Effect of RARα antagonist on downregulation of TF activity on NB4 cells. NB4 cells were incubated with ATRA (lane 2), Am80 (lane 3), or Ch55 (lane 4; 0.01 μmol/L). ATRA (0.01 μmol/L) was added 1 hour later to media containing Ro41-5253 (1 μmol/L; lane 5). Procoagulant activities in NB4 cells were measured as the recalcification time, as described in the Materials and Methods.