Student Travel Award Recipient – Epitope Mapping of αS1-Casein by Microarray Immunoassay Reveals Differences in Ige Binding within Dairy Breeds and Between Water Buffaloes, Sheep, Goats

Maria Lisson, Department of Animal Breeding and Genetics, Justus-Liebig University, Gießen, Germany

Maria Lisson1, Natalija Novak2, Georg Erhardt1
1Department of Animal Breeding and Genetics, Justus-Liebig University, Gießen, Germany 2Department of Dermatology and Allergy, University of Bonn, Germany

The caseins belong to the major allergens in cow milk. Within these proteins, a noticeable genetic variation has been identified in productive and endangered cattle breeds. The genetic variants are characterized by amino acid exchanges or deletions of peptide fragments. Their importance in human nutrition, especially regarding to the allergenic potential, has not yet been adequately exploited. There is an increasing focus on the use of milk proteins from other species to identify an alternative protein sources for patients with cow milk allergy. Nevertheless, due to the high degree of amino acid sequence homology between the proteins from cow and other ruminant species, clinical cross-reactivity exists. This study investigated the influence of the genetic polymorphisms on the IgE binding properties of epitopes from the bovine αs1-casein variants A, B, C, D, E, F, G, H, and I. In addition, differences in IgE binding between epitopes of cow, sheep, goat, water buffalo, and camel were determined. On the basis of the IgE binding epitopes previously identified for αs1-casein of cow and of the corresponding peptides from goat, sheep, water buffalo, and camel, a set of 57 peptides was commercially synthesized and tested by means of microarray immunoassay for IgE binding by using sera from humans with cow milk allergy.
In the 5 αs1-casein variants A, B, C, E, and I, the amino acid substitutions and deletion affected the immunoreactivity of 5 epitopes leading to an abrogation or increase or decrease of IgE binding. Modifications in the immunoreactivity mainly concerned immunodominant epitopes and, in consequence, the allergenicity of the whole proteins is altered.
The majority of sera showed IgE binding to αs1-casein peptides of cow and the homologous counterparts of sheep, goat, as well as water buffalo, whereas peptides of camel were barely recognized. However, in most sera, epitopes from the non bovine species displayed lower immunoreactivities compared with those from cow. Moreover, IgE antibodies of individual sera reacted only with peptides of sheep or goat or water buffalo, or both, but not with the corresponding peptides of cow, even when the peptides were highly similar.
The results of this study demonstrated that genetic polymorphisms of αs1-casein influence the allergenic potential of IgE binding epitopes. Therefore, genetic variants of milk proteins should be taken into account into the search for a suitable protein source for patients with cow milk allergy. Furthermore, it was confirmed that milk from sheep, goat, and water buffalo harbor an allergenic potential due to cross-reactivity with αs1-casein peptides from cow and, consequently, milk from these species are not an appropriate replacement for cow milk in the nutrition of allergic subjects. On the other hand camel milk might be a promising protein source for patients with cow milk allergy.

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