The role of carbohydrate in the blood group N-related epitopes recognised by three new monoclonal antibodies

The specificity of three new monoclonal anti-glycophorin antibodies, reacting preferentially with blood group N antigen, was characterized by means of untreated, enzymatically and chemically modified M and N glycoproteins. All antibodies recognized the NH₂-terminal Leu residue and its amino group, but differed in some other features, including the role of carbohydrate in the epitopes. One of the antibodies (631/3B4, IgM) showed an unusual two-directional dependence of activity on the degree of antigen desialylation. The progressive desialylation of N glycoprotein first caused a strongly increased binding to the epitope, followed by a complete loss of activity. The epitopes for the two remaining antibodies (648/4B5 and 650/4B5, both IgG₁) showed reactivity independent of sialylation, but dependent on the presence of Gal-GalNAc-units. Release of the disaccharide byO-glycanase treatment of N glycoprotein abolished its reactivity with both antibodies.