Cross-reactivity among the pollen proteins of birch and apple trees.

In the spring of 1986, the pollen were collected from apple trees in full blossom, and were investigated for their allergenicity. The patients selected for study were subjects with a combined inhalant allergy to birch pollen and an oral allergy to apple fruit. The apple pollen extract yielded about the same percentage of nondialysable substance as obtained from birch pollen. In contrast to the latter, UV-spectroscopy revealed no flavonoids adsorbed to the apple pollen proteins. Patients with a combined allergy to birch pollen and apple fruit showed positive skin reactions to both birch and apple pollen extract. Inhibition of IgE-binding in RAST to birch pollen was observed by apple pollen extract at a 1000-fold lower potency than the homologous birch allergens. Immunoblotting demonstrated IgG-antibodies in birch-allergic sera cross-reactive with apple pollen components. It is concluded that minor allergenic determinants cross-reactive with birch pollen epitopes occur not only in the fruit, but also in the pollen of the apple tree.