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, Dau 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 Dau c 1.0104 and Dau c 1.0201, and Dau 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; Dau c 1.01 was more antigenic than Dau c 1.02. Both wild-type and mutant Dau 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 1–homologous food allergens.

Clinical implications

The dimer composed of mutants of Dau c 1.0104 and Dau c 1.0201 is a promising candidate vaccine for treatment of carrot allergy because of its high immunogenicity and drastically reduced allergenicity.

Key words: Dau c 1, isoforms, carrot allergen, allergen vaccine, mutation, secondary structure, hypoallergenic variant, monomer, dimer, trimer

Abbreviations used: CD, Circular dichroism, EAST, Enzyme-linked allergosorbent test, SIT, Specific immunotherapy