Elastase-mediated phosphatidylserine receptor cleavage impairs apoptotic cell clearance in cystic fibrosis and bronchiectasis

Cystic fibrosis is characterized by an early and sustained influx of inflammatory cells into the airways and by release of proteases. Resolution of inflammation is normally associated with the orderly removal of dying apoptotic inflammatory cells through cell recognition receptors, such as the phosphatidylserine receptor, CD36, and αv integrins. Accordingly, removal of apoptotic inflammatory cells may be impaired in persistent inflammatory responses such as that seen in cystic fibrosis airways. Examination of sputa from cystic fibrosis and non–cystic fibrosis bronchiectasis patients demonstrated an abundance of apoptotic cells, in excess of that seen in patients with chronic bronchitis. In vitro, cystic fibrosis and bronchiectasis airway fluid directly inhibited apoptotic cell removal by alveolar macrophages in a neutrophil elastase-dependent manner, suggesting that elastase may impair apoptotic cell clearance in vivo. Flow cytometry demonstrated that neutrophil elastase cleaved the phosphatidylserine receptor, but not CD36 or CD32 (FcγRII). Cleavage of the phosphatidylserine receptor by neutrophil elastase specifically disrupted phagocytosis of apoptotic cells, implying a potential mechanism for delayed apoptotic cell clearance in vivo. Therefore, defective airway clearance of apoptotic cells in cystic fibrosis and bronchiectasis may be due to elastase-mediated cleavage of phosphatidylserine receptor on phagocytes and may contribute to ongoing airway inflammation.     

靶向Th17细胞免疫治疗中重度哮喘的作用

支气管哮喘（简称哮喘）是多种炎症细胞和炎性介质参与的慢性气道炎症性疾病。Thl/Th2免疫反应失衡是哮喘主要的发病机制,而嗜酸粒细胞性气道炎症和气道高反应性为哮喘的显著临床特征。Th17细胞通过活化和募集中性粒细胞,促进气道炎症发生发展,尤其与中重度哮喘密切相关。Th17细胞为中重度哮喘提供了潜在的治疗靶点。深入研究Th17细胞分化调控机制,有望为治疗中性粒细胞性哮喘带来新的愿景。     

Diseases to differentiate from COPD, with emphasis on bronchial asthma

Differential diagnosis of chronic obstructive pulmonary disease (COPD) from asthma is not a difficult task for many clinicians. Patients with COPD have a history of heavy smoking and show a slowly progressive dyspnea on exertion and there is little variability in symptoms, and they show a poor response to bronchodilators and corticosteroids. Asthma usually begins in early childhood with atopy, shows episodic dyspnea with wheezing, especially during night and early morning. Some patients, however, show adult onset, irreversible airflow limitation, and neutrophilic airway inflammation. The airway remodeling in asthma may be the cause of confusing pathophysiology. Other diseases showing airway hyperresponsiveness, such as allergic bronchopulmonary aspergillosis, Churg-Strauss syndrome, and left heart failure presenting cardiac asthma, may sometimes show similar clinical pictures to COPD. Chronic airway diseases are also possible candidates for differential diagnosis of COPD. Bronchiectasis, sinobronchial syndrome, diffuse panbronchiolitis, obliterative bronchiolitis, and other chronic airway diseases should be considered. Some interstitial lung diseases, such as smoking-related interstitial lung diseases and lymphangioleiomyomatosis, often show obstructive ventilatory impairment, and therefore should be considered in differential diagnosis of COPD.     

New insights into the relationship between airway inflammation and asthma

Asthma is a condition characterized by variable airflow obstruction, airway hyper-responsiveness (AHR) and airway inflammation which is usually, but not invariably, eosinophilic. Current thoughts on the pathogenesis of asthma are focused on the idea that it is caused by an inappropriate response of the specific immune system to harmless antigens, particularly allergens such as cat dander and house dust mite, that result in Th2-mediated chronic inflammation. However, the relationship between inflammation and asthma is complex, with no good correlation between the severity of inflammation, at least as measured by the number of eosinophils, and the severity of asthma. In addition, there are a number of conditions, such as eosinophilic bronchitis and allergic rhinitis, in which there is a Th2-mediated inflammatory response, but no asthma, as measured by variable airflow obstruction or AHR. Bronchoconstriction can also occur without obvious airway inflammation, and neutrophilic inflammation can in some cases be associated with asthma. When we compared the immunopathology of eosinophilic bronchitis and asthma, the only difference we observed was that, in asthma, the airway smooth muscle (ASM) was infiltrated by mast cells, suggesting that airway obstruction and AHR are due to an ASM mast cell myositis. This observation emphasizes that the features that characterize asthma, as opposed to bronchitis, are due to abnormalities in smooth muscle responsiveness, which could be intrinsic or acquired, and that inflammation is only relevant in that it leads to these abnormalities. It also emphasizes the importance of micro-localization as an organizing principle in physiological responses to airway inflammation. Thus, if inflammation is localized to the epithelium and lamina propria, then the symptoms of bronchitis (cough and mucus hypersecretion) result, and it is only if the ASM is involved -- for reasons that remain to be established -- that asthma occurs.     

Neutrophils and macrophages related to the pathogenesis and disease development of chronic obstructive pulmonary disease by the inflammatory reaction

Chronic obstructive pulmonary disease (COPD) is a chronic airway disorder characterized by obstructive airflow limitation which is not completely reversible with treatment. Inflammatory changes in the peripheral airways, especially those with the diameter less than 2mm (so-called small airway disease) have been speculated to be initial steps of COPD. And so it must be quite clear that neutrophils and macrophages play an essential role in the pathogenesis of these lesions. Studies with bronchoalveolar lavage demonstrated an increase in neutrophil numbers and the neutrophil chemoattractant interleukin-8. Recent studies demonstrated that neutrophils and macrophages are increased and contain a variety of proteases, which are involved in cell infiltration and activation. Studies with gene-engineered animals and anti-cytokine treatment will facilitate better understanding the role of neutrophils and macrophages, and eventual novel therapy.     

Treating neutrophilic inflammation in COPD by targeting ALX/FPR2 resolution pathways

Neutrophilic inflammation persists in COPD despite best current therapies and it is particularly resistant to inhaled glucocorticosteroids. Persistent neutrophil activation not only contributes to matrix breakdown, but can maintain inflammation through the release of endogenous damage associated molecule patterns (DAMPs). Inhibiting excessive neutrophilic inflammation is challenging as many pathogen recognition receptors can initiate migration and the targeting of downstream signaling molecules may compromise essential host defense mechanisms. Here, we discuss new strategies to combat this inflammation in COPD by focusing on the anti-inflammatory role of ALX/FPR2 receptors. ALX/FPR2 is a promiscuous G-protein coupled receptor (GPCR) responding to lipid and peptide agonists that can either switch on acute inflammation or promote resolution of inflammation. We highlight this receptor as an emerging target in the pathogenesis of COPD because known ALX/FPR2 endogenous agonists are enriched in COPD. Serum Amyloid A (SAA) has recently been discovered to be abundantly expressed in COPD and is a potent ALX/FPR2 agonist that unlike almost all other inflammatory chemoattractants, is induced by glucocorticosteroids. SAA not only initiates lung inflammation via ALX/FPR2 but can allosterically modify this receptor so that it no longer transduces pro-resolving signals from endogenous lipoxins that would otherwise promote tissue healing. We propose that there is an imbalance in endogenous and microbial ALX/FPR2 receptor agonists in the inflamed COPD lung environment that oppose protective anti-inflammatory and pro-resolution pathways. These insights open the possibility of targeting ALX/FPR2 receptors using synthetic agonists to resolve persistent neutrophilic inflammation without compromising essential host defense mechanisms.     

A Modeling-Derived Hypothesis on Chronicity in Respiratory Diseases: Desensitized Pathogen Recognition Secondary to Hyperactive IRAK/TRAF6 Signaling

Several chronic respiratory diseases exhibit hyperactive immune responses in the lung: abundant inflammatory mediators; infiltrating neutrophils, macrophages, lymphocytes and other immune cells; and increased level of proteases. Such diseases include cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD) and severe/neutrophilic asthma. Paradoxically, patients with these diseases are also susceptible to detrimental bacterial infection and colonization. In this paper, we seek to explain how a positive feedback mechanism via IL-8 could lead to desensitization of epithelial cells to pathogen recognition thus perpetuating bacterial colonization and chronic disease states in the lung. Such insight was obtained from mathematical modeling of the IRAK/TRAF6 signaling module, and is consistent with existing clinical evidence. The potential implications for targeted treatment regimes for these persistent respiratory diseases are explored.     

The cytokine network in asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are very common inflammatory diseases of the airways. They both cause airway narrowing and are increasing in incidence throughout the world, imposing enormous burdens on health care. Cytokines play a key role in orchestrating the chronic inflammation and structural changes of the respiratory tract in both asthma and COPD and have become important targets for the development of new therapeutic strategies in these diseases.     

Proteinase 3 and neutrophil elastase enhance inflammation in mice by inactivating antiinflammatory progranulin

Neutrophil granulocytes form the body's first line of antibacterial defense, but they also contribute to tissue injury and noninfectious, chronic inflammation. Proteinase 3 (PR3) and neutrophil elastase (NE) are 2 abundant neutrophil serine proteases implicated in antimicrobial defense with overlapping and potentially redundant substrate specificity. Here, we unraveled a cooperative role for PR3 and NE in neutrophil activation and noninfectious inflammation in vivo, which we believe to be novel. Mice lacking both PR3 and NE demonstrated strongly diminished immune complex-mediated (IC-mediated) neutrophil infiltration in vivo as well as reduced activation of isolated neutrophils by ICs in vitro. In contrast, in mice lacking just NE, neutrophil recruitment to ICs was only marginally impaired. The defects in mice lacking both PR3 and NE were directly linked to the accumulation of antiinflammatory progranulin (PGRN). Both PR3 and NE cleaved PGRN in vitro and during neutrophil activation and inflammation in vivo. Local administration of recombinant PGRN potently inhibited neutrophilic inflammation in vivo, demonstrating that PGRN represents a crucial inflammation-suppressing mediator. We conclude that PR3 and NE enhance neutrophil-dependent inflammation by eliminating the local antiinflammatory activity of PGRN. Our results support the use of serine protease inhibitors as antiinflammatory agents.     

Respiratory syncytial virus infection results in airway hyperresponsiveness and enhanced airway sensitization to allergen.

Viral respiratory infections can predispose to the development of asthma by mechanisms that are presently undetermined. Using a murine model of respiratory syncytial virus (RSV) infection, acute infection is associated with airway hyperresponsiveness as well as enhanced responses to subsequent sensitization to allergen. We demonstrate that acute viral infection results in increased airway responsiveness to inhaled methacholine and pulmonary neutrophilic and eosinophilic inflammation. This response is associated with predominant production of Th-1-type cytokines in peribronchial lymph node cells in vitro. Mice sensitized to ovalbumin via the airways after RSV infection developed increased airway responsiveness to methacholine and pulmonary eosinophilic and neutrophilic inflammation, associated with the predominant production of Th-2-type cytokines. Treatment of the mice with anti-IL-5 antibody abolished airway hyperresponsiveness and eosinophilic but not neutrophilic inflammation in both acutely infected mice and mice sensitized after infection. We conclude that RSV infection results in airway hyperresponsiveness in the acute phase and leads to changes in immune function that can enhance the effects of airway sensitization to antigen after infection. In both situations, airway hyperresponsiveness is closely associated with pulmonary eosinophilic inflammation. This model provides a means for further analyzing the influence of viral respiratory infections on airway sensitization and the development of altered airway responsiveness.     

Fenofibrate Attenuates Neutrophilic Inflammation in Airway Epithelia: Potential Drug Repurposing for Cystic Fibrosis

A hallmark of cystic fibrosis (CF) lung disease is neutrophilic airway inflammation. Elevated neutrophil counts have been associated with decreased forced expiratory volume in 1 second and poor clinical measures in patients with CF. Interleukin 8 (IL‐8), epithelial neutrophil activating protein 78 (ENA‐78), tumor necrosis factor alpha (TNF‐α), granulocyte macrophage colony‐stimulating factor (GM‐CSF), and granulocyte colony‐stimulating factor (G‐CSF) contribute to neutrophil activation and disease pathogenesis in the airways of patients with CF. Drugs that modify the production of these chemokines in the airways could potentially benefit CF patients. Thus, we determined the effects of fenofibrate on their production in cell populations obtained from the airways. Human small airway epithelial cells and CF bronchial epithelial cells were treated with IL‐1β to induce inflammation. We cotreated the cells with fenofibrate at concentrations ranging from 10 to 50 μM to determine if this drug could attenuate the inflammation. IL‐8, ENA‐78, TNF‐α, GM‐CSF, and G‐CSF production were measured from the cell culture supernates by ELISA. ANOVA statistical testing was conducted using SPSS 17.0. IL‐1β increased the production of each of the chemokines by several fold. Fenofibrate reduced IL‐1β induced production of each of these neutrophilic chemokines at the concentrations used. IL‐1β increases the production of neutrophilic chemokines in airway epithelial cells. Cotreatment with fenofibrate blunts these processes. Fenofibrate should be explored as a therapeutic option to modulate the abundant neutrophilic inflammation observed in CF.     

Transepithelial migration of neutrophils into the lung requires TREM-1

Acute respiratory infections are responsible for more than 4 million deaths each year. Neutrophils play an essential role in the innate immune response to lung infection. These cells have an armamentarium of pattern recognition molecules and antimicrobial agents that identify and eliminate pathogens. In the setting of infection, neutrophil triggering receptor expressed on myeloid cells 1 (TREM-1) amplifies inflammatory signaling. Here we demonstrate for the first time that TREM-1 also plays an important role in transepithelial migration of neutrophils into the airspace. We developed a TREM-1/3–deficient mouse model of pneumonia and found that absence of TREM-1/3 markedly increased mortality following Pseudomonas aeruginosa challenge. Unexpectedly, TREM-1/3 deficiency resulted in increased local and systemic cytokine production. TREM-1/3–deficient neutrophils demonstrated intact bacterial killing, phagocytosis, and chemotaxis; however, histologic examination of TREM-1/3–deficient lungs revealed decreased neutrophil infiltration of the airways. TREM-1/3–deficient neutrophils effectively migrated across primary endothelial cell monolayers but failed to migrate across primary airway epithelia grown at the air-liquid interface. These data define a new function for TREM-1 in neutrophil migration across airway epithelial cells and suggest that it amplifies inflammation through targeted neutrophil migration into the lung.     

Bronchial hyperresponsiveness and bacterial respiratory infections.

Some studies suggest a potential role for bacterial respiratory tract infections in the development of bronchospasm and the progression of chronic obstructive pulmonary disease (COPD). Patients with bronchiectasis or cystic fibrosis have exaggerated airway reactivity; croup in children can also cause exaggerated upper and lower airway responsiveness. Bronchial obstruction after inhalation of Haemophilus influenzae and other bacteria has been reported. Between January 1989 and June 1990 we and two other centers studied 193 patients suffering from acute exacerbation of asthma. Fifty-two (27%) of these patients had bacteria in their sputum. Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Moraxella catarrhalis, and H influenzae were the most commonly isolated bacterial species. Antibiotics may be of value in the treatment of infective lung disease, not only by killing bacteria but also by preventing increases in bacterial histamine levels within the lung airways. Moreover, an antibiotic of proven efficacy can reduce airway reactivity in patients with bacterial exacerbations of COPD or bronchial asthma. In 12 patients with acute bacterial exacerbation of asthma and high airway reactivity to methacholine, a ten-day course of treatment with cefaclor and existing bronchodilators induced microbiologic cure and a slight but nonsignificant change in airway reactivity in nine patients. Antibiotic therapy has a minor but clear role in the control of acquired bronchial hyperreactivity during bacterial respiratory infections in asthmatic patients; however, because of airway inflammation, an antibiotic's efficacy is evident only when the inflammatory process subsides. Approaches designed to minimize airway reactivity may contribute to the prevention or reversal of respiratory failure during exacerbation of COPD and bronchial asthma.     

Innate immune receptors on neutrophils and their role in chronic lung disease

Neutrophils, the prototypic cells of the innate immune system, are recruited to infected sites to protect the human body from invading pathogens. To accomplish this function, neutrophils sense pathogens and endogenous damage-associated molecules via innate immune receptors, such as Toll-like receptors (TLRs) and other pattern recognition receptors. This defence function is essential for the pulmonary microenvironment where the host is faced with millions of particles and pathogens inhaled daily. Chronic lung diseases, such as cystic fibrosis or chronic obstructive pulmonary disease are characterized by a neutrophil accumulation and chronic bacterial colonization of the airways. Consequently, insights into the role of TLRs on neutrophils in chronic lung diseases are of high relevance for further diagnostic and therapeutic approaches. Here we summarize and discuss recent advances in the expression, regulation and functional role of TLRs on neutrophils in chronic lung diseases.     

Pathogenesis of persistent lymphatic vessel hyperplasia in chronic airway inflammation

Edema occurs in asthma and other inflammatory diseases when the rate of plasma leakage from blood vessels exceeds the drainage through lymphatic vessels and other routes. It is unclear to what extent lymphatic vessels grow to compensate for increased leakage during inflammation and what drives the lymphangiogenesis that does occur. We addressed these issues in mouse models of (a) chronic respiratory tract infection with Mycoplasma pulmonis and (b) adenoviral transduction of airway epithelium with VEGF family growth factors. Blood vessel remodeling and lymphangiogenesis were both robust in infected airways. Inhibition of VEGFR-3 signaling completely prevented the growth of lymphatic vessels but not blood vessels. Lack of lymphatic growth exaggerated mucosal edema and reduced the hypertrophy of draining lymph nodes. Airway dendritic cells, macrophages, neutrophils, and epithelial cells expressed the VEGFR-3 ligands VEGF-C or VEGF-D. Adenoviral delivery of either VEGF-C or VEGF-D evoked lymphangiogenesis without angiogenesis, whereas adenoviral VEGF had the opposite effect. After antibiotic treatment of the infection, inflammation and remodeling of blood vessels quickly subsided, but lymphatic vessels persisted. Together, these findings suggest that when lymphangiogenesis is impaired, airway inflammation may lead to bronchial lymphedema and exaggerated airflow obstruction. Correction of defective lymphangiogenesis may benefit the treatment of asthma and other inflammatory airway diseases.     

The non-neuronal cholinergic system in the airways: an unappreciated regulatory role in pulmonary inflammation?

The parasympathetic neurotransmitter acetylcholine is also synthesised and secreted by non-neuronal cells and modifies their behaviour. This is termed the "non-neuronal cholinergic system" and is present in airway inflammatory cells. Acetylcholine is predominantly pro-inflammatory for lymphocytes and epithelial cells, anti-inflammatory for mast cells and macrophages, both pro- and anti-inflammatory for monocytes, and variable in neutrophils and eosinophils. Expression and function of components of the non-neuronal cholinergic system, for example cholinoceptors, can be modified by nicotine in cigarette smoke, the inflammation of asthma and chronic obstructive pulmonary disease (COPD), and the drugs used in clinical management of these diseases. The non-neuronal cholinergic system of airway inflammatory cells represents a previously unappreciated regulatory pathway, with immunomodulatory effects that potentially influence the inflammation of asthma and COPD.     

Chronic Pseudomonas aeruginosa infection in cystic fibrosis airway disease: metabolic changes that unravel novel drug targets

The cystic fibrosis (CF) airways have an incompletely characterized defect in innate defense that eventually leads to bacterial infection and airway inflammation. Persistent Pseudomonas aerugionsa infection resulting from defective innate immunity and a bacterial phenotypic switch to a more intractable mucoid form inside the airway are now well established as important components of CF pathogenesis. Broad-based factors leading to chronic infection will be discussed with respect to: bacterial virulence in the context of biofilm formation, quorum sensing machinery and alginate overproduction, and failure of innate lung immunity in CF airways. In addition, a controversial question as to whether inflammation or infection comes first during CF airway disease will be addressed. Finally, a new hypothesis, that P. aeruginosa thrives as biofilms within the thickened anaerobic mucus layers, will be developed.     

Occupational exposure to toluene diisocyanate and neutrophilic bronchitis without asthma

Context. Isocyanates represent a leading cause of occupational asthma, and sputum neutrophilia or eosinophilia has been described in subjects with isocyanate-induced occupational asthma after exposure to these chemicals. One case of non-asthmatic eosinophilic bronchitis due to methylene diphenil isocyanates has been reported, but a similar condition in the instance of neutrophilic bronchial inflammation has never been described. Case details. We report a 34-year-old woman, who, 18 months after beginning work in a plastic industry, reported the onset of dry cough at work. Spirometry was normal, reversibility and methacholine challenge tests were negative. A specific inhalation challenge with toluene diisocyanate elicited dry cough without significant changes in respiratory function. Sputum induction showed a post-challenge neutrophil increase. Discussion. The results of our case suggest that the occurrence of a neutrophilic bronchial inflammation without the functional characteristics of occupational asthma as a consequence of exposure to toluene diisocyanate may also be considered, suggesting a diagnosis of occupational non-asthmatic neutrophilic bronchitis.     

Chronic Pseudomonas aeruginosa infection in cystic fibrosis airway disease: metabolic changes that unravel novel drug targets

The cystic fibrosis (CF) airways have an incompletely characterized defect in innate defense that eventually leads to bacterial infection and airway inflammation. Persistent Pseudomonas aerugionsa infection resulting from defective innate immunity and a bacterial phenotypic switch to a more intractable mucoid form inside the airway are now well established as important components of CF pathogenesis. Broad-based factors leading to chronic infection will be discussed with respect to: bacterial virulence in the context of biofilm formation, quorum sensing machinery and alginate overproduction, and failure of innate lung immunity in CF airways. In addition, a controversial question as to whether inflammation or infection comes first during CF airway disease will be addressed. Finally, a new hypothesis, that P. aeruginosa thrives as biofilms within the thickened anaerobic mucus layers, will be developed.     

Neutrophil histamine contributes to inflammation in mycoplasma pneumonia

Mycoplasmas cause chronic inflammation and are implicated in asthma. Mast cells defend against mycoplasma infection and worsen allergic inflammation, which is mediated partly by histamine. To address the hypothesis that mycoplasma provokes histamine release, we exposed mice to Mycoplasma pulmonis, comparing responses in wild-type and mast cell-deficient KitW-sh/KitW-sh (W-sh) mice. Low histamine levels in uninfected W-sh mice confirmed the conventional wisdom that mast cells are principal sources of airway and serum histamine. Although mycoplasma did not release histamine acutely in wild-type airways, levels rose up to 50-fold above baseline 1 week after infection in mice heavily burdened with neutrophils. Surprisingly, histamine levels also rose profoundly in infected W-sh lungs, increasing in parallel with neutrophils and declining with neutrophil depletion. Furthermore, neutrophils from infected airway were highly enriched in histamine compared with naive neutrophils. In vitro, mycoplasma directly stimulated histamine production by naive neutrophils and strongly upregulated mRNA encoding histidine decarboxylase, the rate-limiting enzyme in histamine synthesis. In vivo, treatment with antihistamines pyrilamine or cimetidine decreased lung weight and severity of pneumonia and tracheobronchitis in infected W-sh mice. These findings suggest that neutrophils, provoked by mycoplasma, greatly expand their capacity to synthesize histamine, thereby contributing to lung and airway inflammation.