THROMBIN INDUCES ENDOTHELIAL TYPE-II ACTIVATION IN-VITRO - IL-1 AND TNF-ALPHA-INDEPENDENT IL-8 SECRETION AND E-SELECTIN EXPRESSION

In addition to its role in coagulation, thrombin is involved in the in flammatory process by inducing vessel neutrophilic infiltration. Throm bin induces endothelial P-selectin expression and platelet activating factor release, which participate to induce early neutrophil adhesion and activation. We employed HUVEC and now show that thrombin induces t he production of the chemokine IL-8 in a time- and dose-dependent fash ion. Similarly, thrombin induced E-selectin expression on HUVEC, Both IL-8 secretion and E-selectin expression were preceded by an increase in steady state levels of the respective mRNAs. Thrombin action on HUV EC was inhibited by the specific thrombin inhibitor, hirudin. In addit ion, these effects of thrombin on HUVEC were mimicked by the 14-amino acid thrombin receptor agonist peptide, which triggers the native thro mbin receptor in a similar fashion to thrombin itself. Although IL-1 a nd TNF-alpha also induce IL-8 and E-selectin, the thrombin effects in these experiments were not mediated by those cytokines, since neither IL-1 receptor antagonist nor anti-TNF-alpha Ab inhibited the effects o f thrombin. Furthermore, IL-1 alpha, IL-1 beta, and TNF-alpha were not detected in the supernatants of thrombin-activated HUVEC. Although in tracellular IL-1 alpha was found in thrombin-activated HUVEC, antisens e IL-l Lu had no inhibitory effect on IL-8 secretion. These results de monstrate that in addition to short term endothelial activation, throm bin also functions as a long acting proinflammatory agent by inducing endothelial synthesis of the mediators required for neutrophils activa tion and extravazation during inflammation.