Section of lymph node (human)

Stain: Silver stain (Gomori). Due to the argyrophilia the reticular fibers are black-stained. They are derived from the fibrous capsule and penetrate into the deep cortex (i.e. paracortical area) and are embedded among other fibers such as collagen type III, IV. Note the postcapillary venules (*) which are surrounded by black-stained basement membranes (collagen IV). These specialized venules or so-called high endothelial venules (HEV) are lined by cuboidal or columnar endothelial cells that possess specific receptors for antigen-primed lymphocytes. These are the sites of entry of these lymphocytes into the lymph node (lymphocyte homing mechanism) where they leave the blood stream through these HEV and subsequently by diapedesis between the endothelial cells. B lymphocytes migrate to the lymphatic follicles in the cortex but T lymphocytes remain in the thymus-dependent area of the paracortex.