EVALUATION BY SDS-PAGE AND IMMUNOBLOTTING OF RESIDUAL ANTIGENICITY INHYDROLYZED PROTEIN FORMULAS

Background Extensively hydrolysed protein formulas are widely used as an alternative diet for children with cow's milk allergy. Partially hy drolysed protein formulas have been noted in some studies as useful in the prevention of allergy in infants at high risk of atopy. Although normally well tolerated, these 'hypoallergenic' products have been rep orted to cause serious immunological reactions in very sensitive subje cts. Objective Starting from these considerations, we studied some com mercial hydrolysed formulas in search of biological data supporting th e observed clinical reactions. Methods We set up an electrophoretic me thod sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PA GE) which allowed us to study the molecular weight of peptides contain ed in hydrolysed products. Then, using the immunoblotting technique we evaluated the reactivity of circulating IgE (from serum of children a llergic to cow's milk proteins) with the residual intact proteins and with the peptides present in these formulas. Results Both group of mil k proteins (caseins and whey proteins) were important allergens for ch ildren included in this study. The presence of high-molecular polypept ides was shown in partial hydrolysed formulas as such and in extensive hydrolysed products after protein enrichment by trichloroacetic acid (TCA) precipitation. Intact residual proteins were mainly responsible for the formation of IgE-antigen complexes observed in immunoblotting. More rarely, polypeptides of partial hydrolysed formulas were involve d in immunological responses. Conclusions Both partial and extensive h ydrolysed formulas could induce clinical reactions in very sensitive s ubjects. These responses are mainly associated with allergy to the sma ll amounts of residual intact proteins.