Identification of Sequential IgE-Binding Epitopes on Bovine αs2-Casein in Cow’s Milk Allergic Patients

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Abstract
Background: Caseins are the major allergens responsible for cow’s milk allergy (CMA). We have previously identified the IgE-binding epitopes of the major cow’s milk (CM) proteins except for αs2-casein. Methods: Overlapping decapeptides representing the entire length of αs2-casein were synthesized on a cellulose-derivatized membrane. Sera from 13 CM-allergic children, 4–15 years of age, with a median level of CM-specific IgE >100 kU/l (range 33.7 to > 100 kU/l) were used to identify IgE-binding epitopes. Results: Four major and six minor sequential IgE-binding regions were identified on αs2-casein. The first major region is located in the middle of the protein at amino acids (AA) 83–100, and the other three major regions are located in the carboxy terminal portion of the protein at AA 143–158, 157–172 and 165–188. The minor IgE-binding regions were identified at AA 31–44, 43–56, 93–106, 105–114, 117–128, and 191–200. Conclusion: We identified 10 sequential IgE-binding regions on αs2-casein and performed the first crucial step in the development of immunotherapeutic interventions for CMA.