Abstract
Background - After activation, platelets adhere to neutrophils via P- selectin and β2-integrin. The molecular mechanisms and adhesion events in whole blood exposed to venous levels of hydrodynamic shear in the absence of exogenous activation remain unknown. Methods and Results - Whole blood was sheared at ≃100 s-1. The kinetics of neutrophil-platelet adhesion and neutrophil aggregation were measured in real time by flow cytometry. P- selectin was upregulated to the platelet surface in response to shear and was the primary factor mediating neutrophil-platelet adhesion. The extent of neutrophil aggregation increased linearly with platelet adhesion to neutrophils. Blocking either P-selectin, its glycoprotein ligand PSGL-1, or both simultaneously by preincubation with a monoclonal antibody resulted in equivalent inhibition of neutrophil-platelet adhesion (≃30%) and neutrophil aggregation (≃70%). The residual amount of neutrophil adhesion was blocked with anti-CD11b/CD18. Treatment of blood with prostacyclin analogue ZK36374, which raises cAMP levels in platelets, blocked P-selectin upregulation and neutrophil aggregation to baseline. Complete abrogation of platelet- neutrophil adhesion required both ZK36374 and anti-CD18. Electron microscopic observations of fixed blood specimens revealed that platelets augmented neutrophil aggregation both by forming bridges between neutrophils and through contact-mediated activation. Conclusions - The results are consistent with a model in which venous levels of shear support platelet adherence to neutrophils via P-selectin binding PSGL-1. This interaction alone is sufficient to mediate neutrophil aggregation. Abrogation of platelet adhesion and aggregation requires blocking Mac-1 in addition to PSGL-1 or P-selectin. The described mechanisms are likely of key importance in the pathogenesis and progression of thrombotic disorders that are exacerbated by leukocyte- platelet aggregation.
Original language | English (US) |
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Pages (from-to) | 873-882 |
Number of pages | 10 |
Journal | Circulation |
Volume | 98 |
Issue number | 9 |
DOIs | |
State | Published - Sep 1 1998 |
Keywords
- Blood cells
- Glycoproteins
- Integrins
- Neutrophils
- Platelets
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)