Leukocyte type distribution in blood, on platelet thrombi, and on platelet monolayers. The experimental conditions for the whole blood perfusions are described in the legend to Fig 1. The platelet-adherent leukocytes were detached with EDTA, fixed in 0.5% paraformaldehyde-PBS solution, diluted in modified Tyrode buffer, and analyzed on the FACScan. A fresh blood sample was taken before the perfusion experiments and treated with FACS lysing solution. The leukocyte distributions of a single blood donor are shown as FSC (size) versus SSC (granularity) contour plots. Shown are the contour plots of fresh blood sample (left), leukocytes adhering to platelet thrombi (center), and leukocytes adhering to platelet monolayers (right).