Antibody to Epiglycanin and Radioimmunoassay to Detect Epiglycanin-Related Glycoproteins in Body Fluids of Cancer Patients

Abstract

By means of a radioimmunoassay, which utilized [¹²⁵I]-epiglycanin and anti-epiglycanin antiserum induced in rabbits by injections of viable TA3-Ha ascites cells with Freund's complete adjuvant, picogram quantities of epiglycanin could be detected. Anti-epiglycanin antiserum was similarly produced in allogeneic mice. Unlabeled epiglycanin lost the capacity to compete with [¹²⁵I]epiglycanin in the radioimmunoassay as a result of periodate oxidation or incubation with endo-a-N-acetyl-d-galactosaminidase (Diplococcus pneumoniae), an enzyme found to cleave only the disaccharide β-d-galactopyranosyl-(1-3)-2-acetamido-2-deoxy-d-galactose chain from serine or threonine residues in epiglycanin. Glycosylhydrolases known to cleave α-d-mannose, β-d-galactose (1,4-linked), β-N-acetyl-d-glucosamine, and α-N-acetyl-d-galactosamine did not reduce the activity of epiglycanin. Neuraminidase enhanced the activity twofold to fivefold. The finding that little or no activity was demonstrated by the disaccharide, the reduced disaccharide, or other glycoproteins containing the same disaccharide chain suggested that the antigenic determinant probably involved the disaccharide and a unique amino acid sequence at the site of its attachment. By means of the radioimmunoassay epiglycanin cross-reactive antigens were detected in the peritoneal or pleural fluid and in the sera of patients with metastatic cancer. Lower concentrations of epiglycanin-like antigen(s) were found in the peritoneal fluid of patients with hepatitis or liver cirrhosis but not in normal serum.