Molecular basis of IgE cross-reactivity between human beta-casein and bovine beta-casein, a major allergen of milk

Twenty patients allergic to cow's milk proteins and with high levels of spe cific IgE directed against bovine whole casein were selected to evaluate re activity of their IgE antibodies with human beta-casein. Highly purified hu man and bovine beta-caseins were prepared by selective precipitations and F PLC separation. Their identity and purity were assessed by HPLC, analysis o f amino acid composition, sequencing of the five N-terminal amino acid resi dues and immunochemical tests. Direct and indirect ELISAs were performed us ing human and bovine beta-casein coated into microtiter plates and monoclon al anti-human IgE antibody AChE labelled for revelation. Seven sera contain ed specific IgE directed against human beta-casein. Inhibition studies usin g native human and bovine beta-caseins as well as bovine beta-casein-derive d peptides demonstrated that, depending on the sera, one or several common epitopes located in different parts of the molecule were shared by the two homologous proteins. (C) 2000 Elsevier Science Ltd. All rights reserved.