The effect of varying concentrations of adenosine on TF activity expression on HUVECs stimulated with TNF, thrombin, or PMA. HUVECs were treated for 5 hours with each stimulant: 1,000 U/mL TNF (□), 25 nmol/L thrombin (▪), or 5 nmol/L PMA () in the presence of varying concentrations of adenosine (0, 2.5, 5, and 10 μmol/L). TF activity on HUVEC surface was determined as factor Xa generation using S2222 (see the Materials and Methods). The data are expressed as the percentage of the control (each stimulant induced TF activity in the absence of adenosine). The values represent the mean ± SD of four independent experiments. Statistical analysis was performed using the Student's t-test (*P < .05; **P < .001).