Thrombin-activated human endothelial cells support monocyte adhesion in vitro following expression of intercellular...

Thrombin, a central molecule in coagulation, is also involved in inflammation. Notably, thrombin induces endothelial neutrophil adhesion, P- and E-selectin expression, and chemokine production. We show here that thrombin induces expression of intercellular adhesion molecule-1 (ICAM-1; CD54) and vascular cell adhesion molecule-1 (VCAM-1; CD106) on human umbilical vein endothelial cells (HUVECs) associated with increased adhesion of monocytes. Thrombin increased mRNA steady-state levels and expression of ICAM-1 over 24 hours. Thrombin-induced VCAM-1 expression exhibited unusual kinetics, reaching maximum levels after 6 to 12 hours, but decreasing to near baseline after 24 hours. Thrombin activity on HUVECs was mediated through interaction with its specific receptor, because ICAM-1 and VCAM-1 expression were similarly induced by the 14-amino acid thrombin receptor-activating peptide. Thrombin-induced ICAM-1 and VCAM-1 expression was significantly inhibited by hirudin, but not by interleukin-1 receptor antagonist or anti-tumor necrosis factor alpha monoclonal antibody (MoAb). Thrombin-activated HUVECs significantly increased greater numbers of adhering THP-1 macrophagic cells, peripheral blood mononuclear cells, or purified monocytes than unstimulated HUVECs. This adhesion was inhibited by anti-CD18 and anti-CD49d MoAb, demonstrating that thrombin-induced ICAM-1 and VCAM-1 were functional. These results show that, in addition to selectins, thrombin directly induces a cytokine-independent expression of adhesion molecules of the Ig superfamily on HUVECs that may support firm leukocyte attachment during inflammation.