A double-blind placebo-controlled birch allergy vaccination study II: correlation between inhibition of IgE binding, histamine release and facilitated allergen presentation

The pathogenesis of IgE-mediated allergic disease is closely related to the production of T-helper type 2 (Th2) cytokines, which lead to IgE production pivotal for activation of mast cells and basophils. Proliferating T cells along with eosinophils expanded and attracted by Th2 cytokines are major contributors to the late-phase reaction. The activation of these Th2 cells is strongly enhanced by CD23-mediated IgE facilitated allergen presentation (FAP).

The present study aims to investigate the effect of specific immunotherapy (SIT)-induced allergen-specific non-IgE antibodies (blocking antibodies) on IgE binding to allergen, histamine release (HR) and CD23-mediated allergen uptake in antigen-presenting cells.

Competition between IgE and non-IgE for allergen binding was studied by Advia Centaur antibody measurements, passively sensitized basophils were used to study HR and IgE-facilitated binding of allergen to B cells (FAP) was studied by flow cytometry. FAP measurements were performed both with and without the addition of a reference IgE serum, which was included to obtain optimal complex formation. The serum samples were obtained from birch pollen immunotherapy (n=21) or placebo control patients (n=21) before and after 1 and 2 years of treatment.

Statistically significant reduction of all parameters investigated was observed after 1 year of treatment and the effect was maintained during the second year of treatment. There was a clear correlation between the two FAP measurements and between each of them and the level of T cell activation reported upon previously. Moreover, strong correlations were found between changes in FAP, IgE binding and HR.

The present study clearly demonstrates that SIT induces changes in the composition of serum antibodies that inhibit IgE binding, HR and FAP to a similar extent. This suggests that these measurements, individually or in combination, may be used to monitor the immunological effect of SIT, even though direct correlations to changes in clinical parameters could not be demonstrated.