Effect of coincubation of monocytes (M) with HUVEC on TF activity. 4 × 10⁵ M were incubated with or without HUVEC (2 × 10⁵/well) for 4 hours at 37°C in 7.5% CO₂ . At the end of incubation the cells were washed and resuspended in 300 μL RPMI 1640. TF activity was measured in frozen and thawed samples, as described in Materials and Methods. Bars represent the mean of ten experiments ± SEM. *P < .0001 versus both HUVEC and M incubated alone.