A role for the Platelet Derived Growth Factor (PDGF) has been suggested in the abnormal proliferation of bone marrow fibroblasts occuring during myelofibrosis. To investigate this hypothesis, human bone marrow fibroblasts were isolated, and the cultures were characterized by immunofluorescent staining and electron microscopy. Electron microscopy eliminated the presence of endothelial cells by the absence of Weibel-Palade-Bodies. A positive intra and extra cellular antifibro-nectin staining was observed by immunofluorescent staining. The cultured cells didn’t show any labeling with specific antibodies for factor VIII von Willebrand factor, desmin or macrophage. Following the characterization of the bone marrow fibroblasts, using human pure 125I-PDGF, a specific binding of 125I-PDGF was demonstrated. The binding reached a plateau after 3 hours at 20°C, and after 4 hours at 4°C. Addition of unlabeled PDGF decreased this binding until 25 %.Saturation curve and scatchard analysis indicated two classes of sites with respectively 21,000 sites/aall and 37.000 sites/cell with an apparent Kd of 0.3 X 10-10 M and 0.5 X 10-9 M. Normal human serum at a concentration of 20 % induced a maximal DNA synthesis measured by-3H thymidine incorporation. When PDGF was added alone to the cultured fibroblasts at a concentration of 15 ng/ml, it induced a maximal DNA synthesis of 400 %.In the presence of 5 % of Platelet Poor Plasma (PPP), the same concentration of PDGF (15ng/ml) increased the incorporation of 3H thymidine up to 900%.In conclusion i) PDGF binds to human bone marrow fibroblasts, ii) PDGF stimulates their proliferation. These results are in favour of a role of PDGF in the proliferation of bone marrow fibroblasts associated with the development of myelofibrosis.
A unique population of IgG-expressing plasma cells lacking CD19 is enriched in human bone marrow