Release rate of daughter allergenic species from Cryptomeria japonica pollen grains trapped in air polluted wet deposition

High airborne concentrations of fine allergenic particles of Cryptomeria japonica pollen were determined during the pollen scattering spring seasons in Japan. In particular, this phenomenon was observed in field investigations during sunny days after rainfall. It is considered that the release of daughter allergenic species derived from pollen grains may be induced during urban rainfall events. Hence, it is necessary to do research in order to find the evidence of this phenomenon. There are two major daughter allergenic species produced by pollen in Japan, which are called Cry j 1 and Cry j 2 of Cryptomeria japonica pollen. Allergenic Cry j 1 mainly exists in the pollen wall surface (Ubisch body), while allergenic Cry j 2 is present as a starch granule in the pollen grain, it can be thought that the release mechanism of allergenic Cry j 1 and Cry j 2 species in rainfall should be different. Since the release mechanisms are still not clear, therefore, the aim of this study is to clarify the important mechanisms of elution rate of two kinds of daughter allergenic species when pollen grains are washed out by rainfall and exposed to polluted air. From the analytical results of rainwater samples and model laboratory experiments of simulated rainfall, it was indicated that a great number of pollen grains were trapped in initial rainfall. At the same time, many bursts of pollen grains were also observed in the rainwater. Thus, it is possible that the two daughter allergenic species will be released from the fractions of cell wall, burst pollen and the surfaces of pollen grains. Moreover, ionic concentrations in initial rainfall were higher than following wet deposition, because air pollutants were also abundantly trapped in the initial rainfall. Especially, it was found that the elution rate of allergenic Cry j 1 was increased when in contact with rainwater containing high ionic concentrations. In this case, elution of allergenic Cry j 1 was rapidly increased when in contact with a weak basic solution with high Ca2+ concentrations. Similarly, elution of allergenic Cry j 2 was also prompted from burst pollen washed out by rainfall and exposed to polluted air. Therefore, it is one important factor for the fast release of daughter allergenic species from pollen grains washed out by rainfall and exposed to polluted air including abundantly crustal particles such as road dust and Asian dust.