Structural homology of human, bovine, and porcine milk lactoferrins: evidence for shared antigenic determinants.

Although some degree of structural homology has been demonstrated among lactoferrins of different species, other reports suggest that these proteins are immunologically distinct. Human, bovine, and porcine lactoferrins were purified to homogeneity from colostral whey by affinity chromatography on immobilized single-stranded DNA. Evidence for shared antigenic determinants among human, bovine, and porcine lactoferrins was demonstrated by Ouchterlony immunodiffusion and immuno "dot" blots using whole antisera and purified Ig directed against each species of lactoferrin. There was no evidence that human transferrin was recognized by any of the lactoferrin-specific antisera evaluated. The degree of cross-reactivity between the lactoferrins and their trypsin digestion products was also evaluated after SDS-PAGE by immunoblotting. These data demonstrate that human, porcine, and bovine lactoferrins share common antigenic determinants and are likely to be more homologous in tertiary structures than suggested previously. Thus, investigations of human or bovine lactoferrin metabolism in infants that are based upon immunologic methods alone should be conducted cautiously in those cases where the presence of both human and bovine lactoferrin is suspected.