title: Cross-reactive N-glycans of Api g 5, a high molecular weight glycoprotein allergen from celery, are required for immunoglobulin E binding and activation of effector cells from allergic patients.
abstract: Allergy diagnosis relying on the determination of specific IgE is frequently complicated by the presence of cross-reacting IgE of unclear clinical relevance. Particularly, the anaphylactogenic activity of IgE directed to cross-reactive carbohydrate moieties of glycoproteins from plants and invertebrates has been a matter of debate. In this study, we present the biochemical and immunological characterization of Api g 5, a glycoprotein allergen from celery with homology to FAD containing oxidases. Carbohydrate analysis of the allergen revealed the presence of glycans carrying fucosyl and xylosyl residues, structures previously shown to bind IgE. Chemical deglycosylation of the protein completely abolished binding of serum IgE from all 14 patients tested. Likewise, basophils from a patient allergic to mugwort pollen and celery were stimulated only by native Api g 5, whereas the deglycosylated allergen did not trigger release of histamine. IgE inhibition immunoblots showed that native Api g 5 other than the deglycosylated protein completely inhibited IgE binding to high molecular weight allergens in protein extracts from birch pollen, mugwort pollen, and celery. A similar inhibition was accomplished using the IgE binding oligosaccharide, MUXF, coupled to bovine serum albumin. All these observations taken together confer convincing evidence that IgE directed to cross-reactive carbohydrates is capable of eliciting allergic reactions in vivo.
authors.affiliation: Department of Pathophysiology, University of Vienna, Austria.
authors.forename: Merima
authors.initials: M
authors.lastname: Bublin
authors.forename: Christian
authors.initials: C
authors.lastname: Radauer
authors.forename: Iain B H
authors.initials: IB
authors.lastname: Wilson
authors.forename: Dietrich
authors.initials: D
authors.lastname: Kraft
authors.forename: Otto
authors.initials: O
authors.lastname: Scheiner
authors.forename: Heimo
authors.initials: H
authors.lastname: Breiteneder
authors.forename: Karin
authors.initials: K
authors.lastname: Hoffmann-Sommergruber
mesh_terms: D000485:Allergens / Q000737:chemistry / Q000276:immunology*; D052179:Antigens, Plant; D000077102:Apium / Q000276:immunology*; D001491:Basophils / Q000276:immunology; D003429:Cross Reactions; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D005182:Flavin-Adenine Dinucleotide / Q000032:analysis; D006023:Glycoproteins / Q000737:chemistry / Q000276:immunology*; D006031:Glycosylation; D006636:Histamine Release; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000276:immunology*; D007073:Immunoglobulin E / Q000276:immunology*; D018448:Models, Immunological; D008970:Molecular Weight; D010088:Oxidoreductases / Q000737:chemistry / Q000145:classification; D010940:Plant Proteins / Q000737:chemistry / Q000276:immunology*; D011058:Pollen / Q000276:immunology; D011134:Polysaccharides / Q000737:chemistry / Q000276:immunology
chemical_list: D000485:Allergens; D052179:Antigens, Plant; C477756:Api g 5 allergen, celery; D000939:Epitopes; D006023:Glycoproteins; D010940:Plant Proteins; D011134:Polysaccharides; D005182:Flavin-Adenine Dinucleotide; D007073:Immunoglobulin E; D010088:Oxidoreductases