Biological activity of IgE specific for cross-reactive carbohydrate determinants

The clinical relevance of IgE specific for cross-reactive carbohydrate determinants (CCDs) has been a matter of controversy. Until now, no convincing experiments have been performed to test the biologic significance of individual multivalent allergens that carry multiple carbohydrate epitopes.

We sought to contribute to the understanding of the role of CCD-specific IgE antibodies and to study whether CCD-specific IgE antibodies are able to activate basophils using different multivalent glycoproteins as antigens.

Purified natural tomato beta-fructofuranosidase (nLyc e 2) and rLyc e 2.02 expressed in Escherichia coli were compared by means of histamine release tests. In addition, native and deglycosylated horseradish peroxidase and a neoglycoprotein consisting of a defined glycopeptide (Manalpha1-6[Xylbeta1-2]Manbeta1-4GlcNAcbeta1-4[Fucalpha1-3]GlcNAc) coupled to BSA were used in histamine release assays using stripped basophils from normal donors resensitized with IgE from CCD-reactive patients with food allergy to tomato.

Ten CCD-positive and 2 CCD-negative sera from patients with tomato allergy underwent histamine release testing by using the glycoproteins and nonglycosylated controls as antigens, respectively. All sera induced histamine release with tomato extract (up to 100%), confirming the allergic status of the donors. Four of the CCD-positive sera induced releases ranging from 12% to 82% with all of the glycoproteins but not with the nonglycosylated or monovalent controls. All other sera showed no response or only very weak response to the glycoproteins.

Approximately one third of the CCD-positive sera from patients with tomato allergy have biologically relevant CCD-specific IgE antibodies. Therefore the general claim that CCD-specific IgE is clinically irrelevant has to be reconsidered critically. Hence IgE specific for CCDs should be taken into consideration in the diagnosis and therapy of certain allergies. In the subgroup of patients sensitized to CCDs, the use of natural allergens should be preferred over the use of recombinant allergens expressed in prokaryotic organisms.