Identification of the critical amino acid residues of immunoglobulin E and immunoglobulin G epitopes in β-lactoglobulin by alanine scanning analysis

beta-Lactoglobulin represents one of the major allergens causing cow milk allergy. Few studies have clearly evaluated immunological relationships between IgE- and IgG-binding epitopes of beta-lactoglobulin. For characterization of immunological epitopes, peptides of 15 amino acids (AA) in length were synthesized. Immunoglobulin E- and IgG-binding epitopes were immunolabeled with individual sera from cow milk-allergic patients. Alanine scanning of immunodominant epitopes was used to identify the critical AA of IgE- and IgG-binding epitopes. The results showed that 4 IgE-binding epitopes were identified. Our initial data revealed IgE-binding epitopes at AA 17 to 31, AA 72 to 86, AA 92 to 106, and AA 152 to 166. Threonine 20, Met23, and Asp27 are the critical AA of IgG-binding epitopes. Two IgG epitopes were identified, which were located at AA 22 to 36 and AA 127 to 141. The critical AA of IgG-binding epitopes were Leu26 and Val31. Results obtained from this study will provide necessary information to alter the cDNA to encode a protein capable of activating milk-specific T cells, but with reduced IgE- or IgG-binding capacity.