Allergenic properties of the genetic variants A and B of bovine beta-lactoglobulin.

The principal allergen in cow's milk is beta-lactoglobulin (beta-Lg) which is normally found as equal mixtures of the A and B genetic variants in pooled milk. The A and B variants were purified in large amounts and fed to guinea pigs. After 15 days, circulating immunoglobulins IgG1 and IgG2 to the milk proteins were detected, with a somewhat higher response to beta-Lg A than B. Sensitised guinea pigs succumbed to anaphylactic shock when challenged intracardially with either variant. The higher response is likely to be due to amino acid residues found only in the A variant, lying in surface regions of the molecule.