Production of fetal antigen-bearing erythrocytes in irradiated adult mice grafted with fetal liver hematopoietic cells.

The production of erythrocytes bearing an "immature" antigen (Im+ cells) and a "fetal" antigen (Ft+ cells) has been studied in irradiated adult mice grafted either with fetal liver or adult bone marrow cells. The Im+ cells reach a peak 8-11 days after grafting. Ft+ cells are detected only after graft of fetal liver cells; the younger the liver, the greater the number. Since Ft+ cells are rapidly and briefly produced, they could be the progeny of erythroid-committed precursors, which are particularly numerous among fetal liver cells. Environmental factors directing the erythropoietic differentiation towards Ft+ erythrocytes in fetuses or Ft- erythrocytes in adults are proposed.