The migration of lymphocytes through the endothelium of venules in lymph nodes: an electron microscope study

Abstract The post-capillary venules in the lymph nodes of rats have been examined with the electron microscope. The walls of these vessels normally contain many small lymphocytes, some of which are penetrating the endothelium while others are passing through the periendothelial sheath; most of the lymphocytes lie between the endothelium and the periendothelial sheath. No other leucocyte is normally present. The evidence suggests that these venules are normally the site of a large-scale migration of lymphocytes from the blood into the lymph nodes. A study of serial sections showed that lymphocytes migrate across the vessel wall by entering the endothelial cells and traversing their cytoplasm; they do not pass through the intercellular junctions. On the other hand, in inflamed lymph nodes polymorphs and monocytes emigrate through the venules by penetrating the junctions between endothelial cells. Some of the ‘large lymphocytes’ in thoracic duct lymph from normal rats were found to contain endoplasmic reticulum while others had a prominent Golgi complex.