Endothelial - Leukocyte Adhesion Molecule 1 Stimulates the Adhesive Activity of Leukocyte Integrin CR 3 ( CD 11 b / CD 18 , Mac - 1 , CiJ 2 ) on Human Neutrophils

Two classes of adhesion molecules have well-defined roles in the attachment of unstimulated polymorphonuclear leukocytes (PMN) to cytokine-treated endothelial cells. Endothelial-leukocyte adhesion molecule 1(ELAM-1) on endothelial cells interacts with specific carbohydrate residues on the PMN, and the leukocyte integrins (CD18 antigens) on PMN interact with intracellular adhesion molecule 1 and other structures on endothelium . Here we show that these two classes of molecules can act sequentially in an "adhesion cascade". Interaction of PMN with SLAM-1bearing endothelial cells causes PMN to express enhanced adhesive activity of the integrin CR3 (CD11b/CD18) . Expression of ELAM-1 on the cytokine-treated endothelium appears both necessary and sufficient for the stimulation of CR3 activity since blockade ofELAM-1 with mAbs prevents the activation ofCR3 by cytokine-treated endothelium, and immobilized recombinant ELAM-1 activates CR3. The ability to activate CR3 is shared by chemattractants, suggesting that ELAM-1 may serve as a "tethered chemattractants" This hypothesis is strengthened by the observation that recombinant soluble ELAM-1 directs movement of PMN in chemotaxis chambers. These results suggest a mechanism by which multiple adhesive molecules may function together in diapedesis. ELAM-1 serves both as an adhesin and as a trigger that recruits the participation of additional adhesion molecules. Our results also suggest that ligands for adhesion molecules may also be "receptors" capable of generating intracellular signals.