Immunological IgE Cross-Reactions of Bovine and Human alpha-Lactalbumins in Cow's Milk Allergic Patients
Despite great homology with the equivalent human protein, bovine alpha-lactalbumin (B alpha-La), a major component of whey, has been identified as a major milk allergen. The aim of this study was to investigate the relationship between structure and IgE binding capacity in alpha-Las: (1) the importance of three-dimensional structure using native vs disulfide bridgereduced B alpha-La; and (2) the incidence of amino acid sequence divergence on specific IgE cross-reactivity to human vs bovine alpha-La. Purified native, reduced and S-carboxymethylated B alpha-La and human alpha-La (H alpha-LA) were prepared. Specific IgE of 20 sera from patients with clinically recognized cow's milk protein allergy and positive RAST tests to B alpha-La were measured in original direct and competitive ELISA inhibition tests. All sera containing specific anti-native B alpha -La IgE also reacted with denatured protein, but the IgE levels were generally lower, showing that three-dimensional structure is an important feature in B alpha-La allergenicity but that sequential epitopes are also exposed after protein denaturation. Despite lower IgE levels, all sera also gave significant IgE responses to H alpha-La. Competitive ELISA inhibition confirmed results obtained by direct ELISA. The demonstrated IgE cross-reactivity between B alpha-LA and H alpha-La could be related to the high degree of sequence homology between the two proteins but did not prove to have a clinical significance. However, it is of great interest for a study of the relationship between structure, IgE binding capacity and allergenicity in alpha-Las.
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Document Type: Research Article
Publication date: June 1, 1999