Diverse specificities of five monoclonal antibodies reactive with glycophorin A of human erythrocytes.

Glycophorin A (GPA), the major sialoglycoprotein of human red cells, bears blood group MN determinants, and is a useful marker of the erythroid lineage in differentiating cells. Five monoclonal antibodies that react with GPA and possess a spectrum of serologic properties and fine specificities were obtained by immunization of mice with umbilical cord erythrocytes. Three antibodies, B22A, D22 and E11B, did not agglutinate En(a-) erythrocytes, genetic variants that lack GPA, and F11 and J11A agglutinated these cells very weakly. Antibodies B22A, E11B, and F11 agglutinated protease-treated cells more strongly than untreated erythrocytes, and they appeared to react with a peptide determinant located on the C-terminal side of the site at which trypsin cleaves GPA in the intact erythrocyte. In contrast to B22A and E11B, the hemagglutinating activity of F11 was not inhibited by purified GPA, nor did it bind to GPA in a solid phase immunoassay, but it immunoprecipitated GPA. Antibodies D22 and J11A appeared to be directed against carbohydrate determinants, or conformational determinants created by hydrogen bonding or electrostatic interactions between carbohydrate and protein. A preferential reaction of antibody J11A with MM over NN GPA was demonstrated by its reactions with enzyme-treated erythrocytes, its inhibition by purified GPA or its tryptic fragments, and by an ELISA assay.