Platelet acquired defect in PDGF and beta thromboglobulin content in hairy cell leukaemia: improvement after interferon therapy.

To investigate the platelet contribution to the development of myelofibrosis in hairy cell leukaemia (HCL), we have studied two platelet alpha granule components in 15 patients with HCL before chemotherapy: mitogenic activity was measured by 3H thymidine incorporation in BALB/C 3T3 cells and beta thromboglobulin (beta TG) assayed by radioimmunoassay (RIA). Platelet mitogenic activity and beta TG content were significantly decreased in the patients as compared to the control subjects. The nine patients who were treated with recombinant human interferon (IFN alpha A) were restudied after 4 months of therapy. The levels of both mitogenic activity and beta TG platelet content were significantly increased after IFN alpha-treatment with a complete response in five of the nine treated patients, a partial response in two and no response in the two others. HCL seemed therefore to be responsible for an acquired platelet alpha granule defect. As in the grey platelet syndrome a relationship between this abnormal platelet granule storage and the development of myelofibrosis is suggested in HCL.