IgE antibodies specific for carbohydrates in a patient allergic to gum arabic (Acacia senegal)

The present study deals with the detailed investigation of the IgE antibody response of a gum arabic-allergic patient. The patient showed multiple ser ologic and skin test sensitizations to a range of pollen, other inhalants a nd foods, and bee venom, and to the recombinant allergens Bet vl and Bet v 2. Moreover, the patient's serum reacted strongly to gum-arabic extract. Th e NaIO4-treated and thus deglycosylated extract showed no binding to IgE. I n contrast, removal of the protein backbone by basic hydrolysis did not dep lete the IgE reactivity. Therefore, it is concluded that the gum arabic-spe cific IgE antibodies of this patient were mainly directed against the carbo hydrate fraction of this material. In IgE-inhibition assays, cross-reaction s occurred in the range of 60% between gum arabic and known immunogenic IV- glycans containing alpha 1-3-linked fucose. Since the inhibition graphs wer e not parallel and the inhibition was not complete with heterologue antigen s, the crossreacting epitopes of gum arabic appeared to be different from t he latter well-known cross-reactive carbohydrate determinants (CCD). Inhibi tion may have been caused by a partial immunologic identity of the investig ated carbohydrate moieties. A strong IgE response to the fucose-containing glycan from bromelain was measured in a glycan ELISA that utilizes purified glycopeptides at the solid phase. This response, which may explain the mul tiple sensitizations without clinical significance diagnosed in the patient , could originate from inhalation of pollen, which is known to contain simi lar glycans, or from occupational sensitization during work as a baker and confectioner. Since the gum-arabic protein showed only very weak participat ion in the IgE reactivity, the clinical symptoms of the patient caused by g um arabic may be attributed to carbohydrate epitopes. Due to the repetitive polysaccharide sequence of gum arabic, several epitopes for the cross-link ing of IgE should exist.