Human milk components cross-reacting with antibodies against bovine beta-lactoglobulin

The human whey components cross-reacting with antibodies raised against bovine and/or equine ?-lactoglobulin were screened systematically. The milk of six women on a normal diet was collected within 72 h of confinement and whey components were fractionated by high-speed size exclusion chromatography and reversed-phase techniques. The fractions which were immunoreactive in double diffusion experiments with antisera anti-bovine and/or equine ?-lactoglobulin were subsequently purified by native PAGE and then electroblotted on Pro-blott membrane (Western blotting). Pro-blot membranes were stained in parallel with Coomassie and by immunostaining using antibodies against bovine and/or equine ?-lactoglobulin as first antibody solution. The immunoreactive bands were cut out from the membrane and N-terminally sequenced; all the immunoreactive components were clearly identified as human ?-casein or its (mainly tryptic) fragments. The strong antigenic similarity between human ?-casein and ?-lactoglobulin (bovine and equine) might be of immunological importance; it could mean that breast-fed neonates risk being sensitized to ?-lactoglobulin irrespective of the presence of cow's milk in the mother's diet.