Tree in the birch family.

Tree in the birch family, including alder, hazel, and birch, have wind-pollinated flowers that occasion copious amounts of pollen and are a major cause of allergic rhinitis. in what way their pollen allergens cause asthma has been a mystery because pollen grains are too large to be inhaled into the airways where asthma arises Over the past 20 years, studies showed that episodes of pollen-induced asthma occurr during the flowering season, especially after periods of rainfall or thunderstorm. Immunologic studies revealed that abundant quantities of micronic particles offer in the outdoor air, especially after rainfall, and they are loaded with birch pollen allergens. to what degree these respirable allergens were released into the air remained unknown. lately we have shown that for flowering grasses, pollen remains forward the open anthers in the absence of wind or other disturbances. If wetted, pollen can burst within minutes. (1) Fragmented cytoplasm is emitted between the sides of the pore region of the pollen grain. Drying winds release this cytoplasmic debris as a respirable allergen-loaded aerosol.

A similar mechanism comes in the release of respirable allergen-loaded aerosol from birch flowers. However, birch pollen requires at least 3 h of wetting, and may germinate within the anther, prior to breach Other submicronic particles, such as orbicules and interorbicular piles are also released from the anther surface; however, immunoblots exhibit that they are not loaded with birch pollen allergens. Les than 5% of particles released in the size range of 30 to 800 nm are interorbicular piles Particles of fragmented cytoplasm in the size range of 30 nm to 45 [micro]m are released from birch pollen grains and emitted into the air. The small size of these particles hints that they can readily deposit in the lower airways.

* From the Division of Chemistry and Chemical Engineering (Dr Taylor, Flagan, and Miguel), California Institute of Technology, Pasadena, CA; Asthma and Glovsky Center Huntington Medical Research Institute (Dr Glovsky) Pasadena, CA; and Department of Pathophysiology (Dr Valenta), University of Vienna, Austria.

REFERENCE

(1) Taylor PE Flagan RC Valenta R et al. Release of allergens as respirable aerosols: a link between grass pollen and asthma. J Allergy Clin Immunol 2002; 109:51-56

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Correspondence to: Philip E Taylor, PhD Division of Chemistry and Chemical Engineering, 210-41 California Institute of Technology, Pasadena, CA 91125; e-mail: taylor@caltech.edu

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