Predictive Diagnostic and Prognostic Value of Platelets Microparticles (PMP), but Not of Reticulated Platelets (RP) or CD36 Expression in Essential Thrombocythaemia.

At the present time, Essential Thrombocythaemia (ET) remains an exclusion diagnostic since no diagnostic finding can definitely distinguish between clonal and reactive thrombocytosis (RT). In addition, no biological marker predicts readily the thrombotic risk of ET. We investigated by flowcytometry the diagnosis and prognosis value of PMP, RP and CD36 expression, as platelets parameters easily available in routine laboratory in 34 ET patients and 49 controls. Membrane platelet CD36 expression were stained by indirect immunofluorescence with specific anti-CD36 antibody and anti mouse IgG FITC (Biocytex, France), analyzed on FACSCalibur cytometer (BD), quantified using the calibration beads (Platelet Calibrator, Biocytex) and expressed as antigen molecules/platelet. RP were determined after RNA thiazole orange labeling (10 ng/ml, 45 min, at room temperature, in the dark). Assays performed after TRAP (Thrombin receptor activating peptide) stimulation demonstrated the specificity of the labeling (data not shown). PMP were identified on forward and side scatter after CD41a-PE or isotype control (Immunotech) labeling. ET was diagnosed according to revised PVSG criteria in 11 men and 23 women. The median age was 63 y (24–85) and the median platelet count was 674 x109/l (249–1324). At the time of evaluation, 19 patients received antiplatelets therapy, 9 oral chemotherapy, 10 exhibit arterial thrombosis (AT), 1 venous thrombosis and one, included in the AT group, experimented venous thrombosis as well. RP, CD36 and PMP were significantly increased in ET as compared to controls (P =.01, 10⁻⁴, <10⁻⁵, respectively). RP and CD36 expression were not significantly different between patients according to AT, antiplatelets agents and oral chemotherapy patterns. However PMP were significantly higher in patients with AT than in patients without thrombosis history (P =.02). We could not observe any decrease of PMP in patients with antiplatelets drugs since all patients with thrombosis had also antiplatelets therapy. In conclusion, RP, CD36 and PMP are increased in ET. These platelets parameters are currently evaluated in RT. The effects of antiplatelets agents on PMP and the thrombotic risk will have to be evaluated prospectively.