Specificity studies of an antibody developed against a mucin-type glycoprotein.

The specificity of a new anti-epiglycanin antibody (AE-3) which recognizes a mucin-type glycoprotein, the Human Carcinoma Antigen, found in the blood of patients with carcinomas, was studied. Information regarding the chemical nature of the antibody binding site was obtained by altering the structure of epiglycanin by chemical or enzymic means and testing the product in a competitive binding assay for inhibition of the binding of AE-3 to epiglycanin. The need for a high molecular weight antigen containing clustered T disaccharide, Gal,1-3GalNAc, was demonstrated. The specificity was further explored by inhibition studies with glycopeptides having one to three mono- to disaccharides. The results were interpreted using computer graphics molecular modeling which predicted the specific recognition of hydroxyl groups on oligosaccharides on adjacent amino acids. Thus T antigen O-linked glycopeptide tumour markers can be designed to be distinguished by antibodies by the amount of clustering of their oligosaccharides.