Epitope Mapping of 2S albumins and Comparison of Ara h 2, Ara h 6 and Ara h 7 from Peanut

RATIONALE: Peanut allergy is increasing worldwide. Of all the peanut allergens identified, Ara h 2 has been shown to be most correlated with and diagnostic of peanut allergy. In this work, we probed peptide microarrays with peanut allergic sera to identify and compare the linear epitopes of the peanut conglutinins, Ara h 2, Ara h 6 and Ara h 7 and other potentially cross-reactive tree nut 2S albumins.

METHODS: 15-mer peptides that were offset by 5 amino acids were printed on glass slides. Patient sera were incubated with the slides. IgE and IgG4 binding was detected with a combination of fluorescently-labelled antibodies. The linear epitopes were mapped to molecular models of the 3-dimensional structures of the allergens.

RESULTS: The majority of the epitopes mapped to the surface of the proteins. In addition, while Ara h 6 and Ara h 7 share 77% and 60% homology with Ara h 2, respectively, not all epitopes identified in these conglutins were shared among the three allergens. Common epitopes of cross-reactive 2S albumins in tree nuts were identified.

CONCLUSIONS: These results not only identify important epitopes for 2S albumins as well as Ara h 6 and 7, they demonstrate that while the peanut conglutins share some epitopes, they also have their own unique IgE and IgG4 epitopes and may not necessarily be diagnostically or immunologically equivalent to Ara h 2.