Ara h 2 is the dominant peanut allergen despite similarities with Ara h 6

BACKGROUND: Arachis hypogaea 2 (Ara h 2)-specific IgE is to date the best serologic marker to diagnose peanut allergy. Ara h 6 shares approximately 60% sequence identity and multiple epitopes with Ara h 2. OBJECTIVE: Our aim was to assess the diagnostic utility and relative importance of Ara h 2 and Ara h 6 in peanut allergy. METHODS: A cohort 100 of children was studied. The cohort included chidren who had peanut allergy, children who were sensitized to but tolerant of peanut, and children who were neither sensitized nor allergic to peanut. Levels of specific IgE to peanut and individual allergens were quantified by using ImmunoCAP. ImmunoCAP inhibition experiments and mast cell activation tests in response to both Ara h 2 and Ara h 6 were performed. Statistical analyses were done using SPSS version 14 and Prism version 7 software. RESULTS: Ara h 2–specific IgE and Ara h 6–specific IgE showed the greatest diagnostic accuracy for peanut allergy when compared with specific IgE to peanut and other peanut allergens. Most patients with peanut allergy were sensitized to both Ara h 2 and Ara h 6. Ara h 2 reduced Ara h 2–specific IgE binding more than Ara h 6 did (P < .001), whereas Ara h 6–specific IgE binding was inhibited to a similar degree by Ara h 2 and Ara h 6 (P = .432). In the mast cell activation test, Ara h 2 induced significantly greater maximal reactivity (P = .001) and a lower half maximal effective concentration (P = .002) than did Ara h 6 when testing cosensitized individuals. CONCLUSIONS: Ara h 2–specific IgE and Ara h 6–specific IgE provide the greatest accuracy to diagnose peanut allergy. Ara h 2 is the dominant conglutin in peanut allergy in the United Kingdom, despite a degree of cross-reactivity with Ara h 6.