In vitro morphologic characterization of CD14⁺/VEGFR-2⁺ and CD14⁺/VEGFR-2^- cells. (A) Transmission electron micrographs illustrate that CD14⁺/VEGFR-2⁺ cells demonstrated the presence of tight junctions typical for endothelial cells (arrows; bar = 2 μm) and (B) Weibel-Palade bodies (arrow; bar = 0.5 μm) and (C) produced basement membrane (M; bar = 1μm). (D) CD14⁺/VEGFR-2^- cells in culture did not form colonies, whereas the CD14⁺/VEGFR-2⁺ cells formed colonies initially consisting of rounded cells that, after 1 week, grew out as single elongated cells. After 1 week in culture, only the CD14⁺/VEGFR-2⁺ cells expressed VE-cadherin (black surface staining). (E) Significantly higher numbers of CD14⁺/VEGFR-2⁺ cells were BrdU⁺ compared with CD14⁺/VEGFR-2^- cells.