The endothelium of the high endothelial venule: a specialized endothelium with unique properties.

High endothelial venules (HEV) in lymphoid organs are specialized to facilitate the passage of lymphocytes into lymphoid parenchyma. This is accomplished by a ligand-receptor system on the endothelium and lymphocytes, which differs between lymph nodes and Peyer's patch. Experiments discussed in this paper show that other non-HEV-derived endothelial cells can acquire the characteristics of HEV and that HEV may differentiate under influences from their local micro-environments.