Dutch hazelnut allergic patients are typically sensitized to Cor a 1 and profilin on the basis of primary sensitization to birch pollen Bet v 1 and Bet v 2. These allergens are extremely pepsin-sensitive, thus limiting clinical allergy to OAS. The aim of this study was to investigate whether other (potentially stable) allergens play a role.

Sera were selected from patients (n=60) with history- and/or DBPCFC-proven hazelnut allergy or from subjects (n=18) with high IgE titers to hazelnut but low or absent to apple and birch. Extracts of crude, roasted and pepsin-digested hazelnut were used to assess the stability of IgE epitopes. Extraction of hazelnut at pH2.5 resulted in enrichment for 2S albumin. These extracts and affinity-purified Cor a 1 were used in RAST and immunoblot analyses.

As expected, in the group of patients with proven hazelnut allergy, IgE recognition of Cor a 1 dominated (58/60 with >0.3 IU/ml). In accordance with the lability of Cor a 1, recognition of roasted and pepsin-digested hazelnut was much less frequent: 36% and 12% positives, respectively. Two sera contained IgE antibodies that preferentially recognized hazelnut extract after pepsin-digestion, thus pointing towards neo-epitopes. Among the sera selected on low reactivity to birch/apple, 5/18 recognized hazelnut Cor a 1 but not pollen Cor a 1 or Bet v 1.

Cor a 1 recognition independent from pollen sensitization exists, raising questions about its stability. Pepsin-digestion supports the existence of neo-epitopes.