Bet v 1, the major birch pollen allergen, initiates sensitization to Api g 1, the major allergen in celery: evidence at the T cell level

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Abstract
Due to IgE cross‐reactivity, birch pollen‐allergic individuals frequently develop type I hypersensitivity reactions to celery tuber. We evaluated the T cell response to the major allergen in celeriac, Api g 1, and the cellular cross‐reactivity with its homologous major allergen in birch pollen, Bet v 1. Api g 1‐specific T cell lines (TCL) and clones (TCC) were established from peripheralblood mononuclear cells of allergic patients. Epitope mapping of Api g 1 with overlapping Api g 1‐derived peptides revealed one dominant T cell‐activating region, Api g 1109–126. TCL and TCC generated with Api g 1 cross‐reacted with the birch pollen allergen and, although initially stimulated with the food allergen, cellular responses to Bet v 1 were stronger than to Api g 1. Epitopemapping with Bet v 1‐derived peptides revealed that T cells specific for several distinct epitopes distributed over the complete Bet v 1 molecule could be activated by Api g 1. Bet v 1109–126 was identified as the most important T cell epitope for cross‐reactivity with Api g 1. This epitope shares 72% amino acid sequence similarity with the major T cell‐activating region of the food allergen, Api g 1109–126. Our data provide evidence that humoral as well as cellular reactivity to the major celery allergen is predominantly based on cross‐reactivity with the major birch pollen allergen. The activation of Bet v 1‐specific Th2 cells by Api g 1, in particular outside the pollen season, may have consequences for birch pollen‐allergic individuals.

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