| Abstract: | Exposure to lipopolysaccharides (LPS; 10 micrograms/ml derived from either S. enteritidis or E. coli or to their lipid A moiety alone induced procoagulant activity in cultured human endothelial cells. This exclusively cell-associated activity was identified as tissue factor activity by two criteria: Firstly, the presence of Factor VII was required for its expression and, secondly, clotting was abolished by the addition of the IgG fraction of anti-human tissue factor antibodies. Concomitant analysis of prostacyclin (PGl2) formation by the cells showed a substantial increase in the production of this potent platelet inhibiting substance during exposure to endotoxin. LPS-induced release of PGl2 did not result in refractoriness of the cells to generate new PGl2 as indicated by the retained response to stimulation with 20 microM arachidonic acid. While the release of PGl2 could be inhibited by pretreatment of the cells with 100 microM acetylsalicylic acid (ASA), the induction of tissue factor activity remained unaffected by ASA. In contrast to LPS-free control cultures, ASA did not completely prevent PGl2 formation by human endothelial cells after exposure to LPS suggesting the induction of a cyclooxygenase-independent pathway by LPS. |
