581 ENRICHMENT OF HUMAN F-CELLS IN FETAL-MATERNAL BLOOD MIXTURES

Abstract

Recovery of fetus-origin red cells from maternal venous blood could facilitate diagnosis of fetal hemoglobinopathies by the single cell immunodiffusion method, using specific antibodies to Hb variants. Among 40 Black American women in mid-trimester pregnancy who presented for termination of pregnancy, and who had a Hb A phenotype by electrophoresis, the blood of 9 contained an occasional Hb S-cell. In only these 9 cases were S-cells found in the amniotic fluid. This finding prompted development of an F-cell enrichment procedure, assuming a majority of cells which migrate into maternal circulation from the midtrimester fetus contain Hb F. F-cells in term cord blood and from adults with Hb A, AS, or S were more resistant than A-cells or S-cells to hypotonic stress equivalent to 0.45 gm% NaCl. Cells were also subjected to sequential treatment by low Na and differential centrifugation in a molten agar gradient (45C). This yielded a cell fraction in which F-cells in blood of adults were changed from 6% to 48% and in cord blood from 48% to 90%, whereas centrifugation alone on the latter achieved 74% F-cells. Preliminary observations on enrichment of maternal blood in midtrimester pregnancy are equally promising.