Cristan Herbert

Role of interleukin‐13 in eosinophil accumulation and airway remodelling in a mouse model of chronic asthma

Background Interleukin‐13 is believed to be important in asthmatic inflammation and airway hyper‐reactivity.

Steroid-Resistant Neutrophilic Inflammation in a Mouse Model of an Acute Exacerbation of Asthma

Neutrophilic inflammation in acute exacerbations of asthma tends to be resistant to treatment with glucocorticoids. This may be related to decreased activity and expression of histone deacetylase-2 (HDAC2), which down-regulates expression of proinflammatory genes via recruitment to the glucocorticoid receptor complex. We assessed airway inflammation and response to steroid treatment in a novel mouse model of an acute exacerbation of chronic asthma. Systemically sensitized mice received low-level challenge with aerosolized ovalbumin for 4 weeks, followed by a single moderate-level challenge to induce enhanced inflammation in distal airways. We assessed the effects of pre-treatment with dexamethasone on the accumulation of inflammatory cells in the airways, airway responsiveness to methacholine, expression and enzymatic activity of nuclear proteins including histone acetyl transferase (HAT) and HDAC2, and levels of transcripts for neutrophil chemoattractant and survival cytokines. Dexamethasone suppressed inflammation associated with eosinophil and T-lymphocyte recruitment, but did not prevent neutrophil accumulation or development of airway hyperresponsiveness. Increased activity of HAT was suppressed by steroid treatment, but the marked diminution of HDAC2 activity and increased activity of nuclear factor-kappaB were not reversed. Correspondingly, elevated expression of mRNA for TNF-alpha, granulocyte-macrophage colony-stimulating factor, IL-8, and p21(waf) were also not suppressed by dexamethasone. Levels of lipid peroxidation and protein nitration products were elevated in the acute exacerbation model. We conclude that impaired nuclear recruitment of HDAC2 could be an important mechanism of steroid resistance of the neutrophilic inflammation in exacerbations of asthma. Oxidative stress may contribute to decreased HDAC2 activity.

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

BackgroundThe 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.MethodsFemale 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.ResultsCompared 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.ConclusionsIn 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.

Expression of growth factors by airway epithelial cells in a model of chronic asthma: regulation and relationship to subepithelial fibrosis.

Background Growth factors produced by airway epithelial cells may be important in the pathogenesis of subepithelial fibrosis, a distinctive lesion of chronic human asthma.

Interferon-gamma as a possible target in chronic asthma.

The role of interferon-gamma (IFN-gamma) in asthma is controversial. However, this cytokine has been proposed to play a role both in acute severe asthma and chronic stable asthma. We have shown that in a chronic low-level challenge model of allergic asthma in mice, which replicates characteristic features of airway inflammation and remodelling, the mechanisms of airway hyperreactivity (AHR) are markedly different to those in short-term high-level challenge models. Notably, AHR is independent of various Th2 cytokines and their signalling pathways. However, administration of a neutralising antibody to IFN-gamma suppresses AHR. More recently, we have found that following chronic allergen challenge, but not acute challenge, IFN-gamma-producing CD4+ T cells are demonstrable in peribronchial lymph nodes, both in wild-type mice and in STAT6-/-mice. Treatment with anti-IFN-gamma decreases the number of IFN-gamma-producing CD4+ T cells in both wild-type and gene-targeted mice, providing a possible explanation for the ability of anti-IFN-gamma to inhibit AHR in the setting of chronic challenge. These data further strengthen the notion that the pathogenesis of the lesions of asthma, and especially of AHR, involves a co-operative interaction between Th2 and Th1 cytokines. This may be particularly relevant to acute exacerbations of asthma, in which setting there may be justification for therapeutic inhibition of IFN-gamma.

Early-life viral infection and allergen exposure interact to induce an asthmatic phenotype in mice

BackgroundEarly-life respiratory viral infections, notably with respiratory syncytial virus (RSV), increase the risk of subsequent development of childhood asthma. The purpose of this study was to assess whether early-life infection with a species-specific model of RSV and subsequent allergen exposure predisposed to the development of features of asthma.MethodsWe employed a unique combination of animal models in which BALB/c mice were neonatally infected with pneumonia virus of mice (PVM, which replicates severe RSV disease in human infants) and following recovery, were intranasally sensitised with ovalbumin. Animals received low-level challenge with aerosolised antigen for 4 weeks to elicit changes of chronic asthma, followed by a single moderate-level challenge to induce an exacerbation of inflammation. We then assessed airway inflammation, epithelial changes characteristic of remodelling, airway hyperresponsiveness (AHR) and host immunological responses.ResultsAllergic airway inflammation, including recruitment of eosinophils, was prominent only in animals that had recovered from neonatal infection with PVM and then been sensitised and chronically challenged with antigen. Furthermore, only these mice exhibited an augmented Th2-biased immune response, including elevated serum levels of anti-ovalbumin IgE and IgG1 as well as increased relative expression of Th2-associated cytokines IL-4, IL-5 and IL-13. By comparison, development of AHR and mucous cell change were associated with recovery from PVM infection, regardless of subsequent allergen challenge. Increased expression of IL-25, which could contribute to induction of a Th2 response, was demonstrable in the lung following PVM infection. Signalling via the IL-4 receptor α chain was crucial to the development of allergic inflammation, mucous cell change and AHR, because all of these were absent in receptor-deficient mice. In contrast, changes of remodelling were evident in mice that received chronic allergen challenge, regardless of neonatal PVM infection, and were not dependent on signalling via the IL-4 receptor.ConclusionIn this mouse model, interaction between early-life viral infection and allergen sensitisation/challenge is essential for development of the characteristic features of childhood asthma, including allergic inflammation and a Th2-biased immune response.

CD4(+) T-lymphocytes regulate airway remodeling and hyper-reactivity in a mouse model of chronic asthma.

Asthma is an acute-on-chronic inflammatory disease of the airways, characterized by airflow obstruction and hyper-reactivity of the airways to a variety of stimuli. Chronic asthma is associated with remodeling of the airway wall, which may contribute to hyper-reactivity and fixed airflow obstruction. We used an improved mouse model of chronic asthma to investigate the role of CD4+ T-lymphocytes in airway remodeling and hyper-reactivity. Animals functionally depleted of CD4+ T-lymphocytes by repeated administration of a monoclonal antibody exhibited markedly decreased airway responsiveness. In addition, these mice had greatly diminished subepithelial fibrosis, epithelial thickening, and mucous cell hyperplasia/metaplasia. Chronic inflammation in the airway wall was moderately reduced, with a marked decrease in the accumulation of immunoglobulin-synthesizing plasma cells. However, intraepithelial accumulation of eosinophils was not significantly inhibited and airway epithelial expression of eotaxin was undiminished. This work provides the first experimental evidence that CD4+ T-lymphocytes play a crucial role in the pathogenesis of the lesions of chronic asthma and lends support to the notion that functional inhibition of these cells may be an important therapeutic target.

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).

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

Background Type 2 T helper lymphocytes (Th2 cells) and their cytokine products are important in the pathogenesis of asthma.

Reversibility of airway inflammation and remodelling following cessation of antigenic challenge in a model of chronic asthma

Background Asthma is associated with recruitment of eosinophils, accumulation of chronic inflammatory cells in the airway walls, subepithelial fibrosis and other structural changes of airway wall remodelling. The role of ongoing exposure to allergens in their pathogenesis remains unclear.