In Search of Hypoallergenic Birch Trees: Characterization of PR-10 Genes from Eight Betula Species and Detection of Bet v 1 Isoforms in Birch Pollen Using a Combined Genomics- Proteomics Approach

Bet v 1 is an important cause of hay fever in the northern hemisphere. Bet v 1 isoforms from the European white birch (Betula pendula) have been investigated extensively, but the allergenic potency of other birch species is unknown. PR-10 genes were cloned and sequenced from 8 different birch species, representing all major groups within the genus, to establish the presence of these genes. In total, 134 unique sequences were discovered. Sequences were attributed to different PR-10 genes or pseudogenes that were subdivided into 7 subfamilies. Five subfamilies were common to all birch species. Q-TOF LC-MSE was applied to identify which PR-10/Bet v 1 genes are expressed in pollen and to determine relative abundances of individual isoforms in the pollen proteome. This showed that genes of two subfamilies were expressed in pollen, while each species expressed a mixture of isoforms with at least 4–5 different isoforms. Q-TOF LC-MSE allowed fast screening of Bet v 1 isoforms in pollen by determining the presence and relative abundance of isoforms similar to those with a known high IgE-reactivity (Bet v 1a =PR-10.01A01) and to the hypoallergenic isoform Bet v 1d (=PR-10.01B01). Betula pendula contains a Bet v 1 mixture in which both isoforms with a high and low IgE-reactivity are abundant. The presence of isoforms with high IgE-reactivity is a condition for determining the influence for the allergenicity of this species. Birch species that express isoforms similar to Bet v 1a are predicted to be allergenic as well.