The investigators will enroll 20 AA subjects (10 in Track 1 & 10 in Track 2) and 10 HC subjects (Track 1). There will be no randomization. The choice of allergen will be determined by allergy skin testing. When a subject is allergic to both cat and dust mite, one will be selected with a goal of having a representative sample of cat and dust mite challenges in each cohort. The 10 allergic asthmatic (AA) subjects and HC subjects in Track 1 will undergo preliminary screening tests and provide 200 ml of blood for DC and T cell studies on one occasion. Track 1 subjects will not undergo bronchoscopy, bronchoalveolar lavage, or segmental allergen challenge. The 10 allergic asthmatic (AA) subjects in Track 2 will undergo SAC with either standardized cat or mite allergen. These subjects will also donate 200 ml of blood on two occasions separated by a minimum of 4 weeks and not more than 12 weeks.