Purification and Epitope Mapping of Jug r 4, a Major Walnut Allergen

Background: Tree nut allergy affects approximately 1% of the U.S. population and the prevalence is increasing. Walnut allergy is the most commonly reported tree nut allergy in the United States. This study aimed to investigate the IgE cross-reactivity between walnut allergen Jug r 4 and peanut allergen Ara h 3 in individuals with dual walnut and peanut allergies. Methods: Jug r 4 was purified from whole walnut extract and analyzed via western blot using anti-Ara h 3 antibodies alongside serum IgE from walnut allergic patients. Sera from individuals allergic to both peanuts and walnuts were utilized to examine peptide microarrays comprising synthetic overlapping 15 mer peptides, offset by five amino acids, of Ara h 3 and Jug r 4. These results were compared against computationally predicted IgE epitopes using the Structural Database for Allergic Proteins (SDAP). Additionally, SWISS-MODEL protein modeling software was employed to map IgE epitopes onto Ara h 3 and Jug r 4. Results: Our findings revealed previously unreported IgE epitopes for dual-allergic sera within both allergens, highlighting the locations of empirically determined and SDAP-predicted IgE epitopes. Conclusions: While six epitopes were predicted as cross-reactive, only three were frequently recognized by IgE in dual-allergic individuals, underscoring their potential significance in clinically relevant cross-reactivity.