Antibody binding to venom carbohydrates is a frequent cause for double positivity to honeybee and yellow jacket venom in patients with stinging-insect allergy

Background: Up to 50% of patients with stinging-insect allergy have double-positive RAST results to honeybee and yellow jacket (YJ) venom. True double sensitization and crossreactivity through venom hyaluronidases are considered main reasons for this multiple reactivity. Objective: We investigated the role of antibodies against crossreactive carbohydrate determinants in venom double positivity. Methods: CAP inhibition experiments were performed with crude oilseed rape (OSR) and timothy grass pollen extracts and a neoglycoprotein construct displaying a MUXF glycan, as present in pineapple-stem bromelain (MUXF-BSA). CAP to OSR was used as a rough measure for carbohydrate-specific IgE in individual sera. Results: CAP results to OSR pollen were positive in 2 of 14 single-positive honeybee venom sera, 2 of 16 single-positive,YJ venom sera, and 33 (80.5%) of 41 double-positive sera (P<.00001, <chi>(2) test). CAP inhibition was performed in 16 selected patients with a CAP class of 3 or higher to both venoms. In 9 of 11 patients with a highly positive CAP result to OSR (CAP score to OSR > CAP score to second venom), pollen extracts, MUXF-BSA, or both were able to completely inhibit IgE binding to one of the venoms, whereas this was not them case in 5 patients with a negative or weakly positive CAP result to OSR (CAP score to OSR < CAP score to second venom). Conclusions: The data suggest that carbohydrate-specific IgE is a major cause for the double positivity to honeybee and YJ venom seen in patients with Hymenoptera allergy. Because these antibodies may have low clinical relevance, they may severely impede the correct diagnosis of Hymenoptera venom allergy.