Purification and immunoglobulin E-binding properties of peanut allergen Ara h 6: evidence for cross-reactivity with Ara h 2

Background IgE-binding peanut proteins smaller than 15 kDa were previously identified as potential allergens in the majority of our peanut allergic population. Objective To characterize the novel allergen in order to determine whether it was similar to one of the thus far identified recombinant peanut allergens (Ara h 1-7). Methods An IgE-binding protein of < 15 kDa was purified and identified via N-terminal sequencing. Its IgE-binding properties were investigated using immunoblotting, basophil degranulation, and skin prick testing. Possible cross-reacting epitopes with other peanut allergens were studied using IgE-immunoblotting inhibition. Results The purified protein is a monomeric protein with a molecular weight of 14 981 Da as determined using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectroscopy. The amino acid sequence of the first 39 N-terminal residues is identical to that of Ara h 6, indicating that the allergen is Ara h 6. It is recognized by 20 out of 29 peanut-allergic patients on IgE-immunoblot, and its potent biological functionality is demonstrated by the degranulation of basophils, even at concentrations below 10 pg/mL, and by positive skin prick reactions. Ara h 6 has homology to Ara h 2, especially in the middle part and at the C-terminal part of the protein. Almost complete inhibition of IgE-Ara h 6 interaction with Ara h 2 demonstrates that at least part of the epitopes of Ara h 6 are cross-reactive with epitopes on Ara h 2. Conclusions Peanut-derived Ara h 6 is a biologically active allergen recognized by the majority of our peanut-allergic patient population and can be considered a clinically relevant peanut allergen.