Identification of B-cell epitopes of Bet v 1 involved in cross-reactivity with food allergens

Background:  The pollen-food syndrome (PFS) is an association of food allergies to fruits, nuts, and vegetables in patients with pollen allergy. Mal d 1, the major apple allergen, is one of the most commonly associated food allergens for birch pollen-allergic patients suffering from PFS. Although the reactions are due to cross-reactive IgE antibodies originally raised against pollen Bet v 1, not every Bet v 1-allergic patient develops clinical reactions towards apple.
Aim of the study:  We speculate that distinct IgE epitopes are responsible for the clinical manifestation of PFS. To test this hypothesis we grafted five Mal d 1 stretches onto Bet v 1. The grafted regions were 7- or 8-amino acids long encompassing amino acids residues previously shown to be crucial for IgE recognition of Bet v 1.
Methods:  A Bet v 1-Mal d 1 chimeric protein designated BMC was expressed in Escherichia coli and purified to homogeneity. IgE reactivity of BMC was tested with patients' sera originating from (i) Bet v 1-allergic patients displaying no clinical symptoms upon ingestion of apples; and (ii) Bet v 1-allergic patients displaying allergic symptoms upon ingestion of apples and other Bet v 1-related foods.
Results and conclusion:  Compared to birch pollen-allergic individuals, patients suffering from PFS showed significantly higher IgE reactivity with BMC (chimeric protein). The results suggest that the Mal d 1 regions grafted onto the Bet v 1 sequence comprise important IgE epitopes recognized by Bet v 1-allergic patients suffering from allergy to apples.