THE SIGNIFICANCE OF ISOALLERGENIC VARIATIONS IN PRESENT AND FUTURE SPECIFIC IMMUNOTHERAPY

The isoallergenic variation of the tree pollen major allergens has bee n studied by 2D gel electrophoresis, and by analysis of several recomb inant clones. The studies have included both antibody-based and T cell stimulation assays. Bet v 1, the major allergen of birch, forms at le ast 24 spots when conventional extracts are analyzed by 2D gel electro phoresis. Comparison of Bet v 1-encoding DNA sequences reveals a consi derable number of amino acid substitutions. This sequence variation ca n theoretically account for the number of spots observed in 2D gels. W hereas pools of serum from allergic individuals and monospecific antib odies raised in rabbits bind to most if not all spots in 2D gels, anal yses of individual serum and/or murine monoclonal antibodies show indi vidual patterns of reactivity with various subsets of spots. These obs ervations point to a model in which amino acid substitutions induce lo cal pertubations of the allergen surface, causing differences in epito pe structure. Furthermore, analysis of pollen from individual trees sh ows that each tree produces individual subsets of Bet v 1 spots. When analyzed in stimulation assays, T cell clones also display differences in reactivity to different isoallergens. In conclusion, we have shown that Bet v 1 is heterogenous, and that individual trees produce vario us subsets of isoallergens which display differences in reactivity bot h towards antibodies and T cells. A careful selection of isoform may t herefore be of major importance if recombinant allergens or synthetic peptides are to be used for conventional immunotherapy.