Identification of unique peanut and soy allergens in sera adsorbed with cross-reacting antibodies.

Abstract

Soybean and peanut are members of the legume family and share several common antigenic fractions. Patients allergic to one of these foods have serum IgE antibodies that immunologically cross-react with other legumes. Nevertheless, ingestion of other legumes generally does not induce an allergic reaction, suggesting that cross-reacting antibodies are not clinically relevant. This study was designed to identify unique peanut or soybean antigenic fractions, with sera adsorbed to remove cross-reacting antibodies, thus resulting in sera with IgE antibodies unique to either soy or peanut. Cross-reacting antibodies to soy were removed from the sera of two patients allergic to peanut and soy and three patients allergic to peanut by soy-affinity chromatography. Cross-reacting antibodies to peanut were adsorbed from the sera of a patient allergic to peanut and soy and a patient allergic to peanut by peanut-affinity chromatography. Adequate removal of cross-reacting antibodies was verified by ELISA after each adsorption step. Unadsorbed sera and sera adsorbed to remove cross-reacting antibodies (either to soy or to peanut) were assayed for specific IgE binding to peanut or soy immunoblots. Unique peanut-specific IgE antibodies (i.e., soy antibody-adsorbed) were found to bind to peanut fractions at 46, 29, 25, 19, 17, 14, and 5 kd on immunoblots of whole peanut protein. Similarly, unique soy-specific IgE (i.e., peanut antibody-adsorbed) were found to bind a fraction at 46 kd, and to a lesser extent, to a fraction at 21 kd on immunoblots of whole soy protein. The 73% reduction of IgE antibody binding to peanut by ELISA after adsorption of cross-reacting antibodies indicates extensive cross-reactivity between soy and peanut antigens. Antigen-affinity chromatography is an effective method for removal of cross-reacting antibodies. We identified IgE antibody binding (with sera where cross-reacting antibodies were removed) to several unique antigenic fractions of peanut and soy. Further studies will determine the clinical significance of these fractions in IgE-mediated food hypersensitivity reactions.