Differential response of human and bovine platelets to bovine von Willebrand factor and vascular subendothelium

Human platelets undergo agglutination when stirred with bovine plasma (BP), but bovine platelets do not. The present study has shown that exposure of washed bovine platelets to subthreshold concentrations of adenosine diphosphate or thrombin before stirring restores their sensitivity to BP, and the cells undergo rapid agglutination. This agglutination was prevented by a monoclonal antibody, to glycoprotein GPIb. Flow cytometry studies revealed that exposure of bovine platelets to thrombin caused an increase in their ability to bind antibodies known to react with human GPIb or GPIIb-IIIa receptors. Interaction of bovine and human platelets with vascular subendothelium revealed additional differences in reactivity. Bovine platelets in citrate anticoagulant reacted poorly with subendothelium under flow conditions compared with human platelets. In contrast, bovine platelets in blood with low molecular weight heparin as anticoagulant adhered more readily than human cells. These findings suggest that different mechanisms are involved in hemostasis in human and bovine species.