Monoclonal antibodies to human transferrin: epitopic and phylogenetic analysis.

Monoclonal antibodies (MAbs) are useful reagents for the study of the structure and evolution of specific epitopes. Two MAbs of IgG1 isotype, Tf-1 and Tf-2, which bind human transferrin have been produced and characterized. Both specifically recognize transferrin on immunoblots of serum. Proteolytic digestion with papain or chymotrypsin destroys the epitope recognized by Tf-1 but not Tf-2, demonstrating that the MAbs recognize distinct epitopes. Both epitopes are not recognized after treatment with 2-mercaptoethanol, suggesting that disulfide bond dependent tertiary structure is necessary for epitope integrity. Removal of carbohydrate moieties by treatment with trifluoromethane sulfonic acid likewise results in loss of reactivity. Neither MAb reacts with transferrin of mouse, rabbit or bovine origin. Both were tested for reactivity to a total of ten primate transferrins and showed different patterns of reaction. Tf-2 recognized human, chimpanzee and gorilla transferrins, whereas Tf-1 reacted with all Old World monkeys and one of three New World monkeys tested. Thus, Tf-1 and Tf-2 recognize transferrin epitopes with differential phylogenetic conservation and which are dependent not only on primary aminoacid sequence, but also upon tertiary structure and glycosylation.