Late expression of M and N antigens on glycophorin A during erythroid differentiation.

The M/N blood groups are carried by the major human red cell sialoglycoprotein, glycophorin A. O-glyosidic carbohydrate is needed for the activity, but the M/N specificity is due to amino acid replacements in the NH2-terminal portion of the molecule. We have used monoclonal antibodies specific for M and N blood groups to study their expression during normal erythropoiesis. Here we report that the M/N blood group activities are very weakly or not at all expressed before the polychromatic normoblast stage. Using polyclonal anti-glycophorin A antiserum, it was shown that glycophorin A molecules are already abundantly present on the earliest morphologically recognizable erythroid precursor, the proerythroblast. These findings can be explained by our previous observation that the O-glycosylation of glycophorin A gradually increases during erythroid maturation.