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,
• FEV1 >70% predicted pre-albuterol, > 80% predicted post albuterol
• >12% increase in FEV1 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 CBC with differential, BUN, creatinine, AST, ALT, PT, PTT 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-hIL-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.