More Than One-Half of the Erythroblasts in the Fetal Circulation and Cord Blood Are TUNEL Positive

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Abstract
The relationship between the transfer of fetal cells to the maternal circulation and the identification of cell-free fetal DNA in maternal plasma has raised many questions and prompted us and others to investigate the possible involvement of apoptosis in this process. van Wijk et al. (1) recently reported the presence of a relatively large number of TUNEL (terminal dUTP nuclear end labeling)-positive cells (which the authors considered as being apoptotic cells) in maternal plasma. Sekizawa et al. (2) showed that a large percentage of TUNEL-positive cells in the maternal circulation in posttermination samples were fetal erythroblasts. Thus, these authors suggested that apoptosis of fetal cells induced by the maternal immune system may play a role in the clearance of fetal cells from the maternal circulation without causing inflammatory damage to the mother. The morphology of erythroblasts changes dramatically, however, during terminal erythroid differentiation and enucleation, and some of these changes share similarities with apoptotic processes (3).