IgE mimotopes of birch pollen allergen Bet v 1 induce blocking IgG in mice

BACKGROUND: The induction of nonanaphylactogenic 'blocking' IgG antibodies capable of inhibiting the IgE/allergen interaction represents a favorable therapeutic concept for type I allergy. However, IgG antibodies to allergens may block or enhance specific IgE binding, depending on the recognized epitope. Taking the major birch pollen allergen Bet v 1 as a model, we developed a strategy for the precise induction of IgG antibodies of a desired epitope specificity. METHODS: Random phage display peptide libraries were applied to define peptide structures mimicking natural epitopes (mimotopes) of Bet v 1. Selections were performed with BIP 1, a murine monoclonal antibody known to enhance the IgE binding to Bet v 1, and with anti-Bet v 1 IgE purified from patients' sera. The characterized Bet v 1 mimotopes were used to localize the corresponding epitope at the surface of Bet v 1 by a computer-aided mathematical approach based on the three-dimensional structure and the chemical character of the amino acids. The Bet v 1 mimotopes were further used to immunize BALB/c mice. The specificity of the induced antibodies was tested by immunoblotting and inhibition assays. RESULTS: With the three-dimensional epitope search it became possible to localize a discontinuous IgE epitope on the surface of Bet v 1 in a substantial distance from the IgG epitope of the monoclonal antibody BIP 1. Moreover, we could demonstrate that phage displaying mimotopes are immunogenic vectors for the precise induction of epitope-specific IgG. Immunization with BIP 1 mimotopes induced IgG enhancing the IgE binding to Bet v 1, whereas immunization with IgE mimotopes resulted in IgG capable of blocking human IgE binding in vitro. CONCLUSION: Allergen mimotopes can be used for the induction of anti allergen IgG of desired specificity. We propose that mimotope immunotherapy based on IgE mimotopes generated by biopannings may represent a future concept for therapy of type I allergy.