Monocyte/macrophage function in CFU-ECs. (A) Detection of cell surface expression of CD115 on CFU-EC and ECFC colonies by immunofluorescent staining. CFU-ECs express CD115 (green). Confocal photomicrographs are representative of 5 independent experiments using cells from different donors. Nuclei are stained with Hoechst 33342 (blue) and scale bar represents 200 μm. (B) Representative phase-contrast photomicrograph of CFU-EC colonies exposed to α-naphthyl acetate esterase with and without NaF inhibition. Similar nonspecific esterase activity was seen in CFU-EC colonies from 4 other donors. Scale bar represents 500 μm. (C) RT-PCR analysis of whole peripheral blood MNCs (M), CFU-ECs (C), and ECFCs (E) for gene expression of CD14, CD45, CD115, and β-actin. Left 3 lanes show reactions absent for reverse transcriptase. Results are representative of 5 independent experiments using cells from different donors. (D) Percentage of cells derived from CFU-EC or ECFC colonies that phagocytose E coli. Results represent the mean percentage of cells that phagocytose E coli ± SEM of 5 independent experiments. J774 murine monocytes were used as a positive control. *P < .001 by Student paired t test. (E) CFU-EC–derived cells demonstrate the ability to phagocytose E coli. Representative confocal photomicrographs of J774 murine monocytes, and CFU-EC– and ECFC-derived cells exposed to fluorescein-labeled E coli. Similar results were seen in 4 other experiments with cells derived from different donors. Nuclei are stained with Hoechst 33342 (blue) and scale bar represents 50 μm.