Characterization of circulating erythroid progenitor cells in human newborn blood.

The pattern of in vitro growth of erythroid progenitors in cord blood was assayed by the methyl cellulose culture system. The erythroid nature of colonies in culture was determined by Soret band examination for hemoglobin and by immunofluorescence for specific membrane protein spectrin, as well as by conventional techniques. In contrast to adult blood cultures, we found small but definite erythroid colony growth in the cultures of cord blood progenitors in the absence of added Ep (endogenous erythroid colonies). In addition, in the presence of Ep increased numbers of progenitors were found in cord blood compared with adult blood. Comparison of cultures from newborns, normal adults, anemic adults, and adults with PV and myelofibrosis showed that endogenous erythroid colonies are also found in cultures of patients with PV and myelofibrosis but not in cultures of normal cells and cells from anemic subjects. The physiologic relevance of these endogenous colony-forming cells in newborn blood is unknown; however, we speculate that they may be related to residual extramedullary erythropoiesis at birth.