Detection and quantification of transforming growth factor beta (TGF-beta) and platelet-derived growth factor (PDGF) release by normal human megakaryocytes.

Transforming growth factor beta (TGF-beta) and platelet-derived growth factor (PDGF) are known as protein cytokines involved in differentiation as well as in maturation processes within the hematopoietic system. Both enhance the proliferation and/or collagen synthesis in fibroblasts and are found within the alpha-granules of megakaryocytes. To learn more about the regulation mechanisms involving synthesis and secretion of these cytokines it is important to develop suitable experimental conditions. We have applied the reverse hemolytic plaque assay (RHPA) to CD61+ megakaryocytes prepared from bone marrow of hematologically normal patients. By means of the RHPA, the spontaneous and stimulated secretion of TGF-beta 1 and PDGF could be analyzed at the single cell level. According to morphometric analysis, predominantly small megakaryocytes including precursors (pro- and megakaryoblasts) secrete TGF-beta 1 and PDGF under physiological conditions. Furthermore, the proportion of actively secreting megakaryocytes increased significantly following treatment with recombinant human (rh) IL-3 for 8 h. A slight induction was also appreciated after stimulation with interleukins rhIL-1 or rhIL-11. Because IL-3 as well as IL-11 are known as efficient growth factors for human megakaryocytes in vitro, our data provide insights into the regulatory mechanisms involved in megakaryopoiesis and the development of myelofibrosis.