POOR BIOLOGIC ACTIVITY OF CROSS-REACTIVE IGE DIRECTED TO CARBOHYDRATEDETERMINANTS OF GLYCOPROTEINS

Background: In our outpatient population, approximately one third of p atients sensitized to grass pollen were found to have significant seru m 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 antibodi es directed to cross-reactive carbohydrate determinants (CCD) of glyco proteins might explain these discrepancies. Objective: In this study w e investigated the biologic activity of IgE directed to CCD. Methods: Sera of 32 patients allergic to grass pollen with significant levels o f 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 (patien ts 1 to II) were selected together with four control patients allergic to peanut, on the basis of a positive response on peanut SPT and a hi story 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 perfor med with peanut extract and the isolated peanut major allergens Ara h 1 and Are h 2. In addition, intracutaneous tests with peanut extract w ere performed. Results: In 29 (91%) of 32 patients with discrepant pea nut RAST and SPT responses, anti-CCD IgE (greater than or equal to 0.1 IU/mL) was detected. In patients 1 to II almost complete inhibition o f 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 i nhalant allergens. Conclusion: We conclude that cross-reactive IgE dir ected to carbohydrate determinants of glycoproteins, as found in grass pollen-sensitized patients, has poor biologic activity. It fan theref ore cause positive RAST results without apparent clinical significance .