Allergen-induced inflammation in the nose: a comparison of acute and repeated low-dose allergen exposure.

To investigate allergic rhinitis induced by two experimental provocation models, we compared local inflammation with markers of eosinophil activity in peripheral blood. Patients with strictly seasonal allergic rhinitis were selected and investigated outside the pollen season. An acute challenge with increasing doses of allergen every 15 min until symptoms occurred was performed in nine patients. Nasal lavage and blood samples were taken before and 4 and 24 h after challenge. After a 6-week washout period, 10 patients were submitted to 7 days of repeated low allergen exposures. One small dose (approximately equal to 1/100 of the acute dose) was given each day. Blood and lavage samples were taken prior to and after the period. As control four patients were challenged with diluent only. The acute challenge resulted in sneezing and nasal discharge and blockage and was accompanied by a rise in histamine and eosinophil cationic protein (ECP) in lavage fluid after 4 h and continuing after 24 h, when there also was a rise in the number of eosinophils and ECP in peripheral blood. The repeated low-dose exposures caused very few symptoms but produced increased ECP in the lavage fluid and a trend toward increased histamine concentration. There were no changes in ECP, intracellular EG2 binding, or number of eosinophils in the blood. No changes were seen in the control group. Our findings show that changes in eosinophil mediator release in nasal lavage can be seen after very low, but repeated, allergen exposures despite no, or minimal, clinical symptoms.