Use of allele-specific glycophorin A antibodies to enumerate fetal erythroid cells in maternal circulation.

Abstract

Glycophorin A (GP A) is the most abundant glycosylated protein on the erythrocytecell surface. It is expressed in an erythroid lineage-specific manner, beginning late.in terminal erythrocyte differentiation and restricted to mature erythrocytes, reticulo-cytes, and bone marrow and circulating erythroblasts. It is commonly used as adefinitive marker of erythroid cell-types. The GP A gene is also the genetic determinantof the MN blood group. There are two common alleles at the GPA locus, GPAM andGPAN, that segregate in the human population at approximately equal frequencies.These alleles are codominant, with heterozygotes expressing approximately equalamounts of each form of the protein on their cell surface.We have used this polymorphism at the GPA locus as the basis for an in vivohuman somatic mutation assay, determining the frequency of variant erythrocyteswith allele-loss phenotypes.1,2 This has necessitated the development of sensitiveimmunocytochemical and flow cytometric techniques for detection of these raremutational events. Besides our experience with rare event detection, our work hasgiven us a unique perspective on the genetics of red cell surface markers. We havefound that these techniques could be easily adapted to the task of enumerating and