Variable IgE cross-reactivity between peanut 2S-albumins: The case for measuring IgE to both Ara h 2 and Ara h 6.

BACKGROUND: 2S-albumins Ara h 2 and Ara h 6 are the most potent peanut allergens and levels of specific immunoglobulin E (IgE) towards these proteins are good predictors of clinical reactivity. Because of structural homologies, Ara h 6 is generally considered to cross-react extensively with Ara h 2.
OBJECTIVE: We aimed to quantify the IgE cross-reactivity between Ara h 2 and Ara h 6.
METHODS: Peanut 2S-albumins were purified from raw peanuts. The IgE cross-reactivity between Ara h 2 and Ara h 6 was evaluated with 32 sera from French and US peanut-allergic patients by measuring the residual IgE-binding to one 2S-albumin after depletion of IgE antibodies recognizing the other 2S-albumin. The IgE cross-reactivity between Ara h 2 and Ara h 6 was further investigated by competitive inhibition of IgE-binding and by a model of mast cell degranulation.
RESULTS: A highly variable level of IgE cross-reactivity was revealed among the patients. The mean fraction of cross-reactive IgE antibodies represented only 17.1% of 2S-albumins-specific IgE antibodies and was lower than the mean fraction of IgE specific to Ara h 2 (57.4%) or to Ara h 6 (25.5%). The higher level of Ara h 2-specific IgE was principally due to the IgE-binding capacity of an insertion containing the repeated immunodominant linear epitope DPYSPOH S. The impact of IgE cross-reactivity on diagnostic testing was illustrated with a serum displaying an Ara h 6-specific IgE response of 26 UI/mL that was not associated with the capacity of Ara h 6 to trigger mast cell degranulation. CONCLUSIONS & CLINICAL RELEVANCE: Immunoglobulin E antibodies specific to peanut 2S-albumins are mainly non-cross-reactive, but low-affinity cross-reactivity can affect diagnostic accuracy. Testing IgE-binding to a mixture of 2S-albumins rather than to each separately may enhance diagnostic performance.