Airborne ragweed allergens: association with various particle sizes and short ragweed plant parts.

These investigations were undertaken to size airborne particles by use of a high-volume sampler and to measure the short ragweed allergen activity of airborne particles of different sizes. We found both in vitro and in vivo short ragweed allergen activity in particles of all size ranges including greater than 6, 3 to 6, 1.8 to 3, 1 to 1.8, and 0.3 to 1.0 micron in diameter. Furthermore, we investigated various parts of the short ragweed plant as possible sources of allergen. Plant parts collected before, during, and after the pollination season demonstrated significant in vitro and in vivo allergen activities. We demonstrated allergen activity in various plant parts, especially the inflorescence, as late as November 30. Appreciable ragweed allergenic activity was also associated with particles less than 1 micron in diameter. Collectively, these observations suggest persistent ragweed plant debris in different sized particles as a source of allergen in the air before and after the ragweed pollination season. This may contribute to out-of-season symptoms observed in highly ragweed-sensitive individuals.