Viral respiratory infections are a major cause of asthma exacerbations in children. Of the respiratory viruses associated with exacerbations of asthma, rhinovirus (RV) is the most frequent and important cause of these episodes. We hypothesize that a major mechanism for asthma exacerbations with colds is an initiation or enhancement of existing airway inflammation through the coordinated interaction of RV-infected pulmonary epithelium, with endothelium and infiltrating granulocytes. To cause these effects, we propose that RV infection of airway epithelial cells first induces secretion of inflammatory mediators and cytokines which increase vascular permeability allowing transudation of serum proteins including low density lipoprotein (LDL). LDL can then act directly on epithelial cells to cause additional cytokine/chemokine generation. These epithelial mediators also activate lung endothelial cells to enhance granulocyte adhesion and transmigration. The infiltrating neutrophils and eosinophils are then functionally primed by their interactions with the vascular endothelial adhesion proteins and/or activated by the epithelial mediators. The migrating granulocytes then interact with RV-infected epithelium to cause epithelial damage and increased airway inflammation. The net results of these RV-initiated events are enhanced airway responsiveness, airflow obstruction and asthma exacerbations. To test this hypothesis, primary epithelial cells will be infected (and in select studies, transfected with RV RNA or selected RV components) with RV16 (or control viruses) or treated with LDL and other transudation proteins. The resulting culture media will be assessed for cytokine content (ELISA and RT-PCR) and for its ability to activate pulmonary microvascular endothelial cells (HPMEC) as determined by adhesion molecule expression, and granulocyte adhesion and transmigration. The transmigrated neutrophils and eosinophils will then be assessed for functional phenotype including respiratory burst, cytokine generation, apoptosis, surface receptor expression and adhesion to RV-infected epithelial cells. The effect of RV infection will be determined by granulocyte interaction on RV-infected epithelial cells (or RV-transfected epithelial) in relationship to (1) activation of adherent granulocytes and (2) injury to the RV-infected epithelium by adherent, and presumably activated, granulocytes. Finally, the functional phenotype of airway eosinophils from RV16 infected subjects will be similarly defined to determine the effect of an in vivo virus infection on airway granulocyte interaction with RV-infected epithelial cells; these results will be compared with our in vitro model. The proposed studies will provide new evidence as the mechanisms by which RV-infected epithelial cells cause granulocytic bronchial inflammation and asthma exacerbations.
