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To obtain further information about the distribution and allergenicity of the major allergen Mal d 1 isoforms in different apple varieties, the presence of Mal d 1 protein in several apple varieties and the sequence of Mal d 1 were investigated. Twelve Mal d 1-clones were sequenced from seven apple varieties. The clones were grouped according to the amino acid sequence similarity into two groups, in which these two groups of Mal d 1 isoforms caused a high allergenicity. Different apple varieties with the reported difference in allergenicity showed different expression levels of the major apple allergen Mal d 1. The apple variety, Golden Delicious, which causes a strong allergic reaction from patients with apple allergy, showed the highest level of Mal d 1 protein expression. In contrast, the varieties including Jamba and Gloster, which cause little allergic symptoms, showed least levels of Mal d 1 expression. Thus, we concluded that the divergent allergenicity in different apple varieties depends mainly on the expression level of the major allergen Mal d 1, not on the presence of Mal d 1 isoforms.)
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