Influence of the Priming Effect with Alder Pollen on Nonspecific Bronchial Hyperreactivity of Asthmatics Specifically Allergic to Birch Pollen.

It has been shown that bronchial hyperreactivity in asthmatics specifically allergic to birch pollen is stable during the preseasonal and postseasonal periods and increases during the birch pollen season. Between January and March 1989, warm weather in the southern part of Sweden led to an early emission of hazel and alder pollens. Fourteen asthmatic patients living there were followed and demonstrated an increased nonspecific bronchial hyperreactivity (decreased PC20 methacholine) before the birch pollen season due to a 'priming effect' of related tree pollens.