Studies of hemoglobin expression in erythroid cells of early human fetuses using anti-gamma- and anti-beta-globin chain fluorescent antibodies.

Cells from early human fetuses were analyzed for gamma- and beta-globin expression by means of monospecific and monoclonal anti-gamma- and anti-beta-chain antibodies. We found that gamma-chain synthesis in embryonic (yolk sac) nucleated cells is either absent or it is below the threshold of sensitivity of the fluorescent antibody method (about 0.1 pg of hemoglobin per cell or less). In the earliest embryo studied (38 days old) all the liver-origin erythroid cells were labeled intensely by the anti-gamma-chain monoclonal. The majority of the liver-origin erythroblasts in a 45-day-old fetus were labeled with the anti-beta-chain monoclonal. These findings suggest that beta-gene expression is present in the earliest fetus in which globin expression was studied immunochemically. Histochemical and immunochemical staining of early fetal livers clearly shows that this organ is infiltrated by embryonic erythroblasts of hematogenous origin. The coexistence of embryonal and liver-origin erythroid cells in the early fetuses makes biochemical and molecular analyses of erythropoiesis in these fetuses uninformative unless care is taken to separate the two populations from each other with density methods.