Role of C/EBPα in macrophage differentiation in vivo. C/EBPα^+/+ and C/EBPα^-/- FL cells were transplanted into lethally irradiated mouse recipients in combination with normal BMCs. Four to 6 months after transplantation, peripheral blood (A), PECs (B), and thioglycollate-elicited PECs (C) were analyzed by 3-color flow cytometry for donor-derived (Ly-5.1) granulocyte and macrophage with use of Gr-1, F4/80, and Mac-1 according to the procedures outlined in “Materials and methods.” (D) BMCs were obtained from mice that received transplants, and FACS was performed for donor-derived cells and plated in colony assays in the presence of the indicated cytokines according to the procedures outlined in “Materials and Methods.” These data are presented as the mean colony formation ± the SE and are representative of 2 separate experiments.