Detection of activated platelets and platelet-leukocyte aggregates in horses

Objective-To determine the potential usefulness of tests for detection of platelet activation and platelet-leukocyte aggregates in horses. Samples-Blood from 3 healthy Thoroughbreds. Procedures-Microscopic and flow cytometric assays were used to evaluate spontaneous platelet aggregation, platelet activation, and platelet-leukocyte aggregates. Platelet activation was detected by evaluation of binding of anti-human fibrinogen to unactivated and ADP-, thrombin-, thrombin agonist receptor peptide-, and platelet activating factor-activated platelets. Platelet-leukocyte aggregates were evaluated microscopically and by flow cytometric determination of leukocyte fluorescence that resulted from binding of fluorescently labeled platelets to leukocytes. Results-Equine platelets readily aggregated spontaneously when blood was stirred at low, medium, and high speeds. Compared with unactivated platelets, activated platelets had a marked increase in the percentage of cells with increased fluorescence intensity and in mean fluorescence intensity. Unactivated platelets formed aggregates with neutrophils and monocytes, but not with lymphocytes. Activation of platelets resulted in a calcium-dependent increase in platelet-leukocyte aggregates. Conclusions-Flow cytometric techniques can be used to detect in vitro platelet activation and platelet-leukocyte aggregates in horses. Clinical Relevance-Flow cytometric techniques may be useful for detection of prothrombotic disorders in horses.