The purpose of this study is to examine inflammatory processes in the airway of moderate to severe persistent asthmatics who have persistent bronchial hyperreactivity despite chronic administration of inhaled glucocorticoids. Each participant will undergo bronchoscopic procedures and have assessment of bronchial hyperreactivity at the following two time points: 1) during treatment with inhaled fluticasone; and 2) after acute withdrawal of inhaled fluticasone.