Increased Granulocyte CD11b and Monocyte Tissues Factor Expression in Patients with Essential Thrombocythemia and Thrombosis.

The mechanisms accounting for the increased risk of thrombosis in patients with essential thrombocythemia (ET) are not well known. Recently, a possible role for the granulocytes in the development of thrombosis in ET has been suggested. To analyze the possible relationship between granulocyte activation and a history of thrombosis in ET, granulocyte activation was studied in 53 ET patients (26 with a previous history of thrombosis and 27 without) and 26 healthy controls. Neutrophil and monocyte CD11b expression, monocyte tissue factor (mTF) expression, and platelet-neutrophil (PNC) and platelet-monocyte (PMC) complexes were studied using whole blood cytometry and the results were expressed as percentages and in MESF (molecules of equivalent soluble fluorochrome) units. Granulocyte CD11b and mTF expression were measured at baseline and after activation with lipopolysaccharide (LPS). The results are as follows: 1) ET patients had significantly higher baseline percentages of circulating PNC and PMC as well as neutrophil CD11b MESF expression than the controls (p=0.0001); 2) monocyte CD11b expression was higher in patients with ET and thrombosis (mean 151241 MESF) than in those without (127191 MESF) and in the controls (65717 MESF) (p= 0.0001); 3) mTF baseline surface expression was increased in ET patients as compared with the controls (15635 vs 9385 MESF, p= 0.0001); 4) following LPS activation, patients with ET and previous thrombosis had significantly higher mean percentage of mTF expression than those without thrombosis and the controls (48%, 36% and 25%, respectively) (p= 0.0001). No differences were noted when the results were analysed according to the treatment that the patients were receiving at the time of study. In conclusion, patients with ET and a history of thrombosis show a marked increase in granulocyte activation, especially in monocyte activation, and therefore such alteration might play a role in the pathogenesis in these patients.