Involvement of carbohydrate epitopes in the IgE response of celery-allergic patients

Background: This study was performed to get further insights into antibody responses to cross-reactive carbohydrate determinants (CCD), including init ial experiments to prove the biological activity of anti-CCD IgE. Earlier s tudies have shown that IgE specific for CCD occurs in about 25% of celery-a llergic patients. The clinical significance of these antibody specificities is doubtful. Methods: Patient sera were selected an the basis of a positiv e case history of celery allergy and multiple binding to high molecular wei ght celery allergens on immunoblots. Specific IgE to native and heated cele ry tuber was determined by the enzyme allergosorbent test (EAST). N-glycans were purified after extensive digestion of specific glycoproteins, such as pineapple stem bromelain, bovine fibrin, and human IgG, and used as antige ns in an IgE ELISA as well as in EAST and immunoblotting inhibition experim ents. Dose-related histamine release was performed with BSA neoglycoprotein s containing 3-4 units of the purified glycopeptides. Results: Seven celery -allergic patients were identified who clearly presented IgE against the N- glycan purified from bromelain which is a common structure within the plant kingdom. Chemical defucosylation showed that alpha 1,3-fucose is a key str ucture for IgE binding. In patients with anti-CCD IgE, the maximal inhibiti on of celery EAST by the bromelain glycan ranged from 22 to 100%. Inhibitio n of celery immunoblots by preincubation of patient serum with this glycan led to a quenching of multiple bands at masses >40 kD. After linking the br omelain glycopeptide to BSA, a strong dose-related histamine release was ob tained in a celery-allergic patient, occurring at lower concentrations than with the recombinant major protein allergen from celery, Api g 1. Conclusi ons: Our results demonstrate that IgE specific for CCD is common in celery- allergic patients,and can represent the major proportion of IgE against thi s food. alpha 1,3-fucose was confirmed to be an essential part of the IgE e pitope. Immunoblotting inhibition indicated the presence of this carbohydra te determinant on multiple glycoproteins in celery extract. Although histam ine release was only performed in ? patient, our data show that proteins ca rrying multiple glycan units can be biologically active in patients sensiti zed to CCD.