Immunocytochemical study of a Ca(2+)-ATPase enzyme in the human megakaryocytic lineage.

We report the presence of a Ca(2+)-ATPase in human megakaryocytes (MK) using an immunofluorescence technique on bone marrow smears and especially on normal MK progenitors in culture. This finding is based on the comparative staining of MK with 1) a well-characterized antibody raised against purified rabbit skeletal sarcoplasmic reticulum Ca(2+)-ATPase, 2) antibody P2 raised against the glycoprotein IIb-IIIa complex as a marker of megakaryocytic lineage, and 3) anti-glycophorin A as a marker of erythroid lineage. On bone marrow smears, all cells recognized by P2 were also labeled with the anti-Ca(2+)-ATPase antibody. In culture, a maximum number of MK colonies was observed at day 11. From days 2-4, some MK precursors appeared stained both with the anti-Ca(2+)-ATPase and P2 antibodies; other cells were reactive with both anti-Ca(2+)-ATPase and anti-glycophorin A antibodies. From day 5 of culture, cells were either simultaneously stained with P2 and anti-Ca(2+)-ATPase antibodies or with anti-glycophorin A antibody, but not with the anti-Ca(2+)-ATPase antibody. Besides this first evidence of an early expression of a Ca(2+)-ATPase in MK, this work provides a useful tool for identification of MK by immunofluorescence.

Partial characterization of a fibrinolytic inhibitor produced by cultured endothelial cells derived from human umbilical vein.

A preliminary characterization of a fibrinolytic inhibitor released by human umbilical vein endothelial cells in primary culture is reported. This molecule of Mr comprised between 2 X 10(5) and 10(6) and of alpha 2 mobility precipitates at 43% ammonium sulphate saturation and is totally adsorbed on Concanavalin A Sepharose 4 B. A possible relationship with alpha macroglobulins is discussed.

Recombinant acidic human fibroblast growth factor (aFGF) stimulates murine megakaryocyte colony formation in vitro.

Recombinant acidic human fibroblast growth factor (aFGF) significantly stimulated the formation of megakaryocyte colonies and the size of MK colonies as well as individual MKs in vitro in mice. When aFGF was combined with recombinant mouse interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-6 (IL-6) at their optimal doses, a synergistic action was found between aFGF and IL-3. The activity of aFGF could be completely abrogated by a monoclonal antimouse IL-6 antibody which specifically neutralized the action of mouse IL-6 but not human IL-6. These data indicate that aFGF provides positive growth signals of megakaryocyte progenitor cells, which can give rise to a synergistic action in the presence of IL-3 and which can be abrogated by the antimouse IL-6 antibody.

Adhesion and aggregation of human platelets to rabbit subendothelium. A new approach for investigation: specific antibodies.

An SgG antibody occurring in a recently transfused thrombasthenic patient inhibited all the ADP-mediated aggregations and platelet-platelet interaction (thrombus formation) on rabbit aorta subendothelium; another IgG antibody occurring in a multitransfused Bernard-Soulier patient inhibited ristocetin and bovine factor VIII mediated aggregation and platelet-subendothelium interaction.

In vivo inhibition of megakaryocyte and platelet production by platelet factor 4 in mice.

The in vivo effect of human platelet factor 4 (PF4) on murine megakaryocytopoiesis and thrombopoiesis was studied. Administration of PF4 induced a dose-dependent decrease in the numbers of megakaryocytes and their progenitor cells (CFU-MK), continuing for 1 week after the injection. However, the size of megakaryocytes and their colonies was not changed following PF4 injection. Platelet levels were significantly decreased at days 3-4. The number of CFU-GM was decreased at days 1-2. White blood cells and hemoglobin were unaffected by PF4. These data indicate that PF4 inhibits megakaryocyte and platelet production in vivo by acting on the early stage of megakaryocyte development.

Megakaryocytes and myelofibrosis in gray platelet syndrome.

Studies have been carried out with cultured human megakaryocytes derived from Gray Platelet Syndrome blood and have demonstrated that MK-DGF and MK-F4 are present in the early stages of megakaryocyte maturation (day 5-6) but disappear in the late phase (day 9-11). In Gray platelets total mitogenic activity, PDGF and PF4 amounts were reduced while beta TG and PF4 plasma levels were slightly increased. These findings indicate a possible relationship between the loss of alpha granule contents from the megakaryocytes in the marrow and the myelofibrosis found in Gray platelet disorder and possibly associated in other diseases with platelet or megakaryocyte abnormalities.