Neutrophil autophagy and extracellular DNA traps contribute to airway inflammation in severe asthma

Neutrophil Extracellular Trapping Network Promotes the Pathogenesis of Neutrophil-associated Asthma through Macrophages

Asthma is a complex airway inflammatory disease that can be roughly classified into eosinophilic phenotype and non-eosinophilic phenotype. Most of the latter manifested as airway inflammation dominated by neutrophil infiltration, namely neutrophil-dominated asthma (NA). Neutrophil extracellular trapping (NETs) is a newly discovered antimicrobial mechanism of neutrophils; however, NETs can not only resist killing pathogenic microorganisms, but also promote tissue damage and autoimmune response. In the present study, we successfully established NA model in C57BL/6 mice and observed the increased formation of NETs. In NA mice, the free DNA abundance, the airway resistance, the cell numbers (total cell number, macrophage number, and neutrophil number), and inflammatory cytokine levels were significantly increased while the lung dynamic compliance was significantly reduced. After DNase I treatment, the above indexes in NA mice were all improved. In NA mice, either treatment with macrophage scavenger or IL-1β neutralizing antibody also improved the above-described indexes. In vitro, in human peripheral blood-derived neutrophils, PMA treatment significantly increased the formation of NETs. Furthermore, in macrophages differentiated from THP-1 monocytes, LPS or isolated NETs both significantly increased the levels of cytokines. In conclusion, NETs can stimulate macrophages to secrete IL-1β, which promotes neutrophils infiltration in the airway; infiltrated neutrophils, in turn, generates NETs, which can amplify the tissue damage caused by NETs and macrophages, inducing and aggravating NA.

Single Nucleotide and Copy-Number Variants in IL4 and IL13 Are Not Associated with Asthma Susceptibility or Inflammatory Markers: A Case-Control Study in a Mexican-Mestizo Population

BACKGROUND

Asthma is a complex and chronic inflammatory airway disease. Asthma's etiology is unknown; however, genetic and environmental factors could affect disease susceptibility. We designed a case-control study aimed to evaluate the role of single-nucleotide polymorphisms (SNP), and copy-number variants (CNV) in the IL4 and IL13 genes in asthma susceptibility and their participation in plasma cytokine levels depending on genotypes Methods: We include 486 subjects, divided into asthma patients (AP, n = 141) and clinically healthy subjects (CHS, n = 345). We genotyped three SNP, two in the IL4 and two in the IL13 gene; also, two CNVs in IL4. The IL-4, IL-13 and IgE plasma levels were quantified.

RESULTS

Biomass-burning smoke exposure was higher in the AP group compared to CHS (47.5% vs. 20.9%; p < 0.01, OR = 3.4). No statistical differences were found in the genetic association analysis. In both CNV, we only found the common allele. For the analysis of IL-4, IL-13, and IgE measures stratified by genotypes, no significant association or correlation was found.

CONCLUSION

In the Mexican-mestizo population, SNPs neither CNVs in IL4 nor IL13 are associated with asthma susceptibility or involved serum cytokine levels. Biomass-burning smoke is a risk factor in asthma susceptibility.

Autophagy-driven NETosis is a double-edged sword - Review

Autophagy is a cellular mechanism responsible for delivering protein aggregates or damaged organelles to lysosomes for degradation. It is also simultaneously a precise regulatory process, which is crucial for dealing with hunger, oxidative stress, and pathogen defense. Neutrophil Extracellular Traps (NETs), which form a part of a newly described bactericidal process, are reticular structures composed of a DNA backbone and multiple functional proteins, formed via a process known as NETosis. NETs exert their anti-infection activity by capturing pathogenic microorganisms, inhibiting their spread and inactivating virulence factors. However, NETs may also activate an immune response in non-infectious diseases, leading to tissue damage. Although the mechanism underlying this phenomenon is unclear, a large number of studies have suggested that autophagy may be involved. Autophagy-mediated NETs not only induce inflammation and tissue damage, but can also lead to cell senescence, malignant transformation, and cell death. Autophagy-dependent NETs also play a beneficial role in the hostwith respect to pathogen clearance and immune defense. Through careful review of the literature, we have found that the distinct roles of autophagy in NETosis may be dependent on the extent of autophagy and the specific manner in which it was induced. This article summarizes numerous recent studies, and reviews the role of autophagy-driven NETosis in various diseases, in the hope that this will lead to the development of more effective treatments.

Neutrophil activation in occupational asthma

PURPOSE OF REVIEW

The aim of this review is to emphasize the role of neutrophils in patients with occupational asthma. This review facilitates a better understanding, accurate diagnosis, and proper management of asthmatic reactions provoked at the workplace.

RECENT FINDINGS

Increased recruitment and infiltration of neutrophils are found in patients with occupational asthma. Activated neutrophils release several mediators including pro-inflammatory cytokines and extracellular traps, leading to stimulation of airway epithelium and other inflammatory cells.

SUMMARY

New insights into neutrophils in the pathogenesis of occupational asthma may provide a novel approach to the individual patient with occupational asthma.

Autophagy in chronic lung disease

The development of chronic lung disease occurs as a consequence of multiple cellular events that involve an initial insult which often leads to the development of chronic inflammation, and the dysregulation of cellular proliferation and cell death mechanisms. Multiple cell types in the lung are key to the respiratory and protective/barrier functions necessary to manage the chronic exposures to environmental, mechanical, and oxidative stressors. Autophagy is essential to lung development and homeostasis, as well as the prevention and development of disease. The cellular process involves the collection and removal of unwanted organelles and proteins through lysosomal degradation. In recent years, investigations have addressed the roles of autophagy and selective autophagy in numerous chronic lung diseases. Here, we highlight recent advances on the role of autophagy in the pathogenesis of asthma, chronic obstructive pulmonary disease and emphysema, pulmonary arterial hypertension, and idiopathic pulmonary fibrosis.

Neutrophil extracellular traps activate IL-8 and IL-1 expression in human bronchial epithelia

Neutrophil extracellular traps (NETs) provide host defense but can contribute to the pathobiology of diverse human diseases. We sought to determine the extent and mechanism by which NETs contribute to human airway cell inflammation. Primary normal human bronchial epithelial cells (HBEs) grown at air-liquid interface and wild-type (wt)CFBE41o- cells (expressing wtCFTR) were exposed to cell-free NETs from unrelated healthy volunteers for 18 h in vitro. Cytokines were measured in the apical supernatant by Luminex, and the effect on the HBE transcriptome was assessed by RNA sequencing. NETs consistently stimulated IL-8, TNF-α, and IL-1α secretion by HBEs from multiple donors, with variable effects on other cytokines (IL-6, G-CSF, and GM-CSF). Expression of HBE RNAs encoding IL-1 family cytokines, particularly IL-36 subfamily members, was increased in response to NETs. NET exposure in the presence of anakinra [recombinant human IL-1 receptor antagonist (rhIL-1RA)] dampened NET-induced changes in IL-8 and TNF-α proteins as well as IL-36α RNA. rhIL-36RA limited the increase in expression of proinflammatory cytokine RNAs in HBEs exposed to NETs. NETs selectively upregulate an IL-1 family cytokine response in HBEs, which enhances IL-8 production and is limited by rhIL-1RA. The present findings describe a unique mechanism by which NETs may contribute to inflammation in human lung disease in vivo. NET-driven IL-1 signaling may represent a novel target for modulating inflammation in diseases characterized by a substantial NET burden.

New insights in neutrophilic asthma

PURPOSE OF REVIEW

Recent advances in both murine models and clinical research of neutrophilic asthma are improving our understanding on the etiology and pathophysiology of this enigmatic endotype of asthma. We here aim at providing an overview of our current and latest insights on the pathophysiology and treatment of neutrophilic asthma.

RECENT FINDINGS

Activation of the NLRP3 inflammasome pathway with increased IL-1β has been demonstrated in various studies involving patients with asthma. It has been suggested that type 3 innate lymphoid cells are implicated in the inflammatory cascade leading to neutrophilic inflammation. The role of neutrophil extracellular traps is only at the start of being understood and might be an attractive novel therapeutic target. A diverse panel of nonallergic stimuli, such as cigarette smoke, intensive exercise, cold air or saturated fatty acids, have been linked with neutrophilic airway inflammation. Azithromycin treatment could reduce asthma exacerbations and quality of life in patients with persistent asthma.

SUMMARY

Research of the last few years has accelerated our insights in mechanisms underlying neutrophilic asthma. This is in stark contrast with the lack of efficacy of different therapies targeting neutrophil chemotaxis and/or signalling cascade, such as IL-17A or CXCR2. Macrolide therapy might be a useful add-on therapy for patients with persistent asthma.

Autophagy-mediated regulation of neutrophils and clinical applications

Autophagy, an adaptive catabolic process, plays a cytoprotective role in enabling cellular homeostasis in the innate and adaptive immune systems. Neutrophils, the most abundant immune cells in circulation, are professional killers that orchestrate a series of events during acute inflammation. The recent literature indicates that autophagy has important roles in regulating neutrophil functions, including differentiation, degranulation, metabolism and neutrophil extracellular trap formation, that dictate neutrophil fate. It is also becoming increasingly clear that autophagy regulation is critical for neutrophils to exert their immunological activity. However, evidence regarding the systematic communication between neutrophils and autophagy is insufficient. Here, we provide an updated overview of the function of autophagy as a regulator of neutrophils and discuss its clinical relevance to provide novel insight into potentially relevant treatment strategies.

Role of airway epithelial cells in the development of different asthma phenotypes

The term (bronchial) asthma describes a disorder syndrome that comprises several disease phenotypes, all characterized by chronic inflammation in the bronchial epithelium, with a variety of subsequent functional consequences. Thus, the epithelium in the conducting airways is the main localization of the complex pathological changes in the disease. In this regard, bronchial epithelial cells are not passively affected by inflammatory mechanisms induced by immunological processes but rather actively involved in all steps of disease development from initiation and perpetuation to chronification. In recent years it turned out that bronchial epithelial cells show a high level of structural and functional diversity and plasticity with epigenetic mechanisms playing a crucial role in the regulation of these processes. Thus, it is quite reasonable that differential functional activities of the bronchial epithelium are involved in the development of different asthma phenotypes and/or stages of disease. The current knowledge on this topic will be discussed in this review article.

Inhibitors of nitric oxide synthase can reduce extracellular traps from neutrophils in asthmatic children in vitro

AIM

This study aimed to explore the link between neutrophil extracellular traps (NETs) and childhood asthma, to investigate the ability of nitric oxide (NO) to induce NETs in asthmatic children and find inhibitors to reduce NETs in the NO synthesis pathway.

METHODS

A total of 49 children with mild persistent asthma were included in the study and 20 healthy children's blood samples were collected as healthy controls. Children with asthma were divided into symptomatic and asymptomatic groups according to the presence or absence of symptoms on the day of blood collection. Neutrophils in peripheral blood were isolated and plasma was preserved. NO donor (sodium nitroferricyanide(III) dehydrate [SNP]) could provide NO and proved by a fluorescent probe. A PicoGreen Kit was used to detect the NETs quantificationally. Fluorescence microscopy prepared to observe the main structures of NETs. We measured NETs components (extracellular free double-stranded DNA [dsDNA]) in healthy, symptomatic and asymptomatic groups' plasma samples, and we compared the ability of SNP with phosphate-buffered saline, lipopolysaccharides (LPS), and phorbol 12-myristate 13-acetate (PMA) to induce NETs. NO synthase (NOS) inhibitors were added to see the impact on NETs formation.

RESULTS

Plasma was obtained from all blood samples of 69 children. The neutrophils of 40 asthmatic and 20 healthy children were successfully obtained, the recovery rate was over 95%, and the cell activity was over 80%. There was higher extracellular free dsDNA in the plasma of symptomatic group (n = 27) than asymptomatic group (n = 22) and healthy group (n = 20; P < .05). Studies on neutrophils from 40 children with asthma found that NO can be produced by adding SNP, PMA, and LPS. SNP could induce NETs with dose- and time-dependent. PMA (160 nM) had the strongest ability to induce NETs, LPS (200 ng/mL) followed, SNP (200 µM) was the weakest (P < .05), and the amount of NETs in the asthma group was significantly higher than that in the healthy group (P < .05). NOS inhibitors had the same blocking capacity for PMA- and LPS-induced NETs (P > .05), while NG-nitro- l-arginine methyl ester (500 µM) had the strongest inhibitory effect on SNP induction with time-dependent (P < .05). Inducible NOS was found in the NETs structure.

CONCLUSION

Children with asthma had higher levels of NETs in peripheral blood, especially when they had asthma symptoms. We verified the ability of NO to induce NETs, and found neutrophils from asthmatic children can produce more NETs in vitro. NOS inhibitors blocked this process may provide new therapeutic targets for childhood asthma.

Neutrophil extracellular traps in breast cancer and beyond: current perspectives on NET stimuli, thrombosis and metastasis, and clinical utility for diagnosis and treatment

The formation of neutrophil extracellular traps (NETs), known as NETosis, was first observed as a novel immune response to bacterial infection, but has since been found to occur abnormally in a variety of other inflammatory disease states including cancer. Breast cancer is the most commonly diagnosed malignancy in women. In breast cancer, NETosis has been linked to increased disease progression, metastasis, and complications such as venous thromboembolism. NET-targeted therapies have shown success in preclinical cancer models and may prove valuable clinical targets in slowing or halting tumor progression in breast cancer patients. We will briefly outline the mechanisms by which NETs may form in the tumor microenvironment and circulation, including the crosstalk between neutrophils, tumor cells, endothelial cells, and platelets as well as the role of cancer-associated extracellular vesicles in modulating neutrophil behavior and NET extrusion. The prognostic implications of cancer-associated NETosis will be explored in addition to development of novel therapeutics aimed at targeting NET interactions to improve outcomes in patients with breast cancer.

Developments in the field of allergy in 2017 through the eyes of Clinical and Experimental Allergy

In this article, we described the development in the field of allergy as described by Clinical and Experimental Allergy in 2017. Experimental models of allergic disease, basic mechanisms, clinical mechanisms, allergens, asthma and rhinitis and clinical allergy are all covered.

Transforming growth factor-β1 and eosinophil-derived neurotoxins contribute to the development of work-related respiratory symptoms in bakery workers

Background

In baker's asthma previous studies suggest that adaptive and innate immunity are involved in the development of work-related respiratory symptoms (WRS), where we hypothesized that epithelial cells derive airway inflammation through modulating the release of inflammatory cytokines. Thus, we conducted this study to investigate the role of epithelial cell-derived cytokines in the development of WRS among bakery workers.

Methods

We recruited 385 wheat-exposed subjects with WRS (WRS+)/without WRS (WRS-) working in a single industry and 243 unexposed controls from Ajou Medical Center (Suwon, South Korea). Levels of epithelial cell-derived cytokines (interleukin [IL-8], transforming growth factor-β1 [TGF-β1], eotaxin-2) and inflammatory mediators (eosinophil-derived neurotoxins [EDN]) in sera or cell-free supernatants were measured by ELISA. Human airway epithelial cells (HAECs), A549, were stimulated by wheat flour extracts and co-cultured with peripheral blood neutrophils isolated from 4 asthmatic patients.

Results

Serum TGF-β1 levels were significantly lower in exposed subjects than in unexposed controls, in the WRS+ group than in the WRS- group (P < 0.001 for each). The WRS+ group had a significantly higher level of serum EDN than the WRS- group (P < 0.001). Serum TGF-β1 and EDN levels predicted the development of WRS in exposed subjects (area under the curve [AUC] = 0.719, 72.4% sensitivity/70% specificity; AUC = 0.759, 78.6% sensitivity/60% specificity). From wheat-stimulated HAECs, TGF-β1 release peaked at 6 hours after wheat exposure, while eotaxin-2 peaked at 12 hours. Co-culture of HAECs with neutrophils did not affect TGF-β1 release.

Conclusions

Our results suggest that TGF-β1 may contribute to develop type-2 airway inflammation and WRS. Serum TGF-β1/EDN levels may be potential serum biomarkers for predicting WRS among bakery workers.

Autophagy is involved in allergic rhinitis by inducing airway remodeling

BACKGROUND

Allergic rhinitis (AR) is an allergic disorder affecting 10-40% of the population worldwide. Autophagy has been implicated in numerous biological processes, including aging, immunity, development, and differentiation, and has been shown to affect the pathogenesis of allergic disease and airway remodeling. In this study we attempted to determine the association between autophagy and AR pathogenesis.

METHODS

The severity of nasal and extranasal symptoms was measured with visual analog scale (VAS) scores. Autophagosome formation was detected in the nasal epithelium by transmission electron microscopy (TEM). Western blots and quantitative polymerase chain reaction were used to examine expression levels of autophagic markers. Collagen deposition was detected via Masson trichrome staining and collagen III expression was measured by enzyme-linked immunosorbent assay. Spearman's correlation coefficient was used to assess the relationship between autophagy, AR symptoms, and collagen levels.

RESULTS

Patients with AR had more autophagosomes, increased levels of Beclin-1 mRNA, and higher Beclin-1 and LC3-II protein expression. Collagen III protein expression was also higher in patients with AR than in the controls. Higher expression of Beclin-1 was associated with higher VAS scores (Spearman's rho = 0.905, p < 0.01), higher collagen deposition (Spearman's rho = 0.862, p < 0.01), and higher collagen III protein (Spearman's rho = 0.849, p < 0.01).

CONCLUSION

The autophagosome and autophagic markers are highly expressed in the upper airways of patients with AR and are associated with corresponding changes in airway remodeling markers. Our data suggest a link between autophagy and airway remodeling in AR.

Sestrin2 is involved in asthma: a case-control study

Background

Asthma is a chronic disease that seriously harms the health of patients. Oxidative stress is involved in asthma. As an oxidative stress-inducible protein, sestrin2 is elevated in oxidative stress-related diseases. We aimed to explore whether sestrin2 was involved in asthma.

Methods

Seventy-six subjects (44 in the asthma group, 32 in the control group) were recruited in this study. Plasma sestrin2 levels, peak expiratory flow (PEF), forced expiratory volume in 1 s (FEV₁) % predicted, forced vital capacity (FVC) % predicted and FEV₁/FVC ratio were measured in controls and in asthmatics both during an exacerbation and when controlled after the exacerbation.

Results

The asthma group had a significant higher sestrin2 level than the control group (asthmatics during exacerbation, 1.75 ± 0.53 ng/mL vs. 1.32 ± 0.48 ng/mL, p < 0.001; asthmatics when controlled after the exacerbation, 1.56 ± 0.46 ng/mL vs. 1.32 ± 0.48 ng/mL, p = 0.021, respectively). In addition, sestrin2 was negatively correlated with FEV₁% predicted and FEV₁/FVC ratio in asthmatics during exacerbation (r = − 0.393, p = 0.008; r = − 0.379, p = 0.011; respectively). Moreover, negative correlations between sestrin2 and FEV₁% predicted and FEV₁/FVC ratio also existed in asthmatics when controlled after the exacerbation (r = − 0.543, p < 0.001; r = − 0.433, p = 0.003 respectively). More importantly, multiple linear regression analysis demonstrated that FEV₁% predicted was independently associated with sestrin2 in asthmatics both during exacerbation and when controlled after the exacerbation.

Conclusions

Sestrin2 is involved in asthma. Sestrin2 levels increase in asthmatics both during exacerbation and when controlled after the exacerbation. In addition, sestrin2 is independently associated with FEV₁% predicted.

Prolonged exposure to hypoxia induces an autophagy-like cell survival program in human neutrophils

Neutrophils contribute to low oxygen availability at inflammatory sites through the generation of reactive oxidants. They are also functionally affected by hypoxia, which delays neutrophil apoptosis. However, the eventual fate of neutrophils in hypoxic conditions is unknown and this is important for their effective clearance and the resolution of inflammation. We have monitored the survival and function of normal human neutrophils exposed to hypoxia over a 48 h period. Apoptosis was delayed, and the cells remained intact even at 48 h. However, hypoxia promoted significant changes in neutrophil morphology with the appearance of many new cytoplasmic vesicles, often containing cell material, within 5 hours of exposure to low O₂ . This coincided with an increase in LC3B-II expression, indicative of autophagosome formation and an autophagy-like process. In hypoxic conditions, neutrophils preferentially lost myeloperoxidase, a marker of azurophil granules. Short-term (2 h) hypoxic exposure resulted in sustained potential to generate superoxide when O₂ was restored, but the capacity for oxidant production was lost with longer periods of hypoxia. Phagocytic ability was unchanged by hypoxia, and bacterial killing by neutrophils in both normoxic and hypoxic conditions was substantially diminished after 24 hours. However, pre-exposure to hypoxia resulted in an enhanced ability to kill bacteria by oxidant-independent mechanisms. Our data provide the first evidence for hypoxia as a driver of neutrophil autophagy that can influence the function and ultimate fate of these cells, including their eventual clearance and the resolution of inflammation.

Autophagy induces eosinophil extracellular traps formation and allergic airway inflammation in a murine asthma model

Studies have shown autophagy participation in the immunopathology of inflammatory diseases. However, autophagy role in asthma and in eosinophil extracellular traps (EETs) release is poorly understood. Here, we attempted to investigate the autophagy involvement in EETs release and in lung inflammation in an experimental asthma model. Mice were sensitized with ovalbumin (OVA), followed by OVA challenge. Before the challenge with OVA, mice were treated with an autophagy inhibitor, 3-methyladenine (3-MA). We showed that 3-MA treatment decreases the number of eosinophils, eosinophil peroxidase (EPO) activity, goblet cells hyperplasia, proinflammatory cytokines, and nuclear factor kappa B (NFκB) p65 immunocontent in the lung. Moreover, 3-MA was able to improve oxidative stress, mitochondrial energy metabolism, and Na⁺ , K⁺ -ATPase activity. We demonstrated that treatment with autophagy inhibitor 3-MA reduced EETs formation in the airway. On the basis of our results, 3-MA treatment can be an interesting alternative for reducing lung inflammation, oxidative stress, mitochondrial damage, and EETs formation in asthma.

Extracellular DNA, Neutrophil Extracellular Traps, and Inflammasome Activation in Severe Asthma

Rationale: Extracellular DNA (eDNA) and neutrophil extracellular traps (NETs) are implicated in multiple inflammatory diseases. NETs mediate inflammasome activation and IL-1β secretion from monocytes and cause airway epithelial cell injury, but the role of eDNA, NETs, and IL-1β in asthma is uncertain. Objectives: To characterize the role of activated neutrophils in severe asthma through measurement of NETs and inflammasome activation. Methods: We measured sputum eDNA in induced sputum from 399 patients with asthma in the Severe Asthma Research Program-3 and in 94 healthy control subjects. We subdivided subjects with asthma into eDNA-low and -high subgroups to compare outcomes of asthma severity and of neutrophil and inflammasome activation. We also examined if NETs cause airway epithelial cell damage that can be prevented by DNase. Measurements and Main Results: We found that 13% of the Severe Asthma Research Program-3 cohort is "eDNA-high," as defined by sputum eDNA concentrations above the upper 95th percentile value in health. Compared with eDNA-low patients with asthma, eDNA-high patients had lower Asthma Control Test scores, frequent history of chronic mucus hypersecretion, and frequent use of oral corticosteroids for maintenance of asthma control (all P values <0.05). Sputum eDNA in asthma was associated with airway neutrophilic inflammation, increases in soluble NET components, and increases in caspase 1 activity and IL-1β (all P values <0.001). In in vitro studies, NETs caused cytotoxicity in airway epithelial cells that was prevented by disruption of NETs with DNase. Conclusions: High extracellular DNA concentrations in sputum mark a subset of patients with more severe asthma who have NETs and markers of inflammasome activation in their airways.

MiR-135-5p-p62 Axis Regulates Autophagic Flux, Tumorigenic Potential, and Cellular Interactions Mediated by Extracellular Vesicles During Allergic Inflammation

The objective of this study was to investigate the relationship between autophagy and allergic inflammation. In vitro allergic inflammation was accompanied by an increased autophagic flux in rat basophilic leukemia (RBL2H3) cells. 3-MA, an inhibitor of autophagic processes, negatively regulated allergic inflammation both in vitro and in vivo. The role of p62, a selective receptor of autophagy, in allergic inflammation was investigated. P62, increased by antigen stimulation, mediated in vitro allergic inflammation, passive cutaneous anaphylaxis (PCA), and passive systemic anaphylaxis (PSA). P62 mediated cellular interactions during allergic inflammation. It also mediated tumorigenic and metastatic potential of cancer cells enhanced by PSA. TargetScan analysis predicted that miR-135-5p was a negative regulator of p62. Luciferase activity assay showed that miR-135-5p directly regulated p62. MiR-135-5p mimic negatively regulated features of allergic inflammation and inhibited tumorigenic and metastatic potential of cancer cells enhanced by PSA. MiR-135-5p mimic also inhibited cellular interactions during allergic inflammation. Extracellular vesicles mediated allergic inflammation both in vitro and in vivo. Extracellular vesicles were also necessary for cellular interactions during allergic inflammation. Transmission electron microscopy showed p62 within extracellular vesicles of antigen-stimulated rat basophilic leukemia cells (RBL2H3). Extracellular vesicles isolated from antigen-stimulated RBL2H3 cells induced activation of macrophages and enhanced invasion and migration potential of B16F1 mouse melanoma cells in a p62-dependent manner. Extracellular vesicles isolated from PSA-activated BALB/C mouse enhanced invasion and migration potential of B16F1 cells, and induced features of allergic inflammation in RBL2H3 cells. Thus, miR-135-5p-p62 axis might serve as a target for developing anti-allergy drugs.

A high blood eosinophil count may be a risk factor for incident asthma in population at risk

BACKGROUND

Eosinophilia is considered to be associated with allergic disease and may predict asthma exacerbation. Eosinophils contribute to the pathophysiology and pathogenesis of asthma. However, studies on high blood eosinophil counts (BECs) and incident asthma remain scarce.

OBJECTIVE

To examine whether high BECs are positively associated with incident asthma in adults.

METHODS

Our study included 57975 participants aged from 20 to 79 years from the Shandong multi-center health check-up longitudinal study for Health Management. All patients with determined baseline BECs were ≥20 years old and free from asthma. We defined incident asthma as self-reported new-onset asthma occurring during the 10-year follow-up period. Multivariate modeling employed Poisson regression and Cox proportional hazards models to verify the association between BEC and incident asthma by adjusting demographics and some relevant comorbidities (rhinitis, nasal polyps, pneumonia, bronchitis, and chronic obstructive pulmonary disease).

RESULTS

A BEC ≥110 cells/μL was a risk factor for incident asthma (adjusted IRR = 1.62, 95% CI: 1.05-2.50, P = .028) in the Poisson regression. In the Cox proportional hazards model, the BEC cutoff point for incident asthma was also determined to be 110 cells/μL (HR = 1.59, 95% CI: 1.01-2.51, P = .045).

CONCLUSION

A high BEC is a risk factor for incident asthma, especially when the BEC exceeds 110 cells/μL. This suggests that adults with high BECs are more likely to develop asthma.

NETopathic Inflammation in Chronic Obstructive Pulmonary Disease and Severe Asthma

Neutrophils play a central role in innate immunity, inflammation, and resolution. Unresolving neutrophilia features as a disrupted inflammatory process in the airways of patients with chronic obstructive pulmonary disease (COPD) and severe asthma. The extent to which this may be linked to disease pathobiology remains obscure and could be further confounded by indication of glucocorticoids or concomitant respiratory infections. The formation of neutrophil extracellular traps (NETs) represents a specialized host defense mechanism that entrap and eliminate invading microbes. NETs are web-like scaffolds of extracellular DNA in complex with histones and neutrophil granular proteins, such as myeloperoxidase and neutrophil elastase. Distinct from apoptosis, NET formation is an active form of cell death that could be triggered by various microbial, inflammatory, and endogenous or exogenous stimuli. NETs are reportedly enriched in neutrophil-dominant refractory lung diseases, such as COPD and severe asthma. Evidence for a pathogenic role for respiratory viruses (e.g., Rhinovirus), bacteria (e.g., Staphylococcus aureus) and fungi (e.g., Aspergillus fumigatus) in NET induction is emerging. Dysregulation of this process may exert localized NET burden and contribute to NETopathic lung inflammation. Disentangling the role of NETs in human health and disease offer unique opportunities for therapeutic modulation. The chemokine CXCR2 receptor regulates neutrophil activation and migration, and small molecule CXCR2 antagonists (e.g., AZD5069, danirixin) have been developed to selectively block neutrophilic inflammatory pathways. NET-stabilizing agents using CXCR2 antagonists are being investigated in proof-of-concept studies in patients with COPD to provide mechanistic insights. Clinical validation of this type could lead to novel therapeutics for multiple CXCR2-related NETopathologies. In this Review, we discuss the emerging role of NETs in the clinicopathobiology of COPD and severe asthma and provide an outlook on how novel NET-stabilizing therapies via CXCR2 blockade could be leveraged to disrupt NETopathic inflammation in disease-specific phenotypes.

Enhanced Neutrophil Extracellular Trap Formation in Acute Pancreatitis Contributes to Disease Severity and Is Reduced by Chloroquine

Background: Neutrophil extracellular traps (NETs) are generated when activated neutrophils, driven by PAD4, release their DNA, histones, HMGB1, and other intracellular granule components. NETs play a role in acute pancreatitis, worsening pancreatic inflammation, and promoting pancreatic duct obstruction. The autophagy inhibitor chloroquine (CQ) inhibits NET formation; therefore, we investigated the impact of CQ mediated NET inhibition in murine models of pancreatitis and human correlative studies.

Methods: L-arginine and choline deficient ethionine supplemented (CDE) diet models of acute pancreatitis were studied in wild type and PAD4^−/− mice, incapable of forming NETs. Isolated neutrophils were stimulated to induce NET formation and visualized with fluorescence microscopy. CQ treatment (0.5 mg/ml PO) was initiated after induction of pancreatitis. Biomarkers of NET formation, including cell-free DNA, citrullinated histone H3 (CitH3), and MPO-DNA conjugates were measured in murine serum and correlative human patient serum samples.

Results: We first confirmed the role of NETs in the pathophysiology of acute pancreatitis by demonstrating that PAD4^−/− mice had decreased pancreatitis severity and improved survival compared to wild-type controls. Furthermore, patients with severe acute pancreatitis had elevated levels of cell-free DNA and MPO-DNA conjugates, consistent with NET formation. Neutrophils from mice with pancreatitis were more prone to NET formation and CQ decreased this propensity to form NETs. CQ significantly reduced serum cell-free DNA and citrullinated histone H3 in murine models of pancreatitis, increasing survival in both models.

Conclusions: Inhibition of NETs with CQ decreases the severity of acute pancreatitis and improves survival. Translating these findings into clinical trials of acute pancreatitis is warranted.

Evaluation of Neutrophil Activation Status According to the Phenotypes of Adult Asthma

Purpose

Neutrophils are considered key effector cells in the pathogenic mechanisms of airway inflammation in asthma. This study assessed the activation status of neutrophils in adult asthmatics, and the therapeutic potential of FTY720, a synthetic sphingosine-1-phosphate analog, on activated neutrophils using an in vitro stimulation model.

Methods

We isolated peripheral blood neutrophils (PBNs) from 59 asthmatic patients (including 20 aspirin-exacerbated respiratory disease [AERD] and 39 aspirin-tolerant asthma [ATA] groups). PBNs were stimulated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) or lipopolysaccharide (LPS) and their activation status was determined based on reactive oxygen species (ROS) production, cell surface expression of CD11b, interleukin (IL)-8 and matrix metallopeptidase (MMP)-9 release. PBNs were primed with FTY720 to evaluate its anti-inflammatory action.

Results

In vitro PBN stimulation with fMLP or LPS induced a significant increase in ROS/CD11b/IL-8/MMP-9 levels (P < 0.05 for all). In asthmatics, fMLP-induced ROS level was significantly correlated with values of forced expiratory volume in 1 second/forced vital capacity (r = −0.278; P = 0.036), maximal mid-expiratory flow (r = −0.309; P = 0.019) and PC20 methacholine (r = −0.302; P = 0.029). In addition, ROS levels were significantly higher in patients with AERD and in those with severe asthma than in those with ATA or non-severe asthma (P < 0.05 for all). FTY720 treatment could suppress ROS/CD11b levels, and LPS-induced IL-8 and MMP-9 levels (P < 0.05 for all). Responders to FTY720 treatment had significantly higher neutrophil counts in sputum (P = 0.004).

Conclusions

Our findings suggest a useful in vitro PBN stimulation model for evaluating the neutrophil functional status and the therapeutic potentials of neutrophil-targeting candidates in asthmatics.

Serum Levels of Eosinophil-Derived Neurotoxin: A Biomarker for Asthma Severity in Adult Asthmatics

Purpose

Eosinophilic inflammation is a key component of severe asthma (SA). However, there has been no reliable serum biomarker for the eosinophilic inflammation of SA. We hypothesized that serum eosinophil-derived neurotoxin (EDN) could predict the eosinophilic inflammation of SA in adult asthmatics.

Methods

Severe asthmatics (n = 235), nonsevere asthmatics (n = 898), and healthy controls (n = 125) were enrolled from Ajou University Hospital, South Korea. The serum levels of EDN and periostin were measured by enzyme-linked immunosorbent assay and compared between severe and nonsevere asthmatics. Their associations with total eosinophil count (TEC) and clinical parameters were evaluated; clinical validation of the K-EDN kit for the measurement of serum EDN was evaluated.

Results

Severe asthmatics were older and had longer disease duration with significantly lower levels of forced expiratory volume in 1 second and methacholine PC20 than nonsevere asthmatics. Significant differences were found in TEC or sputum eosinophil count (%) between the groups. The serum levels of EDN and periostin were significantly higher in severe asthmatics than in nonsevere asthmatics and in healthy controls (all P < 0.05). Although significant correlations were found between serum EDN levels measured by the 2 kits (ρ = 0.545, P < 0.0001), higher correlation coefficients between serum EDN levels measured by the K-EDN kit and TEC were higher (ρ = 0.358, P < 0.0001) than those between serum EDN levels measured by the MBL kit and TEC (ρ = 0.319, P < 0.0001) or serum periostin level (ρ = 0.222, P < 0.0001). Multivariate regression analysis demonstrated that serum EDN levels measured by the K-EDN kit predicted the phenotype of SA (P = 0.003), while 2 other biomarkers did not.

Conclusions

The serum EDN level may be a useful biomarker for assessing asthma severity in adult asthmatics.

Serum Periostin Levels: A Potential Serologic Marker for Toluene Diisocyanate-Induced Occupational Asthma

PURPOSE

Toluene diisocyanate (TDI) is a leading cause of occupational asthma (OA). Periostin is a matricellular protein implicated in type 2 immunity-driven asthma. Its pathogenic role in TDI-OA has not been completely elucidated. The present study was performed to investigate the role of periostin in TDI-OA.

MATERIALS AND METHODS

Serum periostin levels were measured in subjects with TDI-OA, asymptomatic TDI-exposure controls (AECs), non-occupational asthmatics (NAs), and unexposed normal controls (NCs). To understand the mechanism by which TDI induces periostin production, primary small airway epithelial cells (SAECs) were cultured under stimulation of TDI and neutrophils from asthmatic patients.

RESULTS

Fifty-three subjects with TDI-OA, 71 AECs, 67 NAs, and 83 NCs were enrolled. Serum periostin levels were significantly higher in TDI-OA subjects than in AECs (p=0.001), NAs (p<0.001), and NCs (p<0.001). In TDI-exposed subjects (TDI-OA and AEC), the PC₂₀ methacholine levels were significantly lower in subjects with a higher periostin level than in those with a lower periostin level. TDI exposure did not increase periostin production directly by SAECs; however, periostin production increased significantly after co-culture with TDI and neutrophils, which was suppressed by an antioxidant. In addition, increased release of TGF-β1 was noted from SAECs when exposed to TDI and neutrophils, which was also suppressed by an antioxidant.

CONCLUSION

These results suggest that an increased periostin level may contribute to the progression of airway inflammation to remodeling in TDI-exposed workers. A high serum periostin level is a potential serologic marker of the phenotype of TDI-OA.

Neutrophils induce smooth muscle hyperplasia via neutrophil elastase-induced FGF-2 in a mouse model of asthma with mixed inflammation

BACKGROUND

Bronchial asthma is traditionally characterized by chronic allergic inflammation, including eosinophilia and elevated Th2 cytokines. Recently, IL-17-derived neutrophil infiltration was shown to correlate with asthma severity and airway remodelling.

OBJECTIVE

To investigate the role of IL-17-derived neutrophils in airway remodelling in chronic bronchial asthma.

METHODS

We utilized house dust mite antigen-induced mouse models of asthma. Intranasal sensitization and chronic antigen challenge caused a mixed allergic inflammation that included eosinophils and neutrophils (Mix-in group). We neutralized IL-17 and fibroblast growth factor (FGF-2) and investigated the mechanism of airway remodelling in the Mix-in group.

RESULTS

The Mix-in group displayed neutrophilic infiltration and high levels of IL-17 in lung tissue. The Mix-in group also exhibited more bronchial smooth muscle hyperplasia. IL-17 neutralization decreased the magnitude of all of these effects in the Mix-in group. Antibody arrays revealed an increase in FGF-2 in the Mix-in Group relative to the Eo-ip group, and FGF-2 elevation was associated with smooth muscle hypertrophy/hyperplasia. High concentrations of neutrophil elastase enhanced E-cadherin/β-catenin signalling in bronchial epithelial cells. Neutrophil elastase inhibitor treatment decreased FGF-2 production and E-cadherin/β-catenin signalling, which inhibited smooth muscle hyperplasia.

CONCLUSION

The IL-17/neutrophil axis may play an important role in airway remodelling by contributing to smooth muscle hypertrophy/hyperplasia in mixed allergic inflammation and accordingly represents an attractive therapeutic target for severe asthma.

Children with Neutrophil-Predominant Severe Asthma Have Proinflammatory Neutrophils With Enhanced Survival and Impaired Clearance

BACKGROUND

Airway neutrophils are abundant in some children with severe asthma, but their functions are poorly understood.

OBJECTIVE

To characterize that the inflammatory airway environment of children with neutrophil-predominant severe asthma promotes neutrophil survival and disrupts neutrophil-associated innate immune defenses.

METHODS

Sixty-seven children with severe asthma refractory to high-dose inhaled corticosteroid treatment undergoing bronchoscopy with bronchoalveolar lavage (BAL) for clinical indications were stratified into neutrophil "high" versus "low" groups on the basis of BAL differential counts. Neutrophil activation markers, functional assays, and phenotyping studies were performed, as well as airway macrophage functional assays. Results were compared with those from children with moderate asthma treated with inhaled corticosteroids.

RESULTS

Children with neutrophil-predominant severe asthma had increased markers of neutrophil activation/degranulation and a greater magnitude of airway proinflammatory cytokine and chemokine release. Primary neutrophils exposed to BAL of these children exhibited greater phagocytic capability and greater neutrophil extracellular trap formation, but a more impaired respiratory burst. Despite greater abundance of airway TGF-β1, the neutrophils were not more apoptotic. Instead, neutrophils had a highly proinflammatory phenotype associated with a number of surface markers that regulate neutrophil activation, recruitment/migration, and granule release. Airway macrophages from children with neutrophil-predominant severe asthma were also more proinflammatory with impaired phagocytosis and increased apoptosis.

CONCLUSIONS

Children with neutrophil-predominant severe asthma have proinflammatory neutrophils with enhanced survival. Airway macrophages are also proinflammatory and dysfunctional and may contribute to global innate immune impairment. Therapies that target neutrophils and related inflammation may be warranted in this subset of children.

Autophagy in Neutrophils: From Granulopoiesis to Neutrophil Extracellular Traps

Autophagy is an evolutionarily conserved intracellular degradation system aiming to maintain cell homeostasis in response to cellular stress. At physiological states, basal or constitutive level of autophagy activity is usually low; however, it is markedly up-regulated in response to oxidative stress, nutrient starvation, and various immunological stimuli including pathogens. Many studies over the last years have indicated the implication of autophagy in a plethora of cell populations and functions. In this review, we focus on the role of autophagy in the biology of neutrophils. Early studies provided a link between autophagy and neutrophil cell death, a process essential for resolution of inflammation. Since then, several lines of evidence both in the human system and in murine models propose a critical role for autophagy in neutrophil-driven inflammation and defense against pathogens. Autophagy is essential for major neutrophil functions, including degranulation, reactive oxygen species production, and release of neutrophil extracellular traps. Going back to neutrophil generation in the bone marrow, autophagy plays a critical role in myelopoiesis, driving the differentiation of progenitor cells of the myeloid lineage toward neutrophils. Taken together, in this review we discuss the functional role of autophagy in neutrophils throughout their life, from their production in the bone marrow to inflammatory responses and NETotic cell death.

Role of clusterin/progranulin in toluene diisocyanate-induced occupational asthma

Toluene diisocyanate (TDI) exposure induces oxidative stress and epithelial cell-derived inflammation, which affect the pathogenesis of TDI-induced occupational asthma (TDI-OA). Recent studies suggested a role for clusterin (CLU) and progranulin (PGRN) in oxidative stress-mediated airway inflammation. To evaluate CLU and PGRN involvement in airway inflammation in TDI-OA, we measured their serum levels in patients with TDI-OA, asymptomatic exposed controls (AECs), and unexposed healthy normal controls (NCs). Serum CLU and PGRN levels were significantly lower in the TDI-OA group than in the AEC and NC groups (P < 0.05). The sensitivity and specificity for predicting the TDI-OA phenotype were 72.4% and 53.4% when either CLU or PGRN levels were below the cutoff values (≤125 μg/mL and ≤68.4 ng/mL, respectively). If both parameters were below the cutoff levels, the sensitivity and specificity were 58.6% and 89.8%, respectively. To investigate CLU and PGRN function, we evaluated their production by human airway epithelial cells (HAECs) in response to TDI exposure and co-culturing with neutrophils. TDI-human serum albumin stimulation induced significant CLU/PGRN release from HAECs in a dose-dependent manner, which positively correlated with IL-8 and folliculin levels. Co-culturing with neutrophils significantly decreased CLU/PGRN production by HAECs. Intracellular ROS production in epithelial cells co-cultured with neutrophils tended to increase initially, but the ROS production decreased gradually at a higher ratio of neutrophils. Our results suggest that CLU and PGRN may be involved in TDI-OA pathogenesis by protecting against TDI-induced oxidative stress-mediated inflammation. The combined CLU/PGRN serum level may be used as a potential serological marker for identifying patients with TDI-OA among TDI-exposed workers.

Autophagy and inflammation in chronic respiratory disease

Persistent inflammation within the respiratory tract underlies the pathogenesis of numerous chronic pulmonary diseases including chronic obstructive pulmonary disease, asthma and pulmonary fibrosis. Chronic inflammation in the lung may arise from a combination of genetic susceptibility and environmental influences, including exposure to microbes, particles from the atmosphere, irritants, pollutants, allergens, and toxic molecules. To this end, an immediate, strong, and highly regulated inflammatory defense mechanism is needed for the successful maintenance of homeostasis within the respiratory system. Macroautophagy/autophagy plays an essential role in the inflammatory response of the lung to infection and stress. At baseline, autophagy may be critical for inhibiting spontaneous pulmonary inflammation and fundamental for the response of pulmonary leukocytes to infection; however, when not regulated, persistent or inefficient autophagy may be detrimental to lung epithelial cells, promoting lung injury. This perspective will discuss the role of autophagy in driving and regulating inflammatory responses of the lung in chronic lung diseases with a focus on potential avenues for therapeutic targeting. Abbreviations AR allergic rhinitis AM alveolar macrophage ATG autophagy-related CF cystic fibrosis CFTR cystic fibrosis transmembrane conductance regulator COPD chronic obstructive pulmonary disease CS cigarette smoke CSE cigarette smoke extract DC dendritic cell IH intermittent hypoxia IPF idiopathic pulmonary fibrosis ILD interstitial lung disease MAP1LC3B microtubule associated protein 1 light chain 3 beta MTB Mycobacterium tuberculosis MTOR mechanistic target of rapamycin kinase NET neutrophil extracellular traps OSA obstructive sleep apnea PAH pulmonary arterial hypertension PH pulmonary hypertension ROS reactive oxygen species TGFB1 transforming growth factor beta 1 TNF tumor necrosis factor.

Autoimmune Responses in Severe Asthma

Asthma and autoimmune diseases both result from a dysregulated immune system, and have been conventionally considered to have mutually exclusive pathogenesis. Autoimmunity is believed to be an exaggerated Th1 response, while asthma with a Th2 underpinning is congruent with the well-accepted Th1/Th2 paradigm. The hypothesis of autoimmune involvement in asthma has received much recent interest, particularly in the adult late-onset non-atopic patients (the “intrinsic asthma”). Over the past decades, circulating autoantibodies against diverse self-targets (beta-2-adrenergic receptors, epithelial antigens, nuclear antigens, etc.) have been reported and subsequently dismissed to be epiphenomena resulting from a chronic inflammatory condition, primarily due to lack of evidence of causality/pathomechanism. Recent evidence of ‘granulomas’ in the lung biopsies of severe asthmatics, detection of pathogenic sputum autoantibodies against autologous eosinophil proteins (e.g., eosinophil peroxidase) and inadequate response to monoclonal antibody therapies (e.g., subcutaneous mepolizumab) in patients with evidence of airway autoantibodies suggest that the role of autoimmune mechanisms be revisited. In this review, we have gathered available reports of autoimmune responses in the lungs, reviewed the evidence in the context of immunogenic tissue-response and danger-associated molecular patterns, and constructed the possibility of an autoimmune-associated pathomechanism that may contribute to the severity of asthma.

Pathological Roles of Neutrophil-Mediated Inflammation in Asthma and Its Potential for Therapy as a Target

Asthma is a chronic inflammatory disease that undermines the airways. It is caused by dysfunction of various types of cells, as well as cellular components, and is characterized by recruitment of inflammatory cells, bronchial hyperreactivity, mucus production, and airway remodelling and narrowing. It has commonly been considered that airway inflammation is caused by the Th2 immune response, or eosinophilia, which is a hallmark of bronchial asthma pathogenesis. Some patients display a neutrophil-dominant presentation and are characterized with low (or even absent) Th2 cytokines. In recent years, increasing evidence has also suggested that neutrophils play a key role in the development of certain subtypes of asthma. This review discusses neutrophils in asthma and potentially related targeted therapies.

Trichothecenes: immunomodulatory effects, mechanisms, and anti-cancer potential

Paradoxically, trichothecenes have both immunosuppressive and immunostimulatory effects. The underlying mechanisms have not been fully explored. Early studies show that dose, exposure timing, and the time at which immune function is assessed influence whether trichothecenes act in an immunosuppressive or immunostimulatory fashion. Recent studies suggest that the immunomodulatory function of trichothecenes is also actively shaped by competing cell-survival and death-signaling pathways. Autophagy may also promote trichothecene immunosuppression, although the mechanism may be complicated. Moreover, trichothecenes may generate an "immune evasion" milieu that allows pathogens to escape host and vaccine immune defenses. Some trichothecenes, especially macrocyclic trichothecenes, also potently kill cancer cells. T-2 toxin conjugated with anti-cancer monoclonal antibodies significantly suppresses the growth of thymoma EL-4 cells and colon cancer cells. The type B trichothecene diacetoxyscirpenol specifically inhibits the tumor-promoting factor HIF-1 in cancer cells under hypoxic conditions. Trichothecin markedly inhibits the growth of multiple cancer cells with constitutively activated NF-κB. The type D macrocyclic toxin Verrucarin A is also a promising therapeutic candidate for leukemia, breast cancer, prostate cancer, and pancreatic cancer. The anti-cancer activities of trichothecenes have not been comprehensively summarized. Here, we first summarize the data on the immunomodulatory effects of trichothecenes and discuss recent studies that shed light on the underlying cellular and molecular mechanisms. These mechanisms include autophagy and major signaling pathways and their crosstalk. Second, the anti-cancer potential of trichothecenes and the underlying mechanisms will be discussed. We hope that this review will show how trichothecene bioactivities can be exploited to generate therapies against pathogens and cancer.

Epithelial folliculin is involved in airway inflammation in workers exposed to toluene diisocyanate

Toluene diisocyanate (TDI) exposure can directly activate and damage airway epithelium. Folliculin (FLCN) is a protein expressed by human airway epithelial cells (HAECs) to maintain airway epithelial integrity and survival. This study investigated the involvement of FLCN in the pathogenesis of TDI-induced occupational asthma (OA). Enzyme-linked immunosorbent assay was used to measure serum levels of FLCN in TDI-exposed subjects (93 TDI-OA patients and 119 asymptomatic exposed controls (AEC)), 200 non-occupational asthma (NOA) patients and 71 unexposed healthy normal controls (NCs). Significantly more subjects in the TDI-OA and AEC groups had high serum levels of FLCN compared to those in the NOA group (P=0.002 and P=0.001, respectively), all of which were higher than the NC group (all P<0.001). The serum level of FLCN was positively correlated with TDI exposure duration (r=0.251, P=0.027), but was negatively correlated with asthma duration of TDI-OA patients (r=−0.329, P=0.029). TDI-exposed subjects with high FLCN levels had higher serum levels of total IgE than those with lower levels. The effects of TDI exposure on FLCN production was investigated by treating HAECs (A549 cells) with TDI-human serum albumin conjugate, which showed increased expression and release of FLCN and interleukin-8 from HAECs. Co-culture with peripheral blood neutrophils also induced FLCN expression and release from HAECs. In conclusion, TDI exposure and TDI-induced neutrophil recruitment into the airways can activate and stimulate HAECs to produce FLCN, which could be involved in airway inflammation in workers exposed to TDI.

Neutrophil Extracellular DNA Traps Induce Autoantigen Production by Airway Epithelial Cells

The hypothesis of autoimmune involvement in asthma has received much recent interest. Autoantibodies, such as anti-cytokeratin (CK) 18, anti-CK19, and anti-α-enolase antibodies, react with self-antigens and are found at high levels in the sera of patients with severe asthma (SA). However, the mechanisms underlying autoantibody production in SA have not been fully determined. The present study was conducted to demonstrate that neutrophil extracellular DNA traps (NETs), cytotoxic molecules released from neutrophils, are a key player in the stimulation of airway epithelial cells (AECs) to produce autoantigens. This study showed that NETs significantly increased the intracellular expression of tissue transglutaminase (tTG) but did not affect that of CK18 in AECs. NETs induced the extracellular release of both tTG and CK18 in a concentration-dependent manner. Moreover, NETs directly degraded intracellular α-enolase into small fragments. However, antibodies against neutrophil elastase (NE) or myeloperoxidase (MPO) attenuated the effects of NETs on AECs. Furthermore, each NET isolated from healthy controls (HC), nonsevere asthma (NSA), and SA had different characteristics. Taken together, these findings suggest that AECs exposed to NETs may exhibit higher autoantigen production, especially in SA. Therefore, targeting of NETs may represent a new therapy for neutrophilic asthma with a high level of autoantigens.

Role of Neutrophil Extracellular Traps in Asthma and Chronic Obstructive Pulmonary Disease

Objective:

Asthma and chronic obstructive pulmonary disease (COPD) are representative chronic inflammatory airway diseases responsible for a considerable burden of disease. In this article, we reviewed the relationship between neutrophil extracellular traps (NETs) and chronic inflammatory airway diseases.

Data Sources:

Articles published up to January 1, 2017, were selected from the PubMed, Ovid Medline, Embase databases, with the keywords of “asthma” or “pulmonary disease, chronic obstructive”, “neutrophils” and “extracellular traps.”

Study Selection:

Articles were obtained and reviewed to analyze the role of NETs in asthma and COPD.

Results:

NETs are composed of extracellular DNA, histones, and granular proteins, which are released from activated neutrophils. Multiple studies have indicated that there are a large amount of NETs in the airways of asthmatics and COPD patients. NETs can engulf and kill invading pathogens in the host. However, disordered regulation of NET formation has shown to be involved in the development of asthma and COPD. An overabundance of NETs in the airways or lung tissue could cause varying degrees of damage to lung tissues by inducing the death of human epithelial and endothelial cells, and thus resulting in impairing pulmonary function and accelerating the progress of the disease.

Conclusions:

Excessive NETs accumulate in the airways of asthmatics and COPD patients. Although NETs play an essential role in the innate immune system against infection, excessive components of NETs can cause lung tissue damage and accelerate disease progression in asthmatics and COPD patients. These findings suggest that administration of NETs could be a novel approach to treat asthma and COPD. Mechanism studies, clinical practice, and strategies to regulate neutrophil activation or directly interrupt NET function in asthmatics and COPD patients are desperately needed.

Advanced Role of Neutrophils in Common Respiratory Diseases

Respiratory diseases, always being a threat towards the health of people all over the world, are most tightly associated with immune system. Neutrophils serve as an important component of immune defense barrier linking innate and adaptive immunity. They participate in the clearance of exogenous pathogens and endogenous cell debris and play an essential role in the pathogenesis of many respiratory diseases. However, the pathological mechanism of neutrophils remains complex and obscure. The traditional roles of neutrophils in severe asthma, chronic obstructive pulmonary diseases (COPD), pneumonia, lung cancer, pulmonary fibrosis, bronchitis, and bronchiolitis had already been reviewed. With the development of scientific research, the involvement of neutrophils in respiratory diseases is being brought to light with emerging data on neutrophil subsets, trafficking, and cell death mechanism (e.g., NETosis, apoptosis) in diseases. We reviewed all these recent studies here to provide you with the latest advances about the role of neutrophils in respiratory diseases.

Autophagy and airway fibrosis: Is there a link?

In the past decade, an emerging process named “autophagy” has generated intense interest in many chronic lung diseases. Tissue remodeling and fibrosis is a common feature of many airway diseases, and current therapies do not prevent or reverse these structural changes. Autophagy has evolved as a conserved process for bulk degradation and recycling of cytoplasmic components to maintain basal cellular homeostasis and healthy organelle populations in the cell. Furthermore, autophagy serves as a cell survival mechanism and can also be induced by chemical and physical stress to the cell. Accumulating evidence demonstrates that autophagy plays an essential role in vital cellular processes, including tissue remodeling. This review will discuss some of the recent advancements made in understanding the role of this fundamental process in airway fibrosis with emphasis on airway remodeling, and how autophagy can be exploited as a target for airway remodeling in asthma and chronic obstructive pulmonary disease.

Autophagy and airway fibrosis: Is there a link?

In the past decade, an emerging process named "autophagy" has generated intense interest in many chronic lung diseases. Tissue remodeling and fibrosis is a common feature of many airway diseases, and current therapies do not prevent or reverse these structural changes. Autophagy has evolved as a conserved process for bulk degradation and recycling of cytoplasmic components to maintain basal cellular homeostasis and healthy organelle populations in the cell. Furthermore, autophagy serves as a cell survival mechanism and can also be induced by chemical and physical stress to the cell. Accumulating evidence demonstrates that autophagy plays an essential role in vital cellular processes, including tissue remodeling. This review will discuss some of the recent advancements made in understanding the role of this fundamental process in airway fibrosis with emphasis on airway remodeling, and how autophagy can be exploited as a target for airway remodeling in asthma and chronic obstructive pulmonary disease.