A CD99-related antigen on endothelial cells mediates neutrophil but not lymphocyte extravasation in vivo

Abstract

CD99 is a long-known leukocyte antigen that does not belong to any of the known protein families. It was recently found on endothelial cells, where it mediates transendothelial migration of human monocytes and lymphocyte recruitment into inflamed skin in the mouse. Here, we show that CD99L2, a recently cloned, widely expressed antigen of unknown function with moderate sequence homology to CD99, is expressed on mouse leukocytes and endothelial cells. Using antibodies, we found that CD99L2 and CD99 are involved in transendothelial migration of neutrophils in vitro and in the recruitment of neutrophils into inflamed peritoneum. Intravital and electron microscopy of cremaster venules revealed that blocking CD99L2 inhibited leukocyte transmigration through the vessel wall (diapedesis) at the level of the perivascular basement membrane. We were surprised to find that, in contrast to CD99, CD99L2 was not relevant for the extravasation of lymphocytes into inflamed tissue. Although each protein promoted cell aggregation of transfected cells, endothelial CD99 and CD99L2 participated in neutrophil extravasation independent of these proteins on neutrophils. Our results establish CD99L2 as a new endothelial surface protein involved in neutrophil extravasation. In addition, this is the first evidence for a role of CD99 and CD99L2 in the process of leukocyte diapedesis in vivo. IntroductionLeukocytes are recruited into inflamed tissue via endothelial adhesion molecules and chemoattractants. [1][2][3][4] Upon docking to the endothelial surface, which is mediated mainly via selectins and leukocyte integrins, leukocytes transmigrate through the vessel wall, a process called diapedesis. 5,6 Leukocytes have been reported to traverse the endothelial cell layer on either a transcellular or a paracellular junctional route. 7,8 Almost all known endothelial membrane and adhesion molecules that participate in the diapedesis process are located at endothelial cell contacts and are therefore likely to participate in the junctional migration of leukocytes.Vascular/endothelial cadherin (VE-cadherin) represents a barrier on this route, because adhesion-blocking antibodies against VE-cadherin accelerate recruitment of leukocytes into inflamed tissue. 9 In contrast to VE-cadherin, all other endothelial cell contact proteins assist in the diapedesis process. All of these proteins except one are members of the immunoglobulin supergene family (Ig-SF), such as platelet-endothelial cell adhesion molecule (PE-CAM)-1, 10,11 members of the junctional adhesion molecule (JAM) family, 12-14 endothelial cell-selective adhesion molecule (ESAM), 15 intercellular adhesion molecule (ICAM)-2 16 and polio virus receptor (PVR), 17 a member of the nectin family. It is not yet known how they function in detail and it will be a challenging goal for the future to elucidate potential cascades and the interplay of these endothelial cell contact proteins during leukocyte diapedesis.One of the most recently identified proteins participating in leukocyte diapedesis is CD...

PECAM-1: A Multi-Functional Molecule in Inflammation and Vascular Biology

“…57 Specifically, although both molecules mediate neutrophil transendothelial cell migration in vitro and in vivo, CD99L2, in contrast to CD99, but similar to another endothelial cell junctional molecule ESAM, does not mediate lymphocyte transmigration in a model of delayed type hypersensitivity. 57,58 Furthermore, as found with PECAM-1, CD99L2 appears to block neutrophil transmigration in vivo at the level of the perivascular basement membrane, though the mechanism by which it can achieve this is at present unclear. 57 Studies from our group have also compared the functional role and potential additive effects of PECAM-1 with JAM-A and ICAM-2.…”

Esm1 Modulates Endothelial Tip Cell Behavior and Vascular Permeability by Enhancing VEGF Bioavailability

“…23,24 All animal procedures were performed in accordance with national and regional laws and regulations and were approved by animal ethics committees. All efforts were made to minimize suffering of the mice.…”

CD99 Triggering in Ewing Sarcoma Delivers a Lethal Signal through p53 Pathway Reactivation and Cooperates with Doxorubicin

“…The crucial biologic processes involving CD99 include lymphocyte development, cell adhesion and monocyte diapedesis, and expression of TCR, MHC class I and II as well as of some adhesion molecules (i.e., ELAM-1, VCAM-1, ICAM-1) by mobilization of these molecules from the Golgi to the plasma membrane (7)(8)(9)(10)(11)(12)(13)(14). In pathology, CD99 is found on the cell surface of EWS, acute lymphoblastic leukemia, thymic tumors, some spindle cell tumors (e.g., synovial sarcoma), hemangiopericytoma, meningioma, and malignant glioma, in which it confers high invasiveness and low survival rates (13,(15)(16)(17)(18).…”