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Biomedical subjects

R F Levine

Publications and source records attributed to R F Levine.

9 recordsLinked to original sources
PubMed1992

Megakaryocytes and megakaryocyte progenitors in human cord blood.

Thrombocytopenia contributes significantly to morbidity in the sick term or preterm infant. However, few data exist on newborn's megakaryocytes and megakaryocyte progenitor cells (CFU-MK). We therefore studied CFU-MK in term and preterm infant cord blood and compared the results with data on CFU-MK from adult bone marrow and adult peripheral blood in a plasma clot culture with postirradiated aplastic canine serum (PIACS) as a source of megakaryocyte colony-stimulating activity. The number of CFU-MK and the number of cells per CFU-MK were counted with an immunofluorescent method at day 12. The effect of T-lymphocyte depletion on cord blood cultures for CFU-MK was studied with PIACS and a partially purified product of PIACS. We also studied individual megakaryocytes from newborns. The number and sizes of circulating megakaryocytes, isolated from adult peripheral blood and term venous cord blood by elutriation, were compared. Term and preterm cord blood contained more CFU-MK than adult peripheral blood. The numbers of CFU-MK in preterm cord blood were comparable to those in adult bone marrow. When the number of cells per colony were compared, cord blood contained significantly more cells than adult marrow CFU-MK. The depletion of T lymphocytes did not significantly change the growth of CFU-MK compared to nondepleted cultures. A substantial number of circulating megakaryocytes were obtained from venous cord blood, though they were significantly smaller than adult peripheral blood megakaryocytes. Since cord blood is easily obtained and contains large numbers of megakaryocytes and CFU-MK, it may provide a convenient model for studying the regulation of fetal megakaryocytopoiesis.

Animals↗
PubMed1992

Familial thrombocytopenia with micromegakaryocytes.

Chronic thrombocytopenia was noted in two siblings and a first cousin. The initial impression was of immune thrombocytopenic purpura (ITP) with decreased megakaryocytes. One patient had splenectomy for presumed chronic ITP but showed no improvement. Bone marrow buffy coat slides were examined in the three children with thrombocytopenia, four normal controls, and five children with "classic" acute ITP. Megakaryocyte size, maturation, and ploidy were determined with Wright-Giemsa and Feulgen-stained material. Mean megakaryocyte diameters were 23.1 microns in the three related patients, 30.8 microns in normal controls, and 63.1 microns in children with "classic" acute ITP. Many "micromegakaryocytes" were noted in the three related children with chronic thrombocytopenia. An exhaustive family history was obtained, which showed multiple points of consanguinity. These patients represent an apparently new autosomal recessive disorder of megakaryocytopoiesis, characterized by disturbed megakaryocyte ploidization and maturation. More sensitive recognition of micromegakaryocytes should be attempted in children with atypical chronic thrombocytopenia, familial history of thrombocytopenia, or patients who have ITP and who have not responded to initial therapy.

Bone Marrow Examination↗
PubMed1991

Thrombocytopenia and absent radii syndrome: defective megakaryocytopoiesis-thrombocytopoiesis.

Thrombocytopenia and absent radii (TAR) syndrome is a congenital defect with osseous abnormalities and thrombocytopenia. It is inherited as an autosomal recessive trait, but the mechanism of thrombocytopenia in this disorder is not clear. We have had the opportunity to study the mechanism of thrombocytopenia in an infant with TAR syndrome. The infant had normal levels of thrombopoietin and megakaryocyte colony-stimulating activity in spite of marked thrombocytopenia. However, the megakaryocyte progenitor cells in the bone marrow produced abnormal colonies with increased numbers of megakaryocytes per colony and small megakaryocytes similar to the small megakaryocyte seen in vivo. These findings suggest that the TAR syndrome in this infant is due to a failure in the production of thrombopoietin or to an abnormal progenitor cell with a maturational defect.

Animals↗
PubMed1991

The effect of flow on the interaction of isolated megakaryocytes with subendothelial extracellular matrix.

We have previously shown that human, guinea pig, or rat megakaryocytes, incubated under static conditions on an extracellular matrix (ECM) produced by endothelial cells, readily adhered to the matrix and underwent platelet-like shape change and thromboxane A2 secretion. We have now exposed megakaryocytes to ECM in a perfusion system similar to that used to study platelets circulated over aortic subendothelium. We used a continuous flow circuit incorporating a parallel plate perfusion chamber. Megakaryocytes were isolated to high purity from guinea pig marrow by centrifugal elutriation and velocity sedimentation. The cells were introduced into the flowing medium while the surface of an ECM-coated coverslip mounted in the chamber was observed continuously by phase-contrast video microscopy for up to 18 hours. Megakaryocytes from the flowing suspension started to adhere to the ECM within seconds. Significant adhesion occurred over a range of shear rates, from 10 to 190 seconds-1, did not appear above 300 seconds-1 and was greatest at a shear rate of 60 seconds-1. Adhesion to the ECM was specific, since there was no adherence to glass coverslips, glutaraldehyde-fixed ECM-coated coverslips, or to endothelial cells cultured on ECM-coated coverslips. At low shear rates large aggregates of megakaryocytes formed on the ECM surface; these could be detached and washed away by higher shear forces. Megakaryocytes thus acquire, even before platelet formation, an adhesive capacity similar to that of platelets. In addition, a significant fraction of the adherent megakaryocytes underwent elongation and pseudopod formation similar to that seen in marrow sinusoids.

Animals↗
PubMed1977

Culture in vitro of isolated guinea pig megakaryocytes: recovery, survival, morphologic changes, and maturation.

Isolated guinea pig megakaryocytes were maintained in liquid cultures for up to 4 days. Megakaryocytes were incubated in siliconized glass vials in Dulbecco's Modified Eagle Medium with 5%-10% guinea pig serum and 2.3% bovine serum albumin. Cultured megakaryocytes did not adhere to glass vials and were almost entirely recovered by aspiration. No reproduction or cell division of megakaryocytes occurred. A small decline in viability occurred promptly on placing the freshly isolated cells in culture medium and could be attributed to reexposure to calcium. On incubation there was little further cell death. Up to 2 days in culture the megakaryocytes remained morphologically intact and appeared similar to megakaryocytes in situ. Megakaryocytes matured in culture with a loss of cytoplasmic basophilia, an increase in granule content, and progressive changes in nuclear configuration. The most mature megakaryocytes developed pseudopod formation but large-scale platelet liberation was not seen. The ability to culture megakaryocytes in vitro will allow more extensive biochemical and physiologic studies of this cell than previously possible.

Animals↗
PubMed1976

Isolation of intact megakaryocytes from guinea pig femoral marrow. Successful harvest made possible with inhibitions of platelet aggregation; enrichment achieved with a two-step separation technique.

Methods have been devised to harvest megakaryocytes from guinea pig femoral marrow and to isolate them in high yield. When marrow tissue was disaggregated the megakaryocytes underwent degenerative changes characterized by the loss of cytoplasmic granules and alterations in membrane topography, similar to the changes seen in aggregating platelets. These morphologic changes were interpreted to mean that megakaryocytes possessed functional attributes of platelets. The use of agents which inhibit platelt aggregation (0.38% sodium citrate. 10(-3) M adenosine, and 2 x 10(-3) M theophylline) in a medium free of bivalent cations prevented these changes. This solution resulted in both an excellent morphologic preservation and a significantly increased recovery of megakaryocytes from marrow tissue. A two-step purification of the intact megakaryocytes was carried out on the basis of their low density and large size, with equilibrium density gradient centrifugation followed by velocity sedimentation. This sequence gave approximately a 100-fold enrichment of megakaryocytes, significantly better than that achieved with either method alone. These techniques for harvesting and concentrating megakaryocytes make it possible for the first time to study megakaryocytes in vitro.

Adenosine↗
PubMed1976

Tannic acid effect on membrane of cell surface origin in guinea pig megakaryocytes and platelets.

Plasma membranes in isolated guinea pig megakaryocytes and washed platelets are poorly stained with the usual methods used to outline cell membranes. The addition of tannic acid and calcium to the initial fixative is useful to enhance electron density of all surface-derived membrane systems in these cells. The method described here shows that the increased electron denisty of membrane after fixation in the presence of tannic acid occurs both at the cell surface and along the invaginated membrane systems.

Animals↗