Isotype-specific binding patterns of serum antibodies to multiple conformational epitopes of Bet v 1.

Abstract

Birch pollen is an important elicitor of respiratory allergy. The major allergen, Bet v 1, binds IgE exclusively via conformational epitopes. We identified Bet v 1-specific epitope repertoires of IgE and IgG from birch pollen-allergic and nonallergic subjects. Chimeric proteins were created by grafting individual epitope-sized, contiguous surface patches of Bet v 1 onto a nonallergenic structural homolog and expressed in Escherichia coli. Binding of IgE, IgG₁, and IgG₄ from sera of 30 birch pollen-allergic and 11 nonallergic subjects to Bet v 1, 13 chimeric proteins, and 4 bacterial Bet v 1 homologs were measured by ELISA. The proportion of epitope-specific in-total Bet v 1-specific IgE and the cross-reactivity of Bet v 1-specific IgE with bacterial homologs were determined by competitive ELISA. Thirteen soluble, correctly folded chimeric proteins were produced. IgE from 27 of 30 birch pollen-allergic patients bound to 1 to 12 chimeric proteins (median, 4.0), with patient-specific patterns evident. Three chimeras binding IgE from the majority of sera were identified, the grafted patches of which overlapped with previously published epitopes. Patterns of IgG₁ and IgG₄ binding to the chimeric proteins did not correspond to the binding patterns of IgE. Sera of 19 of 30 birch pollen-allergic patients contained low amounts of IgE to bacterial homologs. Bacterial proteins were able to partially inhibit IgE binding to Bet v 1. Epitopes recognized by Bet v 1-specific antibodies from birch pollen-allergic patients are specific to each patient and differ between IgE, IgG₁, and IgG₄.