Lymphocytes and monocytes in the aortic intima--An electron-microscopic study in the rat

In an electron-microscopic survey of the aorta in the adult rat, white blood cells were found adhering to the intima; these were invariably lymphocytes or monocytes. Similar cells were also found beneath the endothelium. Counts were not made, but published data indicate that mononuclear cells lying over or within the rat aortic intima are approximately 1 for every 9 endothelial cells. This infiltration by blood-borne cells is interpreted as a pathologic event, possibly in response to a chemical message (antigen?) originating from the underlying media.