis was prevented for at least 5 days as indicated by analysis of nuclear morphology, DNA fragmentation, and phosphatidylserine externalization together with measurements of procaspase-3 processing and caspase activity. Conversely, mitochondrial depolarization declined despite abundant Myeloid Cell Leukemia 1 (MCL-1). At the same time, glutathione levels were maintained and Q-VD-OPh prevented age-associated increases mitochondrial oxidative stress. Regarding functional capacity, we show that phagocytosis, NADPH oxidase activity, chemotaxis, and degranulation were maintained following Q-VD-OPh treatment, albeit to somewhat different extents. Thus, a single 10 μM dose of Q-VD-OPh can sustain human neutrophil viability and function for at least 5 days.

Whole-blood model reveals granulocytes as key sites of dengue virus propagation, expanding understanding of disease pathogenesis

Dengue virus (DENV) infection poses a significant global health threat, yet our understanding of its immunopathogenesis remains incomplete due to limitations of existing models. Here, we establish an in vitro whole-blood model using hirudin, an anticoagulant that preserves complement activity and cellular interactions, to study DENV infection. Our model reveals the susceptibility of all major leukocyte populations to DENV infection, with monocytes and granulocytes demonstrating high permissiveness and production of infectious virus progeny. Notably, granulocytes emerge as previously unrecognized targets of DENV infection, highlighting the importance of studying viral tropism within a physiologically relevant context. We also observed efficient DENV binding to B cells, but limited production of infectious virus, suggesting a potential role in viral sequestration or immune dysregulation. Interestingly, both NK and T cells, while less permissive, were also found to be susceptible to DENV infection. Our ex vivo analysis of whole blood from DENV-infected patients confirms the susceptibility of granulocytes, monocytes, B cells, natural killer cells, and T cells to infection, further validating the clinical relevance of our model. Additionally, we observed dynamic changes in circulating blood cell populations during acute dengue, potentially reflecting both direct virus-mediated effects and immune responses. This whole-blood model offers a valuable tool for investigating the complex interplay between DENV and host factors, facilitating a deeper understanding of dengue pathogenesis and ultimately contributing to the development of novel therapeutic strategies.IMPORTANCEDengue virus (DENV) infection is a significant global health threat, with increasing incidence in endemic regions and expanding geographic range due to factors like global warming. Current models for studying DENV pathogenesis often lack the complexity of the human immune system, hindering the development of effective therapies and vaccines. To address this, we have established the first in vitro whole-blood model using hirudin, preserving critical immune components and cellular interactions. This model reveals granulocytes as previously unrecognized targets of productive DENV infection, challenging existing paradigms of viral tropism. Our ex vivo analysis of patient blood samples confirms the clinical relevance of this finding and validates our model's utility. This unique model offers a powerful platform for future studies to dissect the complex interactions between DENV and the host immune system, including the roles of different leukocyte populations, ultimately informing the development of novel therapeutic strategies to combat this devastating disease.

Schwann cell autotransplantation for the treatment of peripheral nerve injury

Peripheral nerve injury occurs in a relatively large proportion of trauma patients, in whom it generally results in severe functional impairment and permanent disability. At present, however, there are no effective treatments available. Studies have shown that Schwann cells play an indispensable role in removing myelin debris and guiding axonal regeneration, and transplantation using autologous Schwann cells has shown good efficacy for patients with peripheral nerve injury. In recent years, Schwann cell autologous transplantation therapy has become an area of intensive research and is anticipated to provide a new strategy for the clinical treatment of peripheral nerve injury. In this article, we review the rationale for selecting Schwann cell autotransplantation therapy and the latest progress in key aspects of cell transplantation and clinical efficacy, and also summarize the future directions of research on this therapy. All of the above provide a strong basis for the further improvement and clinical promotion of this therapy.

Thermographic assessment of mastitis progression in sahiwal cattle: Insights into the patterns in the natural course of infection

Mastitis is a global concern in the dairy sector, demanding innovative solutions for effective management for quality lifetime milk production. In this study, infrared thermography (IRT) as a non-invasive technology was integrated into routine farm activities for continuous health monitoring of animals. For 30 days, we systematically monitored the udder health status in 40 Sahiwal cows (160 quarters), employing IRT along with the California Mastitis Test (CMT). We also assessed somatic cell count (SCC), microbial identification, and milk quality parameters of representative samples. The thermal imaging data was analyzed, considering both backward propagation from the 0th day to the -10th day and forward propagation from the 0th day to the +10th day. Our findings revealed that on the 0th day, the mean temperatures of the udder surface skin temperature (USST) and teat skin surface temperature (TSST) exhibited differences (p < 0.05) between the quarters affected by sub-clinical mastitis (SCM) and clinical mastitis (CM) in comparison to the healthy quarters, with the highest degree of difference observed. The observed temperature differences between CM and SCM quarters compared to healthy ranged from 1.8 to 3.62 °C and 0.98 to 3.23 °C for USST, and from 1.68 to 3.16 °C and 0.56 to 2.32 °C for TSST, respectively. Furthermore, our observations indicated that both udder and teat quarters responded differently to mastitis. A temperature rise of 1.37 °C in SCM quarters and 1.75 °C in CM quarters was observed between the -10th and -8th day relative to day 0, with the increase being more pronounced in the morning hours. Also, a notable temperature surge occurred during the -2nd and -1st days relative to the 0th day. The log10SCC values and milk quality parameters significantly differed (p < 0.05) between mastitis-affected and healthy samples. In addition, Staphylococcus spp. was identified as the predominant mastitis-causing pathogen in the bacteriological identification conducted in this study. Therefore, IRT efficiently assesses the initiation point of udder infection in Sahiwal cows, aiding in effective udder health management.

Triptolide alleviates acute gouty arthritis caused by monosodium urate crystals by modulating macrophage polarization and neutrophil activity

The present study focused on the efficacy and role of triptolide (TPL) in relieving symptoms of acute gouty arthritis (AGA) in vivo and in vitro. The effects of TPL in AGA were investigated in monosodium urate (MSU)-treated rat ankles, RAW264.7 macrophages, and neutrophils isolated from mouse peritoneal cavity. Observation of pathological changes in the ankle joint of rats. Enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction (RT-qPCR) were performed to detect the expression levels of inflammatory factors and chemokines. The levels of the indicators of macrophage M1/M2 polarization, and the mechanistic targets of Akt and rapamycin complex 2, were determined via western blotting and RT-qPCR. The expression levels of CD86 and CD206 were detected using immunohistochemistry. Neutrophil migration was observed via air pouch experiments in vivo and Transwell cell migration assay in vitro. Myeloperoxidase (MPO) and Neutrophil elastase (NE) release was analyzed by via immunohistochemistry and immunofluorescence. The expression levels of beclin-1, LC3B, Bax, Bcl-2, and cleaved caspase-3 in neutrophils were determined via western blotting and immunofluorescence. Neutrophil apoptosis was detected using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Our results suggest that TPL inhibited inflammatory cell infiltration in rat ankle joints and inflammatory factor and chemokine secretion in rat serum, regulated macrophage polarization through the PI3K/AKT signaling pathway, suppressed inflammatory factor and chemokine expression in neutrophils, and inhibited neutrophil migration, neutrophil extracellular trap formation, transitional autophagy, and apoptosis. This suggests that TPL can prevent and treat MSU-induced AGA by regulating macrophage polarization through the PI3K/Akt pathway and modulating neutrophil activity.

Comparative analysis of formyl peptide receptor 1 and formyl peptide receptor 2 reveals shared and preserved signalling profiles

BACKGROUND AND PURPOSE

The pattern recognition receptors, formyl peptide receptors, FPR1 and FPR2, are G protein-coupled receptors that recognize many different pathogen- and host-derived ligands. While FPR1 conveys pro-inflammatory signals, FPR2 is linked with pro-resolving outcomes. To analyse how the two very similar FPRs exert opposite effects in modulating inflammatory responses despite their high homology, a shared expression profile on immune cells and an overlapping ligand repertoire, we questioned whether the signalling profile differs between these two receptors.

EXPERIMENTAL APPROACH

We deduced EC50 and Emax values for synthetic, pathogen-derived and host-derived peptide agonists for both FPR1 and FPR2 and analysed them within the framework of biased signalling. We furthermore investigated whether FPR isoform-specific agonists affect the ex vivo lifespan of human neutrophils.

KEY RESULTS

The FPRs share a core signature across signalling pathways. Whereas the synthetic WKYMVm and formylated peptides acted as potent agonists at FPR1, and at FPR2, only WKYMVm was a full agonist. Natural FPR2 agonists, irrespective of N-terminal formylation, displayed lower activity ratios, suggesting an underutilized signalling potential of this receptor. FPR2 agonism did not counteract LPS-induced neutrophil survival, indicating that FPR2 activation per se is not linked with a pro-resolving function.

CONCLUSION AND IMPLICATIONS

Activation of FPR1 and FPR2 by a representative agonist panel revealed a lack of a receptor-specific signalling texture, challenging assumptions about distinct inflammatory profiles linked to specific receptor isoforms, signalling patterns or agonist classes. These conclusions are restricted to the specific agonists and signalling pathways examined.

Single-domain antibodies and aptamers drive new opportunities for neurodegenerative disease research

Neurodegenerative diseases (NDs) in mammals, such as Alzheimer's disease (AD), Parkinson's disease (PD), and transmissible spongiform encephalopathies (TSEs), are characterized by the accumulation of misfolded proteins in the central nervous system (CNS). Despite the presence of these pathogenic proteins, the immune response in affected individuals remains notably muted. Traditional immunological strategies, particularly those reliant on monoclonal antibodies (mAbs), face challenges related to tissue penetration, blood-brain barrier (BBB) crossing, and maintaining protein stability. This has led to a burgeoning interest in alternative immunotherapeutic avenues. Notably, single-domain antibodies (or nanobodies) and aptamers have emerged as promising candidates, as their reduced size facilitates high affinity antigen binding and they exhibit superior biophysical stability compared to mAbs. Aptamers, synthetic molecules generated from DNA or RNA ligands, present both rapid production times and cost-effective solutions. Both nanobodies and aptamers exhibit inherent qualities suitable for ND research and therapeutic development. Cross-seeding events must be considered in both traditional and small-molecule-based immunodiagnostic and therapeutic approaches, as well as subsequent neurotoxic impacts and complications beyond protein aggregates. This review delineates the challenges traditional immunological methods pose in ND research and underscores the potential of nanobodies and aptamers in advancing next-generation ND diagnostics and therapeutics.

Pseudomonas aeruginosa in chronic lung disease: untangling the dysregulated host immune response

Pseudomonas aeruginosa is a highly adaptable opportunistic pathogen capable of exploiting barriers and immune defects to cause chronic lung infections in conditions such as cystic fibrosis. In these contexts, host immune responses are ineffective at clearing persistent bacterial infection, instead driving a cycle of inflammatory lung damage. This review outlines key components of the host immune response to chronic P. aeruginosa infection within the lung, beginning with initial pathogen recognition, followed by a robust yet maladaptive innate immune response, and an ineffective adaptive immune response that propagates lung damage while permitting bacterial persistence. Untangling the interplay between host immunity and chronic P. aeruginosa infection will allow for the development and refinement of strategies to modulate immune-associated lung damage and potentiate the immune system to combat chronic infection more effectively.

Phenotypic alteration by dengue virus serotype 2 delays neutrophil apoptosis and stimulates the release of prosurvival secretome with immunomodulatory functions

Neutrophils are the most abundant granuloytes, are phenotypically heterogeneous, and exert detrimental or protective roles during antiviral response. Dengue virus has been reported to activate neutrophils. However, the effect of the dengue virus on the neutrophil phenotypes, survival, and release of inflammatory secretome is yet to be understood. Herein, we investigated the effect of dengue virus serotype 2 (DV-2) on effector functions of naïve neutrophils and studied the impact of its secretome on different immune cells. We found that DV-2 activates purified human neutrophils and causes a significant shift toward the CD16bright/CD62Ldim subtype in a multiplicity of infection and time-dependent manner. These phenotypically altered neutrophils show delayed apoptosis through nuclear factor κB and PI3K pathways and have decreased phagocytic capacity. Treatment of neutrophils with myeloperoxidase and PAD4 inhibitor before DV-2 incubation significantly reduced DV-2-induced double-stranded DNA release, suggesting that myeloperoxidase and PAD4 were involved at early stages for the neutrophil activation and double-stranded DNA release. We also report that DV-2-stimulated neutrophil secretome had a significant effect on viral infection, platelet activation, and naïve neutrophil survival via binding of tumor necrosis factor α to tumor necrosis factor receptor 1/2 receptors. Furthermore, incubation of endothelial cells with the DV-2-stimulated neutrophil secretome potentially inhibits proliferation and wound healing capacity and induces endothelial cell death, which can contribute to endothelial barrier dysfunction. In conclusion, the neutrophil-DV-2 interaction modulates the phenotype of neutrophils and the release of prosurvival and antiviral secretome that may act as a double-edged sword during dengue pathogenesis.

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.

Graphene-based nanomaterials for peripheral nerve regeneration

Emerging nanotechnologies offer numerous opportunities in the field of regenerative medicine and have been widely explored to design novel scaffolds for the regeneration and stimulation of nerve tissue. In this review, we focus on peripheral nerve regeneration. First, we introduce the biomedical problem and the present status of nerve conduits that can be used to guide, fasten and enhance regeneration. Then, we thoroughly discuss graphene as an emerging candidate in nerve tissue engineering, in light of its chemical, tribological and electrical properties. We introduce the graphene forms commonly used as neural interfaces, briefly review their applications, and discuss their potential toxicity. We then focus on the adoption of graphene in peripheral nervous system applications, a research field that has gained in the last years ever-increasing attention. We discuss the potential integration of graphene in guidance conduits, and critically review graphene interaction not only with peripheral neurons, but also with non-neural cells involved in nerve regeneration; indeed, the latter have recently emerged as central players in modulating the immune and inflammatory response and accelerating the growth of new tissue.

Exploring the Relationship between Neutrophil Activation and Different States of Canine L. infantum Infection: Nitroblue Tetrazolium Test and IFN-γ

This study aimed to investigate the role of neutrophils in canine leishmaniosis by assessing neutrophil activation and its relationship with different states of L. infantum infection and antibody and IFN-γ production. Dogs were categorized into five groups: healthy-seronegative (n = 25), healthy-seropositive (n = 21), LeishVet-stage I (n = 25), Leishvet-stage II (n = 41), and LeishVet-stage III-IV (n = 16). Results of the nitroblue tetrazolium reduction test (NBT) showed significantly higher neutrophil activation in stage I (median:17.17, range: [7.33-31.50]%) compared to in healthy-seronegative (4.10 [1.20-18.00]%), healthy-seropositive (7.65 [3.98-21.74]%), stage II (6.50 [1.50-28.70]%), and stage III-IV (7.50 [3.00-16.75]%) groups (p < 0.0001). Healthy-seropositive dogs also displayed higher values than all groups except stage I. Stages II and III-IV did not show significant differences compared to healthy-seronegative. Regarding IFN-γ, stage I dogs had higher concentrations (median:127.90, range: [0-3998.00] pg/mL) than healthy-seronegative (0 [0-109.50] pg/mL) (p = 0.0002), stage II (9.00 [0-5086.00] pg/mL) (p = 0.045), and stage III-IV (3.50 [80.00-548.80] pg/mL) (p = 0.02) dogs. Stage II dogs showed increased IFN-γ compared to healthy-seronegative dogs (p = 0.015), while stage III-IV dogs had no significant differences compared to healthy-seronegative dogs (p = 0.12). Healthy-seropositive dogs had elevated IFN-γ concentrations compared to healthy-seronegative dogs (p = 0.001) and dogs in stage III-IV (p = 0.03). In conclusion, neutrophil activation was higher in dogs with mild disease and healthy-seropositive dogs, and a relationship between neutrophil activation and the production of IFN-γ was found.

The importance of morphological changes in neutrophils in the diagnosis of bacterial infections in dogs with confirmed urinary tract infections in a Veterinary Care Service, Rio de Janeiro, Brazil

Neutrophils (PMNs) are cellular markers used for diagnosing inflammation and/or infections. In this study, the objective was to highlight the importance of recording the toxic morphological alterations of the PMNs as markers of infection in 10 cases, positive bacterial isolation by culture due to dysuria, hematuria and/or fetid urine, as manifestations of urinary tract disease. Smear observations were performed by immersion for counting and morphological evaluations of 3,000 leukocytes in smears and in leukocyte concentrate. One (10.0%) of the dogs had leukocytosis, and two (20.0%) dogs had leukopenia. All animals showed toxic PMNs with positive bacterial culture. None of the cases in the study showed any quantitative alterations in PMNs such as: neutropenia or neutrophilia, where 100% had nuclear displacement of the regenerative type of PMNs to the left. 100% cases had toxic morphological changes: 90.0% had PMNs with toxic granulations, 80.0% had giant rod neutrophils, 70.0% had target PMNs, in 50.0% of those with vacuolation in the cytoplasm, in 40.0% of the animals, the presence of giant PMNs, 10.0% with Döhle bodies, and another animal 10.0% with karyorrhexis. All case studies had at least one association of two types of toxic changes. Toxic morphological alterations observed in PMNs through cystoscopy proved to be more reliable and sensitive in evidencing the diagnosis of infections than the quantitative alterations of absolute values of total leukocytes; therefore, they were essential in the laboratory diagnosis by blood count in the course of infections in dogs.

PKM2/STAT1-mediated PD-L1 upregulation on neutrophils during sepsis promotes neutrophil organ accumulation by serving an anti-apoptotic role

BACKGROUND

Delayed neutrophil apoptosis during sepsis may impact neutrophil organ accumulation and tissue immune homeostasis. Elucidating the mechanisms underlying neutrophil apoptosis may help identify potential therapeutic targets. Glycolysis is critical to neutrophil activities during sepsis. However, the precise mechanisms through which glycolysis regulates neutrophil physiology remain under-explored, especially those involving the non-metabolic functions of glycolytic enzymes. In the present study, the impact of programmed death ligand-1 (PD-L1) on neutrophil apoptosis was explored. The regulatory effect of the glycolytic enzyme, pyruvate kinase M2 (PKM2), whose role in septic neutrophils remains unaddressed, on neutrophil PD-L1 expression was also explored.

METHODS

Peripheral blood neutrophils were isolated from patients with sepsis and healthy controls. PD-L1 and PKM2 levels were determined by flow cytometry and Western blotting, respectively. Dimethyl sulfoxide (DMSO)-differentiated HL-60 cells were stimulated with lipopolysaccharide (LPS) as an in vitro simulation of septic neutrophils. Cell apoptosis was assessed by annexin V/propidium iodide (annexin V/PI) staining, as well as determination of protein levels of cleaved caspase-3 and myeloid cell leukemia-1 (Mcl-1) by Western blotting. An in vivo model of sepsis was constructed by intraperitoneal injection of LPS (5 mg/kg) for 16 h. Pulmonary and hepatic neutrophil infiltration was assessed by flow cytometry or immunohistochemistry.

RESULTS

PD-L1 level was elevated on neutrophils under septic conditions. Administration of neutralizing antibodies against PD-L1 partially reversed the inhibitory effect of LPS on neutrophil apoptosis. Neutrophil infiltration into the lung and liver was also reduced in PD-L1-/- mice 16 h after sepsis induction. PKM2 was upregulated in septic neutrophils and promoted neutrophil PD-L1 expression both in vitro and in vivo. In addition, PKM2 nuclear translocation was increased after LPS stimulation, which promoted PD-L1 expression by directly interacting with and activating signal transducer and activator of transcription 1 (STAT1). Inhibition of PKM2 activity or STAT1 activation also led to increased neutrophil apoptosis.

CONCLUSION

In this study, a PKM2/STAT1-mediated upregulation of PD-L1 on neutrophils and the anti-apoptotic effect of upregulated PD-L1 on neutrophils during sepsis were identified, which may result in increased pulmonary and hepatic neutrophil accumulation. These findings suggest that PKM2 and PD-L1 could serve as potential therapeutic targets.

Neutrophils in Health and Disease: From Receptor Sensing to Inflammasome Activation

Neutrophils—polymorphonuclear cells (PMNs) are the cells of the initial immune response and make up the majority of leukocytes in the peripheral blood. After activation, these cells modify their functional status to meet the needs at the site of action or according to the agent causing injury. They receive signals from their surroundings and “plan” the course of the response in both temporal and spatial contexts. PMNs dispose of intracellular signaling pathways that allow them to perform a wide range of functions associated with the development of inflammatory processes. In addition to these cells, some protein complexes, known as inflammasomes, also have a special role in the development and maintenance of inflammation. These complexes participate in the proteolytic activation of key pro-inflammatory cytokines, such as IL-1β and IL-18. In recent years, there has been significant progress in the understanding of the structure and molecular mechanisms behind the activation of inflammasomes and their participation in the pathogenesis of numerous diseases. The available reports focus primarily on macrophages and dendritic cells. According to the literature, the activation of inflammasomes in neutrophils and the associated death type—pyroptosis—is regulated in a different manner than in other cells. The present work is a review of the latest reports concerning the course of inflammasome activation and inflammatory cytokine secretion in response to pathogens in neutrophils, as well as the role of these mechanisms in the pathogenesis of selected diseases.

Human neutrophils ≠ murine neutrophils: Does it matter?

Human and murine neutrophils differ with respect to representation in blood, receptors, nuclear morphology, signaling pathways, granule proteins, NADPH oxidase regulation, magnitude of oxidant and hypochlorous acid production, and their repertoire of secreted molecules. These differences often matter and can undermine extrapolations from murine studies to clinical care, as illustrated by several failed therapeutic interventions based on mouse models. Likewise, coevolution of host and pathogen undercuts fidelity of murine models of neutrophil-predominant human infections. However, murine systems that accurately model the human condition can yield insights into human biology difficult to obtain otherwise. The challenge for investigators who employ murine systems is to distinguish models from pretenders and to know when the mouse provides biologically accurate insights. Testing with human neutrophils observations made in murine systems would provide a safeguard but is not always possible. At a minimum, studies that use exclusively murine neutrophils should have accurate titles supported by data and restrict conclusions to murine neutrophils and not encompass all neutrophils. For now, the integration of evidence from studies of neutrophil biology performed using valid murine models coupled with testing in vitro of human neutrophils combines the best of both approaches to elucidate the mysteries of human neutrophil biology.

Chlamydia psittaci inhibits apoptosis of human neutrophils by activating P2X7 receptor expression

This study tested the hypothesis that Chlamydia psittaci (C. psittaci) survives and multiplies in human neutrophils by activating P2X7, a nonselective cationic channel receptor expressed constitutively on the surface of these cells. Findings illustrated that P2X7 receptor expression was enhanced in C. psittaci-infected neutrophils. C. psittaci was able to inhibite spontaneous apoptosis of neutrophils through mitochondrial-induced ATP release and IL-8 production. Importantly, inhibiting ATP activation of the P2X7 receptor with AZ10606120 promotes apoptosis, while stimulating P2X7 receptor expression with BzATP delayed spontaneous apoptosis of human neutrophils, suggesting that C. psittaci inhibits apoptosis of human neutrophils by activating P2X7 receptor. This study reveals new insights into the survival advantages of the latent persistent state of C. psittaci and the mechanism by which it evades the innate immune response.

Protective role for C3aR in experimental chronic pyelonephritis

Emerging evidence suggest that C3aR plays important roles in homeostasis, host defense and disease. Although it is known that C3aR is protective in several models of acute bacterial infections, the role for C3aR in chronic infection is largely unknown. Here we show that C3aR is protective in experimental chronic pyelonephritis. Global C3aR deficient (C3ar-/- ) mice had higher renal bacterial load, more pronounced renal histological lesions, increased renal apoptotic cell accumulation, tissue inflammation and extracellular matrix deposition following renal infection with uropathogenic E. coli (UPEC) strain IH11128, compared to WT control mice. Myeloid C3aR deficient (Lyz2-C3ar-/- ) mice exhibited a similar disease phenotype to global C3ar-/- mice. Pharmacological treatment with a C3aR agonist reduced disease severity in experimental chronic pyelonephritis. Furthermore, macrophages of C3ar-/- mice exhibited impaired ability to phagocytose UPEC. Our data clearly demonstrate a protective role for C3aR against experimental chronic pyelonephritis, macrophage C3aR plays a major role in the protection, and C3aR is necessary for phagocytosis of UPEC by macrophages. Our observation that C3aR agonist curtailed the pathology suggests a therapeutic potential for activation of C3aR in chronic infection.

A Host-Directed Approach to the Detection of Infection in Hard-to-Heal Wounds

Wound infection is traditionally defined primarily by visual clinical signs, and secondarily by microbiological analysis of wound samples. However, these approaches have serious limitations in determining wound infection status, particularly in early phases or complex, chronic, hard-to-heal wounds. Early or predictive patient-derived biomarkers of wound infection would enable more timely and appropriate intervention. The observation that immune activation is one of the earliest responses to pathogen activity suggests that immune markers may indicate wound infection earlier and more reliably than by investigating potential pathogens themselves. One of the earliest immune responses is that of the innate immune cells (neutrophils) that are recruited to sites of infection by signals associated with cell damage. During acute infection, the neutrophils produce oxygen radicals and enzymes that either directly or indirectly destroy invading pathogens. These granular enzymes vary with cell type but include elastase, myeloperoxidase, lysozyme, and cathepsin G. Various clinical studies have demonstrated that collectively, these enzymes, are sensitive and reliable markers of both early-onset phases and established infections. The detection of innate immune cell enzymes in hard-to-heal wounds at point of care offers a new, simple, and effective approach to determining wound infection status and may offer significant advantages over uncertainties associated with clinical judgement, and the questionable value of wound microbiology. Additionally, by facilitating the detection of early wound infection, prompt, local wound hygiene interventions will likely enhance infection resolution and wound healing, reduce the requirement for systemic antibiotic therapy, and support antimicrobial stewardship initiatives in wound care.

Teg58, a small regulatory RNA, is involved in regulating arginine biosynthesis and biofilm formation in Staphylococcus aureus

Staphylococcus aureus adapts to different environments by sensing and responding to diverse environmental cues. The responses are coordinately regulated by regulatory proteins, and small regulatory RNAs at the transcriptional and translational levels. Here, we characterized teg58, a SarA repressed sRNA, using ChIP-Seq and RNA-Seq analysis of a sarA mutant. Phenotypic and genetic analyses indicated that inactivation of teg58 led to reduced biofilm formation in a process that is independent of SarA, agr, PIA, and PSMs. RNA-Seq analysis of teg58 mutant revealed up-regulation of arginine biosynthesis genes (i.e., argGH) as well as the ability of the mutant to grow in a chemical defined medium (CDM) lacking L-arginine. Exogenous L-arginine or endogenous induction of argGH led to decreased biofilm formation in parental strains. Further analysis in vitro and in vivo demonstrated that the specific interaction between teg58 and the argGH occurred at the post-transcriptional level to repress arginine synthesis. Biochemical and genetic analyses of various arginine catabolic pathway genes demonstrated that the catabolic pathway did not play a significant role in reduced biofilm formation in the teg58 mutant. Overall, results suggest that teg58 is a regulatory sRNA that plays an important role in modulating arginine biosynthesis and biofilm formation in S. aureus.

CuO-NPs-triggered heterophil extracellular traps exacerbate liver injury in chicks by promoting oxidative stress and inflammatory responses

With the widespread use of copper oxide nanoparticles (CuO-NPs), their potential toxicity to the environment and biological health has attracted close attention. Heterophil extracellular traps (HETs) are an innate immune mechanism of chicken heterophils against adverse stimuli, but excessive HETs cause damage. Here, we explored the effect and mechanism of CuO-NPs on HETs formation in vitro and further evaluated the potential role of HETs in chicken liver and kidney injury. Heterophils were exposed to 5, 10, and 20 µg/mL of CuO-NPs for 2 h. The results showed that CuO-NPs induced typical HETs formation, which was dependent on NADPH oxidase, P38 and extracellular regulated protein kinases (ERK_1/2) pathways, and glycolysis. In in vivo experiments, fluorescence microplate and morphological analysis showed that CuO-NPs elevated the level of HETs in chicken serum and caused liver and kidney damage. Meanwhile, CuO-NPs caused hepatic oxidative stress (MDA, SOD, CAT, and GSH-PX imbalance), and also induced an increase in mRNA expression of their inflammatory and apoptosis-related factors (IL-1β, IL-6, TNF-α, COX-2, iNOS, NLRP3, and Caspase-1, 3, 11). However, these results were significantly altered by DNase I (HETs degradation reagent). In conclusion, the present study demonstrates for the first time that CuO-NPs induce the formation of HETs and that HETs exacerbate pathological damage in chicken liver and kidney by promoting oxidative stress and inflammation, providing insights into immunotoxicity and potential prevention and treatment targets caused by CuO-NPs overexposure.

Neutrophil Survival Signaling During Francisella tularensis Infection

Neutrophils are the most abundant and shortest-lived leukocytes in humans and tight regulation of neutrophil turnover via constitutive apoptosis is essential for control of infection and resolution of inflammation. Accordingly, aberrant neutrophil turnover is hallmark of many disease states. We have shown in previous work that the intracellular bacterial pathogen Francisella tularensis markedly prolongs human neutrophil lifespan. This is achieved, in part, by changes in neutrophil gene expression. Still unknown is the contribution of major neutrophil pro-survival signaling cascades to this process. The objective of this study was to interrogate the contributions of ERK and p38 MAP kinase, Class I phosphoinositide 3-kinases (PI3K), AKT, and NF-κB to neutrophil survival in our system. We demonstrate that both ERK2 and p38α were activated in F. tularensis-infected neutrophils, but only p38α MAPK was required for delayed apoptosis and the rate of cell death in the absence of infection was unchanged. Apoptosis of both infected and uninfected neutrophils was markedly accelerated by the pan-PI3K inhibitor LY2094002, but AKT phosphorylation was not induced, and neutrophil death was not enhanced by AKT inhibitors. In addition, isoform specific and selective inhibitors revealed a unique role for PI3Kα in neutrophil survival after infection, whereas only simultaneous inhibition of PI3Kα and PI3kδ accelerated death of the uninfected controls. Finally, we show that inhibition of NF-κB triggered rapid death of neutrophil after infection. Thus, we defined roles for p38α, PI3Kα and NF-κB delayed apoptosis of F. tularensis-infected cells and advanced understanding of Class IA PI3K isoform activity in human neutrophil survival.

Contribution of Puma to Inflammatory Resolution During Early Pneumococcal Pneumonia

Apoptosis of cells at the site of infection is a requirement for shutdown of inflammatory signaling, avoiding tissue damage, and preventing progression of sepsis. Puma^+/+ and Puma^-/- mice were challenged with TIGR4 strain pneumococcus and cytokines were quantitated from lungs and blood using a magnetic bead panel analysis. Puma^-/- mice exhibited higher lung and blood cytokine levels of several major inflammatory cytokines, including IL-6, G-CSF, RANTES, IL-12, IFN-ϒ, and IP-10. Puma^-/- mice were more susceptible to bacterial dissemination and exhibited more weight loss than their wild-type counterparts. RNA sequencing analysis of whole pulmonary tissue revealed Puma-dependent regulation of Nrxn2, Adam19, and Eln. Enrichment of gene ontology groups differentially expressed in Puma^-/- tissues were strongly correlated to IFN-β and -ϒ signaling. Here, we demonstrate for the first time the role of Puma in prohibition of the cytokine storm during bacterial pneumonia. These findings further suggest a role for targeting immunomodulation of IFN signaling during pulmonary inflammation. Additionally, our findings suggest previously undemonstrated roles for genes encoding regulatory and binding proteins during the early phase of the innate immune response of pneumococcal pneumonia.

Metabolic Reprogramming Mediates Delayed Apoptosis of Human Neutrophils Infected With Francisella tularensis

Neutrophils (polymorphonuclear leukocytes, PMNs) have a distinctively short lifespan, and tight regulation of cell survival and death is imperative for their normal function. We demonstrated previously that Francisella tularensis extends human neutrophil lifespan, which elicits an impaired immune response characterized by neutrophil dysfunction. Herein, we extended these studies, including our transcriptional profiling data, and employed Seahorse extracellular flux analysis, gas chromatography-mass spectrometry metabolite analysis, flow cytometry and several other biochemical approaches to demonstrate that the delayed apoptosis observed in F. tularensis-infected neutrophils is mediated, in part, by metabolic reprogramming. Specifically, we show that F. tularensis-infected neutrophils exhibited a unique metabolic signature characterized by increased glycolysis, glycolytic flux and glucose uptake, downregulation of the pentose phosphate pathway, and complex glycogen dynamics. Glucose uptake and glycolysis were essential for cell longevity, although glucose-6-phosphate translocation into the endoplasmic reticulum was not, and we identify depletion of glycogen as a potential trigger of apoptosis onset. In keeping with this, we also demonstrate that ablation of apoptosis with the pan-caspase inhibitor Q-VD-OPh was sufficient to profoundly increase glycolysis and glycogen stores in the absence of infection. Taken together, our data significantly advance understanding of neutrophil immunometabolism and its capacity to regulate cell lifespan.

Treponema pallidum delays the apoptosis of human polymorphonuclear neutrophils through the intrinsic and extrinsic pathways

Treponema pallidum is a "stealth pathogen" responsible for infectious sexually transmitted diseases. Although neutrophils are usually present in skin lesions of early syphilis, the role of these cells in T. pallidum infection has barely been investigated. Neutrophils are short-lived cells that undergo constitutive apoptosis, and phagocytosis usually accelerates this process. Here, we demonstrated that human polymorphonuclear neutrophils (hPMNs) could phagocytose T. pallidum in vitro. An unexpected discovery was that T. pallidum inhibited hPMNs apoptosis markedly in an opsonin-independent manner. Furthermore, this phenomenon was not affected by bacterial viability, as detected by annexin V, morphology studies, and TUNEL staining. Exploration of the underlying mechanism showed that expression of the cleaved forms of caspase-3, -8, and -9 and effector caspase activity were diminished significantly in T. pallidum-infected hPMNs. T. pallidum also impaired staurosporine- and anti-Fas-induced signaling for neutrophil apoptosis. Of note, these effects were accompanied by inducing the autocrine production of the anti-apoptotic cytokine IL-8. Taken together, our data revealed that T. pallidum could inhibit the apoptosis of hPMNs through intrinsic and extrinsic pathways and provide new insights for understanding the pathogenicity mechanisms of T. pallidum.

The emerging oral pathogen, Filifactor alocis, extends the functional lifespan of human neutrophil

Periodontitis is a chronic inflammatory infectious disease that affects the integrity of tooth‐supporting tissues and has adverse systemic consequences. Advances in sequencing technologies have uncovered organisms that are exclusively found in high numbers in periodontal lesions, such as the gram‐positive anaerobic rod, Filifactor alocis. F. alocis can manipulate neutrophil effector functions, which allows the organism to survive within these granulocytes. Several neutrophil functions have been tested in the context of F. alocis challenge, but the effect of the organism on neutrophil apoptosis is still unknown. RNA sequencing of human neutrophils challenged with F. alocis showed that apoptosis pathways were differentially regulated. Compared to media‐cultured controls, F. alocis‐challenged neutrophils maintain their nuclear morphology, do not stain for Annexin V or 7‐AAD, and have decreased DNA fragmentation. Inhibition of apoptosis by F. alocis involved reduced caspase‐3, −8, and − 9 activation and upregulation of important anti‐apoptotic proteins. Prolonged lifespan was dependent on contact through TLR2/6, and F. alocis‐challenged neutrophils retained their functional capacity to induce inflammation for longer timepoints. This is the first in‐depth characterization of neutrophil apoptotic programs in response to an oral pathogen and provides key information on how bacteria manipulate immune cell mechanisms to maintain a dysregulated inflammatory response.

The Innate Cellular Immune Response in Xenotransplantation

Xenotransplantation is very attractive strategy for addressing the shortage of donors. While hyper acute rejection (HAR) caused by natural antibodies and complement has been well defined, this is not the case for innate cellular xenogeneic rejection. An increasing body of evidence suggests that innate cellular immune responses contribute to xenogeneic rejection. Various molecular incompatibilities between receptors and their ligands across different species typically have an impact on graft outcome. NK cells are activated by direct interaction as well as by antigen dependent cellular cytotoxicity (ADCC) mechanisms. Macrophages are activated through various mechanisms in xenogeneic conditions. Macrophages recognize CD47 as a "marker of self" through binding to SIRPα. A number of studies have shown that incompatibility of porcine CD47 against human SIRPα contributes to the rejection of xenogeneic target cells by macrophages. Neutrophils are an early responder cell that infiltrates xenogeneic grafts. It has also been reported that neutrophil extracellular traps (NETs) activate macrophages as damage-associated pattern molecules (DAMPs). In this review, we summarize recent insights into innate cellular xenogeneic rejection.

Anti-apoptotic effects of human gingival mesenchymal stromal cells on polymorphonuclear leucocytes

OBJECTIVES

Polymorphonuclear leucocytes (PMNs) constitute the first line of host defence and are crucial in maintaining periodontal health. Their survival and function are modulated by mesenchymal stromal cells (MSCs) from different origin. Gingival MSCs (GMSCs) play an important role in maintaining oral health and in the initial inflammatory response. The present study aimed to investigate the effects of GMSCs on PMNs apoptosis and reactive oxygen species (ROS) production.

METHODS

PMNs were either directly incubated with untreated, interleukin (IL)-1β- or tumour necrosis factor (TNF)-α-treated GMSCs or stimulated with their conditioned media. Resulting ROS production was evaluated by dichlorofluorescin diacetate staining, whereas PMNs apoptosis was assessed by Annexin V staining, followed by flow cytometry analysis.

RESULTS

While conditioned media of untreated and TNF-α-treated GMSCs did not affect apoptosis of PMNs, it was significantly delayed by conditioned media of GMSCs treated with IL-1β. In direct co-culture, GMSCs exerted anti-apoptotic effects on PMNs independently of the previous stimulation. However, the strongest impact was observed by IL-1β-treated GMSCs. ROS production of PMNs was not influenced by GMSCs or their conditioned media.

CONCLUSION

This study demonstrates for the first time the immunomodulatory properties of GMSCs towards PMNs, revealing that IL-1β enhances anti-apoptotic effects of GMSCs.

The C5a/C5aR1 Axis Contributes to the Pathogenesis of Acute Cystitis Through Enhancement of Adhesion and Colonization of Uropathogenic E. coli

Our previous work using a murine model of pyelonephritis demonstrated that the C5a/C5aR1 axis plays a pathogenic role in acute kidney infection. In this study, we report that the C5a/C5aR1 axis also plays a pathogenic role in acute bladder infection. C5aR1-deficient mice had reduced bladder bacterial load and attenuated bladder tissue injury, which is associated with reduced expression of terminal α-mannosyl residues (Man) (a potential ligand for type 1 fimbriae of E. coli) at the luminal surface of the bladder epithelium and reduced early bacterial colonization of the bladder. In vitro, C5a stimulation enhanced mannose expression in and facilitated bacterial adhesion/colonization to human bladder epithelial cells. C5a stimulation also upregulated the activation of ERK1/2 and NF-κB signaling and gene expression of proinflammatory cytokines (i.e., Il6, Il1b, Cxcl1, Ccl2) in the epithelial cells, which could drive pro-inflammatory responses leading to tissue injury. Administration of the C5aR1 antagonist effectively reduced bladder bacterial load and tissue injury. Thus, our findings demonstrate a previously unknown pathogenic role for the C5a/C5aR1 axis in bladder infection and suggest that the C5a/C5aR1 axis-mediated upregulation of Man expression, enhancement of bacterial adhesion/colonization, and excessive inflammatory responses contribute to acute bladder infection. These findings improve our understanding of the pathogenesis of bladder infection with therapeutic implications for UTI.

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.

A place for neutrophils in the beneficial pathogen-agnostic effects of the BCG vaccine

The BCG vaccine has long been recognized for reducing the risk to suffer from infectious diseases unrelated to its target disease, tuberculosis. Evidence from human trials demonstrate substantial reductions in all-cause mortality, especially in the first week of life. Observational studies have identified an association between BCG vaccination and reduced risk of respiratory infectious disease and clinical malaria later in childhood. The mechanistic basis for these pathogen-agnostic benefits, also known as beneficial non-specific effects (NSE) of BCG have been attributed to trained immunity, or epigenetic reprogramming of hematopoietic cells that give rise to innate immune cells responding more efficiently to a broad range of pathogens. Furthermore, within trained immunity, the focus so far has been on enhanced monocyte function. However, polymorphonuclear cells, namely neutrophils, are not only major constituents of the hematopoietic compartment but functionally as well as numerically represent a prominent component of the immune system. The beneficial NSEs of the BCG vaccine on newborn sepsis was recently demonstrated to be driven by a BCG-mediated numeric increase of neutrophils (emergency granulopoiesis (EG)). And experimental evidence in animal models suggest that BCG can modulate neutrophil function as well. Together, these findings suggest that neutrophils are crucial to at least the immediate beneficial NSE of the BCG vaccine. Efforts to uncover the full gamut of mechanisms underpinning the broad beneficial effects of BCG should therefore include neutrophils at the forefront.

Typical and atypical properties of peripheral nerve allografts enable novel strategies to repair segmental-loss injuries

We review data showing that peripheral nerve injuries (PNIs) that involve the loss of a nerve segment are the most common type of traumatic injury to nervous systems. Segmental-loss PNIs have a poor prognosis compared to other injuries, especially when one or more mixed motor/sensory nerves are involved and are typically the major source of disability associated with extremities that have sustained other injuries. Relatively little progress has been made, since the treatment of segmental loss PNIs with cable autografts that are currently the gold standard for repair has slow and incomplete (often non-existent) functional recovery. Viable peripheral nerve allografts (PNAs) to repair segmental-loss PNIs have not been experimentally or clinically useful due to their immunological rejection, Wallerian degeneration (WD) of anucleate donor graft and distal host axons, and slow regeneration of host axons, leading to delayed re-innervation and producing atrophy or degeneration of distal target tissues. However, two significant advances have recently been made using viable PNAs to repair segmental-loss PNIs: (1) hydrogel release of Treg cells that reduce the immunological response and (2) PEG-fusion of donor PNAs that reduce the immune response, reduce and/or suppress much WD, immediately restore axonal conduction across the donor graft and re-innervate many target tissues, and restore much voluntary behavioral functions within weeks, sometimes to levels approaching that of uninjured nerves. We review the rather sparse cellular/biochemical data for rejection of conventional PNAs and their acceptance following Treg hydrogel and PEG-fusion of PNAs, as well as cellular and systemic data for their acceptance and remarkable behavioral recovery in the absence of tissue matching or immune suppression. We also review typical and atypical characteristics of PNAs compared with other types of tissue or organ allografts, problems and potential solutions for PNA use and storage, clinical implications and commercial availability of PNAs, and future possibilities for PNAs to repair segmental-loss PNIs.

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.

Neutrophils Culture in Collagen Gel System

Neutrophils (Neu) migrate rapidly to damaged tissue and play critical roles in host defense and tissue homeostasis, including the intestinal epithelia injuries and immune responses. Although their important roles in these diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Moreover, the standard cell culturing on plastic plates (two-dimensional (2D) cultures) does not represent the actual microenvironment where cells reside in tissues. In this study, we developed a new three-dimensional (3D) culture system for human and mouse peripheral blood Neu, which is made of hydrogel. The Neu showed much better cell integrity and less cell debris in the 3D culture system compared to that in 2D culture system. Moreover, the 3D culture system was more suitable for the observation of neutrophil extracellular traps (NETs) stimulated by the classical stimulation phorbol ester (PMA), and other damage associated molecular patterns (DAMPs) such as Lipopolysaccharide (LPS)/ATP, interleukin-1 β (IL-1β) and tumor necrosis factor α (TNFα) than the 2D culture system. Moreover, NETs phenomenon in 3D culture system is similar to that in vivo. In addition, the 3D culture system was evaluated to co-culturing Neu and other parenchymal cells, such as colon mucosal epithelial cell lines. In conclusion, the 3D culture system could maintain better properties of Neu than that in 2D culture system and it may reduce the gap between in vitro an in vivo experimentations.

Genome-wide association studies for immunoglobulin concentrations in colostrum and serum in Chinese Holstein

Background

The early death and health problems of calves caused substantial economic losses in the dairy industry. As the immune system of neonates has not been fully developed, the absorption of maternal immunoglobulin (Ig) from colostrum is essential in protecting newborn calves against common disease organisms in their early life. The overwhelming majority of Ig in bovine whey is transported from the serum. Therefore, Ig concentration in the colostrum and serum of dairy cows are critical traits when estimating the potential disease resistance of its offspring.

Results

Colostrum, blood, and hair follicle samples were collected from 588 Chinese Holstein cows within 24 h after calving. The concentration of total IgG, IgG1, IgG2, IgA and IgM in both colostrum and serum were detected via ELISA methods. With GCTA software, genome-wide association studies (GWASs) were performed with 91,620 SNPs genotyped by GeneSeek 150 K (140,668 SNPs) chips. As a result, 1, 5, 1 and 29 significant SNPs were detected associated with the concentrations of colostrum IgG1, IgG2, IgA IgM, and serum IgG2 at the genome-wide level (P < 3.08E–6); 11, 2, 13, 2, 12, 8, 2, 27, 1 and 4 SNPs were found significantly associated with total IgG, IgG1, IgG2, IgA and IgM in colostrum and serum at the suggestive level (P < 6.15E–5). Such SNPs located in or proximate to (±1 Mb) 423 genes, which were functionally implicated in biological processes and pathways, such as immune response, B cell activation, inflammatory response and NF-kappaB signaling pathways. By combining the biological functions and the known QTL data for immune traits in bovine, 14 promising candidate functional genes were identified for immunoglobulin concentrations in colostrum and serum in dairy cattle, they were FGFR4, FGFR2, NCF1, IKBKG, SORBS3, IGHV1S18, KIT, PTGS2, BAX, GRB2, TAOK1, ICAM1, TGFB1 and RAC3.

Conclusions

In this study, we identified 14 candidate genes related to concentrations of immunoglobulins in colostrum and serum in dairy cattle by performing GWASs. Our findings provide a groundwork for unraveling the key genes and causal mutations affecting immunoglobulin concentrations in colostrum and important information for genetic improvement of such traits in dairy cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08250-5.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Role of Specialized Pro-Resolving Mediators in Modifying Host Defense and Decreasing Bacterial Virulence

Bacterial infection activates the innate immune system as part of the host’s defense against invading pathogens. Host response to bacterial pathogens includes leukocyte activation, inflammatory mediator release, phagocytosis, and killing of bacteria. An appropriate host response requires resolution. The resolution phase involves attenuation of neutrophil migration, neutrophil apoptosis, macrophage recruitment, increased phagocytosis, efferocytosis of apoptotic neutrophils, and tissue repair. Specialized Pro-resolving Mediators (SPMs) are bioactive fatty acids that were shown to be highly effective in promoting resolution of infectious inflammation and survival in several models of infection. In this review, we provide insight into the role of SPMs in active host defense mechanisms for bacterial clearance including a new mechanism of action in which an SPM acts directly to reduce bacterial virulence.

Vitamin D Enhances Neutrophil Generation and Function in Zebrafish (Danio rerio)

Vitamin D (VD) is a major regulator of calcium metabolism in many living organisms. In addition, VD plays a key role in regulating innate and adaptive immunity in vertebrates. Neutrophils constitute an important part of the first line of defense against invading microbes; however, the potential effect of VD on neutrophils remains elusive. Thus, in this study zebrafish in different developmental stages were utilized to identify the potential role of VD in the basal homeostasis and functions of neutrophils. Our results showed that addition of exogenous VD3 promoted granulopoiesis in zebrafish larvae. Reciprocally, neutrophil abundance in the intestine of adult zebrafish with a cyp2r1 mutant, lacking the capacity to 25-hydroxylate VD, was reduced. Moreover, VD-mediated granulopoiesis was still observed in gnotobiotic zebrafish larvae, indicating that VD regulates neutrophil generation independent of the microbiota during early development. In contrast, VD was incapable to influence granulopoiesis in adult zebrafish when the commensal bacteria were depleted by antibiotic treatment, suggesting that VD might modulate neutrophil activity via different mechanisms depending on the developmental stage. In addition, we found that VD3 augmented the expression of il-8 and neutrophil recruitment to the site of caudal fin amputation. Finally, VD3 treatment significantly decreased bacterial counts and mortality in zebrafish infected with Edwardsiella tarda (E. tarda) in a neutrophil-dependent manner. Combined, these findings demonstrate that VD regulates granulopoiesis and neutrophil function in zebrafish immunity.

Extracellular Reactive Oxygen Species (ROS) Production in Fresh Donkey Sperm Exposed to Reductive Stress, Oxidative Stress and NETosis

Jenny shows a large endometrial reaction after semen influx to the uterus with a large amount of polymorphonuclear neutrophils (PMN) migrating into the uterine lumen. PMN act as a sperm selection mechanism through phagocytosis and NETosis (DNA extrudes and, together with proteins, trap spermatozoa). While a reduced percentage of spermatozoa are phagocytosed by PMN, most are found to be attached to neutrophil extracellular traps (NETs). This selection process together with sperm metabolism produces a large amount of reactive oxygen species (ROS) that influence the reproductive success. The present study aimed to determine the extracellular ROS production in both sperm and PMN. With this purpose, (1) donkey sperm were exposed to reductive and oxidative stresses, through adding different concentrations of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂), respectively; and (2) PMN were subjected to NETosis in the presence of the whole semen, sperm, seminal plasma (SP) or other activators such as formyl-methionyl-leucyl-phenylalanine (FMLP). Extracellular ROS production (measured as H₂O₂ levels) was determined with the Amplex^® Red Hydrogen Peroxide/Peroxidase Assay Kit. Donkey sperm showed more resilience to oxidative stress than to the reductive one, and GSH treatments led to greater H₂O₂ extracellular production. Moreover, not only did SP appear to be the main inducer of NETosis in PMN, but it was also able to maintain the extracellular H₂O₂ levels produced by sperm and NETosis.

The Role of Innate Immune Cells in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a very common hepatic pathology featuring steatosis and is linked to obesity and related conditions, such as the metabolic syndrome. When hepatic steatosis is accompanied by inflammation, the disorder is defined as nonalcoholic steatohepatitis (NASH), which in turn can progress toward fibrosis development that can ultimately result in cirrhosis. Cells of innate immunity, such as neutrophils or macrophages, are central regulators of NASH-related inflammation. Recent studies utilizing new experimental technologies, such as single-cell RNA sequencing, have revealed substantial heterogeneity within the macrophage populations of the liver, suggesting distinct functions of liver-resident Kupffer cells and recruited monocyte-derived macrophages with regards to regulation of liver inflammation and progression of NASH pathogenesis. Herein, we discuss recent developments concerning the function of innate immune cell subsets in NAFLD and NASH.

LOX-1 Regulates Neutrophil Apoptosis and Fungal Load in A. Fumigatus Keratitis

PURPOSE

To determine whether LOX-1 regulates neutrophil apoptosis and fungal load in A. fumigatus keratitis.

METHODS

Fas, FasL, CASP3, CASP8, CASP9 and BCL2 were tested in normal and infected corneas of C57BL/6 mice. Mice corneas were infected with A. fumigatus with or without pretreatment of LOX-1 neutralizing antibody or inhibitor (Poly I). Clinical score was recored and HE staining was tested. Fungal load in mice corneas was observed by plate counting. Poly morphonuclear neutrophilic leukocytes (PMNs) were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of LOX-1 neutralizing antibody or Poly I. PCR, western blot and immunostaining tested expression of Fas, FasL, CASP3, CASP8, CASP9, BCL2 and cleaved caspase-3. PMNs infiltration and TUNEL-positive cells were assessed by immunofluorescent staining. Flow cytometry assay tested the percentage of apoptosis neutrophils.

RESULTS

Fas, Fas ligand, caspase-8, caspase-9 and caspase-3 mRNA levels were significantly higher in C57BL/6 mice corneas infected with A. fumigatus than normal corneas. Poly I treatment alleviated the severity and decreased clinical score at 3, 5 and 7 days post infecrion (p.i.). HE staining showed less infiltration in corneal tissue after LOX-1 inhibition. Plate counting experiment showed that number of viable fungus in corneas of Poly I treated group was significantly less than control group. LOX-1 neutralizing antibody or Poly I treatment significantly decreased neutrophil infiltration, the quantity of TUNEL-positive cells, the expression of Fas, Fas ligand, caspase-8, caspase-9, caspase-3, cleaved caspase-3 and the percentage of apoptosis neutrophils compared with control corneas. LOX-1 neutralizing antibody treatment significantly decreased Fas, FasL, CASP3, CASP8, CASP9 and cleaved caspase-3 expression in neutrophils.

CONCLUSION

LOX-1 inhibition decrease neutrophil apoptosis and fungal load in A. fumigatus keratitis.

Influence of sex hormones on the immune response to leishmaniasis

The differences in morbidity and mortality patterns and life expectancy between the sexes are well established in different infectious and parasitic conditions, such as in leishmaniases, in which biological, genetic, sexual and hormonal variations can modulate the immune response indicating greater infectivity, prevalence and clinical severity in men. In this regard, in seeking the understanding of factors related to protection and susceptibility to infection, this review aimed to discuss the influence of sex hormones on the immune response to leishmaniases. In the literature, sex hormone variations promote differences in the innate, humoral and cell-mediated immune response, leading to greater susceptibility, mortality and complications in males. Epidemiological estimates confirm these results, showing a predominance of the disease, in its different clinical forms, in men and suggesting that sexual variations influence immunomodulatory mechanisms since the prevalence of cases comprises the post-puberty and adulthood period. In this perspective, the action of sex hormones has been investigated in different clinical models, highlighting the potential of testosterone in immunosuppression, given its association with greater susceptibility and poor control of parasite load and the induction of cell apoptosis and attenuation of pro-inflammatory signalling pathways. Therefore, hormonal variations influence the immune response among males and females against leishmaniases, in which androgens may present immunosuppressive potential, while steroids present immunomodulatory characteristics.

Selenocompounds and Sepsis: Redox Bypass Hypothesis for Early Diagnosis and Treatment: Part A-Early Acute Phase of Sepsis: An Extraordinary Redox Situation (Leukocyte/Endothelium Interaction Leading to Endothelial Damage)

Significance: Sepsis is a health disaster. In sepsis, an initial, beneficial local immune response against infection evolves rapidly into a generalized, dysregulated response or a state of chaos, leading to multiple organ failure. Use of life-sustaining supportive therapies creates an unnatural condition, enabling the complex cascades of the sepsis response to develop in patients who would otherwise die. Multiple attempts to control sepsis at an early stage have been unsuccessful. Recent Advances: Major events in early sepsis include activation and binding of leukocytes and endothelial cells in the microcirculation, damage of the endothelial surface layer (ESL), and a decrease in the plasma concentration of the antioxidant enzyme, selenoprotein-P. These events induce an increase in intracellular redox potential and lymphocyte apoptosis, whereas apoptosis is delayed in monocytes and neutrophils. They also induce endothelial mitochondrial and cell damage. Critical Issues: Neutrophil production increases dramatically, and aggressive immature forms are released. Leukocyte cross talk with other leukocytes and with damaged endothelial cells amplifies the inflammatory response. The release of large quantities of reactive oxygen, halogen, and nitrogen species as a result of the leukocyte respiratory burst, endothelial mitochondrial damage, and ischemia/reperfusion processes, along with the marked decrease in selenoprotein-P concentrations, leads to peroxynitrite damage of the ESL, reducing flow and damaging the endothelial barrier. Future Directions: Endothelial barrier damage by activated leukocytes is a time-sensitive event in sepsis, occurring within hours and representing the first step toward organ failure and death. Reducing or stopping this event is necessary before irreversible damage occurs.

The Neutrophil

Neutrophils are immune cells with unusual biological features that furnish potent antimicrobial properties. These cells phagocytose and subsequently kill prokaryotic and eukaryotic organisms very efficiently. Importantly, it is not only their ability to attack microbes within a constrained intracellular compartment that endows neutrophils with antimicrobial function. They can unleash their effectors into the extracellular space, where, even post-mortem, their killing machinery can endure and remain functional. The antimicrobial activity of neutrophils must not be misconstrued as being microbe specific and should be viewed more generally as biotoxic. Outside of fighting infections, neutrophils can harness their noxious machinery in other contexts, like cancer. Inappropriate or dysregulated neutrophil activation damages the host and contributes to autoimmune and inflammatory disease. Here we review a number of topics related to neutrophil biology based on contemporary findings.

Platelets orchestrate the resolution of pulmonary inflammation in mice by T reg cell repositioning and macrophage education

Beyond hemostasis, platelets actively participate in immune cell recruitment and host defense, yet their potential in the resolution of inflammatory processes remains unknown. Here, we demonstrate that platelets are recruited into the lung together with neutrophils during the onset of inflammation and alongside regulatory T (T reg) cells during the resolution phase. This partnering dichotomy is regulated by differential adhesion molecule expression during resolution. Mechanistically, intravascular platelets form aggregates with T reg cells, a prerequisite for their recruitment into the lung. This interaction relies on platelet activation by sCD40L and platelet P-selectin binding to PSGL-1 on T reg cells. Physical platelet–T reg cell interactions are necessary to modulate the transcriptome and instruct T reg cells to release the anti-inflammatory mediators IL-10 and TGFβ. Notably, the presence of platelet–T reg cell aggregates in the lung was also required for macrophage transcriptional reprogramming, polarization toward an anti-inflammatory phenotype, and effective resolution of pulmonary inflammation. Thus, platelets partner with successive immune cell subsets to orchestrate both the initiation and resolution of inflammation.

Agonist anti-ChemR23 mAb reduces tissue neutrophil accumulation and triggers chronic inflammation resolution

Resolution of inflammation is elicited by proresolving lipids, which activate GPCRs to induce neutrophil apoptosis, reduce neutrophil tissue recruitment, and promote macrophage efferocytosis. Transcriptional analyses in up to 300 patients with Inflammatory Bowel Disease (IBD) identified potential therapeutic targets mediating chronic inflammation. We found that ChemR23, a GPCR targeted by resolvin E1, is overexpressed in inflamed colon tissues of severe IBD patients unresponsive to anti-TNFα or anti-α4β7 therapies and associated with significant mucosal neutrophil accumulation. We also identified an anti-ChemR23 agonist antibody that induces receptor signaling, promotes macrophage efferocytosis, and reduces neutrophil apoptosis at the site of inflammation. This ChemR23 mAb accelerated acute inflammation resolution and triggered resolution in ongoing chronic colitis models, with a significant decrease in tissue lesions, fibrosis and inflammation-driven tumors. Our findings suggest that failure of current IBD therapies may be associated with neutrophil infiltration and that ChemR23 is a promising therapeutic target for chronic inflammation.