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Use of Allele-specific Glycophorin A Antibodies to Enumerate Fetal Erythroid Cells in Maternal Circulation



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Annals of the New York Academy of Sciences



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Glycophorin A (GPA) is the most abundant glycosylated protein on the erythrocyte cell surface. It is expressed in an erythroid lineage-specific manner, beginning late in terminal erythrocyte differentiation and is restricted to mature erthrocytes, reticulocytes and bone marrow and circulating erythroblasts. It is commonly used as a definitive marker of erythroid cell-types. The GPA gene is also the genetic determinant of the MN blood group. There are two common alleles at the GPA locus, GPA-M and GPA-N, that segregate in the human population at approximately equal frequencies. These alleles are codominant, with heterozygotes expressing approximately equal amounts 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 vivo human somatic mutation assay, determining the frequency of variant erythrocytes with allele-loss phenotypes. This has necessitated the development of sensitive immunocytochemical and flow cytometric techniques for detection of these rare mutational events. We have found that these techniques are easily adapted to the task of enumerating and isolating fetal nucleated erythrocytes. In the present study, a total of 220 sets of cord blood and maternal samples were obtained with informed consent for analysis with the GPA flow cytometric assay. Comparison of the frequency of allele loss and duplication variants (N/N) shows a clear and significant elevation in the mothers known to be carrying N/N babies versus either of the other two genetically defined populations. We would therefore estimate the number of fetal cells in the maternal circulation at term to be approximately the difference between our quantitative measurements of N/N cells in mothers of N/N babies and mothers of either M/M or M/N babies, or ~5 x 10-6 cells labeling distinctively with our allele-specific GPA antibodies.


Medical Specialties | Medicine and Health Sciences | Osteopathic Medicine and Osteopathy

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