Ligation of CD31 (PECAM-1) on Endothelial Cells Increases Adhesive Function of vβ3 Integrin and Enhances β1 Integrin-Mediated Adhesion of Eosinophils to Endothelial Cells

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Abstract
We determined the role of the heterophilic interaction of vβ3 integrin on endothelial cells with CD31 on leukocytes in mediating leukocyte-endothelial cell interactions. Preincubation of interleukin-4 (IL-4)–stimulated human umbilical vein endothelial cells (HUVECs) with anti-CD31 monoclonal antibodies (MoAbs) enhanced eosinophil adhesion to the IL-4–stimulated HUVECs, and the endothelial CD31-induced enhancement of eosinophil adhesion to IL-4–stimulated HUVECs was prevented by anti–vascular cell adhesion molecule-1 (VCAM-1) MoAb and anti–very late activation antigen-4 (VLA-4) MoAb, but not by anti–intercellular adhesion molecule-1 (ICAM-1) MoAb, anti–lymphocyte function-associated antigen-1 (LFA-1) MoAb, anti–P-selectin MoAb, or anti–E-selectin MoAb. CD31 stimulation of HUVECs increased the adhesive function of vβ3 integrin to its ligand RGD peptide, the binding of which reached a maximum at 10 minutes after the stimulation, and the CD31-induced vβ3 integrin activation on HUVECs was inhibited by inhibitors of protein kinase C and phosphatidylinositol 3 kinase (PI3-kinase). Furthermore, anti-vβ3 integrin MoAb and RGD peptide as well as soluble CD31 inhibited endothelial CD31-induced enhancement of eosinophil adhesion to IL-4–stimulated HUVECs. However, anti-vβ3 integrin MoAb had no significant inhibitory effect on the eosinophil adhesion to IL-4–stimulated or unstimulated HUVECs without CD31 stimulation of HUVECs. Finally, CD31 stimulation of eosinophils increased the adhesive function of 4β1 integrin (VLA-4) to its ligand fibronectin and their adhesion to IL-4–stimulated HUVECs in a VLA-4–dependent manner. These results indicate that CD31-mediated inside-out signaling activates vβ3 integrin on endothelial cells, that the heterophilic vβ3 integrin/CD31 interaction induces β1 integrin-mediated adhesion of eosinophils to endothelial cells, and that the heterophilic interaction itself is not significantly involved in firm adhesion of eosinophils to endothelial cells.