Role of carbohydrate moieties in IgE binding to allergenic components of Cupressus arizonica pollen extract

Background A reduction of IgE immunoreactivity after periodate-treatment ha s been previously reported for various glycoprotein allergens. Objective Th e aim of this study was to investigate the role of glycan moiety of a C. ar izonica extract in the binding of patients' IgE and to identify the carbohy drates possibly involved. Methods The reactivity of IgE with C. arizonica extract, before and after p eriodate-treatment, was evaluated by immunoblotting and ELISA inhibition. T he specificity of carbohydrate-reactive IgE was evaluated by ELISA using un related glycoproteins with known sugar composition and structure, such as p ineapple bromelain, honeybee venom phospholipase A(2), and ovalbumin, befor e and after periodate treatment. Results When periodate-treated C. arizonica extract was probed after SDS-PA GE and immunoblotting with patients' IEE, no reactivity could be detected. Furthermore, a very poor inhibitory activity of the periodate-treated C. ar izonica extract as compared with the untreated sample could be observed in the ELISA inhibition experiments performed using C. arizonica extract as an tigen. When phospholipase A(2) and bromelain were used as antigens in ELISA , they were recognized by patients' IgE, whereas ovalbumin was negative. Tr eatment of phospholipase A(2) and bromelain with periodate completely aboli shes the IgE reactivity. Conclusion A large portion of the IgE reactivity of Cupressaceae-allergic s ubjects appears to be associated with sugar moieties of C. arizonica extrac t which appear to be shared by bromelain and phospholipase A2, thus suggest ing that the IgE of patients reacting with such epitopes probably react wit h beta 1-->2 xylose, alpha 1-->3 fucose and/or alpha 1-->6 fucose.