Cross-reactive Carbohydrate Determinant Contributes to the False Positive IgE Antibody to Peanut

Background: The importance of peanut allergy has not been well recognized in Japanese society. IgE antibody to peanut can be, however, detected in patients without clinical peanut allergy. Methods: Clinical characteristics of 14 patients (aged 1―8 years) with peanut allergy were evaluated. IgE antibodies to peanut from patients with and without clinical peanut allergy were compared with those to soybean and other nuts. To examine the role of cross-reactive carbohydrate determinant (CCD) on the clinically false positive detection of peanut IgE, horseradish peroxidase (HRP) and bromelain specific IgE were measured by Uni CAP IgE kit. Inhibition of peanut IgE by HRP was also examined. Results: The patients repeatedly experienced potentially life-threatening symptoms, including anaphylaxis. Sera from patients with peanut allergy had negative or relatively low IgE antibodies to other nuts. However, clinically false positive peanut IgE showed significant correlation-coefficients with soybean, almond, chestnut, pistachio, macadamia and cashew (r = 0.61―1.00). Anti-HRP and anti-bromelain IgE antibodies were detected in the clinically false positive sera, but not in the sera from patients with peanut allergy. Two out of four clinically false positive peanut IgE antibodies were significantly inhibited by HRP. Conclusions: Social education about the features of peanut allergy is needed in Japan. Anti-CCD IgE antibody was suggested to be one of the mechanisms contributing to the false positive detection of peanut IgE. Detection of anti-HRP or anti-bromelain IgE can be a useful tool to recognize the presence of anti-CCD antibodies.