Platelet Modulation of Polymorphonuclear Leukocyte Shear Induced Aggregation

A cone and plate viscometer and Coulter Counter were used to study platelet modulation of polymorphonuclear leukocyte (PMNL) aggregation caused by controlled shear stress. As an index of aggregation, the large-particle percentage (LPP) was calculated. This represents the ratio of aggregated cell count to total cell count. PMNL suspensions in buffer (1 .0 x iO cells per milliliter. final concentration) did not show any aggregate formation at shear stresses below 1 50 dynes/cm2 for one minute exposure time (LPP < 3%). However, there was PMNL aggregation in mixed PMNL and platelet-rich plasma suspensions in this shear stress range. Supernatant plasma from sheared platelets initiated PMNL aggregation at moderate shear stress (1 50 dynes/cm2 for one minute; LPP. 20.3% ± 2.5%). In contrast. platelet release factors, such as adenosine diphosphate (2 zmol/L) and serotonin (2 smol/L) did not cause PMNL aggregation (LPP. 2.9% ± 1 .2% and 3.3% ±