BET-V-1, THE MAJOR BIRCH POLLEN ALLERGEN, AND MAL-D-1, THE MAJOR APPLE ALLERGEN, CROSS-REACT AT THE LEVEL OF ALLERGEN-SPECIFIC T-HELPER CELLS

Background: Food allergy to apple is frequent in individuals allergic to tree pollen. The major allergens of birch, Bet v 1, and apple, Mal d 1, have been cloned and sequenced and display a high degree of seque nce identity, Leading to IgE crossreactivity. Objective: We sought to investigate cross-reactivity between Bet v 1 and Mal d 1 at the level of allergen-specific T lymphocytes. Methods: PBMCs of 13 patients alle rgic to birch pollen with oral allergy syndrome to apple were stimulat ed with rBet v 1 and rMal d 1, respectively, thereby establishing alle rgen-specific T-cell lines and T-cell clones. rMal d 1-specific T-cell cultures were tested for reactivity with rBet v 1, and rBet v 1-speci fic T cells were analyzed for reactivity with apple allergen. Cytokine production patterns in response to specific stimulation were evaluate d. A selection of cross-reacting T-cell clones was mapped for epitope specificity by the use of overlapping Bet v 1- derived peptides. Resul ts: Nineteen Mal d 1-specific T-cell clones were produced, 79% of whic h cross-reacted with Bet v 1. Eight of 18 Bet v I-specific T-cell clon es cross-reacted with Mal d 1. Six peptides representing cross-reactiv e T-cell epitopes could be identified. The respective fragments from b irch and apple displayed approximately 50% amino acid identity. Sevent y percent of the cross-reactive T-cell clones revealed a T-H2-like cyt okine production pattern. Conclusion: The results indicate that cross- reactivity between apple and birch pollen Leading to the clinical oral allergy syndrome occurs not only at the serologic, but also at the ce llular level.