Red blood cell and platelet induced differentiation of endothelial cells into capillary-like structure.

We cultivated endothelial cells of human umbilical vein origin in the presence of red blood cells and platelet-rich plasma, and observed the phenomena which occurred in the petri dish under phase contrast microscopy. Many small particles were observed after an overnight incubation. We washed the dish two times, then added thrombin to the dish. The network of thread-like strands appeared within 10 to 20 minutes of the addition, and at the same time the small particles adhered on the surface of the strands, swelled and fused gradually to cover the surface of the strands completely. Within 30 to 60 minutes the network of the strands changed into a capillary-like structure. These phenomena were not observed if we omitted red blood cells or platelet-rich plasma. Studies by transmission electron microscopy revealed that the inner surface of the lumen of the structure was covered with cells. The cells isolated from the lumen by trypsin grew to confluence in the conventional culture medium, and showed vWF antigen on their surface. These observations indicated that the method described is useful for in vitro study of angiogenesis.