Nitrogen dioxide increases eosinophil activation in the early-phase response to nasal allergen provocation

Recent studies have suggested that exposure to air pollutants may sensitise susceptible individuals to allergen. We have investigated the effect of exposure for 6 h to 400 ppb NO2 on nasal airways resistance (NAR) and changes in inflammatory mediators (IMs) in nasal lavage in subjects with a history of seasonal allergic rhinitis. In this single blind crossover study, 8 patients were randomised to exposure to either air or 400 ppb NO2 in air and evaluated for changes in NAR and IM, before and after exposure. Another 8 patients were further challenged with allergen after similar exposure regimes and then evaluated for changes in NAR and IMs. Exposure to air or NO2 did not alter either NAR or the levels of eosinophil cationic protein (ECP), mast cell tryptase (MCT), myeloperoxidase (MPO) or interleukin (IL)-8 in nasal lavage. MCT was significantly increased after allergen challenge following exposure to both air and NO2. In contrast, ECP was significantly increased by allergen challenge only after exposure to NO2. Neither MPO nor IL-8 were altered after allergen challenge. These results suggest that NO2 may increase eosinophil activation in the early-phase response to nasal allergen provocation in allergic rhinitis.