Background IgE antibodies against carbohydrate epitopes have been identified recently as a major cause of in vitro double positivity to honeybee (HB) and vespid venom in patients with stinging-insect allergy. As these antibodies possibly have low clinical relevance they may be misleading in the diagnosis of venom allergy.
Objective To confirm the role of carbohydrate epitopes in double positivity and to locate the responsible glycoallergens in HB and yellow jacket (YJ) venom by western blot.
Methods Immunoblot inhibition using HB venom, YJ venom and two glycoprotein sources displaying 1-3-fucosylated N-glycans (i.e. oilseed rape (OSR) pollen, and the synthetic neo-glycoprotein fucosylated/xylosylated N-glycans from bromelain coupled to bovine serum albumin (MUXF-BSA)) as inhibitors were performed with sera from 15 double-positive patients with stinging-insect allergy. Additionally, reactivity with blotted hymenoptera venoms of a carbohydrate-specific rabbit antiserum against OSR pollen was investigated.
Results Major venom glycoallergens binding with carbohydrate-specific human IgE and rabbit IgG were detected in HB venom at 42 (hyaluronidase (HYA)), 46, 65 and 95 kDa, and in YJ venom at 38 and 43 kDa (HYA). Antibody binding to these allergens was completely lost after periodate treatment. Glycans of HB phospholipase were bound by patients' IgE only after protein denaturation. In 10 of the 15 patients the reactivity was with the second venom because of carbohydrates alone. The high-molecular-weight glycoallergens identified in HB venom probably correspond to similar proteins described earlier, including allergens B and C. The 38-kDa YJ allergen might represent a homologue of V mac 3.
Conclusions The data confirm the proposed role of carbohydrate-specific IgE in double positivity to HB and YJ venom and shed new light on some previously described minor hymenoptera allergens of uncertain clinical significance. The consideration of carbohydrate-specific IgE may allow to discriminate between patients with potentially relevant and patients with non-relevant double sensitization.