Selective counteractive effect of RARα antagonist on upregulation of TM activity on HUVECs. Changes in TM cofactor activity in protein C activation on HUVECs were measured after exposure to 1 μmol/L ATRA (lane 2) or Ro41-5253 (lane 3) for 24 hours. Cells were also incubated with Ro41-5253 (1 μmol/L), and ATRA (1 μmol/L) was added 1 hour later (lane 4).