The migration of lymphocytes across the vascular endothelium in lymph nodes: a scanning electron microscopic study.

Endothelial cells of Postcapillary Venules (PCV) and the passage of lymphocytes through the wall of PCV were investigated with Scanning Electron Microscope (SEM) in mesenteric lymph nodes of rats. Individual endothelial cells of PCV in the lymph node did not have flat surface or were not typically cubic, but swelled at the central part assuming a foot ball-like shape. Circulating lymphocytes are considered to migrate into lymphatic tissues through the wall of PCV from the blood stream. Two hypotheses, inter-endothelial cell passage and intra-endothelial cell passage, have been proposed. The three-dimensional studies on lymphocytes passing the wall with SEM confirmed that migrating lymphocytes pushes their way through the intercellular space with pressing the adjoining endothelial cells from beginning to end, supporting the former hypothesis. Invasion of lymphocytes into endothelial cells were not observed.