Concentrations of major grass group 5 allergens in pollen grains and atmospheric particles: implications for hay fever and allergic asthma sufferers sensitized to grass pollen allergens

Background Grass pollen allergens are the most important cause of hay fever and allergic asthma during summer in cool temperate climates. Pollen count s provide a guide to hay fever sufferers. However, grass pollen, because of its size, has a low probability of entering the lower airways to trigger a sthma. Yet, grass pollen allergens are known to be associated with atmosphe ric respirable particles. Objective, We aimed (1) to determine the concentration of group 5 major all ergens in (a) pollen grains of clinically important grass species and (b) a tmospheric particles (respirable and nonrespirable) and (2) to compare the atmospheric allergen load with clinical data to assess different risk facto rs for asthma and hay fever. Methods We have performed a continuous 24 h sampling of atmospheric particl es greater and lower than 7.2 mu m in diameter during the grass pollen seas on of 1996 and 1997 (17 October 1996- 16 January 1997) by means of a high v olume cascade impactor at a height of about 15 m above ground in Melbourne. Using Western analysis, we assessed the reactivity of major timothy grass allergen Phl p 5 specific monoclonal antibody (MoAb) against selected polle n extracts. A MoAb-based ELISA was then employed to quantify Phl p 5 and cr oss-reactive allergens in pollen extracts and atmospheric particles larger and smaller than 7.2 mu m. Results Phl p 5-specific MoAb detected group 5 allergens in tested grass po llen extracts, indicating that the ELISA employed here determines total gro up 5 allergen concentrations. On average, 0.05 ng of group 5 allergens were detectable per grass pollen grain. Atmospheric group 5 allergen concentrat ions in particles < 7.2 mu m were significantly correlated with grass polle n counts (r(s) = 0.842, P<0.001). On dry days, 37% of the total group 5 all ergen load, whereas upon rainfall, 57% of the total load was detected in re spirable particles. After rainfall, the number of starch granule equivalent s increased up to 10-fold; starch granule equivalent is defined as a hypoth etical potential number of airborne starch granules based on known pollen c ount data. This indicates that rainfall tended to wash out large particles and contributed to an increase in respirable particles containing group 5 a llergens by bursting of pollen grains. Four day running means of group 5 al lergens in respirable particles and of asthma attendances (delayed by 2 day s) were shown to be significantly correlated (P < 0.001). Conclusion Here we present, for the first time, an estimation of the total group 5 allergen content in respirable and nonrespirable particles in the a tmosphere of Melbourne. These results highlight the different environmental risk factors for hay fever and allergic asthma in patients, as on days of rainfall following high grass pollen count, the risk for asthma sufferers i s far greater than on days of high pollen count with no associated rainfall . Moreover, rainfall may also contribute to the release of allergens from f ungal spores and, along with the release of free allergen molecules from po llen grains, may be able to interact with other particles such as pollutant s (i.e. diesel exhaust carbon particles) to trigger allergic asthma.