Identification of Pru du 6 as a potential marker allergen for almond allergy

Background: Oral food challenges have demonstrated that diagnosis of almond allergy based on extract-sIgE tests display low specificity. Molecular allergy diagnosis is expected to improve accuracy, but its value in diagnosing almond allergy remains unknown.

Objective: To identify relevant almond allergens and examine their ability to improve almond allergy diagnosis.

Methods: IgE-reactive proteins were purified from almond kernels. IgE-binding to almond extract and the allergens was analyzed by quantitative ELISA using sera from 18 subjects with a proven almond allergy. The control group consisted of sera from 18 subjects allergic to peanut and/or tree nuts but tolerant to almond.

Results: Three IgE-binding proteins were identified: legumin (Pru du 6), alpha-hairpinin (Pru du 8) and mandelonitrile lyase (Pru du 10). Positive IgE (≥0.35 kU/L) to almond extract showed 94% sensitivity but only 33% specificity. IgE to Pru du 6 maintained high sensitivity (83%) and provided superior specificity (78%). Sera from almond-allergic subjects had significantly higher IgE levels to almond extract (P<0.0001) and Pru du 6 (P<0.0001) than sera from tolerant donors. Sensitization to Pru du 6 was highly specific for almond allergy, while frequencies of sensitization to legumins from peanut, walnut, hazelnut, and cashew were similar in both groups. IgE to Pru du 8 and Pru du 10 was less sensitive (41% and 67%), but showed specificities of 100% and 61%.

Conclusion: The use of almond allergens markedly increases the diagnostic specificity compared to the extract. Pru du 6 is a potential new molecular marker for almond allergy.

Keywords: almond allergens; diagnostic specificity; food allergy; molecular allergy diagnosis; tree nut allergy.