Human endothelial cells derived by trypsinization of umbilical vein and artery were grown in
cell culture and compared with fibroblasts grown from explants of umbilical cord. Two types
of cells were recognized in endothelial cultures: endothelial cells proper and macrophages.
The former replicated very slowly and could not be maintained by subculture. Macrophages
constituted about 5% of the total cell popu-lation. They replicated slightly more rapidly than
the true endothelial cells and were not derived from these cells. Neither cell type was …