AbstractGlycoprotein VI (GPVI) is an essential platelet collagen receptor; therefore, the inhibition of GPVI-collagen interactions may be an attractive antithrombotic strategy. We have previously shown that targeting of GPVI with antibodies leads to the depletion of the receptor and to long-term antithrombotic protection in mice. An alternative agent to interfere with GPVI-collagen interactions might be soluble GPVI acting as a competitive inhibitor, thereby averting undesired effects on platelets. To test this, we expressed soluble dimeric human GPVI, comprising the extracellular domain of the receptor fused to the human immunoglobulin Fc domain (GPVI-Fc), and compared its antithrombotic potential with that of anti-GPVI antibodies in mice. In contrast to a recent report, we found by intravital fluorescence microscopy and ultrasonic flow measurements that GPVI-Fc had no effect on platelet adhesion and thrombus formation at the injured arterial wall, whereas anti-GPVI antibodies profoundly inhibited these processes. Similar results were obtained with a fusion protein comprising the extracellular domain of mouse GPVI and human IgG-Fc. This indicates that direct targeting of GPVI provides significantly stronger protection against arterial thrombosis than soluble GPVI dimer.