AIM: To explore the effects of CD40-CD40 ligand (CD40L) interaction on endothelial cells (ECs) procoagulant activity. METHODS: A co-incubation system of macrophage membrane with ECs was established. The changes in ECs procoagulant activity and tissue factor (TF) expression were studied by anti-CD40L antibody blocking analysis. RESULTS: Coincubation with macrophage membrane (cell ratio 1∶1) for 6 hours resulted in a 10.9-fold increase ( P