While the prevalence of apple allergy in food allergic patients is
generally below 2 %, apple allergy is most frequently associated with birch
pollinosis in Northern Europe and North America. 40 to 90 % of birch
pollen allergic patients are sensitized to this fruit. Apple is known as
one of the major foods involved in so-called "Oral Allergy Syndrome", which
presents IgE-mediated symptoms occurring mainly at the mucosa of lips,
tongue and throat after ingestion of apples and other fruits. Systemic
reactions including anaphylaxis occur more often in apple allergic patients
without related pollinosis. The present data collection reviews detailed
information on prevalence and symptoms of apple allergy as well as cross-reactivities,
molecular biological and allergenic properties of the major apple allergens,
and allergenic potencies of different varieties and ripening stages of
apples in tabular form. The allergens are unstable to conventional processing
of the fruits like canning, pulping or heating, therefore adverse reactions
occur almost exclusively after ingestion of fresh fruits. Due to the labile
nature of apple allergens the diagnostic accuracy is highly dependent on
the quality of extracts used in testing procedures. Cross-reactive inhalant
allergens are tree pollen (predominantly birch) and to a lesser degree
mugwort and grass pollen. The major pollen-associated apple allergen
is the Bet v 1 homolog protein Mal d 1. Besides Mal d 1, a 31-kDa allergen
was highly prevalent in patients with associated tree pollen allergy. Proteins
with Mr about 34 kDa and 60 kDa and a profilin homolog allergen are proven
to be cross-reactive to pollens. The major allergen in a patient population
without pollinosis is the lipid-transfer protein Mal d 3, which is suggested
to be cross-reactive to homolog proteins in peach and pear.
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