Allergenicity and antigenicity of wild-type and mutant, monomeric, and dimeric carrot major allergen Dau c 1: Destruction of conformation, not oligomerization, is the roadmap to save allergen vaccines

Background: Carrot allergy is caused by primary sensitization to birch pollen. Continuous carrot exposure results in additional Dau c 1-specific allergic responses. Thus, immunotherapy with birch pollen may not improve the food allergy. Objective: Evaluation of mutation and oligomerization of the major carrot allergen, Dan c 1, in regard to alteration of antibody binding capacities, structure, and the ability to induce blocking IgG antibodies. Methods: Measurement of IgE reactivities to monomers, dimers of wild-type and mutant Dan c 1.0104 and Dan c 1.0201, and Dan c 1.0104 trimer, their ability to induce blocking antibodies in mice, and their allergenic potency by histamine release. Results: The reactivity of human IgE to the mutant dimer was reduced on average by 81%. Sera of immunized Balb/c mice showed specific IgG similar to the human IgE antibody response; Dan c 1.01 was more antigenic than Dan c 1.02. Both wild-type and mutant Dan c 1 variants induced cross-reacting IgG, which blocked binding of human IgE. The mutants were more antigenic than the wild-type forms, and the dimers induced higher IgG responses in mice than the monomers. The results of the histamine release experiments corroborated the findings of the antibody binding studies. Conclusion: Destruction of native conformation rather than oligomerization is the appropriate strategy to reduce the allergenicity of Bet v I-homologous food allergens. Clinical implications: The dimer composed of mutants of Dau c 1.0104 and Dan c 1.0201 is a promising candidate vaccine for treatment of carrot allergy because of its high immunogenicity and drastically reduced allergenicity.