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 microg/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 microg/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.