Cytometric analysis of high shear-induced platelet microparticles and effect of cytokines on microparticle generation.

Abstract

Background: Microparticles released from platelets may play a role in the normal hemostatic response to vascular injury, because they exhibit prothrombinase activity. Microparticles are generated by high shear stress and may be formed in diseased small arteries and arterioles in various clinical settings. However, the surface composition of high shear-induced platelet microparticles is unknown. It was recently shown that some cytokines modulate platelet activation. However, no reports are available concerning the effect of cytokines on high shear-induced platelet aggregation (SIPA) microparticle generation.

Materials and methods: Measurement of SIPA was performed with a cone-plate viscometer. The conformational characteristics of high shear (108 dynes/cm(2))-induced platelet microparticles were analyzed by flow cytometry and confocal laser scanning microscopy. Effects of cytokines for high SIPA microparticle generation were also analyzed using flow cytometry.

Results: The overall pattern of monoclonal antibody binding in high shear-induced microparticles was almost the same as that in activated platelets under high shear stress. Microparticles exhibited markedly increased Annexin V binding. In fluorescent confocal images, small and fine regions of fluorescence (microparticles) were recognized separate from platelet fluorescence. Thrombopoietin not only induced platelet activation, as demonstrated by CD62P expression, but also increased the number of microparticles. Erythropoietin and interleukin-6 enhanced only microparticle generation.

Conclusions: These results suggest that microparticles possessing procoagulant activity are released by platelet activation when levels of certain cytokines increase under high shear stress in various clinical settings.