Platelet membrane abnormalities in myeloproliferative disorders: decrease in glycoproteins Ib and IIb/IIIa complex is associated with deficient receptor function.

The number and functional activity of membrane glycoproteins (GP) Ib and IIb/IIIa were investigated in platelets from 11 patients with myeloproliferative disorders (MPD). Three patients had essential thrombocythaemia, two had chronic myeloid leukaemia and six had polycythaemia vera. The numbers of GPIb and GPIIb/IIIa molecules were detected on the platelet surface using different 125I-labelled monoclonal antibodies. The functional properties of GPIb and GPIIb/IIIa were evaluated using purified 125I-labelled asialo von Willebrand factor (vWF) and purified 125I-labelled fibrinogen, respectively, in a binding assay. Binding of the anti-GPIIb/IIIa antibody was decreased by 40% in almost all patients studied and, when measured, it was accompanied by decreased fibrinogen binding to activated platelets. Binding of anti-GPIb antibodies to platelets was also slightly decreased or virtually the same in eight out of 11 patients. The decrease correlated with decreased binding of asialo vWF. The increased plasma glycocalicin levels, measured in four patients, depended on the high platelet count. Scatchard analysis revealed normal receptor binding affinity for all ligands tested in all but one patient. In this report we demonstrate that abnormalities in the concentrations of GPIIb/IIIa membrane proteins are commonly present in patients with MPD, while a decrease in GPIb concentration is also seen, although in fewer patients. These abnormalities are accompanied by a concurrent decrease in the respective receptor functions. These findings may explain part of the haemorrhagic tendency often encountered in MPD.