Impact of Cross-reactivity between Major Peanut Allergens Ara h 2 and Ara h 6 on Specific IgE Measurements

RATIONALE: Serum IgE responses toward Ara h 2 and Ara h 6 are good predictors of clinical reactivity to peanut. As these 2S-albumins are 59% homologous and adopt similar tertiary structure, we aimed to evaluate how cross-reactivity can influence specific IgE measurements.

METHODS: Ara h 2 and Ara h 6 were purified from raw peanuts or produced in E. coli in order to ensure absence of cross-contamination. Cross-reactivity between allergens was then evaluated with 26 sera from peanut-allergic patients by measuring the residual IgE binding to one 2S-albumin after depletion of IgE antibodies specific to the other 2S-albumin. Specificity and affinity were further investigated by competitive inhibition of IgE binding and by degranulation of RBL-SX38 cells.

RESULTS: Although the profile of IgE specificity was highly variable among the different sera, IgE responses to 2S-albumins were mainly due to antibodies specific to Ara h 2 or to Ara h 6, with only 17% of IgE binding due to cross-reactive IgE antibodies. Moreover, relevance of this cross-reactivity depends on the affinity of the IgE binding, as illustrated by two sera displaying comparable IgE responses to Ara h 6 but related to different capacities of Ara h 6 to induce mast cell degranulation.

CONCLUSIONS: Despite high structural homologies between Ara h 2 and Ara h 6, IgE responses to 2S-albumins do not result predominantly from cross-reactive antibodies. However, as direct binding to coated allergens reveals indistinctly low and high-affinity binding, the clinical relevance of this cross-reactivity needs to be further investigated.