Objective— Activated platelets rapidly adhere to monocytes and upregulate the expression of tissue factor (TF), the major trigger of the coagulation cascade. In this study, we examined the effect of abciximab, a nonselective glycoprotein IIb/IIIa-receptor antagonist, on monocyte TF expression in thrombin receptor activator–stimulated whole blood in vitro.

Methods and Results— Abciximab (50 μg/mL) reduced the mass of platelets attached to monocytes, measured by the mean fluorescence intensity (MFI) of CD42b on CD14⁺ cells, 1 (CD42b, 471±197 versus 1073±217 MFI, mean±SD, P<0.05), 5, and 10 minutes after thrombin receptor activator stimulation of whole blood to the same extent as anti–P-selectin (50 μg/mL; 288±177 MFI, P<0.05) when determined by flow cytometry. In parallel, the expression of the platelet activation marker P-selectin colocalized with CD14⁺ monocytes was reduced up to 25% by abciximab at the same time points. Expression of monocyte TF antigen (CD14⁺/TF⁺, 39.9±8.7% versus 66.3±19.9%, P<0.05), chromogenic TF-activity (TF, 8.4±1.9 versus 13.2±2.8 U, arbitrary units, P<0.05), and TF mRNA was suppressed in the presence of abciximab as a consequence of reduced platelet mass attached to monocytes.

Conclusions— Our data suggest that heterotypic monocyte-platelet aggregates are a target for abciximab, which suppresses monocyte TF because of a reduction of monocyte-platelet cross talk.