Neutrophil priming: the cellular signals that say 'amber' but not 'green'

The vacuolar anti-Pseudomonal activity of neutrophil primary granule peptidyl-arginine deiminase enzymes

The role of neutrophils in host defense involves several cell processes including phagocytosis, degranulation of antimicrobial proteins, and the release of neutrophil extracellular traps (NETs). In turn, dysregulated cell activity is associated with the pathogenesis of airway and rheumatic diseases, in which neutrophil-derived enzymes including peptidyl-arginine deiminases (PADs) play a role. Known physiological functions of PADs in neutrophils are limited to the activity of PAD isotype 4 in histone citrullination in NET formation. The aim of this study was to extend our knowledge on the role of PADs in neutrophils and, specifically, bacterial killing within the confines of the phagocytic vacuole. Human neutrophils were fractionated by sucrose gradient ultracentrifuge and PADs localized in subcellular compartments by Western blot analysis. Direct interaction of PADs with Pseudomonas aeruginosa (P. aeruginosa) was assessed by flow cytometry and Western blot overlay. The participation of neutrophil PAD2 and PAD4 in killing of P. aeruginosa was assessed by inclusion of PAD-specific inhibitors. In vitro, bactericidal activity of recombinant human PAD2 or PAD4 enzymes against P. aeruginosa was determined by enumeration of colony-forming units (CFU). Together with neutrophil elastase (NE), PAD2 and PAD4 were localized to primary granules and, following activation with particulate stimuli, were degranulated in to the phagocytic vacuole. In vitro, PAD2 and PAD4 bound P. aeruginosa (p = 0.04) and significantly reduced bacterial survival to 49.1 ± 17.0 (p < 0.0001) and 48.5 ± 13.9% (p < 0.0001), respectively. Higher antibacterial activity was observed at neutral pH levels with the maximum toxicity at pH 6.5 and pH 7.5, comparable to the effects of neutrophil bactericidal permeability increasing protein. In phagosomal killing assays, inclusion of the PAD2 inhibitor, AFM-30a, or PAD4 inhibitor, GSK484, significantly increased survival of P. aeruginosa (AFM-30a, p = 0.05; and GSK484, p = 0.0079). Results indicate that PAD2 and PAD4 possess antimicrobial activity and are directly involved in the neutrophil antimicrobial processes. This study supports further research into the development of PAD-based antimicrobials.

Function and regulation of GPR84 in human neutrophils

Human neutrophils are components of the innate immune system and are the most abundant white blood cells in the circulation. They are professional phagocytes and express several G protein-coupled receptors (GPCRs), which are essential for proper neutrophil functions. So far, the two formyl peptide receptors, FPR1 and FPR2, have been the most extensively studied group of neutrophil GPCRs, but recently, a new group, the free fatty acid (FFA) receptors, has attracted growing attention. Neutrophils express two FFA receptors, GPR84 and FFA2, which sense medium- and short-chain fatty acids respectively, and display similar activation profiles. The exact pathophysiological role of GPR84 is not yet fully understood, but it is generally regarded as a pro-inflammatory receptor that mediates neutrophil activation. In this review, we summarize current knowledge of how GPR84 affects human neutrophil functions and discuss the regulatory mechanisms that control these responses, focusing on the similarities and differences in comparison to the two FPRs and FFA2. LINKED ARTICLES: This article is part of a themed issue GPR84 Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.10/issuetoc.

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

Cytomegalovirus durably primes neutrophil oxidative burst

Cytomegalovirus (CMV) is a ubiquitous herpes virus that infects most humans, thereafter persisting lifelong in tissues of the host. It is a known pathogen in immunosuppressed patients, but its impact on immunocompetent hosts remains less understood. Recent data have shown that CMV leaves a significant and long-lasting imprint in host immunity that may confer some protection against subsequent bacterial infection. Such innate immune activation may come at a cost, however, with potential to cause immunopathology. Neutrophils are central to many models of immunopathology, and while acute CMV infection is known to influence neutrophil biology, the impact of chronic CMV infection on neutrophil function remains unreported. Using our murine model of CMV infection and latency, we show that chronic CMV causes persistent enhancement of neutrophil oxidative burst well after resolution of acute infection. Moreover, this in vivo priming of marrow neutrophils is associated with enhanced formyl peptide receptor expression, and ultimately constitutive c-Jun N-terminal kinase phosphorylation and enhanced CD14 expression in/on circulating neutrophils. Finally, we show that neutrophil priming is dependent on viral load, suggesting that naturally infected human hosts will show variability in CMV-related neutrophil priming. Altogether, these findings represent a previously unrecognized and potentially important impact of chronic CMV infection on neutrophil responsiveness in immunocompetent hosts.

Impact of dual neutralization of TNF-α and IL-1β along with Gentamicin treatment on the functions of blood and splenic neutrophils and its role on improvement of S. aureus induced septic arthritis

Researches of recent past years have emphasized potential of antibiotics to improve septic arthritis but as multi-drug resistant strains like MRSA are emerging fast, new alternative therapeutic advances are high in demand. This study aims to figure out the role of neutrophils in regulating inflammatory responses of S. aureus induced septic arthritis while using TNF-α Ab or IL-1β Ab along with antibiotic gentamicin or both in combination. In this study, role of anti-oxidant enzymes were investigated and correlated with generated ROS level. While expression of TLR2, TNFR2, MMP2, RANKL, SAPK/JNK in the spleen were evaluated through western blot. Serum activity of IL-8, IL-10, IL-12, OPG, OPN, CRP was assessed using ELISA. Flow cytometry study evaluated inflamed neutrophil population. Results have shown TNF-α neutralization along with gentamicin was able to reduce arthritic swelling prominently. While combination therapy effectively reduced blood neutrophil ROS activity, arginase activity, MPO activity along with spleen bacterial burden. Serum OPG, CRP, IL-10 level got reduced while serum OPN, IL-8 and IL-12 level enhanced in treatment groups, showing mitigation of inflammatory damage. Overall, it is a novel work that observed how antibiotic and antibody therapy enhanced neutrophil function positively to combat sepsis. This study may not be fully applicable in clinical trials as it is performed with animal model. Clinical trials include crystalline and inflammatory arthritides, trauma, neoplasm. Interdisciplinary collaboration between radiology, orthopaedic surgery and knowledge of animal system responses may give better idea to find proper therapeutic approach in future research works.

The Role of Cytokines in Neutrophil Development, Tissue Homing, Function and Plasticity in Health and Disease

Neutrophils are crucial innate immune cells and comprise 50-70% of the white blood cell population under homeostatic conditions. Upon infection and in cancer, blood neutrophil numbers significantly increase because of the secretion of various chemo- and cytokines by, e.g., leukocytes, pericytes, fibroblasts and endothelial cells present in the inflamed tissue or in the tumor microenvironment (TME). The function of neutrophils in cancer has recently gained considerable attention, as they can exert both pro- and anti-tumorigenic functions, dependent on the cytokine milieu present in the TME. Here, we review the effect of cytokines on neutrophil development, tissue homing, function and plasticity in cancer and autoimmune diseases as well as under physiological conditions in the bone marrow, bloodstream and various organs like the spleen, kidney, liver, lung and lymph nodes. In addition, we address several promising therapeutic options, such as cytokine therapy, immunocytokines and immunotherapy, which aim to exploit the anti-tumorigenic potential of neutrophils in cancer treatment or block excessive neutrophil-mediated inflammation in autoimmune diseases.

Mechanosensitive traction force generation is regulated by the neutrophil activation state

The generation of traction forces by neutrophils regulates many crucial effector functions responsible for host defense, such as attachment, spreading, migration, phagocytosis, and NETosis. The activation state of the cell is a strong determinant of the functional efficacy of the neutrophil; however, the effect of activation on traction force production has not yet been determined experimentally. Previously, the mapping of cellular-generated forces produced by human neutrophils via a Traction Force Microscopy (TFM) method has required a three-dimensional imaging modality to capture out-of-plane forces, such as confocal or multiphoton techniques. A method newly developed in our laboratories can capture out-of-plane forces using only a two-dimensional imaging modality. This novel technique-combined with a topology-based single particle tracking algorithm and finite element method calculations-can construct high spatial frequency three-dimensional traction fields, allowing for traction forces in-plane and out-of-plane to the substrate to now be differentially visualized and quantified with a standard epifluorescence microscope. Here we apply this technology to determine the effect of neutrophil activation on force generation. Sepsis is a systemic inflammatory response that causes dysregulated neutrophil activation in vivo. We found that neutrophils from septic patients produced greater total forces than neutrophils from healthy donors and that the majority of this dysregulation occurred in-plane to the substrate. Ex vivo activation of neutrophils from healthy donors showed differential consequences depending on activation stimuli with mechanosensitive force decreases observed in some cases. These findings demonstrate the feasibility of epifluorescence-based microscopy in mapping traction forces to ask biologically significant questions regarding neutrophil function.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Novel neutrophil phenotypic signature in pediatric patients with type 1 diabetes and diabetic ketoacidosis

Type 1 diabetes (T1D) is a chronic inflammatory condition sometimes complicated by acute diabetic ketoacidosis (DKA). A subset of patients with T1D develop DKA independent of known risk factors. This study tested the hypothesis that circulating polymorphonuclear leukocytes (PMN) from children with T1D and DKA would exhibit a primed phenotype and that the signature would be unique in patients predisposed to have DKA. Using a prospective cohort study design, neutrophil phenotype was assessed in 30 patients with T1D seen in endocrinology clinic for routine care, 30 patients with acute DKA, and 36 healthy donors. Circulating PMN from patients with DKA display a primed phenotype with increased basal cell-surface CD11b, L-selectin shedding, and enhanced fMLF-elicited reactive oxygen species (ROS) production. Moreover, PMN from T1D patients both with and without DKA lack the capacity to be further primed by incubation with TNF-α, a classic priming stimulus. Primed PMN phenotypic signatures demonstrated are independent of hemoglobin A1c, the premier biological marker for DKA risk, and are consistent with a hyperinflammatory state. A single nucleotide polymorphism in TLR-1 (1805G>T), known to be associated with a hyperinflammatory PMN phenotype, correlated with DKA. This study elucidated a novel phenotypic signature in circulating PMN from children with T1D with and without DKA, and suggests the possibility of a previously unrecognized PMN phenotype with potential clinical implications. Immunophenotype and genotype may be applicable as biomarkers for DKA risk stratification in patients with T1D.

Identifying key components and therapeutic targets of the immune system in hidradenitis suppurativa with an emphasis on neutrophils

Hidradenitis suppurativa (HS) is a chronic, inflammatory, recurrent and debilitating skin disease of the hair follicle unit that typically develops after puberty. The disorder is characterized by comedones, painful inflammatory nodules, abscesses, dermal tunnels and scarring, with a predilection for intertriginous areas of the body (axillae, inguinal and anogenital regions). Recruitment of neutrophils to HS lesion sites may play an essential role in the development of the painful inflammatory nodules and abscesses that characterize the disease. This is a review of the major mediators involved in the recruitment of neutrophils to sites of active inflammation, including bacterial components (endotoxins, exotoxins, capsule fragments, etc.), the complement pathway anaphylatoxins C3a and C5a, tumour necrosis factor-alpha, interleukin (IL)-17, IL-8 (CXCL8), IL-36, IL-1, lipocalin-2, leukotriene B4, platelet-activating factor, kallikreins, matrix metalloproteinases, and myeloperoxidase inhibitors. Pharmacological manipulation of the various pathways involved in the process of neutrophil recruitment and activation could allow for successful control and stabilization of HS lesions and the remission of active, severe flares.

Neutrophil Extracellular Traps Tied to Rheumatoid Arthritis: Points to Ponder

In recent years, neutrophil extracellular traps at the forefront of neutrophil biology have proven to help capture and kill pathogens involved in the inflammatory process. There is growing evidence that persistent neutrophil extracellular traps drive the pathogenesis of autoimmune diseases. In this paper, we summarize the potential of neutrophil extracellular traps to drive the pathogenesis of rheumatoid arthritis and experimental animal models. We also describe the diagnosis and treatment of rheumatoid arthritis in association with neutrophil extracellular traps.

A peripheral neutrophil-related inflammatory factor predicts a decline in executive function in mild Alzheimer's disease

Background

Studies suggest a role of the innate immune system, including the activity of neutrophils, in neurodegeneration related to Alzheimer’s disease (AD), but prospective cognitive data remain lacking in humans. We aimed to investigate the predictive relationship between neutrophil-associated inflammatory proteins in peripheral blood and changes in memory and executive function over 1 year in patients with AD.

Methods

Participants with AD were identified from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Neutrophil gelatinase-associated lipocalin (NGAL), myeloperoxidase (MPO), interleukin-8 (IL-8), macrophage inflammatory protein-1 beta (MIP-1β), and tumor necrosis factor (TNF) were assayed by luminex immunofluorescence multiplex assay at baseline. Confirmatory factor analysis was used to test an underlying neutrophil associated plasma inflammatory factor. Composite z-scores for memory and executive function were generated from multiple tests at baseline and at 1 year. A multiple linear regression model was used to investigate the association of the baseline inflammatory factor with changes in memory and executive function over 1 year.

Results

Among AD patients (n = 109, age = 74.8 ± 8.1, 42% women, Mini Mental State Examination [MMSE] = 23.6 ± 1.9), the neutrophil-related inflammatory proteins NGAL (λ = 0.595, p < .001), MPO (λ = 0.575, p < .001), IL-8 (λ = 0.525, p < .001), MIP-1β (λ = 0.411, p = .008), and TNF (λ = 0.475, p < .001) were found to inform an underlying factor. Over 1 year, this inflammatory factor predicted a decline in executive function (β = − 0.152, p = 0.015) but not memory (β = 0.030, p = 0.577) in models controlling for demographics, brain atrophy, white matter hyperintensities, the ApoE ε4 allele, concomitant medications, and baseline cognitive performance.

Conclusions

An inflammatory factor constructed from five neutrophil-related markers in peripheral blood predicted a decline in executive function over 1 year in people with mild AD.

Neutrophils in community-acquired pneumonia: parallels in dysfunction at the extremes of age

"Science means constantly walking a tight rope" Heinrich Rohrer, physicist, 1933. Community-acquired pneumonia (CAP) is the leading cause of death from infectious disease worldwide and disproportionately affects older adults and children. In high-income countries, pneumonia is one of the most common reasons for hospitalisation and (when recurrent) is associated with a risk of developing chronic pulmonary conditions in adulthood. Pneumococcal pneumonia is particularly prevalent in older adults, and here, pneumonia is still associated with significant mortality despite the widespread use of pneumococcal vaccination in middleand high-income countries and a low prevalence of resistant organisms. In older adults, 11% of pneumonia survivors are readmitted within months of discharge, often with a further pneumonia episode and with worse outcomes. In children, recurrent pneumonia occurs in approximately 10% of survivors and therefore is a significant cause of healthcare use. Current antibiotic trials focus on short-term outcomes and increasingly shorter courses of antibiotic therapy. However, the high requirement for further treatment for recurrent pneumonia questions the effectiveness of current strategies, and there is increasing global concern about our reliance on antibiotics to treat infections. Novel therapeutic targets and approaches are needed to improve outcomes. Neutrophils are the most abundant immune cell and among the first responders to infection. Appropriate neutrophil responses are crucial to host defence, as evidenced by the poor outcomes seen in neutropenia. Neutrophils from older adults appear to be dysfunctional, displaying a reduced ability to target infected or inflamed tissue, poor phagocytic responses and a reduced capacity to release neutrophil extracellular traps (NETs); this occurs in health, but responses are further diminished during infection and particularly during sepsis, where a reduced response to granulocyte colony-stimulating factor (G-CSF) inhibits the release of immature neutrophils from the bone marrow. Of note, neutrophil responses are similar in preterm infants. Here, the storage pool is decreased, neutrophils are less able to degranulate, have a reduced migratory capacity and are less able to release NETs. Less is known about neutrophil function from older children, but theoretically, impaired functions might increase susceptibility to infections. Targeting these blunted responses may offer a new paradigm for treating CAP, but modifying neutrophil behaviour is challenging; reducing their numbers or inhibiting their function is associated with poor clinical outcomes from infection. Uncontrolled activation and degranulation can cause significant host tissue damage. Any neutrophil-based intervention must walk the tightrope described by Heinrich Rohrer, facilitating necessary phagocytic functions while preventing bystander host damage, and this is a significant challenge which this review will explore.

A Novel Standardized Cannabis sativa L. Extract and Its Constituent Cannabidiol Inhibit Human Polymorphonuclear Leukocyte Functions

Cannabis and cannabinoids offer significant therapeutic benefits for a wide scope of pathological conditions. Among them, the clinical issues rooted in inflammation stand out, nonetheless, the underlying mechanisms are not yet plainly understood. Circumstantial evidence points to polymorphonuclear leukocytes (PMN) as targets for the anti-inflammatory effects of cannabis. Therefore, we conducted this study to assess the effects of CM5, a novel Cannabis sativa L. extract standardized in 5% cannabidiol (CBD), on human PMN functions, including cell migration, oxidative metabolism and production of tumour necrosis factor (TNF)-α. We then sought to investigate whether such effects could be ascribed to its content in CBD. Cell migration was assessed by the Boyden chamber assay, oxidative metabolism by means of spectrofluorimetric measurement of reactive oxygen species (ROS) production, and TNF-α was measured by real time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Results show that both CM5 and CBD inhibit PMN migration, ROS and TNF-α production, indicating that CBD may be the main item responsible for the effects of CM5. CM5 is however more potent than CBD on cell migration and TNF-α production, and less effective on ROS production, suggesting that beyond CBD, other components of the cannabis plant may contribute to the biological effects of the extract. As a whole, such results support the use of cannabis standardized extract and CBD to stem inflammation; however, they also warrant in-depth investigation of the underlying cellular and molecular mechanisms to better exploit their therapeutic potential.

Paralogs of Common Carp Granulocyte Colony-Stimulating Factor (G-CSF) Have Different Functions Regarding Development, Trafficking and Activation of Neutrophils

Mammalian granulocyte colony-stimulating factor (G-CSF; CSF3) is a primary cytokine that promotes the development, mobilization, and activation of neutrophils and their precursors. Teleosts have been reported to possess two paralogs as a likely result of the teleost-wide whole genome duplication (WGD) event, but functional divergence of G-CSF paralogs remains poorly understood. Common carp are an allotetraploid species owing to an additional WGD event in the carp lineage and here, we report on genomic synteny, sequence similarity, and phylogeny of four common carp G-CSF paralogs (g-csfa1 and g-csfa2; g-csfb1 and g-csfb2). G-csfa1 and g-csfa2 show differential and relatively high gene expression levels, while g-csfb1 and g-csfb2 show low basal gene expression levels in most tissues. All paralogs are expressed higher in macrophages than in other leukocyte sub-types and are highly up-regulated by treatment of macrophages with mitogens. Recombinant G-CSFa1 and G-CSFb1 both promoted the proliferation of kidney hematopoietic cells, while only G-CSFb1 induced the differentiation of kidney cells along the neutrophil-lineage. Colony-forming unit assays revealed that G-CSFb1 alone stimulates the formation of CFU-G colonies from head- and trunk-kidney whereas the combination of G-CSFa1 and G-CSFb1 stimulates the formation of both CFU-G and CFU-GM colonies. Recombinant G-CSFa1 and G-CSFb1 also exhibit chemotactic activity against kidney neutrophils and up-regulation of cxcr1 mRNA expression was highest in neutrophils after G-CSFb1 stimulation. Furthermore, G-CSFb1 more than G-CSFa1 induced priming of kidney neutrophils through up-regulation of a NADPH-oxidase component p47 phox . In vivo administration of G-CSF paralogs increased the number of circulating blood neutrophils of carp. Our findings demonstrate that gene duplications in teleosts can lead to functional divergence between paralogs and shed light on the sub-functionalization of G-CSF paralogs in cyprinid fish.

A robust intracellular metabolite extraction protocol for human neutrophil metabolic profiling

Neutrophils are phagocytic innate immune cells that play essential roles in host defence, but are also implicated in inflammatory diseases such as rheumatoid arthritis (RA) where they contribute to systemic inflammation and joint damage. Transcriptomic analysis of neutrophils has revealed significant changes in gene expression in neutrophils activated in vitro by cytokines and in vivo during inflammation in RA. However, there are no reports on the global metabolomic changes that occur as a consequence of this activation. The aim of this study was to establish protocols for the study of changes in the metabolome of human neutrophils using 1H NMR spectroscopy. Sample preparation and spectral analysis protocols were optimised using neutrophils isolated by Ficoll-Paque, with decreased washing steps and inclusion of a heat-shock step to quench metabolite turnover. Cells were incubated ± PMA for 15 min in HEPES-free media and samples were analysed by NMR using a 700 MHz NMR Avance IIIHD Bruker NMR spectrometer equipped with a TCI cryoprobe. Chenomx, Bruker TopSpin and AMIX software were used to process spectra and identify metabolites. Principal Component Analysis (PCA) and signalling pathway analysis was carried out using Metaboanalyst. Cell number and number of scans (NS) were optimised as >3.6 million cells and 512 NS. 327 spectral bins were defined in the neutrophil spectra, of which 287 (87.7%) were assigned to 110 metabolites that included: amino acids, peptides and analogues; carbohydrates, carbonyls and alcohols; nucleotides, nucleosides and analogues; lipids and lipid-like molecules; benzenoids; and other organic compounds. 43 metabolites changed at least 1.5 fold (increase or decrease) after the addition of PMA for 5 or 15 min. Pathway analysis revealed that PMA affected nicotinate and nicotinamide metabolism, aminoacyl-tRNA biosynthesis and glycolysis, suggesting a redirection of glucose metabolism from glycolysis to the pentose phosphate pathway and production of NADPH for activation of the NADPH oxidase and subsequent respiratory burst. We have developed protocols for the study of human neutrophils by 1H NMR spectroscopy. Importantly, this methodology has sufficient sensitivity and reproducibility to detect changes in metabolite abundance from cell numbers typically collected from clinical samples or experiments with multiple assay conditions.

Neutrophil phenotypes in health and disease

Neutrophils are one of the most important effector cells of the innate immune response (1). They are traditionally seen as a homogenous population of short-lived cells mainly involved in the defence against extracellular microorganisms by phagocytosis and intracellular killing (1,2). The cells contain a large armamentarium that aids in this function and ranges from the production of reactive oxygen species by a membrane-bound NADPH oxidase to cytotoxic proteins and peptides residing in the different granules present in the cytoplasm (3). Recently, the view of neutrophils belonging to a homogenous population of cells has been challenged, and several neutrophil phenotypes have been described that exhibit specialized functions, such as involvement in tissue repair, tumour killing and immune regulation (4). It is not clear whether these cells belong to separate parallel lineages originating from the bone marrow or that neutrophils become instructed in the distant tissues, thus changing their phenotypes. In addition, functional heterogeneity in a phenotypically homogenous population of neutrophils adds to the complexity of neutrophil phenotypes(5). This article will review the current literature describing the heterogeneity within the neutrophil compartment with respect to both phenotype and function in health and disease.

Neutrophil and T-Cell Homeostasis in the Closed Eye

Purpose

This study sought to examine the changes and phenotype of the tear neutrophil and T-cell populations between early eyelid closure and after a full night of sleep.

Methods

Fourteen healthy participants were recruited and trained to wash the ocular surface with PBS for at-home self-collection of ocular surface and tear leukocytes following up to 1 hour of sleep and a full night of sleep (average 7 hours), on separate days. Cells were isolated, counted, and incubated with fluorescently labeled antibodies to identify neutrophils, monocytes, and T cells. For neutrophil analysis, samples were stimulated with lipopolysaccharide (LPS) or calcium ionophore (CaI) before antibody incubation. Flow cytometry was performed.

Results

Following up to 1 hour of sleep, numerous leukocytes were collected (2.6 × 105 ± 3.0 × 105 cells), although significantly (P < 0.005) more accumulated with 7 hours of sleep (9.9 × 105 ± 1.2× 106 cells). Neutrophils (65%), T cells (3%), and monocytes (1%) were identified as part of the closed eye leukocyte infiltration following 7 hours of sleep. Th17 cells represented 22% of the total CD4+ population at the 7-hour time point. Neutrophil phenotype changed with increasing sleep, with a downregulation of membrane receptors CD16, CD11b, CD14, and CD15, indicating a loss in the phagocytic capability of neutrophils.

Conclusions

Neutrophils begin accumulating in the closed eye conjunctival sac much earlier than previously demonstrated. The closed eye tears are also populated with T cells, including a subset of Th17 cells. The closed eye environment is more inflammatory than previously thought and is relevant to understanding ocular homeostasis.

Neutrophil Phenotype Correlates With Postoperative Inflammatory Outcomes in Infants Undergoing Cardiopulmonary Bypass

OBJECTIVES

Infants with congenital heart disease frequently require cardiopulmonary bypass, which causes systemic inflammation. The goal of this study was to determine if neutrophil phenotype and activation status predicts the development of inflammatory complications following cardiopulmonary bypass.

DESIGN

Prospective cohort study.

SETTING

Tertiary care PICU with postoperative cardiac care.

PATIENTS

Thirty-seven patients 5 days to 10 months old with congenital heart disease requiring cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Laboratory and clinical data collected included length of mechanical ventilation, acute kidney injury, and fluid overload. Neutrophils were isolated from whole blood at three time points surrounding cardiopulmonary bypass. Functional analyses included measurement of cell surface protein expression and nicotinamide adenine dinucleotide phosphate oxidase activity. Of all patients studied, 40.5% displayed priming of nicotinamide adenine dinucleotide phosphate oxidase activity in response to N-formyl-Met-Leu-Phe stimulation 24 hours post cardiopulmonary bypass as compared to pre bypass. Neonates who received steroids prior to bypass demonstrated enhanced priming of nicotinamide adenine dinucleotide phosphate oxidase activity at 48 hours. Patients who displayed priming post cardiopulmonary bypass were 8.8 times more likely to develop severe acute kidney injury as compared to nonprimers. Up-regulation of neutrophil surface CD11b levels pre- to postbypass occurred in 51.4% of patients, but this measure of neutrophil priming was not associated with acute kidney injury. Subsequent analyses of the basal neutrophil phenotype revealed that those with higher basal CD11b expression were significantly less likely to develop acute kidney injury.

CONCLUSIONS

Neutrophil priming occurs in a subset of infants undergoing cardiopulmonary bypass. Acute kidney injury was more frequent in those patients who displayed priming of nicotinamide adenine dinucleotide phosphate oxidase activity after cardiopulmonary bypass. This pilot study suggests that neutrophil phenotypic signature could be used to predict inflammatory organ dysfunction.

Neutrophils to the ROScue: Mechanisms of NADPH Oxidase Activation and Bacterial Resistance

Reactive oxygen species (ROS) generated by NADPH oxidase play an important role in antimicrobial host defense and inflammation. Their deficiency in humans results in recurrent and severe bacterial infections, while their unregulated release leads to pathology from excessive inflammation. The release of high concentrations of ROS aids in clearance of invading bacteria. Localization of ROS release to phagosomes containing pathogens limits tissue damage. Host immune cells, like neutrophils, also known as PMNs, will release large amounts of ROS at the site of infection following the activation of surface receptors. The binding of ligands to G-protein-coupled receptors (GPCRs), toll-like receptors, and cytokine receptors can prime PMNs for a more robust response if additional signals are encountered. Meanwhile, activation of Fc and integrin directly induces high levels of ROS production. Additionally, GPCRs that bind to the bacterial-peptide analog fMLP, a neutrophil chemoattractant, can both prime cells and trigger low levels of ROS production. Engagement of these receptors initiates intracellular signaling pathways, resulting in activation of downstream effector proteins, assembly of the NADPH oxidase complex, and ultimately, the production of ROS by this complex. Within PMNs, ROS released by the NADPH oxidase complex can activate granular proteases and induce the formation of neutrophil extracellular traps (NETs). Additionally, ROS can cross the membranes of bacterial pathogens and damage their nucleic acids, proteins, and cell membranes. Consequently, in order to establish infections, bacterial pathogens employ various strategies to prevent restriction by PMN-derived ROS or downstream consequences of ROS production. Some pathogens are able to directly prevent the oxidative burst of phagocytes using secreted effector proteins or toxins that interfere with translocation of the NADPH oxidase complex or signaling pathways needed for its activation. Nonetheless, these pathogens often rely on repair and detoxifying proteins in addition to these secreted effectors and toxins in order to resist mammalian sources of ROS. This suggests that pathogens have both intrinsic and extrinsic mechanisms to avoid restriction by PMN-derived ROS. Here, we review mechanisms of oxidative burst in PMNs in response to bacterial infections, as well as the mechanisms by which bacterial pathogens thwart restriction by ROS to survive under conditions of oxidative stress.

Pathobiology of neutrophil-epithelial interactions

Polymorphonuclear neutrophils (PMNs) are innate immune system cells that play an essential role in eradicating invading pathogens. PMN migration to sites of infection/inflammation requires exiting the microcirculation and subsequent crossing of epithelial barriers in mucosa-lined organs such as the lungs and intestines. Although these processes usually occur without significant damage to surrounding host tissues, dysregulated/excessive PMN transmigration and resultant bystander-tissue damage are characteristic of numerous mucosal inflammatory disorders. Mechanisms controlling PMN extravasation have been well characterized, but the molecular details regarding regulation of PMN migration across mucosal epithelia are poorly understood. Given that PMN migration across mucosal epithelia is strongly correlated with disease symptoms in many inflammatory mucosal disorders, enhanced understanding of the mechanisms regulating PMN transepithelial migration should provide insights into clinically relevant tissue-targeted therapies aimed at ameliorating PMN-mediated bystander-tissue damage. This review will highlight current understanding of the molecular interactions between PMNs and mucosal epithelia and the associated functional consequences.

Priming of the neutrophil respiratory burst: role in host defense and inflammation

Neutrophils are the major circulating white blood cells in humans. They play an essential role in host defense against pathogens. In healthy individuals, circulating neutrophils are in a dormant state with very low efficiency of capture and arrest on the quiescent endothelium. Upon infection and subsequent release of pro-inflammatory mediators, the vascular endothelium signals to circulating neutrophils to roll, adhere, and cross the endothelial barrier. Neutrophils migrate toward the infection site along a gradient of chemo-attractants, then recognize and engulf the pathogen. To kill this pathogen entrapped inside the vacuole, neutrophils produce and release high quantities of antibacterial peptides, proteases, and reactive oxygen species (ROS). The robust ROS production is also called 'the respiratory burst', and the NADPH oxidase or NOX2 is the enzyme responsible for the production of superoxide anion, leading to other ROS. In vitro, several soluble and particulate agonists induce neutrophil ROS production. This process can be enhanced by prior neutrophil treatment with 'priming' agents, which alone do not induce a respiratory burst. In this review, we will describe the priming process and discuss the beneficial role of controlled neutrophil priming in host defense and the detrimental effect of excessive neutrophil priming in inflammatory diseases.

Tumor Necrosis Factor α-Dependent Neutrophil Priming Prevents Intestinal Ischemia/Reperfusion-Induced Bacterial Translocation

BACKGROUND

Intestinal ischemia/reperfusion (I/R) causes barrier impairment and bacterial influx. Protection against I/R injury in sterile organs by hypoxic preconditioning (HPC) had been attributed to erythropoietic and angiogenic responses. Our previous study showed attenuation of intestinal I/R injury by HPC for 21 days in a neutrophil-dependent manner.

AIM

To investigate the underlying mechanisms of neutrophil priming by HPC, and explore whether adoptive transfer of primed neutrophils is sufficient to ameliorate intestinal I/R injury.

METHODS

Rats raised in normoxia (NM) and HPC for 3 or 7 days were subjected to sham operation or superior mesenteric artery occlusion for I/R challenge. Neutrophils isolated from rats raised in NM or HPC for 21 days were intravenously injected into naïve controls prior to I/R.

RESULTS

Similar to the protective effect of HPC-21d, I/R-induced mucosal damage was attenuated by HPC-7d but not by HPC-3d. Naïve rats reconstituted with neutrophils of HPC-21d rats showed increase in intestinal phagocytic infiltration and myeloperoxidase activity, and barrier protection against I/R insult. Elevated free radical production, and higher bactericidal and phagocytic activity were observed in HPC neutrophils compared to NM controls. Moreover, increased serum levels of tumor necrosis factor α (TNFα) and cytokine-induced neutrophil chemoattractant-1 (CINC-1) were seen in HPC rats. Naïve neutrophils incubated with HPC serum or recombinant TNFα, but not CINC-1, exhibited heightened respiratory burst and bactericidal activity. Lastly, neutrophil priming effect was abolished by neutralization of TNFα in HPC serum.

CONCLUSIONS

TNFα-primed neutrophils by HPC act as effectors cells for enhancing barrier integrity under gut ischemia.

Phenotypic and functional characteristics of HLA-DR+ neutrophils in Brazilians with cutaneous leishmaniasis

The protozoan Leishmania braziliensis causes cutaneous leishmaniasis (CL) in endemic regions. In murine models, neutrophils (PMNs) are recruited to the site of infection soon after parasite inoculation. However, the roles of neutrophils during chronic infection and in human disease remain undefined. We hypothesized that neutrophils help maintain a systemic inflammatory state in subjects with CL. Lesion biopsies from all patients with CL tested contained neutrophils expressing HLA-DR, a molecule thought to be restricted to professional antigen-presenting cells. Although CL is a localized disease, a subset of patients with CL also had circulating neutrophils expressing HLA-DR and the costimulatory molecules CD80, CD86, and CD40. PMNs isolated from a low-density leukocyte blood fraction (LD-PMNs) contained a higher percentage of HLA-DR⁺ PMNs than did normal-density PMNs. In vitro coculture experiments suggested LD-PMNs do not suppress T cell responses, differentiating them from MDSCs. Flow-sorted HLA-DR⁺ PMNs morphologically resembled conventional PMNs, and they exhibited functional properties of PMNs. Compared with conventional PMNs, HLA-DR⁺ PMNs showed increased activation, degranulation, DHR123 oxidation, and phagocytic capacity. A few HLA-DR⁺ PMNs were observed in healthy subjects, and that proportion could be increased by incubation in either inflammatory cytokines or in plasma from a patient with CL. This was accompanied by an increase in PMN hladrb1 mRNA, suggesting a possible connection between neutrophil "priming" and up-regulation of HLA-DR. These data suggest that PMNs that are primed for activation and that also express surface markers of antigen-presenting cells emerge in the circulation and infected tissue lesions of patients with CL.

Mechanisms Underlying Interferon-γ-Induced Priming of Microglial Reactive Oxygen Species Production

Microglial priming and enhanced reactivity to secondary insults cause substantial neuronal damage and are hallmarks of brain aging, traumatic brain injury and neurodegenerative diseases. It is, thus, of particular interest to identify mechanisms involved in microglial priming. Here, we demonstrate that priming of microglia with interferon-γ (IFN γ) substantially enhanced production of reactive oxygen species (ROS) following stimulation of microglia with ATP. Priming of microglial ROS production was substantially reduced by inhibition of p38 MAPK activity with SB203580, by increases in intracellular glutathione levels with N-Acetyl-L-cysteine, by blockade of NADPH oxidase subunit NOX2 activity with gp91ds-tat or by inhibition of nitric oxide production with L-NAME. Together, our data indicate that priming of microglial ROS production involves reduction of intracellular glutathione levels, upregulation of NADPH oxidase subunit NOX2 and increases in nitric oxide production, and suggest that these simultaneously occurring processes result in enhanced production of neurotoxic peroxynitrite. Furthermore, IFNγ-induced priming of microglial ROS production was reduced upon blockade of Kir2.1 inward rectifier K⁺ channels with ML133. Inhibitory effects of ML133 on microglial priming were mediated via regulation of intracellular glutathione levels and nitric oxide production. These data suggest that microglial Kir2.1 channels may represent novel therapeutic targets to inhibit excessive ROS production by primed microglia in brain pathology.

Heparin Interaction with the Primed Polymorphonuclear Leukocyte CD11b Induces Apoptosis and Prevents Cell Activation

Heparin is known to have anti-inflammatory effects, yet the mechanisms are not completely understood. In this study, we tested the hypothesis that heparin has a direct effect on activated polymorphonuclear leukocytes (PMNLs), changing their activation state, and can explain its anti-inflammatory effect. To test our hypothesis, we designed both in vitro and ex vivo studies to elucidate the mechanism by which heparin modulates PMNL functions and therefore the inflammatory response. We specifically tested the hypothesis that priming of PMNLs renders them more susceptible to heparin. Amplified levels of CD11b and increased rate of superoxide release manifested PMNL priming. Increase in cell priming resulted in a dose-dependent increase in heparin binding to PMNLs followed by augmented apoptosis. Blocking antibodies to CD11b inhibited heparin binding and abolished the apoptotic response. Moreover, heparin caused a significant dose-dependent decrease in the rate of superoxide release from PMNLs, which was blunted by blocking antibodies to CD11b. Altogether, this study shows that the interaction of heparin with the PMNL CD11b results in cell apoptosis and explains heparin's anti-inflammatory effects.

Could CD64 expression be used as a predictor of positive culture results in children with febrile neutropenia?

Background

Early recognition of infectious processes in neutropenic patients is hampered by the fact that these processes may have dissimilar and non-specific clinical presentations. CD64 is a neutrophil surface marker that is not expressed in non-sensitized neutrophils. When the neutrophil is exposed to tumor necrosis factor-alpha it is activated and is measured via the CD64 index.

Methods

This paper evaluated the relationship between the index value of CD64 on the first day of febrile neutropenia and a positive blood culture. The correlations with white blood count, C-reactive protein and erythrocyte sedimentation rate were also evaluated. This case–control, prospective, diagnostic study included 64 episodes of neutropenia. Case group (n = 14) comprised positive blood cultures, and the control group (n = 50), negative blood cultures.

Results

The median rates of CD64 were 2.1 (σ ± 3.9) in the case group and 1.76 (σ ± 5.02) in the control group. There was no correlation between the value of the CD64 index and blood cultures. The CD64 index was also not correlated with C-reactive protein positivity. Furthermore, the CD64 index was not able to predict blood culture positivity. The sensitivity was 64.3%, the specificity was 42%, the positive predictive value was 23.7% and the negative predictive value was 80%. For C-reactive protein, the sensitivity, specificity, positive predictive value, and negative predictive value were 71.4%, 32%, 22.7%, and 80%, respectively.

Conclusion

The CD64 index is not suitable for predicting the positivity of blood cultures in this specific population of patients with febrile neutropenia.

Neutrophil elastase induces inflammation and pain in mouse knee joints via activation of proteinase-activated receptor-2

BACKGROUND AND PURPOSE

Neutrophil elastase plays a crucial role in arthritis. Here, its potential in triggering joint inflammation and pain was assessed, and whether these effects were mediated by proteinase-activated receptor-2 (PAR2).

EXPERIMENTAL APPROACH

Neutrophil elastase (5 μg) was injected into the knee joints of mice and changes in blood perfusion, leukocyte kinetics and paw withdrawal threshold were assessed. Similar experiments were performed in animals pretreated with the neutrophil elastase inhibitor sivelestat, the PAR2 antagonist GB83, the p44/42 MAPK inhibitor U0126 and in PAR2 receptor knockout (KO) mice. Neutrophil elastase activity was also evaluated in arthritic joints by fluorescent imaging and sivelestat was assessed for anti-inflammatory and analgesic properties.

KEY RESULTS

Intra-articular injection of neutrophil elastase caused an increase in blood perfusion, leukocyte kinetics and a decrease in paw withdrawal threshold. Sivelestat treatment suppressed this effect. The PAR2 antagonist GB83 reversed neutrophil elastase-induced synovitis and pain and these responses were also attenuated in PAR2 KO mice. The MAPK inhibitor U0126 also blocked neutrophil elastase-induced inflammation and pain. Active neutrophil elastase was increased in acutely inflamed knees as shown by an activatable fluorescent probe. Sivelestat appeared to reduce neutrophil elastase activity, but had only a moderate anti-inflammatory effect in this model.

CONCLUSIONS AND IMPLICATIONS

Neutrophil elastase induced acute inflammation and pain in knee joints of mice. These changes are PAR2-dependent and appear to involve activation of a p44/42 MAPK pathway. Blocking neutrophil elastase, PAR2 and p44/42 MAPK activity can reduce inflammation and pain, suggesting their utility as therapeutic targets.

Defining the phenotype of neutrophils following reverse migration in zebrafish

Stimulation of neutrophil reverse migration presents an attractive, alternative therapeutic pathway to driving inflammation resolution. However, little is known about whether the activity of wound-experienced neutrophils is altered and whether encouraging dispersal of such neutrophils back into the body may have undesirable consequences. This study used a zebrafish tail transection inflammation model, in combination with a photoconvertible neutrophil transgenic line, to allow internally controlled, simultaneous comparison of reverse-migrated neutrophils with naïve neutrophils in the presence and absence of secondary insult. Detailed microscopy revealed that reverse-migrated neutrophils exhibited an activated morphology but responded normally to secondary insult and are able to mount an effective antimicrobial response to Staphylococcus aureus. These results support a model in which reverse-migrated neutrophils exhibit no long-term behavioral alterations and encourage the notion of enhanced reverse migration as a viable target for pharmaceutical manipulation.

C-type lectin domain family 12, member A: A common denominator in Behçet's syndrome and acute gouty arthritis

C-type lectin domain family 12, member A (CLEC12A) is a C-type lectin-like pattern recognition receptor capable of recognizing monosodium urate crystals. Monosodium urate crystals, the causative agents of gout are also among the danger-associated molecular patterns reflecting cellular injury/cell death. In response to monosodium urate crystals, CLEC12A effectively inhibits granulocyte and monocyte/macrophage functions and hence acts as a negative regulator of inflammation. Behçet's syndrome and gout are autoinflammatory disorders sharing certain pathological (neutrophilic inflammation), clinical (exaggerated response to monosodium urate crystals) and therapeutic (colchicine) features. We propose the hypothesis that decreased expression of CLEC12A is a common denominator in the hyperinflammatory responses observed in Behçet's syndrome and gout. Major lines of evidence supporting this hypothesis are: (1) Downregulation/deficiency of CLEC12A is associated with hyperinflammatory responses. (2) CLEC12A polymorphisms with functional and clinical implications have been documented in other inflammatory diseases. (3) Colchicine, a fundamental therapeutic agent used both in Behçet's syndrome and gout is shown to oppose the downregulation of CLEC12A. (4) Behçet's syndrome and gout are characterized by a hyperinflammatory response to monosodium urate crystals and other than gout, Behçet's syndrome is the only inflammatory condition exhibiting this exaggerated response. (5) Genomewide linkage and association studies of Behçet's syndrome collectively point to 12p12-13, the chromosomal region harboring CLEC12A. (6) Patients with severe forms of Behçet's syndrome underexpress CLEC12A with respect to patients with mild forms of the disease. If supported by well-designed, rigorous experiments, the forementioned hypothesis pertinent to CLEC12A will carry important implications for therapy, designing experimental models, and uncovering immunopathogenic mechanisms in Behçet's syndrome and gout.

Neutrophil oxidative burst capacity for peri-operative immune monitoring in trauma patients

BACKGROUND

Post injury immune dysfunction can result in serious complications. Measurement of biomarkers may guide the optimal timing of surgery in clinically borderline patients and therefore prevent complications.

AIM

peri-operative measurement of neutrophil oxidative burst capacity as an indicator of the immune response to major orthopaedic surgical procedures.

METHODS

Prospective cohort study of trauma patients aged ≥16 yrs with pelvic, acetabular, femoral shaft or tibial shaft fractures requiring surgical intervention. Blood samples were taken immediately pre-op and at 30 min, 7, 24 and 72-9 6 h post-operatively. Neutrophil oxidative burst capacity was measured both with and without stimulation by formyl-methionyl-leucyl-phenylalanine (fMLP, a chemotactic factor). Clinical outcomes measured were mortality, length of stay, MOF, pneumonia, acute respiratory distress syndrome (ARDS) and sepsis.

RESULTS

100 consecutive orthopaedic trauma patients were enrolled over a 16 month period. 78% were male, with a mean age of 42 ± 18 years and an average ISS of 19 ± 13. Neutrophil oxidative burst capacity was significantly elevated at 7 h (p = 0.006) and 24 h (p = 0.022) post operatively. Patients who developed infective complications (pneumonia and sepsis) had higher levels of oxidative burst capacity pre-operatively (pneumonia: 1.52 ± 0.93 v 0.99 ± 0.66 p = 0.032, sepsis: 1.39 ± 0.86 v 0.97 ± 0.56 p = 0.024) and at 24 h post op (pneumonia: 2.72 ± 2.38 v 1.12 ± 0.63 p = < 0.001, sepsis: 2.16 ± 2.09 v 1.10 ± 0.54 p = < 0.001). When analysed by operation type, no statistical difference was seen between major and minor operations. No correlation was found between length of stay, length of ICU stay, ISS or age and neutrophil oxidative burst capacity at any time point.

CONCLUSIONS

Neutrophil oxidative burst capacity response to orthopaedic trauma surgery is associated with the infective post injury complications. There was no correlation between magnitude of injury or operation and oxidative burst capacity. These results are promising for the development of tools for prediction of post-operative complications and guidance for optimal timing for surgical intervention.

The multifactorial role of neutrophils in rheumatoid arthritis

Of all cells implicated in the pathology of rheumatoid arthritis (RA), neutrophils possess the greatest cytotoxic potential, owing to their ability to release degradative enzymes and reactive oxygen species. Neutrophils also contribute to the cytokine and chemokine cascades that accompany inflammation, and regulate immune responses via cell-cell interactions. Emerging evidence suggests that neutrophils also have a previously unrecognised role in autoimmune diseases: neutrophils can release neutrophil extracellular traps (NETs) containing chromatin associated with granule enzymes, which not only kill extracellular microorganisms but also provide a source of autoantigens. For example, citrullinated proteins that can act as neoepitopes in loss of immune tolerance are generated by peptidylarginine deiminases, which replace arginine with citrulline residues, within neutrophils. Indeed, antibodies to citrullinated proteins can be detected before the onset of symptoms in patients with RA, and are predictive of erosive disease. Neutrophils from patients with RA have an increased tendency to form NETs containing citrullinated proteins, and sera from such patients contain autoantibodies that recognize these proteins. Thus, in addition to their cytotoxic and immunoregulatory role in RA, neutrophils may be a source of the autoantigens that drive the autoimmune processes underlying this disease.

Linezolid dampens neutrophil-mediated inflammation in methicillin-resistant Staphylococcus aureus-induced pneumonia and protects the lung of associated damages

BACKGROUND

Linezolid is considered as a therapeutic alternative to the use of glycopeptides for the treatment of pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA). Clinical studies reported a potent survival advantage conferred by the oxazolidinone and called into question the use of glycopeptides as first-line therapy.

METHODS

In a mouse model of MRSA-induced pneumonia, quantitative bacteriology, proinflammatory cytokine concentrations in lung, myeloperoxidase activity, Ly6G immunohistochemistry, and endothelial permeability were assessed to compare therapeutic efficacy and immunomodulative properties of linezolid and vancomycin administered subcutaneously every 12 hours.

RESULTS

Significant antibacterial activity was achieved after 48 hours of treatment for linezolid and vancomycin. Levels of interleukin 1β, a major proinflammatory cytokine, and macrophage inflammatory protein 2, a chemokine involved in the recruitment of neutrophils, were decreased by both antimicrobials. Only linezolid was able to dramatically reduce the production of tumor necrosis factor α. Analysis of myeloperoxidase activity and Ly6G immunostaining showed a dramatic decrease of neutrophil infiltration in infected lung tissues for linezolid-treated animals. A time-dependent increase of endothelial permeability was observed for the control and vancomycin regimens. Of interest, in the linezolid group, decreased endothelial permeability was detected 48 hours after infection.

CONCLUSIONS

Our results indicate that linezolid could be superior to vancomycin for the management of MRSA pneumonia by attenuating an excessive inflammatory reaction and protecting the lung from pathogen-associated damages.

Inhibition of NADPH oxidase prevents acute lung injury in obese rats following severe trauma

Lung capillary filtration coefficient (Kf) and impacts of oxidative stress have not been determined in the setting of severe trauma, especially in obese patients who exhibit increased lung injury. We hypothesized that severe trauma leads to a greater increase in lung Kf in obesity due to exacerbated production of and/or vulnerability to oxidative stress. Severe trauma was induced in lean and obese Zucker rats by muscle injury, fibula fracture, and bone component injection to both hindlimbs, with or without 24-h treatments of apocynin, a NADPH oxidase (NOX) inhibitor. Lung wet/dry weight ratios, lung vascular Kf, lung neutrophil counts, lung NOX and myeloperoxidase (MPO) activity, and plasma IL-6 levels were measured 24 h after trauma. In an additional study, lungs were isolated from nontrauma lean and obese rats to determine the acute effect of phenazime methosulfate, a superoxide donor, on pulmonary vascular Kf. After trauma, compared with lean rats, obese rats exhibited greater increases in lung capillary Kf, neutrophil accumulation, NOX and MPO activity, and plasma IL-6. The lung wet/dry weight ratio was increased in obese rats but not in lean rats. Apocynin treatment decreased lung Kf, neutrophil counts, NOX and MPO activities, wet/dry weight ratio, and plasma IL-6 in obese rats. Phenazime methosulfate treatment resulted in a greater increase in lung Kf in nontrauma obese rats compared with nontrauma lean rats. These results suggest that obese rats are susceptible to lung injury following severe trauma due to increased production of and responsiveness to pulmonary oxidative stress.

Differential effects of cadmium administration on peripheral blood granulocytes in rats

Infiltration of circulatory inflammatory cells is a common histopathological finding in target organs following cadmium administration, but there is paucity of data concerning their activity. In this study, the effects of sublethal (1 mg/kg) cadmium on peripheral blood polymorphonuclear (PMN) cells were examined 48 h following administration in rats, when tissue (liver and lung) infiltration of these cells was observed. Cadmium administration resulted in systemic inflammatory cytokine and acute phase response with an increase in circulatory neutrophil numbers and cells that express CD11b molecules. Rise in basic aspects of oxidative activity including intracellular myeloperoxidase (MPO), reactive oxygen (nitroblue tetrazolium/NBT cytochemical assay) and nitrogen (Griess assay) species production was observed in PMNs from cadmium-administered rats. A decrease in levels of mRNA for IL-1β, TNF-α and IL-6 was noted, but production of these cytokines was affected differentially. Described effects of cadmium on PMNs add further to the understanding of inflammatory potential of this environmental contaminant.

Assessment of priming of the human neutrophil respiratory burst

Neutrophils play an essential role in host defense against microbial pathogens and in the inflammatory reaction. Upon activation, neutrophils produce reactive oxygen species (ROS) such as superoxide anion (O2 (∙-)), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl), a process referred to as the respiratory burst. The enzyme responsible for this process is called the NADPH oxidase or respiratory burst oxidase. This multicomponent enzyme system is composed of two transmembrane proteins (p22phox and gp91phox/NOX2, which form the cytochrome b558), three cytosolic proteins (p47phox, p67phox, p40phox), and a GTPase (Rac1 or Rac2), which assemble at membrane sites upon cell activation. The NADPH oxidase is in a resting state in circulating neutrophils, and its activation can be induced by a large number of soluble and particulate agents such as the formylated peptide, formyl-methionyl-leucyl-phenylalanine (fMLF). This activation can be enhanced or "primed" by pro-inflammatory cytokines, LPS and other agents. Priming is a "double-edged sword" process as it contributes to a rapid and efficient elimination of the pathogens but can also induce the generation of large quantities of toxic ROS that can damage surrounding tissues and participate to inflammation. In this chapter, we describe the techniques used to measure priming of the NADPH oxidase in human neutrophils.

Cytokines and chemokines at the crossroads of neuroinflammation, neurodegeneration, and neuropathic pain

Cytokines and chemokines are proteins that coordinate the immune response throughout the body. The dysregulation of cytokines and chemokines is a central feature in the development of neuroinflammation, neurodegeneration, and demyelination both in the central and peripheral nervous systems and in conditions of neuropathic pain. Pathological states within the nervous system can lead to activation of microglia. The latter may mediate neuronal and glial cell injury and death through production of proinflammatory factors such as cytokines and chemokines. These then help to mobilize the adaptive immune response. Although inflammation may induce beneficial effects such as pathogen clearance and phagocytosis of apoptotic cells, uncontrolled inflammation can result in detrimental outcomes via the production of neurotoxic factors that exacerbate neurodegenerative pathology. In states of prolonged inflammation, continual activation and recruitment of effector cells can establish a feedback loop that perpetuates inflammation and ultimately results in neuronal injury. A critical balance between repair and proinflammatory factors determines the outcome of a neurodegenerative process. This review will focus on how cytokines and chemokines affect neuroinflammation and disease pathogenesis in bacterial meningitis and brain abscesses, Lyme neuroborreliosis, human immunodeficiency virus encephalitis, and neuropathic pain.

Inhibition of pre-B cell colony-enhancing factor (PBEF/NAMPT/visfatin) decreases the ability of human neutrophils to generate reactive oxidants but does not impair bacterial killing

NAMPT, also known as PBEF and visfatin, can act extracellularly as a cytokine-like molecule or intracellularly as a NAMPT, regulating NAD biosynthesis in the NAD salvage pathway. Inhibitors of NAMPT have anti-inflammatory and anticancer activity and are finding use as therapeutic agents. In view of the importance of NAD metabolism in neutrophil function, we determined the effects of NAMPT inhibition on a variety of neutrophil functions associated with their role in host protection against infections. Incubation of human neutrophils with the NAMPT inhibitor APO866 decreased neutrophil NAD(P)/H levels in a dose- and time-dependent manner but without a concomitant change in cell viability. NAMPT inhibition did not affect the expression of a number of cell-surface receptors involved in adhesion and opsono-phagocytosis, but the respiratory burst was decreased significantly. Whereas opsono-phagocytosis of Staphylococcus aureus was unaffected by NAMPT inhibition, intraphagosomal oxidant production was decreased. However, the killing efficiency of neutrophils was unaffected. These data indicate that therapeutic NAMPT inhibition is unlikely to have deleterious effects on host protection against infections, in spite of this ability to down-regulate neutrophil respiratory burst activity significantly.

Therapeutic options for transfusion related acute lung injury; the potential of the G2A receptor

Priming of polymorphonuclear leukocytes (PMNs) enhances their adhesion to endothelium, the release of their granule content and their production of reactive oxygen species. These effects are etiological in transfusion related acute lung injury (TRALI) and many clinically important mediators of TRALI prime PMNs. A priming activity that develops over time in stored blood products has been shown to be due to the accumulation of lysophospatidylcholines (lyso-PCs) and has been found to be related clinically to TRALI. Lyso- PCs prime PMNs activating the G2A receptor and several inhibitors of this receptor, which could potentially be therapeutic in TRALI, have been identified. Recent work has described early steps in the signaling from the G2A receptor which has revealed potential targets for novel antagonists of lyso-PC mediated priming via G2A. Additionally, characterization of the process by which lyso-PCs are generated in stored blood products could allow development of inhibitors and additive solutions to block their formation in the first place.

Oral warfarin affects peripheral blood leukocyte IL-6 and TNFα production in rats

Warfarin is a Vitamin K (VK) antagonist that affects Vitamin K-dependent (VKD) processes, including blood coagulation, as well as processes unrelated to hemostasis such as bone growth, calcification, and growth of some cell types. In addition, warfarin exerts influence on some non-VKD-related activities, including anti-tumor and immunomodulating activity. With respect to the latter, both immune stimulating and suppressive effects have been noted in different experimental systems. To explore the in vivo immunomodulatory potential of warfarin on one type of activity (i.e., cytokine production) in two different immune cell populations (i.e., mononuclear or polymorphonuclear cells), effects of subchronic oral warfarin intake in rats on pro-inflammatory cytokine (i.e., TNFα, IL-6) production by peripheral blood mononuclear and polymorphonuclear cells (granulocytes) was examined. Differential effects of warfarin intake on TNFα and IL-6 were noted, depending on the type of peripheral blood leukocytes and on the cytokine examined. Specifically, a lack of effect on TNFα and a priming of IL-6 production by mononuclear cells along with a decrease in TNFα and a lack of effect on IL-6 in polymorphonuclear cells were seen in warfarin-exposed hosts. The cell- and cytokine-dependent effects from subchronic oral warfarin intake on peripheral blood leukocytes demonstrated in this study could, possibly, differentially affect reactions mediated by these cells. Ultimately, the observed effects in rats might have implications for those humans who are on long-term/prolonged warfarin therapy.

Neutrophil priming by hypoxic preconditioning protects against epithelial barrier damage and enteric bacterial translocation in intestinal ischemia/reperfusion

Intestinal ischemia/reperfusion (I/R) induces mucosal barrier dysfunction and bacterial translocation (BT). Neutrophil-derived oxidative free radicals have been incriminated in the pathogenesis of ischemic injury in various organs, but their role in the bacteria-containing intestinal tract is debatable. Primed neutrophils are characterized by a faster and higher respiratory burst activity associated with more robust bactericidal effects on exposure to a second stimulus. Hypoxic preconditioning (HPC) attenuates ischemic injury in brain, heart, lung and kidney; no reports were found in the gut. Our aim is to investigate whether neutrophil priming by HPC protects against intestinal I/R-induced barrier damage and bacterial influx. Rats were raised in normoxia (NM) or kept in a hypobaric hypoxic chamber (380 Torr) 17 h/day for 3 weeks for HPC, followed by sham operation or intestinal I/R. Gut permeability was determined by using an ex vivo macromolecular flux assay and an in vivo magnetic resonance imaging-based method. Liver and spleen homogenates were plated for bacterial culturing. Rats raised in HPC showed diminished levels of BT, and partially improved mucosal histopathology and epithelial barrier function compared with the NM groups after intestinal I/R. Augmented cytokine-induced neutrophil chemoattractant (CINC)-1 and -3 levels and myeloperoxidase activity correlated with enhanced infiltration of neutrophils in intestines of HPC-I/R compared with NM-I/R rats. HPC alone caused blood neutrophil priming, as shown by elevated production of superoxide and hydrogen peroxide on stimulation, increased membrane translocation of cytosolic p47(phox) and p67(phox), as well as augmented bacterial-killing and phagocytotic activities. Neutrophil depletion reversed the mucosal protection by HPC, and aggravated intestinal leakiness and BT following I/R. In conclusion, neutrophil priming by HPC protects against I/R-induced BT via direct antimicrobial activity by oxidative respiratory bursts and through promotion of epithelial barrier integrity for luminal confinement of enteric bacteria.