The receptor for advanced glycation end products (RAGE) contributes to the inflammatory response in many acute and chronic diseases. In this context, RAGE has been identified as a ligand for the ␤ 2 -integrin Mac-1 under static in vitro conditions. Because intercellular adhesion molecule (ICAM)-1 also binds ␤ 2 -integrins, we studied RAGE ؊/؊ , Icam1 ؊/؊ , and RAGE ؊/؊ Icam1 ؊/؊ mice to define the relative contribution of each ligand for leukocyte adhesion in vivo. We show that trauma-induced leukocyte adhesion in cremaster muscle venules is strongly dependent on RAGE and ICAM-1 acting together in an overlapping fashion. Additional in vivo experiments in chimeric mice lacking endothelium-expressed RAGE and ICAM-1 located the adhesion defect to the endothelial compartment. Using microflow chambers coated with P-selectin, CXCL1, and soluble RAGE (sRAGE) demonstrated that sRAGE supports leukocyte adhesion under flow conditions in a Mac-1-but not LFA-1-dependent fashion. A static adhesion assay revealed that wild-type and RAGE ؊/؊ neutrophil adhesion and spreading were similar on immobilized sRAGE or fibrinogen. These observations indicate a crucial role of endotheliumexpressed RAGE as Mac-1 ligand and uncover RAGE and ICAM-1 as a new set of functionally linked adhesion molecules, which closely cooperate in mediating leukocyte adhesion during the acute traumainduced inflammatory response in vivo. IntroductionLeukocyte recruitment into inflamed tissue follows a well-defined cascade of events, beginning with the capture of free-flowing leukocytes to the vessel wall and subsequent leukocyte rolling along and adhesion to the inflamed endothelial layer. 1,2 During rolling, leukocytes get into close contact with the endothelial surface, which allows endothelial bound chemokines to interact with their specific receptors on the leukocyte surface. This triggers the activation of integrins, which leads to firm leukocyte arrest on the endothelium. In addition, integrindependent signaling events induce cytoskeletal rearrangements and cell polarization, modifications necessary in helping to prepare the attached leukocyte to spread and crawl in search for its way out of the vasculature into tissue. [2][3][4][5][6] Recent evidence has shown that the ␤ 2 -integrin Mac-1 is crucially involved in transducing Syk-dependent signaling events necessary for sustained leukocyte adhesion. [7][8][9] The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor that has been identified to be a major player in chronic inflammatory conditions. 10,11 This has been mainly attributed to its strong effects on perpetuating nuclear factor-B (NF-B) activation and NF-Bdependent signaling 10,11 and its ability to induce its own expression. 10,12 Besides its function as a signaling molecule, RAGE also binds to Mac-1, which has been demonstrated under in vitro conditions. 13 In addition, a reduction of leukocyte extravasation into the inflamed peritoneal cavity was found in RAGE Ϫ/Ϫ mice after intraperitoneal application of th...

BackgroundThe receptor for advanced glycation endproducts, RAGE, is involved in the pathogenesis of many inflammatory conditions, which is mostly related to its strong activation of NF-κB but also due to its function as ligand for the β2-integrin Mac-1. To further dissect the stimulus-dependent role of RAGE on leukocyte recruitment during inflammation, we investigated β2-integrin-dependent leukocyte adhesion in RAGE-/- and Icam1-/- mice in different cremaster muscle models of inflammation using intravital microscopy.ResultsWe demonstrate that RAGE, but not ICAM-1 substantially contributes to N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced leukocyte adhesion in TNF-α-pretreated cremaster muscle venules in a Mac-1-dependent manner. In contrast, fMLP-stimulated leukocyte adhesion in unstimulated cremaster muscle venules is independent of RAGE, but dependent on ICAM-1 and its interaction with LFA-1. Furthermore, chemokine CXCL1-stimulated leukocyte adhesion in surgically prepared cremaster muscle venules was independent of RAGE but strongly dependent on ICAM-1 and LFA-1 suggesting a differential and stimulus-dependent regulation of leukocyte adhesion during inflammation in vivo.ConclusionOur results demonstrate that RAGE and ICAM-1 differentially regulate leukocyte adhesion in vivo in a stimulus-dependent manner.