Inhibition of CD23-dependent facilitated allergen binding to B cells following vaccination with genetically modified hypoallergenic Bet v 1 molecules

Background Vaccination with hypoallergenic recombinant Bet v 1 derivatives (Bet v 1 fragments and Bet v 1 trimer) is associated with the induction of IgG antibodies specific to natural Bet v 1. Objective To investigate whether IgG antibodies induced following vaccination with genetically modified hypoallergenic Bet v 1 derivatives are able to inhibit IgE-facilitated binding of allergen-IgE complexes to B cells. Methods Sera from 46 patients obtained before and after subcutaneous vaccination with Bet v 1 trimer (n = 14), Bet v 1 fragments (n = 11) or placebo (n = 21) were incubated with recombinant (r) Bet v 1 and an indicator serum (IS) from a birch pollen-allergic patient with high CD23 binding capacity. Bet v 1 immune complexes were added to a CD23-expressing B cell line and co-operative binding of Bet v1-IgE complexes to CD23 was measured with a polyclonal anti-IgE FITC antibody using a bio-functional cellular flow cytometric assay. Results When sera from patients vaccinated with rBet v 1 derivatives were incubated with Bet v 1 and the IS, a reduction of IgE binding to CD23 was observed. This effect was not seen when sera from placebo-treated patients were used. The decrease in CD23/IgE binding was statistically significant in the trimer group [pre-vs. post-specific immunotherapy (SIT): P = 0.02; trimer vs. placebo: P<0.04] but not in the Bet v 1 fragments-treated group. Trimer-treated patients had higher levels of Bet v 1-specific IgG than fragment-treated patients. The degree of inhibitory activity of IgE-facilitated allergen binding correlated with Bet v 1-specific IgG levels following SIT (R = 0.492; P = 0.012). Conclusion Vaccination with both recombinant Bet v 1 derivatives induces Bet v 1-specific IgG antibodies, which are able to inhibit the co-operative binding of allergen-IgE complexes to CD23, and may thereby reduce allergen-specific T cell responses.