Background Soybean occasionally causes food allergy but its major allergens have not been sufficiently confirmed. The relationship between food allergy and food-specific IgG4 has also not been defined.
Objective We investigated the allergenicity of soybean proteins and the clinical significance of soybean-specific IgG4.
Methods We detected IgE- and IgG4-binding proteins in soybean by immunoblotting with sera from 30 soybean-sensitive patients (including seven patients with positive soybean challenge tests). The extract from soybeans was fractionated into tbe whey fraction and the globulin fraction.
Results Ten and eight proteins were detected as IgE- and IgG4-binding proteins, respectively, with a significant difference between tbe patient and control groups. Among the IgE-binding proteins, the proteins with molecular weights of 20000 and 58000 in the whey traction, and 26000 and 31000 in the globulin Traction, had a particularly high IgE detection rate and high specificity. Two patients with positive challenge tests showed a quite different pattern in which only a protein with a molecular weight of 78000 in the globulin fraction was detectable with serum IgE in both patients. The majority of lgG4-binding proteins were not consistent witb tbe IgE-binding proteins. The strong reactivity of lgG4 was observed in all five infants among seven patients with positive challenge tests, and three of them had a very weak IgE reactivity.
Conclusions There were various antigenic proteins in soybean. Five proteins with molecular weights of 20000 and 58000 in the whey fraction, and 26000. 31000 and 78000 in the globulin fraction, were considered major allergens in the IgE-mediated reaction. Results of IgE- and IgG4-immunoblotting suggested that soybean-specific IgG4 may act anaphy lactically in patients witb soybean allergy.