Thrombin‐induced adherence of neutrophils to cultured endothelial monolayers: Increased endothelial adhesiveness

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Abstract
We examined the effects of α‐thrombin on the adherence of neutrophils to endothelial cell monolayers. Endothelial cells derived from the ovine pulmonary artery and ovine neutrophils were used. Thrombin (10−8 M) resulted in a time‐dependent increase in neutrophil adherence to the endothelium. The response was concentration‐dependent with a maximal response at 10−8 M. Thrombin did not induce neutrophil adherence either to plastic or to endothelial cell‐derived matrix. The adherence response was inhibited in the presence of α‐thrombin that had been inactivated with anti‐thrombin III (1U:1U) or with hirudin (1 U/ml). However, the addition of either anti‐thrombin III or hirudin simultaneously with α‐thrombin to the cultured endothelial monolayers did not prevent neutrophil adherence. The monoclonal antibody MoAb 60.3, which precipitates a complex of four neutrophil surface glycoproteins (CDw18) was used to further characterize the reaction. MoAb 60.3 decreased the thrombin‐induced adherence of neutrophils to the endothelial monolayer. Addition of 10−8 M thrombin to the endothelial monolayer for 60 min, followed by washing the endothelium with fresh medium, caused resting neutrophils to adhere to the endothelial monolayers. MoAb 60.3 decreased neutrophil adherence to the washed endothelium. The factor(s) responsible for adherence was partially transferable. Medium obtained from incubating endothelial monolayers with thrombin (10−8 M) for 60 min, adding hirudin to the medium to inactivate thrombin, and transferring it to untreated endothelial monolayers, elicited neutrophil adherence. The response was less than that obtained with thrombin alone (22.9 ± 2.3% vs. 12.9 ± 3.3%). The results indicate that the catalytic site of the thrombin molecule is responsible for the adherent activity. Thrombin elicits a rapid activation of endothelial cells with a response that involves the expression of endothelial adhesion sites and sites that interact with the neutrophil CDw18 adhesive glycoprotein complex. In addition, soluble transferable factor(s) which are generated by the endothelium also contribute to thrombin‐induced neutrophil adherence.