Differences in respiratory syncytial virus and influenza infection in a house-dust-mite-induced asthma mouse model: consequences for steroid sensitivity.

A significant number of clinical asthma exacerbations are triggered by viral infection. We aimed to characterize the effect of virus infection in an HDM (house dust mite) mouse model of asthma and assess the effect of oral corticosteroids. HDM alone significantly increased eosinophils, lymphocytes, neutrophils, macrophages and a number of cytokines in BAL (bronchoalveolar lavage), all of which were sensitive to treatment with prednisolone (with the exception of neutrophils). Virus infection also induced cell infiltration and cytokines. RSV (respiratory syncytial virus) infection in HDM-treated animals further increased all cell types in BAL (except eosinophils, which declined), but induced no further increase in HDM-elicited cytokines. However, while HDM-elicited TNF-α (tumour necrosis factor-α), IFN-γ (interferon-γ), IL (interleukin)-2, IL-5 and IL-10 were sensitive to prednisolone treatment, concomitant infection with RSV blocked the sensitivity towards steroid. In contrast, influenza infection in HDM- challenged animals resulted in increased BAL lymphocytes, neutrophils, IFN-γ, IL-1ß, IL-4, IL-5, IL-10 and IL-12, but all were attenuated by prednisolone treatment. HDM also increased eNO (exhaled NO), which was further increased by concomitant virus infection. This increase was only partially attenuated by prednisolone. RSV infection alone increased BAL mucin. However, BAL mucin was increased in HDM animals with virus infection. Chronic HDM challenge in mice elicits a broad inflammatory response that shares many characteristics with clinical asthma. Concomitant influenza or RSV infection elicits differing inflammatory profiles that differ in their sensitivity towards steroids. This model may be suitable for the assessment of novel pharmacological interventions for asthmatic exacerbation.