Cross-reactivity among peanuts and tree nuts

Authors: Maleki, Soheila; Grimm, Casey; Charles, Tysheena; Cheng, Hsiaopo; SCHEIN, CATHERINE - University Of Texas Medical Branch

Submitted to: UJNR Food & Agricultural Panel Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/2/2015
Publication Date: 10/19/2015
Citation: Maleki, S.J., Grimm, C.C., Charles, T.J., Cheng, H., Schein, C.H. 2015. Cross-reactivity among peanuts and tree nuts. UJNR Food & Agricultural Panel Proceedings. 2014:16-18.

Interpretive Summary: Our previous work established that certain sequences in walnut allergens are very similar, according to the property distance (PD) tool of the Structural Database of Allergenic Proteins (SDAP)5, to known IgE-binding linear epitopes of peanut allergens. We also showed that a walnut peptide identified by its similarity to an immunodominant Ara h 2 IgE epitope could compete with this allergen for binding to IgE in allergic patient sera.5 We have also identified multiple similar IgE-binding sequences in walnuts and peanuts using the PD tool and graphical mapping that can bind IgE antibodies in the sera of many patients allergic to nut proteins. Several of the newly identified IgE epitopes in walnut allergens were in the NTP of the walnut vicilin protein Jug r 2. In this work, we show that certain linear peptides from the sequences of the patients cross-reactive to both walnut and peanut recognize epitopes in the NTPs of Ara h 1 and Jug r 2 in a similar fashion. To further test this, a 13mer PCP-consensus peptide that bound IgE in sera of patients and could compete with Ara h 2 for binding to patient IgE was synthesized. Antibodies generated against this consensus peptide detected protein bands in the extracts of multiple tree nuts, corresponding to bands of proteins that also bind IgE from patient sera. These results show that several sequences in nut allergens could contribute to the high degree of clinically significant cross-reactivity between peanuts and tree nuts. We show that at least one of these newly predicted peptide epitopes is capable of binding the same group of IgE antibodies that are specific for Ara h 2. These results extend our previous observation that many similar epitope sequences may contribute to the extreme reactions that nuts can cause in sensitive individuals. Additionally, because IgE from the same individual bound to Jug r 2 NTP as well as similar polypeptide sequences in Ara h 2, this could explain some cases of peanut/walnut cross-reactivity. The ramifications for this work are significant for handling patients with severe allergies, for the detection of potentially cross-reactive allergenic proteins, and for generating or selecting new immunotherapeutic peptides, proteins for treatment of multiple nut allergies simultaneously, and perhaps even development of new nut cultivars with reduced allergenic potential. Future studies will involve other well-known allergens and epitopes thereof. The current peptides will be screened with additional sera from allergic patients to determine if clinically relevant cross-reactive epitopes can be identified.

Technical Abstract: Approximately 30% of peanut allergic individuals also have allergies to tree nuts and vise versa. Our previous work has shown that the structural data base for allergic proteins (SDAP) can identify similar IgE binding areas that may be important for cross-reactivity between allergens. Using SPOTs membranes and microarray analysis, we identified a group of peptides that were recognized by patients with cross reactivity to both walnuts and peanuts, and another group that were recognized by all of the sera from nut allergic patients. Several of these sequences were from the N-terminal pro sequence (NTP) of the walnut allergen Jug r 2, all of which were similar, according to the property distance (PD) scale in the Structural Database of Allergenic Proteins (SDAP), to an immunodominant IgE epitope of Ara h 2. An antibody was generated against a consensus sequence peptide, based on IgE binding peptide repeats in Ara h 2 Jug r 2-NTP. This antibody was shown to recognized many proteins in other nuts and legumes. These proteins were then identified, by digestion and mass spectrometry, to be major allergens previously identified in other tree nuts. Therefore, a group of conserved, similar IgE binding regions, not necessarily within the same family of proteins, could account for the high degree of cross reactivity between peanuts and many different nuts and seeds.