INCREASED PLATELET CD36 CONSTITUTES A COMMON MARKER IN MYELOPROLIFERATIVE DISORDERS

The distribution of the major platelet membrane glycoproteins (GP), Ib , IX, IIb-IIIa and TV (or CD36), which play important roles as recepto rs for adhesive molecules in haemostasis and thrombosis, was studied i n 34 patients with myeloproliferative disorders (MPD): 13 had essentia l thrombocythaemia (ET), 12 had polycythaemia vera (PV) and nine had c hronic myelogenous leukaemia (CML). Only occasionally were modificatio ns of the numbers of GPIb or GPIIb-IIIa measured using the binding of specific radiolabelled antibodies to platelets. In contrast, 2-3-fold increases of the total CD36 content and the surface CD36 expression we re measured in almost all patients studied, using a radioimmunoassay a nd the direct binding of the radiolabelled antibody, FA6-152, to the p latelet surface, respectively. These results indicate that the abnorma lity affected both the external and internal CD36 pools. Therefore pla telet CD36 may be a useful tool for the diagnosis and the follow-up of MPD patients. Surface CD36 has been proposed as a platelet receptor f or thrombospondin, an adhesive glycoprotein that is released from plat elets upon activation and promotes aggregate formation. Despite a 2-fo ld increase of CD36 molecules, resting and thrombin-activated platelet s from ET patients expressed the same amount of thrombospondin as norm al platelets, suggesting that there is not a direct correlation betwee n the CD36 expression and thrombospondin binding either spontaneously or after activation.