Expression of junctional adhesion molecules on the human lymphatic endothelium

Human lymphatic vessels express several leukocyte adhesion molecules. The study here investigated the expression of three junctional adhesion molecules (JAM) which are a newly reported glycoprotein family of adhesion molecules on human lymphatic endothelium. In this study, JAM-1 and JAM-3 but not JAM-2 were detected in cultured human neonatal dermal lymphatic endothelial cells (LEC) at the gene and protein levels by microarray, RT-PCR, real-time PCR, and immunohistochemical analysis. The JAM-1 and JAM-3 expression was not altered in the TNF-α-treated LEC or in the untreated cells. In human tissue, the expression of JAM-1, and the expression of JAM-1, JAM-2, and JAM-3 were observed in collecting lymphatic vessels of uninflamed small intestine, and in initial lymphatics of inflamed tongue and uninflamed gingival tissue. It is thought that JAM-2 mRNA could be produced in mature vascular endothelium but not in cultured cells, and that human intestinal and oral lymphatic vessels usually express JAM-1, JAM-2, and JAM-3. There were initial lymphatics simultaneously expressing JAM-1, JAM-2, and JAM-3 in the mucosal connective tissue papillae of gingival tissue. The three JAM expressions on the lymphatic endothelium may contribute to both seal the cell–cell contact at interendothelial junctions and also allow lymphocytes to transmigrate into lymphatic vessels from tissue, independent of inflammatory cytokines.