Chapter 27 Aerobiology of pollen and fungal allergens

Abstract

Clinically important pollinosis is primarily due to flowering plants with wind-dispersed pollens. Although these anemophilous species form a minority of flowering plants, they produce prodigious amounts of pollen. Entemophilous (insect-pollinated) plants produce relatively few pollen grains. Plants having only a portion of their pollen grains airborne are termed amphiphilous. Their role in pollinosis is not clear. The pollen-producing organs, stamens, consist of an anther attached to a filament. Allergenic pollens develop in and are released from pollen sacs contained in the anthers. Pollen sacs are lined with a nutritive cell layer, the tapetum. During its formation, each immature pollen grain secretes about itself a clear layer, the intine. Around this the tapetum deposits a multilayer exine composed of a polymer, sporopollenin. Release of pollen from the anther is known as anthesis. Drying creates gaps in the anther wall through which pollen escapes. Airborne pollen levels tend to increase during warm, dry, clear conditions and fall during cool, moist periods. Although pollen grains can travel several hundred miles, concentrations of windbome pollens generally decrease sharply within a few hundred meters of their source. Intact pollen grains are presumed to be the primary carriers of allergen, but ragweed allergens have been associated with particles <5 km, and Amb a I (antigen E) activity has been found in submicronic particles. Pollen allergens can be extracted from the somatic portion of ragweed plants and may become airborne in vegetable debris. Furthermore, allergens might be eluted from pollen grains deposited on moist surfaces, with dispersion of the resultant extract in droplets. Air sampling relies on recovery of pollen grains for microscopic evaluation. The gravity (Durham) sampler uses greased microslides for pollen collection. This obsolete device is limited by uncertainty in the volume of air sampled and a tendency to