Dissociation of T helper type 2 cytokine-dependent airway lesions from signal transducer and activator of transcription 6 signalling in experimental chronic asthma

House dust mite-induced endoplasmic reticulum stress mediates MUC5AC hypersecretion via TBK1 in airway epithelium

Purpose: Endoplasmic reticulum (ER) stress regulates mucus hypersecretion, and may activate downstream factors via TBK1 signaling to induce gene expression. However, it remains unclear whether ER stress promotes airway mucus secretion through the TBK1 pathway. We aimed to investigate the role of the TBK1 pathway in the regulation of MUC5AC expression in a mouse model of house dust mite (HDM)-induced allergic asthma. Materials and Methods: Mice with HDM-induced asthma and human bronchial epithelial BEAS-2B cells were treated with amlexanox, an anti-allergy drug (25 μM), or 4-PBA (10 mM). Tissue and cell samples were collected. Tissue samples were stained with hematoxylin and eosin (H&E) or periodic acid Schiff (PAS) to evaluate pathology. Protein expression was analyzed by western blotting and immunofluorescence. Results: Mice exposed to HDM presented ER stress and hypersecretion of mucus Muc5ac from airway epithelial cells (p < 0.001). Similar results were observed in BEAS-2B cells following exposure to HDM. Both in vivo and in vitro studies revealed that HDM-induced ER stress induced MUC5AC overexpression via TBK1 signaling. Amlexanox and 4-PBA markedly reduced mucus production and weakened the TBK1 signal, which mediates MUC5AC hypersecretion. Conclusion: TBK1 plays a pivotal role in HDM-induced ER stress, leading to overproduction of MUC5AC in the asthmatic airway epithelium. The overproduction of MUC5AC can be significantly decreased by inhibiting TBK1 or ER stress using 4-PBA. These findings highlight potential target-specific therapies for patients with chronic allergic asthma.

Protocatechuic acid supplement alleviates allergic airway inflammation by inhibiting the IL-4Rα-STAT6 and Jagged 1/Jagged2-Notch1/Notch2 pathways in allergic asthmatic mice

OBJECTIVE AND DESIGN

To clarify the effects of dietary supplementation of protocatechuic acid (PCA) and in-depth mechanisms on allergic asthma in ovalbumin (OVA)-induced mice.

MATERIALS

Female BALB/c mice were randomly divided into three groups (n = 10 in each group): control group, OVA-induced allergic asthma group, and OVA plus PCA group.

TREATMENT

Dietary supplementation of PCA was achieved by adding 50 mg/kg PCA to AIN 93G diet for 25 days.

METHODS

Peripheral blood cells, pulmonary inflammatory cell infiltration, the levels of IL-4, IL-5, and IL-13 in bronchoalveolar lavage fluid (BALF), the mRNA levels of Th2-related genes in the lungs, and the protein expressions of the IL-4Rα-STAT6 and the Jagged1/Jagged2-Notch1/Notch2 signaling pathways were measured.

RESULTS

Significantly reduced inflammatory cells infiltration and mucosal hypersecretion in the lung tissues, repaired levels of interleukin IL-4, IL-5, and IL-13 in the BALF, and decreased mRNA expression of IL-4, IL-5, and GATA3 were observed in OVA plus PCA group. Moreover, PCA treatment down-regulated the protein levels of IL-4Rα-STAT6 and Jagged1/Jagged2-Notch1/Notch2 signaling pathways.

CONCLUSIONS

Dietary supplement of PCA alleviated allergic asthma partly through suppressing the IL-4Rα-STAT6 and Jagged1/Jagged2-Notch1/Notch2 signaling pathways in mice. Our study provided the theoretic basis of PCA used as functional food in preventing allergic asthma.

Bu-Shen-Yi-Qi formula ameliorates airway remodeling in murine chronic asthma by modulating airway inflammation and oxidative stress in the lung

Bu-Shen-Yi-Qi formula (BSYQF) could suppress chronic airway inflammation according to previous studies. However, there is relatively little direct experimental evidence to evaluate the effects of BSYQF treatment on airway remodeling in chronic asthma. Recent evidence suggests that oxidative stress is involved in airway inflammation and airway remodeling in chronic asthma. BSYQF which includes various of chemical components having antioxidant effects, could be beneficial in attenuating airway remodeling in chronic asthma. The purpose of this study was to elucidate the effect of BSYQF treatment on airway remodeling and investigate its potential mechanisms in chronic asthma. To develop the murine models of chronic asthma, BALB/c mice were sensitized and challenged to ovalbumin for 8 weeks. BSYQF (5, 10, 20 g raw herbs/kg body weight) or tiotropium bromide (0.1 mM) were administered orally and intranasal instillation, respectively. The effect of BSYQF on pulmonary inflammation and remodeling was evaluated. The parameters of oxidative stress in the lung were analyzed. BSYQF treatment reduced airway hyperresponsiveness (AHR), Th2 response including IL-4, IL-13, and OVA-specific IgE and IgG1, transforming growth factor-β (TGF-β), vascular endothelium growth factor (VEGF), airway inflammation and airway remodeling including smooth muscle thickening and peribronchial collagen deposition. As for oxidative stress, BSYQF treatment reduced reactive oxygen species (ROS), Malondialdehyde (MDA), NO, and the expression of inducible nitric oxide synthase (iNOS), but increased significantly glutathione (GSH) /Oxidized glutathione(GSSH) ratios in the lung, restored mitochondrial ultrastructural changes of bronchial epithelia and ATP levels in the lung. In summary, this study suggested that BSYQF treatment ameliorated airway remodeling and alleviated asthmatic features in chronic asthma models. Anti-inflammatory and antioxidant effect of BSYQF may explain why BSYQF has effects on preventing airway remodeling.

Modeling TH 2 responses and airway inflammation to understand fundamental mechanisms regulating the pathogenesis of asthma

In this review, we highlight experiments conducted in our laboratories that have elucidated functional roles for CD4⁺ T-helper type-2 lymphocytes (T_H 2 cells), their associated cytokines, and eosinophils in the regulation of hallmark features of allergic asthma. Notably, we consider the complexity of type-2 responses and studies that have explored integrated signaling among classical T_H 2 cytokines (IL-4, IL-5, and IL-13), which together with CCL11 (eotaxin-1) regulate critical aspects of eosinophil recruitment, allergic inflammation, and airway hyper-responsiveness (AHR). Among our most important findings, we have provided evidence that the initiation of T_H 2 responses is regulated by airway epithelial cell-derived factors, including TRAIL and MID1, which promote T_H 2 cell development via STAT6-dependent pathways. Further, we highlight studies demonstrating that microRNAs are key regulators of allergic inflammation and potential targets for anti-inflammatory therapy. On the background of T_H 2 inflammation, we have demonstrated that innate immune cells (notably, airway macrophages) play essential roles in the generation of steroid-resistant inflammation and AHR secondary to allergen- and pathogen-induced exacerbations. Our work clearly indicates that understanding the diversity and spatiotemporal role of the inflammatory response and its interactions with resident airway cells is critical to advancing knowledge on asthma pathogenesis and the development of new therapeutic approaches.

Mouse models of severe asthma: Understanding the mechanisms of steroid resistance, tissue remodelling and disease exacerbation

Severe asthma has significant disease burden and results in high healthcare costs. While existing therapies are effective for the majority of asthma patients, treatments for individuals with severe asthma are often ineffective. Mouse models are useful to identify mechanisms underlying disease pathogenesis and for the preclinical assessment of new therapies. In fact, existing mouse models have contributed significantly to our understanding of allergic/eosinophilic phenotypes of asthma and facilitated the development of novel targeted therapies (e.g. anti-IL-5 and anti-IgE). These therapies are effective in relevant subsets of severe asthma patients. Unfortunately, non-allergic/non-eosinophilic asthma, steroid resistance and disease exacerbation remain areas of unmet clinical need. No mouse model encompasses all features of severe asthma. However, mouse models can provide insight into pathogenic pathways that are relevant to severe asthma. In this review, as examples, we highlight models relevant to understanding steroid resistance, chronic tissue remodelling and disease exacerbation. Although these models highlight the complexity of the immune pathways that may underlie severe asthma, they also provide insight into new potential therapeutic approaches.

Lyn regulates mucus secretion and MUC5AC via the STAT6 signaling pathway during allergic airway inflammation

Hypersecretion of mucus is an important component of airway remodeling and contributes to the mucus plugs and airflow obstruction associated with severe asthma phenotypes. Lyn has been shown to down-regulate allergen-induced airway inflammation. However, the role of Lyn in mucin gene expression remains unresolved. In this study, we first demonstrate that Lyn overexpression decreased the mucus hypersecretion and levels of the muc5ac transcript in mice exposed to ovalbumin (OVA). Lyn overexpression also decreased the infiltration of inflammatory cells and the levels of IL-13 and IL-4 in OVA-challenged airways. Whereas Lyn knockdown increased the IL-4 or IL-13-induced MUC5AC transcript and protein levels in the human bronchial epithelial cell line, 16HBE, Lyn overexpression decreased IL-4- or IL-13-induced MUC5AC transcript and protein levels. Overexpression of Lyn also decreased the expression and phosphorylation of STAT6 in OVA-exposed mice, whereas Lyn knockdown increased STAT6 and MUC5AC levels in 16HBE cells. Finally, chromatin immunoprecipitation analysis confirmed that Lyn overexpression decreased the binding of STAT6 to the promoter region of Muc5ac in mice exposed to OVA. Collectively, these findings demonstrated that Lyn overexpression ameliorated airway mucus hypersecretion by down-regulating STAT6 and its binding to the MUC5AC promoter.

Wheezing and itching: The requirement for STAT proteins in allergic inflammation

The development of allergic inflammation requires the orchestration of gene expression from the inflamed tissue and from the infiltrating immune cells. Since many of the cytokines that promote allergic inflammation signal through hematopoietin family receptors, the Signal Transducer and Activator of Transcription (STAT) family have obligate roles in pro-allergic cytokine-induced gene regulation in multiple cell types. In this review, we summarize work defining the contribution of each of the STAT family members to the development of allergic inflammation, using data from mouse models of allergic inflammation, studies on patient samples and correlations with single nucleotide polymorphisms in STAT genes.

FLLL31, a derivative of curcumin, attenuates airway inflammation in a multi-allergen challenged mouse model

Signal transducer and activator of transcription protein 3 (STAT3), one of the major regulators of inflammation, plays multiple roles in cellular transcription, differentiation, proliferation, and survival in human diseases. Dysregulation of STAT3 is related to the severe airway inflammation associated with asthma. FLLL31 is a newly developed compound based on the herbal medicine curcumin, which specifically suppresses the activation of STAT3. However, the function of FLLL31 on inflammatory diseases, especially on the regulation of airway inflammation, has not been fully studied. In our prior investigations, we developed a mouse model that was challenged with a mixture of DRA allergens (including house dust mite, ragweed, and Aspergillums species) to mimic the severe airway inflammation observed in human patients. In this study, we performed a series of experiments on the inflammatory regulation activities of FLLL31 in both in vitro cultured cells and our in vivo DRA-challenged mouse model. Our results show that FLLL31 exhibits anti-inflammatory effects on macrophage activation, lymphocyte differentiation, and pro-inflammatory factor production. Importantly, FLLL31 significantly inhibited airway inflammation and recruitment of inflammatory cells in the DRA-challenged mouse model. Based on these results, we conclude that FLLL31 is a potential therapeutic agent that can be used against severe airway inflammation diseases.

The endogenous Th17 response in NO2-promoted allergic airway disease is dispensable for airway hyperresponsiveness and distinct from Th17 adoptive transfer

Severe, glucocorticoid-resistant asthma comprises 5-7% of patients with asthma. IL-17 is a biomarker of severe asthma, and the adoptive transfer of Th17 cells in mice is sufficient to induce glucocorticoid-resistant allergic airway disease. Nitrogen dioxide (NO2) is an environmental toxin that correlates with asthma severity, exacerbation, and risk of adverse outcomes. Mice that are allergically sensitized to the antigen ovalbumin by exposure to NO2 exhibit a mixed Th2/Th17 adaptive immune response and eosinophil and neutrophil recruitment to the airway following antigen challenge, a phenotype reminiscent of severe clinical asthma. Because IL-1 receptor (IL-1R) signaling is critical in the generation of the Th17 response in vivo, we hypothesized that the IL-1R/Th17 axis contributes to pulmonary inflammation and airway hyperresponsiveness (AHR) in NO2-promoted allergic airway disease and manifests in glucocorticoid-resistant cytokine production. IL-17A neutralization at the time of antigen challenge or genetic deficiency in IL-1R resulted in decreased neutrophil recruitment to the airway following antigen challenge but did not protect against the development of AHR. Instead, IL-1R-/- mice developed exacerbated AHR compared to WT mice. Lung cells from NO2-allergically inflamed mice that were treated in vitro with dexamethasone (Dex) during antigen restimulation exhibited reduced Th17 cytokine production, whereas Th17 cytokine production by lung cells from recipient mice of in vitro Th17-polarized OTII T-cells was resistant to Dex. These results demonstrate that the IL-1R/Th17 axis does not contribute to AHR development in NO2-promoted allergic airway disease, that Th17 adoptive transfer does not necessarily reflect an endogenously-generated Th17 response, and that functions of Th17 responses are contingent on the experimental conditions in which they are generated.

Interleukin-13 signaling and its role in asthma

Asthma affects nearly 300 million people worldwide. The majority respond to inhaled corticosteroid treatment with or without beta-adrenergic agonists. However, a subset of 5 to 10% with severe asthma do not respond optimally to these medications. Different phenotypes of asthma may explain why current therapies show limited benefits in subgroups of patients. Interleukin-13 is implicated as a central regulator in IgE synthesis, mucus hypersecretion, airway hyperresponsiveness, and fibrosis. Promising research suggests that the interleukin-13 pathway may be an important target in the treatment of the different asthma phenotypes.

The pharmacological modulation of allergen-induced asthma

Aeroallergens are the most common triggers for the development of asthma. Recent birth cohort studies have identified viral infections occurring against a background of aeroallergen sensitization as a potent risk factor for initiation of asthma. Viral infection enhances immunopathogenic potential of pre-existing inhalant allergy via modulating airway mucosal dendritic cells. By using an allergen inhalation challenge clinical model, studies have shown that the late asthma response (LAR) is associated with more pronounced allergen-induced airway inflammation and airway hyperresponsiveness. The degree of airway eosinophilia, regulated by bone marrow progenitor cells and interleukin-5 level, correlates with the magnitude of the LAR and the increase in hyperresponsiveness. Both myeloid and plasmacytoid dendritic cell subsets have been involved in the pathogenesis of allergen-induced LAR. Myeloid dendritic cells are responsible for the allergen presentation and induction of inflammation and plasmacytoid dendritic cells play a role in the resolution of allergen-induced inflammation. A variety of potential new classes of asthma medication has also been evaluated with the allergen inhalation challenge in mild asthmatic subjects. Examples are TPI ASM8, an inhaled anti-sense oligonucleotide drug product, which attenuated both early and LARs via inhibition of the target gene mRNA of chemokine receptor 3, and the common β chain of interleukin-3, interleukin-5 and granulocyte-macrophage colony-stimulating factor receptor. Anti-human antibody interleukin-13 (IM-638) significantly attenuated both early and late allergen-induced asthma response. Pitrakinra, which targets both interleukin-4 and interleukin-13, substantially diminishes allergen-induced airway responses. Allergen-induced airway responses are a valuable way to evaluate the activity of possible new therapies in asthmatic airways.

Can anti-IgE therapy prevent airway remodeling in allergic asthma?

Airway remodeling is a central feature of asthma. It is exemplified by thickening of the lamina reticularis and structural changes to the epithelium, submucosa, smooth muscle, and vasculature of the airway wall. Airway remodeling may result from persistent airway inflammation. Immunoglobulin E (IgE) is an important mediator of allergic reactions and has a central role in airway inflammation and asthma-related symptoms. Anti-IgE therapies (such as omalizumab) have the potential to block an early step in the allergic cascade and therefore have the potential to reduce airway remodeling. The reduction in free IgE levels following anti-IgE therapy leads to reductions in high-affinity IgE receptor (FcεRI) expression on mast cells, basophils, and dendritic cells. This combined effect results in attenuation of several markers of inflammation, including peripheral and bronchial tissue eosinophilia and levels of granulocyte macrophage colony-stimulating factor, interleukin (IL)-2, IL-4, IL-5, and IL-13. Considering the previously demonstrated anti-inflammatory effects of anti-IgE therapy, along with results from a small study showing continued benefit after discontinuation of long-term treatment, a larger study to assess its effect on markers of airway remodeling is underway.

Altered expression of microRNA in the airway wall in chronic asthma: miR-126 as a potential therapeutic target

Background

The role of microRNAs (miRNAs) in regulating gene expression is currently an area of intense interest. Relatively little is known, however, about the role of miRNAs in inflammatory and immunologically-driven disorders. In a mouse model, we have previously shown that miRNAs are potentially important therapeutic targets in allergic asthma, because inhibition of miR-126, one of a small subset of miRNAs upregulated in the airway wall, effectively suppressed Th2-driven airway inflammation and other features of asthma. In the present study, we extended investigation of the therapeutic potential of miRNA inhibition to our well-established model of chronic asthma.

Methods

Female BALB/c mice were systemically sensitised with ovalbumin (OVA) and chronically challenged with low mass concentrations of aerosolised OVA for up to 6 weeks. Airway tissue was obtained by blunt dissection and RNA was isolated for miRNA profiling. On the basis of the results obtained, animals were subsequently treated with either an antagomir to miR-126 (ant-miR-126) or a scrambled control antagomir once weekly during the 6 weeks of chronic challenge, and the effects on airway inflammation and remodelling were assessed using established morphometric techniques.

Results

Compared to naïve mice, there was selective upregulation of a modest number of miRNAs, notably miR-126, in the airway wall tissue of chronically challenged animals. The relative increase was maximal after 2 weeks of inhalational challenge and subsequently declined to baseline levels. Compared to treatment with the scrambled control, ant-miR-126 significantly reduced recruitment of intraepithelial eosinophils, but had no effect on the chronic inflammatory response, or on changes of airway remodelling.

Conclusions

In this model of chronic asthma, there was an initial increase in expression of a small number of miRNAs in the airway wall, notably miR-126. However, this later declined to baseline levels, suggesting that sustained changes in miRNA may not be essential for perpetuation of chronic asthma. Moreover, inhibition of miR-126 by administration of an antagomir suppressed eosinophil recruitment into the airways but had no effect on chronic inflammation in the airway wall, or on changes of remodelling, suggesting that multiple miRNAs are likely to regulate the development of these lesions.

Cytokine/anti-cytokine therapy - novel treatments for asthma?

Asthma is a chronic inflammatory disease of the airways and there are no preventions or cures. Inflammatory cells through the secretion of cytokines and pro-inflammatory molecules are thought to play a critical role in pathogenesis. Type 2 CD4(+) lymphocytes (Th2 cells) and their cytokines predominate in mild to moderate allergic asthma, whereas severe steroid-resistant asthma has more of a mixed Th2/Th1 phenotype with a Th17 component. Other immune cells, particularly neutrophils, macrophages and dendritic cells, as well structural cells such as epithelial and airway smooth muscle cells also produce disease-associated cytokines in asthma. Increased levels of these immune cells and cytokines have been identified in clinical samples and their potential role in disease demonstrated in studies using mouse models of asthma. Clinical trials with inhibitors of cytokines such as interleukin (IL)-4, -5 and tumour necrosis factor-α have had success in some studies but not others. This may reflect the design of the clinical trials, including treatments regimes and the patient population included in these studies. IL-13, -9 and granulocyte-macrophage colony-stimulating factor are currently being evaluated in clinical trials or preclinically and the outcome of these studies is eagerly awaited. Roles for IL-25, -33, thymic stromal lymphopoietin, interferon-γ, IL-17 and -27 in the regulation of asthma are just emerging, identifying new ways to treat inflammation. Careful interpretation of results from mouse studies will inform the development and application of therapeutic approaches for asthma. The most effective approaches may be combination therapies that suppress multiple cytokines and a range of redundant and disconnected pathways that separately contribute to asthma pathogenesis. Astute application of these approaches may eventually lead to the development of effective asthma therapeutics. Here we review the current state of knowledge in the field.

Blocking induction of T helper type 2 responses prevents development of disease in a model of childhood asthma

Early-life respiratory viral infections are linked to subsequent development of allergic asthma in children. We assessed the underlying immunological mechanisms in a novel model of the induction phase of childhood asthma. BALB/c mice were infected neonatally with pneumonia virus of mice, then sensitized intranasally with ovalbumin following recovery. Animals were challenged with low levels of aerosolized ovalbumin for 4 weeks to induce changes of chronic asthma, then received a single moderate-level challenge to elicit mild acute allergic inflammation. To inhibit the initial induction of a T helper type 2 (Th2) response, we administered neutralizing antibodies against interleukin (IL)-4 or IL-25, then assessed development of airway inflammation and remodelling. Anti-IL-4 administered during chronic challenge prevented development of chronic and acute allergic inflammation, as well as goblet cell hyperplasia/metaplasia, but features of remodelling such as subepithelial fibrosis and epithelial hypertrophy were unaffected. In contrast, anti-IL-25 had limited effects on the airway inflammatory response but prevented key changes of remodelling, although it had no effect on goblet cells. Both antibodies suppressed development of a Th2 response, while anti-IL-25 also promoted a Th17 response. In further experiments, anti-IL-25 was administered in early life alone, and again had limited effects on airway inflammation, but prevented development of airway wall remodelling. We conclude that in this murine model of childhood asthma, administration of anti-IL-4 or anti-IL-25 prevents development of some key features of asthma, suggesting that suppression of development of a Th2 response during the neonatal period or later in childhood could be effective for primary prevention.

Attenuated expression of tenascin-C in ovalbumin-challenged STAT4-/- mice

Background

Asthma leads to structural changes in the airways, including the modification of extracellular matrix proteins such as tenascin-C. The role of tenascin-C is unclear, but it might act as an early initiator of airway wall remodelling, as its expression is increased in the mouse and human airways during allergic inflammation. In this study, we examined whether Th1 or Th2 cells are important regulators of tenascin-C in experimental allergic asthma utilizing mice with impaired Th1 (STAT4-/-) or Th2 (STAT6-/-) immunity.

Methods

Balb/c wildtype (WT), STAT4-/- and STAT6-/- mice were sensitized with intraperitoneally injected ovalbumin (OVA) followed by OVA or PBS airway challenge. Airway hyperreactivity (AHR) was measured and samples were collected. Real time PCR and immunohistochemistry were used to study cytokines and differences in the expression of tenascin-C. Tenascin-C expression was measured in human fibroblasts after treatment with TNF-α and IFN-γ in vitro.

Results

OVA-challenged WT mice showed allergic inflammation and AHR in the airways along with increased expression of TNF-α, IFN-γ, IL-4 and tenascin-C in the lungs. OVA-challenged STAT4-/- mice exhibited elevated AHR and pulmonary eosinophilia. The mRNA expression of TNF-α and IFN-γ was low, but the expression of IL-4 was significantly elevated in these mice. OVA-challenged STAT6-/- mice had neither AHR nor pulmonary eosinophilia, but had increased expression of mRNA for TNF-α, IFN-γ and IL-4. The expression of tenascin-C in the lungs of OVA-challenged STAT4-/- mice was weaker than in those of OVA-challenged WT and STAT6-/- mice suggesting that TNF-α and IFN-γ may regulate tenascin-C expression in vivo. The stimulation of human fibroblasts with TNF-α and IFN-γ induced the expression of tenascin-C confirming our in vivo findings.

Conclusions

Expression of tenascin-C is significantly attenuated in the airways of STAT4-/- mice, which may be due to the impaired secretion of TNF-α and IFN-γ in these mice.

Alveolar macrophages stimulate enhanced cytokine production by pulmonary CD4+ T-lymphocytes in an exacerbation of murine chronic asthma

The mechanisms underlying the exaggerated distal airway inflammation and hyperresponsiveness that characterize acute exacerbations of asthma are largely unknown. Using BALB/c mouse experimental models, we demonstrated a potentially important role for alveolar macrophages (AM) in the development of an allergen-induced exacerbation of asthma. To induce features of airway inflammation and remodeling characteristic of mild chronic asthma, animals were systemically sensitized and exposed to low mass concentrations (≈3 mg/m(3)) of aerosolized ovalbumin for 30 minutes per day, 3 days per week, for 4 weeks. A subsequent single moderate-level challenge (≈30 mg/m(3)) was used to trigger an acute exacerbation. In chronically challenged animals, cytokine expression by AM was not increased, whereas after an acute exacerbation, AM exhibited significantly enhanced expression of proinflammatory cytokines, including interleukin (IL) 1β, IL-6, CXCL-1, and tumor necrosis factor α. In parallel, there was a marked increase in the expression of several cytokines by CD4(+) T-lymphocytes, notably the Th2 cytokines IL-4 and IL-13. Importantly, AM from an acute exacerbation stimulated the expression of Th2 cytokines when cocultured with CD4(+) cells from chronically challenged animals, and their ability to do so was significantly greater than AM from either chronically challenged or naïve controls. Stimulation was partly dependent on interactions involving CD80/86. We conclude that in an acute exacerbation of asthma, enhanced cytokine expression by AM may play a critical role in triggering increased expression of cytokines by pulmonary CD4(+) T-lymphocytes.

MicroRNA-21 is up-regulated in allergic airway inflammation and regulates IL-12p35 expression

Allergic airway inflammation is characterized by marked in situ changes in gene and protein expression, yet the role of microRNAs (miRNAs), a new family of key mRNA regulatory molecules, in this process has not yet been reported. Using a highly sensitive microarray-based approach, we identified 21 miRNAs with differential expression between doxycycline-induced lung-specific IL-13 transgenic mice (with allergic airway inflammation) and control mice. In particular, we observed overexpression of miR-21 and underexpression of miR-1 in the induced IL-13 transgenic mice compared with control mice. These findings were validated in two independent models of allergen-induced allergic airway inflammation and in IL-4 lung transgenic mice. Although IL-13-induced miR-21 expression was IL-13Ralpha1 dependent, allergen-induced miR-21 expression was mediated mainly independent of IL-13Ralpha1 and STAT6. Notably, predictive algorithms identified potential direct miR-21 targets among IL-13-regulated lung transcripts, such as IL-12p35 mRNA, which was decreased in IL-13 transgenic mice. Introduction of pre-miR-21 dose dependently inhibited cellular expression of a reporter vector harboring the 3'-untranslated region of IL-12p35. Moreover, mutating miR-21 binding sites in IL-12p35 3'-untranslated region abrogated miR-21-mediated repression. In summary, we have identified a miRNA signature in allergic airway inflammation, which includes miR-21 that modulates IL-12, a molecule germane to Th cell polarization.

Airway eosinophilic inflammation is attenuated in conserved noncoding sequence-1-deficient mice

BACKGROUND

Conserved noncoding sequence-1 (CNS-1) is an important regulatory element for T helper 2 cytokine expression. IL-4, IL-5 and IL-13 expression as well as serum IgE level were attenuated in CNS-1-/- mice.

METHOD

CNS-1-/- and CNS-1+/+ mice were sensitized with ovalbumin (OVA) followed by antigen challenge. The number of eosinophils and T helper 2 cytokine concentration in the bronchoalveolar lavage fluid, OVA-specific IgE antibody (Ab) in the serum and bronchial responsiveness to methacholine were examined.

RESULTS

Bronchoalveolar lavage fluid eosinophilia was significantly attenuated in CNS-1-/- mice compared to CNS-1+/+ mice, which were sensitized with OVA/aluminum once. OVA-specific IgE Ab was also attenuated. When mice were sensitized with OVA/aluminum twice, induction of eosinophilia and OVA-specific IgE Ab was not significantly different between CNS-1-/- and CNS-1+/+ mice.

CONCLUSION

CNS-1 locus regulates eosinophilic inflammation in vivo.

MAP kinases mediate interleukin-13 effects on calcium signaling in human airway smooth muscle cells

Interleukin-13 (IL-13) has been strongly implicated in the pathogenesis of allergic asthma through animal models that have shown that IL-13 is both necessary and sufficient to cause airway hyperresponsiveness (AHR). Airway smooth muscle (ASM) is a primary effector of AHR, and IL-13 increases the responsiveness of ASM, by increasing Ca(2+) release intracellularly, to bronchoconstrictors such as histamine. The mechanisms and signaling pathways mediating this effect are incompletely understood. We have investigated the pathways through which IL-13 regulates the Ca(2+) response to histamine in primary human ASM cell cultures. Functional IL-13 receptors were demonstrated by IL-13-mediated phosphorylation of signal transducer and activator of transcription 6 (STAT6) and mitogen-activated protein kinases (MAPKs). IL-13 increased Ca(2+) responses to histamine. The augmentation of Ca(2+) signaling was not affected by inhibition of STAT6 or p38 MAPK signaling but was prevented by concurrent inhibition of c-jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) MAPKs. This inhibition did not affect the IL-13-induced increase in histamine receptors. We conclude that IL-13 induces potentiation of Ca(2+) responses to contractile agonists by affecting mechanisms downstream of receptors. JNK and ERK MAPKs modulate these mechanisms.

IL-13 as a therapeutic target for respiratory disease

Interleukin-13 (IL-13) is a critical mediator of asthma pathology. On B cells, monocytes, epithelial cells, and smooth muscle cells, IL-13 acts through the IL-13Ralpha1/IL-4Ralpha complex to directly induce activation responses that contribute to atopic disease. In human populations, genetic polymorphisms in IL-13, its receptor components, or the essential signaling element STAT6, have all been associated with increased risk of atopy and asthma. Animal studies using IL-13 deficient mice, IL-13 transgenic animals, and IL-13 neutralization strategies have confirmed an essential role for this cytokine in driving major correlates of asthma pathology, including airway hyperresponsiveness (AHR), lung eosinophilia, mucus generation, and fibrosis. Ongoing studies continue to define both overlapping and distinct roles for IL-13 and the related cytokine, IL-4, in promoting asthmatic changes. Furthermore, new evidence concerning the role of the "decoy" receptor, IL-13Ralpha2, has prompted re-evaluation of the receptor forms that underlie the numerous activities of IL-13. In this review, we summarize the essential role of IL-13 in asthma, compare the relative contributions of IL-13 and IL-4 to key aspects of the asthmatic phenotype, and outline novel therapeutic strategies to target this critical cytokine.

IL-9- and mast cell-mediated intestinal permeability predisposes to oral antigen hypersensitivity

Previous mouse and clinical studies demonstrate a link between Th2 intestinal inflammation and induction of the effector phase of food allergy. However, the mechanism by which sensitization and mast cell responses occurs is largely unknown. We demonstrate that interleukin (IL)-9 has an important role in this process. IL-9-deficient mice fail to develop experimental oral antigen-induced intestinal anaphylaxis, and intestinal IL-9 overexpression induces an intestinal anaphylaxis phenotype (intestinal mastocytosis, intestinal permeability, and intravascular leakage). In addition, intestinal IL-9 overexpression predisposes to oral antigen sensitization, which requires mast cells and increased intestinal permeability. These observations demonstrate a central role for IL-9 and mast cells in experimental intestinal permeability in oral antigen sensitization and suggest that IL-9-mediated mast cell responses have an important role in food allergy.

Suppression of cytokine expression by roflumilast and dexamethasone in a model of chronic asthma

BACKGROUND

In a mouse model of mild chronic asthma, both inflammation and remodelling can be suppressed by dexamethasone (a glucocorticoid) and roflumilast (a selective phosphodiesterase-4 inhibitor).

OBJECTIVE

To better understand the underlying molecular mechanisms, we investigated the effects of treatment on airway expression of inflammation-related cytokines, as well as on epithelial expression of growth factors.

METHODS

BALB/c mice systemically sensitized to ovalbumin were challenged with aerosolized antigen for 6 weeks and treated with roflumilast or dexamethasone during the final 2 weeks. Expression of mRNA, for a variety of cytokines and growth factors, was assessed in selectively dissected proximal airways or in airway epithelium obtained by laser capture microdissection.

RESULTS

In the airway wall of vehicle-treated challenged animals, there was significantly elevated expression of mRNA for a variety of pro-inflammatory and T helper type 2 cytokines, as well as for IFN-gamma. All these cytokines were suppressed by dexamethasone. Treatment with roflumilast reduced expression of IL-17A, TNF-alpha, granulocyte-macrophage colony-stimulating factor and IL-6, but did not inhibit other cytokines. Both drugs suppressed the enhanced expression of mRNA for growth factors such as TGF-beta1 and FGF-2 in airway epithelium.

CONCLUSIONS

Whereas dexamethasone non-specifically inhibits numerous mediators involved in inflammation and the immune response, roflumilast selectively inhibits a subset of pro-inflammatory cytokines and growth factors. These mediators and/or the cells that produce them may have critical roles in the pathogenesis of the lesions of chronic asthma.

Interleukin-4 and interleukin-13 enhance human bronchial smooth muscle cell proliferation

BACKGROUND

T(H)2 inflammation and bronchial smooth muscle cell (BSMC) hyperplasia are characteristic features of asthma, but whether these phenomena are linked remains unknown. This study aims to define the effect of the T(H)2 cytokines IL-4 and IL-13 on human BSMC proliferation when administered alone or in combination with the fibroblast growth factor 2 (FGF2) growth factor. In addition, the effects of the proinflammatory mediators TNFalpha and IL-1 beta and the involvement of members of the well-known family of platelet-derived growth factor (PDGF) mitogens were tested.

METHODS

BSMC proliferation was measured by crystal violet staining and PDGF and PDGF receptor (PDGFR) expression were determined by RT-PCR, immunocytochemistry, ELISA, flow cytometry and dot plot analysis.

RESULTS

Neither IL-4 nor IL-13 alone induced BSMC proliferation, despite both being potent inducers of PDGF-CC. However, following a pretreatment with FGF2, which increased PDGFR alpha chain expression, both IL-4 and IL-13 increased FGF2-induced BSMC proliferation in a time- and concentration-dependent manner. TNFalpha and IL-1 beta did not affect basal or FGF2-induced BSMC proliferation, but both proinflammatory mediators enhanced the proliferative synergism between FGF2 and the T(H)2 cytokines.

CONCLUSIONS

IL-4 and IL-13 potently induce FGF2-primed BSMC proliferation via an autocrine loop involving PDGFRalpha and PDGF-CC, and this proliferative synergism is amplified by proinflammatory cytokines.

Building better mouse models of asthma

Allergic asthma is a complex disease that has been modeled extensively in small rodents. Airway eosinophilia and changes in lung function have been documented using a variety of protocols. However, recent efforts have improved these models by trying to replicate the structural remodeling that occurs in the lung as a consequence of chronic allergen-driven inflammation. This review documents the recent developments in protocols and systems designed to examine pathways leading to allergen-induced airway remodeling.

Allergen-induced airway remodelling

Airway remodelling is associated with chronic asthma but it remains unclear whether it results from airway inflammation in response to allergens or immune-mediated events such as viral infections. Although the acute inflammation associated with asthma has been modelled extensively both in vitro and in vivo, the structural changes occurring in the lung have only recently been investigated. These in vitro, in vivo and in silico systems have been designed to examine the pathways leading to allergen-induced airway remodelling and have enabled investigators to draw conclusions about the participation of key cells and molecules in the development of allergen-induced airway remodelling. However, fundamental questions remain regarding the genesis of remodelling as well as the relationship between functional symptoms and pathological changes that occur. In this review the key questions relating allergen exposure to development of remodelling are discussed, as well as the steps that are being undertaken to investigate them.

Airway hyperreactivity in exacerbation of chronic asthma is independent of eosinophilic inflammation

We have developed an animal model to investigate the mechanisms underlying an acute exacerbation of chronic asthma. Sensitized BALB/c mice were exposed to aerosolized ovalbumin, either as chronic low-level challenge (mass concentration approximately 3 mg/m(3)) for 4 wk, a single moderate-level challenge (approximately 30 mg/m(3)), or chronic low-level followed by single moderate-level challenge (the acute exacerbation group). Compared with animals receiving chronic challenge alone, mice in the acute exacerbation group exhibited a more marked inflammatory response, with involvement of intrapulmonary airways and lung parenchyma, and increased numbers of lymphocytes and eosinophils in bronchoalveolar lavage fluid. They also developed airway hyperreactivity (AHR) to methacholine, demonstrable as increased transpulmonary resistance and decreased compliance. This pattern of AHR was absent in chronically challenged animals, but was also present in animals given single moderate-level challenge. However, compared with animals receiving a single moderate-level challenge, inflammation and AHR were induced more rapidly in the acute exacerbation group. Eosinophil-deficient GATA1 Deltadbl mice exhibited undiminished AHR in the acute exacerbation model. We conclude that in mice with pre-existing airway lesions resembling mild chronic asthma, exposure to a moderately high concentration of inhaled antigen induces features of an acute exacerbation. The inflammatory response involves distal airways and is associated with a distinct pattern of AHR, which develops independent of the enhanced eosinophilic inflammation.

Anti-IL-13 monoclonal antibody inhibits airway hyperresponsiveness, inflammation and airway remodeling

Asthma is a chronic inflammatory disease characterized by reversible bronchial constriction, pulmonary inflammation and airway remodeling. Current standard therapies for asthma provide symptomatic control but fail to target the underlying disease pathology. Furthermore, no therapeutic agent is effective in preventing airway remodeling. Interleukin 13 (IL-13) is a pleiotropic cytokine produced mainly by T cells. A substantial amount of evidence suggests that IL-13 plays a critical role in the pathogenesis of asthma. Therefore, a neutralizing anti-IL-13 monoclonal antibody could provide therapeutic benefits to asthmatic patients. To test the concept we have generated a neutralizing rat anti-mouse IL-13 monoclonal antibody, and evaluated its effects in a chronic mouse model of asthma. Chronic asthma-like response was induced in ovalbumin (OVA) sensitized mice by repeated intranasal OVA challenges. After weeks of challenge, mice developed airway hyperresponsiveness (AHR) to methacholine stimulation, severe airway inflammation, hyper mucus production, and subepithelial fibrosis. When given at the time of each intranasal OVA challenge, anti-IL-13 antibody significantly suppressed AHR, eosinophil infiltration, proinflammatory cytokine/chemokine production, serum IgE, and most interestingly, airway remodeling. Taken together, these results strongly suggest that a neutralizing anti-human IL-13 monoclonal antibody could be an effective therapeutic agent for asthma.

Airway remodeling in asthma

PURPOSE OF REVIEW

This overview summarizes some the more recent studies of remodeling in patients with asthma, studies using animal models to study the interaction of cell types and mediators, and studies using in vitro models to assess the effects of mitogenic stimuli, including mechanical strain, on mesenchymal cells and extracellular matrix proteins. The aim is to demonstrate how the term remodeling is becoming increasingly less specific as reductionism is applied to this field of study.

RECENT FINDINGS

Specific areas of recent interest include plasticity of airway smooth muscle and fibroblast phenotype; the role of the extracellular matrix and its relation to the function of the airway smooth muscle and the mechanical properties of the airway wall; mitogenic stimuli arising from damaged epithelium, fibroblasts, smooth muscle cells, mast cells, eosinophils, and mechanical stress; extracellular and intracellular signaling in fibroblasts and smooth muscle cells; and therapeutic targets among the many pathways of remodeling-pathways that may be distinct from those involved in inflammation. The potential functional consequences of some of these findings call into question the role of remodeling. In some respects, it may represent a continuum from inflammation to scarring, but it may also be a protective response to altered airway mechanics caused by ongoing tissue damage or by abnormal airway structure present from early in life.

SUMMARY

The diverse areas of research in this field are increasingly making the term remodeling as useful (or not) as the word asthma, because both can be used to describe simultaneously a large number of processes that may or may not be related to each other.

Expression and regulation of small proline-rich protein 2 in allergic inflammation

Asthma is a complex inflammatory pulmonary disorder that is on the rise despite intense ongoing research. We aimed to elucidate novel pathways involved in the pathogenesis of asthma. Employing asthma models induced by different allergens (ovalbumin and Aspergillus fumigatus), we uncovered the involvement of two members of the small proline-rich protein (SPRR) family, SPRR2a and SPRR2b, known to be involved in epithelial differentiation but not allergic disease. In situ hybridization revealed induction of SPRR2 signal in a subset of bronchial epithelial cells and mononuclear cells associated with inflammation after allergen challenge. Allergen-induced SPRR2 mRNA accumulation in the lung occurred in a time-dependent manner, with peak expression 10-96 h after a second ovalbumin challenge. Transgenic overexpression of interleukin (IL)-13 in the lungs resulted in a marked increase of SPRR2 expression, and allergen-induced SPRR2 expression was significantly decreased in IL-13-deficient mice. Studies in gene-targeted mice revealed that allergen-induced SPRR2 was dependent upon STAT6. Finally, we aimed to determine if the induction of SPRR2 by allergen was tissue specific. Notably, SPRR2 was markedly increased in the small intestine after induction of allergic gastrointestinal inflammation. Thus, SPRR2 is an allergen- and IL-13-induced gene in experimental allergic responses that may be involved in disease pathophysiology.

The rise of the phoenix: the expanding role of the eosinophil in health and disease

We have entered a new phase in the evolution of our understanding of the role of the eosinophil with a greater appreciation of novel potential functions that may be ascribed to this enigmatic cell type. This review not only provides an update to our current understanding of the various immunobiological roles for the eosinophil, but also attracts attention to some novel observations predicting functions beyond its putative effector role. These observations include the intriguing possibility that the eosinophil may possess the capacity to regulate the immune and inflammatory responses in diseases such as asthma.

Zinc metabolism in airway epithelium and airway inflammation: basic mechanisms and clinical targets. A review

In addition to basic housekeeping roles in metalloenzymes and transcription factors, dietary zinc (Zn) is an important immunoregulatory agent, growth cofactor, and cytoprotectant with anti-oxidant, anti-apoptotic, and anti-inflammatory roles. These properties of Zn are of particular importance in maintaining homeostasis of epithelial tissues which are at the front line of defense. This review is about the role of Zn in airway epithelium (AE). The first part focuses on the cellular biology of Zn, and what is known about its distribution and function in AE. The second part of the review considers evidence for altered Zn metabolism in asthma and other chronic diseases of airway inflammation. Important issues arise from a potential therapeutic perspective as to the optimal ways to monitor circulating and epithelial Zn levels in patients and the most effective means of supplementing these levels.

Interleukin-4 receptor signaling pathways in asthma pathogenesis

Asthma is a chronic allergic inflammatory disease, the initiation and progression of which is dependent on the cytokines interleukin (IL)-4 and IL-13 acting through related receptor complexes. Disease pathogenesis is effected by intracellular signaling pathways that couple primarily to specific motifs within the intracellular domain of the IL-4 receptor alpha chain (IL-4Ralpha), a subunit that is common to the IL-4 and IL-13 receptor complexes. Recent studies using genetic approaches have identified distinct functions for the respective IL-4Ralpha-coupled signaling pathways in regulating both early and chronic stages of asthma. Polymorphisms in components of the IL-4 and IL-13 cytokine-receptor axes are associated with allergy and asthma, suggesting that variations among individuals in the activity of this pathway contribute to disease susceptibility and manifestations.

Regulation of found in inflammatory zone 1 expression in bleomycin-induced lung fibrosis: role of IL-4/IL-13 and mediation via STAT-6

Found in inflammatory zone (FIZZ)1, also known as resistin-like molecule alpha, belongs to a novel class of cysteine-rich secreted protein family, named FIZZ/resistin-like molecule, with unique tissue expression patterns. FIZZ1 is induced in alveolar type II epithelial cells (AECs) in bleomycin (BLM)-induced lung fibrosis, and found to induce myofibroblast differentiation in vitro. The objective of this study was to elucidate the regulation of AEC FIZZ1 expression in pulmonary fibrosis. AECs were isolated from rat lungs and the effects of a number of cytokines on FIZZ1 expression were evaluated by RT-PCR. Of all cytokines examined, only IL-4 and IL-13 were effective in stimulating FIZZ1 expression in AECs. Stimulation by IL-4/IL-13 was accompanied by increases in phosphorylated STAT6 and JAK1. FIZZ1 expression was also stimulated by transfection with a STAT6 expression plasmid, but was inhibited by antisense oligonucleotides directed against STAT6. In vivo studies showed that compared with wild-type controls, both IL-4- and IL-13-deficient mice showed reduced BLM-induced lung FIZZ1 expression and fibrosis, which were essentially abolished in IL-4 and IL-13 doubly deficient mice. Furthermore, STAT6-deficient mice showed marked reduction in BLM-induced lung FIZZ1 expression. Thus, IL-4 and IL-13 are potent inducers of AEC FIZZ1 expression via STAT6 and play key roles in BLM-induced lung FIZZ1 expression and fibrosis. This represents a potential mechanism by which IL-4/IL-13 could play a role in the pathogenesis of lung fibrosis.

Chronic intestinal nematode infection induces Stat6-independent interleukin-5 production and causes eosinophilic inflammatory responses in mice

The role of Stat6 (signal transducers and activators of transcription) in the recruitment and activation of eosinophils has been studied in detail in asthma and other allergic diseases. In this study, we demonstrated that eosinophil responses occur in a Stat6-independent manner in mice infected with the intestinal nematode, Nippostrongylus brasiliensis. Stat6-deficient (Stat6(-/-)) mice cannot expel N. brasiliensis and establish chronic infections. Prominent blood and intestinal eosinophilia were induced after day 14 postinfection (p.i.) and maintained at this level in Stat6(-/-) mice, whereas in wild-type mice eosinophil responses reached a peak on day 10 p.i. and declined thereafter. The introduction of a secondary infection of N. brasiliensis into wild-type mice induced rapid and exaggerated eosinophilia, whereas secondary infection in Stat6(-/-) mice resulted in almost the same eosinophil responses as those of the primary infection, suggesting a lack of memory responses. Blood eosinophilia was also induced in Stat6(-/-) mice implanted with N. brasiliensis in the small intestine, suggesting that intestinal exposure to parasitic antigen is sufficient to induce eosinophil responses. Furthermore, this prominent eosinophil response of Stat6(-/-) mice after day 14 was closely associated with an increase of interleukin (IL)-5 production in serum and intestine. Neither IL-4 nor eotaxin were significantly induced in Stat6(-/-) mice after infection with N. brasiliensis. We also found that mRNA for IL-5, GATA-3 and eosinophil peroxidase (EPO) are induced in the intestine of Stat6(-/-) mice on day 14 p.i. Taken together, these results provide evidence for Stat6-independent IL-5 production and subsequent eosinophil responses after chronic infection with N. brasiliensis.

Effects of anticytokine therapy in a mouse model of chronic asthma

The relative contribution of Th2 and Th1 cytokines to the pathogenesis of lesions of chronic asthma remains poorly understood. To date, therapeutic inhibition of Th2 cytokines has proved disappointing. We used a clinically relevant model of chronic allergic asthma in mice to compare the effects of administering neutralizing antibodies to interleukin (IL)-13, IL-5, and interferon-gamma (IFN-gamma) to animals with established disease. As has been observed in clinical studies, anti-IL-5 inhibited both inflammation and remodeling but had no effect on airway responsiveness to methacholine. Anti-IL-13 effectively suppressed eosinophil recruitment and accumulation of chronic inflammatory cells in the airways. This treatment also partially suppressed changes of airway wall remodeling, including goblet cell hyperplasia/metaplasia and subepithelial fibrosis, but had limited ability to inhibit airway hyperreactivity (AHR). In contrast, treatment with anti-IFN-gamma markedly suppressed AHR. This antibody inhibited accumulation of chronic inflammatory cells but did not affect eosinophil recruitment or changes of remodeling. We conclude that inhibition of IL-5 is beneficial and that inhibition of IL-13 has considerable potential as a therapeutic strategy in chronic asthma, that IFN-gamma may play an important role in the pathogenesis of AHR, and that co-operative interaction between Th2 and Th1 cytokines contributes to the pathogenesis of the lesions of chronic asthma.

Transcript signatures in experimental asthma: identification of STAT6-dependent and -independent pathways

The analysis of polygenic diseases such as asthma poses a challenging problem. In an effort to provide unbiased insight into disease pathogenesis, we took an empirical approach involving transcript expression profiling of lung tissue from mice with experimental asthma. Asthmatic responses were found to involve sequential induction of 4.7% of the tested genome; notably, there was ectopic expression of a series of genes not previously implicated in allergic or pulmonary responses. Genes were widely distributed throughout all chromosomes, but preferentially included genes involved in immunity, development, and homeostasis. When asthma was induced by two independent experimental regimens, unique gene transcript profiles were found depending upon the mode of disease induction. However, the majority of genes were common to both models representing an asthma signature genome. Analysis of STAT6-deficient mice revealed that an unexpectedly large segment of the asthma genes were STAT6 independent; this correlated with sustained inflammatory events in these mice. Notably, induction of asthma in STAT6-deficient mice resulted in gene induction not seen in wild-type mice. These results raise concern that therapeutic blockade of STAT6 in the asthmatic setting may reprogram the genetic signature, resulting in alternative lung pathology, which we indeed observed in STAT6-deficient mice. These results provide unprecedented insight into the complex steps involved in the pathogenesis of allergic airway responses; as such, these results have significant therapeutic and clinical implications.

Do mouse models of allergic asthma mimic clinical disease?

Experimental mouse models of allergic asthma established almost 10 years ago offered new opportunities to study disease pathogenesis and to develop new therapeutics. These models focused on the factors governing the allergic immune response, on modeling clinical behavior of allergic asthma, and led to insights into pulmonary pathophysiology. Although mouse models rarely completely reproduce all the features of human disease, after sensitization and respiratory tract challenges with antigen, wild-type mice develop a clinical syndrome that closely resembles allergic asthma, characterized by eosinophilic lung inflammation, airway hyperresponsiveness (AHR), increased IgE, mucus hypersecretion, and eventually, airway remodeling. There are, however, differences between mouse and human physiology that threaten to limit the value of mouse models. Three examples of such differences relate to both clinical manifestations of disease and underlying pathogenesis. First, in contrast to patients who have increased methacholine-induced AHR even when they are symptom-free, mice exhibit only transient methacholine-induced AHR following allergen exposure. Second, chronic allergen exposure in patients leads to chronic allergic asthma, whereas repeated exposures in sensitized mice causes suppression of disease. Third, IgE and mast cells, in humans, mediate early- and late-phase allergic responses, though both are unnecessary for the generation of allergic asthma in mice. Taken together, these observations suggest that mouse models of allergic asthma are not exact replicas of human disease and thus, question the validity of these models. However, observations from mouse models of allergic asthma support many existing paradigms, although some novel discoveries in mice have yet to be verified in patients. This review presents an overview of the clinical aspects of disease in mouse models of allergic asthma emphasizing (1). the factors influencing the pathophysiological responses during the initiation and perpetuation of disease, (2). the utility of mouse models for studying clinical manifestations of disease, and (3). the applicability of mouse models for testing new treatments for allergic asthma.