IgE cross-reactivity between the major peanut allergen Ara h 2 and the nonhomologous allergens Ara h 1 and Ara h 3

Background: Ara h 1, a vicilin; Ara h 2, a 2S albumin; and Ara h 3, a legumin, are major peanut allergens. Ara h 2 is an important predictor of clinical reactivity to peanut, but cosensitization to all 3 allergens is correlated with the severity of patients' symptoms. Objective: We investigated whether cosensitization to these 3 allergens is caused by IgE cross-reactivity, despite the fact that they do not display obvious structural or sequence similarities. Methods: IgE cross-inhibitions were performed with purified Ara h 1, Ara h 2, and Ara h 3 and IgG-depleted sera from 10 patients with peanut allergy. After an in silico search for similar peptides, IgE ELISA inhibition assays with synthetic peptides were performed. Results: Ara h 2 inhibited IgE binding to Ara h 1 (average, 86% +/- 13%) and Ara h 3 (average, 96% +/- 6%). IgE binding to Ara h 2 was inhibited by Ara h 1 by 78% +/- 15% and by Ara h 3 by 80% +/- 6%. A subsequent sequence comparison showed that these nonhomologous allergens contained several similar surface-exposed peptides. IgE binding to Ara h 2-derived peptides was completely inhibited by Ara h 1 and Ara h 3. A mixture of these peptides reduced IgE binding to Ara h 1 and Ara h 3 by 20% to 60% and to Ara h 2 by 49% to 89%. Conclusion: Occurrence of similar sequences in the 3 major peanut allergens accounts for the high extent of cross-reactivity among them.