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 chemica l nature of the antibody binding site was obtained by altering the structur e 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 epiglyca nin. The need for a high molecular weight antigen containing clustered T di saccharide, Gal beta 1-3GalNAc, was demonstrated. The specificity was furth er explored by inhibition studies with glycopeptides having one to three mo no- to disaccharides. The results were interpreted using computer graphics molecular modeling which predicted the specific recognition of hydroxyl gro ups on oligosaccharides on adjacent amino acids. Thus T antigen O-linked gl ycopeptide tumour markers can be designed to be distinguished by antibodies by the amount of clustering of their oligosaccharides.