Major allergens in soybean and clinical significance of IgG4 antibodies investigated by IgE- and IgG4-immunoblotting with sera from soybean-sensitive patients.

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 the 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 the patient and control groups. Among the IgE-binding proteins, the proteins with molecular weights of 20,000 and 58,000 in the whey fraction, and 26,000 and 31,000 in the globulin fraction, 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 78,000 in the globulin fraction was detectable with serum IgE in both patients. The majority of IgG4-binding proteins were not consistent with the IgE-binding proteins. The strong reactivity of IgG4 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 20,000 and 58,000 in the whey fraction, and 26,000, 31,000 and 78,000 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 anaphylactically in patients with soybean allergy.