The purpose of this study is to identify the genes in important airway cells that are specifically expressed following inhalation of house dust mite allergen among study subjects with either allergic asthma or healthy normal phenotypes. This approach is designed to identify novel genes associated with both asthma pathogenesis (differentially expressed in the exposure-response study) and asthma susceptibility (genetically associated with asthma in a linkage/association study) for drug targets.