Nasal allergen challenge procedure
A first nasal allergen challenge was performed to titrate the allergen dose eliciting a positive response. Briefly, nasal allergen challenge was performed as previously described by administering increasing doses of a grass pollen allergen extract (Stallergenes Greer) every 10 minutes by means of a nasal pump spray delivery device (14). A Lebel score > 5 was considered as a positive response (15). After a washout period of 4 weeks, patients underwent two nasal allergen challenges with either a single threshold dose of the grass pollen allergen extract (Stallergenes Greer) or a diluent (saline solution) in a randomized order at least 4 weeks apart. All the challenges were performed outside the grass pollen season, and none of the subjects was exposed to any other relevant respiratory allergens.