Objective--Collagen and thrombin are the strongest physiological platelet agonists, acting through different receptors, among which glycoprotein VI (GPVI) and protease-activated receptors, respectively, are the essential ones. In mice, targeting of GPVI with the monoclonal antibody JAQ1 induces depletion of the receptor from circulating platelets, resulting in abolished collagen responses and long-lasting antithrombotic protection.

Methods and Results--Mice were treated with JAQ1, and the early effects of this treatment were analyzed. In addition to the known abolition of the collagen reactivity, this treatment also affected platelet response to thrombin but not other agonists. In platelets from JAQ1-treated mice, thrombin-induced activation of integrin IIb3, the surface expression of P-selectin, and the procoagulant activity were decreased on days 1 and 2, then progressively recovered and returned to normal on day 5. In parallel, the mice were transiently protected from lethal tissue factor-induced pulmonary thromboembolism (100% survivors versus 40% in control group), which appeared to be based on a decreased generation and activity of intravascular thrombin.

Conclusions--Anti-GPVI treatment induces 2-phase antithrombotic protection in mice consisting of a partial and transient inhibition of thrombin responses in platelets and a prolonged and complete loss of the collagen response.