MULTIPLICITY OF CROSS-REACTIVE EPITOPES ON BET-V-I AS DETECTED WITH MONOCLONAL-ANTIBODIES AND HUMAN IGE

Six monoclonal antibodies against Bet nu I, the major cross-reactive a llergen of birch pollen (Betula verrucosa), were obtained. Four did no t react with fruits, but two monoclonal antibodies (mAbs) (5H8 and 9C1 1) were reactive with apple and other fruits. These two cross-reactive antibodies reacted with identical or overlapping sites, but differed in their relative degree of cross-reactivity toward various fruits and hazelnut. Cross-reactive human IgE antibodies reacted with a nonoverl apping epitope, as indicated by results of a two-site radioimmunoassay (RIA) with the fruit-reactive mAb 9C11. By isoelectric focusing (IEF) in conjunction with immunoblotting, a maximum of seven isoforms could be distinguished, Depletion of birch-pollen extract for Bet nu I with the most reactive mAb (7F7) removed approximately 95% of the IgE cros s-reactivity between birch pollen and apple extract. The remaining 5%, cross-reactive material was still capable of inhibiting the binding o f IgE to apple allergen completely, and was reactive with mAbs 5H8 and 3C4. By means of IEF/immunoblot, it was shown that these mAbs recogni ze an isoform of Bet nu I that is poorly, if at all, recognized by mAb 7F7. These results illustrate the heterogeneity of Bet nu I, both wit h respect to the cross-reactive sites as well as to the backbone struc ture. This type of heterogeneity has possible implications for the use of monoclonal antibodies in allergen standardization.