A reversible defect of platelet PDGF content in myeloproliferative disorders.

Platelet PDGF (platelet derived growth factor), platelet associated IgG and plasma levels of circulating immune complexes were measured in patients with chronic myeloproliferative disorders (primary myelofibrosis, primary proliferative polycythaemia and essential thrombocythaemia). Platelet PDGF was low in 11/12 patients, immune complexes were elevated in 11/16, and PlAIgG was elevated in all 14 patients in whom it was measured. There was no significant correlation between platelet PDGF and plasma levels of immune complexes (r = -0.5, P greater than 0.1). Treatment with busulphan and prednisolone for 2-3 months restored normal levels of platelet PDGF and suppressed plasma immune complex levels. Plasmapheresis lowered levels of immune complexes but had no effect on platelet PDGF. These results indicate that the low platelet PDGF levels in chronic myeloproliferative disorders represent a reversible defect which is not directly related to the presence of immune complexes.