In vitro proliferation of endothelial cells from kitten retinal capillaries.

When microvessel (predominantly capillary) fragments freshly isolated from the retinas of young kittens are incubated in tissue culture medium, we observe the slow outgrowth of cells that appear to be derived from the capillary endothelium. The cells grow as a monolayer with a tightly packed, mosaic-like array. Electron microscopy of these cells reveals "tight junctions" (zonulae occludentes) resembling those found in the endothelium of intact capillaries.