Specificity of I g E antibodies from patients allergic to goat's milk and tolerant to cow's milk determined with plasmin‐derived peptides of bovine and caprine β‐caseins

Scope Despite a sequence homology of 90% between bovine and caprine β‐caseins ( CN ), I g E antibodies from patients allergic to goat's milk ( GM ), but tolerant to cow's milk ( CM ), recognize caprine β‐ CN without cross‐reacting with bovine β‐ CN . We investigated this lack of cross‐reactivity by evaluating the I g E ‐reactivity toward peptides isolated from plasmin hydolysates of bovine and caprine β‐ CN . Methods and results The I g E ‐binding capacity of plasmin‐derived peptides was evaluated with sera from 10 CM ‐allergic patients and 12 GM ‐allergic/ CM ‐tolerant patients. In CM ‐allergic patients, I g E reactivity of caprine fragments (f29‐107) and (f108‐207), but not (f1‐28), was similar to that of the bovine counterparts. In contrast, all bovine fragments were poorly recognized by I g E antibodies from GM ‐allergic/ CM ‐tolerant patients. The peptide (f29‐107) was generally the most immunoreactive fragment of caprine β‐ CN . By using synthetic peptides, the immunodominant I g E ‐binding epitope recognized by most GM ‐allergic/ CM ‐tolerant patients was located in the caprine domain 49–79. Conclusion The restricted specificity of the I g E response toward the caprine β‐ CN in GM ‐allergic/ CM ‐tolerant patients is mainly directed against the domain 49–79, which differs from its bovine counterpart by only three amino acid substitutions.