Development of new IgE specificities to allergenic components in birch pollen extract during specific immunotherapy studied with immunoblotting and Pharmacia CAP System™

Background: New IgE sensitizations to proteins in allergen extracts have been shown to occur during allergen-specific immunotherapy (IT). However little is known about the kinetics of the changes in antibody reactivities. Methods: Twenty-four allergic children and adults were treated with birch pollen rush IT (RIT). Fifteen matched patients served as allergic controls. Sera were obtained at regular intervals for up to three years and analyzed with immunoblotting and Pharmacia CAP System(TM) with recombinant (r) birch pollen allergens (rBet v 1, rBet v 2, and rBet v 4). Results: All birch-allergic patients had specific IgE to the major birch pollen allergen Bet v 1, but only three had IgE to rBet v 2 and/or rBet v 4 at the beginning of the study. New IgE sensitizations developed in 65% of the birch RIT-treated patients when studied by immunoblotting. Twenty-nine percent of the patients developed new sensitizations to rBet v 2 and/or rBet v 4 during RIT as measured by Pharmacia CAP System. Generally, new specific IgE reactivities occurred after at least one year of RIT, and only at low levels (< I kU(A)/l). Conclusions: Sensitization to additional allergenic pollen components frequently occurs during prolonged birch RIT. However, the IgE levels are low and the clinical relevance is not known.