Aeroallergens of plant origin: Molecular basis and aerobiological significance

Abstract

This review presents an update on the sources and molecular basis of aeroallergens of plants, derived from pollen, seeds, leaf and stem detritus and their protein molecules. These aeroallergens are a natural component of the atmosphere, either because of their natural function or human activity. Pollen is a source of allergens within the 10-200 #m size range, and while most allergenic pollen types account for only 20-30~ of total annual pollen catch, during their flowering season, they are usually the dominant type. Tree pollen commences the season in winter, with birch pollen counts in Scandinavia being the highest daily pollen counts yet reported and a major allergen, a 14-kDa protein, which is similar to pathogenesis-related proteins. Grass pollen follows in spring, and is unique as its two immunodominant allergens, a 35-kDa glycoprotein and 28-32-kDa protein, are in different cellular sites: the cytosol and surface of pollen grains; and in intracellular starch granules. The allergens at the pollen surface are not inhalable and can interact only with the eyes, nasal and oral cavities. Starch granules are released to the atmospheric aerosol when grains rupture in rainwater. These are a major source of allergen-containing micronic particles, which are important because they are inhalable. At the same time, allergen molecules are present in the aerosol, and these can bind to soot particles, and so be respired deep into the airways. The major Japanese cedar pollen allergen has been detected both within the pollen and in orbicules; particles less than 1 tLm that line the anther cavity and can be released into the air when dehiscence occurs. Ragweed is the major cause of late summer hayfever in eastern North America, where its pollen accounts for up to 41% of the annual pollen catch. It is a major source of aeroallergens in both respirable and non-respirable size ranges. As a result of human activity, dusts derived from seeds and cereal grains during transport, storage and milling provide a source of micronic particles, containing potent allergens that can trigger allergic disease.

Persistent pollen exposure during infancy is associated with increased risk of subsequent childhood asthma and hayfever

“…Thus, all subjects living in Melbourne during the study period should receive similar exposures to grass pollen [17]. Pollen was measured at only one site.…”

“…Secondly, we used daily measurements of 24-hour average pollen concentrations for grass and others (which include trees, weeds, and herbs) pollens in grains per m 3 available from a Burkard volumetric trap located at the University of Melbourne [16] for the 495 MACS children born between October 1991 and January 1994. We were unable to differentiate between different types of grass pollen using a Burkard trap and visual identification [17].…”

“…We first defined as birth 'inside' or 'outside' the pollen season using a pollen season definition (between mid September to end of January) as defined by the Melbourne Pollen Collection laboratory [15]. We were unable to differentiate between different types of grass pollen using a Burkard trap and visual identification [17]. The grass pollen season is usually 3 months.…”

Localisation of a carbohydrate epitope recognised by human IgE in pollen of Cupressaceae

“…In general, if pollen were to remain whole, as occurs in dry conditions, it would be too large to be inhaled and the allergens would only be able to induce an allergic reaction in the upper respiratory tract (Ong et al 1995). However, conditions of high relative air humidity, such as those normally found on the mucosal surface of the upper respiratory tract, cause pollen to rupture, with the consequent release of micronic fragments, which can be inhaled and thus cause allergic reactions (Ong et al 1995).…”

“…However, conditions of high relative air humidity, such as those normally found on the mucosal surface of the upper respiratory tract, cause pollen to rupture, with the consequent release of micronic fragments, which can be inhaled and thus cause allergic reactions (Ong et al 1995). In Cupressus sempervirens, over 50% of pollen grains have been shown to rupture in water (Grilli Caiola et al 2000).…”