Concentrations of the major birch tree allergen Bet v 1 in pollen and respirable fine particles in the atmosphere

Background: Birch tree pollen allergens are an important cause of early spring hay fever and allergic asthma. Pollen counts provide a guide for individuals with birch pollen allergy. However, birch pollen, because of its size, has a low probability of entering the lower airways to trigger asthma, Yet birch pollen allergens are known to be associated with respirable particles present in the atmosphere. Objective: We sought to determine the concentration of major allergen Bet v 1 in birch pollen and respirable particles in the atmosphere during the birch pollen season. Methods: We used a two-site monoclonal antibody-based assay (ELISA) to quantitate Bet v 1 in pollen extracts and high-volume air sampler filters collecting particles larger and smaller than 7.2 mu m. Results: Bet v 1 (0.006 ng) is detectable per birch pollen grain, of which 0.004 ng is present in aqueous extracts (13.9% of soluble proteins), Atmospheric Bet v 1 concentrations are correlated with birch pollen counts, Heavy rainfall tended to wash out pollen and particles, indicated by a mean daily Bet v 1 concentration of 0.12 ng/m(3) (20 pollen equivalents), but light rainfall produced a dramatic increase in allergen-loaded respirable particles with Bet vl concentrations of 1.2 ng/m(3) (200 pollen equivalents). Conclusion: These results highlight the different environmental risk factors for hay fever and allergic asthma in patients sensitized to Bet v 1. Light rainfall causes an increase in respirable particles; hence, this is an important risk factor for asthma.