Regulation of Functional and Morphological Aspects of High Endothelium in Mouse
Lymphocyte migration and recirculation between lymphoid and also nonlymphoid tissues is essential for effective immunological surveillance. The entrance of blood-borne lymphocytes into peripheral lymphoid organs, such as lymph nodes and Peyer’s patches, occurs at particular vascular sites, so called post-capillary high endothelial venules (HEV;1,2). The endothelium of these HEV is unique in it’s capacity to mediate lymphocyte extravasation, and its characteristic cuboidal or ‘high’ cellular appearance. From recent investigations, it has become clear that subtile mechanisms are controlling a balanced and selective immigration of lymphocytes and lymphocyte subsets via HEV into mucosal and non-mucosal lymphoid tissues (3,4). Major contributions to studying lymphocyte extravasation and homing via interaction with high endothelium have been the production of monoclonal antibodies (MABs) against lymphocyte ‘homingreceptors’ for HEV (5,6,7), and the development of an elegant in vitro assays for lymphocyte-binding to HEV in frozen sections by Stamper and Woodruff (8). With these tools the nature and many aspects of the regulation of homing receptors on lymphocytes and lymphocyte subsets have been unraveled. However, little is known of the nature and regulation mechanisms of the specific sets of ligands on high endothelium involved in lymphocyte binding, nor about why this endothelium develops it’s characteristic high appearance and what mechanisms regulate this process. In this paper we will address mechanisms controlling specific functional and morphological qualities of high endothelium. We summarize some previous results obtained with HEV-specific MAB MECA-325, e.g. expression of the MECA-325 antigen in chronic inflammation and induction of the antigen in cultured endothelial cells by lymphokines (9,10). In addition, an in vivo model is described in which severe depletion of recirculating lymphocytes by irradiation affects endothelial height but not its lymphocyte-binding capacity or MECA-325 antigen expression. By injecting recirculating lymphocytes the characteristic high endothelial cell appearance can be quickly restored.
KeywordsControl Lymph Node Homing Receptor Mononuclear Cell Infiltrate Peripheral Lymphoid Organ Recirculate Lymphocyte
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