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

BackgroundThe 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.MethodsHorse 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.ResultsAll 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.ConclusionOur data do not support the claim that Curly Horses are less allergenic than other breeds.