Diesel Exhaust Particles and Leukotriene Production

Inclusion Criteria: 1. Age 18 to 65 years old. 2. Positive prick (epicutaneous) skin test to standardized cat with a wheal equal to or greater than 3 mm and with a surrounding flare. 3. Ability to give informed consent. Exclusion Criteria: 1. Pregnancy or breast-feeding. (Pregnancy and the period during breast feeding can affect nasal congestion and be a confounder in this regard.) 2. Systemic corticosteroid use within the previous three months or anytime during the challenge protocol. 3. Topical nasal corticosteroid use within the past month or anytime during the challenge protocol. 4. Systemic antihistamines or decongestant use within past two weeks or anytime during the trial. 5. Chronic sinusitis or chronic non-allergic rhinitis. 6. Use of reserpine. 7. Cigarette smoking within the past year or during the challenge protocol 8. Use of topical nasal antihistamines, chromoglycolates (chromolyn, Cromlon®), decongestants or non-steroidal anti-inflammatory agents (NSIADS) within the preceding week or anytime during the challenge protocol. 9. Present or treatment within the past 10 years with allergy immunotherapy (injections). 10. Present or past treatment with anti-IgE therapy. 11. Any unusual exposure to air pollutants (e.g., working as a diesel mechanic) that, in the opinion of the investigators, might compromise the individual's ability to participate in the study. 12. Living arrangement where the subject has a cat dwelling within the subject's habitation. 13. Any serious heart, lung, neurological or kidney disease that in the opinion of the investigators would impair the individual's ability to participate in the study. 14. Use of asthma-required medications.