Isolation of human megakaryocytes by immunomagnetic beads

Impact of elevated plasma serotonin on global gene expression of murine megakaryocytes

Background

Serotonin (5-HT) is a biogenic amine that also acts as a mitogen and a developmental signal early in rodent embryogenesis. Genetic and pharmacological disruption of 5-HT signaling causes various diseases and disorders via mediating central nervous system, cardiovascular system, and serious abnormalities on a growing embryo. Today, neither the effective modulators on 5-HT signaling pathways nor the genes affected by 5-HT signal are well known yet.

Methodology/Principal Findings

In an attempt to identify the genes altered by 5-HT signaling pathways, we analyzed the global gene expression via the Illumina array platform using the mouse WG-6 v2.0 Expression BeadChip containing 45,281 probe sets representing 30,854 genes in megakaryocytes isolated from mice infused with 5-HT or saline. We identified 723 differentially expressed genes of which 706 were induced and 17 were repressed by elevated plasma 5-HT.

Conclusions/Significance

Hierarchical gene clustering analysis was utilized to represent relations between groups and clusters. Using gene ontology mining tools and canonical pathway analyses, we identified multiple biological pathways that are regulated by 5-HT: (i) cytoskeletal remodeling, (ii) G-protein signaling, (iii) vesicular transport, and (iv) apoptosis and survival. Our data encompass the first extensive genome-wide based profiling in the progenitors of platelets in response to 5-HT elevation in vivo.

Serotonin uptake rates in platelets from angiotensin II-induced hypertensive mice

Angiotensin II (Ang II) is a critical component of the renin-angiotensin system that contributes to hypertension. Although platelets in blood from hypertensive subjects have an abnormal biological profile, it is unclear if circulating Ang II influences platelet aggregation or thrombus formation. One of the abnormalities presented to the platelets during hypertension is an elevated plasma concentration of serotonin (5-HT) caused by reduced 5-HT uptake secondary to loss of the 5-HT transporter (SERT) on the platelet plasma membrane. In the current study, we evaluated in vivo platelet function after 7 days of subcutaneous Ang II infusion to establish hypertension in mice and additionally assessed the biology of isolated platelets exposed to Ang II in vitro. The administration of Ang II elevated systolic blood pressure, but markers of platelet activation including P-selectin and PEJon/A staining were not changed. However, the aggregation response to collagen was reduced in isolated platelets from Ang II-infused mice, which also showed reduced 5-HT uptake by SERT. In vitro exposure of isolated platelets to Ang II also resulted in a loss of surface SERT associated with a reduced aggregation response to collagen. These abnormalities were reversed by increasing concentrations of the Ang II receptor antagonist, valsartan. Interestingly, SERT KO mice failed to fully develop hypertension in response to Ang II infusion and isolated platelets from these animals were insensitive to the anti-aggregatory influence of Ang II. Thus, Ang II blunts the aggregation responses of platelets and the mechanism underlying this action may involve a loss of SERT on the platelet plasma membrane. The latter event depletes intracellular 5-HT in platelets, an event that is associated with reduced aggregation. The widespread use of antihypertensive drugs that target the renin-angiotensin system suggest the potential clinical utility of our findings and emphasize the importance of understanding the impact of Ang II on platelet function.

The prospective isolation of viable, high ploidy megakaryocytes from adult murine bone marrow by fluorescence activated cell sorting

Mature megakaryocytes (MM) can be up to 65 μM in diameter and due to their size, viable and pure MM populations have been difficult to isolate in large numbers. Here in, we report a fluorescence activated cell sorting (FACS) method by which viable and pure populations of 8 N, 16 N, 32 N, and 64 N MM can be isolated from murine bone marrow (BM).

Megakaryocyte chimerism after allogeneic stem cell transplantation in children

The aim of this study was to investigate the extent and the clinical implications of mixed chimerism in megakaryocytes after stem cell transplantation (SCT). Polymerase chain reaction analyzing allele length polymorphisms was used to determine the origin of immunomagnetically isolated megakaryocytes and leukocyte subpopulations after SCT in 13 children. Eleven were unselected consecutive cases while two were included due to known leukocyte mixed chimerism. Recipient DNA was detected in the megakaryocytes in six out of the 11 cases at levels between 1 and 100%. Coinciding mixed chimerism in the leukocyte populations was detected in two of the 11 cases. Of the two selected cases with known leukocyte mixed chimerism, two boys with aplastic anemia and Wiskott-Aldrich syndrome had 1-5 and 70% recipient megakaryocytes, respectively. Although the four relapses or deaths, within the 13 months of observation, were restricted to patients with multilineage or isolated megakaryocyte (n = 1) mixed chimerism, it was not possible to link any other apparent clinical problems, except a prolonged thrombocytopenia in one case, to the mixed chimerism in this limited study group.

Moesin, the major ERM protein of lymphocytes and platelets, differs from ezrin in its insensitivity to calpain

The ERM proteins, ezrin, radixin and moesin, provide regulated linkage of the cytoskeleton with the plasma membrane, particularly in cell surface projections. Ezrin and moesin were found co-expressed, and radixin was not detected, in human blood lymphocytes, monocytes and neutrophils. Moesin is the quantitatively dominant ERM protein in these cells and the only one in platelets. Because Ca signaling pathways involving calpain cleavages are important in blood cells, we examined ERM protein sensitivity to this protease. A striking difference was discovered: sensitivity of ezrin and resistance of moesin (and radixin) to calpain. In intact stimulated lymphocytes, ezrin was cleaved, while moesin was not, strongly suggesting that differential sensitivity to calpain contributes to specialized functions of these proteins.

Synergistic effects of erythropoietin and interleukin-6 on the in vitro proplatelet process formation of rat megakaryocytes

The recombinant hemopoietic factors of megakaryocyte potentiator (MEG-POT) were studied to compare their activity in stimulating proplatelet process formation (PPF) with thrombopoietin (TPO, c-MpI ligand). For the assay, a highly enriched (> 95%) population of more than 90% viable megakaryocytes was isolated from rat bone marrow using the immunomagnetic beads method and cultured with fetal calf serum (FCS) or in a serum-free condition. Megakaryocytes developing slender beaded cytoplasmic processes (proplatelet processes) were observed on both inverted phase contract microscopy and scanning electron microscopy. A large number of proplatelet process clusters were dose-dependently formed with the addition of varying doses of recombinant erythropoietin (rEpo) and interleukin-6 (rIL-6) as well as TPO. Epo and IL-6 were demonstrated to act synergistically solely at low doses in the development of PPF (P < 0.05). Other recombinant factors such as IL-11, leukemia inhibitory factor (LIF) and erythroid differentiation factor (EDF) appeared weak or ineffective. From these in vitro observations, it was suggested that a synergism of Epo and IL-6 might play a significant role in the terminal stage of megakaryocyte maturation leading to platelet release.

Investigation of megakaryopoiesis in myelosuppressed bone marrow using immunogold-silver staining (IGSS)

To determine the frequencies and differential counts of megakaryocytes after cytoreductive treatment in nucleated low-density (1.060 g/ml) bone marrow cells (BMNC) of dogs an immunogold-silver staining (IGSS) technique with the lineage specific monoclonal antibody 2F9 was established. This antibody recognizes the glycoprotein IIb/IIIa complex expressed on the surface of canine megakaryocytes and platelets. The IGSS technique enables not only the detection of megakaryocytes occurring at a low frequency (0.1-0.2%), but also the discrimination between the different maturation stages of megakaryocytes due to cell size, nuclear morphology and cytoplasmic staining. By the use of this technique, small lymphoid megakaryocytic cells were identified. Comparable numbers of megakaryocyte colony-forming cells in 2F9-depleted and nondepleted BMNC suspensions (25.7 +/- 5.0 vs. 25.3 +/- 5.1 Meg-CFC/10(5) BMNC) indicate that these small 2F9 positive cells are nonclonogenic precursors of megakaryoblasts. To prove the applicability of IGSS, serial examinations of bone marrow samples from dogs treated with recombinant human interleukin-6 (IL-6) after exposure to 2.4 Gy total body irradiation (TBI) were performed. The results of the microscopic evaluation indicate that, in the recovery phase after TBI, IL-6 induced an earlier and stronger increase in megakaryocyte frequency in comparison to the control. Interestingly, all maturation stages of the megakaryocytic lineage took part in this IL-6 induced improvement of megakaryocyte recovery.

Identification and characterization of a novel related adhesion focal tyrosine kinase (RAFTK) from megakaryocytes and brain

We have isolated a cDNA encoding a novel human intracytoplasmic tyrosine kinase, termed RAFTK (for a related adhesion focal tyrosine kinase). In addition, we have cloned and characterized the murine homolog of the human RAFTK cDNA. Comparison of the deduced amino acid sequences of human RAFTK and murine Raftk cDNAs revealed 95% homology, indicating that RAFTK is highly conserved between these species. The RAFTK cDNA clone, encoding a polypeptide of 1009 amino acids, has closest homology (48% identity, 65% similarity) to the focal adhesion kinase (pp125FAK). Comparison of the deduced amino acid sequences also indicates that RAFTK, like pp125FAK, lacks a transmembrane region, myristylation sites, and SH2 and SH3 domains. In addition, like pp125FAK, RAFTK contains a kinase domain flanked by large N-terminal (426 residues) and C-terminal (331 residues) domains, and the C-terminal region contains a predicted proline-rich stretch of residues. In fetal tissues, RAFTK expression was abundant in brain, and low levels were observed in lung and liver. In adult tissues, it was less restricted, indicating that RAFTK expression is developmentally up-regulated. Expression of RAFTK was also observed in human CD34+ marrow cells, primary bone marrow megakaryocytes, platelets, and various areas of brain. The human RAFTK gene was assigned to human chromosome 8 using genomic DNAs from human/rodent somatic cell hybrid lines. The mouse Raftk gene was mapped to chromosome 14, closely linked to gonadotropin-releasing hormone. Using specific antibodies for RAFTK, a approximately 123-kDa protein from the human megakaryocytic CMK cell line was immunoprecipitated. Treatment of the megakaryocytic CMK cells with thrombin caused a rapid induction of tyrosine phosphorylation of RAFTK protein. The structural features of RAFTK suggest that it is a member of the focal adhesion kinase gene family and may participate in signal transduction in human megakaryocytes and brain as well as in other cell types.

Establishment and characterization of a new human mesothelioma cell line (T-85) from malignant peritoneal mesothelioma with remarkable thrombocytosis

A mesothelioma cell line, termed T-85, was established from a patient with malignant peritoneal mesothelioma and remarkable thrombocytosis (1.4 x 10(6)/mm3). Electron microscopically, two types of mesothelioma cells have been characterized; the major type of cells with dense-cored granules in the cytoplasm and the minor one with evenly dense granules. Immunologically, the cells showed staining for interleukin-6 (IL-6), cytokeratin, collagen type IV, vimentin, laminin, fibronectin and Factor VIII-related antigen. Quantitation by ELISA revealed a high concentration of IL-6 in T-85 cell culture supernatants. RT-polymerase chain reaction of T-85 cells showed two positive bands of cDNA at 628 and 251 base pairs indicating the constitutive expression of IL-6 and IL-6 receptor mRNA. Moreover, prominent pro-platelet process formation activity in T-85 cell culture supernatants indicated the presence of a thrombopoietic activity due mainly to IL-6 but not the c-Mpl ligand or erythropoietin. However, the fact that 15% of PPF activity remained in the supernatants treated with anti-IL-6 antibody indicated the presence of another thrombopoietic substance. T-85 is so far the first mesothelioma cell line derived from a case with remarkable thrombocytosis.

Novel monoclonal antibody reactive with thrombin-sensitive 74-kDa glycoproteins present on platelets and megakaryocytes both from mouse and rat

A monoclonal antibody (designated 1C2) that reacts only with mouse platelets and megakaryocytes among hematopoietic cells was established by immunizing mouse platelets to an Armenian hamster. 1C2 reactive mouse molecule (1C2 antigen) was a surface glycoprotein with molecular weight of 74 kDa. Side by side comparison revealed that 4A5, a rat monoclonal antibody against mouse platelet, immunoprecipitated the identical molecule to 1C2 antigen. Of particular interest, 1C2 also labeled rat tissues with an identical pattern to that of mouse tissues and recognized a 74-kDa protein from rat platelets. Reactivity of 1C2 to mouse and rat platelets decreased when they were treated with thrombin. Following thrombin treatment of mouse platelets, 1C2 reactive 69-kDa protein appeared in the supernatants. Mouse and rat 1C2 antigens purified on 1C2-coated beads were cleaved by thrombin to generate 69-kDa fragments, establishing that 1C2 antigen is a direct substrate for thrombin. 1C2 is the first antibody to platelets and megakaryocytes of mouse and rat whose reactive molecule is well characterized, i.e., substrate for thrombin. 1C2 can be a useful tool in studying megakaryocytopoiesis and thrombopoiesis in rodent systems.

Simultaneous measurements of megakaryocyte-associated IgG (MAIgG) and platelet-associated IgG (PAIgG) in chronic idiopathic thrombocytopenic purpura

We have simultaneously measured platelet-associated IgG (PAIgG) and megakaryocyte-associated IgG (MAIgG) in 30 untreated patients with chronic idiopathic thrombocytopenic purpura (CITP). Megakaryocytes were purified from bone marrow by 35% Percoll gradient centrifugation, followed by negative immunopanning using magnetic immunobeads. The normal range of MAIgG in 30 healthy donors was 15.5 +/- 10.0 ng/10(5) megakaryocytes, whereas MAIgG in the 30 CITP patients was 140 +/- 59.3 ng/10(5) megakaryocytes, although the values were widely distributed. From the PAIgG and MAIgG data, CITP patients were classified into three types; type I (PAIgG < 200 ng/10(7) platelets and MAIgG < 150 ng/10(5) megakaryocytes), type II (PAIgG > 200 ng and MAIgG > 150 ng), and type III (PAIgG < 200 ng and MAIgG > 150 ng). Patients with types I and III had good clinical courses, but, in contrast, patients with type II responded poorly to steroid therapy followed by splenectomy or became refractory to treatment. In splenectomized patients, MAIgG of responder was promptly decreased to normal range and, in contrast, that of non-responder was persistently elevated. These results indicate that anti-platelet autoantibodies are able to bind with megakaryocytes in the bone marrow as well as with platelets in the peripheral blood, and the results also suggest that megakaryopoiesis in CITP is heterogeneous. Simultaneous measurement of PAIgG and MAIgG may predict the clinical outcome of CIPT.

Platelet glycoprotein IIb gene expression as a model of megakaryocyte-specific expression

Glycoprotein (GP)IIb/IIIa is an integrin complex normally restricted in its expression to platelets and the megakaryocytes from which they are derived. This complex functions as a receptor for fibrinogen and other ligands and is involved in platelet aggregation. The receptor complex is expressed at high levels during final megakaryocyte differentiation. Further, while GPIIIa is expressed in other tissues as part of the vitronectin receptor, GPIIb is only expressed on maturing megakaryocytes and the platelets derived from them. Thus studies of the GPIIb gene may serve as a model of gene regulation during this process. Over the past several years, the genes for both GPIIb and IIIa have been cloned and analyzed. The GPIIb gene contains 30 exons over 18 kilobases (kb). The transcriptional start site has been determined and there does not appear to be a TATA-box immediately upstream of this site. Studies have been done to define regulatory elements upstream of the transcriptional start site. Most of these studies focused on the human promoter and on studies using megakaryocytic cell lines. These studies have defined several important tissue-specific promoter elements including a GATA454 site (454 basepairs upstream of the transcriptional start site that involves a GATA-binding consensus sequence), a GATA54 site and an Ets35 site (that involves an Ets-binding consensus sequence). Expression studies with megakaryocytic cell lines suggest that each of these sites effects expression approximately threefold. Further, an Ets510 site was also described that had a similar effect. While these studies were underway, we pursued studies of the rat 5'-flanking region using a rat primary marrow expression system. Qualitatively, our data support the human data; however, quantitatively, we found significant differences from the human studies done in cell lines. We found that the major tissue-specific promoter element was the GATA454 site. Mutations altering this site result in an approximately fiftyfold drop in expression. In comparison, eliminating the Ets510 site by truncation or point mutation had only a twofold effect on expression. Mutations at the Ets35 site did effect expression at a high level, decreasing expression approximately fifteenfold, while mutations at the GATA54 site effected expression by approximately ninefold. In addition, using 50 bp deletions, we have preliminarily defined two domains from -450 to -351 bp and -150 to -101 bp upstream of the transcriptional start site that effected expression. The former appears to contain a positive regulatory element, while the latter appears to be a silencer element.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of CD34+ human hemopoietic progenitor cells from the peripheral blood: enzyme-, carbohydrate- and immunocytochemistry, morphometry, and ultrastructure

Following an immunomagnetic isolation and enrichment procedure, CD34+ cells were harvested from the peripheral blood of about 50 healthy donors. A battery of cytochemical staining reactions, monoclonal and carbohydrate-specific antibodies, proliferation markers and lectins was applied on smears and sections from paraffin-embedded pellets. Additionally, a morphometric analysis and ultrastructural investigation was carried out. More than 95% of the total yield of progenitor cells expressed CD34 and CD43 (MT1) and of these about 90% CD45 (LCA) and 25% CD45A (MT2). The CD34+/CD45RA-population was thought to represent very primitive, probably not lineage-restricted stem cells. On the other hand, reactivity with ANAE, CD11c, CD15, CD20, Ret40f, KiM1P, and CD61 (ranging between 1 to 20%) was considered to indicate a transition into more differentiated elements of hemopoiesis. The failure to detect any staining with proliferation markers (Ki-67/MIB 1, PCNA, KiS1) was in keeping with a quiescent status. Carbohydrate antigens revealed a pattern which underlines the fact that the CD34 and CD43 antigens belong to the family of heavily O-glycosylated sialomucins. Blood group antigens which are located at the peripheral regions of mucin-oligosaccharides (H type 2, Lewis, Lewis) could be demonstrated, but not A, B, Sialyl-Lewis and Lewis. Morphometric analysis revealed that CD34+ progenitors were larger than small lymphocytes. Electron microscopy showed a relatively primitive cytoplasmic organization and numerous tiny magnetic beads clustered at the plasma membrane.

Magnetic activated cell sorting (MACS)--a new immunomagnetic method for megakaryocytic cell isolation: comparison of different separation techniques

Megakaryocytes are difficult to isolate because of their fragility, their tendency to aggregate, and their varying sizes. For purification of cells at different stages of maturation and of different sizes (ploidy classes) we developed an immunomagnetic cell sorting method (MACS) to enrich the whole spectrum of the megakaryocytic cell lineage. The use of small magnetic beads coupled to various antibodies and labelling with fluorescent antibodies allowed direct analysis of enrichment and evaluation of the isolated fraction without further staining or detachment procedures. CD 61 (Y2/51), a monoclonal antibody directed against platelet glycoprotein IIIa, was employed to perform the separation procedure. An enrichment up to 47% of CD 61-positive cells with an average of 37% and a recovery rate of 37% was obtained by using the MACS technique. Pre-enrichment by Percoll density centrifugation, followed by MACS separation, resulted in an enrichment of 65% and a recovery rate of 67%. The relative amount of small megakaryocytic cells in only MACS-enriched cell populations, however, was higher than in Percoll/MACS fractions. As a parameter of vitality we tested cytokine secretion of the enriched megakaryocytes in reverse haemolytic plaque assays. Secretion of IL-1, IL-6, GM-CSF, and PDGF with and without stimulation by phorbol myristate acetate was demonstrable at the single cell level.

Immunomagnetic separation as a final purification step of liver endothelial cells

We describe a fast and reproducible method that can be used as a final step in obtaining pure populations of liver endothelial cells. This method employs endothelial cell specific lectin covalently bound to magnetic polystyrene beads (Dynabeads). Evonymus europaeus agglutinin (EEA)-coated Dynabeads were used to purify monkey liver endothelium from Percoll gradient separated nonparenchymal cells. EEA-coated beads were also successfully used to purify monkey aortic endothelial cells. The endothelial cells grew to confluence as a cobblestonelike monolayer, expressed Factor VIII related antigen, and incorporated acetylated-low density lipoprotein. The magnetic beads seemed not to modify the normal properties of the isolated endothelium, thus facilitating their use in experimental studies. This immunomagnetic separation technique may be applicable for purification of endothelial cells from a wide variety of tissue sources.

Characterization of adhesive interactions between human endothelial cells and megakaryocytes

Cell-cell adhesion is essential for many immunological functions and is believed to be important in the regulation of hematopoiesis. Adhesive interactions between human endothelial cells and megakaryocytes were characterized in vitro using the CMK megakaryocytic cell line as well as marrow megakaryocytes. Although there was no adhesion between unactivated human umbilical vein endothelial cells (HUVEC) and megakaryocytes, treatment of HUVEC with inflammatory cytokines such as IL-1 beta, tumor necrosis factor alpha, INF-gamma, or the phorbol ester phorbol myristate acetate (PMA) resulted in a time- and dose-dependent increase in adhesion. Stimulation of marrow megakaryocytes or CMK cells with the cytokines IL-1 beta, GM-CSF, IL-6, IL-3, or PMA augmented their adhesion to endothelium. Monoclonal antibodies against the LFA-1 subunit of the leukocyte adherence complex CD18 inhibited the binding of marrow megakaryocytes or CMK cells to HUVEC. Adhesion blocking experiments also demonstrated that the VLA-4/VCAM-1 pathway was important for megakaryocyte attachment to HUVEC. Adhesion promoted maturation of megakaryocytic cells as measured by increased expression of glycoproteins GpIb and GpIIb/IIIa and by increased DNA content. These observations suggest that alterations in megakaryocyte adhesion may occur during inflammatory conditions, mediated by certain cytokines, resulting in augmented megakaryocyte maturation.

Response of a human megakaryocytic cell line to thrombin: increase in intracellular free calcium and mitogen release

The CHRF-288-11 cell line has been previously shown to exhibit properties consistent with a megakaryocytic origin. The response of these cells to thrombin has now been investigated. Thrombin treatment of CHRF-288-11 cells results in both an increase in intracellular free calcium levels and secretion of mitogenic activity and beta-thromboglobulin. Cell viability is not affected. The mitogenic activity released from the cells is due primarily to the presence of basic fibroblast growth factor. Immunohistochemical data indicate a packaging of basic fibroblast growth factor into granular structures. Trypsin and phorbol 12-myristate 13-acetate also initiate release of mitogenic activity from this cell line, whereas under non-stirred conditions collagen and ADP do not. Through measurements of intracellular calcium levels it was determined that thrombin pretreatment of cells ablates a further response to thrombin, but does not block an increase in intracellular calcium levels due to trypsin. This suggests that these two agonists may act through different mechanisms. The thrombin-induced release reaction is inhibited almost completely by the reagents hirudin and dipyridamole, and only partially by indomethacin. These data indicate that the CHRF-288-11 cell line should provide an excellent model system in which to study the packaging of factors into granules which undergo regulated release.

Effects of transforming growth factor beta on megakaryocytic cell fusion and endomitosis

Transforming growth factor beta (TGF-beta) is a cytokine secreted by megakaryocytes and platelets which inhibits the proliferation of megakaryocyte progenitors in vitro. We have studied the effects of TGF-beta on more mature megakaryocytes, using cell lines CMK, DAMI, and CHRF as well as isolated human marrow megakaryocytes as models. Proliferation of these megakaryocytic cell lines was inhibited by TGF-beta 1 at concentrations of 10-100 ng/ml. Although these cell lines secreted small amounts of TGF-beta (up to 100 pg/ml), it was predominantly in an inactive form. Upon induction with 12-phorbol 13-myristate acetate (PMA), they secreted greater amounts of TGF-beta (500-1250 pg/ml), most of which was still inactive in a bioassay. Addition of exogenous active TGF-beta 1 had no effect on ploidy of unstimulated megakaryocytic cell lines or on [3H]thymidine incorporation of isolated human marrow megakaryocytes. Following PMA induction, exogenous TGF-beta 1 had a significant inhibitory effect on ploidy in DAMI cells but not CMK or CHRF cells, suggesting that the phenomenon is restricted to DAMI cells. Because certain cell lines may fuse in vitro, and phorbol esters can promote this phenomenon, we investigated the possibility that fusion was contributing to the increase in ploidy in megakaryocytic cells. Unstimulated megakaryocytic cells did not show spontaneous fusion; when PMA was added to the cultures, fusion was markedly increased, particularly in DAMI cells. These results demonstrate that in vitro fusion accounts for a proportion of the apparent increase in DNA content of megakaryocytic cell lines upon induction with PMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Combining counterflow centrifugal elutriation and glycoprotein Ib-dependent purification of human megakaryocytes: efficacy and selectivity

To estimate the efficacy of human megakaryocyte purification techniques, mixtures of known numbers of megakaryocytes with a known ploidy range and of bone marrow or peripheral blood mononuclear cells were made. These artificial bone marrow samples were submitted to either a counterflow centrifugal elutriation or Percoll density separation followed by the glycoprotein Ib-dependent agglutination procedure. Also crude bone marrow samples were submitted to counterflow centrifugal elutriation directly followed by a glycoprotein Ib-dependent agglutination. The counterflow centrifugal elutriation resulted in a mean megakaryocyte recovery of 81% (mean 81% +/- 2.3). Purification by glycoprotein Ib-dependent agglutination after either a Percoll density separation or counterflow centrifugal elutriation resulted in a recovery of 61% (mean 61% +/- 15%) and 81% (mean 81% +/- 6) respectively. Purity of the resulting material was 87% (mean 87% +/- 11) and 83% (mean 83% +/- 5) respectively. The various isolation procedures did not affect the ploidy distribution of megakaryocytes greater than or equal to 8N. Counterflow centrifugal elutriation was preferred as the preparing step before glycoprotein Ib-dependent agglutination because of the lower variability in recovery and purity of megakaryocyte populations. When large numbers of rather pure and mature megakaryocytes are required, counterflow centrifugal elutriation followed by the glycoprotein Ib-dependent agglutination is a relatively simple method to purify human megakaryocytes without an appreciable loss in ploidy class greater than or equal to 8N.

Immunomagnetic bead isolation of megakaryocytes from guinea-pig bone marrow: effect of recombinant interleukin-6 on size, ploidy and cytoplasmic fragmentation

Guinea-pig bone marrow megakaryocytes were isolated using an antibody to platelet glycoprotein Ib and a second antibody conjugated to magnetic beads. The procedure yielded an average of 644,800 megakaryocytes from two guinea-pigs with an average viability of 83%. All of the platelet glycoprotein Ib positive cells also expressed the platelet glycoprotein IIb-IIIa complex. The size and ploidy of megakaryocytes isolated by this technique were analysed in the presence of 10 ng/ml of interleukin-6 (IL-6). Without IL-6 megakaryocyte size increased significantly after 24 h, but an even larger increase in size occurred in the presence of IL-6. The modal ploidy class was 16N with an average of 19% 2N, 2.6% 4N, 16.4% 8N, 50.8% 16N and 11.1% 32N cells as determined by flow cytometry. Measurements made by microspectrophotometry were in close agreement. After 24 h incubation there was a significant rise in the percentage of 2N and 32N cells. The ploidy distribution after 24 h with IL-6 was the same as the control. Megakaryocytes cultured in the absence of serum on collagen gels did not form pseudopods and fragment, as occurs with serum (Leven et al, 1987). Addition of IL-6 to the serum-free cultures caused megakaryocytes to form extensive proplatelet extensions. We conclude that large numbers of pure guinea-pig bone marrow megakaryocytes can be isolated by immunomagnetic bead selection, including low ploidy immature megakaryocytes. Spontaneous maturation occurred as evidenced by the increase in megakaryocyte size and ploidy. IL-6 altered megakaryocyte size and morphology but not ploidy, indicating that these different characteristics of megakaryocytes may be regulated separately.

Osteotropic factor responsiveness of highly purified populations of early and late precursors for human multinucleated cells expressing the osteoclast phenotype

Recently we have adapted human long-term bone marrow cultures to form multinucleated cells (MNC) that express the osteoclast phenotype and used semisolid culture techniques to identify early (bipotent) and late (unipotent) mononuclear precursors for these MNC. The early precursor can form both osteoclast-like MNC and macrophage polykaryons; the late precursor forms only osteoclast-like MNC. In this study we examined the effects of osteotropic hormones and cytokines of MNC formation from highly purified populations of these early or late mononuclear precursor cells. MNC expressing the osteoclast phenotype were identified by their cross-reactivity with the 23c6 monoclonal antibody, which preferentially identifies osteoclasts. 1,25-(OH)2D3 (10(-8) M), IL-1 beta (10 u/ml), and IL-6 (100 pg/ml) stimulated formation of 23c6-positive MNC from highly purified populations of early or late precursor cells. In contrast, PTH (50 ng/ml) did not act directly on late precursor cells but only stimulated 23c6-positive MNC formation from early precursors. These results show that (1) 1,25-(OH)2D3, IL-1 beta, and IL-6 can stimulate 23c6-positive MNC formation from a highly enriched population of early and late precursors, and (2) PTH does not act on late precursors but may act indirectly on the late precursors.