IgE-binding and histamine-release capabilities of the main carbohydrate component isolated from the major allergen of olive tree pollen, Ole e 1

Background: Pollen from olive trees (Olea europaea) is a cause of pollinosi s and an aggravating of asthma in Mediterranean regions. Recently, Ole e 1, the major allergen from olive tree pollen, has been isolated and its amino acid sequence has been elucidated. It is a glycoprotein whose carbohydrate moiety is involved in an IgE-binding epitope responsible for cross-reactiv ity among plant glycoproteins. However, the allergenicity of the free carbo hydrate side chains remains to be clarified. Objective: The purpose of this study was to isolate the main carbohydrate c omponent of Ole e 1 allergen and analyze its IgE-binding and histamine-rele ase capabilities. Methods: Deglycosylation treatment of Ole e 1 with PNGase F and gel exclusi on chromatography were used to isolate the main sugar component of the alle rgen. Sera of patients who are allergic to olive pollen and sera sensitive to Ole e 1 have been used in dot blotting assays of IgE binding to the isol ated carbohydrate. Heparinized whole blood obtained from patients sensitive to Ole e 1 were stimulated by the free carbohydrate; the resulting histami ne release was measured. Results: The main sugar component of Ole el has been isolated. Free carbohy drate was able to bind IgE from sera of patients allergic to olive pollen; the sera of 65% of these patients contained anticarbohydrate reacting IgE, and 100% of those patients were sensitive to Ole e 1. The free carbohydrate promoted in vitro histamine release from basophils of sensitized patients. Conclusion: The carbohydrate moieties of allergenic glycoproteins can const itute significant determinants on the binding to IgE of the sera from patie nts who are hypersensitive and can be responsible for inducing histamine re lease from blood cells.