Recombinant soybean protein beta-conglycinin alpha'-subunit expression and induced hypersensitivity reaction in rats

The major storage protein in soybean seed is beta-conglycinin and this protein has been identified as being responsible for food-allergic reactions in several species. However, the mechanism through which beta-conglycinin induces an allergic reaction has not yet been elucidated. In addition, assessing the antigenic activity of beta-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 beta-conglycinin alpha'-subunit.

We established an Escherichia coli expression system to obtain beta-conglycinin alpha'-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 beta-conglycinin alpha'-subunit.

Pure beta-conglycinin alpha'-subunit was obtained by expression in E. coli. The recombinant proteins were shown to have the same biological activity as the natural beta-conglycinin alpha'-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 alpha'-subunit. Histamine release of mast cells was also elevated in vitro.

Our results indicate that the beta-conglycinin alpha'-subunit possesses an intrinsic immune-stimulating capacity and that it can induce an allergic reaction. Moreover, this study showed that beta-conglycinin alpha'-subunit-induced anaphylaxis is IgE mediated, and mast cell degranulation and histamine release are associated with anaphylactic symptoms.