Participation of α_IIbβ₃ in platelet microparticle generation by collagen plus thrombin

We investigated the role of α_IIbβ₃ in microparticle generation by normal and thrombasthenic platelets stimulated with collagen plus thrombin. Microparticle generation by normal platelets was scarcely inhibited by monoclonal antibodies for glyco-protein lb and glycoprotein IX. Although one monoclonal anti-α α_IIbβ₃ antibody (NNKY1-32) partly inhibited microparticle generation, 3 other monoclonal anti-α α_IIbβ₃ antibodies had little effect. However, the combination of 4 monoclonal anti- α_IIbβ₃ antibodies or treatment with a polyclonal anti- α_IIbβ₃ antibody significantly inhibited microparticle generation (p < 0.05). Microparticle generation by thrombasthenic platelets also occurred after stimulation with collagen plus thrombin, although at a significantly lower level compared with normal platelets. Monoclonal antibodies for resting α_IIbβ₃, P-selectin, activated α_IIbβ₃ and β₂-glycoprotein I bound to microparticles from healthy platelets. In contrast, only a monoclonal antibody for β₂-glycoprotein I bound to thrombasthenic microparticles. These results suggest that microparticle generation by collagen plus thrombin occurs via two different mechanisms which are dependent and independent of α_IIbβ₃, respectively. The α_IIbβ₃-dependent mechanism appears to require activation of α_IIbβ₃.