Epitopes with similar physicochemical properties contribute to cross reactivity between peanut and tree nuts

Authors: Nesbit, Jacqueline; SCHEIN, CATHERINE - University Of Texas Medical Branch; BRAUN, BENJAMIN - Stanford University; GIPSON, STEPEHEN - Oak Ridge Institute For Science And Education (ORISE); Cheng, Hsiaopo; Hurlburt, Barry; Maleki, Soheila

Submitted to: Molecular Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2020
Publication Date: 5/19/2020
Citation: Nesbit, J.B., Schein, C.H., Braun, B.A., Gipson, S.A.Y., Cheng, H., Hurlburt, B.K., Maleki, S.J. 2020. Epitopes with similar physicochemical properties contribute to cross reactivity between peanut and tree nuts. Molecular Immunology. 122:223-231. https://doi.org/10.1016/j.molimm.2020.03.017.
DOI: https://doi.org/10.1016/j.molimm.2020.03.017

Interpretive Summary: Previously, the structural database for allergic proteins (SDAP) predicted a cross-reactive walnut immunoglobulin E antibody (IgE, from the blood of nut allergic individuals) binding site in a walnut allergen, Jug r 2 leader sequence (J2LS) from a known peanut allergen Ara h 2, IgE binding site, which was then experimentally proven. Currently, the same tool was used to predict peptides that react with a common amino acid sequence (or peptide) derived from the same IgE binding peptide of Ara h 2 and the cross-reactive IgE epitopes of the J2LS. An antibody against the common amino acid sequence (csAB) was used to assess cross-reactivity with allergens in other tree nuts that had been predicted to react by SDAP. SDAP computer-based predictions was used in combination with csAB to identify allergens in nuts that contain similar sequences that can contribute to cross-reactivity between peanuts and tree nuts. Sequences similar to the common peptide, found in many IgE binding nut and seed allergens, are immunologically important IgE binding peptides that may contribute to clinically symptomatic cross-reactivity between peanuts and tree nuts. These findings may contribute to improving diagnostic tools.

Technical Abstract: IgE epitopes with similar physicochemical properties (PCPs) within unrelated proteins were determined to contribute to cross-reactivity among nuts. We assessed if IgE-binding peptides with similar PCPs are prevalent and repeated within nut allergens, contributing to their cross reactivity. PCP-consensus peptides (cp, 13 aa and 31 aa) were identified from alignment of repeated sequences in Jug r 2 leader sequence (J2LS) and cross-reactive epitopes in the 2S albumins of peanut and synthesized. The 13 aa cp (13cp) was used to produce a rabbit consensus peptide antibody (cpAB) for ELISA and western blots with various nut extracts followed by mass spectrometric identification. A similarity search in the Structural Database of Allergenic Proteins (SDAP) predicted peptides similar to the 13cp in peanut (PN) and tree nuts (TN), which were assessed for IgE binding with ELISA and by peptide microarrays. Repeats, similar to 13cp are present in multiple allergens. The cpAB binds specifically to allergens in extracts of the different nuts, including almond (Pru du 6), walnut (Jug r 2) and peanut (Ara h 2). Most of the peptides similar to the 13cp were recognized by IgE from nut allergic patient sera on microarrays. IgE binding to various nut extracts was inhibited by J2LS and 31cp indicating that these PCP sequences are similar enough to be interchangeable. Sequences similar to the 13cp, found in many immunodominant nut and seed allergens, are dominant IgE epitopes that may contribute to clinically relevant cross-reactivity between peanuts and tree nuts. These findings may contribute to improving diagnostic tools.