In vivo evidence of the phagocytosis of activated platelets by circulating neutrophils. Purified platelets, either activated (A) or resting (B), were injected in the tail vein of C57BL/6 mice. Platelet activation was achieved with thrombin. The molecule was then inactivated by addition of hyrudin, as described in “In vivo injection and clearance of activated platelets.” (C) 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 (x axis, hours) and neutrophils with adherent (■) or internalized () platelets were identified by flow cytometry. More than 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 ± SEM; 5 to 7 animals were assessed per point.