DEVELOPMENTAL REGULATION OF VASCULAR ADDRESSIN EXPRESSION - A POSSIBLE ROLE FOR SITE-ASSOCIATED ENVIRONMENTS

Tissue selective traffic of lymphocytes into different lymphoid organs is mediated by adherence of blood borne lymphocytes to specialized en dothelial cells lining the high endothelial venules (HEV) in lymphoid organs. Lymphocytes discriminate between HEV in peripheral lymph nodes and in mucosal lymphoid tissues by means of membrane associated lymph ocyte homing receptors adhering to their putative HEV ligands, the vas cular addressins. The expression of particular vascular addressins on HEV is site- or tissue-selective and may be directed by factors unique to a specific location or lymph node environment. In this study we in vestigated the impact of regional environments on lymph node HEV diffe rentiation and function. Experimentally, this problem was approached b y the transplantation of lymph nodes from one region to a second regio n. The sites selected for receipt of tissues were the mesentery, a muc osal site, and the popliteal fossa, a peripheral site. We found that t he phenotype of lymph node HEV following transplantation was influence d by both donor age and transplantation site. The transplantation site could influence vascular addressin expression, when tissues were obta ined from late fetal or early neonatal donors and not when obtained fr om adult donors. Transplanted adult tissues retained their pre-transpl antation vascular addressin expression phenotype regardless of transpl antation site. Thus the endothelium within adult lymph nodes may be co mmitted to expression of a particular addressin or addressins during l ymph node development. It is also possible that regulatory cells or st ructures present within lymph nodes at the time of transplantation dir ect vascular addressin expression following tissue engraftment. These studies show that regional environments of the lymph nodes could play a role in HEV differentiation and function during lymph node developme nt.