Cross-allergenicity among celery, cucumber, carrot, and watermelon

Cross-reactive allergens may be responsible for the clustering of food allergies seen in patients hypersensitive to fruits and vegetables. The pooled sera of six individuals were used to investigate cross-antigenicity among freshly prepared extracts of celery (Cy), cucumber (Cc), carrot (Ct), and watermelon (W). Each patient demonstrated clinical allergy to one or more study foods and, with the exception of Ct in two cases, had IgE to all four extracts by skin test or ELISA. In comparisons of each food against itself and the other three antigens, ELISA inhibition assays demonstrated allergenic similarity among Cy, Cc, Ct, and W by their similar slopes and 50% inhibition concentrations (2.0-7.3 micrograms/mL). In contrast, mountain cedar pollen (MC) produced at 50% inhibition of each food which was 10-fold higher (26.9-70.8 micrograms/mL) and had a flatter slope. Immunoblots of individual sera showed a 15-kD protein band common to all four foods. Pooled sera immunoblot inhibitions (100 and 5 micrograms/mL) demonstrated mutual inhibition of all bands in each of the four foods with the exception of a 28-kD protein of W uniquely inhibited by itself. We conclude that Cy, Cc, Ct, and W possess shared antigens that may account for clustering of these food allergies in patients.