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.
Existing asthma models develop tolerance when chronically exposed to the same allergen.
To establish a chronic model that sustains features of asthma long after discontinuation of allergen exposure.
We immunized and exposed mice to a combination of single, double or triple allergens (dust-mite, ragweed, and Aspergillus) intranasally for 8 weeks. Airway hyperreactivity and morphological features of asthma were studied 3 weeks after the allergen exposure. Signaling effects of the allergens were studied on dendritic cells.
Sensitization and repeated exposure to a single allergen induced tolerance. Sensitization to double, and especially triple allergens broke through tolerance and established AHR, eosinophilic inflammation, mast cell and smooth muscle hyperplasia, mucus production and airway remodeling that persisted at least 3 weeks after allergen exposure. Mucosal exposure to triple allergens in the absence of an adjuvant was sufficient to induce chronic airway inflammation. Anti-IL5 and -IL13 antibodies inhibited inflammation and AHR in the acute asthma model but not in the chronic triple allergen model. Multiple allergens produce a synergy in p38 MAPK signaling and maturation of dendritic cells, which provides a heightened T cell co-stimulation at a level that cannot be achieved with a single allergen.
Sensitivity to multiple allergens leads to chronic asthma in mice. Multiple allergens synergize in dendritic cell signaling and T cell stimulation that allows escape from the single allergen-associated tolerance development.
We have developed a model of chronic asthma that allows for the study and treatment of long-lasting features of asthma obviating the need for acute de novo allergen challenges.
chronic asthma; mouse; inflammation; airway hyperreactivity; tolerance; dendritic cells
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
Atopic asthma is a chronic disease of the airways that has taken on epidemic proportions in the industrialized world. The increase in asthma rates has been linked epidemiologically to the rapid disappearance of Helicobacter pylori, a bacterial pathogen that persistently colonizes the human stomach, from Western societies. In this study, we have utilized mouse models of allergic airway disease induced by ovalbumin or house dust mite allergen to experimentally examine a possible inverse correlation between H. pylori and asthma. H. pylori infection efficiently protected mice from airway hyperresponsiveness, tissue inflammation, and goblet cell metaplasia, which are hallmarks of asthma, and prevented allergen-induced pulmonary and bronchoalveolar infiltration with eosinophils, Th2 cells, and Th17 cells. Protection against asthma was most robust in mice infected neonatally and was abrogated by antibiotic eradication of H. pylori. Asthma protection was further associated with impaired maturation of lung-infiltrating dendritic cells and the accumulation of highly suppressive Tregs in the lungs. Systemic Treg depletion abolished asthma protection; conversely, the adoptive transfer of purified Treg populations was sufficient to transfer protection from infected donor mice to uninfected recipients. Our results thus provide experimental evidence for a beneficial effect of H. pylori colonization on the development of allergen-induced asthma.
The endoplasmic reticulum (ER) stress response participates in many chronic inflammatory and autoimmune diseases. In the current study, we sought to examine the contribution of ER stress transducers in the pathogenesis of three principal facets of allergic asthma: inflammation, airway fibrosis, and airways hyperresponsiveness.
House Dust Mite (HDM) was used as an allergen for in vitro and in vivo challenge of primary human and murine airway epithelial cells. ER stress transducers were modulated using specific small interfering RNAs (siRNAs) in vivo. Inflammation, airway remodeling, and hyperresponsiveness were measured by total bronchoalveolar lavage (BAL) cell counts, determination of collagen, and methacholine responsiveness in mice, respectively.
Challenge of human bronchiolar and nasal epithelial cells with HDM extract induced the ER stress transducer, activating transcription factor 6 α (ATF6α) as well as protein disulfide isomerase, ERp57, in association with activation of caspase-3. SiRNA-mediated knockdown of ATF6α and ERp57 during HDM administration in mice resulted in a decrease in components of HDM-induced ER stress, disulfide mediated oligomerization of Bak, and activation of caspase-3. Furthermore, siRNA-mediated knockdown of ATF6α and ERp57 led to decreased inflammation, airway hyperresponsiveness and airway fibrosis.
Collectively, our work indicates that HDM induces ER stress in airway epithelial cells and that ATF6α and ERp57 play a significant role in the development of cardinal features of allergic airways disease. Inhibition of ER stress responses may provide a potential therapeutic avenue in chronic asthma and sub-epithelial fibrosis associated with loss of lung function.
Allergen; HDM; Unfolded protein response; ER stress; Apoptosis; Asthma; Airway fibrosis
Severe asthma is characterised by persistent inflammation, hyperreactivity and remodeling of the airways. No efficient treatment is available, this is particularly the case for steroid resistant phenotypes. Our aim therefore was to develop a preclinical model showing characteristics of severe human asthma including steroid insensitivity. Mice were first sensitized with ovalbumin, extracts of cockroach or house dust mite followed by a challenge period of seven weeks. Further to this, an additional group of mice was sensitized with all three allergens and then challenged with allergen alternating weekly between allergens. All three allergens applied separately to the mice induced comparably strong Th2-type airway inflammation, airway hyperreactivity and airway remodeling, which was characterised by fibrosis and increased smooth muscle thickness. In contrast, application of all three allergens together resulted in a greater Th2 response and increased airway hyperreactivity and a stronger albeit not significant remodeling phenotype compared to using HDM or CRA. In this triple allergen model dexamethasone application, during the last 4 weeks of challenge, showed no suppressive effects on any of these parameters in this model. In contrast, both TLR7 agonist resiquimod and TLR9 agonist CpG-ODN reduced allergen-specific IgE, eosinophils, and collagen I in the lungs. The TLR9 agonist also reduced IL-4 and IL-5 whilst increasing IFN-γ and strongly IL-10 levels in the lungs, effects not seen with the TLR7 agonist. However, neither TLR agonist had any effect on airway hyperreactivity and airway smooth muscle mass. In conclusion we have developed a severe asthma model, which is steroid resistant and only partially sensitive to TLR7 and TLR9 agonist treatment. This model may be particular useful to test new potential therapeutics aiming at treating steroid resistant asthma in humans and investigating the underlying mechanisms responsible for steroid insensitivity.
Asthma is a chronic inflammatory disease of the airways associated with structural changes and airway remodeling. Interleukin (IL)-9 has pleiotropic effects on both inflammatory cells and airway structural cells, which are involved in asthma pathogenesis. We evaluated the effects of IL-9 blockade on chronic airway inflammation.
Acute airway inflammation was induced in Balb/c mice using aerosolized ovalbumin (OVA), whereas chronic asthma was induced by OVA exposure for 5 weeks with anti-IL-9 or isotype-matched antibody (Ab) treatment during the OVA challenge. Inflammatory cells in bronchoalveolar lavage fluid (BALF) were counted and lung tissues were stained to detect cellular infiltration, mucus deposition, and collagen accumulation. The levels of interferon (IFN)-γ, IL-4, IL-5, IL-9, IL-17, and immunoglobulin E (IgE) in BALF were measured using enzyme linked immunosorbent assays, and profiles of inflammatory cells and subsets of T helper (Th) cells were analyzed using flow cytometry.
IL-9, IL-17, and IFN-γ levels were significantly increased in the chronic group compared to the acute asthma group. However, the number of IL-9-positive cells was not affected, with a decrease in Th17 cells in OVA-challenged caspase-1 knockout mice. Numbers of eosinophils, neutrophils, B cells, mast cells, and Th17 cells decreased after administration of anti-IL-9 Ab. Total IgE, IL-5, IL-9, and IL-17 levels were also lower in the anti-IL-9 group.
Our results suggest that anti-IL-9 Ab treatment inhibits pulmonary infiltration of inflammatory cells and cytokine production, especially IL-17. These results provide a basis for the use of an anti-IL-9 Ab to combat IL-17-mediated airway inflammation.
Interleukin-9; allergic asthma; T helper 17; anti-interleukin-9 antibody
The development of chronic allergic dermatitis in early life has been associated with increased onset and severity of allergic asthma later in life. However, the mechanisms linking these two diseases are poorly understood. Here, we report that the development of oxazolone-induced chronic allergic dermatitis, in a mouse model, caused enhanced ovalbumin-induced allergic asthma after resolution of the former disease. Our findings show that oxazolone-induced dermatitis caused a marked increase in tissue mast cells, which persisted long after the resolution of this disease. Subsequent ovalbumin sensitization and airway challenge of mice that had recovered from dermatitis resulted in increased allergic airway hyperreactivity. The findings demonstrate that the accumulation of mast cells during dermatitis has the detrimental effect of increasing allergic airway hypersensitivity. Importantly, our findings also show that exposure to a given allergen can modify the immune response to an unrelated allergen.
Allergy; Fc receptors; IgE; Mast cells/basophils; Skin; Rodent
Repeated exposure to inhaled allergen can cause airway inflammation, remodeling and dysfunction that manifests as the symptoms of allergic asthma. We have investigated the role of the cytokine interleukin-13 (IL-13) in the generation and persistence of airway cellular inflammation, bronchial remodeling and deterioration in airway function in a model of allergic asthma caused by chronic exposure to the aeroallergen House Dust Mite (HDM).
Mice were exposed to HDM via the intranasal route for 4 consecutive days per week for up to 8 consecutive weeks. Mice were treated either prophylactically or therapeutically with a potent neutralising anti-IL-13 monoclonal antibody (mAb) administered subcutaneously (s.c.). Airway cellular inflammation was assessed by flow cytometry, peribronchial collagen deposition by histocytochemistry and airway hyperreactivity (AHR) by invasive measurement of lung resistance (RL) and dynamic compliance (Cdyn). Both prophylactic and therapeutic treatment with an anti-IL-13 mAb significantly inhibited (P<0.05) the generation and maintenance of chronic HDM-induced airway cellular inflammation, peribronchial collagen deposition, epithelial goblet cell upregulation. AHR to inhaled methacholine was reversed by prophylactic but not therapeutic treatment with anti-IL-13 mAb. Both prophylactic and therapeutic treatment with anti-IL-13 mAb significantly reversed (P<0.05) the increase in baseline RL and the decrease in baseline Cdyn caused by chronic exposure to inhaled HDM.
These data demonstrate that in a model of allergic lung disease driven by chronic exposure to a clinically relevant aeroallergen, IL-13 plays a significant role in the generation and persistence of airway inflammation, remodeling and dysfunction.
Increased mast cell (MC) density and changes in their distribution in airway tissues is thought to contribute significantly to the pathophysiology of asthma. However, the time sequence for these changes and how they impact small airway function in asthma is not fully understood. The aim of the current study was to characterise temporal changes in airway MC density and correlate these changes with functional airway responses in sheep chronically challenged with house dust mite (HDM) allergen.
MC density was examined on lung tissue from four spatially separate lung segments of allergic sheep which received weekly challenges with HDM allergen for 0, 8, 16 or 24 weeks. Lung tissue was collected from each segment 7 days following the final challenge. The density of tryptase-positive and chymase-positive MCs (MCT and MCTC respectively) was assessed by morphometric analysis of airway sections immunohistochemically stained with antibodies against MC tryptase and chymase.
MCT and MCTC density was increased in small bronchi following 24 weeks of HDM challenges compared with controls (P<0.05). The MCTC/MCT ratio was significantly increased in HDM challenged sheep compared to controls (P<0.05). MCT and MCTC density was inversely correlated with allergen-induced increases in peripheral airway resistance after 24 weeks of allergen exposure (P<0.05). MCT density was also negatively correlated with airway responsiveness after 24 challenges (P<0.01).
MCT and MCTC density in the small airways correlates with better lung function in this sheep model of chronic asthma. Whether this finding indicates that under some conditions mast cells have protective activities in asthma, or that other explanations are to be considered requires further investigation.
Repeated airway challenges with House Dust Mite (HDM) allergen results in marked remodelling and mast cell hyperplasia in the small airways of allergic sheep. We now examine mast cell activation and its association with small airway function and remodelling in these sheep using a novel segmental allergen challenge approach.
Eight allergic sheep received weekly intra-lung challenges of HDM to the left caudal lung for 24 weeks. Eight separate sheep were used as controls. Baseline lung function was assessed in the left caudal segments of all sheep throughout the challenge regime using a wedged-bronchoscope technique. Airway tissue was collected from challenged segments from all sheep, 7 days following the final intra-lung challenge. The airway tissues were immunohistochemically labelled for chymase-mast cells and eosinophils. Collagen and airway smooth muscle content were assessed on Masson's Trichrome stained sections.
Resting lung function in the left caudal segment is elevated in 4 out of 8 sheep at the end of the repeated allergen challenge regime. Chymase mast cell density was significantly increased in the small bronchial walls of the HDM-challenged group compared to the control group (52 ± 8 vs 8 ± 4; P < 0.01). There were significant increases in bronchial collagen deposition in HDM-exposed segments compared to control segments (0.17 ± 0.02 vs 0.11 ± 0.02 mm2/BM, P < 0.05). A correlation analysis of individual sheep data showed that there was a trend for a direct association between the increases in bronchial collagen deposition and the density of chymase-labelled mast cells (rs = 0.71, P = 0.088). Eosinophil density in the small bronchial walls of HDM-challenged segments was also significantly increased compared to controls (65 ± 19 vs 11 ± 3 cells/mm2, P < 0.001), but not associated with collagen content. The bronchial smooth muscle content was not different between HDM-challenged and unexposed control segments.
The results show that repeated exposure to allergen results in significant increases in density of chymase-labelled mast cells, together with increased levels of collagen content in the small airways. The segmental challenge protocol allows for a novel approach to characterise the progressive remodelling events occurring in the small airways in chronic asthma.
Mast cell numbers and allergen specific IgE are increased in the lungs of patients with allergic asthma and this can be reproduced in mouse models. The increased number of mast cells is likely due to recruitment of mast cell progenitors that mature in situ. We hypothesized that formation of IgE immune complexes in the lungs of sensitized mice increase the migration of mast cell progenitors to this organ. To study this, a model of allergic airway inflammation where mice were immunized with ovalbumin (OVA) in alum twice followed by three daily intranasal challenges of either OVA coupled to trinitrophenyl (TNP) alone or as immune complexes with IgE-anti-TNP, was used. Mast cell progenitors were quantified by a limiting dilution assay. IgE immune complex challenge of sensitized mice elicited three times more mast cell progenitors per lung than challenge with the same dose of antigen alone. This dose of antigen challenge alone did not increase the levels of mast cell progenitors compared to unchallenged mice. IgE immune complex challenge of sensitized mice also enhanced the frequency of mast cell progenitors per 106 mononuclear cells by 2.1-fold. The enhancement of lung mast cell progenitors by IgE immune complex challenge was lost in FcRγ deficient mice but not in CD23 deficient mice. Our data show that IgE immune complex challenge enhances the number of mast cell progenitors in the lung through activation of an Fc receptor associated with the FcRγ chain. This most likely takes place via activation of FcεRI, although activation via FcγRIV or a combination of the two receptors cannot be excluded. IgE immune complex-mediated enhancement of lung MCp numbers is a new reason to target IgE in therapies against allergic asthma.
Lung epithelial cells can influence immune responses to airway allergens1,2. Airway epithelial cells also undergo apoptosis after encountering environmental allergens3; yet, relatively little is known about how these are cleared, and their effect on airway inflammation. Here we show that airway epithelial cells efficiently engulf apoptotic epithelial cells and secrete anti-inflammatory cytokines, dependent upon intracellular signalling by the small GTPase Rac1. Inducible deletion of Rac1 expression specifically in airway epithelial cells in a mouse model resulted in defective engulfment by epithelial cells and aberrant anti-inflammatory cytokine production. Intranasal priming and challenge of these mice with house dust mite extract or ovalbumin as allergens led to exacerbated inflammation, augmented Th2 cytokines and airway hyper-responsiveness, with decreased interleukin (IL)-10 in bronchial lavages. Rac1-deficient epithelial cells produced much higher IL-33 upon allergen or apoptotic cell encounter, with increased numbers of nuocyte-like cells1,4,5. Administration of exogenous IL-10 ‘rescued’ the airway inflammation phenotype in Rac1-deficient mice, with decreased IL-33. Collectively, these genetic and functional studies suggest a new role for Rac1-dependent engulfment by airway epithelial cells and in establishing the anti-inflammatory environment, and that defects in cell clearance in the airways could contribute to inflammatory responses towards common allergens.
Chronic airway disorders, including chronic obstructive pulmonary disease (COPD), cystic fibrosis, and asthma, are associated with persistent pulmonary inflammation and goblet cell metaplasia and contribute to significant morbidity and mortality worldwide. While the molecular pathogenesis of these disorders is actively studied, little is known regarding the transcriptional control of goblet cell differentiation and mucus hyperproduction. Herein, we demonstrated that pulmonary allergen sensitization induces expression of FOXM1 transcription factor in airway epithelial and inflammatory cells. Conditional deletion of the Foxm1 gene from either airway epithelium or myeloid inflammatory cells decreased goblet cell metaplasia, reduced lung inflammation, and decreased airway resistance in response to house dust mite allergen (HDM). FOXM1 induced goblet cell metaplasia and Muc5AC expression through the transcriptional activation of Spdef. FOXM1 deletion reduced expression of CCL11, CCL24, and the chemokine receptors CCR2 and CX3CR1, resulting in decreased recruitment of eosinophils and macrophages to the lung. Deletion of FOXM1 from dendritic cells impaired the uptake of HDM antigens and decreased cell surface expression of major histocompatibility complex II (MHC II) and costimulatory molecule CD86, decreasing production of Th2 cytokines by activated T cells. Finally, pharmacological inhibition of FOXM1 by ARF peptide prevented HDM-mediated pulmonary responses. FOXM1 regulates genes critical for allergen-induced lung inflammation and goblet cell metaplasia.
Human rhinovirus is a key viral trigger for asthma exacerbations. To date, murine studies investigating rhinovirus-induced exacerbation of allergic airways disease have employed systemic sensitisation/intranasal challenge with ovalbumin. In this study, we combined human-rhinovirus infection with a clinically relevant mouse model of aero-allergen exposure using house-dust-mite in an attempt to more accurately understand the links between human-rhinovirus infection and exacerbations of asthma. Adult BALB/c mice were intranasally exposed to low-dose house-dust-mite (or vehicle) daily for 10 days. On day 9, mice were inoculated with human-rhinovirus-1B (or UV-inactivated human-rhinovirus-1B). Forty-eight hours after inoculation, we assessed bronchoalveolar cellular inflammation, levels of relevant cytokines/serum antibodies, lung function and responsiveness/sensitivity to methacholine. House-dust-mite exposure did not result in a classical TH2-driven response, but was more representative of noneosinophilic asthma. However, there were significant effects of house-dust-mite exposure on most of the parameters measured including increased cellular inflammation (primarily macrophages and neutrophils), increased total IgE and house-dust-mite-specific IgG1 and increased responsiveness/sensitivity to methacholine. There were limited effects of human-rhinovirus-1B infection alone, and the combination of the two insults resulted in additive increases in neutrophil levels and lung parenchymal responses to methacholine (tissue elastance). We conclude that acute rhinovirus infection exacerbates house-dust-mite-induced lung disease in adult mice. The similarity of our results using the naturally occurring allergen house-dust-mite, to previous studies using ovalbumin, suggests that the exacerbation of allergic airways disease by rhinovirus infection could act via multiple or conserved mechanisms.
Astragali radix Antiasthmatic Decoction (AAD), a traditional Chinese medication, is found effective in treating allergic diseases and chronic cough. The purpose of this study is to determine whether this medication could suppress allergen-induced airway hyperresponsiveness (AHR) and remodeling in mice, and its possible mechanisms.
A mouse model of chronic asthma was used to investigate the effects of AAD on the airway lesions. Mice were sensitized and challenged with ovalbumin (OVA), and the extent of AHR and airway remodeling were characterized. Cells and cytokines in the bronchoalveolar lavage fluid (BALF) were examined.
AAD treatment effectively decreased OVA-induced AHR, eosinophilic airway inflammation, and collagen deposition around the airway. It significantly reduced the levels of IL-13 and TGF-β1, but exerted inconsiderable effect on INF-γ and IL-10.
AAD greatly improves the symptoms of allergic airway remodeling probably through inhibition of Th2 cytokines and TGF-β1.
Astragalus Antiasthmatic Decoction; Airway hyperresponsiveness; Airway remodeling
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.
Asthma is a leading cause of morbidity in children. Risk factors include chronic exposure to allergens and air pollution. While chronically activated mast cells contribute to the pathophysiology of asthma in part through their proteases such as chymase and tryptase, previous studies of airway mast cell abundance and distribution in asthmatics have been inconsistent. To determine whether repeated episodic exposures to environmental pollutants during postnatal lung development alter airway mast cell abundance and distribution, we exposed infant rhesus monkeys to a known human allergen, house dust mite antigen (HDMA), and/or a known environmental pollutant, ozone (O3), and quantitatively compared the abundance of tryptase- or chymase-positive mast cells in three airway levels. Mast cells are resident in multiple compartments of the airway wall in infant rhesus monkeys raised from birth in filtered air. Tryptase- and chymase-positive cells were most abundant in trachea and least in terminal bronchioles. The majority of tryptase-positive and almost all chymase-positive cells were in extracellular matrix and smooth muscle bundles. Chronic exposure to HDMA elevated the abundance of both tryptase- and chymase-positive cells in the trachea and intrapulmonary bronchi. Neither exposure to O3 nor HDMA + O3 increased mast cell accumulations in the airway wall. We conclude that during postnatal airway development (1) mast cells are a resident airway cell population even in the absence of toxic air contaminants; (2) aeroallergen exposure alters large airway mast cell distribution and abundance, increasing chymase-positive mast cells; and (3) this response is attenuated by exposure to oxidant air pollutants.
HDMA; lung development; mast cells; ozone; childhood asthma
HIF-1α is a transcription factor that is activated during hypoxia and inflammation and is a key regulator of angiogenesis in vivo. During the development of asthma, peribronchial angiogenesis is induced in response to aeroallergens and is thought to be an important feature of sustained chronic allergic inflammation. Recently, elevated HIF-1α levels have been demonstrated in both the lung tissue and bronchoalveolar lavage of allergic patients, respectively. Therefore, we investigated the role of HIF-1α on the development of angiogenesis and inflammation following acute and chronic allergen exposure. Our data shows that intranasal exposure to house dust mite (HDM) increases the expression of HIF-1α in the lung, whilst reducing the expression of the HIF-1α negative regulators, PHD1 and PHD3. Blockade of HIF-1α in vivo, significantly decreased allergic inflammation and eosinophilia induced by allergen, due to a reduction in the levels of IL-5 and Eotaxin-2. Importantly, HIF-1α blockade significantly decreased levels of VEGF-A and CXCL1 in the lungs, which in turn led to a profound decrease in the recruitment of endothelial progenitor cells and a reduction of peribronchial angiogenesis. Furthermore, HDM or IL-4 treatment of primary lung macrophages resulted in significant production of both VEGF-A and CXCL1; inhibition of HIF-1α activity abrogated the production of these factors via an up-regulation of PHD1 and PHD3. These findings suggest that novel strategies to reduce the expression and activation of HIF-1α in lung macrophages may be used to attenuate allergen-induced airway inflammation and angiogenesis through the modulation of VEGF-A and CXCL1 expression.
This study provides new insights into the role of HIF-1α in the development of peribronchial angiogenesis and inflammation in a murine model of allergic airway disease. These findings indicate that strategies to reduce activation of macrophage derived HIF-1α may be used as a target to improve asthma pathology.
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.
Allergic asthma is caused by abnormal immunoreactivity against allergens such as house dust mites among which Dermatophagoides farinae (Der f) is a common species. Currently, immunotherapy is based on allergen administration, which has variable effect from patient to patient and may cause serious side effects, principally the sustained risk of anaphylaxis. DNA vaccination is a promising approach by triggering a specific immune response with reduced allergenicity.
The aim of the study is to evaluate the effects of DNA immunization with Der f1 allergen specific DNA on allergic sensitization, inflammation and respiratory function in mice.
Mice were vaccinated 28 and 7 days before allergen exposure with a Der f1-encoding plasmid formulated with a block copolymer. Asthma was induced by skin sensitization followed by intra-nasal challenges with Der f extract. Total lung, broncho-alveolar lavage (BAL) and spleen cells were analyzed by flow cytometry for their surface antigen and cytokine expression. Splenocytes and lung cell IFN-γ production by CD8+ cells in response to Der f CMH1-restricted peptides was assessed by ELISPOT. IgE, IgG1 and IgG2a were measured in serum by ELISA. Specific bronchial hyperresponsiveness was assessed by direct resistance measurements.
Compared to animals vaccinated with an irrelevant plasmid, pVAX-Der f1 vaccination induced an increase of B cells in BAL, and an elevation of IL-10 and IFN-γ but also of IL-4, IL-13 and IL-17 producing CD4+ lymphocytes in lungs and of IL-4 and IL-5 in spleen. In response to CD8-restricted peptides an increase of IFN-γ was observed among lung cells. IgG2a levels non-specifically increased following block copolymer/DNA vaccination although IgE, IgG1 levels and airways resistances were not impacted.
Conclusions & Clinical Relevance
DNA vaccination using a plasmid coding for Der f1 formulated with the block copolymer 704 induces a specific immune response in the model of asthma used herein.
Allergic inflammation and severe allergic reactions (anaphylaxis) are important in allergen induced diseases. Bacterial products such as lipopolysaccharide (LPS) are ubiquitous and can facilitate allergen induced Th2 immune responses. Phosphatase SHP-1 is critical in regulating immunological homeostasis and in allergen induced Th2 immune responses in the lung. However, the mechanisms underlying the initiation of allergic inflammation and allergen induced anaphylaxis are still not completely elucidated and it is unclear whether SHP-1 plays any role in LPS-induced airway inflammation and in allergen-induced anaphylaxis. In this study we tested the hypothesis that phosphatase SHP-1 plays an important role in allergic inflammation and anaphylaxis and determined whether its effects are through regulation of mast cell functions. SHP-1 deficient (mev/+ and mev/mev) and mast cell deficient (KitW-sh) mice were examined in their responses to LPS airway stimulation and to ovalbumin (OVA) allergen induced systemic anaphylaxis. Compared to wild type mice, mev/+ mice had significantly enhanced LPS induced airway inflammation and OVA induced anaphylactic responses, including hypothermia and clinical symptoms. These changes were mast cell dependent as KitW-sh mice had reduced responses whereas adoptive transfer of mast cells restored the responses. However, T and B cells were not involved and macrophages did not play a significant role in LPS induced airway inflammation. Interestingly, basophil differentiation from SHP-1 deficient bone marrow cells was significantly reduced. These findings provided evidence that through regulation of mast cell functions SHP-1 plays a critical role as a negative regulator in allergic inflammation and in allergen induced anaphylaxis. In addition, SHP-1 seems to be required for normal basophil development.
Macrophage migration inhibitory factor (MIF) has recently been forwarded as a critical regulator of inflammatory conditions, and it has been hypothesized that MIF may have a role in the pathogenesis of asthma and chronic obstructive pulmonary disease (COPD). Hence, we examined effects of MIF immunoneutralization on the development of allergen-induced eosinophilic inflammation as well as on lipopolysaccharide (LPS)-induced neutrophilic inflammation in lungs of mice. Anti-MIF serum validated with respect to MIF neutralizing capacity or normal rabbit serum (NRS) was administered i.p. repeatedly during allergen aerosol exposure of ovalbumin (OVA)-immunized mice in an established model of allergic asthma, or once before instillation of a minimal dose of LPS into the airways of mice, a tentative model of COPD. Anti-MIF treatment did not affect the induced lung tissue eosinophilia or the cellular composition of bronchoalveolar lavage fluid (BALF) in the asthma model. Likewise, anti-MIF treatment did not affect the LPS-induced neutrophilia in lung tissue, BALF, or blood, nor did it reduce BALF levels of tumor necrosis factor-alpha (TNF-alpha) and macrophage inflammatory protein-1alpha (MIP-1alpha). The present data suggest that MIF is not critically important for allergen-induced eosinophilic, and LPS-induced neutrophilic responses in lungs of mice. These findings do not support a role of MIF inhibition in the treatment of inflammatory respiratory diseases.
The mechanisms underlying exacerbation of asthma induced by respiratory syncytial virus (RSV) infection have been extensively studied in human and animal models. However, most of these studies focused on acute inflammation and little is known of its long-term consequences on remodelling of the airway tissue.
The aim of the study was to use a murine model of prolonged allergen-induced airway inflammation to investigate the effect of RSV infection on allergic airway inflammation and tissue remodelling.
We subjected mice to RSV infection before or during the chronic phase of airway challenges with OVA and compared parameters of airway inflammation and remodelling at the end-point of the prolonged allergen-induced airway inflammation protocol.
RSV infection did not affect the severity of airway inflammation in any of the groups studied. However, RSV infection provoked airway remodelling in non-sensitized, allergen-challenged mice that did not otherwise develop any of the features of allergic airways disease. Increased collagen synthesis in the lung and thickening of the bronchial basal membrane was observed in non-sensitized allergen-challenged mice only after prior RSV infection. In addition, fibroblast growth factor (FGF)-2 but not TGF-β1 was increased in this group following RSV infection.
Our data show for the first time that RSV infection can prime the lung of mice that are not previously systemically sensitized, to develop airway remodelling in response to allergen upon sole exposure via the airways. Moreover, our results implicate RSV-induced FGF-2 in the remodelling process in vivo.
airway allergic inflammation; airway remodelling; asthma; RSV
Sensitizations to house dust mites (HDM) trigger strong exacerbated allergen-induced inflammation of the skin and airways mucosa from atopic subjects resulting in atopic dermatitis as well as allergic rhinitis and asthma. Initially, the Th2-biased HDM allergic response was considered to be mediated only by allergen B- and T-cell epitopes to promote allergen-specific IgE production as well as IL-4, IL-5, and IL-13 to recruit inflammatory cells. But this general molecular model of HDM allergenicity must be revisited as a growing literature suggests that stimulations of innate immune activation pathways by HDM allergens offer new answers to the following question: what makes an HDM allergen an allergen? Indeed, HDM is a carrier not only for allergenic proteins but also microbial adjuvant compounds, both of which are able to stimulate innate signaling pathways leading to allergy. This paper will describe the multiple ways used by HDM allergens together with microbial compounds to control the initiation of the allergic response through engagement of innate immunity.