The differences in significance of alpha 2,3Gal-linked and alpha 2,6GalNAc-linked sialic acid residues in blood group M- and N-related epitopes recognized by various monoclonal antibodies.

The blood group M and N determinants of glycophorin A (GPA) contain O-linked oligosaccharide chains with alpha 2,3Gal-linked and alpha 2,6GalNAc-linked sialic acid residues which are required for the activity of most epitopes recognized by various anti-M and anti-N antibodies. In order to check whether these two types of sialic acid residues differ in their contribution to antigenic properties, the GPA-M and GPA-N preparations with monosialylated oligosaccharide chains were obtained and tested for binding of anti-M and anti-N monoclonal antibodies (MAbs). The GPAs with sialic acid residues linked to Gal (GPA2,3) were obtained by selective resialylation of asialoGPAs with alpha 2,3-sialyl-transferase. These preparations were tested by inhibition of binding of MAbs to enzyme-linked immunosorbent assay (ELISA) plates coated with the respective untreated target antigens. The GPAs with sialic acid residues linked to GalNAc (GPA2,6) were generated by treating GPAs adsorbed on ELISA plates with Newcastle disease virus (NDV) isolate (expressing sialidase specific for alpha 2,3Gal linkage), which was followed by testing the binding of MAbs to NDV-treated antigens. Different patterns of activity were obtained among 14 MAbs specific for sialic acid-dependent epitopes (eight anti-M and six anti-N). The results indicated that at least half of the MAbs showed distinct requirements for the presence of only one of two kinds of sialic acid residues (Gal or GalNAc linked) in the epitope. Only four MAbs (two anti-M and two anti-N) did not react with any of the 'monosialylated' forms of GPA.(ABSTRACT TRUNCATED AT 250 WORDS)