Role of conformational and linear epitopes in the achievement of tolerance in cow's milk allergy

Background: Cow's milk (CM) is one of the leading causes of food allergy in children. However, approximately 85% of milk-allergic children become clinically tolerant to CM within the first 3 years of life. The mechanisms involved in the achievement of tolerance remain unknown. Objective: To study whether IgE antibodies from children with persistent cow's milk allergy (CMA) differ from children who become clinically tolerant in their ability to recognize linear and conformational epitopes of α_s1- and β-casein. Methods: Thirty-six milk-allergic children were included in the study: 11 of the children became clinically tolerant, and 25 had persistent CMA. Blood was obtained from all patients during the time they showed clinical reactions to milk challenge. Six non-milk-allergic children served as controls. Specific IgE antibodies against linear (denatured) as well as conformational (native) milk proteins were determined by probing dot-blots with patients' sera. In addition, selected decapeptides from α_s1- and β-casein, previously found to be suggestive of persistent CMA, were synthesized on a cellulose-derivatized membrane and probed with individual sera from 10 patients who outgrew CMA and from 10 patients with persistent CMA. Results: Analysis of immunodot-blots showed that, in comparison to tolerant patients, milk-allergic children with persistent symptoms had a significantly higher ratio of specific IgE antibodies to linearized than to native α- and β-casein (P<0.005 and P<0.02, respectively). Comparing the selected decapeptides, six of the 10 patients with persistent allergy recognized the peptide corresponding to amino acids 69-78 from α_s1-casein while none of the patients who outgrew CMA had IgE binding to this epitope. Conclusion: Patients with persistent milk allergy possess higher detectable levels of IgE antibodies to linear epitopes from α_s1- and β-casein than children who have achieved tolerance. Specific IgE binding to particular linear epitopes in α_s1-casein may be a predictive factor for persistence of CMA.