Role of ERK-1/2 in the induction of TF expression in monocytes by the HIT Ab complex. (A) Monocytes were preincubated for 30 minutes with anti-FcγRI Ab (10 μg/mL) or control Ab before the addition of KKO (100 μg/mL) + heparin (1 U/mL) + PF4 (10 μg/mL). Total ERK1 and phospho-ERK1/2 were measured by ELISA. (B-C) Monocytes were preincubated for 1 hour with MEK1 inhibitor PD98059 (50 μg/mL) or control Ab before the addition of KKO (100 μg/mL) + heparin (1 U/mL) + PF4 (10 μg/mL). Cellular TF (B) and MP TF activity in MPs isolated from the cell supernatant fluid (C) were measured. The results are from 3 independent experiments. The HIT complex refers to addition of KKO + PF4 + heparin. **P < .01 and *P < .05.