Immunochemical characterization of Glycine max L. Merr. var Raiden, as a possible hypoallergenic substitute for cow's milk-allergic patients

Background Cows' milk allergy (CMA) is the most common cause of food allergy in infancy. The only proven treatment is the complete elimination of cows' milk proteins (CMPs) from the diet by means of hypoallergenic formulas. Soybean-based formulae are widely used although intolerance to soy has been reported to occur in 15-40% of infants with CMA. Objective The aim of this work was to analyse the in vitro reactivity of the soybean cultivar Raiden, which naturally lacks glycinin A(4)A(5)B(3), to evaluate whether this genotype could be a safe CMP substitute for CMA patients. Methods The reactivity of conventional soybean (CS) and Raiden soybean (RS) genotypes and also recombinant glycinin A(4)A(5)B(3) and alpha beta-conglycinin with casein-specific monoclonal antibodies and CMP-specific polyclonal serum was evaluated by immunoblotting and ELISA. A sequential competitive ELISA with the polyclonal antiserum and different soluble inhibitors was performed. In addition, an indirect ELISA with sera of atopic children with CMA was carried out to analyse the IgE-binding capacity of the different soybean components. Results We have shown that CS contains four components that cross-react with CMP, while RS has only one. The remaining cross-reactive component in RS was identified as alpha-subunit beta-conglycinin. By means of inhibitory ELISA, we demonstrated that CS, RS and the alpha-subunit beta-conglycinin extracts inhibited the binding of CMP-specific antibodies to the CMP-coated solid phase. Finally, we showed that CS, RS and the recombinant proteins were recognized by human CMP-specific IgE antibodies. Conclusions This work shows that although Raiden has fewer cross-reactive components than conventional soybean, it still has a residual cross-reactive component: the alpha-subunit beta-conglycinin. This reactivity might make this genotype unsuitable to treat CMA and also explains adverse reactions to soybean in CMA infants.