Human mast cell and airway smooth muscle cell interactions: implications for asthma

Mast cell MrgprB2 in neuroimmune interaction in IgE-mediated airway inflammation and its modulation by β-arrestin2

Introduction

Allergic asthma has been linked to the activation of mast cells (MCs) by the neuropeptide substance P (SP), but the mechanism underlying this neuroimmune interaction is unknown. Substance P produced from cutaneous nociceptors activates MCs via Mas-related G-protein-coupled receptor B2 (MrgprB2) to enhance type 2 immune response in experimental atopic dermatitis in mice. We recently showed that the adapter protein β-arrestin2 (β-arr2) contributes to MrgprB2-mediated MC chemotaxis. The goals of this study were to determine if MrgprB2 facilitates neuroimmune interaction in IgE (FcεRI)-mediated allergic airway inflammation (AAI) and to assess if this response is modulated by β-arr2.

Methods

Wild-type (WT), MrgprB2-/- mice and mice with MC-specific deletion of β-arr2 (Cpa3Cre+ /β-arr2fl/fl ) were passively sensitized with anti-TNP-IgE and challenged with antigen. The generation of SP and MC recruitment in the lung were determined by immunofluorescence and toluidine blue staining, respectively. The transcripts for Tac1, MrgprB2, TNF-α, and Th2 cytokines in lung tissue were assessed by RT-PCR, and the release of selected cytokines in bronchoalveolar lavage (BAL) was determined by ELISA. Eosinophil and neutrophil recruitment in lung tissue and BAL were determined by immunofluorescence staining and flow cytometry, respectively. Goblet cell hyperplasia was determined by periodic acid-Schiff staining.

Results

Following IgE sensitization and antigen challenge in WT mice, SP generation, and MC recruitment, transcripts for Tac1, MrgprB2, TNF-α, and Th2 cytokine were upregulated when compared to the control challenge. TNF-α, Th2 cytokine production, eosinophil/neutrophil recruitment, and goblet cell hyperplasia were also increased. These responses were significantly reduced in MrgprB2-/- and Cpa3Cre+ /β-arr2fl/fl mice.

Discussion

The data presented herein suggest that SP-mediated MrgprB2 activation contributes to AAI and goblet cell hyperplasia in mice. Furthermore, these responses are modulated by β-arr2, which promotes MC recruitment to facilitate their activation through FcεRI.

Mast cell function in prostate inflammation, fibrosis, and smooth muscle cell dysfunction

Intraurethral inoculation of mice with uropathogenic Escherichia coli (CP1) results in prostate inflammation, fibrosis, and urinary dysfunction, recapitulating some but not all of the pathognomonic clinical features associated with benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). In both patients with LUTS and CP1-infected mice, we observed increased numbers and activation of mast cells and elevated levels of prostate fibrosis. Therapeutic inhibition of mast cells using a combination of a mast cell stabilizer, cromolyn sodium, and the histamine 1 receptor antagonist cetirizine di-hydrochloride in the mouse model resulted in reduced mast cell activation in the prostate and significant alleviation of urinary dysfunction. Treated mice showed reduced prostate fibrosis, less infiltration of immune cells, and decreased inflammation. In addition, as opposed to symptomatic CP1-infected mice, treated mice showed reduced myosin light chain-2 phosphorylation, a marker of prostate smooth muscle contraction. These results show that mast cells play a critical role in the pathophysiology of urinary dysfunction and may be an important therapeutic target for men with BPH/LUTS.NEW & NOTEWORTHY LUTS-associated benign prostatic hyperplasia is derived from a combination of immune activation, extracellular matrix remodeling, hyperplasia, and smooth muscle cell contraction in prostates of men. Using a mouse model, we describe the importance of mast cells in regulating these multiple facets involved in the pathophysiology of LUTS. Mast cell inhibition alleviates both pathology and urinary dysfunction in this model, suggesting the potential for mast cell inhibition as a therapeutic that prevents and reverses pathology and associated symptomology.

Mast cell effects on esophageal smooth muscle and their potential role in eosinophilic esophagitis and achalasia

Mast cells and eosinophils are the key effector cells of allergic disorders. Although most studies on eosinophilic esophagitis (EoE), an allergic disorder of the esophagus, have focused on the role of eosinophils, recent studies suggest a major role for mast cells in causing the clinical manifestations of this disease. Cellular and animal studies have demonstrated that mast cells can cause esophageal muscle cells to proliferate and differentiate into a more contractile phenotype, and that mediators released by degranulating mast cells such as tryptase and histamine can activate smooth muscle contraction pathways. Thus, activated mast cells in the esophageal muscularis propria might cause esophageal motility abnormalities, including the failure of lower esophageal sphincter relaxation typical of achalasia. In addition, mast cells have been implicated in the pathogenesis of a number of neurodegenerative disorders of the central nervous system such as Alzheimer's and Parkinson's diseases, because degranulating mast cells release proinflammatory and cytotoxic mediators capable of damaging neurons. Such mast cell degranulation in the myenteric plexus of the esophagus could cause the loss of enteric neurons that characterizes achalasia. In this report, we review the molecular mechanisms of esophageal smooth muscle contraction, and how mast cells products might affect that muscle and cause neurodegeneration in the esophagus. Based on these data, we present our novel, conceptual model for an allergy-induced form of achalasia mediated by mast cell activation in the esophageal muscularis propria.

A novel ELISA method to determine human MrgX2 in chronic urticaria

BACKGROUND

Mas-related G-protein coupled receptor member X2 (MrgX2) directly mediates drug-induced pseudo allergic reactions. Skin mast cell MrgX2 is upregulated in severe chronic urticaria (CU). Mast cells and leukocytes are key effector cells in allergic reactions and undergo degranulation upon stimulation. It is unknown whether circulating MrgX2 expression can be detected occurs in the whole blood of CU patients and reflects pseudo-allergic reaction. There is no effective method for its detection. Therefore, an enzyme-linked immuno-sorbent assay (ELISA) for MrgX2 was developed.

METHODS

Monoclonal and polyclonal MrgX2 specific antibodies were obtained from rabbits and mice immunized by MrgX2 peptides prepared. Indirect ELISA and Dot blot were used to determine antibody titers before a sandwich ELISA for MrgX2 was established. The whole blood from healthy subjects and CU patients was used to detect MrgX2 concentrations. The use of feasibility of this MrgX2-ELISA as a clinical detection tool was explored and diagnostic purposes was assessed.

RESULTS

The sandwich antibody ELISA method for MrgX2 was established with good linearity regression (R² = 0.9910). The lowest detection limit was 3.125 ng/mL. The quantification limit was 6.25 ng/mL. The sandwich ELISA for MrgX2 have good stability and high specificity. The initial truncation value of MrgX2 was 60.91 ng/mL (95% confidence interval). The whole blood MrgX2 concentrations in CU patients (median 98.01 ± 4.317 ng/mL, n = 75) was significantly increased compared to healthy subjects (58.09 ± 1.418 ng/mL, n = 75), with significant difference (p < 0.0001) and higher accuracy of (AUC = 0.8795). Comprehensive the frequency analysis of MrgX2 expression in 75 CU patients reference frequency distribution and ROC curve analysis, determined the threshold for CU patients as 71.23 ng/mL, with 81.33% sensitivity and 90.67% specificity.

CONCLUSION

MrgX2-ELISA provides a useful and convenient method for detecting MrgX2 in whole blood samples. The MrgX2-ELISA will help improve the understanding of the role of MrgX2 in regulating chronic urticaria.

Leukotriene D4 role in allergic asthma pathogenesis from cellular and therapeutic perspectives

Asthma is a chronic inflammatory and allergic disease that is mainly characterized by reversible airway obstruction and bronchial hyperresponsiveness. The incidence of asthma is increasing with more than 350 million people worldwide are affected. Up to now, there is no therapeutic option for asthma and most of the prescribed drugs aim to ameliorate the symptoms of the disease especially during the acute exacerbations after trigger exposure. Asthma is a heterogonous disease that involves interactions between inflammatory mediators and cellular components within the disease microenvironment including inflammatory and structural cells. Cysteinyl leukotrienes (cys-LTs) are inflammatory lipid mediators that have potent roles in asthma pathogenesis. CysLTs consisting of LTC₄, LTD₄, and LTE₄ are mainly secreted by leukocytes and act through three main G-protein coupled receptors (CysLT₁R, CysLT₂R, and CysLT₃R). LTD₄ is the most potent bronchoconstrictor which gives it the priority to be discussed in detail in this review. LTD₄ binds with high affinity to CysLT₁R and many studies showed that using CysLT₁R antagonists such as montelukast has a beneficial effect for asthmatics especially in corticosteroid refractory cases. Since asthma is a heterogeneous inflammatory disease of many cell types involved in the disease pathogenies and LTD₄ has a special role in inflammation and bronchoconstriction, this review highlights the role of LTD₄ on each cellular component in asthma and the benefits of using CysLT₁R antagonists in ameliorating LTD₄-induced effects.

An Allosteric Anti-tryptase Antibody for the Treatment of Mast Cell-Mediated Severe Asthma

Severe asthma patients with low type 2 inflammation derive less clinical benefit from therapies targeting type 2 cytokines and represent an unmet need. We show that mast cell tryptase is elevated in severe asthma patients independent of type 2 biomarker status. Active β-tryptase allele count correlates with blood tryptase levels, and asthma patients carrying more active alleles benefit less from anti-IgE treatment. We generated a noncompetitive inhibitory antibody against human β-tryptase, which dissociates active tetramers into inactive monomers. A 2.15 Å crystal structure of a β-tryptase/antibody complex coupled with biochemical studies reveal the molecular basis for allosteric destabilization of small and large interfaces required for tetramerization. This anti-tryptase antibody potently blocks tryptase enzymatic activity in a humanized mouse model, reducing IgE-mediated systemic anaphylaxis, and inhibits airway tryptase in Ascaris-sensitized cynomolgus monkeys with favorable pharmacokinetics. These data provide a foundation for developing anti-tryptase as a clinical therapy for severe asthma.

Bitter Taste Receptors: an Answer to Comprehensive Asthma Control?

PURPOSE OF REVIEW

Asthma is marked by peculiar pathological features involving airway contraction, an impinging inflammation in the lungs, and an inexorably progressive remodeling of pulmonary architecture. Current medications for management of asthma exacerbations fail to optimally mitigate these pathologies, which is partly due to the intrinsic heterogeneity in the development and progression of asthma within different populations. In recent years, the discovery of the ectopic expression of TAS2Rs in extraoral tissues and different cell types, combined with significant strides in gaining mechanistic understanding into receptor signaling and function, has revealed the potential to target TAS2Rs for asthma relief.

RECENT FINDINGS

TAS2R activation leads to relaxation of airway smooth muscle cells and bronchodilation. In addition, findings from preclinical studies in murine model of asthma suggest that TAS2R agonists inhibit allergen-induced airway inflammation, remodeling, and hyperresponsiveness. In this review, we expand on the opportunity presented by TAS2Rs in the development of a comprehensive asthma treatment that overcomes the limitations set forth by current asthma therapeutics.

Bitter Taste Receptors for Asthma Therapeutics

Clinical management of asthma and chronic obstructive pulmonary disease (COPD) has primarily relied on the use of beta 2 adrenergic receptor agonists (bronchodilators) and corticosteroids, and more recently, monoclonal antibody therapies (biologics) targeting specific cytokines and their functions. Although these approaches provide relief from exacerbations, questions remain on their long-term efficacy and safety. Furthermore, current therapeutics do not address progressive airway remodeling (AR), a key pathological feature of severe obstructive lung disease. Strikingly, agonists of the bitter taste receptors (TAS2Rs) deliver robust bronchodilation, curtail allergen-induced inflammatory responses in the airways and regulate airway smooth muscle (ASM) cell proliferation and mitigate features of AR in vitro and in animal models. The scope of this review is to provide a comprehensive and systematic insight into our current understanding of TAS2Rs with an emphasis on the molecular events that ensue TAS2R activation in distinct airway cell types and expand on the pleiotropic effects of TAS2R targeting in mitigating various pathological features of obstructive lung diseases. Finally, we will discuss specific opportunities that could help the development of selective agonists for specific TAS2R subtypes in the treatment of asthma.

Allergic asthma: an overview of metabolomic strategies leading to the identification of biomarkers in the field

Allergic asthma is a prominent disease especially during childhood. Indoor allergens, in general, and particularly house dust mites (HDM) are the most prevalent sensitizers associated with allergic asthma. Available data show that 65-130 million people are mite-sensitized world-wide and as many as 50% of these are asthmatic. In fact, sensitization to HDM in the first years of life can produce devastating effects on pulmonary function leading to asthmatic syndromes that can be fatal. To date, there has been considerable research into the pathological pathways and structural changes associated with allergic asthma. However, limitations related to the disease heterogeneity and a lack of knowledge into its pathophysiology have impeded the generation of valuable data needed to appropriately phenotype patients and, subsequently, treat this disease. Here, we report a systematic and integral analysis of the disease, from airway remodelling to the immune response taking place throughout the disease stages. We present an overview of metabolomics, the management of complex multifactorial diseases through the analysis of all possible metabolites in a biological sample, obtaining a global interpretation of biological systems. Special interest is placed on the challenges to obtain biological samples and the methodological aspects to acquire relevant information, focusing on the identification of novel biomarkers associated with specific phenotypes of allergic asthma. We also present an overview of the metabolites cited in the literature, which have been related to inflammation and immune response in asthma and other allergy-related diseases.

Emerging understanding of the mechanism of action of Bronchial Thermoplasty in asthma

Bronchial Thermoplasty (BT) is an endoscopic treatment for moderate-to-severe asthma patients who are uncontrolled despite optimal medical therapy. Effectiveness of BT has been demonstrated in several randomized clinical trials. However, the asthma phenotype that benefits most of this treatment is unclear, partly because the mechanism of action is incompletely understood. BT was designed to reduce the amount of airway smooth muscle (ASM), but additional direct and indirect effects on airway pathophysiology are expected. This review will provide an overview of the different components of airway pathophysiology including remodeling, with the ASM as the key player. Current concepts in the understanding of BT clinical effectiveness with a focus on its impact on airway remodeling will be reviewed.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Th2 cytokine-primed airway smooth muscle cells induce mast cell chemotaxis via secretion of ATP

OBJECTIVE

Mast cell infiltration into airway smooth muscle (ASM) bundle is an important feature of asthma. Extracellular adenosine triphosphate (eATP) contributes to the initiation of airway inflammation. eATP induces mast cells migration by acting through purinergic receptors. CD39 is an ectonucleotidase that degrades ATP to ADP and AMP. Whether eATP participates in the migration of mast cell towards ASM cells is still unknown.

METHODS

Airway smooth muscle cells (ASMCs) were isolated from C57/BL6J mice sensitized and challenged with OVA. ASMCs were in vitro cultured and stimulated with IL-4 + IL-13 in the presence or absence of exogenous CD39 or CD39 inhibitor ARL67156. ATP level in the supernatants was measured with ATP content determination kit. CXCL10 concentration in the ASMCs supernatants was measured by ELISA, the mRNA expression of CXCL10 in ASMCs was determined with real-time PCR. Human mast cell line HMC-1 was cultured in Iscove's-Modified Dubecco's Medium. The expression of CXCR3 in HMC-1 cells was determined with flow cytometry and real-time PCR, respectively. HMC-1 migration rates were determined with transwell system.

RESULTS

In the supernatants of Th2 cytokine-stimulated ASMCs, ATP level was higher than that without stimulation. CD39 decreased, whereas ARL67156 increased ATP level in the supernatants. Both ATP and the supernatants of Th2 cytokine-stimulated ASMCs induced migration of HMC-1 cells. The surface and mRNA expression of CXCR3 in HMC-1 cells, and the mRNA expression and secretion of CXCL10 in ASMCs were increased after stimulation with ATP or Th2 cytokines. All these effects were partially inhibited by CD39.

CONCLUSION

Our data suggested ASMCs in the asthma microenvironment promoted the migration of mast cells via secretion of ATP and the expression of CXCL10/CXCR3 axis. CD39 could reverse this effect and may be a new target for the treatment of asthma.

Bronchoprovocation tests in asthma: direct versus indirect challenges

PURPOSE OF REVIEW

This review describes different bronchoprovocation tests and their merits in diagnosing asthma.

RECENT FINDINGS

A new indirect challenge test using dry powder mannitol has been made available and has been systematically validated and tested in different populations.

SUMMARY

Airway hyperresponsiveness (AHR) is a characteristic feature of asthma, and its measurement using direct inhalation challenges, particularly with inhaled methacholine or histamine, or indirect challenges using stimuli such as exercise, dry air hyperpnea, distilled water, hypertonic saline and mannitol, and the pharmacological agent adenosine monophosphate is important in establishing a correct diagnosis. Direct challenge tests are sensitive and have a high negative predictive value to exclude asthma. This is particularly true in excluding asthma as a diagnosis in patients with symptoms that suggest asthma, but are caused by another condition. Indirect AHR correlates better with eosinophilic airway inflammation. Therefore, indirect challenge tests are seen as more specific. A newer indirect challenge test that uses a kit containing prepacked capsules of dry powder mannitol in different doses is safe and efficient to use. Indirect challenge tests are superior to direct challenge tests to confirm the presence of asthma.

Regulation of pulmonary inflammation by mesenchymal cells

Pulmonary inflammation and tissue remodelling are common elements of chronic respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and pulmonary hypertension (PH). In disease, pulmonary mesenchymal cells not only contribute to tissue remodelling, but also have an important role in pulmonary inflammation. This review will describe the immunomodulatory functions of pulmonary mesenchymal cells, such as airway smooth muscle (ASM) cells and lung fibroblasts, in chronic respiratory disease. An important theme of the review is that pulmonary mesenchymal cells not only respond to inflammatory mediators, but also produce their own mediators, whether pro-inflammatory or pro-resolving, which influence the quantity and quality of the lung immune response. The notion that defective pro-inflammatory or pro-resolving signalling in these cells potentially contributes to disease progression is also discussed. Finally, the concept of specifically targeting pulmonary mesenchymal cell immunomodulatory function to improve therapeutic control of chronic respiratory disease is considered.

Time- and concentration-dependent effects of exogenous serotonin and inflammatory cytokines on mast cell function

Mast cells play a significant role in both the innate and adaptive immune response; however, the tissue-bound nature of mast cells presents an experimental roadblock to performing physiologically relevant mast cell experiments. In this work, a heterogeneous cell culture containing primary culture murine peritoneal mast cells (MPMCs) was studied to characterize the time-dependence of mast cell response to allergen stimulation and the time- and concentration-dependence of the ability of the heterogeneous MPMC culture to uptake and degranulate exogenous serotonin using high performance liquid chromatography (HPLC) coupled to an electrochemical detector. Additionally, because mast cells play a central role in asthma, MPMCs were exposed to CXCL10 and CCL5, two important asthma-related inflammatory cytokines that have recently been shown to induce mast cell degranulation. MPMC response to both allergen exposure and cytokine exposure was evaluated for 5-HT secretion and bioactive lipid formation using ultraperformance liquid chromatography coupled to an electrospray ionization triple quadrupole mass spectrometer (UPLC-MS/MS). In this work, MPMC response was shown to be highly regulated and responsive to subtle alterations in a complex environment through time- and concentration-dependent degranulation and bioactive lipid formation. These results highlight the importance of selecting an appropriate mast cell model when studying mast cell involvement in allergic response and inflammation.

Human Lung Mast Cell Products Regulate Airway Smooth Muscle CXCL10 Levels

In asthma, the airway smooth muscle (ASM) produces CXCL10 which may attract CXCR3⁺ mast/T cells to it. Our aim was to investigate the effects of mast cell products on ASM cell CXCL10 production. ASM cells from people with and without asthma were stimulated with IL-1β, TNF-α, and/or IFNγ and treated with histamine (1–100 μM) ± chlorpheniramine (H1R antagonist; 1 μM) or ranitidine (H2R antagonist; 50 μM) or tryptase (1 nM) ± leupeptin (serine protease inhibitor; 50 μM), heat-inactivated tryptase, or vehicle for 4 h or 24 h. Human lung mast cells (MC) were isolated and activated with IgE/anti-IgE and supernatants were collected after 2 h or 24 h. The supernatants were added to ASM cells for 48 h and ASM cell CXCL10 production detected using ELISA (protein) and real-time PCR (mRNA). Histamine reduced IL-1β/TNF-α-induced CXCL10 protein, but not mRNA, levels independent of H1 and H2 receptor activation, whereas tryptase and MC 2 h supernatants reduced all cytokine-induced CXCL10. Tryptase also reduced CXCL10 levels in a cell-free system. Leupeptin inhibited the effects of tryptase and MC 2 h supernatants. MC 24 h supernatants contained TNF-α and amplified IFNγ-induced ASM cell CXCL10 production. This is the first evidence that MC can regulate ASM cell CXCL10 production and its degradation. Thus MC may regulate airway myositis in asthma.

Are mast cells instrumental for fibrotic diseases?

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disorder of unknown etiology characterized by accumulation of lung fibroblasts and extracellular matrix deposition, ultimately leading to compromised tissue architecture and lung function capacity. IPF has a heterogeneous clinical course; however the median survival after diagnosis is only 3–5 years. The pharmaceutical and biotechnology industry has made many attempts to find effective treatments for IPF, but the disease has so far defied all attempts at therapeutic intervention. Clinical trial failures may arise for many reasons, including disease heterogeneity, lack of readily measurable clinical end points other than overall survival, and, perhaps most of all, a lack of understanding of the underlying molecular mechanisms of the progression of IPF. The precise link between inflammation and fibrosis remains unclear, but it appears that immune cells can promote fibrosis by releasing fibrogenic factors. So far, however, therapeutic approaches targeting macrophages, neutrophils, or lymphocytes have failed to alter disease pathogenesis. A new cell to garner research interest in fibrosis is the mast cell. Increased numbers of mast cells have long been known to be present in pulmonary fibrosis and clinically correlations between mast cells and fibrosis have been reported. More recent data suggests that mast cells may contribute to the fibrotic process by stimulating fibroblasts resident in the lung, thus driving the pathogenesis of the disease. In this review, we will discuss the mast cell and its physiological role in tissue repair and remodeling, as well as its pathological role in fibrotic diseases such as IPF, where the process of tissue repair and remodeling is thought to be dysregulated.

Antigen-induced mast cell expansion and bronchoconstriction in a mouse model of asthma

Lung mastocytosis and antigen-induced bronchoconstriction are common features in allergic asthmatics. It is therefore important that animal models of asthma show similar features of mast cell inflammation and reactivity to inhaled allergen. We hypothesized that house dust mite (HDM) would induce mastocytosis in the lung and that inhalation of HDM would trigger bronchoconstriction. Mice were sensitized with intranasal HDM extract, and the acute response to nebulized HDM or the mast cell degranulating compound 48/80 was measured with respiratory input impedance. Using the constant-phase model we calculated Newtonian resistance (Rn) reflecting the conducting airways, tissue dampening (G), and lung elastance (H). Bronchoalveolar lavage fluid was analyzed for mouse mast cell protease-1 (mMCP-1). Lung tissue was analyzed for cytokines, histamine, and α-smooth muscle actin (α-SMA), and histological slides were stained for mast cells. HDM significantly increased Rn but H and G remained unchanged. HDM significantly expanded mast cells compared with control mice; at the same time mMCP-1, α-SMA, Th2 cytokines, and histamine were significantly increased. Compound 48/80 inhalation caused bronchoconstriction and mMCP-1 elevation similarly to HDM inhalation. Bronchoconstriction was eliminated in mast cell-deficient mice. We found that antigen-induced acute bronchoconstriction has a distinct phenotype in mice. HDM sensitization caused lung mastocytosis, and we conclude that inhalation of HDM caused degranulation of mast cells leading to an acute bronchoconstriction without affecting the lung periphery and that mast cell-derived mediators are responsible for the development of the HDM-induced bronchoconstriction in this model.

Macrophage TNF-α mediates parathion-induced airway hyperreactivity in guinea pigs

Organophosphorus pesticides (OPs) are implicated in human asthma. We previously demonstrated that, at concentrations that do not inhibit acetylcholinesterase activity, the OP parathion causes airway hyperreactivity in guinea pigs as a result of functional loss of inhibitory M2 muscarinic receptors on parasympathetic nerves. Because macrophages are associated with asthma, we investigated whether macrophages mediate parathion-induced M2 receptor dysfunction and airway hyperreactivity. Airway physiology was measured in guinea pigs 24 h after a subcutaneous injection of parathion. Pretreatment with liposome-encapsulated clodronate induced alveolar macrophage apoptosis and prevented parathion-induced airway hyperreactivity in response to electrical stimulation of the vagus nerves. As determined by qPCR, TNF-α and IL-1β mRNA levels were increased in alveolar macrophages isolated from parathion-treated guinea pigs. Parathion treatment of alveolar macrophages ex vivo did not significantly increase IL-1β and TNF-α mRNA but did significantly increase TNF-α protein release. Consistent with these data, pretreatment with the TNF-α inhibitor etanercept but not the IL-1β receptor inhibitor anakinra prevented parathion-induced airway hyperreactivity and protected M2 receptor function. These data suggest a novel mechanism of OP-induced airway hyperreactivity in which low-level parathion activates macrophages to release TNF-α-causing M2 receptor dysfunction and airway hyperreactivity. These observations have important implications regarding therapeutic approaches for treating respiratory disease associated with OP exposures.

Secreted factors from human mast cells trigger inflammatory cytokine production by human airway smooth muscle cells

BACKGROUND

A notable feature of allergic asthma is the infiltration of mast cells into smooth muscle in the human airway. Thus, mast cells and human airway smooth muscle (hASM) cells are likely to exhibit mutual functional modulation via direct cell-cell contact or through released factors. This study examined mast cell modulation of hASM cell cytokine release.

METHODS

The mast cell line HMCα was used to model mast cell function. hASM cells were either co-cultured directly with resting or IgE/antigen-stimulated HMCα cells or treated with HMCα-conditioned media to examine the impact on cytokine release. The activation pathways triggered in hASM cells by the mast cell-derived factors were examined through the use of selective inhibitors and by Western blotting.

RESULTS

HMCα cells, or their conditioned media, induced the expression of cytokines (IL-8 and IL-6) by hASM cells at both the mRNA and the protein level. Cytokine expression in hASM cells was greatly amplified when HMCα cells were IgE/antigen-activated. The effects of the conditioned media were not mediated by the chemokines MCP-1 and MIP-1α or by exosomes. While the mast cell-derived factor(s) increased p38(MAPK) phosphorylation in hASM cells, cytokine production was not inhibited by the p38(MAPK) inhibitor SB203580. hASM cell production of IL-8 induced by HMCα condition media but not IL-6 was, however, attenuated by the Src tyrosine kinase inhibitor PP2.

CONCLUSIONS

Our study shows that the release of soluble mediators by activated mast cells can stimulate hASM cells to elicit production of proinflammatory cytokines that may then exacerbate airway inflammation in asthma.

Mast cell tryptase stimulates myoblast proliferation; a mechanism relying on protease-activated receptor-2 and cyclooxygenase-2

BACKGROUND

Mast cells contribute to tissue repair in fibrous tissues by stimulating proliferation of fibroblasts through the release of tryptase which activates protease-activated receptor-2 (PAR-2). The possibility that a tryptase/PAR-2 signaling pathway exists in skeletal muscle cell has never been investigated. The aim of this study was to evaluate whether tryptase can stimulate myoblast proliferation and determine the downstream cascade.

METHODS

Proliferation of L6 rat skeletal myoblasts stimulated with PAR-2 agonists (tryptase, trypsin and SLIGKV) was assessed. The specificity of the tryptase effect was evaluated with a specific inhibitor, APC-366. Western blot analyses were used to evaluate the expression and functionality of PAR-2 receptor and to assess the expression of COX-2. COX-2 activity was evaluated with a commercial activity assay kit and by measurement of PGF2α production. Proliferation assays were also performed in presence of different prostaglandins (PGs).

RESULTS

Tryptase increased L6 myoblast proliferation by 35% above control group and this effect was completely inhibited by APC-366. We confirmed the expression of PAR-2 receptor in vivo in skeletal muscle cells and in satellite cells and in vitro in L6 cells, where PAR-2 was found to be functional. Trypsin and SLIGKV increased L6 cells proliferation by 76% and 26% above control, respectively. COX-2 activity was increased following stimulation with PAR-2 agonist but its expression remained unchanged. Inhibition of COX-2 activity by NS-398 abolished the stimulation of cell proliferation induced by tryptase and trypsin. Finally, 15-deoxy-Δ-12,14-prostaglandin J2 (15Δ-PGJ2), a product of COX-2-derived prostaglandin D2, stimulated myoblast proliferation, but not PGE2 and PGF2α.

CONCLUSIONS

Taken together, our data show that tryptase can stimulate myoblast proliferation and this effect is part of a signaling cascade dependent on PAR-2 activation and on the downstream activation of COX-2.

Human lung mast cells modulate the functions of airway smooth muscle cells in asthma

BACKGROUND

Activated mast cell densities are increased on the airway smooth muscle in asthma where they may modulate muscle functions and thus contribute to airway inflammation, remodelling and airflow obstruction.

OBJECTIVES

To determine the effects of human lung mast cells on the secretory and proliferative functions of airway smooth muscle cells from donors with and without asthma.

METHODS

Freshly isolated human lung mast cells were stimulated with IgE/anti-IgE. Culture supernatants were collected after 2 and 24 h and the mast cells lysed. The supernatants/lysates were added to serum-deprived, subconfluent airway smooth muscle cells for up to 48 h. Released chemokines and extracellular matrix were measured by ELISA, proliferation was quantified by [(3) H]-thymidine incorporation and cell counting, and intracellular signalling by phospho-arrays.

RESULTS

Mast cell 2-h supernatants reduced CCL11 and increased CXCL8 and fibronectin production from both asthmatic and nonasthmatic muscle cells. Leupeptin reversed these effects. Mast cell 24-h supernatants and lysates reduced CCL11 release from both muscle cell types but increased CXCL8 release by nonasthmatic cells. The 24-h supernatants also reduced asthmatic, but not nonasthmatic, muscle cell DNA synthesis and asthmatic cell numbers over 5 days through inhibiting extracellular signal-regulated kinase (ERK) and phosphatidylinositol (PI3)-kinase pathways. However, prostaglandins, thromboxanes, IL-4 and IL-13 were not involved in reducing the proliferation.

CONCLUSIONS

Mast cell proteases and newly synthesized products differentially modulated the secretory and proliferative functions of airway smooth muscle cells from donors with and without asthma. Thus, mast cells may modulate their own recruitment and airway smooth muscle functions locally in asthma.

Mast cells mediate hyperoxia-induced airway hyper-reactivity in newborn rats

Premature infants are at increased risk of developing airway hyper-reactivity (AHR) after oxidative stress and inflammation. Mast cells contribute to AHR partly by mediator release, so we sought to determine whether blocking mast cell degranulation or recruitment prevents hyperoxia-induced AHR, mast cell accumulation, and airway smooth muscle (ASM) changes. Rats were exposed at birth to air or 60% O2 for 14 d, inducing significantly increased AHR in the latter group, induced by nebulized methacholine challenge and measured by forced oscillometry. Daily treatment (postnatal d 1-14) with intraperitoneal cromolyn prevented hyperoxia-induced AHR, as did treatment with imatinib on postnatal d 5-14, compared with vehicle treated controls. Cromolyn prevented mast cell degranulation in the trachea but not hilar airways and blocked mast cell accumulation in the hilar airways. Imatinib treatment completely blocked mast cell accumulation in tracheal/hilar airway tissues. Hyperoxia-induced AHR in neonatal rats is mediated, at least in part, via the mast cell.

Suppression of allergen-induced respiratory dysfunction and airway inflammation in sensitized guinea pigs by Mn(II)(Me(2)DO2A), a novel superoxide scavenger compound

Reactive oxygen species produced during allergic inflammation are key players of the pathophysiology of asthma, leading to oxidative tissue injury and inactivation of endogenous manganese superoxide dismutase (MnSOD). On this ground, removal of excess superoxide anion by scavenger molecules would be beneficial and protective. Here we show that a novel manganese(II)-containing polyamine-polycarboxylic compound, termed Mn(II)(Me(2)DO2A), with potent superoxide dismuting properties decreases the respiratory and histopathological lung abnormalities due to allergen inhalation in a model of ovalbumin (OA)-induced allergic asthma-like reaction in sensitized guinea pigs. Severe respiratory dysfunction in response to OA aerosolic challenge arose rapidly in the sensitized animals and was accompanied by bronchoconstriction, alveolar hyperinflation, mast cell activation, increased leukocyte infiltration (evaluated by myeloperoxidase assay), oxidative lung tissue injury (evaluated by the thiobarbituric-acid-reactive substances and nitrotyrosine immunostaining), decay of endogenous MnSOD activity, production of pro-inflammatory prostaglandins, and lung cell apoptosis. Treatment with Mn(II)(Me(2)DO2A) (15mg/kg, given 1h before allergen challenge), but not the inactive congener Zn(II)(Me(2)DO2A) lacking redox-active metal site, significantly attenuated all the above functional, histopathological and biochemical parameters of allergic inflammation and restored the levels of MnSOD activity. In conclusion, our findings support the potential therapeutic use of Mn(II)(Me(2)DO2A) as novel superoxide scavenger drug in asthma and anaphylactic reactions.

Regulation of human mast cell and basophil function by anaphylatoxins C3a and C5a

Allergic diseases such as asthma result from inappropriate immunologic responses to common environmental allergens in genetically susceptible individuals. Following allergen exposure, interaction of dendritic cells (DC) with CD4(+) T cells leads to the production of Th2 cytokines, which induce B cells to synthesize IgE molecules (sensitization phase). These IgE molecules bind to their high affinity receptors (FcvarepsilonRI) on the surface of mast cells and basophils and their subsequent cross-linking by allergen results in the release of preformed and newly synthesized mediators, which cause bronchoconstriction, lung inflammation and airway hyperresponsiveness (AHR) in asthma (effector phase). The complement components C3a and C5a levels are increased in the lungs of patients with asthma and are likely generated via the actions of both allergen and mast cell proteases. In vivo studies with rodents have shown that while C3a facilitates allergen sensitization in some models C5a inhibits this response. Despite this difference, both anaphylatoxins promote lung inflammation and AHR in vivo indicating that cells other than DC and T cells likely mediate the functional effects of C3a and C5a in asthma. This review focuses on the contribution of C3a and C5a in the pathogenesis of asthma with a particular emphasis on mast cells and basophils. It discusses the mechanisms by which anaphylatoxins activate mast cells and basophils and the associated signaling pathways via which their receptors are regulated by priming and desensitization.

Chitosan-hyaluronic acid nanoparticles loaded with heparin for the treatment of asthma

The purpose of this study was to produce mucoadhesive nanocarriers made from chitosan (CS) and hyaluronic acid (HA), and containing the macromolecular drug heparin, suitable for pulmonary delivery. For the first time, this drug was tested in ex vivo experiments performed in mast cells, in order to investigate the potential of the heparin-loaded nanocarriers in antiasthmatic therapy. CS and mixtures of HA with unfractionated or low-molecular-weight heparin (UFH and LMWH, respectively) were combined to form nanoparticles by the ionotropic gelation technique. The resulting nanoparticles loaded with UFH were between 162 and 217 nm in size, and those prepared with LMWH were 152 nm. The zeta potential of the nanoparticle formulations ranged from +28.1 to +34.6 mV, and in selected nanosystems both types of heparin were associated with a high degree of efficiency, which was approximately 70%. The nanosystems were stable in phosphate buffered saline (PBS), pH 7.4, for at least 24h, and released 10.8% of UFH and 79.7% of LMWH within 12h of incubation. Confocal microscopy experiments showed that fluorescent heparin-loaded CS-HA nanoparticles were effectively internalized by rat mast cells. Ex vivo experiments aimed at evaluating the capacity of heparin to prevent histamine release in rat mast cells indicated that the free or encapsulated drug exhibited the same dose-response behaviour.

Airway injury as a mechanism for exercise-induced bronchoconstriction in elite athletes

Exercise-induced bronchoconstriction (EIB) is a consequence of evaporative water loss in conditioning the inspired air. The water loss causes cooling and dehydration of the airway surface. One acute effect of dehydration is the release of mediators, such as prostaglandins, leukotrienes, and histamine, that can stimulate smooth muscle, causing contraction and a change in vascular permeability. Inspiring cold air increases dehydration of the surface area and causes changes in bronchial blood flow. This article proposes that the pathogenesis of EIB in elite athletes relates to the epithelial injury arising from breathing poorly conditioned air at high flows for long periods of time or high volumes of irritant particles or gases. The evidence to support this proposal comes from many markers of injury. The restorative process after injury involves plasma exudation and movement of cells into the airways, a process repeated many times during a season of training. This process has the potential to expose smooth muscle to a wide variety of plasma- and cell-derived substances. The exposure to these substances over time can lead to an alteration in the contractile properties of the smooth muscle, making it more sensitive to mediators of bronchoconstriction. It is proposed that cold-weather athletes have airway hyperresponsiveness (AHR) to pharmacologic agents as a result of epithelial injury. In those who are allergic, AHR can also be expressed as EIB. The role of beta(2)-receptor agonists in inhibiting and enhancing the development of AHR and EIB is discussed.

Heparin and structurally related polymers attenuate eotaxin-1 (CCL11) release from human airway smooth muscle

BACKGROUND AND PURPOSE

The glycosaminoglycan heparin has anti-inflammatory activity and is exclusively found in mast cells, which are localized within airway smooth muscle (ASM) bundles of asthmatic airways. Interleukin (IL)-13 induces the production of multiple inflammatory mediators from ASM including the eosinophil chemoattractant chemokine, eotaxin-1. Heparin and related glycosaminoglycan polymers having structurally heterogeneous polysaccharide side chains that varied in molecular weight, sulphation and anionic charge were used to identify features of the heparin molecule linked to anti-inflammatory activity.

EXPERIMENTAL APPROACH

Cultured human ASM cells were stimulated with interleukin (IL)-13 in the absence or presence of heparin and related polymers. Eotaxin-1 was quantified using chemokine antibody arrays and ELISA.

KEY RESULTS

Unfractionated heparin attenuated IL-13-dependent eotaxin-1 production and this effect was reproduced with low molecular weight heparins (3 and 6 kDa), demonstrating a minimum activity fragment of at least 3 kDa. N-desulphated, 20% re-N-acetylated heparin (anticoagulant) was ineffective against IL-13-dependent eotaxin-1 production compared with 90% re-N-acetylated (anticoagulant) or O-desulphated (non-anticoagulant) heparin, suggesting a requirement for N-sulphation independent of anticoagulant activity. Other sulphated molecules with variable anionic charge and molecular weight exceeding 3 kDa (dextran sulphate, fucoidan, chondroitin sulphate B) inhibited IL-13-stimulated eotaxin-1 release to varying degrees. However, non-sulphated dextran had no effect.

CONCLUSIONS

Inhibition of IL-13-dependent eotaxin-1 release by heparin involved but did not depend upon sulphation, though loss of N-sulphation reduced the attenuating activity, which could be restored by N-acetylation. This anti-inflammatory effect was also partially dependent on anionic charge, but independent of molecular size above 3 kDa and the anticoagulant action of heparin.

Tryptase activates TGFbeta in human airway smooth muscle cells via direct proteolysis

Transforming growth factor beta (TGFbeta) is a key remodelling factor in asthma. It is produced as a latent complex and the main limiting step in TGFbeta bioavailability is its activation. Mast cell tryptase has been shown to stimulate the release of functionally active TGFbeta from human airway smooth muscle (ASM) cells [P. Berger, P.O. Girodet, H. Begueret, O. Ousova, D.W. Perng, R. Marthan, A.F. Walls, J.M. Tunon de Lara, Tryptase-stimulated human airway smooth muscle cells induce cytokine synthesis and mast cell chemotaxis, FASEB J. 17 (2003) 2139-2141]. The aim of this study was to determine if tryptase could cause TGFbeta activation as well as expression in ASM cells via its receptor, proteinase-activated receptor 2 (PAR2). Tryptase caused TGFbeta activation without affecting levels of total TGFbeta. This effect was inhibited by the selective tryptase inhibitor FUT175 and leupeptin but not mimicked by the PAR2 activating peptide SLIGKV-NH(2). Furthermore, the ASM cells used in the study did not express PAR2. The results indicate that tryptase activates TGFbeta via a PAR2-independent proteolytic mechanism in human ASM cells and may help understanding the role of tryptase in asthma.

The mast cell and allergic diseases: role in pathogenesis and implications for therapy

Mast cells have long been recognized for their role in the genesis of allergic inflammation; and more recently for their participation in innate and acquired immune responses. Mast cells reside within tissues including the skin and mucosal membranes, which interface with the external environment; as well as being found within vascularized tissues next to nerves, blood vessels and glandular structures. Mast cells have the capability of reacting both within minutes and over hours to specific stimuli, with local and systemic effects. Mast cells express the high affinity IgE receptor (FcepsilonRI) and upon aggregation of FcepsilonRI by allergen-specific IgE, mast cells release and generate biologically active preformed and newly synthesized mediators which are involved in many aspects of allergic inflammation. While mast cells have been well documented to be essential for acute allergic reactions, more recently the importance of mast cells in reacting through pattern recognition receptors in innate immune responses has become recognized. Moreover, as our molecular understanding of the mast cell has evolved, novel targets for modulation have been identified with promising therapeutic potential.

Esophageal subepithelial fibrosis in children with eosinophilic esophagitis

OBJECTIVES

Esophageal subepithelial fibrosis has been reported in adults with eosinophilic esophagitis (EE). Our goal was to determine the prevalence of esophageal fibrosis in children with EE, to determine whether it is specific for EE, and to correlate it with clinical and pathological features.

PATIENTS AND METHODS

Twenty-one children with EE, 7 with eosinophilic gastroenteritis, 6 with gastroesophageal reflux disease, and 17 control children were studied. Distal esophageal biopsy specimens containing lamina propria were evaluated for extent of subepithelial collagen deposition by use of trichrome staining. Fibrosis was defined as abnormally increased collagen deposition, determined after the establishment of normal patterns on sections of esophagus from pediatric autopsies. Maximum numbers of intraepithelial and lamina propria eosinophils per high-power field by hematoxylin and eosin staining and mast cells per high-power field by immunohistochemical staining for tryptase were determined. Eosinophil and mast cell degranulation in epithelium and lamina propria was determined by use of immunohistochemical staining for major basic protein and tryptase, respectively. The patients' records were reviewed.

RESULTS

Esophageal subepithelial fibrosis was present in 12 (57%) patients with EE, 1 with eosinophilic gastroenteritis, 0 with gastroesophageal reflux disease, and 1 control patient. Forty-two percent of those with fibrosis had dysphagia, 80% of whom had food impactions; these symptoms were present only in patients with fibrosis. Within the EE group, fibrosis was not associated with duration of symptoms or with increasing numbers of infiltrating eosinophils/mast cells, but it was associated with eosinophil degranulation.

CONCLUSIONS

Esophageal subepithelial fibrosis is prevalent in EE and is specific for the disease in children. It is associated with dysphagia, and it may explain and predict future esophageal dysmotility. Fibrosis is related to the extent of esophageal eosinophil activation, as evidenced by eosinophil degranulation.

Differential regulation of chemokine expression by Th1 and Th2 cytokines and mechanisms of eotaxin/CCL-11 expression in human airway smooth muscle cells

BACKGROUND

Airway smooth muscle (ASM) cells may contribute to the pathogenesis of asthma including airway inflammation and remodeling. We focused our study on the regulation of chemokine expression by cytokines and analyzed the mechanisms of eotaxin/CCL-11 expression in ASM cells.

METHODS

Human ASM cells were cultured in vitro and treated with IL-4, interferon-gamma (IFNgamma), and tumor necrosis factor-alpha (TNFalpha). Secretion of chemokines into the culture medium was analyzed by ELISA. Expression of eotaxin mRNA was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Binding of transcription factor signal transducer activator of transcription (STAT) 6 to the eotaxin promoter-derived DNA was analyzed by pull-down Western blot. To assess transcriptional regulation of eotaxin, cells were transfected with eotaxin promoter-luciferase reporter plasmids, and activity was determined by dual luciferase assay.

RESULTS

The Th2 cytokine IL-4 preferentially stimulated the expression of the CC chemokine receptor (CCR) 3-ligand chemokines eotaxin, eotaxin-3, and MCP-4. The Th1 cytokine IFNgamma stimulated the expression of chemokines IP-10 and RANTES. IL-4 stimulated nuclear translocation of signal transducer activator of transcription 6 (STAT6) and its binding to the eotaxin promoter region. IL-4 activated the eotaxin promoter and its activity was inhibited by mutation of the binding site for STAT6 in the promoter.

CONCLUSIONS

The Th2 cytokine IL-4 preferentially stimulated the expression of CCR3 ligand chemokines including eotaxin in ASM cells. The transcription factor STAT6 may play a pivotal role in the activation of eotaxin transcription in response to IL-4.

Prolonged exposure to hyperoxia increases perivascular mast cells in rat lungs

Prolonged hyperoxia, as may be used to treat patients with severe hypoxemia, can lead to lung injury, respiratory failure, and death. Resident mast cells play important roles in regulating the lung response to changing environmental conditions, as evidenced by their roles in asthma and airway hyperresponsiveness. In this study we evaluated the effect of prolonged hyperoxia on the number and distribution of mast cells in the rat lung. In rats maintained in normoxia, mast cells were distributed primarily in the loose connective tissue surrounding large bronchioles and vessels of the lung. In rats exposed to normobaric hyperoxia for 72 hr, mast cell number in lung sections increased significantly, and mast cells were found preferentially accumulated around vessels throughout the lung. Notably, mast cells around smaller vessels were abundant in hyperoxic lungs but rare in normoxic lungs. Also, mast cells were increased in the pleura of lungs exposed to hyperoxia. These changes in mast cell number and distribution in response to hyperoxia were evident in aged (22-month-old) rats as well as young (3-month-old) rats. As mast cell-derived mediators have many effects, e.g., on vascular leak and vascular tone, positioning of increased mast cell numbers throughout the lung vasculature may be an important contributor to changes in lung function subsequent to persistent hyperoxia.

Budesonide effects on Clara cell under normal and allergic inflammatory condition

Clara cells are nonciliated secretory cells implicated in lung homeostasis by the synthesis of immunomodulatory and host defense products, being one of the most important the CC16 protein. In this study, we compared the effects of budesonide (BUD), an inhaled corticoid, on Clara cell biology and its ability to reverse morphofunctional changes induced in an allergic airway hyper-responsiveness mouse model. In normal mice, exposure to BUD induced morphological changes compatible with a state of maximal differentiation on CC16 positive cells which developed a prominent cupola filled up with numerous mitochondria rich in CYP2E1, a member of the cytochrome P450 family. Consequently, CYP2E1 expression raised significantly. Exposure to OVA provoked hypertrophy of Clara cells and an increment in their number per millimeter of basal membrane. These cells acquired a mucous cell phenotype characterized by a notorious expansion of the secretory granular content. Synthesis of CC16 was greatly up-regulated concurrent to the finding of MUC5AC expression and the increment of epidermal growth factor receptor (EGFR). Mitochondrial content decreased significantly with a consequent reduction in CYP2E1 expression. After BUD treatment of OVA-challenged animals, the majority of Clara cells regained their normal morphology and functional characteristics; CYP2E1 levels raised when compared to the OVA exposed group. The BUD potential to differentiate Clara cells appeared to be important for the regression of the profound changes generated by the allergic injury. These results demonstrated the wide range of stimuli that can modify different aspects of Clara cell biology, and highlighted the effects of budesonide as a modulator of P450 enzymes, which probably contributes to a complementary antiinflamatory activity.

Mast cell migration to Th2 stimulated airway smooth muscle from asthmatics

BACKGROUND

Mast cell microlocalisation within the airway smooth muscle (ASM) bundle is an important determinant of the asthmatic phenotype. We hypothesised that mast cells migrate towards ASM in response to ASM derived chemokines.

METHODS

Primary ASM cultures from subjects with and without asthma were stimulated with interleukin (IL)-1beta, IL-4, and IL-13 alone and in combination. Mast cell chemotaxis towards these ASM supernatants was investigated, and the chemotaxins mediating migration by using specific blocking antibodies for stem cell factor (SCF) and the chemokine receptors CCR3, CXCR1, 3 and 4 as well as the Gi inhibitor pertussis toxin and the tyrosine kinase inhibitor genistein were defined. The concentrations of CCL11, CXCL8, CXCL10, TGF-beta, and SCF in the supernatants were measured and the effect of non-asthmatic ASM supernatants on the mast cell chemotactic activity of asthmatic ASM was examined.

RESULTS

Human lung mast cells and HMC-1 cells migrated towards Th2 stimulated ASM from asthmatics but not non-asthmatics. Mast cell migration was mediated through the combined activation of CCR3 and CXCR1. CCL11 and CXCL8 expression by ASM increased markedly after stimulation, but was similar in those with and without asthma. ASM supernatants from non-asthmatics inhibited mast cell migration towards the asthmatic ASM supernatant.

CONCLUSION

Th2 stimulated ASM from asthmatics is chemotactic for mast cells. Non-asthmatic ASM releases a mediator or mediators that inhibit mast cell migration towards stimulated asthmatic ASM. Specifically targeting mast cell migration into the ASM bundle may provide a novel treatment for asthma.

ADAM33: a newly identified gene in the pathogenesis of asthma

There is much to find out about this fascinating and complex molecule in relation to the development and progression of asthma. Added to it are three further new asthma/allergy genes identified by positional cloning: PDH Finger Protein II (PHF11) on chromosome 13q14, which encodes NY-REN-34 a protein first described in patients with renal cell carcinoma [67]; Dipeptidyl diptidase 10 (DDP10) on chromosome 2q14 [68]; and G protein-coupled receptor for asthma susceptibility (GPRA) on chromosome 7p [69]. For each of these genes, as is the case for ADAM33, determining their normal function(s) and how these become disordered in asthma is the future challenge.

Tissue-specific renin-angiotensin system in pulmonary lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease found in middle-aged women, is characterized by cystic lung destruction and abdominal tumors (e.g., angiomyolipomas, lymphangioleimyomas), resulting from proliferation of abnormal-appearing, smooth muscle-like cells (LAM cells). The LAM cells, in combination with other cells, form nodular structures within the lung interstitium and in the walls of the cysts. LAM cells contain mutations in the tuberous sclerosis complex TSC1 and/or TSC2 genes, which lead to dysregulation of the mammalian target of rapamycin, affecting cell growth and proliferation. Proliferation and migration of vascular smooth muscle cells and production of angiogenic factors are regulated, in part, by angiotensin II. To determine whether a LAM-specific renin-angiotensin system might play a role in the pathogenesis of LAM, we investigated the expression of genes and gene products of this system in LAM nodules. mRNA for angiotensinogen was present in RNA isolated by laser-captured microdissection from LAM nodules. Angiotensin I-converting enzyme and chymase-producing mast cells were present within the LAM nodules. We detected renin in LAM cells, as determined by the presence of mRNA and immunohistochemistry. Angiotensin II type 1 and type II receptors were identified in LAM cells by immunohistochemistry and immunoblotting of microdissected LAM nodules. Angiotensin II is localized in cells containing alpha-smooth muscle actin (LAM cells). A LAM-specific renin-angiotensin system appears to function within the LAM nodule as an autocrine system that could promote LAM cell proliferation and migration, and could represent a pharmacologic target.

Human airway smooth muscle cells express eotaxin in response to signaling following mast cell contact

BACKGROUND

Asthma is a chronic inflammatory disease of the airways. Mast-cell (MC)-derived cytokines may mediate both airway inflammation and remodeling. It has also been shown that airway smooth muscle cells (ASMC) can be a source of proinflammatory cytokines. In the human airways, MC-ASMC cell interactions may have pivotal effects on modulating inflammation.

OBJECTIVES

We wanted to know whether the production of eotaxin, an important proinflammatory cytokine, through a cell-to-cell contact mechanism of human ASMC activation by MC was mediated by p38 MAPK.

METHODS

We cocultured normal humanASMC with a human MC line (HMC-1) and assayed for the production of eotaxin.

RESULTS

When cultured together, human ASMC and HMC-1 contact induced eotaxin secretion. Separation of HMC-1 and human ASMC by a porous membrane inhibited this induction. Coculturing of human ASMC with HMC-1 induced increased expression of eotaxin gene mRNA. HMC-1-derived cellular membranes caused an increase in eotaxin production in human ASMC. Activation of p38 MAPK was also seen in cocultures by Western blot, whereas eotaxin production in cocultures was significantly inhibited by the p38 inhibitor SB203580.

CONCLUSION

These novel studies reveal the importance of cell-to-cell interactions in the complex milieu of airway inflammation.

The extracellular deposition of mast cell products is increased in hypertrophic airways smooth muscles in allergic asthma but not in nonallergic asthma

BACKGROUND

Bronchial asthma is characterized by airways smooth muscle hypertrophy and infiltration of mast cells in the bronchial mucosa. The aim of this investigation was to study the distribution of mast cells in different compartments in the bronchial mucosa of allergic and nonallergic asthma in relation to airways remodeling.

METHODS

Bronchial biopsies were obtained from 29 subjects with allergic and nonallergic asthma and healthy controls. The biopsies were stained for mast cells by means of the tryptase specific antibody AA1. Extracellular deposition of mast cell products were judged on a semi-quantitative scale. Mast cells per mm(2) were counted in epithelium, lamina propria and the smooth muscle compartment. Smooth muscle was visualized by actin antibodies and the proportion of staining of the biopsy estimated. Laminin and tenascin layers were visualized by their respective antibodies.

RESULTS

Airways smooth muscle thickness was greater in allergic vs nonallergic asthma (P < 0.001). Mast cells were increased in all three compartments in both allergic and nonallergic asthma, with significantly higher numbers in smooth muscles in allergic asthma (P < 0.03). The extracellular deposition of mast cell products was more common in allergic than nonallergic asthma in lamina propria and smooth muscles (P = 0.025; P = 0.002, respectively). In patients with allergic asthma the numbers of mast cells with extracellular deposition of mast cell products were significantly correlated to the thickness of the laminin and tenascin layers.

CONCLUSION

Our results suggest that there are large differences between allergic and nonallergic asthmatics as to mast cell activation and airways smooth muscle thickness. Our data implies that mast cells are causally involved in structural alterations in allergic asthma.

Some structural determinants of the antiproliferative effect of heparin-like molecules on human airway smooth muscle

Accumulation of airway smooth muscle (ASM) and its infiltration by mast cells are key pathological features of airway remodelling in asthma. Heparin, a major component of mast cell granules, inhibits ASM proliferation by an unknown mechanism. Here, unfractionated heparins and related glycosaminoglycans having structurally heterogeneous polysaccharide side chains that varied in molecular weight, sulphation and anionic charge were used to identify features of the heparin molecule that were required for its antiproliferative activity in cultured human ASM cells. Proliferation induced by 10% fetal bovine serum (FBS) was abrogated by two unfractionated commercial heparin preparations (Sigma and Multiparin) and this effect was reproduced with each of three low-molecular weight heparin preparations (3, 5 and 6 kDa, respectively), demonstrating that antiproliferative activity resided in at least a 3 kDa heparin fraction. N-desulphated 20% re-acetylated (N-de) heparin (anticoagulant) and O-desulphated heparin (O-de) (non-anticoagulant) fractions also inhibited FBS-dependent proliferation (rank potency: Sigma heparin > O-de > N-de) suggesting that the antiproliferative action of heparin involved N-sulphation but was independent of its anticoagulant activity. Other sulphated molecules with variable anionic charge (dextran sulphate, fucoidan, chondroitin sulphates A or B, heparan sulphate) inhibited proliferation to varying degrees, as did the non-sulphated molecules hyaluronic acid and poly-L-glutamic acid. However, nonsulphated dextran had no effect. In summary, attenuation of FBS-dependent proliferation of human ASM by heparin involves but does not depend upon sulphation, although loss of N-sulphation reduces antiproliferative activity. This antiproliferative effect is independent of anionic charge and the anticoagulant actions of heparin.

Reduction of antigen-induced respiratory abnormalities and airway inflammation in sensitized guinea pigs by a superoxide dismutase mimetic

Reactive oxygen species have been implicated in the pathogenesis of asthma and, in atopic asthmatics, endogenous superoxide dismutase (SOD) enzyme levels are known to decrease. This suggests that replacing a failed endogenous SOD enzyme system with a mimetic of the endogenous enzyme would be beneficial and protective. In this study we demonstrate that removal of superoxide by the SOD mimetic (SODm) M40403 reduces the respiratory and histopathological lung abnormalities due to ovalbumin (OA) aerosol in a model of allergic asthma-like reaction in sensitized guinea pigs. Both respiratory abnormalities and bronchoconstriction in response to OA challenge are nearly absent in naïve animals, while they sharply became severe in sensitized animals. In addition, OA aerosol induced a reduction of MnSOD activity which was paralleled with bronchiolar lumen reduction, pulmonary air space hyperinflation, mast cell degranulation, eosinophil infiltration, bronchial epithelial cell apoptosis, increase in myeloperoxidase activity, malonyldialdehyde production and 8-hydroxy-2'-deoxyguanosine formation in the lung tissue, as well as elevation of PGD2 in the bronchoalveolar lavage fluid. Treatment with M40403 restored the levels of MnSOD activity and significantly reduced all the above parameters. In summary, our findings support the potential therapeutic use of SOD mimetics in asthma and anaphylactic reactions and account for a critical role for superoxide in acute allergic asthma-like reaction in actively sensitized guinea pig.

Exercise-induced bronchoconstriction: pathogenesis

There is still active debate on the acute mechanism of exercise-induced bronchoconstriction (EIB). Although it is unlikely that vasoconstriction and hyperemia of the bronchial vasculature are essential events for EIB, it is likely that this vasculature enhances the airway response to dehydration and contributes to the pathogenesis of EIB, particularly in elite athletes. Accumulating evidence suggests that airway smooth muscle (ASM) becomes more sensitive as a result of repeated exposure to bulk plasma in response to airway injury from dehydration. Recent evidence also demonstrates sufficient concentrations of mediators that could affect ASM. Paradoxically, mediator release from mast cells may be enhanced and their contractile effects greater when beta(2)-receptor agonists are taken daily. The effect of drugs that have the potential to reduce microvascular leak and reduce or inhibit release or action of these mediators needs to be investigated in elite athletes.

Airway smooth muscle cells enhance C3a-induced mast cell degranulation following cell-cell contact

Growing evidence suggests that anaphylatoxins, C3a and C5a, play important roles in innate immunity and may also participate in the pathogenesis of asthma. Previous studies with animal models and immunohistochemistry analysis of lung tissue indicated that anaphylatoxins may regulate airway hyperresponsiveness (AHR) in asthma via the activation of their cell surface G protein-coupled receptors (C3aR and C5aR) in airway smooth muscle (ASM) cells. Using RT-PCR, flow cytometry, and confocal microscopy, we made the surprising observation that while C3aR and C5aR were expressed in human mast cells, they were not present in cultured primary human or murine ASM cells. Furthermore, we could not detect C3aR in smooth muscle-positive cells of human trachea or bronchus. Interestingly, incubation of human mast cells with ASM cells, but not its culture supernatant, caused a significant enhancement of C3a-induced mast cell degranulation. Although stem cell factor (SCF) and its receptor c-kit are constitutively expressed on ASM cells and mast cells, respectively, neutralizing antibodies to SCF and c-kit failed to inhibit ASM cell-mediated enhancement of mast cell degranulation. However, dexamethasone-treated ASM cells were normal for cell surface SCF expression but were significantly less effective in enhancing C3a-induced mast cell degranulation when compared with untreated cells. These findings suggest that cell-cell interaction between ASM cells and mast cells, via a SCF-c-kit-independent but dexamethasone-sensitive mechanism, enhances C3a-induced mast cell degranulation, which likely regulates ASM function, thus contributing to the pathogenesis of asthma.

Anaphylatoxin C3a receptors in asthma

The complement system forms the central core of innate immunity but also mediates a variety of inflammatory responses. Anaphylatoxin C3a, which is generated as a byproduct of complement activation, has long been known to activate mast cells, basophils and eosinophils and to cause smooth muscle contraction. However, the role of C3a in the pathogenesis of allergic asthma remains unclear. In this review, we examine the role of C3a in promoting asthma. Following allergen challenge, C3a is generated in the lung of subjects with asthma but not healthy subjects. Furthermore, deficiency in C3a generation or in G protein coupled receptor for C3a abrogates allergen-induced responses in murine models of pulmonary inflammation and airway hyperresponsiveness. In addition, inhibition of complement activation or administration of small molecule inhibitors of C3a receptor after sensitization but before allergen challenge inhibits airway responses. At a cellular level, C3a stimulates robust mast cell degranulation that is greatly enhanced following cell-cell contact with airway smooth muscle (ASM) cells. Therefore, C3a likely plays an important role in asthma primarily by regulating mast cell-ASM cell interaction.

Benefit from anti-inflammatory treatment during clinical remission of atopic asthma

STUDY OBJECTIVES

Subjects with atopic asthma often experience a disappearance of symptoms around puberty. However, airway inflammation and remodeling may persist. It is unknown whether those findings warrant prolonged anti-inflammatory treatment despite the absence of symptoms. In this study, we investigated whether a short course of combined anti-inflammatory treatment would, also in this specific patient population, diminish airway inflammation and/or remodeling.

DESIGN

A double-blind, randomized placebo-controlled trial was conducted in 28 asymptomatic subjects with a history of atopic asthma, with established bronchial hyperresponsiveness to methacholine (MCh) as non-invasive indicator of ongoing airway pathology.

INTERVENTIONS

Intervention consisted of the salmeterol/fluticasone propionate combination (SFC) product (50/250 microg bid via the Diskus inhaler) or placebo for 3 months.

MEASUREMENTS

The change in lung function (FEV1), bronchial response to MCh and adenosine monophosphate (AMP), the fraction of nitric oxide in exhaled air (FENO) and quality of life (QOL) scores were measured. Also, bronchial biopsies were taken and cryo sections immunostained for eosinophils (major basic protein, MBP) and mast cells (tryptase and chymase) before and after treatment. The change in reticular basement membrane (RBM) thickness, one of the parameters of airway remodeling, was also determined.

RESULTS

SFC treatment improved hyperresponsiveness to MCh (P = 0.014) as well as AMP (P = 0.011), and reduced FENO (P < 0.001) significantly as compared with placebo. Lung function tended to improve (NS). Furthermore, SFC treatment reduced tryptase in the subepithelium of bronchial biopsy specimens (P = 0.01), and slightly reduced RBM thickness (P = 0.05). However, eosinophils in (sub)epithelium were not significantly affected; neither were chymase levels, blood eosinophils or QOL scores.

CONCLUSIONS

We found that 3 months of treatment with fluticasone propionate and salmeterol reduced airway hyperresponsiveness, FENO and tryptase density in the airway mucosa as markers of airway inflammation. MBP density in the airway mucosa and QOL were, however, unchanged. The clinical relevance of these findings, especially with respect to the long-term outcome, has not been determined yet.