Long-term intense exposure to grass pollen can mask positive effects of allergenic immunotherapy on non-specific bronchial hyperresponsiveness

INTRODUCTION: There are many potential factors that can modulate bronchial reactivity, including exposure to allergens, viral infections, and medications. The aim of this study was to analyze the effect of grass pollination intensity on the bronchial reactivity in seasonal allergic rhinitis (SAR) patients subjected to subcutaneous allergenic immunotherapy (SCIT). MATERIAL AND METHODS: This study, performed between 2005 and 2008, included 41 patients with confirmed sensitivity to grass pollens and predominating symptoms of SAR, randomly assigned to desensitization by pre-seasonal or maintenance SCIT. Bronchial provocation challenge with histamine was performed before the onset of immunotherapy, and repeated three times after each pollen season covered by this study. Bronchial reactivity was analyzed with regard to grass pollination intensity in 2005–2008 (air concentration of grass pollen grains, seasonal number of days when air concentration of grass pollen reached at least 20 or 50 grains per 1 m(3)). RESULTS: After 3 years of SCIT, a significant decrease in bronchial responsiveness was observed in the analyzed group as confirmed by an increase in PC(20) FEV(1) histamine values (p = 0.001). An inverse tendency was observed after 2 years of SCIT, however. This second year of SCIT corresponded to the 2007 season, when a significantly higher number of days with at least 50 grains of pollen per 1 m(3) of air was recorded. CONCLUSIONS: Fluctuations in pollination intensity observed during consecutive years of immunotherapy can influence bronchial reactivity in patients subjected to SCIT (ISRCTN Register: ISRCTN 86562422).