Leukocyte-platelet interaction in patients with essential thrombocythemia and polycythemia vera

Objective. Circulating polymorphonuclear leukocyte (PMN) activation occurs in patients with essential thrombocythemia (ET) and polycythemia vera (PV). We want to define whether this phenomenon plays a role in the formation of circulating PMN-platelet aggregates in these conditions. Methods. In 80 patients (46 ET and 34 PV) and 50 control subjects, we conducted a flow cytometric analysis to evaluate the levels of PMN-platelet aggregates (defined as the percentage of CD11b-positive PMN coexpressing a platelet-specific marker, i.e., CD42b or CD62P) and the levels of activated PMN and activated platelets. In addition, the in vitro PMN-platelet aggregate formation in response to N-formyl-methionyl-leucyl-phenylalanine (f-MLP)-induced activation of PMN was studied. Results. Significantly high PMN-platelet aggregates in ET and PV patients were found and were associated with increased PMN surface CD11b and surface platelet CD62P expression. In vitro f-MLP stimulation upregulated PMN-CD11b expression and simultaneously increased CD11b/CD42b and CD11b/CD62P aggregates, without affecting platelet surface antigens. In ET patients receiving aspirin, the increments in f-MLP-induced PMN-CD11b and in PMN-platelet aggregates were significantly lower versus ET subjects not treated with aspirin. Conclusion. Our data show that in ET and PV patients PMN activation plays an important role in increasing circulating PMN-platelet aggregates and suggest that aspirin treatment may decrease their formation. (c) 2005 International Society for Experimental Hematology. Published by Elsevier Inc.