Mutational analysis of major, sequential IgE-binding epitopes in αs1-casein, a major cow's milk allergen

Abstract

Background: Allergy to cow's milk is common in early childhood, and no therapy other than avoidance exists. In murine models of peanut allergy, immunotherapy with mutated, engineered, proteins appears promising. Objective: We sought to identify the critical amino acids (AAs) for immunoglobulin E (IgE) binding within the major B-cell epitopes of αs1-casein, a major cow's milk allergen. This will provide the necessary information to alter the cDNA to encode a protein capable of activating milk-specific T cells, but with reduced IgE-binding capacity. Methods: For mutational analysis of the IgE-binding epitopes, peptides of 10-14 AAs in length were synthesized on a derivatized cellulose membrane with single or multiple AA substitutions. Membranes were immunolabeled with pooled sera from 15 cow's-milk-allergic patients and with 8 individual sera. Results: With the pooled sera, substitution of a single AA led to complete abrogation of IgE binding to 2 of 8 peptides and diminished binding in the remainder. Substitution of multiple AAs led to an abrogation of binding in the remaining peptides. In 4 of the 8 peptides, the critical AA identified with pooled sera did not result in significant reduction of IgE binding with 1 or more individual patients. For these patients, other critical AAs were identified, indicating a more heterogeneous pattern in IgE recognition. Conclusion: This study indicates that single or multiple AA substitutions within IgE-binding epitopes result in reduced binding of milk-specific IgE antibodies by patients' sera. However, for future immunotherapeutic interventions with mutated peptides, critical AAs should be evaluated with individual patient sera to determine B-cell-epitope beterogeneity.