Recombinant Soybean Protein β-Conglycinin α′-Subunit Expression and Induced Hypersensitivity Reaction in Rats

Abstract

Background: The major storage protein in soybean seed is β-conglycinin and this protein has been identified as being responsible for food-allergic reactions in several species. However, the mechanism through which β-conglycinin induces an allergic reaction has not yet been elucidated. In addition, assessing the antigenic activity of β-conglycinin by studying the activity of a subunit has rarely been conducted. Therefore, the objective of the present study was to characterize the antigenic specificity of the β-conglycinin α′-subunit. Methods: We established an Escherichia coli expression system to obtain β-conglycinin α′-subunit. The fusion proteins were then used in a rat model to induce a hypersensitive reaction. Immunoblotting, IgE and IgG1 level, histamine release, and passive cutaneous anaphylaxis reactions and intestinal histology were tested to assess the allergenic activity of the β-conglycinin α′-subunit. Results: Pure β-conglycinin α′-subunit was obtained by expression in E. coli. The recombinant proteins were shown to have the same biological activity as the natural β-conglycinin α′-subunit using immunoblotting analysis. Both the IgE and IgG1 level in serum and the histamine concentration in the intestine were increased while passive cutaneous anaphylactic reactions were induced in Brown Norway rats by intragastric gavage with the α′-subunit. Histamine release of mast cells was also elevated in vitro. Conclusions: Our results indicate that the β-conglycinin α′-subunit possesses an intrinsic immune-stimulating capacity and that it can induce an allergic reaction. Moreover, this study showed that β-conglycinin α′-subunit-induced anaphylaxis is IgE mediated, and mast cell degranulation and histamine release are associated with anaphylactic symptoms.