Transcellular migration of lymphocytes through the walls of the smooth-surfaced squamous endothelial venules in the lymph node: Evidence for the direct entry of lymphocytes into the blood circulation of the lymph node

Abstract

Observations by scanning (SEM) and transmission electron microscopy (TEM) show that the so-called postcapillary or high endothelial venules of the lymph nodes of the mouse are followed distally by venules of wider caliber, lined with a simple squamous endothelium, free from patent apertures and lacking the characteristic surface relief of the venules of immediate postcapillary location ( Cho and De Bruyn, 1979 ). Lymphocytes are in passage through the walls of these squamous endothelial venules. SEM shows that this transmural passage is transcellular, i.e., through the endothelial cell body and not through their cell junctions. A temporary migration pore is formed in the endothelial cytoplasm, which closes after the transcellular lymphocyte passage is completed. The SEM and TEM images of these sites of transcellular passage support the supposition that lymphocytes enter the blood circulation through the walls of these squamous endothelial venules.