Transforming growth factor beta 1 (TGF beta 1) gene expression by eosinophils in asthmatic airway inflammation

Controversy surrounding the increased expression of TGF beta 1 in asthma

Asthma is a waxing and waning disease that leads to structural changes in the airways, such as subepithelial fibrosis, increased mass of airway smooth muscle and epithelial metaplasia. Such a remodeling of the airways futher amplifies asthma symptoms, but its etiology is unknown. Transforming growth factor β1 is a pleiotropic cytokine involved in many fibrotic, oncologic and immunologic diseases and is believed to play an essential role in airway remodeling that occurs in asthmatic patients. Since it is secreted in an inactive form, the overall activity of this cytokine is not exclusively determined by its level of expression, but also by extensive and complex post-translational mechanisms, which are all importanin modulating the magnitude of the TGFβ1 response. Even if TGFβ1 upregulation in asthma is considered as a dogma by certain investigators in the field, the overall picture of the published litterature is not that clear and the cellular origin of this cytokine in the airways of asthmatics is still a contemporaneous debate. On the other hand, it is becoming clear that TGFβ1 signaling is increased in the lungs of asthmatics, which testifies the increased activity of this cytokine in asthma pathogenesis. The current work is an impartial and exhaustive compilation of the reported papers regarding the expression of TGFβ1 in human asthmatics. For the sake of comparison, several studies performed in animal models of the disease are also included. Inconsistencies observed in human studies are discussed and conclusions as well as trends from the current state of the litterature on the matter are proposed. Finally, the different points of regulation that can affect the amplitude of the TGFβ1 response are briefly revised and the possibility that TGFβ1 is disregulated at another level in asthma, rather than simply in its expression, is highlighted.

IL-5-induced hypereosinophilia suppresses the antigen-induced immune response via a TGF-beta-dependent mechanism

Although eosinophils play an essential role in allergic inflammation, their role has recently been under controversy. Epidemic studies suggest that hypereosinophilia induced by parasite infection could suppress subsequent Ag sensitization, although the mechanism has not been fully clarified. In this study, we investigated whether eosinophils could suppress the Ag-specific immune response in the airway. BALB/c mice were sensitized and airway challenged with OVA. Systemic hypereosinophilia was induced by delivery of an IL-5-producing plasmid. IL-5 gene delivery suppressed the Ag-specific proliferation and cytokine production of CD4+ T cells in the spleen. IL-5 gene delivery before OVA sensitization significantly suppressed airway eosinophilia and hyperresponsiveness provoked by subsequent OVA airway challenge, while delivery during the OVA challenge did not suppress them. This IL-5-induced immune suppression was abolished in eosinophil-ablated mice, suggesting an essential role of eosinophils. IL-5 treatment increased the production of TGF-beta1 in the spleen, and we demonstrated that the main cellular source of TGF-beta1 production was eosinophils, using eosinophil-ablated mice and depletion study. TGF-beta1, but not IL-5 itself, suppressed the Ag-specific immune response of CD4+ T cells in vitro. Furthermore, IL-5 treatment enhanced phosphorylation of Smad2 in CD4+ T cells. Finally, a TGF-beta type I receptor kinase inhibitor restored this IL-5-induced immune suppression both in vitro and in vivo. These results suggest that IL-5-induced hypereosinophilia could suppress sensitization to Ag via a TGF-beta-dependent mechanism, thus suppressed allergic airway inflammation. Therefore, hypereosinophilia could reveal an immunosuppressive effect in the early stage of Ag-induced immune response.

Chronic intranasal administration of mould spores or extracts to unsensitized mice leads to lung allergic inflammation, hyper-reactivity and remodelling

Allergic asthma is a serious multifaceted disease characterized by eosinophil-rich airway inflammation, airway hyperreactivity and airway wall modifications known as remodelling. We previously demonstrated that the spores of two allergenic moulds, Alternaria alternata and Cladosporium herbarum, were potent inducers of immunoglobulin E (IgE) production. Moreover, mice sensitized by two intraperitoneal injections before intranasal challenge with A. alternata or C. herbarum spores developed an allergic lung inflammation and hyperreactivity. Here we report on the effect of chronic intranasal administration of C. herbarum spores or A. alternata extracts to unsensitized BALB/c mice. Our results demonstrate that this chronic treatment led to an increase of total serum IgE and the appearance of specific IgE and IgG1. Total cell number in bronchoalveolar lavage fluid from treated mice was highly increased compared to phosphate-buffered-saline-treated mice because of the accumulation of macrophages, neutrophils, lymphocytes and eosinophils. Airway hyperreactivity appeared after 3 weeks (extract) and 7 weeks (spores) and was maintained during the whole treatment. Increased interleukin-13 mRNA expression in the lungs and T helper type 2 cytokines (interleukin-4, -5, -6 and -13) and transforming growth factor-beta secretion in bronchoalveolar lavage fluid were also observed. Lung hydroxyproline and fibronectin contents indicated increased fibrosis in mice treated with mould allergen. These observations were confirmed by histological analysis demonstrating airway wall remodelling and strong mucus production. These observations show that this model, using chronic intranasal administration of relevant particulate allergens, is an interesting tool for the study of mechanisms leading to allergic pulmonary diseases and lung remodelling.

Eosinophils: singularly destructive effector cells or purveyors of immunoregulation?

Eosinophils are granulocytes typically associated with immune responses to a limited number of specific insults, including helminth infection and exposure to various allergens. Moreover, the overwhelming consensus from the literature is that eosinophils evolved as uniquely destructive leukocytes with cytotoxic activities as an adaptation for host defense. However, recent studies now suggest that the parochial caricature of eosinophils as effector cells with nonspecific killing abilities that evolved as a host defense mechanism against large nonphagotizable parasites is incomplete. A new paradigm has emerged describing eosinophils as initial responders to cell death/tissue damage that are a part of remodeling/repair processes and, more importantly, significant contributors to localized innate and acquired immune responses as well as systemic adaptive immunity. Significantly, this new paradigm does not preclude roles for eosinophils in host defense leading to tissue damage but instead suggests the equal importance of eosinophil-associated regulatory mechanisms modulating local tissue immune responses. The goal of this review is to summarize the data in support of this new paradigm. In turn, we believe that this expanded role provides a probable explanation for the presence of eosinophils in diverse disease settings such as asthma, allergy, cancer, transplant rejection, gastrointestinal inflammation, and viral or helminth infection.

Rapid and strong induction of apoptosis in human eosinophils by anti-CD30 mAb-coated microspheres and phagocytosis by macrophages

BACKGROUND

Eosinophils represent a potential therapeutic target in allergic diseases. We previously reported that two clones of anti-CD30 mAbs (HRS-4 and Ber-H8) induced extremely rapid and intense apoptosis in human eosinophils in vitro, but only when the mAbs were immobilized on plates [Matsumoto K, J Immunol 2004;172:2186]. As the initial step towards clinical application of these anti-CD30 mAbs in the treatment of allergic diseases, we made an attempt to clarify two issues; first, whether or not anti-CD30 mAb-coated microspheres can efficiently induce apoptosis in human eosinophils, and second, whether or not these apoptotic eosinophils can be phagocytosed by macrophages without the release of granular proteins.

METHODS

Purified human eosinophils were treated with anti-CD30 mAb-coated polystyrene microspheres (diameter, 1.44 mum). Apoptosis was determined by annexin V-binding. For the phagocytosis assay, eosinophils were co-cultured with monocyte-derived human macrophages or PMA-pretreated U-937 cells. Phagocytosis was determined by light microscopy and by the eosinophil-derived neurotoxin (EDN) concentration in the supernatant.

RESULTS

Anti-CD30 mAb-coated, but not control IgG1-coated microspheres significantly reduced eosinophil survival in a dose-dependent manner. Marked phagocytosis of the apoptotic eosinophils by macrophages was also observed when the eosinophils were treated with anti-CD30 mAb-coated microspheres. The apoptotic eosinophils released large amounts of EDN in the absence of macrophages; however, the EDN levels were significantly decreased when the eosinophils were co-cultured with macrophages.

CONCLUSIONS

Anti-CD30 mAb-coated microspheres are capable of inducing rapid and strong apoptosis in human eosinophils. Furthermore, the apoptotic eosinophils were also phagocytosed by macrophages with minimal release of the granular proteins.

Chemokines and their receptors as potential targets for the treatment of asthma

Asthma is a chronic and sometimes fatal disease, which affects people of all ages throughout the world. Important hallmarks of asthma are airway inflammation and remodelling, with associated bronchial hyperresponsiveness and variable airflow obstruction. These features are orchestrated by cells of both the innate (eosinophils, neutrophils and mast cells) and the adaptive (T(H)2 T cells) immune system, in concert with structural airway cells. Chemokines are important for the recruitment of both immune and structural cells to the lung, and also for their microlocalisation within the lung tissue. Specific blockade of the responses elicited by chemokines and chemokine receptors responsible for the pathological migration of airway cells could therefore be of great therapeutic interest for the treatment of asthma.

Profibrotic effect of IL-9 overexpression in a model of airway remodeling

IL-9 overexpression protects against alveolar fibrosis induced by crystalline silica particles. This cytokine is also involved in allergic asthma. In the present study, we examined the effect of IL-9 overexpression on the subepithelial fibrotic response, a feature of asthmatic remodeling, induced by chronic exposure to Alternaria alternata extract. IL-9-overexpressing mice (Tg5) and their wild-type counterparts (FVB) were intranasally exposed to A. alternata extract or PBS (controls) twice a week during 3 mo. At the end of the allergic challenge, enhanced pause (Penh) measured in response to methacholine and fibrotic parameters, such as collagen and fibronectin lung content, were significantly higher in Tg5 compared with FVB. Staining of lung sections with Masson's Trichrome also showed more collagen fibers in peribronchial areas of treated Tg5 mice. A similar recruitment of inflammatory cells was observed in challenged FVB and Tg5 mice, except for eosinophils, which were significantly more abundant in the lung of Tg5. High serum levels of IgE and IgG1 in both strains indicated that FVB and Tg5 developed a strong type 2 immune response. The concentration of the eosinophil chemoattractant RANTES and the profibrotic mediator connective tissue growth factor (CTGF) was higher in the BAL of challenged Tg5 than FVB. These results demonstrate a profibrotic role of IL-9 in an airway remodeling model, possibly involving eosinophils and CTGF. These data also highlight a dual role of IL-9 in lung fibrosis, being anti- or profibrotic depending on the alveolar or airway localization of the process, respectively.

Interleukin-10 regulates transforming growth factor-beta signaling in cultured human bronchial epithelial cells

BACKGROUND

The basic pathological features of bronchial asthma can be explained on the basis of chronic airway inflammation, involving inflammatory cells such as T cells (particularly type 2 helper T, Th2, cells) and mast cells, and airway remodeling. Many aspects of airway remodeling remain unclear at the molecular level. Recent attention has focused on the role of transforming growth factor (TGF)-beta, a fibrogenic cytokine, in airway remodeling. Currently available evidence suggests that airway remodeling is caused by an imbalance in regulatory mechanisms mediated by Smads, a family of signal-transducing molecules.

OBJECTIVES

We studied the effects of the Th2 cytokines interleukin (IL)-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF), and the regulatory cytokine IL-10 on the expression of inhibitory Smad7 protein in bronchial epithelial cells.

METHODS

Real-time reverse-transcriptase polymerase chain reaction was employed.

RESULTS

Stimulation with IL-10 upregulated the expression of Smad7 compared with control. Neither IL-5 nor GM-CSF induced Smad7 expression. Smad7 expression was upregulated by IL-10 plus either IL-5 or GM-CSF. IL-10 inhibited the expression of TGF-beta-inducible early gene, which is known to downregulate Smad7 expression.

CONCLUSIONS

Our results suggest that IL-10 acts as a regulatory cytokine in the inhibition of airway inflammation.

Genetic polymorphisms in transforming growth factor beta-1 (TGFB1) and childhood asthma and atopy

Transforming growth factor beta-1 (TGFB1) may influence asthma by modulating allergic airway inflammation and airway remodeling. The role of single nucleotide polymorphisms (SNPs) of TGFB1 in asthma remains inconclusive. We examined TGFB1 SNPs in relation to asthma risk and degree of atopy among 546 case-parent triads, consisting of asthmatics aged 4-17 years and their parents in Mexico City. Atopy to 24 aeroallergens was determined by skin prick tests. We genotyped five TGFB1 SNPs, including two known functional SNPs [C-509T (rs1800469), T869C (rs1982073)] and three others (rs7258445, rs1800472, rs8179181), using TaqMan and Masscode assays. We analyzed the data using log-linear and polytomous logistic methods. Three associated SNPs, including the two known functional SNPs, were statistically significantly related to asthma risk. Individuals carrying the T allele of C-509T had an increased risk of asthma [relative risk (RR)=1.42, 95% confidence interval (CI)=1.08-1.87 for one copy; RR (95%CI)=1.95 (1.36-2.78) for two copies]. For T869C, the RRs (95%CI) were 1.47 (1.09-1.98) for one and 2.00 (1.38-2.90) for two copies of the C allele. Similar results were found for rs7258445. The haplotype containing all three risk alleles conferred an increased risk of asthma (RR=1.48, 95% CI=1.11-1.95 for one copy; RR=1.77, 95% CI=1.22-2.57 for two copies). These three SNPs were also related to the degree of atopy. This largest study to date of genetic variation in TGFB1 and asthma and atopy adds to increasing evidence for a role in these disorders.

Cutting Edge: Deficiency of Macrophage Migration Inhibitory Factor Impairs Murine Airway Allergic Responses

Increased levels of macrophage migration inhibitory factor (MIF) in serum, sputum, and bronchioalveolar lavage fluid (BALF) from asthmatic patients and time/dose-dependent expression of MIF in eosinophils in response to phorbol myristate acetate suggest the participation of MIF in airway inflammation. In this study, we examined inflammation in OVA-sensitized mouse lungs in wild-type and MIF-deficient mice (MIF(-/-)). We report increased MIF in the lung and BALF of sensitized wild-type mice. MIF(-/-) mice demonstrated significant reductions in serum IgE and alveolar inflammatory cell recruitment. Reduced Th1/Th2 cytokines and chemokines also were detected in serum or BALF from MIF(-/-) mice. Importantly, alveolar macrophages and mast cells, but not dendritic cells or splenocytes, from MIF(-/-) mice demonstrated impaired CD4+ T cell activation, and the reconstitution of wild-type mast cells in MIF(-/-) mice restored the phenotype of OVA-induced airway inflammation, revealing a novel and essential role of mast cell-derived MIF in experimentally induced airway allergic diseases.

Regulation of airway smooth muscle alpha-actin expression by glucocorticoids

Airway smooth muscle hypertrophy appears to be present in severe asthma. However, the effect of corticosteroids on airway smooth muscle cell size or contractile protein expression has not been studied. We examined the effects of dexamethasone, fluticasone, and salmeterol on contractile protein expression in transforming growth factor (TGF)-beta-treated primary bronchial smooth muscle cells. Dexamethasone and fluticasone, but not salmeterol, each reduced expression of alpha-smooth muscle actin and the short isoform of myosin light chain kinase. Steady-state alpha-actin mRNA level and stability were unchanged, consistent with posttranscriptional control. Fluticasone significantly decreased alpha-actin protein synthesis following treatment with the transcriptional inhibitor actinomycin D, indicative of an inhibitory effect on mRNA translation. Fluticasone also significantly increased alpha-actin protein turnover. Finally, fluticasone reduced TGF-beta-induced incorporation of alpha-actin into filamentous actin, cell length, and cell shortening in response to ACh and KCl. We conclude that glucocorticoids reduce human airway smooth muscle alpha-smooth muscle actin expression and incorporation into contractile filaments, as well as contractile function, in part by attenuation of mRNA translation and enhancement of protein degradation.

Airway remodeling and airway smooth muscle in asthma

Airway remodeling in asthma has been recognized as structural changes of airways such as smooth muscle hypertrophy (an increase in size of airway smooth muscle cells) and hyperplasia (an increase in the number of airway smooth muscle cells), thickening and fibrosis of sub-epithelial basement membrane, hypertrophy of bronchial glands, goblet cell hyperplasia, and thickening of airway epithelium. In these pathological changes, airway smooth muscle remodeling has been recognized as one of the most important factors related to in vitro and in vitro airway responsiveness and the severity of asthma. Both hypertrophy and hyperplasia have been shown in asthmatic airways by morphometrical analyses, although there is a wide variation in the contribution of each mechanism in each patient. Such changes could also be recognized as a phenotypic modulation of airway smooth muscle. On the background of airway smooth muscle remodeling, the existence of several contributing factors, such as inflammatory mediators, growth factors, cytokines, extra-cellular matrix proteins, and genetic factors have been suggested. On the other hand, recent studies revealed that airway smooth muscle could also be a source of inflammatory mediators promoting airway inflammation. In this article, the recent understanding in the mechanisms of airway smooth muscle remodeling in asthma, its relations to airway inflammation and airway physiology, and possible usefulness of early intervention with inhaled glucocorticoids have been discussed.

Association between a TGFbeta1 promoter polymorphism and rhinosinusitis in aspirin-intolerant asthmatic patients

BACKGROUND

Rhinosinusitis is highly associated with aspirin-intolerant asthma (AIA). The risk of aspirin intolerance is higher in people with rhinosinusitis than in those without it. Recently, the role of transforming growth factor beta1 (TGFbeta1) in the pathogenesis of chronic rhinosinusitis has come under investigation. The goal of this study was to evaluate the association of TGFbeta1 gene polymorphism with an AIA phenotype in the Korean population.

METHODS

A promoter polymorphism of the TGFbeta1 gene, TGFbeta1-509C>T, and a coding polymorphism (L10P), were genotyped in 203 patients with AIA, 324 patients with aspirin-tolerant asthma (ATA), and 456 normal controls (NC). Serum TGFbeta1 levels were determined by ELISA.

RESULTS

The TGFbeta1-509C>T polymorphism was not significantly associated with the AIA phenotype; however, a significant association with the prevalence of rhinosinusitis in AIA (P=0.012), but not in ATA (P>0.05), was observed. When stratified by the presence of rhinosinusitis, the frequency of T allele carriers (CT or TT genotype) of TGFbeta1-509C>T was significantly higher in AIA (87.1%) compared to ATA (52.9%, P<0.001, OR=6.0, 95% CI=3.3-11.1). In addition, AIA patients carrying the TGFbeta1-509T allele showed a lower serum TGFbeta1 level compared to AIA patients carrying the TGFbeta1-509 CC genotype, especially when stratified by the presence of rhinosinusitis (P=0.002).

CONCLUSION

Our results show that the TGFbeta1 polymorphisms are not associated with the AIA phenotype in the Korean population, but may contribute to the development of the AIA phenotype with rhinosinusitis.

Airway remodeling in asthma and its influence on clinical pathophysiology

Bronchial asthma has been characterized by chronic and allergic airway inflammation, which induces cytological and histological changes in the airway structure over time. These changes have been called airway remodeling, which includes goblet cell hyperplasia, subepithelial fibrosis, and hyperplasia and hypertrophy of airway smooth muscle cells. Airway epithelium in asthma is often occupied with goblet cells, which contain secretory granules. Airway wall thickness increases because of subepithelial fibrosis, and hyperplasia and hypertrophy of airway smooth muscle cells and submucosal glands. Airway remodeling, therefore, can often cause irreversible airflow limitation, an increase of airway hyperresponsiveness and severity of asthma. Recent studies have demonstrated the molecular and cellular mechanisms of goblet cell hyperplasia, subepithelial fibrosis, and hyperplasia and hypertrophy of airway smooth muscle cells. Several lines of evidence suggest that airway remodeling has been induced by cytokines and mediators produced in chronic allergic airway inflammation. Thus, early intervention with inhaled corticosteroid may prevent progress of airway remodeling by suppressing allergic airway inflammation.

Airway remodeling from bench to bedside: current perspectives

Bronchospasm and airway inflammation can lead to a constellation of irreversible changes in airway structure termed remodeling. Remodeling theory offers insight into the permanent biomechanical and pathologic alterations of asthmatic airways. Structural changes seen in asthmatic patients can include thickening of the airway wall reticular basement membrane (RBM), the presence of an abnormal elastic fiber network, and alterations in airway cartilage structure. Although steroid therapy is helpful in symptomatic control, it does not remedy structural alterations or many aspects of the inflammatory milieu. This article discusses several studies and supports the need for further investigation.

Neutrophil-derived elastase induces TGF-beta1 secretion in human airway smooth muscle via NF-kappaB pathway

Neutrophils are infiltrated in airways of individuals with more severe and chronic asthma, with uncertain significance. Airway smooth muscle (ASM), apart from its contractile properties, is critically involved in the pathogenesis of asthma by producing inflammatory mediators. In the present study, we investigated the impact of neutrophil-derived elastase (NE) on ASM in terms of TGF-beta1 release, and we explored the underlying mechanisms. Primary ASM cells were serum starved for 24 h before stimulation with NE (0.01-0.5 microg/ml). TGF-beta1 in supernatant was determined by ELISA and mRNA quantified by real-time RT-QPCR. NF-kappaB nuclear translocation and activation was examined by Western blotting and kappaB-2 dEGFP reporter gene assay. Association of IL-1 receptor-associated kinase (IRAK) with MyD88 was studied by co-immunoprecipitation and Toll-like receptor 4 (TLR4) determined by FACS scan and Western blotting. We demonstrated that NE enhanced TGF-beta1 release in a time-dependent manner. This induction was inhibited by actinomycin D (5 mM), cycloheximide (5 mM), and NF-kappaB inhibitors, including pyrrolidine dithiocarbamate (PDTC, 1 mM), aspirin (2.5 mM), and sodium salyicylate (2.5 mM). Stimulation with NE was rapidly followed by association of IRAK with MyD88, phosphorylation of IkappaBalpha, and nuclear translocation of p65 with increased transactivation activity. We also found that TLR4 levels were reduced upon NE treatment. These data suggest that NE upregulates TGF-beta1 gene expression and release via My88/IRAK/NF-kappaB pathway, possibly through activation of TLR4, and shed light on a potential role of neutrophils in the pathogenesis of asthma.

Transcription factors T-bet and GATA-3 regulate development of airway remodeling

RATIONALE

Airway remodeling is an important feature of chronic asthma that causes irreversible airflow obstruction. Although asthma is considered to be a Th2 disease, the role of T-bet and GATA-3, the key transcription factors for differentiation toward Th1 and Th2 cells, in the pathogenesis of airway remodeling is poorly understood.

OBJECTIVES

We therefore examined the effects of GATA-3 or T-bet induction of Th1/Th2 bias on the development of airway remodeling in mice.

METHODS

The development of airway remodeling after repeated allergen challenges was analyzed using transgenic mice overexpressing either GATA-3 or T-bet.

MAIN RESULTS

The degrees of subepithelial fibrosis and airway smooth muscle hyperplasia after repeated allergen exposure were significantly enhanced in mice overexpressing GATA-3, compared with wild-type mice. Allergen-induced goblet cell hyperplasia and mucus hypersecretion were significantly lower in mice overexpressing T-bet than in wild-type mice. Eosinophilic airway inflammation increased in mice overexpressing GATA-3, but decreased in mice overexpressing T-bet after repeated allergen exposure. Cytokine analysis revealed that the Th1/Th2 cytokine balance shifted to Th2 in lung homogenates and lung T cells of mice overexpressing GATA-3, whereas this balance shifted to Th1 in those of mice overexpressing T-bet after allergen exposure. Lung transforming growth factor-beta and eotaxin levels were associated with the degree of subepithelial fibrosis and eosinophilic airway inflammation, respectively.

CONCLUSIONS

Overall, the results indicate that development of airway remodeling is regulated by the lung Th1/Th2 bias induced by GATA-3 and T-bet.

IL-17E upregulates the expression of proinflammatory cytokines in lung fibroblasts

BACKGROUND

IL-17E is a new TH2 cytokine that promotes airway eosinophilia in mice. IL-17E proinflammatory activity has been proposed to involve induction of cytokine and chemokine production. Recruitment of inflammatory cells may be mediated by tissue-resident cells.

OBJECTIVE

This study aimed to evaluate whether fibroblasts represent a target of IL-17E for the production of eosinophil active mediators in the lung.

METHODS

Expression of IL-17B receptor (IL-17BR), a receptor for IL-17E, was evaluated by immunofluorescent staining, Western blot, and real-time PCR in human primary lung fibroblasts. Mediator production was analyzed by using real-time PCR and ELISA after stimulation of fibroblasts with IL-17E alone or in combination with TNF-alpha and TGF-beta1. Expression of IL-17E and of eosinophil major basic protein was evaluated by immunohistochemistry in bronchial biopsies from subjects with asthma.

RESULTS

Human primary lung fibroblasts constitutively expressed IL-17BR. IL-17BR mRNA levels were increased in cells stimulated with TNF-alpha and decreased with TGF-beta1. IL-17E slightly upregulated CC chemokine ligand (CCL)-5, CCL-11, GM-CSF, and CXC chemokine ligand (CXCL)-8 mRNA in fibroblasts. Moreover, IL-17E and TNF-alpha synergistically induced GM-CSF and CXCL-8 mRNA. IL-17E also potentiated the upregulation of CXCL-8 transcripts observed with TGF-beta1. In contrast, TGF-beta1 decreased IL-17E-induced CCL-11 mRNA. The capacity of IL-17E to enhance GM-CSF and CXCL-8 responses to TNF-alpha was accompanied by production and secretion of both proteins by lung fibroblasts. Finally, IL-17E was detected in asthma in eosinophil-infiltrated bronchial submucosa.

CONCLUSION

IL-17E may contribute to the induction and maintenance of eosinophilic inflammation in the airways by acting on lung fibroblasts. This study supports a role for IL-17E in asthma pathophysiology.

Fibroblast growth factor 2 and transforming growth factor beta1 synergism in human bronchial smooth muscle cell proliferation

Bronchial smooth muscle cell (BSMC) hyperplasia is a typical feature of airway remodeling and contributes to airway obstruction and hyperresponsiveness in asthma. Fibroblast growth factor 2 (FGF-2) and transforming growth factor beta1 (TGF-beta1) are sequentially upregulated in asthmatic airways after allergic challenge. Whereas FGF-2 induces BSMC proliferation, the mitogenic effect of TGF-beta1 remains controversial, and the effect of sequential FGF-2 and TGF-beta1 co-stimulation on BSMC proliferation is unknown. This study aimed to assess the individual and sequential cooperative effects of FGF-2 and TGF-beta1 on human BSMC proliferation and define the underlying mechanisms. Mitogenic response was measured using crystal violet staining and [3H]-thymidine incorporation. Steady-state mRNA and protein levels were measured by semiquantitative RT-PCR, Western blot, and ELISA, respectively. TGF-beta1 (0.1-20 ng/ml) alone had no effect on BSMC proliferation, but increased the proliferative effect of FGF-2 (2 ng/ml) in a concentration-dependent manner (up to 6-fold). Two distinct platelet-derived growth factor receptor (PDGFR) inhibitors, AG1296 and Inhibitor III, as well as a neutralizing Ab against PDGFRalpha, partially blocked the synergism between these two growth factors. In this regard, TGF-beta1 increased PDGF-A and PDGF-C mRNA expression as well as PDGF-AA protein expression. Moreover, FGF-2 pretreatment increased the mRNA and protein expression of PDGFRalpha and the proliferative effect of exogenous PDGF-AA (140%). Our data suggest that FGF-2 and TGF-beta1 synergize in BSMC proliferation and that this synergism is partially mediated by a PDGF loop, where FGF-2 and TGF-beta1 upregulate the receptor (PDGFRalpha) and the ligands (PDGF-AA and PDGF-CC), respectively. This powerful synergistic effect may thus contribute to the hyperplastic phenotype of BSMC in remodeled asthmatic airways.

TGF-beta1 increases proliferation of airway smooth muscle cells by phosphorylation of map kinases

BACKGROUND

Airway remodeling in asthma is the result of increased expression of connective tissue proteins, airway smooth muscle cell (ASMC) hyperplasia and hypertrophy. TGF-beta1 has been found to increase ASMC proliferation. The activation of mitogen-activated protein kinases (MAPKs), p38, ERK, and JNK, is critical to the signal transduction associated with cell proliferation. In the present study, we determined the role of phosphorylated MAPKs in TGF-beta1 induced ASMC proliferation.

METHODS

Confluent and growth-arrested bovine ASMCs were treated with TGF-beta1. Proliferation was measured by [3H]-thymidine incorporation and cell counting. Expressions of phosphorylated p38, ERK1/2, and JNK were determined by Western analysis.

RESULTS

In a concentration-dependent manner, TGF-beta1 increased [3H]-thymidine incorporation and cell number of ASMCs. TGF-beta1 also enhanced serum-induced ASMC proliferation. Although ASMCs cultured with TGF-beta1 had a significant increase in phosphorylated p38, ERK1/2, and JNK, the maximal phosphorylation of each MAPK had a varied onset after incubation with TGF-beta1. TGF-beta1 induced DNA synthesis was inhibited by SB 203580 or PD 98059, selective inhibitors of p38 and MAP kinase kinase (MEK), respectively. Antibodies against EGF, FGF-2, IGF-I, and PDGF did not inhibit the TGF-beta1 induced DNA synthesis.

CONCLUSION

Our data indicate that ASMCs proliferate in response to TGF-beta1, which is mediated by phosphorylation of p38 and ERK1/2. These findings suggest that TGF-beta1 which is expressed in airways of asthmatics may contribute to irreversible airway remodeling by enhancing ASMC proliferation.

Eosinophil-fibroblast interactions induce fibroblast IL-6 secretion and extracellular matrix gene expression: implications in fibrogenesis

BACKGROUND

Eosinophils are frequently associated with tissue remodeling and fibrosis in allergic and other diseases and animal models. Their close physical proximity to fibroblasts at sites of tissue remodeling strongly implicates them in fibrogenesis, including subepithelial fibrosis and airway remodeling characteristic of asthma.

OBJECTIVE

To identify the mediators and characterize the mechanisms underlying the fibrogenic activities of eosinophils.

METHODS

A coculture system of blood eosinophils or eosinophil cell lines with normal fibroblasts was used to assess their ability to induce a fibrogenic fibroblast phenotype, including IL-6 secretion and mRNA expression, and induction of genes involved in extracellular matrix production and homeostasis. The mediators of these responses were identified by using transwell barrier cocultures, eosinophil-conditioned media, and cytokine-specific antibody neutralization.

RESULTS

Eosinophil-fibroblast coculture induced potent fibroblast IL-6 secretion and mRNA expression, responses further enhanced by IL-5. The soluble nature of the eosinophil-derived mediators was demonstrated by using eosinophil-fibroblast coculture in the presence of permeable transwell barriers, and fibroblast culture in eosinophil-conditioned media, indicating that cell contact was not required. Induction of fibroblast IL-6 expression was accompanied by increased expression of fibronectin and the extracellular matrix regulatory genes plasminogen activator inhibitor 1 and tissue inhibitor of metalloproteinase 1. Antibody neutralization identified the principal eosinophil-derived mediator of fibroblast IL-6 expression as IL-1beta (>60%), with lesser contributions from IL-1alpha, IL-4, and TGF-beta (10% to 20%).

CONCLUSION

Eosinophils express at least 2 potent mediators (IL-1beta and TGF-beta) that induce a fibrogenic fibroblast phenotype, strongly supporting a role for the eosinophil in the dysregulation of extracellular matrix homeostasis and consequent tissue remodeling and fibrosis in eosinophil-associated diseases.

Secretory IgA induces antigen-independent eosinophil survival and cytokine production without inducing effector functions

BACKGROUND

Eosinophils in human beings reside in tissues, especially the mucosal tissues of the gastrointestinal tract and inflamed airways. Secretory IgA (S-IgA) is the predominant antibody secreted by these tissues and likely plays a role in the innate immune response.

OBJECTIVE

Because eosinophils and S-IgA are often colocalized in mucosal tissues, we examined the potential regulatory effects of S-IgA without antigens on survival, gene expression, and effector functions of human eosinophils.

METHODS

Eosinophils were incubated with S-IgA in solution without antigens (soluble S-IgA) or with S-IgA immobilized to mimic multivalent antigen cross-linking. Eosinophil activation was monitored by superoxide anion generation and degranulation. Survival was assessed between 24 and 96 hours. Gene and protein expression were examined by microarray and ELISA. Eosinophil lysates were examined by immunoblot for extracellular signal-regulated kinase (ERK) phosphorylation.

RESULTS

Immobilized S-IgA stimulated eosinophil superoxide production and degranulation; soluble S-IgA did not. Although immobilized S-IgA inhibited eosinophil survival in vitro, soluble S-IgA enhanced survival; this involved autocrine production of GM-CSF. Soluble S-IgA without antigens induced increases in mRNA levels of various cytokines, chemokines, signal transduction molecules, antiapoptotic factors, and cell surface markers. By using ELISA, we confirmed protein expression of selected mediators. Eosinophil interaction with soluble S-IgA likely involves FcalphaRI (CD89) and ERK pathway activation.

CONCLUSION

Secretory IgA without multivalent antigens may regulate survival and gene expression of eosinophils. Eosinophils in mucosal tissues can be either primed for action (cytokine production and survival) or fully activated (degranulation and superoxide release) by different forms of S-IgA.

Transforming growth factor-beta induces airway smooth muscle hypertrophy

Although smooth muscle hypertrophy is present in asthmatic airways, little is known about the biochemical pathways regulating airway smooth muscle protein synthesis, cell size, or accumulation of contractile apparatus proteins. We sought to develop a model of airway smooth muscle hypertrophy in primary cells using a physiologically relevant stimulus. We hypothesized that transforming growth factor (TGF)-beta induces hypertrophy in primary bronchial smooth muscle cells. Primary human bronchial smooth muscle cells isolated from unacceptable lung donor tissue were studied. Cells were seeded on uncoated plastic dishes at 50% confluence and TGF-beta was added. Experiments were performed in the absence of serum. TGF-beta increased cell size and total protein synthesis, expression of alpha-smooth muscle actin and smooth muscle myosin heavy chain, formation of actomyosin filaments, and cell shortening to acetylcholine. Further, TGF-beta increased airway smooth muscle alpha-actin synthesis in the presence of the transcriptional inhibitor actinomycin D, evidence that translational control is a physiologically important element of the observed hypertrophy. TGF-beta induced the phosphorylation of eukaryotic translation initiation factor-4E-binding protein, a signaling event specifically involved in translational control. Finally, two inhibitors of 4E-binding protein phosphorylation, the phosphoinositol 3-kinase inhibitor LY294002 and a phosphorylation site mutant of 4E-binding protein-1 that dominantly inhibits eukaryotic initiation factor-4E, each blocked TGF-beta-induced alpha-actin expression and cell enlargement. We conclude that TGF-beta induces hypertrophy of primary bronchial smooth muscle cells. Further, phosphorylation of 4E-binding protein is required for the observed hypertrophy.

Association of transforming growth factor-beta1 single nucleotide polymorphism C-509T with allergy and immunological activities

BACKGROUND

A single nucleotide polymorphism (SNP) C-509T within the tumor growth factor beta1 (TGFbeta1) gene has been associated with atopic asthma and asthma severity. To further understand the mechanisms involved, the association of C-509T with allergy, T-lymphocyte proliferation and plasma TGFbeta1 concentration has been explored in a case-control study with allergic and non-allergic subjects.

METHODS

The recruited subjects including allergic (n = 38) and nonallergic (n = 25) participants have been genotyped for C-509T using allele discrimination assay. Association of C-509T with allergy status was examined using logistic regression analysis in both dominant and recessive models. Association of C-509T with T-cell proliferation in control and antigen-stimulated peripheral blood mononuclear cells (PBMCs), plasma TGFbeta1 and total IgE level were tested by multiple regression analysis.

RESULTS

Individuals with homozygous mutant TT genotype showed a higher risk of allergy (TT: odds ratio = 5.099, 95% confidence limit: 1.355-19.190, p = 0.016) after covariates were adjusted. A trend to increased plasma TGFbeta1 in subjects with T allele has been discovered. In the meantime, the T allele is associated with lower T cell proliferation in controls and maximum response to above antigens. A low T-cell proliferation is correlated with higher plasma TGFbeta1 concentration (p < 0.01). The in vitro studies confirmed the suppressing effect of TGFbeta1 on T-cell proliferation at physiological range. A significant inhibitory effect on IL-4 production was also observed.

CONCLUSIONS

A C to T base change in TGFbeta1 SNP C-509T has been associated with a higher risk of allergy. The mechanisms are not clear. Elevated TGFbeta1 levels associated with the C-509T polymorphism might suppress immune activation as well as Th2 cytokine production.

Therapeutic administration of Budesonide ameliorates allergen-induced airway remodelling

BACKGROUND

Airway inflammation and remodelling are important pathophysiologic features of chronic asthma. Although current steroid use demonstrates anti-inflammatory activity, there are limited effects on the structural changes in the lung tissue.

OBJECTIVE

We have used a mouse model of prolonged allergen challenge that exhibits many of the salient features of airway remodelling in order to investigate the anti-remodelling effects of Budesonide.

METHODS

Treatment was administered therapeutically, with dosing starting after the onset of established eosinophilic airway inflammation and hyper-reactivity.

RESULTS

Budesonide administration reduced airway hyper-reactivity and leukocyte infiltration in association with a decrease in production of the Th2 mediators, IL-4, IL-13 and eotaxin-1. A reduction in peribronchiolar collagen deposition and mucus production was observed. Moreover, our data show for the first time that, Budesonide treatment regulated active transforming growth factor (TGF)-beta signalling with a reduction in the expression of pSmad 2 and the concomitant up-regulation of Smad 7 in lung tissue sections.

CONCLUSIONS

Therefore, we have determined that administration of Budesonide modulates the progression of airway remodelling following prolonged allergen challenge via regulation of inflammation and active TGF-beta signalling.

Connective tissue growth factor and vascular endothelial growth factor from airway smooth muscle interact with the extracellular matrix

Airway remodeling describes the structural changes that occur in the asthmatic airway that include airway smooth muscle hyperplasia, increases in vascularity due to angiogenesis, and thickening of the basement membrane. Our aim in this study was to examine the effect of transforming growth factor-beta on the release of connective tissue growth factor and vascular endothelial growth factor from human airway smooth muscle cells derived from asthmatic and nonasthmatic patients. In addition we studied the immunohistochemical localization of these cytokines in the extracellular matrix after stimulating bronchial rings with transforming growth factor-beta. Connective tissue growth factor and vascular endothelial growth factor were released from both cell types and colocalized in the surrounding extracellular matrix. Prostaglandin E2 inhibited the increase in connective tissue growth factor mRNA but augmented the release of vascular endothelial growth factor. Matrix metalloproteinase-2 decreased the amount of connective tissue growth factor and vascular endothelial growth factor, but not fibronectin deposited in the extracellular matrix. This report provides the first evidence that connective tissue growth factor may anchor vascular endothelial growth factor to the extracellular matrix and that this deposition is decreased by matrix metalloproteinase-2 and prostaglandin E2. This relationship has the potential to contribute to the changes that constitute airway remodeling, therefore providing a novel focus for therapeutic intervention in asthma.

Asthmatic changes in mice lacking T-bet are mediated by IL-13

Mice with a targeted deletion of the T-bet gene exhibit spontaneous airway hyperresponsiveness (AHR), airway inflammation, enhanced recovery of T(h)2 cytokines from bronchoalveolar lavage fluid, sub-epithelial collagen deposition and myofibroblast transformation. Here we analyze the mechanisms responsible for the chronic airway remodeling observed in these mice. CD4+ T cells isolated from the lung of T-bet-deficient mice were spontaneously activated CD44(high)CD69(high) memory T cells, with a typical T(h)2 cytokine profile. Neutralization of IL-13 but not IL-4 resulted in amelioration of AHR in airways of mice lacking T-bet. IL-13 blockade also led to reduced eosinophilia and decreased vimentin, transforming growth factor beta (TGF-beta) and alpha smooth muscle actin (alphaSMA) levels. T-bet(-/-) lung fibroblasts proliferated very rapidly and released increased amounts of TGF-beta. Interestingly, neutralization of TGF-beta ameliorated aspects of the chronic airway remodeling phenotype but did not reduce AHR. These data highlight a T-bet-directed function for IL-13 in controlling lung remodeling that is both dependent on and independent of its interaction with TGF-beta in the asthmatic airway.

Manipulation of allergen-induced airway remodeling by treatment with anti-TGF-beta antibody: effect on the Smad signaling pathway

Airway inflammation and remodeling are important pathophysiologic features of chronic asthma. Previously, we have developed a mouse model of prolonged allergen challenge which exhibits many characteristics of chronic asthma such as goblet cell hyperplasia and subepithelial collagen deposition, in association with an increase in lung expression of the profibrotic mediator, TGF-beta. The aim of this study was to determine the effects of blockade of TGF-beta on the development of airway inflammation and remodeling using our murine model of prolonged allergen challenge. Importantly anti-TGF-beta Ab was administered therapeutically, with dosing starting after the onset of established eosinophilic airway inflammation. Therapeutic treatment of mice with anti-TGF-beta Ab significantly reduced peribronchiolar extracellular matrix deposition, airway smooth muscle cell proliferation, and mucus production in the lung without affecting established airway inflammation and Th2 cytokine production. Thus, our data suggest that it might be possible to uncouple airway inflammation and remodeling during prolonged allergen challenge. In addition, anti-TGF-beta Ab treatment was shown to regulate active TGF-beta signaling in situ with a reduction in the expression of phospho-Smad 2 and the concomitant up-regulation of Smad 7 in lung sections. Therefore, this is the first report to suggest that anti-TGF-beta Ab treatment prevents the progression of airway remodeling following allergen challenge even when given in a therapeutic mode. Moreover, the molecular mechanism behind this effect may involve regulation of active TGF-beta signaling.

Airway remodeling in asthma: therapeutic implications of mechanisms

Asthma is currently recognized as a chronic inflammatory disorder of the airways that leads to tissue injury and subsequent structural changes collectively called airway remodeling. Transgenic modeling of inflammatory mediators allows for the discovery of unexpected effects, dissection of downstream signaling events, and clues to future therapies.

Anti-interleukin-5 therapy for asthma and hypereosinophilic syndrome

Interleukin 5 (IL-5) is a key cytokine in the regulation of eosinophilia and eosinophil activation in humans. Monoclonal antibodies to anti-IL-5 have become available for use in clinical studies in humans. This article discusses the rationale for the use of anti-IL-5 therapy in asthma and hypereosinophilic syndrome and summarizes the available clinical data on the use of anti-IL-5 to treat these disorders.

Comparison of TGF-beta 1 concentrations in bronchoalveolar fluid of horses affected with heaves and of normal controls

Airway remodeling may play an important role in heaves pathophysiology. Transforming growth factor-beta 1 (TGF-beta1) is a potent profibrotic cytokine, which might contribute to airway wall thickening and fibrosis of bronchiolar and alveolar submucosa. An ELISA designed for the measurement of human TGF-beta1 was used to measured total TGF-beta1 released in bronchoalveolar lavage fluid (BALF) of normal horses and of those affected with heaves in remission. The specificity of the assay for TGF-beta1 of the horse was confirmed using recombinant equine TGF-beta1. The influence of hay exposure on TGF-beta1 release in the airways was also examined by stabling horses in a dusty environment. TGF-beta1 was found in the BALF of all horses. However, no significant difference between basal concentration of TGF-beta1 in BALF of control horses versus that of horses affected with heaves was found. Furthermore, no differences were identified in these populations 1 and 9 days after allergen challenge. In conclusion, these data indicate that TGF-beta1 is released in BALF fluid of horses in biologically active concentrations. Other studies are necessary for a better definition of the role of this cytokine within the lung, as our study does not establish a causal relationship between TGF-beta1 and the pathophysiology of heaves in the horse.

A critical role for eosinophils in allergic airways remodeling

Features of chronic asthma include airway hyperresponsiveness, inflammatory infiltrates, and structural changes in the airways, termed remodeling. The contribution of eosinophils, cells associated with asthma and allergy, remains to be established. We show that in mice with a total ablation of the eosinophil lineage, increases in airway hyperresponsiveness and mucus secretion were similar to those observed in wild-type mice, but eosinophil-deficient mice were significantly protected from peribronchiolar collagen deposition and increases in airway smooth muscle. These data suggest that eosinophils contribute substantially to airway remodeling but are not obligatory for allergen-induced lung dysfunction, and support an important role for eosinophil-targeted therapies in chronic asthma.

Danger signals derived from stressed and necrotic epithelial cells activate human eosinophils

Eosinophilic granulocytes are found in tissues with an interface with the external environment, such as the gastrointestinal, genitourinary and respiratory tracts. These leucocytes have been associated with tissue damage in a variety of diseases. The aim of this study was to evaluate whether necrotic epithelial cells can activate eosinophils. The danger theory postulates that cells of the innate immune system primarily recognize substances that signal danger to the host. We damaged epithelial cell lines derived from the genital (HeLa cells), respiratory (HEp-2 cells) and intestinal tracts (HT29 cells) and assessed their capacity to cause eosinophilic migration, release of putative tissue-damaging factors, such as eosinophil peroxidase (EPO) and eosinophil cationic protein (ECP), as well as secretion of tissue-healing factors, e.g. fibroblast growth factors (FGF)-1 and -2 and transforming growth factor (TGF)-beta1. We found that necrotic intestinal cells induced chemotaxis in human eosinophils. EPO release was elicited in eosinophils stimulated with necrotic cells derived from all cell lines, as well as from viable HEp-2 and HT29 cells. Release of ECP was only seen in eosinophils incubated with necrotic intestinal or genital cells, not viable ones. Both necrotic intestinal and genital cells elicited FGF-2 secretion from eosinophils. TGF-beta1 was released from eosinophils exposed to viable and necrotic HT29 cells. These findings indicate that eosinophils are able to recognize and be activated by danger signals released from damaged epithelial cells, which may be of importance in understanding the role of eosinophils in the various inflammatory conditions in which they are involved.

Synthetic responses in airway smooth muscle

Human airway smooth muscle (ASM) has several properties and functions that contribute to asthma pathogenesis, and increasing attention is being paid to its synthetic capabilities. ASM can promote the formation of the interstitial extracellular matrix, and in this respect, ASM from asthmatic subjects compared with normal subjects responds differently, both qualitatively and quantitatively. Thus, ASM cells are important regulating cells that potentially contribute to the known alterations within the extracellular matrix in asthma. In addition, through integrin-directed signaling, extracellular matrix components can alter the proliferative, survival, and cytoskeletal synthetic function of ASM cells. ASM also functions as a rich source of biologically active chemokines and cytokines that are capable of perpetuating airway inflammation in asthma and chronic obstructive pulmonary disease by promoting recruitment, activation, and trafficking of inflammatory cells in the airway milieu. Emerging evidence shows that airway remodeling may also be a result of the autocrine action of secreted inflammatory mediators, including T(H)2 cytokines, growth factors, and COX-2-dependent prostanoids. Finally, ASM cells contain both beta(2)-adrenergic receptors and glucocorticoid receptors and may represent a key target for beta(2)-adrenergic receptor agonist/corticosteroid interactions. Combinations of long-acting beta(2)-agonists and corticosteroids appear to have additive and/or synergistic effects in inhibiting inflammatory mediator release and the migration and proliferation of ASM cells.

Reduced eosinophil pro-fibrogenic effect in severe childhood asthma compared to mild disease: an effect of corticosteroids?

Eosinophils play an important role in inflammation and probably in airway remodeling in asthma. We previously demonstrated that eosinophils from atopic subjects display pro-fibrogenic properties towards lung fibroblasts partially by preformed transforming growth factor-beta (TGF-beta). We hypothesized that the pro-fibrogenic potential of eosinophils is increased in children with life-threatening asthma (LTA). Six children with atopic LTA clinically well-controlled by inhaled corticosteroids (ICS) and 5 children with atopic mild asthma (MA) treated only with inhaled beta(2)-agonists were investigated. The effects of their peripheral blood eosinophils on fibroblast proliferation and lattice contraction were investigated. In addition, TGF-beta(1) and IL-6 eosinophil content were also evaluated. Unexpectedly, eosinophils from LTA increased fibroblast proliferation (5.4-fold) and gel contraction (1.1-fold) significantly less than those from MA. TGF-beta(1) but not IL-6 eosinophil content in LTA was significantly lower than that in MA (2.7-fold). In vitro, addition of dexamethasone on eosinophils stimulated by mast cells resulted in a marked decrease in their TGF-beta(1) content by 1.6-fold. In conclusion, eosinophils from children with ICS-treated LTA displayed significantly less pro-fibrogenic properties than those from MA treated only with beta(2)-agonists. Our data suggest that the pro-fibrogenic effect of eosinophils might be influenced by treatment with ICS in childhood asthma.

Early growth response gene 1-mediated apoptosis is essential for transforming growth factor beta1-induced pulmonary fibrosis

Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β₁ has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β₁ in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β₁–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β₁ to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β₁ produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β₁–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β₁–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β₁ in vivo and define the critical role of Egr-1 in the TGF-β₁ phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β₁–induced fibrosis and remodeling.

Immunomodulatory cytokines in asthmatic inflammation

The development of asthmatic inflammation involves a complex array of cytokines that promote the recruitment and activation of a number of different immune cells. While factors involved in initiating and establishing inflammation are well characterized, the process by which this pro-inflammatory cascade is regulated is less well understood. The identification and characterization of immunomodulatory cytokines in asthma has been a difficult proposition. Many of the putative regulatory factors have pleiotropic bioactivities and have been characterized as pro-inflammatory in association with certain pathologic conditions. This chapter addresses the potential role of several endogenous factors which appear to attenuate asthmatic inflammation. Understanding the integration of these factors into the regulation of the inflammatory process will likely result in novel therapeutic approaches.

Prolonged allergen challenge in mice leads to persistent airway remodelling

BACKGROUND

Inflammatory infiltrates, airway hyper-responsiveness, goblet cell hyperplasia and subepithelial thickening are characteristic of chronic asthma. Current animal models of allergen-induced airway inflammation generally concentrate on the acute inflammation following allergen exposure and fail to mimic all of these features.

OBJECTIVE

The aim of this study was to use a murine model of prolonged allergen-induced airway inflammation in order to characterize the cells and molecules involved in the ensuing airway remodelling. Moreover, we investigated whether remodelling persists in the absence of continued allergen challenge.

METHODS

Acute pulmonary eosinophilia and airways hyper-reactivity were induced after six serial allergen challenges in sensitized mice (acute phase). Mice were subsequently challenged three times a week with ovalbumin (OVA) (chronic phase) up to day 55. To investigate the persistence of pathology, one group of mice were left for another 4 weeks without further allergen challenge (day 80).

RESULTS

The extended OVA challenge protocol caused significant airway remodelling, which was absent in the acute phase. Specifically, remodelling was characterized by deposition of collagen as well as airway smooth muscle and goblet cell hyperplasia. Importantly, these airway changes, together with tissue eosinophilia were sustained in the absence of further allergen challenge. Examination of cytokines revealed a dramatic up-regulation of IL-4 and tumour growth factor-beta1 during the chronic phase. Interestingly, while IL-4 levels were significantly increased during the chronic phase, levels of IL-13 fell. Levels of the Th1-associated cytokine IFN-gamma also increased during the chronic phase.

CONCLUSION

In conclusion, we have demonstrated that prolonged allergen challenge results in persistent airway wall remodelling.

Smad and p38-MAPK signaling mediates apoptotic effects of transforming growth factor-beta1 in human airway epithelial cells

Transforming growth factor-beta1 (TGF-beta1) belongs to a family of multifunctional cytokines that regulate a variety of biological processes, including cell differentiation, proliferation, and apoptosis. The effects of TGF-beta1 are cell context and cell cycle specific and may be signaled through several pathways. We examined the effect of TGF-beta1 on apoptosis of primary human central airway epithelial cells and cell lines. TGF-beta1 protected human airway epithelial cells from apoptosis induced by either activation of the Fas death receptor (CD95) or by corticosteroids. This protective effect was blocked by inhibition of the Smad pathway via overexpression of inhibitory Smad7. The protective effect is associated with an increase in the cyclin-dependent kinase inhibitor p21 and was blocked by the overexpression of key gatekeeper cyclins for the G1/S interface, cyclins D1 and E. Blockade of the Smad pathway by overexpression of the inhibitory Smad7 permitted demonstration of a TGF-beta-mediated proapoptotic pathway. This proapoptotic effect was blocked by inhibition of the p38 MAPK kinase signaling with the inhibitor SB-203580 and was associated with an increase in p38 activity as measured by a kinase assay. Here we demonstrate dual signaling pathways involving TGF-beta1, an antiapoptotic pathway mediated by the Smad pathway involving p21, and an apoptosis-permissive pathway mediated in part by p38 MAPK.

The effect of eosinophils on collagen gel contraction and implications for tissue remodelling

Asthma is characterized by an eosinophilic inflammation and a subepithelial fibrosis in the airways. Eosinophils contain several cytotoxic substances, such as eosinophil cationic protein (ECP), which can promote inflammation and cause tissue damage. This has generated the hypothesis that eosinophils may drive remodelling of extracellular matrix (ECM). To investigate the role of eosinophils we used an in vitro model for remodelling, the three-dimensional collagen gel contraction assay. Two sources of eosinophils were used in this study, isolated human peripheral eosinophils (purity > 95%) and stimulated [interleukin (IL)-5, IL-3 and granulocyte macrophage-colony stimulating factor (GM-CSF)] HL-60 clone 15 cells. Human eosinophils or HL-60 cells were cast together with human lung fibroblasts (HFL1) in type I collagen gels. Both types of eosinophils augmented fibroblast-mediated collagen gel contraction in a time and concentration-dependent manner. At 48 h, the gel area in HFL1/eosinophil co-culture was 46.5% +/- 0.5 (mean +/- s.e.m.) of initial area and in HFL1 culture 52.3% +/- 0.1 (P < 0.001). Respective figures for HFL1/stimulated HL-60 co-culture and HFL1 culture only were 44.1% +/- 0.5 and 52.4% +/- 0.4 (P < 0.001). The release of ECP was increased when fibroblasts were cultured with eosinophils compared to eosinophils cultured alone. In addition, native ECP added to fibroblast gel cultures also augmented contraction. Our results suggest that eosinophils may interact with mesenchymal cells, promoting remodelling of ECM and that ECP constitutes one potential eosinophil-derived mediator driving this process. We conclude that this may be one important mechanism by which eosinophil-ECM interactions will lead to airway tissue remodelling in asthma.

Ovalbumin-induced airway inflammation and fibrosis in mice also exposed to ozone

A murine model of allergen-induced airway inflammation was used to examine the effects of exposure to ozone on airway inflammation and remodeling. Sensitized BALB/c mice were exposed to ovalbumin aerosol for 4 wk before and after 2 wk of exposure to either 0.2 ppm or 0.5 ppm ozone. Other groups of mice were exposed to ovalbumin aerosol for 6 wk with continuous concurrent exposure to ozone during wk 1-6, or during intermittent concurrent exposure to ozone. Lung inflammation was measured by quantitative differential evaluation of lung lavage cells and by histological evaluation of stained lung sections. Alterations in lung structure (airway fibrosis) were evaluated by quantitative biochemical analysis of microdissected airways. The same total number of cells was observed in lavage fluid from animals exposed for 4 wk to ovalbumin alone or to ovalbumin for 4 wk immediately before or after exposure to 2 wk of 0.2 or 0.5 ppm ozone. Mice exposed to ovalbumin for 6 wk with concurrent exposure to either 0.2 ppm or 0.5 ppm ozone during wk 3-6 had a significant decrease in the total number of cells recovered by lavage. Values as low as 7% of the cell number found in mice exposed to ovalbumin aerosol alone were observed in the mice exposed to ovalbumin plus 0.2 ppm ozone during wk 3-6. There were significant differences in the cell differential counts in the lavage fluid from mice exposed to ovalbumin alone as compared with values from mice exposed to ovalbumin and ozone under all of the protocols studied. When ozone was given for 2 wk prior to ovalbumin exposure (Experiment 1), there were a high percentage of macrophages and low percentages of lymphocytes and eosinophils in the lung lavage. When ozone was given for 2 wk after ovalbumin exposure (Experiment 2), there were a moderate percentage of macrophages, a low percentage of eosinophils, and a high percentage of lymphocytes in the lung lavage. When ozone and ovalbumin were given simultaneously (Experiments 3 and 4), there were a high percentage of macrophages in the lavage with 0.2 ppm ozone and a high percentage of eosinophils. Ozone appears to antagonize the specific inflammatory effects of ovalbumin exposure, especially when given before or during exposure to ovalbumin. Airway remodeling was examined by two different quantitative methods. None of the groups exposed concurrently to ovalbumin and ozone had a significant increase in airway collagen content as compared to the matched groups of mice exposed to ovalbumin alone. The findings were consistent with an additive response of mice to simultaneous exposure to ovalbumin and ozone. Ozone exposure alone for 6 wk did not affect the number of goblet cells in the airways, while mice exposed to ovalbumin aerosol alone for 6 wk had about 25% goblet cells in their conducting airways. Concurrent exposure to ovalbumin and 0.2 ppm ozone caused significant increases in goblet cells (to 43% of total cells) in the conducting airways of the exposed mice. We conclude that when mice with allergen-induced airway inflammation induced by ovalbumin are also exposed to ozone, the lung inflammatory response may be modified, but that this altered response is dependent on the sequence of exposure and the concentration of ozone to which they are exposed. At the concentrations of ozone tested, we did not see changes in airway fibrosis. However, goblet-cell hyperplasia appeared to be increased in mice exposed concurrently to ovalbumin and 0.2 ppm ozone.

Inhibition of airway remodeling in IL-5-deficient mice

To determine the role of IL-5 in airway remodeling, IL-5-deficient and WT mice were sensitized to OVA and challenged by repetitive administration of OVA for 3 months. IL-5-deficient mice had significantly less peribronchial fibrosis (total lung collagen content, peribronchial collagens III and V) and significantly less peribronchial smooth muscle (thickness of peribronchial smooth muscle layer, alpha-smooth muscle actin immunostaining) compared with WT mice challenged with OVA. WT mice had a significant increase in the number of peribronchial cells staining positive for major basic protein and TGF-beta. In contrast, IL-5-deficient mice had a significant reduction in the number of peribronchial cells staining positive for major basic protein, which was paralleled by a similar reduction in the number of cells staining positive for TGF-beta, suggesting that eosinophils are a significant source of TGF-beta in the remodeled airway. OVA challenge induced significantly higher levels of airway epithelial alphaVbeta6 integrin expression, as well as significantly higher levels of bioactive lung TGF-beta in WT compared with IL-5-deficient mice. Increased airway epithelial expression of alphaVbeta6 integrin may contribute to the increased activation of latent TGF-beta. These results suggest an important role for IL-5, eosinophils, alphaVbeta6, and TGF-beta in airway remodeling.

Severe asthma

Severe asthma is a term that is commonly used to describe patients with refractory, brittle, near fatal, and difficult-to-control asthma. Patients with severe asthma typically experience persistent symptoms despite medical therapy, report decreased quality of life and suffer an accelerated loss of lung function. The role of genetics, environmental exposure, and infection in the development of more severe asthma is the focus of ongoing research. While pathologic changes in these patients are now believed to involve lung parenchyma, in addition to large and small airways, the independent contribution of each of these compartments to the severe asthma phenotype is not well defined. The clinical evaluation of severe asthma patients should include investigating conditions commonly associated with severe asthma, such as gastroesophageal reflux disease, vocal cord dysfunction, and rhinosinusitis. In addition, advanced imaging techniques, measurement of exhaled gas or sputum indices, and airway biopsy are tools that may aid in evaluating severe asthma patients in the near future. Management of patients with severe asthma requires a comprehensive approach that includes non-pharmacological and pharmacological measures. Combination antiinflammatory and long-acting bronchodilator therapy remains the mainstay of management.

Role of interleukin-5 and eosinophils in allergen-induced airway remodeling in mice

Asthma is a chronic inflammatory disease characterized by variable bronchial obstruction, hyperresponsiveness, and by tissue damage known as airway remodeling. In the present study we demonstrate that interleukin (IL)-5 plays an obligatory role in the airway remodeling observed in experimental asthma. BALB/c mice sensitized by intraperitoneal injections of ovalbumin and exposed daily to aerosol of ovalbumin for up to 3 wk, develop eosinophilic infiltration of the bronchi and subepithelial and peribronchial fibrosis. The lesions are associated with increased amounts of hydroxyproline in the lungs and elevated levels of eosinophils and transforming growth factor (TGF)-beta1 in the bronchoalveolar lavage fluid. After 1 wk of allergen challenge, TGF-beta is mainly produced by eosinophils accumulated in the peribronchial and perivascular lesions. At a later stage of the disease, the main source of TGF-beta is myofibroblasts, identified by alpha-smooth muscle actin mAb. We show that all these lesions, including fibrosis, are abolished in sensitized and allergen-exposed IL-5 receptor-null mice, whereas they are markedly accentuated in IL-5 transgenic animals. More importantly, treatment of wild-type mice with neutralizing anti-IL-5 antibody, administered before each allergen challenge, almost completely prevented subepithelial and peribronchial fibrosis. These findings demonstrated that eosinophils are involved in allergen-induced subepithelial and peribronchial fibrosis probably by producing a fibrogenic factor, TGF-beta1.

Transforming growth factor-beta and its role in asthma

Transforming growth factor-beta (TGF-beta) is an important fibrogenic and immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TGF-beta: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating into the initiation and resultion of inflammatory and immune responses in the airways. TGF-beta is also involved in the remodelling of the airway wall, and has in particular been related to the subepithelial fibrosis. TGF-beta is produced in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial and smooth muscle cells. By releasing TGF-beta, these different cell types may then participate into the increased levels of TGF-beta observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, these results suggest that TGF-beta may play a role in inflammation in asthma. However, as its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TGF-beta in the airways.

Transforming growth factor-beta1 promoter polymorphism C-509T is associated with asthma

Transforming growth factor-beta1 (TGF-beta1) is increased in the lungs of individuals with asthma and may modulate airway inflammation and remodeling. Some genetic studies have found that a C-to-T single-nucleotide polymorphism (C-509T) in the TGF-beta1 gene promoter may be associated with altered gene expression and asthma phenotype. To build on these data, we performed a case-control association study at this locus involving 527 subjects with asthma and 170 control subjects without asthma. All individuals were white. Genotyping at 49 unlinked polymorphisms indicated that a subset of case subjects and all control subjects were well matched and without evidence of population stratification. Logistic regression was used to model the effects of age, sex, and genotype on case-control status. The diagnosis of asthma was positively associated with the T allele and TT genotype under a codominant model (odds ratio, 2.98; 95% confidence interval, 1.45 to 6.25; p = 0.003). Total serum IgE, eosinophil count, and FEV1% predicted levels were not associated with this polymorphism. Furthermore, we show that the C-509T polymorphism alters TGF-beta1 promoter-reporter activity and promoter interactions with the transcription factor Yin Yang 1. We conclude that the T allele of C-509T is associated with the diagnosis of asthma and may enhance TGF-beta1 gene transcription.