IgE and IgG binding epitopes on alpha-lactalbumin and beta-lactoglobulin in cow's milk allergy

Cow's milk is one of the most common causes of food allergy in the first years of life. We recently defined IgE and IgG binding epitopes for alpha(s1)-casein, a major cow's milk allergen, and found an association between recognition of certain epitopes and clinical symptoms of cow's milk allergy (CMA). Since alpha-lactalbumin (ALA) and beta-lactoglobulin (BLG) are suspected to be significant allergens in cow's milk, we sought to determine the structure of sequential epitopes recognized by IgE antibodies to these proteins. We further sought to assess the pattern of epitope recognition in association with the clinical outcome of CMA.

According to the known amino acid sequence of ALA and BLG, 57 and 77 overlapping decapeptides (offset by two amino acids), respectively, were synthesized on a cellulose derivatized membrane. Sera from 11 patients 4-18 years of age with persistent CMA (IgE to cow's milk >100 kU(A)/l) were used to identify IgE binding epitopes. In addition, 8 patients < 3 years of age and likely to outgrow their milk allergy (IgE to cow's milk < 30 kU(A)/l) were used to investigate the differences in epitope recognition between patients with 'persistent' and those with 'transient' CMA. Seven patients 4-18 years of age were used for assessing the IgG binding regions.

In patients with persistent allergy, four IgE binding and three IgG binding regions were identified on ALA, and seven IgE and six IgG binding epitopes were detected on BLG. The younger patients that are likely to outgrow their allergy recognized only three of these IgE binding epitopes on BLG and none on ALA.

The presence of IgE antibodies to multiple linear allergenic epitopes may be a marker of persistent CMA. The usefulness of IgE binding to distinct epitopes on whey proteins in defining the patients that would have a lifelong CMA needs to be investigated in further studies.