Proteomic analysis of horse hair extracts provides no evidence for the existence of a hypoallergenic Curly Horse breed

Background: The American Bashkir Curly Horse is frequently advertised to horse-allergic riders and claimed to be a so-called hypoallergenic breed that elicits fewer symptoms. Previous studies quantifying selected allergens in different breeds did not find a reduced allergen content in Curly Horses. Here, we provide a comprehensive proteomic analysis of horse hair extracts and a molecular analysis of the major allergen Equ c 1 with the aim of identifying differences in the Curly Horse breed that might explain their presumed reduced allergenic potential. Methods: Horse hair extracts were prepared from Curly and American Quarter Horse breeds, separated by gender and castration status, extracts from other breeds served as controls. Extracts and native Equ c 1 (nEqu c 1) were analyzed by mass spectrometry. IgE-binding capacities of nEqu c 1 and its recombinant variants were tested by ELISA using sera of patients sensitized to horses. Structures and ligand binding abilities were analyzed by computational modeling and fluorescence quenching assays. Results: All known respiratory horse allergens are present in hair extracts of Curly and Quarter Horses and share identical allergen-specific peptides. Lipocalin allergens are the most abundant proteins in horse hair extracts and contain several post-translational modifications. We identified two new variants of Equ c 1 that have similar IgE-binding capacities but show structural differences in their binding cavities and altered ligand binding behavior. There are no differences in IgE-binding of Equ c 1 derived from Curly Horses compared to other horse breeds. Conclusion: Our data do not support the claim that Curly Horses are less allergenic than other breeds.