Eosinophilic Airway Inflammation and Mepolizumab

Inclusion Criteria: * Males or females age 18 to 50 yrs, * History of asthma based upon presence of asthma symptoms such as cough, shortness of breath, wheeze or chest tightness, * positive skin-prick test to a House Dust Mite extract, * Forced expiratory volume at one second \>70% predicted pre-albuterol, \> 80% predicted post albuterol * \>12% increase in Forced expiratory volume at one second following inhaled albuterol (180 µg) and/or * airway responsiveness to methacholine (PC20 \<8mg/ml). * \> 20% immediate drop in FEV1 following inhaled antigen challenge. * Safety laboratory assessments within normal ranges (labs to include complete blood count with differential, blood urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, Prothrombin time, Partial Thromboplastin Time, and platelet count) * Female subjects of child-bearing potential must have a negative urine pregnancy test (urine HCG) within 48 hours of the methacholine challenge at Visit 2 and agree to use a reliable method of birth control for the duration of the study (reliable methods of birth control can include abstinence, barrier methods, oral contraceptives, injection contraceptives or skin absorption contraceptives). * In the opinion of the investigator, capable and willing to grant written informed consent and cooperate with study procedures and requirements. Exclusion Criteria: * Use of inhaled or systemic corticosteroids or leukotriene inhibitors within 1 month of screening. * Treatment with Omalizumab (anti-IgE) within 9 months of screening visit * Concomitant use of any other monoclonal antibody * Respiratory infection within 4 weeks of study * Unstable asthma as indicated by self-report of increased symptoms or increased beta-agonist use over the previous 2 weeks. * Female subjects who are pregnant, nursing or have a pregnancy planned during the course of study * Current smokers (defined as smoked within the last year) or a former smoker with a history of \>5 pack years. * Major health problems such as heart disease, type I and II diabetes or lung diseases other than asthma. Decisions regarding this criteria will be based upon the judgment of the investigator. * Previous malignancy. * Medication other than for asthma, allergies or contraception and that the investigator feels may interfere with the conduct of study (e.g. monoamine oxidase inhibitors and B-adrenergic antagonists in any form) * Known history of allergic reaction to previous antibody administration. * Prior treatment with an anti-interleukin-5 monoclonal antibody, * Use of an investigational drug within 30 days of entering the study, * History of noncompliance with medical regimens or subjects who are considered unreliable.