Parvalbumin, a cross-reactive fish allergen, contains IgE-binding epitopes sensitive to periodate treatment and Ca2+ depletion

Background: Type I allergy to fish is a severe health problem in countries in which a large percentage of the population derive income from fishing. Objective: The aim of the study was to characterize crossreactive IgE-binding components in six different fish species (cod, tuna, salmon, perch, carp, and eel). The effect of reducing extraction conditions, periodate treatment, and depletion of Ca2+ on binding of IgE to the allergens was investigated. Methods: Extracts were prepared under nonreducing and reducing conditions, IgE-binding components were characterized by IgE immunoblotting, and cross-reactive epitopes were studied by IgE-immunoblot inhibition experiments. To reveal calcium-sensitive or carbohydrate-containing epitopes, nitrocellulose-blotted extracts were exposed to ethylene glycol bis(beta-aminoethyl ether) -N,N,N',N'-tetraacetic acid (EGTA) and periodate. Results: Sera from all patients allergic to fish (n = 30) displayed IgE reactivity to parvalbumin, a 12 kd protein present in fish extracts from six different species. Reducing extraction conditions had no effect on IgE binding to parvalbumins, whereas periodate treatment and depletion of protein-bound calcium led to a substantial reduction of IgE binding. Parvalbumins from six different species contained cross-reactive IgE epitopes Conclusion: Parvalbumin represents a cross-reactive fish allergen. It contains IgE epitopes that are sensitive to periodate treatment and Ca2+-depletion.