Involvement of Carbohydrate Epitopes in the IgE Response of Celery–Allergic Patients

Abstract

Background: This study was performed to get further insights into antibody responses to cross–reactive carbohydrate determinants (CCD), including initial experiments to prove the biological activity of anti–CCD IgE. Earlier studies have shown that IgE specific for CCD occurs in about 25% of celery–allergic patients. The clinical significance of these antibody specificities is doubtful. Methods: Patient sera were selected on the basis of a positive case history of celery allergy and multiple binding to high molecular weight celery allergens on immunoblots. Specific IgE to native and heated celery 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 antigens in an IgE ELISA as well as in EAST and immunoblotting inhibition experiments. Dose–related histamine release was performed with BSA neoglycoproteins 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 α1,3–fucose is a key structure for IgE binding. In patients with anti–CCD IgE, the maximal inhibition of celery EAST by the bromelain glycan ranged from 22 to 100%. Inhibition 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 bromelain glycopeptide to BSA, a strong dose–related histamine release was obtained in a celery–allergic patient, occurring at lower concentrations than with the recombinant major protein allergen from celery, Api g 1. Conclusions: Our results demonstrate that IgE specific for CCD is common in celery–allergic patients, and can represent the major proportion of IgE against this food. α1,3–fucose was confirmed to be an essential part of the IgE epitope. Immunoblotting inhibition indicated the presence of this carbohydrate determinant on multiple glycoproteins in celery extract. Although histamine release was only performed in 1 patient, our data show that proteins carrying multiple glycan units can be biologically active in patients sensitized to CCD.

Assessing Genetically Modified Crops to Minimize the Risk of Increased Food Allergy: A Review

“…For some individuals the CCDs do not seem to elicit allergic responses either because the affinity of binding is low, because there are no other IgE epitopes on the protein or for some other reason [69, 99]. In other cases, it appears that the CCD is responsible for eliciting a mast cell response [100,101,102]. However, it is clear that the rest of the protein structure must play a role in IgE recognition.…”

Close-up of the Immunogenic α1,3-Galactose Epitope as Defined by a Monoclonal Chimeric Immunoglobulin E and Human Serum Using Saturation Transfer Difference (STD) NMR

“…The role of CCDs as a cause of allergic symptoms still is controversial (4). IgE against classical CCDs has been shown to be clinically relevant (5)(6)(7)(8), but artificial or recombinant glycoproteins did not show clear cut effects in mediator release assays or skin prick tests (9,10).…”

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“…The cross-reactive carbohydrate determinants, structures containing α-1,3-fucose and β-1,2-xylose bound to proteins via N-glycoside linkages, are highly immunogenic in mammals; some celery-allergic patients exclusively display IgEbinding to these determinants of molecular weight > 45 kDa. However, any clinical significance of cross-reactive carbohydrate determinants-specific IgE is still a matter of debate (Aalberse, 1998;Fotisch et al, 1999). …”