In vivo evidence that circulating activated platelets cause neutrophil degranulation.

<p>Purified platelets from wild type or Psel ^−/− mice were activated (or not) and injected in the tail vein of wild type C57BL/6 mice. Platelet activation was achieved with thrombin. The molecule was then inactivated by addition of hyrudin. Neutrophil myeloperoxidase content, platelet P-selectin expression and platelet-neutrophil heterotypic aggregates were assessed by flow cytometry as described in the Methods. Panel A shows the effect of the in vivo injection of the buffer used for platelet activation, containing both thrombin and hyrudin. Blood was retrieved at different times after injection (hours, x axis) and neutrophils with adherent (filled symbols) or internalized (grey symbols) platelets were identified by flow cytometry. >70% of circulating neutrophils were engaged in the internalization and adhesion of activated, but not resting, platelets after 1 hour. The fraction of circulating neutrophils with internalized and adherent platelets returned to background levels 24 hours after the injection. Results are expressed as mean±S.E.M. 5–7 animals were assessed per each point.