Summary

Monocytes play a pivotal role in both the inflammatory andcoagulation responses, which may be mediated through avariety of adhesion molecules on the cell surface, includingintercellular adhesion molecule-1 (ICAM-1). Monocytes alsopossess thrombin receptors. In the current study,we have demonstratedthat thrombin can upregulate ICAM-1 mRNA andinduce ICAM-1 expression on the monocyte in vitro and that, invivo, higher monocyte ICAM-1 expression is observed in pregnancy(which is characterised by a physiological increase inthrombin generation). In pregnant subjects, a positive correlationbetween monocyte ICAM-1 expression and a number ofmarkers of vascular/thrombotic disease (including blood group, acquired activated protein C resistance and non-fasting plasmatriglyceride levels) was observed.We also observed a significantrelationship between monocyte ICAM-1 expression and solubleplasma ICAM-1 levels, which would be consistent with acontribution of monocytic ICAM-1 to the levels of free ICAM-1 observed in plasma during pregnancy.Consistent with a role in fibrinogen binding, our preliminaryin vivo results suggest that monocyte ICAM-1 expression maybe a useful marker of the thrombotic/inflammatory response,although further work is required to assess the relationship ofmonocyte ICAM-1 expression in thrombotic disorders.