We identified a novel Junctional Adhesion Molecule by a selective RNA display method. The protein was named JAM-2 based on its 30–40% homology to JAM and VE-JAM. The three JAMs define a novel subset of immunoglobulin superfamily molecules which will be referred to as JAM-1 (JAM), JAM-2 and JAM-3 (VE-JAM). JAM-2 is highly expressed by HEVs and lymphatic endothelial cells in lymphoid organs, suggesting that it may play a role in lymphocyte recirculation. The role of JAM-2 in inter-endothelial junctions has been addressed using endothelial cells over-expressing JAM-2 protein. These cells have an increased ability to sustain lymphocyte transmigration in agreement with the pattern of expression found in vivo. Transfected cells are also more permeable to FITC-dextran. Furthermore, an antibody directed against the extracellular domain of JAM-2 is able to partially block the transmigration. Our findings suggest that JAM-2 may facilitate lymphocyte extravasation across HEVs by rendering the inter-endothelial junctions more leaky. The role of JAM-2 in inflammatory processes will be discussed.

Reference

1. Aurrand-Lions M, Duncan L, Ballestrem C, Imhof BA. JAM-2, a novel immunoglobulin superfamily molecule, expressed by endothelial and lymphatic cells. J Biol Chem. 2001;276:2733–41