Identification of sequential IgE-binding epitopes on bovine α_s2-casein in cow's milk allergic patients

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 α_s2-casein. Methods: Overlapping decapeptides representing the entire length of α_s2-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 > 100kU/l) were used to identify IgE-binding epitopes. Results: Four major and six minor sequential IgE-binding regions were identified on α_s2-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 α_s2-casein and performed the first crucial step in the development of immunotherapeutic interventions for CMA.