Soy allergy due to cross reactions to major birch pollen allergen Bet v 1

The most prevalent soy allergy in Central Europe is based on birch pollen-related cross reactions. Due to structure similarities of birch pollen major allergen Bet v 1 and soy allergen Gly m 4, 75% of birch pollen-allergic subjects show serological IgE-mediated cross reactions to the soy protein Gly m 4 from the family of Bet v 1-homologue, pathogenesis-related (PR)-10 proteins. Interestingly, only 10% of birch pollen-allergic patients develop clinical symptoms after ingestion of non- or slighty processed soy products (soy flakes, soy milk, tofu, diatery powders with soy isolate). Predominantly local oropharyngeal symptoms can lead to massive and severe swellings of throat or facial areas with dramatic severity. In addition, systemic reactions with urticarial, gastrointestinal and cardiovascular symptoms have been described. A typical case history of reactions with quick onset after ingestion of mildly processed soy products together with a strong allergic sensitization to birch pollen represent highly suggestive diagnostic clues. Native soy products are more useful for skin testing than commercial soy extracts due to labile Gly in 4 and its low abundance of 0.01 - 0.1% in total soy protein. For the same reason crude soy extracts are not sensitive enough for allergen-specific IgE detection in case of suspected Gly m 4-induced soy allergy. Recently introduced recombinant Gly m 4 is superior in demonstrating specific IgE. In case of established birch pollen-associated, clinically relevant soy allergy non- or hardly processed soy products should be avoided. Subsequent declaration of soy products about potential risks for birch pollen-allergic subjects might be helpful for future avoidance and instant diagnosis of the usually unexpected reactions. Heated and strongly processed products like soy sauce, textured soy proteins, roasted soy beans or soy oil are unlikely to represent inherent risks due to their low Gly m 4 content. Soy allergy on the basis of birch pollen-related crossreactions should be publicized more frequently.