When antibodies of class IgE against the peanut proteins Ara h2 and Ara h6 are detected in a patient sample, this finding points with high probability to a clinical peanut allergy. After eating a peanut, the binding between IgE antibodies and their target proteins leads to the activation of mast cells. The activated immune cells secrete messenger substances which finally stimulate sometimes severe allergic reactions.
Ara h2 and Ara h6 belong to the group of 2S albumins – storage proteins that exist in various seeds and represent important allergens in vegetable food. Little attention in allergy diagnostics had been paid so far to a third 2S albumin, Ara h7. Authors of a recent publication, however, have now classified it as another important peanut allergen. They analyzed blood samples of 40 peanut allergic and 40 peanut tolerating persons (with positive and negative peanut challenge, respectively) for IgE against the peanut allergens Ara h1, h2, h3, h6 and h7 using an immunoblot (EUROIMMUN). As a result, IgE against Ara h7 turned out to be highly predictive for a clinical peanut allergy, similar to Ara h2 and Ara h6. Although 68% of the allergic cohort presented IgE against all three 2S albumins, individual patients were tested positive for IgE against only one of the three proteins. Therefore, the scientists discourage physicians from testing serum samples for IgE against single 2S albumin to prevent misdiagnoses .
On the EUROLINE DPA-Dx Peanut line blot, the three 2S albumins Ara h2, h6 and h7 are combined with Ara h1, Ara h3 and Ara h9. Also IgE antibodies against these three peanut proteins are associated with an increased risk of severe allergic reactions. The blot profile is completed by the allergens Ara h5 and Bet v1 which, in contrast to the other proteins, are associated with rather mild (cross) reactions to peanuts.