The constituents and mechanisms of generation of ‘endothelial cell—colony forming units’

Aims The formation of endothelial cell-colony forming units (EC-CFUs) is increased by vascular injury, although their function in vivo is unclear. We, therefore, examined the constituents of EC-CFUs and the mechanisms of their generation. Methods and results We performed immunohistochemical characterization of EC-CFUs and their mononuclear precursors. Using fluores-cent-activated cell sorting, we evaluated the capacity of mononuclear subpopulations to generate EC-CFUs, and mon-itored their migratory behaviour when co-incubated with EC-CFUs. Time-lapse microscopy was used to observe colony maturation. Cellular proliferation within EC-CFUs was assessed using bromodeoxyuridine (BrdU) and anti-proliferative agents. EC-CFUs exhibited typical endothelial characteristics; however, several endothelial markers were weakly expressed or absent. Macrophage and lymphocyte antigens were intensely expressed. EC-CFUs readily incorpo-rated BrdU, and failed to develop in the presence of anti-proliferative agents (P, 0.01; n 12). Time-lapse microscop