Identification of immunogenic maize proteins in a casein hydrolysate formula

Cow's milk-based formulas used for infants with cow's milk allergy are based on hydrolyzed proteins. The formulas that are successful in preventing allergic responses are extensively hydrolyzed. Nevertheless, reactions to such formulas are occasionally reported, and protein material of higher molecular weight than expected has been detected by binding immunoglobulin E (IgE) from patients' sera. This paper presents the identification of high-molecular-weight material in the extensively hydrolyzed casein formula, Nutramigen. The material was concentrated by simple centrifugation. The proteins in the pellet were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and protein-containing bands were analyzed by protein sequencing after electroblotting. The proteins were identified as maize zeins, which are water-insoluble proteins of apparent M(r) 20,000 and 23,000, presumably originating from the maize starch in Nutramigen. Rabbits immunized with this formula developed antibodies against zeins but not against milk proteins. The maize zeins are probably identical to the recently reported components in Nutramigen (1), detected by binding of IgE from milk allergic patients, but not correlated to clinical allergic reactivity. The clinical relevance of maize proteins in Nutramigen remains to be established.