Specific interaction of IgE antibodies with a carbohydrate epitope of honey bee venom phospholipase A2

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Abstract
Phospholipase A2 (E.C. 3.1.1.4.) is a major allergen of honey bee venom. It exists in a glycosylated and an unglycosylated variant. Both forms and the glycopeptide isolated after exhaustive proteolytic digestion were tested in RAST and RAST inhibition studies. IgE from 11 of 14 bee venom allergy sera exhibited significantly higher, and in two cases exclusive, affinity towards glycosylated phospholipase. In RAST inhibition experiments using phospholipase coupled to discs five of the sera were completely inhibited by glycopeptide at 0.1 mg/ml; four sera were partially inhibited and two sera could not be inhibited. Glycoasparagine, lacking all amino acids except the carbohydrate-linking asparagine, inhibits IgE-binding to glycopeptide discs up to 100%. These data clearly demonstrate that an oligosaccharide of a structural type frequently found in glycoproteins can represent an epitope which is recognized by IgE antibodies from allergic patients, which are specifically directed against the parent glycoprotein.