Binding specificities of eight monoclonal antibodies to human glycophorin A--studies with McM, and MkEn(UK) variant human erythrocytes and M- and MNV-type chimpanzee erythrocytes.
Four newly derived mouse monoclonal antibodies to human glycophorin A are described. Three of these antibodies bind preferentially to the N form of glycophorin A; the fourth recognizes a shared determinant of the M and N forms. All four antibodies are directed toward the 39 amino acid, amino-terminal portion of the protein, and the N-specific antibodies require for binding the presence of N-acetyl-neuraminic acid on the glycosidically linked oligosaccharides. Cross-reaction of the N-specific antibodies to homozygous MM erythrocytes appears to result from binding to glycophorin B. In addition, these antibodies together with four previously reported glycophorin monoclonal antibodies, including two that specifically recognize the M form of glycophorin A, were tested for binding to McM and MkEn(UK) variant human erythrocytes and M- and MNV-type chimpanzee erythrocytes. Results obtained for five of the six M- or N-specific monoclonal antibodies point to the general immunodominance of the amino-terminal serine-leucine polymorphism and the requirement for sialic acid. One of the two M-specific monoclonal antibodies, 9A3, discriminates between the M, N, and Mc forms of glycophorin A solely on the basis of the amino-terminal serine-leucine polymorphism. The other M-specific antibody, 6A7, requires a more complex determinant involving the glycine-glutamic acid polymorphism at the fifth position in the sequence as well. The epitopes for all three N-specific monoclonal antibodies include the amino terminal leucine that occurs in the N form of glycophorin A and may also include the glutamic acid that occurs at position five. Our studies support the proposed Lepore-type glycophorin A-B hybrid gene rearrangement for the En(UK) allele found in the English En(a-) family. The data also confirm the expression of the M-like glycoprotein on chimpanzee erythrocytes and the presence of a human glycophorin B-like antigen on the MNV-type cells.