P222 | RETICULATED PLATELETS CONTRIBUTION TO TISSUE FACTOR AND TRANSFORMING GROWTH FACTOR-BETA GENERATION IN PRIMARY MYELOFIBROSIS

In Primary Myelifibrosis (PMF) the platelets contribute to the vascular complication and fibrosis. We focused on the reticulated immature platelets as in PMF there is an increased platelet turnover. It also is reported that the reticulated platelets (RPs) are more hyperactive than clonal platelets and responsible for the increased release of tissue factor (TF) and tranforming growth factor-beta (TGF-beta) markers of vascular risk and fibrosis progression, respectively. Therefore, we measured the proportion of the RPs and the count of the mature platelets (MPs) and the surface expression of P-selectin and CD41/CD61 complex (glycoprotein IIB/IIIa) as markers of platelet activation on RPs and mature platelets (MPs). We also measured TF and TGF-beta. We studied 75 JAK2-mutated patients diagnosed with PMF according to ICC/WHO criteria. Of 75 patients, 45 were low-risk DIPSS and 30 were intermediate-1-risk DIPSS. All patients had a mean age of 55 years (35-55 years). Nobody had inherited or acquired thrombotic risk or comorbidities. The mutation was conducted by ARMS-PCR gel electrophoresis. RPs and MPs were measured by automated hematology analyzer (Mindray BC-6800) as Immature Platelet Fraction-IPF (%) and as count platelet (109/L) respectively. P-selectin and CD41/CD61 complex were measured by flow cytometry and TF and TGF-beta by ELISA. All patients had high IPF (35±8 % (normal value 0.9-10.0%) and normal MPs (446x10 (normal value 150-450x109/L). RPs showed a significant increase in the expression of P-selectin (45±2% (normal value <6%) and a significant decrease in the expression of CD41/CD61 complex (<5% (normal value ≥70%), while MPs exhibited a non-significant increase in the expression of P-selectin (12±2%) and a non-significant decrease in expression of CD41/CD61 complex (41%). All patients had high TF (250±220 pg/ml (normal value 4.4±2.7 pg/ml) and high TGF-beta (25±5 ng/ml (normal value 4±2 ng/ml). A positive correlation there was between TF and RPs and between TGF-beta and RPs and between TF and CD41/cD61 complex and between TGF.-beta and CD41/CD61 complex. These results suggest a vicious circle that push towards coagulation and fibrosis. Whether low doses of aspirin could have an important impact in this context. is to be investigated.