HIGH ENDOTHELIAL VENULES OF THE RAT LYMPH-NODE - A REVIEW AND A QUESTION - IS THEIR ACTIVITY ANTIGEN-SPECIFIC

Background: The high endothelial venules (HEVs) of the lymph nodes are sites for transvascular lymphocyte traffic. Due mostly to the wide sc ale of variations manifested by the HEVs and to frequently restricted conditions of observation, reports often differed on their morphologic al or functional features, which has led to opposing views on aspects of the functioning of HEVs. Methods: In the present review, we analyze previous reports and attempt to derive comprehensive proposals to rec oncile variations in actual observations under diverse conditions. Res ults: This analysis shows that the features typical of the HEV endothe lial cells (HEV cells) are stimulated to emerge by antigens and the pr oper lymphocytes and mediators. The stimulation would implicate draine d lymphocytes migrating in the perivascular channel, immediately cuffi ng an HEV's endothelium. A marked pleomorphism of HEV cells betrays th e fact that they undergo individual stimulation and a somewhat heterog eneous activity. Other facts indicate that the subendothelial spaces o f HEV cells are sites of interactions between drained lymphocytes, HEV cells, and recruited blood lymphocytes. Facts also reveal time- and s ite-related variations in the intensity of recruitment of blood lympho cytes by HEV cells and topographically related variations in the natur e of the recruited cells. Conclusions: Analysis of same other observat ions, often ignored, lead to the conclusion that recruitment of lympho cytes by HEV cells for the sake of participating in local specific imm une activities is antigen specific, despite the implication of homing receptors of lymphocytes. (C) 1996 Wiley-Liss, Inc.