Allergic asthma is caused by inhaled allergens and it is characterized by airway eosinophilia as well as mucus hypersecretion which can lead to airflow obstruction. Despite the association of increased IL-6 levels with human atopic asthma, the contribution of IL-6 to the development of allergic airway inflammation triggered by inhaled allergens remains unclear. In this study, we examined the role of IL-6 in a mouse model of allergic airway inflammation induced by direct airway exposure to extracts of Aspergillus fumigatus, a common allergen in humans. We show here that inhaled A. fumigatus extracts rapidly triggers the production of IL-6 in the airways. IL-6 appears to be dispensable for the recruitment of eosinophils to the lung during the development of allergic airway inflammation. However, IL-6 is essential for mucus hypersecretion by airway epithelial cells triggered in response to inhaled A. fumigatus antigens. Impaired mucus production caused by IL-6 deficiency correlates with a severe reduction in the levels of IL-13, a major inducer of mucin glycoproteins. Thus, IL-6 is a key regulator of specific hallmark features of allergic airway inflammation, and it could be a potential target for pulmonary diseases that are associated with goblet cell metaplasia and mucus hypersecretion.
Lung; Allergy; Fungal; Rodent; Cytokines
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.
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.
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).
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-β1 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-γ also increased during the chronic phase.
In conclusion, we have demonstrated that prolonged allergen challenge results in persistent airway wall remodelling.
airway remodelling; allergic airway inflammation; asthma; eosinophils; Th2 cytokines
Allergic asthma is characterized by Th2 type inflammation, leading to airway hyperresponsivenes, mucus hypersecretion and tissue remodeling. S-Nitrosoglutathione reductase (GSNOR) is an alcohol dehydrogenase involved in the regulation of intracellular levels of S-nitrosothiols. GSNOR activity has been shown to be elevated in human asthmatic lungs, resulting in diminished S-nitrosothiols and thus contributing to increased airway hyperreactivity. Using a mouse model of allergic airway inflammation, we report that intranasal administration of a new selective inhibitor of GSNOR, SPL-334, caused a marked reduction in airway hyperreactivity, allergen-specific T cells and eosinophil accumulation, and mucus production in the lungs in response to allergen inhalation. Moreover, SPL-334 treatment resulted in a significant decrease in the production of the Th2 cytokines IL-5 and IL-13 and the level of the chemokine CCL11 (eotaxin-1) in the airways. Collectively, these observations reveal that GSNOR inhibitors are effective not only in reducing airway hyperresponsiveness but also in limiting lung inflammatory responses mediated by CD4+ Th2 cells. These findings suggest that the inhibition of GSNOR may provide a novel therapeutic approach for the treatment of allergic airway inflammation.
Both nature and induced regulatory T (Treg) lymphocytes are potent regulators of autoimmune and allergic disorders. Defects in endogenous Treg cells have been reported in patients with allergic asthma, suggesting that disrupted Treg cell-mediated immunological regulation may play an important role in airway allergic inflammation. In order to determine whether adoptive transfer of induced Treg cells generated in vitro can be used as an effective therapeutic approach to suppress airway allergic inflammation, exogenously induced Treg cells were infused into ovalbumin-sensitized mice prior to or during intranasal ovalbumin challenge. The results showed that adoptive transfer of induced Treg cells prior to allergen challenge markedly reduced airway hyperresponsiveness, eosinophil recruitment, mucus hyper-production, airway remodeling, and IgE levels. This effect was associated with increase of Treg cells (CD4+FoxP3+) and decrease of dendritic cells in the draining lymph nodes, and with reduction of Th1, Th2, and Th17 cell response as compared to the controls. Moreover, adoptive transfer of induced Treg cells during allergen challenge also effectively attenuate airway inflammation and improve airway function, which are comparable to those by natural Treg cell infusion. Therefore, adoptive transfer of in vitro induced Treg cells may be a promising therapeutic approach to prevent and treat severe asthma.
Reactive oxygen species (ROS) play a crucial role in the pathogenesis of acute and chronic respiratory diseases. Antioxidants have been found to ameliorate airway inflammation and hyperresponsiveness in animal models employing short-term exposure to allergen. However, little data are available on the effect of antioxidants on airway remodeling and signaling pathways in chronic asthma. In the present study, we used a long-term exposure murine model of allergic airway disease to evaluate the effects of an antioxidant, L-2-oxothiazolidine-4-carboxylic acid (OTC) or α-lipoic acid (LA) on airway remodeling, focusing on the ROS-related hypoxia-inducible signaling. Long-term challenge of ovalbumin (OVA) increased ROS production, airway inflammation, and airway hyperresponsiveness, and developed features of airway remodeling such as excessive mucus secretion, subepithelial fibrosis, and thickening of the peribronchial smooth muscle layer. Administration of OTC or LA reduced these features of asthma, including airway remodeling, which was accompanied by suppression of transforming growth factor-β1, vascular endothelial growth factor, and T-helper 2 cytokines. In addition, OVA-induced activation of nuclear factor-κB (NF-κB), nuclear factor erythroid 2p45-related factor-2 (Nrf2), hypoxia-inducible factor (HIF)-1α, and HIF-2α was reduced by OTC or LA. Our results also showed that OTC or LA down-regulated phosphoinositide 3-kinase activity and decreased phosphorylation of p38 mitogen-activated protein kinase but not extracellular signal-regulated kinase 1/2 or c-Jun N-terminal kinase. These findings demonstrate that OTC and LA can inhibit activation of NF-κB, Nrf2, and HIF, leading to attenuate allergen-induced airway remodeling.
airway remodeling; antioxidant; hypoxia-inducible factor; nuclear factor erythroid 2p45-related factor-2; nuclear factor-κB; oxidative stress
Inhalation of antigen in immunized mice induces an infiltration of eosinophils into the airways and increased bronchial hyperreactivity as are observed in human asthma. We employed a model of late-phase allergic pulmonary inflammation in mice to address the role of leukotrienes (LT) in mediating airway eosinophilia and hyperreactivity to methacholine. Allergen intranasal challenge in OVA-sensitized mice induced LTB4 and LTC4 release into the airspace, widespread mucus occlusion of the airways, leukocytic infiltration of the airway tissue and broncho-alveolar lavage fluid that was predominantly eosinophils, and bronchial hyperreactivity to methacholine. Specific inhibitors of 5- lipoxygenase and 5-lipoxygenase-activating protein (FLAP) blocked airway mucus release and infiltration by eosinophils indicating a key role for leukotrienes in these features of allergic pulmonary inflammation. The role of leukotrienes or eosinophils in mediating airway hyperresponsiveness to aeroallergen could not be established, however, in this murine model.
Fibroproliferative airway remodelling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. In vitro studies have shown that maturation of ASM cells to a (hyper)contractile phenotype is dependent on laminin, which can be inhibited by the laminin-competing peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). The role of laminins in ASM remodelling in chronic asthma in vivo, however, has not yet been established.
Using an established guinea pig model of allergic asthma, we investigated the effects of topical treatment of the airways with YIGSR on features of airway remodelling induced by repeated allergen challenge, including ASM hyperplasia and hypercontractility, inflammation and fibrosis. Human ASM cells were used to investigate the direct effects of YIGSR on ASM proliferation in vitro.
Topical administration of YIGSR attenuated allergen-induced ASM hyperplasia and pulmonary expression of the proliferative marker proliferating cell nuclear antigen (PCNA). Treatment with YIGSR also increased both the expression of sm-MHC and ASM contractility in saline- and allergen-challenged animals; this suggests that treatment with the laminin-competing peptide YIGSR mimics rather than inhibits laminin function in vivo. In addition, treatment with YIGSR increased allergen-induced fibrosis and submucosal eosinophilia. Immobilized YIGSR concentration-dependently reduced PDGF-induced proliferation of cultured ASM to a similar extent as laminin-coated culture plates. Notably, the effects of both immobilized YIGSR and laminin were antagonized by soluble YIGSR.
These results indicate that the laminin-competing peptide YIGSR promotes a contractile, hypoproliferative ASM phenotype in vivo, an effect that appears to be linked to the microenvironment in which the cells are exposed to the peptide.
Regulatory T cells (Treg) play a decisive role in many diseases including asthma and allergen-induced lung inflammation. However, little progress has been made developing new therapeutic strategies for pulmonary disorders. In the current study we demonstrate that cytokine:antibody complexes of IL-2 and anti-IL-2 mAb reduce the severity of allergen-induced inflammation in the lung by expanding Tregs in vivo. Unlike rIL-2 or anti-IL-2 mAb treatment alone, IL-2:anti-IL-2 complexes dampened airway inflammation and eosinophilia while suppressing IL-5 and eotaxin-1 production. Mucus production, airway hyperresponsiveness to methacholine, and parenchymal tissue inflammation were also dramatically reduced following IL-2:anti-IL-2 treatment. The suppression in allergic airway disease was associated with a marked expansion of Tregs (IL-10+CD4+CD25+ and Foxp3+CD4+CD25+) in the tissues, with a corresponding decrease in effector T cell responses. The ability of IL-2:anti-IL-2 complexes to suppress airway inflammation was dependent on Treg-derived IL-10, as IL-10+/+, but not IL-10-/- Tregs, were capable of mediating the suppression. Furthermore, a therapeutic protocol using a model of established airway allergy highlighted the ability of IL-2:anti-IL-2 complexes to expand Tregs and prevent successive airway inflammation and airway hyperresponsiveness. This study suggests that endogenous Treg therapy may be a useful tool to combat the rising incidence of allergic airway disease.
Airways inflammation is thought to play a central role in the pathogenesis of asthma. However, the precise role that individual inflammatory cells and mediators play in the development of airways hyperreactivity and the morphological changes of the lung during allergic pulmonary inflammation is unknown. In this investigation we have used a mouse model of allergic pulmonary inflammation and interleukin (IL) 5-deficient mice to establish the essential role of this cytokine and eosinophils in the initiation of aeroallergen-induced lung damage and the development of airways hyperreactivity. Sensitization and aerosol challenge of mice with ovalbumin results in airways eosinophilia and extensive lung damage analogous to that seen in asthma. Aeroallergen-challenged mice also display airways hyperreactivity to beta-methacholine. In IL-5-deficient mice, the eosinophilia, lung damage, and airways hyperreactivity normally resulting from aeroallergen challenge were abolished. Reconstitution of IL-5 production with recombinant vaccinia viruses engineered to express this factor completely restored aeroallergen-induced eosinophilia and airways dysfunction. These results indicate that IL-5 and eosinophils are central mediators in the pathogenesis of allergic lung disease.
Rationale: Asthma is characterized by increases in airway resistance, pulmonary remodeling, and lung inflammation. The cytokine transforming growth factor (TGF)-β has been shown to have a central role in asthma pathogenesis and in mouse models of allergic airway disease.
Objectives: To determine the contribution of TGF-β to airway hyperresponsiveness (AHR), we examined the time course, source, and isoform specificity of TGF-β production in an in vivo mouse asthma model. To then elucidate the function of TGF-β in AHR, inflammation, and pulmonary fibrosis, we examined the effects of blocking TGF-β signaling with neutralizing antibody.
Methods: Mice were sensitized and challenged with ovalbumin (OVA) to establish allergic airway disease. TGF-β activity was neutralized by intranasal administration of monoclonal antibody.
Measurements and Main Results: TGF-β1 protein levels were increased in OVA-challenged lungs versus naive controls, and airway epithelial cells were shown to be a likely source of TGF-β1. In addition, TGF-β1 levels were elevated in OVA-exposed IL-5–null mice, which fail to recruit eosinophils into the airways. Neutralization of TGF-β1 with specific antibody had no significant effect on airway inflammation and eosinophilia, although anti–TGF-β1 antibody enhanced OVA-induced AHR and suppressed pulmonary fibrosis.
Conclusions: These data show that TGF-β1 is the main TGF-β isoform produced after OVA challenge, with a likely cellular source being the airway epithelium. The effects of blocking TGF-β1 signaling had differential effects on AHR, fibrosis, and inflammation. While TGF-β neutralization may be beneficial to abrogating airway remodeling, it may be detrimental to lung function by increasing AHR.
lung; mice; hypersensitivity; cytokines
Rationale: Although there have been numerous studies on the development of allergen-induced inflammation, the mechanisms leading to resolution of inflammation remain poorly understood. This represents an important consideration because failure to resolve allergen driven inflammation potentially leads to irreversible airway remodeling, characteristic of chronic asthma.
Objectives: We investigated the resolution of allergic inflammation and identified the factors responsible.
Methods: BALB/c and C57BL/6 mice were sensitized to ovalbumin and challenged through the airways to induce allergic inflammation. Mice were analyzed at 24 hours and 7 days after the final challenge.
Measurements and Main Results: Airway hyperreactivity (AHR) and increased mucus production were present 7 days after the cessation of allergen challenge in BALB/c mice. Persisting AHR correlated with the continued presence of Th2 cells but not eosinophils in the lungs. The role of Th2 cells in maintaining AHR was confirmed using blocking antibodies against T1/ST2, IL-4, and IL-13 during the resolution period. Moreover, AHR in the “Th1 type” C57BL/6 mouse strain was resolved 1 week after allergen challenge, concomitant with clearance of Th2 cells from the lung. Expression of the T1/ST2 ligand, IL-33, also correlated with maintenance of AHR.
Conclusions: We have used blockade of Th2 function and strain differences to show for the first time that resolution of allergic inflammation and AHR may be dependent on the T1/ST2-IL-33 pathway and the presence of Th2 cells, suggesting they are necessary not only for the development of an allergic response but also for its maintenance.
Th2 cells; IL-13; IL-4
Signal transducers and activators of transcription 6 (STAT6) is essential for interleukin 4–mediated responses, including class switching to IgE and induction of type 2 T helper cells. To investigate the role of STAT6 in allergic asthma in vivo, we developed a murine model of allergen-induced airway inflammation. Repeated exposure of actively immunized C57BL/6 mice to ovalbumin (OVA) aerosol increased the level of serum IgE, the number of eosinophils in bronchoalveolar lavage (BAL) fluid, and airway reactivity. Histological analysis revealed peribronchial inflammation with pulmonary eosinophilia in OVA-treated mice. In STAT6-deficient (STAT6−/−) C57BL/6 mice treated in the same fashion, there were no eosinophilia in BAL and significantly less peribronchial inflammation than in wild-type mice. Moreover STAT6−/− mice had much less airway reactivity than wild-type mice. These findings suggest that STAT6 plays a crucial role in the pathogenesis of allergen-induced airway inflammation.
Steroid treatment of allergic eosinophilic airway diseases is considered to attenuate cell recruitment by inhibiting several chemokines and to cause eosinophil clearance through inducement of apoptosis of these cells. However, roles of these mechanisms in the actions of steroids in vivo have not been fully established. Also, as regards clearance of tissue eosinophils other mechanisms than apoptosis may operate in vivo.
This study explores anti-inflammatory effects of steroids instituted during either development or resolution of airway allergic inflammation.
Immunized mice were subjected to week-long daily allergen challenges (ovalbumin). Steroid treatment was instituted either amidst the challenges or exclusively post-allergen challenge. CC chemokines, goblet cell hyperplasia, occurrence of eosinophil apoptosis, and airway tissue as well as lumen eosinophilia were examined at different time-points.
Daily steroids instituted amid the allergen challenges non-selectively attenuated a range of chemokines, permitted egression of tissue eosinophils into airway lumen to increase, and reduced development of lung tissue eosinophilia. Steroid treatment instituted post-challenge selectively inhibited the CC-chemokine regulation upon activation, normal T cell expressed and secrted (RANTES), permitted continued egression of eosinophils into airway lumen, and resolved the tissue eosinophilia. Eosinophil apoptosis rarely occurred at development and resolution of the allergic eosinophilic inflammation whether the animals were steroid treated or not. However, anti-Fas monoclonal antibodies given to mice with established eosinophilia post-challenge produced apoptosis of the tissue eosinophils indicating that apoptotic eosinophils, if they occur, are well detectible in vivo.
Airway tissue eosinophils are likely eliminated through egression into airway lumen with little involvement of apoptosis and phagocytosis. Our data further suggest that therapeutic steroids may resolve airway inflammation by permitting clearance of tissue eosinophils through egression and inhibiting RANTES-dependent cell recruitment to lung tissues.
apoptosis; asthma; chemokines; glucocorticoids
Chronic allergic asthma is characterized by Th2-typed inflammation, and contributes to airway remodeling and the deterioration of lung function. However, the initiating factor that links airway inflammation to remodeling is unknown. Thymic stromal lymphopoietin (TSLP), an epithelium-derived cytokine, can strongly activate lung dendritic cells (DCs) through the TSLP-TSLPR and OX40L-OX40 signaling pathways to promote Th2 differentiation. To determine whether TSLP is the underlying trigger of airway remodeling in chronic allergen-induced asthma, we induced allergic airway inflammation in mice by intranasal administration of house dust mite (HDM) extracts for up to 5 consecutive weeks. We showed that repeated respiratory exposure to HDM caused significant airway eosinophilic inflammation, peribronchial collagen deposition, goblet cell hyperplasia, and airway hyperreactivity (AHR) to methacholine. These effects were accompanied with a salient Th2 response that was characterized by the upregulation of Th2-typed cytokines, such as IL-4 and IL-13, as well as the transcription factor GATA-3. Moreover, the levels of TSLP and transforming growth factor beta 1 (TGF-β1) were also increased in the airway. We further demonstrated, using the chronic HDM-induced asthma model, that the inhibition of Th2 responses via neutralization of TSLP with an anti-TSLP mAb reversed airway inflammation, prevented structural alterations, and decreased AHR to methacholine and TGF-β1 level. These results suggest that TSLP plays a pivotal role in the initiation and persistence of airway inflammation and remodeling in the context of chronic allergic asthma.
Reactive oxygen species (ROS) play a crucial role in the pathogenesis of acute and chronic respiratory diseases. Antioxidants have been found to ameliorate airway inflammation and hyperresponsiveness in animal models employing short-term exposure to allergen. However, little data are available on the effect of antioxidants on airway remodeling and signaling pathways in chronic asthma.
In the present study, we used a long-term exposure murine model of allergic airway disease to evaluate the influence of an antioxidant, L-2-oxothiazolidine-4-carboxylic acid (OTC) or α-lipoic acid (LA) on airway remodeling and to explore possible transcription factors and kinases involved in this effect.
Long-term challenge of ovalbumin (OVA) increased ROS production, airway inflammation, and airway hyperresponsiveness, and developed features of airway remodeling such as excessive mucus secretion, subepithelial fibrosis, and thickening of the peribronchial smooth muscle layer. Administration of OTC or LA reduced these features of asthma including airway remodeling, which was accompanied by suppression of transforming growth factor-β1, vascular endothelial growth factor, and T-helper 2 cytokines. In addition, OVA-induced activation of nuclear factor-κB (NF-κB), nuclear factor erythroid 2p45-related factor-2 (Nrf2), hypoxia-inducible factor (HIF)-1α, and HIF-2α was reduced by OTC or LA. Our results also showed that OTC or LA down-regulated phosphoinositide 3-kinase activity and decreased phosphorylation of p38 mitogen-activated protein kinase but not extracellular signal-regulated kinase 1/2 or c-Jun N-terminal kinase.
These findings demonstrate that OTC and LA can inhibit activation of NF-κB, Nrf2, and HIF and thus attenuate allergen-induced airway remodeling, suggesting that antioxidants may provide therapeutic benefit in chronic asthma and other airway disorders.
The role of inducible NO synthase (iNOS) in allergic airway inflammation remains elusive. We tested the hypothesis that iNOS plays different roles during acute versus chronic airway inflammation. Acute and chronic mouse models of OVA-induced airway inflammation were used to conduct the study. We showed that iNOS deletion was associated with a reduction in eosinophilia, mucus hypersecretion, and IL-5 and IL-13 production upon the acute protocol. Such protection was completely abolished upon the chronic protocol. Interestingly, pulmonary fibrosis observed in wild-type mice under the chronic protocol was completely absent in iNOS−/− mice despite persistent IL-5 and IL-13 production, suggesting that these cytokines were insufficient for pulmonary fibrosis. Such protection was associated with reduced collagen synthesis and indirect but severe TGF-β modulation as confirmed using primary lung smooth muscle cells. Although activation of matrix metalloproteinase-2/-9 exhibited little change, the large tissue inhibitor of metalloproteinase-2 (TIMP-2) increase detected in wild-type mice was absent in the iNOS−/− counterparts. The regulatory effect of iNOS on TIMP-2 may be mediated by peroxynitrite, as the latter reversed TIMP-2 expression in iNOS−/− lung smooth muscle cells and fibroblasts, suggesting that the iNOS–TIMP-2 link may explain the protective effect of iNOS-knockout against pulmonary fibrosis. Analysis of lung sections from chronically OVA-exposed iNOS−/− mice revealed evidence of residual but significant protein nitration, prevalent oxidative DNA damage, and poly(ADP-ribose) polymerase-1 activation. Such tissue damage, inflammatory cell recruitment, and mucus hypersecretion may be associated with substantial arginase expression and activity. The results in this study exemplify the complexity of the role of iNOS in asthma and the preservation of its potential as a therapeutic a target.
It is widely assumed that apoptosis of eosinophils is a central component of resolution of allergic airway disease. However, this has not been demonstrated in human allergic airways in vivo. Based on animal in vivo observations we hypothesised that steroid-induced resolution of human airway eosinophilic inflammation involves inhibition of CCL5 (RANTES), a CC-chemokine regulating eosinophil and lymphocyte traffic, and elimination of eosinophils without evident occurrence of apoptotic eosinophils in the diseased tissue.
To determine mucosal eosinophilia, apoptotic eosinophils, general cell apoptosis and cell proliferation, and expression of CCL5 and CCL11 (eotaxin) in human allergic airway tissues in vivo at resolution of established symptomatic eosinophilic inflammation.
Twenty-one patients with intermittent (birch and/or grass) allergic rhinitis received daily nasal allergen challenges for two seven days' periods separated by more than two weeks washout. Five days into these "artificial pollen seasons", nasal treatment with budesonide was instituted and continued for six days in a double blinded, randomized, placebo-controlled, and crossover design. This report is a parallel group comparison of nasal biopsy histochemistry data obtained on the final day of the second treatment period.
Treatments were instituted when clinical rhinitis symptoms had been established. Compared to placebo, budesonide reduced tissue eosinophilia, and subepithelial more than epithelial eosinophilia. Steroid treatment also attenuated tissue expression of CCL5, but CCL11 was not reduced. General tissue cell apoptosis and epithelial cell proliferation were reduced by budesonide. However, apoptotic eosinophils were not detected in any biopsies, irrespective of treatment.
Inhibition of CCL5-dependent recruitment of cells to diseased airway tissue, and reduced cell proliferation, reduced general cell apoptosis, but not increased eosinophil apoptosis, are involved in early phase steroid-induced resolution of human allergic rhinitis.
Long-term and unresolved airway inflammation and airway remodeling, characteristic features of chronic asthma, if not treated could lead to permanent structural changes in the airways. Aldose reductase (AR), an aldo-sugar and lipid aldehyde metabolizing enzyme, mediates allergen-induced airway inflammation in mice, but its role in the airway remodeling is not known. In the present study, we have examined the role of AR on airway remodeling using ovalbumin (OVA)-induced chronic asthma mouse model and cultured human primary airway epithelial cells (SAECs) and mouse lung fibroblasts (mLFs).
Airway remodeling in chronic asthma model was established in mice sensitized and challenged twice a week with OVA for 6 weeks. AR inhibitor, fidarestat, was administered orally in drinking water after first challenge. Inflammatory cells infiltration in the lungs and goblet cell metaplasia, airway thickening, collagen deposition and airway hyper-responsiveness (AHR) in response to increasing doses of methacholine were assessed. The TGFβ1-induced epithelial-mesenchymal transition (EMT) in SAECs and changes in mLFs were examined to investigate AR-mediated molecular mechanism(s) of airway remodeling.
In the OVA-exposed mice for 6 wks inflammatory cells infiltration, levels of inflammatory cytokines and chemokines, goblet cell metaplasia, collagen deposition and AHR were significantly decreased by treatment with AR inhibitor, fidarestat. Further, inhibition of AR prevented TGFβ1-induced altered expression of E-cadherin, Vimentin, Occludin, and MMP-2 in SAECs, and alpha-smooth muscle actin and fibronectin in mLFs. Further, in SAECs, AR inhibition prevented TGFβ1- induced activation of PI3K/AKT/GSK3β pathway but not the phosphorylation of Smad2/3.
Our results demonstrate that allergen-induced airway remodeling is mediated by AR and its inhibition blocks the progression of remodeling via inhibiting TGFβ1-induced Smad-independent and PI3K/AKT/GSK3β-dependent pathway.
Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and a cellular infiltrate dominated by eosinophils. Numerous epidemiological studies have related the exacerbation of allergic asthma with an increase in ambient inhalable particulate matter from air pollutants. This is because inhalable particles efficiently deliver airborne allergens deep into the airways, where they can aggravate allergic asthma symptoms. However, the cellular mechanisms by which inhalable particulate allergens (pAgs) potentiate asthmatic symptoms remain unknown, in part because most in vivo and in vitro studies exploring the pathogenesis of allergic asthma use soluble allergens (sAgs). Using a mouse model of allergic asthma, we found that, compared with their sAg counterparts, pAgs triggered markedly heightened airway hyperresponsiveness and pulmonary eosinophilia in allergen-sensitized mice. Mast cells (MCs) were implicated in this divergent response, as the differences in airway inflammatory responses provoked by the physical nature of the allergens were attenuated in MC-deficient mice. The pAgs were found to mediate MC-dependent responses by enhancing retention of pAg/IgE/FcεRI complexes within lipid raft–enriched, CD63+ endocytic compartments, which prolonged IgE/FcεRI-initiated signaling and resulted in heightened cytokine responses. These results reveal how the physical attributes of allergens can co-opt MC endocytic circuitry and signaling responses to aggravate pathological responses of allergic asthma in mice.
Allergic asthma is a debilitating disease of the airways characterized by airway hyperresponsiveness, eosinophilic inflammation, goblet cell metaplasia with associated mucus hypersecretion, and airway wall remodelling events, particularly subepithelial fibrosis and smooth muscle cell hyperplasia. Animal models that accurately mimic these hallmarks of allergic airways disease are critical for studying mechanisms associated with the cellular and structural changes that lead to disease pathogenesis. Aspergillus fumigatus, is a common aeroallergen of human asthmatics. The intratracheal (IT) delivery of A. fumigatus conidia into the airways of sensitized mice has been described as a model of allergic disease. Here, we compared the IT model with a newly developed inhalation (IH) challenge model. The IH model allowed multiple fungal exposures, which resulted in an exacerbation to the allergic asthma phenotype. Increased recruitment of eosinophils and lymphocytes, the hallmark leukocytes of asthma, were noted with the IH model as compared to the IT model in which macrophages and neutrophils were more prominent. Immunoglobulin E (IgE) production was significantly greater after IH challenge, while that of IgG2a was higher after IT challenge. Airway wall remodelling was pronounced in IH-treated mice, particularly after multiple allergen challenges. Although the IT model may be appropriate for the examination of the played by innate cells in the acute response to fungus, it fails to consistently reproduce the chronic remodelling hallmarks of allergic asthma. The ability of the IH challenge to mimic these characteristics recommends it as a model suited to study these important events.
Aspergillus fumigatus; Allergic asthma; Inhalation challenge model
Allergic airway disease is characterized by eosinophilic inflammation, mucus hypersecretion and increased airway resistance. Fungal antigens are ubiquitous within the environment and are well know triggers of allergic disease. Bacterial products are also frequently encountered within the environment and may alter the immune response to certain antigens. The consequence of simultaneous exposure to bacterial and fungal products on the lung adaptive immune response has not been explored. Here we show that oropharyngeal aspiration of fungal lysates (Candida albicans, Aspergillus fumigatus) promotes airway eosinophilia, secretion of Th2 cytokines and mucus cell metaplasia. In contrast, oropharyngeal exposure to bacterial lysates (Pseudomonas aeruginosa) promotes airway inflammation characterized by neutrophils, Th1 cytokine secretion and no mucus production. More importantly, administration of bacterial lysates together with fungal lysates deviates the adaptive immune response to a Th1 type associated with neutrophilia and diminished mucus production. The immunomodulatory effect that bacterial lysates have on the response to fungi is TLR4-independent but MyD88 dependent. Thus, different types of microbial products within the airway can alter the host's adaptive immune response, and potentially impact the development of allergic airway disease to environmental fungal antigens.
T helper cells; Lung inflammation; cytokines; immune responses; eosinophils
Chronic allergic asthma is characterized by Th2-polarized inflammation and leads to airway remodeling and fibrosis but the mechanisms involved are not clear. To determine whether epithelial-mesenchymal transition contributes to airway remodeling in asthma, we induced allergic airway inflammation in mice by intranasal administration of house dust mite (HDM) extract for up to 15 consecutive weeks. We report that respiratory exposure to HDM led to significant airway inflammation and thickening of the smooth muscle layer in the wall of the large airways. Transforming growth factor beta-1 (TGF-β1) levels increased in mouse airways while epithelial cells lost expression of E-cadherin and occludin and gained expression of the mesenchymal proteins vimentin, alpha-smooth muscle actin (α-SMA) and pro-collagen I. We also observed increased expression and nuclear translocation of Snail1, a transcriptional repressor of E-cadherin and a potent inducer of EMT, in the airway epithelial cells of HDM-exposed mice. Furthermore, fate-mapping studies revealed migration of airway epithelial cells into the sub-epithelial regions of the airway wall. These results show the contribution of EMT to airway remodeling in chronic asthma-like inflammation and suggest that Th2-polarized airway inflammation can trigger invasion of epithelial cells into the subepithelial regions of the airway wall where they contribute to fibrosis, demonstrating a previously unknown plasticity of the airway epithelium in allergic airway disease.
Asthma is a serious health and socioeconomic issue all over the world, affecting more than 300 million individuals. The disease is considered as an inflammatory disease in the airway, leading to airway hyperresponsiveness, obstruction, mucus hyper-production and airway wall remodeling. The presence of airway inflammation in asthmatic patients has been found in the nineteenth century. As the information in patients with asthma increase, paradigm change in immunology and molecular biology have resulted in an extensive evaluation of inflammatory cells and mediators involved in the pathophysiology of asthma. Moreover, it is recognized that airway remodeling into detail, characterized by thickening of the airway wall, can be profound consequences on the mechanics of airway narrowing and contribute to the chronic progression of the disease. Epithelial to mesenchymal transition plays an important role in airway remodeling. These epithelial and mesenchymal cells cause persistence of the inflammatory infiltration and induce histological changes in the airway wall, increasing thickness of the basement membrane, collagen deposition and smooth muscle hypertrophy and hyperplasia. Resulting of airway inflammation, airway remodeling leads to the airway wall thickening and induces increased airway smooth muscle mass, which generate asthmatic symptoms. Asthma is classically recognized as the typical Th2 disease, with increased IgE levels and eosinophilic inflammation in the airway. Emerging Th2 cytokines modulates the airway inflammation, which induces airway remodeling. Biological agents, which have specific molecular targets for these Th2 cytokines, are available and clinical trials for asthma are ongoing. However, the relatively simple paradigm has been doubted because of the realization that strategies designed to suppress Th2 function are not effective enough for all patients in the clinical trials. In the future, it is required to understand more details for phenotypes of asthma.
asthma; remodeling; epithelial to mesenchymal transition; Th2 cells; cytokines; Th17 cells; Th9 cell
Activated mast cells, eosinophils, and basophils infiltrate the airways of asthmatics as a result of an overexuberant T helper 2 (Th2) cell immune response that drives the production of IgE, primes mast cells and basophils, and promotes tissue eosinophilia and mast cell hyperplasia. Recent evidence demonstrates that these innate effectors can be activated outside of this classical Th2 cell paradigm and that they have additional roles in promoting the development of innate and adaptive pulmonary inflammation. There is also an appreciation for the role of airway epithelial cells in orchestrating allergic pulmonary inflammation. Emerging data from basic research highlights the involvement of many unique pathways in the inflammation triggered by complex native allergens and microbes at the airway mucosal surface. Here we review the role of effector cells and airway epithelial cells in augmenting and, at times, bypassing traditional Th2 cell-mediated allergic inflammation.
Allergic asthma is a dysregulation of the immune system which leads to the development of Th2 responses to innocuous antigens (allergens). Some infections and microbial components can re-direct the immune response toward the Th1 response, or induce regulatory T cells to suppress the Th2 response, thereby inhibiting the development of allergic asthma. Since Acinetobacter baumannii infection can modulate lung cellular and cytokine responses, we studied the effect of A. baumannii in modulating airway eosinophilia in a mouse model of allergic asthma. Ovalbumin (OVA)-sensitized mice were treated with live A. baumannii or phosphate buffered saline (PBS), then intranasally challenged with OVA. Compared to PBS, A. baumannii treatment significantly reduced pulmonary Th2 cytokine and chemokine responses to OVA challenge. More importantly, the airway inflammation in A. baumannii-treated mice was strongly suppressed, as seen by the significant reduction of the proportion and the total number of eosinophils in the bronchoalveolar lavage fluid. In addition, A. baumannii-treated mice diminished lung mucus overproduction and pathology. However, A. baumannii treatment did not significantly alter systemic immune responses to OVA. Serum OVA-specific IgE, IgG1 and IgG2a levels were comparable between A. baumannii- and PBS-treated mice, and tracheobronchial lymph node cells from both treatment groups produced similar levels of Th1 and Th2 cytokines in response to in vitro OVA stimulation. Moreover, it appears that TLR-4 and IFN-γ were not directly involved in the A. baumannii-induced suppression of airway eosinophilia. Our results suggest that A. baumannii inhibits allergic airway inflammation by direct suppression of local pulmonary Th2 cytokine responses to the allergen.