IgE‐cross‐blocking antibodies to Fagales following sublingual immunotherapy with recombinant Bet v 1

BACKGROUND Evidence has accumulated that birch pollen immunotherapy reduces rhinoconjunctivitis to pollen of birch-homologous trees. Therapeutic efficacy has been associated with IgE-blocking IgG antibodies. We have recently shown that sera collected after sixteen weeks of sublingual immunotherapy with recombinant Bet v 1 (rBet v 1-SLIT)display strongIgE-blocking bioactivity for Bet v 1. Here, we assessedwhetherrBet v 1-SLIT-induced IgG antibodiesdisplay cross-blocking activity to related allergensin Fagalespollen. METHODS IgE, IgG1 and IgG4 reactivity to recombinantBet v 1, Aln g 1, Car b 1, Ost c 1, Cor a 1, Fag s 1, Cas s 1, and Que a 1 were assessed in pre- and post-SLIT samplesof 17 individuals by ELISA. A basophil inhibition assay using stripped basophils re-sensitized with a serum pool containing high Bet v 1-specific IgElevels was established and used to assess CD63 expression in response toallergens after incubation with pre-SLIT or post-SLIT samples.IgG1 and IgG4 wasdepleted from post-SLIT samples to assess its contribution toIgE-cross-blocking. RESULTS rBet v 1-SLIT boostedcross-reactive IgE antibodies and induced IgG1 and IgG4 antibodieswith inter- and intra-individuallydiffering reactivity tothe homologs. Highly variablecross-blocking activitiesof post-SLIT samples to the different allergens werefound. IgG1 and IgG4 antibodies displayed cross-blocking activity with individual variance. CONCLUSIONS Our mechanistic approach suggested that immunotherapy with the reference allergen Bet v 1 induces individual repertoires of cross-reactive IgG1 and IgG4 antibodies. The cross-blocking bioactivity of these antibodies was also highly variable and neither predictable from protein homology nor IgE-cross-reactivity.