Evidence of Cross-Reactivity between Different Seed Storage Proteins from Hazelnut (Corylus avellana) and Walnut (Juglans regia) Using Recombinant Allergen Proteins.

Seed storage proteins are extremely stable allergens in nuts, seeds, and legumes and are responsible for the most severe allergic reactions to these foods. The cross-reactivity between seed storage proteins from different sources has not been studied at a molecular level so far. This study aimed to ascertain the cross-reactivity between walnut and hazelnut seed storage proteins using recombinant allergens. Sera from 13 consecutive patients with severe primary walnut and/or hazelnut allergy and hypersensitive to both nuts were studied. IgE specific for rCor a 9, rCor a 14, and rJug r 1 was measured, and inhibition experiments were carried out by measuring IgE reactivity after absorption of patients' sera with freshly prepared walnut extract. All 13 sera showed strong IgE reactivity against walnut 2S albumin, Jug r 1, 12 reacted to hazelnut 2S albumin, Cor a 14, and 8 to the hazelnut legumin, Cor a 9. In inhibition experiments, absorption of sera with whole walnut extract led to the complete disappearance of IgE reactivity to Jug r 1 in 12/13 cases, as expected, but also to the complete disappearance of specific IgE to Cor a 14 in 9/12 sera, and of IgE reactivity to Cor a 9 in 7/8. In the remaining cases a dramatic drop in IgE reactivity was observed. The study shows that patients primarily allergic to either walnut or hazelnut showing a skin or serological reactivity to the other nut also are potentially at risk of severe allergic reactions caused by cross-reactivity between 2S albumins and legumins.