Ovalbumin challenge models of asthma offer many opportunities for increasing our understanding of the pathogenetic mechanisms underlying this disease, as well as for identifying novel therapeutic targets. There is no single "classical" model, because numerous alternatives exist with respect to the choice of mouse strain, method of sensitisation, route and duration of challenge, and approach to assessing the host response. Moreover, the limitations of these models need to be recognised when attempting to interpret experimental findings. Nevertheless, careful use of well-defined models allows investigators to answer specific questions that are otherwise difficult to address.

These results imply a critical role for IL-13 in accumulation of intraepithelial eosinophils in chronic asthma, as well as in epithelial and subepithelial remodelling. In addition, they suggest that in chronic asthma, IL-13 may be capable of signalling via a pathway that does not involve IL-4Ralpha.

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.

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.

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-kB were not reversed. Correspondingly, elevated expression of mRNA for TNF-a, granulocytemacrophage 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.

Phosphodiesterase (PDE) inhibitors have potential as alternatives or adjuncts to glucocorticoid therapy in asthma. We compared roflumilast (a selective PDE4 inhibitor) with pentoxifylline (a nonselective inhibitor) and dexamethasone in ameliorating the lesions of chronic asthma in a mouse model. BALB/c mice sensitized to ovalbumin were chronically challenged with aerosolized antigen for 6 weeks. During weeks 5 and 6, groups of animals were treated with roflumilast or dexamethasone by daily gavage or with pentoxifylline by daily intraperitoneal injection. Airway hyper-reactivity (AHR) was evaluated by wholebody plethysmography and airway lesions by histomorphometry and immunohistochemistry. Compared with vehicle alone, treatment with roflumilast or dexamethasone significantly reduced accumulation of eosinophils and chronic inflammatory cells, subepithelial collagenization, and thickening of the airway epithelium. Dexamethasone also reduced goblet cell hyperplasia/metaplasia, subepithelial accumulation of transforming growth factor-␤1, and epithelial cytoplasmic immunoreactivity for nuclear factor-B. Treatment with pentoxifylline inhibited only eosinophil recruitment and epithelial thickening. Roflumilast and dexamethasone slightly decreased AHR, whereas this was significantly reduced by pentoxifylline. Thus, in this model of chronic asthma, both roflumilast and dexamethasone were potent inhibitors of airway inflammation and remodeling. Roflumilast did not diminish accumulation of transforming growth factor-␤1, suggesting that it might affect remodeling by mechanisms distinct from glucocorticoids.

S100A8 is considered proinflammatory by activating TLR4 and/or the receptor for advanced glycation end products. The aim was to investigate inflammatory effects of S100A8 in murine lung. S100A8 was administered to BALB/c mice by nasal inhalation and genes induced over a time-course assessed. LPS was introduced intranasally either alone or 2 h after pretreatment of mice with intranasal application of S100A8 or dexamethasone. A Cys42-Ala42 mutant S100A8 mutant was used to assess whether S100A8’s effects were via pathways that were dependent on reactive oxygen species. S100A8 induced IL-10 mRNA, and expression was apparent only in airway epithelial cells. Importantly, it suppressed acute lung injury provoked by LPS inhalation by suppressing mast-cell activation and induction of mediators orchestrating leukocyte recruitment, possibly by reducing NF-κB activation via an IκBα/Akt pathway and by downmodulating pathways generating oxidative stress. The Cys42-Ala42 S100A8 mutant did not induce IL-10 and was less immunosuppressive, indicating modulation by scavenging oxidants. S100A8 inhibition of LPS-mediated injury was as potent, and outcomes were remarkably similar to immunosuppression by dexamethasone. We challenge the notion that S100A8 is an agonist for TLR4 or the receptor for advanced glycation end products. S100A8 induced IL-10 in vivo and initiates a feedback loop that attenuates acute lung injury.

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.