Two- and three-dimensional ultrastructural observation of two cell angiogenesis in human granulation tissue.

The growth of endothelial sprouts from capillary walls in human granulation tissue has been examined by two- and three-dimensional electron microscopy using a serial sectioning method. Within the parent capillary wall endothelial sprouts composed of two layers of relatively immature endothelium was demonstrated. Three-dimensional reconstruction revealed that the two layered endothelial projections extended and/or migrated outward in a bicellular configuration, the slit-like lumen of the endothelial sprout connecting with the parent capillary lumen. These ultrastructural appearances have not been reported previously with sequential composition to the morphological progression of the sprout. In the cytoplasm of the endothelial sprout, abundant intermediate filaments were assumed to play a mechanical role, tension resistance, in the development of the endothelial sprout. The active endothelial sprout in granulation tissue was considered to be at least partially responsible for the growth of the capillary network and subsequent development of granulation tissue.