Clinical role of a lipid transfer protein that acts as a new apple-specific allergen

Background: Allergy to apple is commonly associated with birch pollinosis b ecause the two share homologous allergens. However, some patients have appl e allergy but no birch pollinosis, suggesting that there are allergens that do not crossreact with birch, Objective: The aim of the study was to evaluate the IgE reactivity pattern to an apple extract in subjects with allergic reactions to apple, with and without birch hay fever. Methods: Forty-three patients with oral allergy syndrome for apple and posi tive open food challenge, skin prick test, and serum specific IgE antibodie s to apple were admitted to the study. Thirty-two had birch pollinosis (doc umented by specific IgE for birch) and II were not allergic to birch. The I gE reactivity pattern to apple extract was identified by SDS-PAGE and immun oblotting. The consistent allergen, a 9-kd protein, was then purified by HP LC and characterized by periodic acid-Schiff staining, isoelectric point, a nd N-terminal amino acid sequencing. Results: The sera from 28% of patients allergic to apple with birch pollino sis, but from all patients allergic only to apple, recognized the 9-kd prot ein. This protein has an isoelectric point of 7.5 and is not glycosylated. Determination of its partial amino acid sequence showed that it belongs to the family of Lipid transfer proteins, which act as major allergens in Prun oideae fruits. Conclusions: These results indicate that a lipid transfer protein is an imp ortant allergen in patients allergic to apple but not to birch pollen. The prevalent IgE reactivity to this allergen in subjects with no birch pollino sis and the physicochemical characteristics of this protein suggest that se nsitization may occur through the oral route.