Clinically Relevant IgE-Cross-Reactivity of Nut AllergensEPA Grant Number: R834066
Title: Clinically Relevant IgE-Cross-Reactivity of Nut Allergens
Investigators: Schein, Catherine H. , Maleki, Soheila , Teuber, Susanne
Institution: The University of Texas Medical Branch - Galveston , USDA - NRCS , University of California - Davis
EPA Project Officer: McOliver, Cynthia
Project Period: December 1, 2008 through November 30, 2011
Project Amount: $409,927
RFA: Exploratory Investigations in Food Allergy (2007) RFA Text | Recipients Lists
Research Category: Food Allergy , Health Effects , Health
Peanuts and tree nuts cause severe allergic response and even anaphylaxis. At least 30% of peanut allergic patients are also sensitive ("cross-react") to tree nuts such as walnuts, pecans, almonds or cashews, as these contain similar proteins. Considerable effort has gone into determining areas of the linear sequences of these proteins, particularly from peanut, that bind IgE in the sera of patients. However, few studies have investigated the relevance of patterns of linear epitope recognition to clinically important cross-reactivity.
The hypotheses that will be tested are 1) that the affinity of the IgE-epitope interaction dictates clinically relevant crossreactivity among nuts, and 2) that computational tools developed as part of the Structural Database of Allergenic Proteins (SDAP) can detect IgE epitopes responsible for cross reactions among distantly related nut proteins, according to their common physicochemical properties
A combined computational and experimental approach to identifying the structural and physicochemical properties of IgE binding sequences that mediate cross-reactions in nut proteins will be used. Sera from the UC Davis Peanut and Tree Nut Sera Bank will be used. Starting from the well defined linear epitopes of peanut proteins, we will use tools from the Structural Database of Allergenic Proteins (SDAP) to identify similar sequences in allergenic proteins of tree nuts, especially walnut. These will be characterized by SPOTs analysis, and quantitatively using fluoresence anisotropy, and the results correlated with the clinical profile of patients with specific or non-specific sensitivity to nut proteins. Preliminary data has shown that walnut sequences with low physical distance (PD) scores to known peanut epitopes bind IgE from patients sensitive to both peanuts and walnuts. In this work, cross reactive peptides will be characterized structurally, using models of the allergens, and correlated with their binding affinity for IgE from patient sera and with the ability of the parent allergenic protein to stimulate basophils passively sensitized with sera from patients. Clinically characterized human sera from peanut and walnut allergic individuals will be utilized in immunoblot or SPOTS analysis, which will consist of synthetic, known or predicted peptide epitopes of individual allergens of peanut and walnut. The sera used in the analysis will be obtained from individuals with either 1) known clinical cross-reactivity or 2) those known to be tolerant of the other nut under study, but with or without IgE cross-reactivity to peanut and walnut. Specific peptides identified to be important will then be synthesized and used to determine the affinity of peptide-IgE interactions (Kd) by fluorescence anisotropy. The strongest to weakest IgE binding epitopes of the allergens, bound by sera from individuals with known allergy or just irrelevant IgE cross-reactivity, will be identified by these experiments. Sequence similarity, identity and strength of cross reactivity will be used to refine the existing computational model and test its predictive capacity.
All data resulting from this study will be catalogued in SDAP .This work will generate important information relating the structure/ physicochemical properties of cross-reactive IgE epitopes to clinical response, and model factors that underlie allergen recognition by the immune system. The IgE epitopes of tree nut and peanut allergens likely to be responsible for cross-reactions will be characterized. This can be used to estimate the risk, that a novel protein will provoke an allergic response, and to predict clinical cross-reactivity of a patient to various nuts as a future diagnostic tool.