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

Abstract

A reduction of IgE immunoreactivity after periodate-treatment has been previously reported for various glycoprotein allergens. The aim of this study was to investigate the role of glycan moiety of a C. arizonica extract in the binding of patients' IgE and to identify the carbohydrates possibly involved. The reactivity of IgE with C. arizonica extract, before and after periodate-treatment, was evaluated by immunoblotting and ELISA inhibition. The specificity of carbohydrate-reactive IgE was evaluated by ELISA using unrelated glycoproteins with known sugar composition and structure, such as pineapple bromelain, honeybee venom phospholipase A₂, and ovalbumin, before and after periodate treatment. When periodate-treated C. arizonica extract was probed after SDS-PAGE and immunoblotting with patients' IgE, no reactivity could be detected. Furthermore, a very poor inhibitory activity of the periodate-treated C. arizonica extract as compared with the untreated sample could be observed in the ELISA inhibition experiments performed using C. arizonica extract as antigen. When phospholipase A₂ and bromelain were used as antigens in ELISA, they were recognized by patients' IgE, whereas ovalbumin was negative. Treatment of phospholipase A₂ and bromelain with periodate completely abolishes the IgE reactivity. A large portion of the IgE reactivity of Cupressaceae-allergic subjects appears to be associated with sugar moieties of C. arizonica extract which appear to be shared by bromelain and phospholipase A₂, thus suggesting that the IgE of patients reacting with such epitopes probably react with β 1 → 2 xylose, α 1 → 3 fucose and/or α 1 → 6 fucose.