Poor biologic activity of cross-reactive IgE directed to carbohydrate determinants of glycoproteins.

BACKGROUND: In our outpatient population, approximately one third of patients sensitized to grass pollen were found to have significant serum levels of anti-peanut IgE in the RAST, without positive peanut skin prick test (SPT) response and without peanut-related allergic symptoms. It was suggested earlier that poor biologic activity of IgE antibodies directed to cross-reactive carbohydrate determinants (CCD) of glycoproteins might explain these discrepancies.
OBJECTIVE: In this study we investigated the biologic activity of IgE directed to CCD.
METHODS: Sera of 32 patients allergic to grass pollen with significant levels of anti-peanut IgE, a negative response on peanut SPT, and no symptoms of peanut allergy were tested for the presence of anti-CCD IgE. Eleven of these patients with greater than 3.0 IU/ml anti-peanut IgE (patients 1 to 11) were selected together with four control patients allergic to peanut, on the basis of a positive response on peanut SPT and a history of peanut allergy (patients 12 to 15). Inhibition of the peanut RAST was performed by using proteinase K-treated grass pollen extract as a CCD source. Basophil histamine release assays (BHRAs) were performed with peanut extract and the isolated peanut major allergens Ara h 1 and Ara h 2. In addition, intracutaneous tests with peanut extract were performed.
RESULTS: In 29 (91%) of 32 patients with discrepant peanut RAST and SPT responses, anti-CCD IgE (> or =0.1 IU/ml) was detected. In patients 1 to 11 almost complete inhibition of the peanut RAST with CCD was found (94.3% +/- 5.5%; mean +/- SD). In contrast, in the patients allergic to peanut only partial inhibition (59%) was found in one subject (p = 0.002, Mann-Whitney test). In the BHRAs and the intracutaneous tests of patients with discrepant peanut RAST and SPT results, reactivity was found only at high concentrations of peanut allergens. When related to specific IgE levels, reactivity to peanut allergens in the BHRAs of these patients was found to be at least a factor of 1000 less when compared with reactivity to control inhalant allergens.
CONCLUSION: We conclude that cross-reactive IgE directed to carbohydrate determinants of glycoproteins, as found in grass pollen-sensitized patients, has poor biologic activity. It can therefore cause positive RAST results without apparent clinical significance.