Granulocyte apoptosis in the pathogenesis and resolution of lung disease

Effects of Modified Melatonin Release on Human Colostrum Neutrophils to Induce Death in the MCF-7 Cell Line

Cancer is one of the diseases with the highest mortality rate today, with breast cancer being the second most common type among the Brazilian population. Due to its etiological complexity and inefficiency of treatments, studies have focused on new forms of treatment. Among these forms of treatment, hormonal therapy seems to be an excellent auxiliary mechanism in tumoricidal activity, and melatonin has great potential as a modulator of the immune system. Thus, the present study is aimed at evaluating the effect of the hormone melatonin on the coculture of colostrum polymorphonuclear cells and MCF-7 cancer cells and evaluates the effect of this hormone using a modified transport system. A feasibility analysis was performed by fluorescence microscopy at three cell incubation times, 2 hours, 24 hours, and 72 hours. The measurement of cytokines in the cell supernatant occurred in 24 hours, and the apoptosis assay was performed in 72 hours using flow cytometry. The results showed higher levels of cell viability in groups treated with melatonin and less viability in groups containing a coculture of polymorphonuclear cells and MCF-7 after 72 hours of incubation. Furthermore, the apoptosis and necrosis rates were higher in coculture polymorphonuclear and MCF-7 cells, especially in groups containing microemulsion as a modified release agent. These data suggest that melatonin, especially if associated with a modified release system, has immunomodulatory effects on human colostrum polymorphonuclear cells. These cells can play a crucial role in the resolution of the tumor through their mediation and inflammatory action.

β1 Integrin regulates adult lung alveolar epithelial cell inflammation

Integrins, the extracellular matrix receptors that facilitate cell adhesion and migration, are necessary for organ morphogenesis; however, their role in maintaining adult tissue homeostasis is poorly understood. To define the functional importance of β1 integrin in adult mouse lung, we deleted it after completion of development in type 2 alveolar epithelial cells (AECs). Aged β1 integrin-deficient mice exhibited chronic obstructive pulmonary disease-like (COPD-like) pathology characterized by emphysema, lymphoid aggregates, and increased macrophage infiltration. These histopathological abnormalities were preceded by β1 integrin-deficient AEC dysfunction such as excessive ROS production and upregulation of NF-κB-dependent chemokines, including CCL2. Genetic deletion of the CCL2 receptor, Ccr2, in mice with β1 integrin-deficient type 2 AECs impaired recruitment of monocyte-derived macrophages and resulted in accelerated inflammation and severe premature emphysematous destruction. The lungs exhibited reduced AEC efferocytosis and excessive numbers of inflamed type 2 AECs, demonstrating the requirement for recruited monocytes/macrophages in limiting lung injury and remodeling in the setting of a chronically inflamed epithelium. These studies support a critical role for β1 integrin in alveolar homeostasis in the adult lung.

Delayed neutrophil apoptosis in granulomatosis with polyangiitis: dysregulation of neutrophil gene signature and circulating apoptosis-related proteins

Objectives: Neutrophil apoptosis is mandatory for resolving inflammation and is regulated by expression of pro- and anti-apoptotic genes. We studied neutrophils isolated from patients with granulomatosis with polyangiitis (GPA) to investigate apoptosis alterations and to identify transcriptional and circulating factors affecting this process.Method: We enrolled 36 patients (18 in active stage, 18 in remission) and 18 healthy controls. Circulating levels of tumour necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage migration inhibitory factor, plasminogen activator inhibitor-1, interferon-γ, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, platelet endothelial cell adhesion molecule-1, soluble Fas (sFas), sFas ligand, survivin, and pentraxin-3 (PTX3) were evaluated by enzyme-linked immunosorbent assay/Luminex; circulating apoptotic neutrophils by flow cytometry; and apoptosis-related gene transcripts by real-time polymerase chain reaction.Results: Patients had decreased fractions of circulating apoptotic neutrophils and delayed neutrophil apoptosis was present in vitro. Circulating levels of TNF-α, GM-CSF, sFas, and PTX3 were higher in GPA. Delayed neutrophil apoptosis was accompanied by decreased mRNA of pro-apoptotic genes and transcription factors (DIABLO, PMAIP1, BAX, CASP3, CASP7, RUNX3, E2F1, TP53) and increased anti-apoptotic CFLAR and BCL2A1 mRNA. TNF-α and sFas levels correlated with circulating apoptotic neutrophils and expression of apoptosis genes. Stimulation with TNF-α of neutrophils from controls significantly down-regulated E2F1 and CASP3 expression.Conclusions: Circulating neutrophils in GPA have anti-apoptotic phenotype involving both intrinsic and extrinsic pathways of apoptosis. This is accompanied by increased levels of circulating pro-survival factors (GM-CSF, TNF-α, sFas), independent of disease activity. Anti-apoptotic phenotype of neutrophils in GPA is reproduced by exposure to low concentrations of TNF-α.

NR4A orphan nuclear receptor family members, NR4A2 and NR4A3, regulate neutrophil number and survival

The lifespan of neutrophils is plastic and highly responsive to factors that regulate cellular survival. Defects in neutrophil number and survival are common to both hematologic disorders and chronic inflammatory diseases. At sites of inflammation, neutrophils respond to multiple signals that activate protein kinase A (PKA) signaling, which positively regulates neutrophil survival. The aim of this study was to define transcriptional responses to PKA activation and to delineate the roles of these factors in neutrophil function and survival. In human neutrophil gene array studies, we show that PKA activation upregulates a significant number of apoptosis-related genes, the most highly regulated of these being NR4A2 and NR4A3 Direct PKA activation by the site-selective PKA agonist pair N6/8-AHA (8-AHA-cAMP and N6-MB-cAMP) and treatment with endogenous activators of PKA, including adenosine and prostaglandin E2, results in a profound delay of neutrophil apoptosis and concomitant upregulation of NR4A2/3 in a PKA-dependent manner. NR4A3 expression is also increased at sites of neutrophilic inflammation in a human model of intradermal inflammation. PKA activation also promotes survival of murine neutrophil progenitor cells, and small interfering RNA to NR4A2 decreases neutrophil production in this model. Antisense knockdown of NR4A2 and NR4A3 homologs in zebrafish larvae significantly reduces the absolute neutrophil number without affecting cellular migration. In summary, we show that NR4A2 and NR4A3 are components of a downstream transcriptional response to PKA activation in the neutrophil, and that they positively regulate neutrophil survival and homeostasis.

Prognostic Value of Eosinophil to Leukocyte Ratio in Patients with ST-Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention

Aim: Leukocyte profile has been related to clinical outcome in patients with ST-segment elevation (STE) myocardial infarction (MI). However, whether eosinophil to leukocyte ratio (ELR) predicts clinical outcome in patients who have undergone primary percutaneous coronary intervention (PCI) remains unclear. Therefore, we examined the prognostic value of ELR in this patient population.

Methods: We retrospectively analyzed the data of 331 consecutive patients who underwent primary PCI for STEMI between January 2009 and March 2015. All leukocyte types were counted and ELR was calculated for all patients 24 h after hospital admission. The primary study endpoint was major adverse cardiac events (MACEs) within up to one year of follow-up duration.

Results: MACEs including cardiac deaths in 9.4% of the patients, MI in 1.5%, and target lesion or vessel revascularization in 10.3%, occurred within one year in 68 patients (20.5%). The mean ELR was significantly lower in patients with MACEs than in patients without MACEs (0.20 ± 0.51 vs. 0.49 ± 0.66, respectively; p < 0.001). An ELR < 0.1 at 24 h was identified as the best cut-off value for mortality prediction. Multivariate analysis identified that an ELR < 0.1 (odds ratio [OR] = 0.38; 95% confidence interval [CI] = 0.22–0.67; p < 0.001) and chronic kidney disease (OR = 2.38; CI = 1.33–4.24; p = 0.003) are independent predictors of MACEs.

Conclusion: In primary PCI patients with STEMI, ELR at 24 h was an independent predictor of MACEs in addition to the usual coronary risk factors and commonly used biomarkers.

Reverse Migration of Neutrophils: Where, When, How, and Why?

Neutrophil migration to injured and pathogen-infected tissues is a fundamental component of innate immunity. An array of cellular and molecular events mediate this response to collectively guide neutrophils out of the vasculature and towards the core of the ensuing inflammatory reaction where they exert effector functions. Advances in imaging modalities have revealed that neutrophils can also exhibit motility away from sites of inflammation and injury, although it is unclear under what circumstances this reverse migration is a physiological protective response, and when it has pathophysiological relevance. Here we review different types of neutrophil reverse migration and discuss the current understanding of the associated mechanisms. In this context we propose clarifications to the existing terminology used to describe the many facets of neutrophil reverse migration.

Impact of alginate-producing Pseudomonas aeruginosa on alveolar macrophage apoptotic cell clearance

Pseudomonas aeruginosa infection is a hallmark of lung disease in cystic fibrosis. Acute infection with P. aeruginosa profoundly inhibits alveolar macrophage clearance of apoptotic cells (efferocytosis) via direct effect of virulence factors. During chronic infection, P. aeruginosa evades host defense by decreased virulence, which includes the production or, in the case of mucoidy, overproduction of alginate. The impact of alginate on innate immunity, in particular on macrophage clearance of apoptotic cells is not known. We hypothesized that P. aeruginosa strains that exhibit reduced virulence impair macrophage clearance of apoptotic cells and we investigated if the polysaccharide alginate produced by mucoid P. aeruginosa is sufficient to inhibit alveolar macrophage efferocytosis. Rat alveolar or human peripheral blood monocyte (THP-1)-derived macrophage cell lines were exposed in vitro to exogenous alginate or to wild type or alginate-overproducing mucoid P. aeruginosa prior to challenge with apoptotic human Jurkat T-lymphocytes. The importance of LPS contamination and that of structural integrity of alginate polymers was tested using alginate of different purities and alginate lyase, respectively. Alginate inhibited alveolar macrophage efferocytosis in a dose- and time-dependent manner. This effect was augmented but not exclusively attributed to lipopolysaccharide (LPS) present in alginates. Alginate-producing P. aeruginosa inhibited macrophage efferocytosis by more than 50%. A mannuronic-specific alginate lyase did not restore efferocytosis inhibited by exogenous guluronic-rich marine alginate, but had a marked beneficial effect on efferocytosis of alveolar macrophages exposed to mucoid P. aeruginosa. Despite decreased virulence, mucoid P. aeruginosa may contribute to chronic airway inflammation through significant inhibition of alveolar clearance of apoptotic cells and debris. The mechanism by which mucoid bacteria inhibit efferocytosis may involve alginate production and synergy with LPS, suggesting that alginate lyase may be an attractive therapeutic approach to airway inflammation in cystic fibrosis and other chronic obstructive pulmonary diseases characterized by P. aeruginosa colonization.

HIF-mediated innate immune responses: cell signaling and therapeutic implications

Leukocytes recruited to infected, damaged, or inflamed tissues during an immune response must adapt to oxygen levels much lower than those in the circulation. Hypoxia inducible factors (HIFs) are key mediators of cellular responses to hypoxia and, as in other cell types, HIFs are critical for the upregulation of glycolysis, which enables innate immune cells to produce adenosine triphosphate anaerobically. An increasing body of evidence demonstrates that hypoxia also regulates many other innate immunological functions, including cell migration, apoptosis, phagocytosis of pathogens, antigen presentation and production of cytokines, chemokines, and angiogenic and antimicrobial factors. Many of these functions are mediated by HIFs, which are not only stabilized posttranslationally by hypoxia, but also transcriptionally upregulated by inflammatory signals. Here, we review the role of HIFs in the responses of innate immune cells to hypoxia, both in vitro and in vivo, with a particular focus on myeloid cells, on which the majority of studies have so far been carried out.

A comparative study of apoptosis in reticular and erosive oral lichen planus

The oral lichen planus (OLP) is a chronic inflammatory disease, probably autoimmune, with different clinical forms. The most common types are the reticular and the erosive ones. Apoptosis participates in the destruction of basal keratinocytes, but its role in the perpetuation of the subepithelial lymphocytic infiltrates was not yet investigated. To evaluate the involvement of apoptosis in the epithelium and in subepithelial lymphocytic infiltrates, 15 samples of reticular and erosive OLP and 10 samples of healthy oral mucosa were collected and processed histologically. Apoptosis was quantified in the epithelium and in inflammatory cell infiltrates. TUNEL reaction was used to measure apoptosis in the infiltrates. Erosive OLP showed more intense epithelial apoptosis than reticular OLP and controls. In contrast, apoptosis in the inflammatory cell infiltrates was more frequent in reticular than in erosive OLP. Lymphocytes were the predominant cells within the inflammatory cell infiltrates and were more frequent in erosive OLP than in reticular type. These results suggest that different apoptotic levels are involved in the erosive/reticular switch in OLP, determining different clinical presentations. In conclusion, decreased apoptosis in inflammatory infiltrates may contribute to the persistence of T lymphocytes, worsening the attack to the epithelium in erosive OLP.

Different anti-apoptotic effects of normal and asthmatic serum on normal eosinophil apoptosis depending on house dust mite-specific IgE

We investigated the effect of asthmatic serum on constitutive eosinophil apoptosis in normal subjects. Eosinophil apoptosis in normal subjects was inhibited by asthmatic serum but not normal serum. In a detailed analysis based on the presence of house dust mite (HDM) IgE, HDM IgE-positive (+) asthmatic serum was more effective for eosinophil apoptosis than that of HDM IgE-negative (-) asthmatic serum. HDM IgE+ asthmatic serum inhibited both HDM IgE- and HDM IgE+ normal eosinophil apoptosis, and HDM IgE- asthmatic serum suppressed eosinophil apoptosis of HDM IgE+ normal. HDM IgE- normal serum did not inhibit either HDM IgE- or HDM IgE+ normal eosinophil apoptosis, and HDM IgE+ normal serum inhibited HDM IgE+ normal eosinophil apoptosis. The kind of HDM IgE (Dermatophagoides pteronissinus-specific IgE and Dermatophagoides farinae-specific IgE) was not related to the effect of asthmatic serum on eosinophil apoptosis. Extracts of DP and DF, Der p1, and Der p2, were not effective for eosinophil apoptosis. HDM IgE+ asthmatic serum inhibited cleavage of procaspase 9 and procaspase 3. Asthmatic serum induced Akt and ERK phosphorylation, and ERK activation was suppressed by AKTi. Taken together, asthmatic serum inhibited normal eosinophil apoptosis via PI3K/Akt/ERK cascade. The novel approach taken in this study provided better insight into HDM-associated anti-apoptotic mechanism of eosinophils in patients with asthma.

SOCS3 dictates the transition of divergent time-phased events in granulocyte TNF-α signaling

Tumor-necrosis factor-α (TNF-α)-driven nuclear factor-κB (NF-κB) activation and apoptosis are opposing pathways; the growing recognition of these conflicting roles of TNF-α is perplexing. Here, we show that inflammation and apoptosis are time-phased events following TNF-α signaling and that emergence of suppressor of cytokine signaling 3 (SOCS3) expression limits the ongoing NF-κB activation and promotes apoptosis; further, we suggest an altered view of how inflammatory diseases are initiated and sustained. In vitro, TNF-α (50 ng/ml) induced granulocyte SOCS3 protein, inhibited nuclear accumulation of the p65NF-κB subunit and enhanced apoptosis, as shown by DNA laddering, annexin V positivity, and overexpression of caspase-3 and Bax in the late phase, whereas the early phase was marked by NF-κB activation. Conversely, SOCS3 knockdown by small interfering RNA (siRNA) inhibited granulocyte apoptosis and enhanced nuclear accumulation of p65 and 5' lipooxygenase expression in the late phase of TNF-α signaling. As apoptosis is associated with SOCS3 abundance, we suggest that these divergent TNF-α-driven events are time-phased, interconnected, opposing control mechanisms and one of the central features through which the immune system resolves pulmonary inflammation. Dysregulation may initiate mucosal inflammation, thus changing the landscape of asthma therapy.

Living and dying for inflammation: neutrophils, eosinophils, basophils

Neutrophils, eosinophils, and basophils play essential roles during microbe-induced and sterile inflammation. The severity of such inflammatory processes is controlled, at least in part, by factors that regulate cell death and survival of granulocytes. In recent years, major progress has been made in understanding the molecular mechanisms of granulocyte cell death and in identifying novel damage- and pathogen-associated molecular patterns as well as regulatory cytokines impacting granulocyte viability. Furthermore, an increased interest in innate immunity has boosted our overall understanding of granulocyte biology. In this review, we describe and compare factors and mechanisms regulating neutrophil, eosinophil, and basophil lifespan. Because dysregulation of death pathways in granulocytes can contribute to inflammation-associated immunopathology, targeting granulocyte lifespan could be therapeutically promising.

Resolution of inflammation: mechanisms and opportunity for drug development

Inflammation is a beneficial host reaction to tissue damage and has the essential primary purpose of restoring tissue homeostasis. Inflammation plays a major role in containing and resolving infection and may also occur under sterile conditions. The cardinal signs of inflammation dolor, calor, tumor and rubor are intrinsically associated with events including vasodilatation, edema and leukocyte trafficking into the site of inflammation. If uncontrolled or unresolved, inflammation itself can lead to further tissue damage and give rise to chronic inflammatory diseases and autoimmunity with eventual loss of organ function. It is now evident that the resolution of inflammation is an active continuous process that occurs during an acute inflammatory episode. Successful resolution requires activation of endogenous programs with switch from production of pro-inflammatory towards pro-resolving molecules, such as specific lipid mediators and annexin A1, and the non-phlogistic elimination of granulocytes by apoptosis with subsequent removal by surrounding macrophages. These processes ensure rapid restoration of tissue homeostasis. Here, we review recent advances in the understanding of resolution of inflammation, highlighting the pharmacological strategies that may interfere with the molecular pathways which control leukocyte survival and clearance. Such strategies have proved beneficial in several pre-clinical models of inflammatory diseases, suggesting that pharmacological modulation of the resolution process may be useful for the treatment of chronic inflammatory diseases in humans.

Zebrafish as a model for the study of neutrophil biology

To understand inflammation and immunity, we need to understand the biology of the neutrophil. Whereas these cells can readily be extracted from peripheral blood, their short lifespan makes genetic manipulations impractical. Murine knockout models have been highly informative, and new imaging techniques are allowing neutrophils to be seen during inflammation in vivo for the first time. However, there is a place for a new model of neutrophil biology, which readily permits imaging of individual neutrophils during inflammation in vivo, combined with the ease of genetic and chemical manipulation. The zebrafish has long been the model of choice for the developmental biology community, and the availability of genomic resources and tools for gene manipulation makes this an attractive model. Zebrafish innate immunity shares many features with mammalian systems, including neutrophils with morphological, biochemical, and functional features, also shared with mammalian neutrophils. Transgenic zebrafish with neutrophils specifically labeled with fluorescent proteins have been generated, and this advance has led to the adoption of zebrafish, alongside existing models, by a number of groups around the world. The use of these models has underpinned a number of key advances in the field, including the identification of a tissue gradient of hydrogen peroxide for neutrophil recruitment following tissue injury and direct evidence for reverse migration as a regulatable mechanism of inflammation resolution. In this review, we discuss the importance of zebrafish models in neutrophil biology and describe how the understanding of neutrophil biology has been advanced by the use of these models.

Bax/Mcl-1 balance affects neutrophil survival in intermittent hypoxia and obstructive sleep apnea: effects of p38MAPK and ERK1/2 signaling

BACKGROUND

Prolonged neutrophil survival is evident in various cardiovascular and respiratory morbidities, in hypoxic conditions in-vitro and in patients with obstructive sleep apnea (OSA) characterized by nightly intermittent hypoxia (IH). This may lead to persistent inflammation, tissue injury and dysfunction. We therefore investigated by a translational approach the potential contribution of the intrinsic stress-induced mitochondrial pathway in extending neutrophil survival under IH conditions. Thus, neutrophils of healthy individuals treated with IH in-vitro and neutrophils of OSA patients undergoing nightly IH episodes in-vivo were investigated. Specifically, the balance between pro-apoptotic Bax and anti-apoptotic Mcl-1 protein expression, and the potential involvement of p38MAPK and ERK1/2 signaling pathways in the control of Mcl-1 expression were investigated.

METHODS

Purified neutrophils were exposed to IH and compared to normoxia and to sustained hypoxia (SH) using a BioSpherix-OxyCycler C42 system. Bax and Mcl-1 levels, and p38MAPK and ERK1/2 phosphorylation were determined by western blotting. Also, Bax/Mcl-1 expression and Bax translocation to the mitochondria were assessed by confocal microscopy in pre-apoptotic neutrophils, before the appearance of apoptotic morphology. Co-localization of Bax and mitochondria was quantified by LSM 510 CarlZeiss MicroImaging using Manders Overlap Coefficient. A paired two-tailed t test, with Bonferroni correction for multiple comparisons, was used for statistical analysis.

RESULTS

Compared to normoxia, IH and SH up-regulated the anti-apoptotic Mcl-1 by about 2-fold, down-regulated the pro-apoptotic Bax by 41% and 27%, respectively, and inhibited Bax co-localization with mitochondria before visible morphological signs of apoptosis were noted. IH induced ERK1/2 and p38MAPKs phosphorylation, whereas SH induced only p38MAPK phosphorylation. Accordingly, both ERK and p38MAPK inhibitors attenuated the IH-induced Mcl-1 increase. In SH, only p38MAPK inhibition decreased Mcl-1 expression. Similar to neutrophils of healthy subjects exposed to IH (0.97± 0.2), in OSA neutrophils, Bax/Mcl-1 ratio was significantly lower compared to normoxic controls (1.0±0.5 vs.1.99±0.3, p=0.015), and Bax did not co-localize with mitochondria.

CONCLUSIONS

These findings suggest that decreased Bax/Mcl-1 balance promotes neutrophil survival in IH in-vitro as well as in OSA patients. Moreover, Bax/Mcl-1 protein function in IH and SH might be regulated by different signal transduction pathways, highlighting a novel regulatory function through ERK1/2 signaling in IH.

R-roscovitine reduces lung inflammation induced by lipoteichoic acid and Streptococcus pneumoniae

Bacterial pneumonia remains associated with high morbidity and mortality. The gram-positive pathogen Streptococcus pneumoniae is the most common cause of community-acquired pneumonia. Lipoteichoic acid (LTA) is an important proinflammatory component of the gram-positive bacterial cell wall. R-roscovitine, a purine analog, is a potent cyclin-dependent kinase (CDK)-1, -2, -5 and -7 inhibitor that has the ability to inhibit the cell cycle and to induce polymorphonuclear cell (PMN) apoptosis. We sought to investigate the effect of R-roscovitine on LTA-induced activation of cell lines with relevance for lung inflammation in vitro and on lung inflammation elicited by either LTA or viable S. pneumoniae in vivo. In vitro R-roscovitine enhanced apoptosis in PMNs and reduced tumor necrosis factor (TNF)-α and keratinocyte chemoattractant (KC) production in MH-S (alveolar macrophage) and MLE-12/MLE-15 (respiratory epithelial) cell lines. In vivo R-roscovitine treatment reduced PMN numbers in bronchoalveolar lavage fluid during LTA-induced lung inflammation; this effect was reversed by inhibiting apoptosis. Postponed treatment with R-roscovitine (24 and 72 h) diminished PMN numbers in lung tissue during gram-positive pneumonia; this step was associated with a transient increase in pulmonary bacterial loads. R-roscovitine inhibits proinflammatory responses induced by the gram-positive stimuli LTA and S. pneumoniae. R-roscovitine reduces PMN numbers in lungs upon LTA administration by enhancing apoptosis. The reduction in PMN numbers caused by R-roscovitine during S. pneumoniae pneumonia may hamper antibacterial defense.

Roles of neutrophils in the regulation of the extent of human inflammation through delivery of IL-1 and clearance of chemokines

This study examined the establishment of neutrophilic inflammation in humans. We tested the hypotheses that neutrophil recruitment was associated with local CXCL8 production and that neutrophils themselves might contribute to the regulation of the size of the inflammatory response. Humans were challenged i.d. with endotoxin. Biopsies of these sites were examined for cytokine production and leukocyte recruitment by qPCR and IHC. Additional in vitro models of inflammation examined the ability of neutrophils to produce and sequester cytokines relevant to neutrophilic inflammation. i.d. challenge with 15 ng of a TLR4-selective endotoxin caused a local inflammatory response, in which 1% of the total biopsy area stained positive for neutrophils at 6 h, correlating with 100-fold up-regulation in local CXCL8 mRNA generation. Neutrophils themselves were the major source of the early cytokine IL-1β. In vitro, neutrophils mediated CXCL8 but not IL-1β clearance (>90% clearance of ≤2 nM CXCL8 over 24 h). CXCL8 clearance was at least partially receptor-dependent and modified by inflammatory context, preserved in models of viral infection but reduced in models of bacterial infection. In conclusion, in a human inflammatory model, neutrophils are rapidly recruited and may regulate the size and outcome of the inflammatory response through the uptake and release of cytokines and chemokines in patterns dependent on the underlying inflammatory stimulus.

Annexin A1 modulates natural and glucocorticoid-induced resolution of inflammation by enhancing neutrophil apoptosis

This study aimed at assessing whether AnxA1, a downstream mediator for the anti-inflammatory effects of GCs, could affect the fate of immune cells in tissue exudates, using LPS-induced pleurisy in BALB/c mice. AnxA1 protein expression in exudates was increased during natural resolution, as seen at 48-72 h post-LPS, an effect augmented by treatment with GC and associated with marked presence of apoptotic neutrophils in the pleural exudates. The functional relevance of AnxA1 was determined using a neutralizing antibody or a nonspecific antagonist at FPR/ALXRs: either treatment inhibited both spontaneous and GC-induced resolution of inflammation. Injection of Ac2-26 (100 μg, given 4 h into the LPS response), an AnxA1-active N-terminal peptide, promoted active resolution and augmented the extent of neutrophil apoptosis. Such an effect was prevented by the pan-caspase inhibitor zVAD-fmk. Mechanistically, resolution of neutrophilic inflammation was linked to cell apoptosis with activation of Bax and caspase-3 and inhibition of survival pathways Mcl-1, ERK1/2, and NF-κB. These novel in vivo data, using a dynamic model of acute inflammation, provide evidence that AnxA1 is a mediator of natural and GC-induced resolution of inflammation with profound effects on neutrophil apoptosis.

TNF-related apoptosis-inducing ligand (TRAIL) regulates inflammatory neutrophil apoptosis and enhances resolution of inflammation

Novel therapeutics targeting neutrophilic inflammation are a major unmet clinical need in acute and chronic inflammation. The timely induction of neutrophil apoptosis is critical for inflammation resolution, and it is thought that acceleration of apoptosis may facilitate resolution at inflammatory sites. We previously demonstrated that a death receptor ligand, TRAIL, accelerates neutrophil apoptosis in vitro. We examined the role of TRAIL in neutrophil-dominant inflammation in WT and TRAIL-deficient mice. TRAIL deficiency did not alter constitutive neutrophil apoptosis, whereas exogenous TRAIL accelerated apoptosis of murine peripheral blood neutrophils. We compared TRAIL-deficient and WT mice in two independent models of neutrophilic inflammation: bacterial LPS-induced acute lung injury and zymosan-induced peritonitis. In both models, TRAIL-deficient mice had an enhanced inflammatory response with increased neutrophil numbers and reduced neutrophil apoptosis. Correction of TRAIL deficiency and supraphysiological TRAIL signaling using exogenous protein enhanced neutrophil apoptosis and reduced neutrophil numbers in both inflammatory models with no evidence of effects on other cell types. These data indicate the potential therapeutic benefit of TRAIL in neutrophilic inflammation.

Rosette nanotubes inhibit bovine neutrophil chemotaxis

Migration of activated neutrophils that have prolonged lifespan into inflamed organs is an important component of host defense but also contributes to tissue damage and mortality. In this report, we used biologically-inspired RGD-tagged rosette nanotubes (RNT) to inhibit neutrophil chemotaxis. We hypothesize that RGD-RNT will block neutrophil migration through inhibition of MAPK. In this report, RNT conjugated to lysine (K–RNT) and arginine-glycine-aspartic acid-serine-lysine (RGDSK-RNT) were co-assembled in a molar ratio of 95/5. The effect of the resulting composite RNT (RGDSK/K–RNT) on neutrophil chemotaxis, cell signaling and apoptosis was then investigated. Exposure to RGDSK/K–RNT reduced bovine neutrophil migration when compared to the non-treated group (p < 0.001). Similar effect was seen following treatment with ERK1/2 or p38 MAPK inhibitors. Phosphorylation of the ERK1/2 and p38 MAPK was inhibited at 5 min by RGDSK/K–RNT (p < 0.05). The RGDSD/K-RNT did not affect the migration of neutrophils pre-treated with αvβ3 integrin antibody suggesting that both bind to the same receptor. RGDSK/K–RNT did not induce apoptosis in bovine neutrophils, which was suppressed by pre-exposing them to LPS (p < 0.001). We conclude that RGDSK/K–RNT inhibit phosphorylation of ERK1/2 and p38 MAPK and inhibit chemotaxis of bovine neutrophils.

Secondary necrosis of apoptotic neutrophils induced by the human cathelicidin LL-37 is not proinflammatory to phagocytosing macrophages

Cathelicidins are CHDP with essential roles in innate host defense but also more recently associated with the pathogenesis of certain chronic diseases. These peptides have microbicidal potential and the capacity to modulate innate immunity and inflammatory processes. PMN are key innate immune effector cells with pivotal roles in defense against infection. The appropriate regulation of PMN function, death, and clearance is critical to innate immunity, and dysregulation is implicated in disease pathogenesis. The efferocytosis of apoptotic PMN, in contrast to necrotic cells, is proposed to promote the resolution of inflammation. We demonstrate that the human cathelicidin LL-37 induced rapid secondary necrosis of apoptotic human PMN and identify an essential minimal region of LL-37 required for this activity. Using these LL-37-induced secondary necrotic PMN, we characterize the consequence for macrophage inflammatory responses. LL-37-induced secondary necrosis did not inhibit PMN ingestion by monocyte-derived macrophages and in contrast to expectation, was not proinflammatory. Furthermore, the anti-inflammatory effects of apoptotic PMN on activated macrophages were retained and even potentiated after LL-37-induced secondary necrosis. However, this process of secondary necrosis did induce the release of potentially harmful PMN granule contents. Thus, we suggest that LL-37 can be a potent inducer of PMN secondary necrosis during inflammation without promoting macrophage inflammation but may mediate host damage through PMN granule content release under chronic or dysregulated conditions.

Cyclin-dependent kinase inhibitor drugs as potential novel anti-inflammatory and pro-resolution agents

The cyclin-dependent kinase inhibitor (CDKi) drugs such as R-roscovitine have emerged as potential anti-inflammatory, pharmacological agents that can influence the resolution of inflammation. Usually, once an inciting inflammatory stimulus has been eliminated, resolution proceeds by prompt, safe removal of dominant inflammatory cells. This is accomplished by programmed cell death (apoptosis) of prominent effector, inflammatory cells typified by the neutrophil. Apoptosis of neutrophils ensures that toxic neutrophil granule contents are securely packaged in apoptotic bodies and expedites phagocytosis by professional phagocytes such as macrophages. A panel of CDKi drugs have been shown to promote neutrophil apoptosis in a concentration- and time-dependent manner and the archetypal CDKi drug, R-roscovitine, overrides the anti-apoptotic effects of powerful survival factors [including lipopolysaccharide (LPS) and granulocyte macrophage-colony stimulating factor (GM-CSF)]. Inflammatory cell longevity and survival signalling is integral to the inflammatory process and any putative anti-inflammatory agent must unravel a complex web of redundancy in order to be effective. CDKi drugs have also been demonstrated to have significant effects on other cell types including lymphocytes and fibroblasts indicating that they may have pleiotropic anti-inflammatory, pro-resolution activity. In keeping with this, CDKi drugs like R-roscovitine have been reported to be efficacious in resolving established animal models of neutrophil-dominant and lymphocyte-driven inflammation. However, the mechanism of action behind these powerful effects has not yet been fully elucidated. CDKs play an integral role in the regulation of the cell cycle but are also recognized as participants in processes such as apoptosis and transcriptional regulation. Neutrophils have functional CDKs, are transcriptionally active and demonstrate augmented apoptosis in response to CDKi drugs, while lymphocyte proliferation and secretory function are inhibited. This review will discuss current understanding of the processes of inflammation and resolution but will focus on CDKis and their potential mechanisms of action.

The rise and rise of Staphylococcus aureus: laughing in the face of granulocytes

Recent developments in the study of host-pathogen interactions have fundamentally altered our understanding of the nature of Staphylococcus aureus infection, and previously held tenets regarding the role of the granulocyte are being cast aside. Novel mechanisms of pathogenesis are becoming evident, revealing the extent to which S. aureus can evade neutrophil responses successfully by resisting microbicides, surviving intracellularly and subverting cell death pathways. Developing a detailed understanding of these complex strategies is especially relevant in light of increasing staphylococcal virulence and antibiotic resistance, and the knowledge that dysfunctional neutrophil responses contribute materially to poor host outcomes. Unravelling the biology of these interactions is a challenging task, but one which may yield new strategies to address this, as yet, defiant organism.

Neutrophil apoptosis and the resolution of infection

Polymorphonuclear leukocytes (PMNs) are the most abundant white cell in humans and an essential component of the innate immune system. PMNs are typically the first type of leukocyte recruited to sites of infection or areas of inflammation. Ingestion of microorganisms triggers production of reactive oxygen species and fusion of cytoplasmic granules with forming phagosomes, leading to effective killing of ingested microbes. Phagocytosis of bacteria typically accelerates neutrophil apoptosis, which ultimately promotes the resolution of infection. However, some bacterial pathogens alter PMN apoptosis to survive and thereby cause disease. Herein, we review PMN apoptosis and the ability of microorganisms to alter this important process.

Hypoxia. Hypoxia, hypoxia inducible factor and myeloid cell function

With little in the way of effective therapeutic strategies to target the innate immune response, a better understanding of the critical pathways regulating neutrophil and macrophage responses in inflammation is key to the development of novel therapies. Hypoxia inducible factor (HIF) was originally identified as a central transcriptional regulator of cellular responses to oxygen deprivation. However, the HIF signalling pathway now appears, in myeloid cells at least, to be a master regulator of both immune cell function and survival. As such, understanding the biology of HIF and its regulators may provide new approaches to myeloid-specific therapies that are urgently needed.

The generation of highly purified primary human neutrophils and assessment of apoptosis in response to Toll-like receptor ligands

Neutrophils are crucial components of our defence against microbial assault. They are short-lived cells, with regulation of their lifespan being a primary mechanism involved in the regulation of their function. Delay of apoptosis facilitates their clearance of pathogens, whilst appropriate induction of cell death facilitates wound healing. A variety of methods are available to study neutrophil function: purification of human neutrophils and analysis of their lifespan are described here.

Basic science of the innate immune system and the lung

Infections of the lung are prevented first by denial of access, mediated by humoral and cellular systems that obscure the pathogen's target, simultaneously acting to kill and clear the pathogen. Where pathogens penetrate these initial defence systems, rapid detection of their presence is achieved by their engagement with a large family of pattern recognition receptors, including Toll-like receptors, retinoic-acid-inducible gene-like helicases and Nod-like receptors. Activation of a coordinated inflammatory response is achieved by cooperative signalling between sentinel leucocytes such as alveolar macrophages and lung tissue, following which a profound pro-inflammatory response mobilizes phagocytes such as neutrophils and monocytes to the lung. Resolution of the innate immune response, largely dependent upon neutrophil apoptosis, results in restoration of normal tissue architecture. In chronic disease, dysregulated inflammation maintains these systems in a state of constant activation, potentially resulting in tissue damage and progressive disease.

Pathways regulating lipopolysaccharide-induced neutrophil survival revealed by lentiviral transduction of primary human neutrophils

Human neutrophils express Toll-like receptor 4 (TLR4) at low levels, and the role of this receptor in neutrophil responses to microbial stimuli has been questioned. Genetic manipulation of these cells to enable the study of the role of proteins such as TLR4 in their function is challenging. Here, we show that primary human neutrophils rapidly express novel proteins such as enhanced green fluorescent protein (eGFP) after transduction with lentivirus. Stimulation of transduced neutrophils with lipopolysaccharide (LPS) resulted in increased cell survival, which was inhibited when neutrophils were transduced with a lentivirus encoding a dominant negative (dn) TLR4 protein. LPS-induced survival was also inhibited by lentiviruses encoding dnMyD88 or a truncated TRIF (Toll/interleukin-1R homologous domain-containing adapter protein inducing interferon-beta) molecule, whilst, in contrast, neutrophil survival was enhanced by overexpression of kinase-mutated interleukin-1 receptor-associated kinase 1 (kmIRAK-1), which activated nuclear factor (NF)-kappaB. These studies provide proof of the role of TLR4 in human neutrophil biology, have begun to elucidate TLR-dependent pathways regulating neutrophil survival, and demonstrate that neutrophils can be genetically manipulated to enhance or inhibit survival.

Febrile-range hyperthermia accelerates caspase-dependent apoptosis in human neutrophils

Human neutrophilic polymorphonuclear leukocytes (PMNs) are central to innate immunity and are responsible for clearance of pathogens. PMNs undergo a tightly regulated apoptosis program that allows for timely clearance of PMNs without extravasation of toxic intracellular contents. We investigated the rate of spontaneous apoptosis of human peripheral blood PMNs cultured at basal (37 degrees C) and febrile-range (39.5 degrees C) temperatures (FRT). We found that PMN apoptosis is accelerated at FRT, reaching approximately 90% completion by 8 h at 39.5 degrees C vs 18 h at 37 degrees C based on morphologic criteria. Caspase-8 activation peaked within 15 min of PMN exposure to FRT, and subsequent activation of caspase-3 and -9, cleavage of the BH3 (Bcl-2 homology domain 3) only protein Bid, and mitochondrial release of cytochrome c were also greater in FRT-exposed PMNs. Inhibition of caspase-3, -8, and -9 conferred comparable protection from apoptosis in FRT-exposed PMNs. These results demonstrate that exposure to FRT enhances caspase-8 activation and subsequent mitochondrial-dependent and mitochondrial-independent apoptosis pathways. The PMN survival factors G-CSF, GM-CSF, and IL-8 each prolonged PMN survival at 37 degrees C and 39.5 degrees C, but did not reduce the difference in survival at the two temperatures. In a mouse model of intratracheal endotoxin-induced alveolitis, coexposure to FRT (core temperature approximately 39.5 degrees C) doubled the proportion of bronchoalveolar PMNs undergoing apoptosis compared with euthermic mice. This process may play an important role in limiting inflammation and tissue injury during febrile illnesses.

Toll-like receptor (TLR)-based networks regulate neutrophilic inflammation in respiratory disease

The neutrophil is a crucial early defence against microbial infection, but neutrophilic inflammation can result in devastating acute and chronic inflammatory diseases. In the lungs, the neutrophil is a principal part of the pathology of the acute respiratory distress syndrome, and its activation may also be of substantial importance in chronic obstructive pulmonary disease and some forms of asthma. Induction of neutrophil recruitment in response to microbial attack requires activation of TLR (Toll-like receptor)-based signalling pathways and the concerted actions of multiple cell types, including sentinel cells such as monocytes and macrophages acting together with tissue cell types such as the epithelium or smooth-muscle cell. The present review describes some of these networks and the resulting potential for their targeting in respiratory disease.

Secondary necrosis in multicellular animals: an outcome of apoptosis with pathogenic implications

In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane, followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation. In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be reviewed.

Relevance of granulocyte apoptosis to resolution of inflammation at the respiratory mucosa

The respiratory mucosa is responsible for gas exchange and is therefore, of necessity, exposed to airborne pathogens, allergens, and foreign particles. It has evolved a multi-faceted, physical and immune defense system to ensure that in the majority of instances, potentially injurious invaders are repelled. Inflammation, predominantly mediated by effector cells of the granulocyte lineage including neutrophils and eosinophils, is a form of immune defense. Where inflammation proves unable to remove an inciting stimulus, chronic inflammatory disease may supervene because of the potential for tissue damage conferred by the presence of large numbers of frustrated, activated granulocytes. Successful recovery from inflammatory disease and resolution of inflammation rely on the clearance of these cells. Ideally, they should undergo apoptosis prior to phagocytosis by macrophage, dendritic, or epithelial cells. The outcome of inflammation can have serious sequelae for the integrity of the respiratory mucosa leading to disease. Therapeutic strategies to drive resolution of inflammation may be directed at the induction of granulocyte apoptosis and the enhancement of granulocyte clearance.

Both TLR2 and TLR4 are required for the effective immune response in Staphylococcus aureus-induced experimental murine brain abscess

Toll-like receptors (TLRs) play central roles in the innate reaction to bacterial products and transmit specific immune responses against these pathogens. TLRs are expressed on numerous cell types, including innate immune cells, and on astrocytes, neurons, and microglial cells of the central nervous system (CNS). Lipoproteins and lipopolysaccharides are specifically recognized by TLR2 and TLR4, respectively. We examined the in vivo role of TLR2 and TLR4 in Staphylococcus aureus-induced brain abscess. Phenotypically, 87% of TLR2(-/-) mice and 43% of TLR4(-/-) mice died whereas all wild-type (WT) mice recovered. Clearance of bacteria from the CNS was significantly delayed in TLR2(-/-) mice compared with TLR4(-/-) and WT animals. Recruitment of granulocytes and macrophages to the CNS, as well as microglial activation and expansion, was up-regulated in TLR2(-/-) mice. Although inflammation persisted especially in the CNS of TLR2(-/-) mice, but also of TLR4(-/-) mice, WT mice terminated the infection more effectively. Collectively, these data show that the immune response to experimental S. aureus-induced brain abscess depends crucially on the recognition of S. aureus by TLR2 but that TLR4 is also required for an optimal intracerebral immune response in this disorder.

Impairment of apoptotic cell engulfment by pyocyanin, a toxic metabolite of Pseudomonas aeruginosa

RATIONALE

Cystic fibrosis lung disease is characterized by accumulation of apoptotic neutrophils, indicating impaired clearance of dying cells. Pseudomonas aeruginosa, the principal microbial pathogen in cystic fibrosis, manipulates apoptosis induction via production of toxic metabolites. Whether these metabolites, particularly pyocyanin, can also modulate apoptotic cell engulfment is unknown.

OBJECTIVES

To assess the effects of pyocyanin on apoptotic cell engulfment by macrophages in vitro and in vivo and to investigate potential mechanisms of the observed effects.

METHODS

Human monocyte-derived macrophages were treated with pyocyanin before challenge with apoptotic neutrophils, apoptotic Jurkat cells, or latex beads, and phagocytosis was assessed by light microscopy and flow cytometry. Effects of pyocyanin production on apoptotic cell clearance in vivo were assessed in a murine model, comparing infection by wild-type or pyocyanin-deficient P. aeruginosa. Oxidant production was investigated using fluorescent probes and pharmacologic inhibition and Rho GTPase signaling by immunoblotting and inhibitor studies.

MEASUREMENTS AND MAIN RESULTS

Pyocyanin treatment impaired macrophage engulfment of apoptotic cells in vitro, without inducing significant macrophage apoptosis, whereas latex bead uptake was preserved. Macrophage ingestion of apoptotic cells was reduced and late apoptotic/necrotic cells were increased in mice infected with pyocyanin-producing P. aeruginosa compared with the pyocyanin-deficient strain. Inhibition of apoptotic cell uptake involved intracellular generation of reactive oxygen species (ROS) and effects on Rho GTPase signaling. Antioxidants or blockade of Rho signaling substantially restored apoptotic cell engulfment.

CONCLUSIONS

These studies demonstrate that P. aeruginosa can manipulate the inflammatory microenvironment through inhibition of apoptotic cell engulfment, and suggest potential strategies to limit pulmonary inflammation in cystic fibrosis.

Histamine reverses IL-5-afforded human eosinophil survival by inducing apoptosis: pharmacological evidence for a novel mechanism of action of histamine

Eosinophils are essential inflammatory cells in the pathogenesis of asthma and atopic conditions. Histamine, released from mast cells and basophils in response to allergen exposure, is a critical mediator in the allergic response. Histamine exerts its effects via four unequivocally characterized histamine receptors, H(1-4). Several functions of eosinophils have previously been shown to be stimulated by histamine. However, its effects on eosinophil apoptosis are unknown. The aim of the present study was to resolve the effects of histamine on constitutive apoptosis of human eosinophils and on the survival-enhancing action of interleukin (IL)-5. Additional experiments were conducted to elucidate the histamine receptor(s) involved in any response seen and the associated signal transduction cascade. Human isolated peripheral blood eosinophils were cultured in the absence or presence of histamine, IL-5 and receptor antagonists/agonists or mediator inhibitors/analogues. Apoptosis was assessed by measuring the relative DNA content of propidium iodide (PI)-stained cells and the effects were confirmed by morphological analysis with bright field microscopy. Caspase activities were assessed by using commercial Caspase-Glo 3/7, 8 and 9 luminescence assays. Histamine (10-100 microM) partially reversed IL-5-induced human eosinophil survival by enhancing apoptosis as assessed by measuring the relative DNA content of PI-stained cells. This effect was not mediated through any of the known histamine receptors or through non-specific activation of 5-hydroxytryptamine receptors or alpha-adrenoceptors. Moreover, the reversal of IL-5-inhibited eosinophil apoptosis by histamine seemed not to utilize the conventional intracellular second-messenger pathways including cyclic AMP, protein kinase A or phospholipase C. Inhibition of caspase 6 and caspases 1, 10 or 12 reversed the effects of histamine but also inhibited apoptosis in general. In conclusion, the data presented herein indicate that histamine induces human eosinophil apoptosis in the presence of a survival-prolonging cytokine by a mechanism that does not apparently involve the activation of any of the currently known histamine receptor subtypes. The possibility exists that another, as yet unidentified, histamine receptor may exist in human eosinophils that regulates survival, although the participation of histamine receptor-independent mechanisms cannot be excluded.

Targeting the networks that underpin contiguous immunity in asthma and chronic obstructive pulmonary disease

Recent advances in the field of innate immunity have driven an important reappraisal of the role of these processes in airway disease. Various strands of evidence indicate that resident cells, such as macrophages and epithelial cells, have central importance in the initiation of inflammation. Macrophage activation has the potential to regulate not just typical aspects of innate immunity but also, via a variety of intricate cell-cell networks, adaptive responses and responses characterized by Th2-type cytokine production. In turn, such adaptive immune processes modify the phenotype and function of the innate immune system. Cooperative responses between monocytic cells and tissue cells are likely to be crucial to the generation of effective inflammatory responses, and a realization of the importance of these networks is providing a new way of identifying antiinflammatory therapies. Importantly, the repeated cycles of allergic and nonallergic inflammation that comprise chronic human airway disease are not necessarily well described by current terminology, and we propose and describe a concept of contiguous immunity, in which continual bidirectional cross-talk between innate and adaptive immunity describes disease processes more accurately.