Background: Cow's milk is one of the most frequent food allergens. Whole casein appears to be highly allergenic. It corresponds to an association of four different proteins, alpha(s1)-, alpha(s2)-, beta- and kappa-caseins in approximate proportions of 40, 10, 40, and 10%, respectively.
Methods: These different components were thus purified and used as immobilized antigens in an original enzyme immunoassay to measure specific serum IgE response in a population of 58 children (median age 11 months) allergic to cow's milk who were sensitive to whole casein.
Results: A great variability was observed in the affinity and specificity of specific IgE responses in milk-allergic patients' sera. 85% of the patients presented IgE against each of the four caseins. Statistically higher amounts of specific IgE were found to be directed against the most abundant fractions (alpha[s1]- and beta-casein). Co- and/or cross-sensitization to the different caseins were seen in most of the patients sensitive to whole casein.
Conclusion: These results suggest that both distinct and common epitopes may occur on these different caseins. The major site of phosphorylation which is the most conserved domain in three caseins could be involved in the IgE response to casein and in immunocross-reactivity between these proteins.