Neutrophil phenotypes in chronic lung disease

Correlation of neutrophil percentage-to-albumin ratio with lung function in American adults: a population study

BACKGROUND

Chronic respiratory diseases pose a significant threat to global health, underscoring the urgent need for effective preventative and therapeutic interventions. The neutrophil-to-albumin ratio (NPAR), an emerging biomarker for inflammation and nutritional status, has shown promising associations with respiratory health, necessitating an investigation into its potential for predicting lung function decline.

OBJECTIVE

This study aimed to delineate the relationship between the NPAR and pulmonary function within a sample of the American adult population and assess the viability of the NPAR as a prognostic indicator for compromised lung function.

METHODS

With data available from the National Health and Nutrition Examination Survey (NHANES) for the years 2007 to 2012, 10,055 American adults who met the exclusion criteria were included in the current study. Multivariate linear regression, smoothed curve fitting, and subgroup analyses were applied to evaluate the associations observed between the NPAR and lung function indicators.

RESULTS

Even after accounting for all potential confounding factors, a significant inverse relationship persisted between the NPAR and key lung function indicators, including forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and peak expiratory flow rate (PEF). This association remained robust even after potential confounding factors were considered. Subgroup analysis revealed that the negative correlation was more pronounced in certain demographic groups, such as young individuals, males, and current smokers. The study also revealed an "N-shaped" relationship between the NPAR and fractional exhaled nitric oxide (FENO), suggesting that the NPAR may play a role in promoting airway inflammation.

CONCLUSIONS

A significant correlation between the NPAR and the decline in lung function among American adults was revealed in this research, emphasizing the potential clinical relevance of the NPAR as a respiratory health biomarker, as well as the importance of considering systemic inflammation in the management and prevention of respiratory disorders.

Understanding CXCR2 antagonism with a dynamic allosteric ternary complex model

The CXC chemokine receptor 2 (CXCR2) antagonist SB265610 displays different patterns of antagonism using in vitro binding and cell-based assays. In addition, CXCR2 antagonists, although likely sharing a similar allosteric binding mechanism, display different patterns in the same cell-based assays. Furthermore, clinical studies with CXCR2 antagonists had mixed success in demonstrating target modulation and efficacy, despite favorable exposures based on published binding affinities. Herein, we aimed to understand the mechanism leading to these apparent inconsistencies with a dynamic allosteric ternary complex model. The model was applied in analyzing both in vitro data and clinical neutrophil counts data of CXCR2 antagonists. We extended previous hypotheses into a unified hypothesis, which postulates that, although allosteric binding of a CXCR2 antagonist is not affected by the endogenous agonist, the antagonism is surmountable as the antagonist loses its potency with increased concentrations of endogenous agonist because of the hyperbolic relationship between agonist-occupied receptor and biological response (which is possibly a result of receptor reserve). Antagonists with slow binding kinetics are apparently insurmountable, but only under unsteady-state conditions. Dynamic allosteric ternary complex model following this hypothesis can describe both in vitro and clinical data of CXCR2 antagonists. The inconsistent patterns of CXCR2 antagonism are interpreted as potential receptor reserve in cell-based assays with unsteady-state binding for some compounds. Because the binding process likely reaches quasi steady state in clinical trials, the lack of pharmacology effect for some antagonists is due to suboptimal potency rather than fast binding kinetics. This model may be applicable to other receptors to help predict clinical responses of allosteric antagonists. SIGNIFICANCE STATEMENT: Known CXC chemokine receptor 2 (CXCR2) antagonists are allosteric and do not compete with endogenous agonists. However, this antagonism is surmountable in some assays, but not others, and for some antagonists, but not others. This study proposes a unified hypothesis to explain observed inconsistent antagonism patterns and apply a mechanistic model to link in vitro findings with clinical outcomes. This study improves our understanding of the pharmacology of CXCR2 antagonists and facilitates the future discovery of antagonists with similar mechanisms for CXCR2 or other G protein-coupled receptors.

Enhanced insights into the neutrophil-driven immune mechanisms during Mycoplasma pneumoniae infection

Mycoplasma pneumoniae (MP) infections represent a significant component of community-acquired pneumonia, especially in children, invoking a complex neutrophil-mediated immune response, crucial for host defense. This review consolidates current knowledge on the role of neutrophils in MP infection, focusing on their recruitment, migration and activation, as well as the molecular mechanisms underpinning these processes. Significant findings indicate that specific bacterial components, notably CARDS toxin and lipoproteins, intensify neutrophil recruitment via signaling pathways, including the IL-23/IL-17 axis and G-CSF. Furthermore, neutrophils engage in a series of responses, including phagocytosis, degranulation and NETosis, to combat infection effectively. However, dysregulated neutrophil activity can lead to exacerbated lung injury, highlighting the delicate balance required in neutrophil responses. Age and immunodeficiency also emerge as critical factors influencing the severity of MP infections. This review emphasizes the dual role of neutrophils in both defending against and exacerbating MP infections, suggesting that targeted therapeutic strategies could mitigate the adverse effects while enhancing beneficial neutrophil functions.

The role of neutrophils in chronic cough

Chronic cough is a common disorder lasting more than 8 weeks and affecting all age groups. The evidence supporting the role of neutrophils in chronic cough pathology is based on many patients with chronic cough developing airway neutrophilia. How neutrophils influence the development of chronic cough is unknown. However, they are likely involved in multiple aspects of cough etiology, including promoting airway inflammation, airway remodeling, hyper-responsiveness, local neurogenic inflammation, and other possible mechanisms. Neutrophilic airway inflammation is also associated with refractory cough, poor control of underlying diseases (e.g., asthma), and insensitivity to cough suppressant therapy. The potential for targeting neutrophils in chronic cough needs exploration, including developing new drugs targeting one or more neutrophil-mediated pathways or altering the neutrophil phenotype to alleviate chronic cough. How the airway microbiome differs, plays a role, and interacts with neutrophils in different cough etiologies is poorly understood. Future studies should focus on understanding the relationship between the airway microbiome and neutrophils.

Blood Neutrophil Counts Define Specific Clusters of Bronchiectasis Patients: A Hint to Differential Clinical Phenotypes

We sought to investigate differential phenotypic characteristics according to neutrophil counts, using a biostatistics approach in a large-cohort study from the Spanish Online Bronchiectasis Registry (RIBRON). The 1034 patients who met the inclusion criteria were clustered into two groups on the basis of their blood neutrophil levels. Using the Mann-Whitney U test to explore potential differences according to FACED and EFACED scores between the two groups, a neutrophil count of 4990 cells/µL yielded the most balanced cluster sizes: (1) above-threshold (n = 337) and (2) below-threshold (n = 697) groups. Patients above the threshold showed significantly worse lung function parameters and nutritional status, while systemic inflammation levels were higher than in the below-threshold patients. In the latter group, the proportions of patients with mild disease were greater, while a more severe disease was present in the above-threshold patients. According to the blood neutrophil counts using biostatistics analyses, two distinct clinical phenotypes of stable patients with non-CF bronchiectasis were defined. Patients falling into the above-threshold cluster were more severe. Severity was characterized by a significantly impaired lung function parameters and nutritional status, and greater systemic inflammation. Phenotypic profiles of bronchiectasis patients are well defined as a result of the cluster analysis of combined systemic and respiratory variables.

Overview of positron emission tomography in functional imaging of the lungs for diffuse lung diseases

Positron emission tomography (PET) is a quantitative molecular imaging modality increasingly used to study pulmonary disease processes and drug effects on those processes. The wide range of drugs and other entities that can be radiolabeled to study molecularly targeted processes is a major strength of PET, thus providing a noninvasive approach for obtaining molecular phenotyping information. The use of PET to monitor disease progression and treatment outcomes in DLD has been limited in clinical practice, with most of such applications occurring in the context of research investigations under clinical trials. Given the high costs and failure rates for lung drug development efforts, molecular imaging lung biomarkers are needed not only to aid these efforts but also to improve clinical characterization of these diseases beyond canonical anatomic classifications based on computed tomography. The purpose of this review article is to provide an overview of PET applications in characterizing lung disease, focusing on novel tracers that are in clinical development for DLD molecular phenotyping, and briefly address considerations for accurately quantifying lung PET signals.

Respiratory exposure to PM2.5 soluble extract induced chronic lung injury by disturbing the phagocytosis function of macrophage

Exposure to airborne urban particles is a contributing factor for the development of multiple types of respiratory diseases; its pathological role as a cause of lung injury is still unclear. In this study, PM2.5 soluble extract was collected, and its toxicological effect on lung pathological changes was examined. To assess its pathological mechanism, Human Monocyte-Like Cell Line, THP-1, and mouse macrophage, RAW264.7, were used to determine the effects of PM2.5 soluble extract on cell toxicity, phagocytosis, and transcriptome. We found that PM2.5 soluble extract exposure activated NF-κB and MAPK signaling pathways, then induces the production of pro-inflammatory cytokines. RNA-seq results showed that the transcription profiles, including 1213 genes, have been changed in responses to PM2.5 exposure. Additionally, PM2.5 led to phagocytic dysfunction, which may exacerbate the cause of lung injury. Exposure to PM2.5 soluble extract triggers the death of respiratory macrophages, impairs its phagocytosis capacity, thus delaying the inflammatory cell clearance in the lung, which results in chronic lung injury.

Involvement of the Innate Immune System in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common, socially significant disease characterized by progressive airflow limitation due to chronic inflammation in the bronchi. Although the causes of COPD are considered to be known, the pathogenesis of the disease continues to be a relevant topic of study. Mechanisms of the innate immune system are involved in various links in the pathogenesis of COPD, leading to persistence of chronic inflammation in the bronchi, their bacterial colonization and disruption of lung structure and function. Bronchial epithelial cells, neutrophils, macrophages and other cells are involved in the development and progression of the disease, demonstrating multiple compromised immune mechanisms.

Spontaneous formation of neutrophil extracellular traps is associated with autophagy

Neutrophils release neutrophil extracellular traps (NETs), via NETosis, as a defense mechanism against pathogens. Neutrophils can release NETs spontaneously; however, the mechanisms underlying spontaneous NETosis remain unclear. Neutrophils isolated from healthy donors were tested for NET formation and autophagy at 1, 6, 12, and 24 h after incubation. Autophagy response was evaluated in response to various autophagy inducers and inhibitors. The relationship between autophagy and NETosis was detected in vivo using an ovalbumin-induced mouse model of asthma. We found that the increase in the proportion of spontaneous NETosis was time-dependent. The number of autophagy-positive cells also increased over time and LC3B protein played an integral role in NET formation. Trehalose (an inducer of mTOR-independent autophagy) treatment significantly increased NET formation, whereas rapamycin (an mTOR-dependent autophagy inducer) did not increase NET release by neutrophils. Compared with the control group, 3-methyladenine (an autophagy sequestration inhibitor) and hydroxychloroquine sulfate (autophagosome-lysosome fusion inhibitor) treatments significantly reduced the percentage of NET-positive cells. In vivo studies on ovalbumin-induced asthma lung sections revealed NETs and LC3B and citH3 proteins were found to co-localize with DNA. Our findings suggest that autophagy plays a crucial role in aging-related spontaneous NETosis.

Inflammation, Ageing and Diseases of the Lung: Potential therapeutic strategies from shared biological pathways

Lung diseases disproportionately affect elderly individuals. The lungs form a unique environment: a highly elastic organ with gaseous exchange requiring the closest proximity of inhaled air containing harmful agents and the circulating blood volume. The lungs are highly susceptible to senescence, with age and "inflammageing" creating a pro-inflammatory environment with a reduced capacity to deal with challenges. Whilst lung diseases may have disparate causes, the burden of ageing and inflammation provides a common process which can exacerbate seemingly unrelated pathologies. However, these shared pathways may also provide a common route to treatment, with increased interest in drugs which target ageing processes across respiratory diseases. In this review, we will examine the evidence for the increased burden of lung disease in older adults, the structural and functional changes seen with advancing age and assess what our expanding knowledge of inflammation and ageing pathways could mean for the treatment of lung disease.

Efficacy and specificity of different methods for human neutrophil extracellular trap isolation and handling

Introduction

Although in vitro incubation of various cell types with neutrophil extracellular traps (NETs) is commonly used to investigate the influence of NETs on cellular function, it is unclear which human NET isolation and handling protocol is superior. The present study sought to assess the efficacy (yield and purity) and efficiency (time taken) of different available human NET isolation and handling protocols.

Material and methods

Neutrophils isolated from human blood were stimulated using phorbol 12-myristate 13-acetate. Four distinct protocols were used to isolate NETs, and the yield was quantified using fluorimetry.

Results

Addition of the restriction enzyme AluI prior to centrifugation is unique to the most effective NET isolation method, yielding a NET concentration of 1077.22 ±229.04 ng/ml (at 523 nm) measured with PicoGreen. Immediate centrifugation to pellet neutrophils is unique to the most efficient method.

Conclusions

Balancing protocol efficacy and efficiency, the method incorporating centrifugation for 5 min at 450 × γ to pellet neutrophils is more than adequate.

Leukocyte Function in COPD: Clinical Relevance and Potential for Drug Therapy

Chronic obstructive pulmonary disease (COPD) is a progressive lung condition affecting 10% of the global population over 45 years. Currently, there are no disease-modifying treatments, with current therapies treating only the symptoms of the disease. COPD is an inflammatory disease, with a high infiltration of leukocytes being found within the lung of COPD patients. These leukocytes, if not kept in check, damage the lung, leading to the pathophysiology associated with the disease. In this review, we focus on the main leukocytes found within the COPD lung, describing how the release of chemokines from the damaged epithelial lining recruits these cells into the lung. Once present, these cells become active and may be driven towards a more pro-inflammatory phenotype. These cells release their own subtypes of inflammatory mediators, growth factors and proteases which can all lead to airway remodeling, mucus hypersecretion and emphysema. Finally, we describe some of the current therapies and potential new targets that could be utilized to target aberrant leukocyte function in the COPD lung. Here, we focus on old therapies such as statins and corticosteroids, but also look at the emerging field of biologics describing those which have been tested in COPD already and potential new monoclonal antibodies which are under review.

Classes of drugs that target the cellular components of inflammation under clinical development for COPD

INTRODUCTION

The persistent inflammation that characterizes COPD and affects its natural course also impacting on symptoms has prompted research to find molecules that can regulate the inflammatory process but still available anti-inflammatory therapies provide little or no benefit in COPD patients. Consequently, numerous anti-inflammatory molecules that are effective in animal models of COPD have been or are being evaluated in humans.

AREAS COVERED

In this article we describe several classes of drugs that target the cellular components of inflammation under clinical development for COPD.

EXPERT OPINION

Although the results of many clinical trials with new molecules have often been disappointing, several studies are underway to investigate whether some of these molecules may be effective in treating specific subgroups of COPD patients. Indeed, the current perspective is to apply a more personalized treatment to the patient. This means being able to better define the patient's inflammatory state and treat it in a targeted manner. Unfortunately, the difficulty in translating encouraging experimental data into human clinical trials, the redundancy in the effects induced by signal-transmitting substances and the nonspecific effects of many classes that are undergoing clinical trials, do not yet allow specific inflammatory cell types to be targeted.

Catching "Early" COPD - The Diagnostic Conundrum

Chronic obstructive pulmonary disease (COPD) remains a leading cause of morbidity and mortality worldwide. Despite this, there has been little progress so far in terms of disease-modifying therapies over the last few decades and this is in part due to poor understanding of the definition and mechanisms surrounding early disease before it becomes established and increasingly complex. In this review, the nuances and difficulty in defining early disease in COPD are discussed. There are clear benefits in identifying patients early; however, usually diagnosis is made in the presence of significant lung damage. We consider what can be learned of early disease from COPD studies and highlight the lack of inclusion of young smokers (who may be at risk of COPD) or those with mild disease. We discuss promising clinical measures that are being used in an effort to detect early disease. These include symptom assessment, lung physiology measures and computed tomography (CT) imaging modalities. There is emerging evidence for the role of neutrophils and their proteinases in early COPD. This may form an important biomarker to investigate the pathophysiological processes of early COPD. Given the importance of the early disease, it is recommended that future COPD studies focus on capturing the earliest manifestations of disease, to understand the initiating mechanisms and to identify novel treatment targets.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

The Secretive Life of Neutrophils Revealed by Intravital Microscopy

Neutrophils are the most abundant circulating leukocyte within the blood stream and for many years the dogma has been that these cells migrate rapidly into tissues in response to injury or infection, forming the first line of host defense. While it has previously been documented that neutrophils marginate within the vascular beds of the lung and liver and are present in large numbers within the parenchyma of tissues, such as spleen, lymph nodes, and bone marrow (BM), the function of these tissue resident neutrophils under homeostasis, in response to pathogen invasion or injury has only recently been explored, revealing the unexpected role of these cells as immunoregulators or immune helpers and also unraveling their heterogeneity and plasticity. Neutrophils are highly motile cells and the use of intravital microscopy (IVM) to image cells within their environment with little manipulation has dramatically increased our understanding of the function, migratory behavior, and interaction of these short-lived cells with other innate and adaptive immune cells. Contrary to previous dogma, these studies have shown that marginated and tissue resident neutrophils are the first responders to pathogens and injury, critical in limiting the spread of infection and contributing to the orchestration of the subsequent immune response. The interplay of neutrophils, with other neutrophils, leukocytes, and stroma cells can also modulate and tune their early and late response in order to eradicate pathogens, minimize tissue damage, and, in certain circumstances, contribute to tissue repair. In this review, we will follow the extraordinary journey of neutrophils from their origin in the BM to their death, exploring their role as tissue resident cells in the lung, spleen, lymph nodes, and skin and outlining the importance of neutrophil subsets, their functions under homeostasis, and in response to infection. Finally, we will comment on how understanding these processes in greater detail at a molecular level can lead to development of new therapeutics.

Neutrophil Modulation in Alpha-1 Antitrypsin Deficiency

Neutrophils have been implicated in the pathogenesis of alpha-1 antitrypsin deficiency (AATD) since the first descriptions of the disease. Neutrophil proteinases can cause all lung manifestations of AATD, from small airways destruction, to emphysema, to chronic bronchitis and airflow obstruction. Initially, it was proposed that neutrophil functions were normal in AATD, responding in an initially physiological manner to a high burden of pulmonary inflammation. More recent studies have shed new light on this, describing changes in neutrophil responses (a modulation of usual cellular functions) in the presence of inflammation or infection which might enhance tissue damage while impeding bacterial clearance, providing some evidence to support there being an AATD neutrophil phenotype. Many facets of neutrophil function in AATD can be explained by the loss of alpha-1 antitrypsin (AAT) in diverse biological processes. If this were the only reason for altered neutrophil functions, one would predict similar disease presentation across affected people. However, this is not the case. Despite similar (low) levels of AAT, lung disease is extremely variable in AATD, with some patients suffering a significant burden of lung disease and some much less, irrespective of smoking habits and, in some cases, despite augmentation therapy. This review will explore how complex neutrophil responses are and how they are altered with age, inflammation and AATD. Further, it will discuss the need to understand more completely which aspects of AATD-associated disease are driven by neutrophils and how patients more susceptible to neutrophil dysfunction could be identified to potentially stratify treatment approaches.

CXCR2 antagonist for patients with chronic obstructive pulmonary disease with chronic mucus hypersecretion: a phase 2b trial

Background

Oral CXC chemokine receptor 2 (CXCR2) antagonists have been shown to inhibit neutrophil migration and activation in the lung in preclinical and human models of neutrophilic airway inflammation. A previous study with danirixin, a reversible CXCR2 antagonist, demonstrated a trend for improved respiratory symptoms and health status in patients with COPD.

Methods

This 26-week, randomised, double-blind, placebo-controlled phase IIb study enrolled symptomatic patients with mild-to-moderate COPD at risk for exacerbations. Patients received danirixin 5, 10, 25, 35 or 50 mg twice daily or placebo in addition to standard of care. Primary end-points were the dose response of danirixin compared with placebo on the incidence and severity of respiratory symptoms (Evaluating Respiratory Symptoms in COPD [E-RS:COPD] scores) and safety. Secondary end-points included the incidence of moderate-severe exacerbations, health status (COPD Assessment test, CAT) and health-related quality of life HRQoL (St. George Respiratory Questionnaire-COPD, SGRQ-C).

Results

A total of 614 participants were randomized to treatment. There were no improvements in E-RS:COPD, CAT or SGRQ-C scores in participants treated with any dose of danirixin compared to placebo; a larger than expected placebo effect was observed. There was an increased incidence of exacerbation in the danirixin-treated groups and an increased number of pneumonias in participants treated with danirixin 50 mg.

Conclusions

The robust placebo and study effects prohibited any conclusions on the efficacy of danirixin. However, the absence of a clear efficacy benefit and the observed increase in exacerbations in danirixin-treated groups suggests an unfavorable benefit-risk profile in patients with COPD.

Trial registration

This study was registered with clinicaltrials.gov, NCT03034967.

Importance of validating antibody panels: Anti-PD-L1 clone binds AF700 fluorophore

Researchers routinely use antibodies to assess the expression levels of proteins on the surface or intracellularly in a variety of different cell types. In this current study we highlight the importance of careful validation of antibodies for analysis of protein expression by flow cytometry and how failure to do so can significantly impact the interpretation of the data generated leading to false-positive results. There has been increasing awareness of the role the programmed death receptor 1 (PD-1) pathway plays in health and disease and a potential that programme death ligand 1 (PD-L1) may play a role in inflammatory disease. We aimed to investigate PD-L1 expression on human neutrophils isolated from healthy individuals and patients diagnosed with chronic obstructive pulmonary disease (COPD). We observed an increase in surface expression of PD-L1 by human neutrophils when incubated with AlexaFluor™700-conjugated anti-CD16. Through careful interrogation and antibody validation, we found a novel interaction between a commercially available anti-PD-L1 antibody and the AlexaFluor™700 fluorophore, resulting in this observed increase in PD-L1 signal. Surface expression of PD-L1 was not observed on neutrophils from healthy volunteers or patients with COPD when clone 29E.2A3 of anti-PD-L1 was not used with AlexaFluor™700-conjugated anti-CD16. This highlights the importance of robust antibody validation to ensure antibody compatibility in the context of multi-parametric flow cytometry panels. We also show that, without these validation experiments, novel neutrophil phenotypes could be falsely reported - an important consideration when there is increasing interest in neutrophil heterogeneity.