Summary. Although the disease is well described, the pathogenesis of bone marrow fibrosis in idiopathic myelofibrosis still remains unclear. We previously reported elevated intraplatelet transforming growth factor-β (TGF-β) levels in patients with this myeloproliferative disorder, compared with healthy subjects. Here, in a series of 16 patients, we show that TGF-β expression is also increased in patients' periperal blood mononuclear cells (PBMC): (i) at the mRNA level analysed by Northern blot hybridization and/or reverse transcription-polymerase chain reaction (RT-PCR): (ii) and/or at the secreted peptide level as evaluated in conditioned media from patients' mononuclear cells by a growth inhibition assay on CC164 cells.
By immunostaining with a polyclonal anti-TGF-β1 antibody, TGF-β was localized in morphologically heterogenous cells; these cells were characterized as megakaryocytes by labelling with a gpIIbIIIa monoclonal antibody.
Thus we provide evidence that both TGF-β and megakaryocytes are linked in the pathogenesis of idiopathic myelofibrosis.