Viral infections, most commonly by human rhinovirus (HRV), are the most frequent cause of asthma attacks. In theory, chemokine production by HRV-infected epithelial cells induces the recruitment of inflammatory cells to the airways, which in turn elaborate cytokines and mediators capable of increasing airway responses. This paradigm, however, fails to explain why asthmatics experience manifestations of lower airways disease following colds while normals do not. This proposal tests the novel hypothesis that pre-existing airways disease, either allergic or non-allergic, modifies the polarization state of airway macrophages, leading to an altered response to rhinovirus infection. Consistent with this, our pilot data indicate that allergen sensitization and challenge with ovalbumin (OVA) alters the response to HRV infection from a neutrophilic response to a Th2-dominant, combined neutrophilic and eosinophilic response that is mediated in part by macrophage production of eotaxin-1/CCL11 and MCP-1/CCL2. HRV-infected macrophages produce eotaxin-1 and MCP-1 in vivo and ex vivo, and macrophage depletion attenuates HRV-enhanced airway eosinophilic inflammation and hyperresponsiveness. Finally, macrophages from OVA-treated mice show increased expression of the alternative activation markers Arg-1, Ym-1 and MGL-2. The overall airway response to HRV infection depends not only on pro-inflammatory pathways but also the antiviral response. It has been hypothesized that asthmatics are prone to HRV-induced exacerbations due to deficient interferon (IFN) production. However, reduced IFN production may be accompanied by attenuated inflammatory responses, which would tend to protect against asthma exacerbation. Indeed, our pilot data show that HRV1B-infected Toll-like receptor-3 -/- mice with lower IFN responses show reduced airways inflammation and responsiveness. In this application, we will examine the signaling intermediates required for HRV-induced IFN expression in vivo, and test whether impaired IFN production leads to increased HRV-induced airway inflammation. We propose the following Specific Aims:
Specific Aim 1. Determine the effects of preexisting airways disease on HRV responses.
Specific Aim 2. Determine the role of the macrophage in HRV-induced exacerbations of pre- existing airways disease in mice.
Specific Aim 3. Determine the effect of impaired IFN production on viral load and airway inflammation in vivo. Completion of this work, which includes both animal and human studies, will provide a new paradigm for poorly-understood viral-induced asthma attacks, identify molecular targets for therapeutic intervention, introduce a device for detection of respiratory viruses, and directly test the hypothesis that impaired IFN production leads to more severe asthma exacerbations.
Viral infections, most commonly caused by rhinovirus, are the most frequent cause of asthma attacks. This application seeks to understand the cellular and biochemical mechanisms underlying rhinovirus-induced asthma exacerbations. It proposes a new paradigm in which rhinovirus infects alternatively polarized macrophages, resulting in exaggerated pro-inflammatory responses. Insight provided from the proposed studies may lead to new treatments for asthma and other chronic airways diseases.
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