Immunological effects induced by biological natural aerosols (pollen and spores)

Pollen and spores are natural biological aerosols, mostly wind transported. Most of them are deposited within the upper respiratory tract. Only such particles with a diameter from 0,5-5 mu are believed to reach the alveoli. Most pollen do not deposit into the lower airways because their diameter is larger than 10 mu. Therefore, the mechanism of pollen induced asthma seems to be obscure. This phenomenon might be explained by some hypotheses. It could be possible that particles produced as natural biological aerosols with a size distribution smaller than pollens cause the asthma. Another version explaining the pollen induced asthma may arise from the fact, that pollen grains pass the digestive tract and involve the lung via bloodstream. In view of the fact that reflex action releases a bronchoconstriction has led to the conclusion that pollen grains contracted the mucosa of the upper airways induce the obstruction of the bronchi.