Murine Long-term Bone Marrow Cultures Research Articles

The effects of interleukin-1 beta and gamma-quantum braking radiation on mesenchymal progenitor cells

In murine bone-marrow stromal microenvironment cells and in human multipotent mesenchymal stromal cells (MMSCs), proinflammatory cytokine interleukin-1 beta (IL-1β) serves as a growth factor. In murine bone tissue, IL-1β expression increases in vivo after irradiation. Here, we have presented our evaluation of the effects of exogenous IL-1β on the expression of NF-kB transcription factors in human MMSCs and stromal layer cells of murine long-term bone marrow cultures (LTBMCs). The cytokine signaling pathway was also activated in murine LTBMC by braking electron radiation in doses of 3-12 Gy. The level of expression of genes that code for IL-1β, IL-1β type-I receptor and NF-kB and IKK protein families have been studied at different time points post exposure. In both human and murine stromal cells, exogenous IL-1β led to an increase in the level of expression of its own gene, while levels of expression of NF-kB and IKK gene families were not substantially changed. Nevertheless, in human cells, a significant correlation between levels of expression of IL-1β and all NF-kB family genes was detected. It points to a similarity in IL-1β signal pathways in mesenchymal and hematopoietic cells, where the posttranslational modifications of NF-kB transcription factors play a major role. The irradiation of murine LTBMC resulted in a transient increase in the expression of genes that code NF-kB transcription factors and IL-1β. These results indicate an important role of Rel, Rela, Relb, and Nfkb2 genes in the induction of IL-1β signal pathway in murine stromal cells. An increase in IL-1β expression after the irradiation of stromal cells may be related to both the induction of inflammation due to massive cell death and to a profound stimulation of the expression of this proinflammatory cytokine expression.

Investigation of the Mesenchymal Stem Cell Compartment by Means of a Lentiviral Barcode Library.

The hematopoietic bone marrow microenvironment is formed by proliferation and differentiation of mesenchymal stem cells (MSCs). The MSC compartment has been less studied than the hematopoietic stem cell compartment. To characterize the structure of the MSC compartment, it is necessary to trace the fate of distinct mesenchymal cells. To do so, mesenchymal progenitors need to be marked at the single-cell level. A method for individual marking of normal and cancer stem cells based on genetic "barcodes" has been developed for the last 10 years. Such approach has not yet been applied to MSCs. The aim of this study was to evaluate the possibility of using such barcoding strategy to mark MSCs and their descendants, colony-forming units of fibroblasts (CFU-Fs). Adherent cell layers (ACLs) of murine long-term bone marrow cultures (LTBMCs) were transduced with a lentiviral library with barcodes consisting of 32+ 3 degenerate nucleotides. Infected ACLs were suspended, and CFU-F derived clones were obtained. DNA was isolated from each individual colony, and barcodes were analyzed in marked CFU-F-derived colonies by means of conventional polymerase chain reaction and Sanger sequencing. Barcodes were identified in 154 marked colonies. All barcodes appeared to be unique: there were no two distinct colonies bearing the same barcode. It was shown that ACLs included CFU-Fs with different proliferative potential. MSCs are located higher in the hierarchy of mesenchymal progenitors than CFU-Fs, so the presented data indicate that MSCs proliferate rarely in LTBMCs. A method of stable individual marking and comparing the markers in mesenchymal progenitor cells has been developed in this work. We show for the first time that a barcoded library of lentiviruses is an effective tool for studying stromal progenitor cells.

Parathyroid Hormone (1–34) Treatment Induces Hematopoietic Precursor Cell Expansion in Murine Long-Term Bone Marrow Culture.

Parathyroid hormone (PTH) induces activation and increases the number of osteoblasts. An increase the stem cells number (Lin-Sca1+cKit+) was observed in mice after 4 weeks of PTH treatment, that suggest osteoblasts participation in regulation of hematopoiesis (Calvi, et al., 2003, Nature, 425, 841). Long-term bone marrow culture (LTBMC) was used for the study of PTH influence on hematopoietic progenitors of different stages of maturation. Rat PTH (1–34) (final concentration, 10−7M) was supported during whole culture period. Cell number, colony-forming units in culture (CFU-GM, CFU-C-21 days) and cobblestone area forming cells (CAFC) were measured during 10 weeks. The number of mature cells in culture did not changed during PTH treatment. The number of studied progenitors did not changed significantly during 3 and 6 weeks of PTH treatment. The number of CFU-GM, CFU-C-21 days and CAFC 14 days, CAFC 21 days, CAFC 28 days increased 7 –10 fold in suspension fraction of LTBMC after 10 weeks of PTH treatment.Table 1. Number of different precursor cells in suspension fraction of LTBMC after PTH treatment.To evaluate the possibility of stem cells expansion by using of PTH treated adherent cell layers (ACL) of LTBMC, the PTH-treated for 4 and 8 weeks cultures, were irradiated with 40 Gy and seeded with 2 × 106 bone marrow cells depleted of adherent cells. Following 24 hours the number of survived CAFC 8 – 28 was analyzed. On PTH-treated ACL the number of CAFC 21 increased 2,7 ± 0,4 fold as compared with fresh bone marrow or culture with non-treated ACLs. The number of CAFC 28, which characterizes the number of marrow repopulating cells, increased 2 fold only after cultivation on ACL treated with PTH for 8 weeks.Table 2. CAFC number in bone marrow cultivated 24 hours on PTH treated ACL of LTBMCThe data suggest possibility to increase stem cell expansion ex vivo on pharmacologically manipulated microenvironment.Time of cultivation, weeksSpecificity of progenitorNumber of precursors, per 100000 cellsControlControlPTH treatment3CFU-GM50 ± 5.277 ± 5.66CFU-GM33 ± 431 ± 5.910CFU-GM20 ± 4.8147.5 ± 3.53CFU-C-2155 ± 5.976.6 ± 11.210CFU-C-2111.5 ± 1.7102.0 ± 2.03CAFC-721.620.36CAFC-725.926.910CAFC-70.93.03CAFC-211.010.696CAFC-210.430.4810CAFC-210.283.113CAFC-280.320.556CAFC-280.120.1410CAFC-280.10.82Age of CAFC (days)Number of CAFC per 2 x 10^6 bone marrow cellsnot treatedPTH (4 weeks)PTH (8 weeks)CAFC-7424.1804.5647.5CAFC-14262.5529.8295.2CAFC-2193.5272.7226.2CAFC-2838.330.179.2

Low level of gene transfer to and engraftment of murine bone marrow cells from long-term bone marrow cultures

Objective We wanted to determine whether the long-term bone marrow culture (LTBMC) transduction system would lead to efficient gene transfer and engraftment of murine repopulating hematopoietic stem cells (HSC), particularly in nonablated recipients. Materials and Methods Congenic mouse strains expressing Ly 5.1 or Ly 5.2 and the GP+E86 cell line producing the MGirL22Y vector carrying the gene for enhanced GFP were used. Murine LTBMCs were established and demi-depopulated on days 7 and 14 with addition of vector supernatant on days 8 and 15. Results Cell recovery on day 21 was 21.3% ± 3.8% of input cells and CFU-C recovery was 9.7 ± 3.4% as compared with CFU-C of input cells. In vitro transduction efficiency determined by CFU-C expressing GFP was 22.2% ± 1.6%. In irradiated (950 cGy) mice transplanted with 2 × 10 6 LTBMC cells, 94% of nucleated cells in the blood at week 16 were of donor origin. However, GFP was only detected at low level in a few animals at week 4 and not later. Analysis of bone marrow from these mice at week 20 did not show any GFP expression and semiquantitative PCR revealed a transgene level of < 1%. When 3.5–20.8 × 10 6 LTBMC cells (corresponding to 20–100 × 10 6 fresh cells) were transplanted to nonablated recipients, no engraftment or GFP expression were detected. Competitive repopulation experiments showed that the long-term repopulation ability (LTRA) of the LTMC cells was only 7% of fresh cells. Conclusion These results indicate that LTBMC transduction of murine cells leads to low-level transduction of progenitors, no gene transfer to repopulating stem cells, and reduction in LTRA in ablated and nonablated recipients.

METABOLISM OF DOXORUBICIN IN LONG-TERM BONE MARROW CULTURES AND SR-4987 STROMAL ESTABLISHED CELL LINE

The metabolism of doxorubicin was studied in murine long-term bone marrow cultures (LTBMC) and in SR-4987 established stromal cells in comparison with primary cultures of murine and rat hepatocytes. The toxicity of metabolites was verified by testing their effects on the clonogenicity of granulo-macrophage progenitors. Metabolic activity was compared in subcellular fractions of SR-4987 cells and murine hepatocytes. Doxorubicin was transformed in long-term bone marrow cultures, SR-4987 cells and murine/rat hepatocytes to less toxic metabolites: 13-OH doxorubicin and a less polar metabolite which were non-toxic on granulo-macrophage progenitors. Among the hemopoietic compartments, stromal cells were responsible for the biotransformation of doxorubicin. The capability of the SR-4987 established stromal cell line to metabolize doxorubicin was higher than that of primary cultures of hepatocytes and bone marrow, and the highest activity was concentrated in the microsomes. These results suggest that in vitro models using primary cell cultures and established cell lines could be a useful tool for investigating the mechanisms underlying detoxification in the bone marrow stromal population.

Captopril inhibits the proliferation of hematopoietic stem and progenitor cells in murine long-term bone marrow cultures.

Drugs used mainly for the treatment of hypertension, such as angiotensin I-converting enzyme (ACE) inhibitors, can cause pancytopenia. The underlying cause of this side effect remains unknown. In the present study, long-term bone marrow cultures (LTBMCs) were utilized to evaluate the role of captopril (D-3-mercapto-2-methylpropionyl-L-proline), one of the potent ACE inhibitors, in regulating hematopoietic stem/progenitor cell proliferation. Captopril (10(-6) M final concentration) was added to LTBMCs at the beginning of the culture period and at weekly intervals for six weeks. There was no toxicity to the bone marrow cells as measured by the unchanged cell number in the nonadherent layer during the whole culture period, and there was an increased cellularity of the adherent layer at the end of the six weeks of treatment. However, captopril decreased the proportion of granulocyte-macrophage colony-forming cells (GM-CFCs) in S phase at weeks 2 and 3 as well as that of high proliferative potential colony-forming cells (HPP-CFCs) at week 3 in the nonadherent layer. There was no change in the kinetics of the GM-CFCs and HPP-CFCs present in the adherent layer. These results suggest that captopril causes myelosuppression by inhibiting hematopoietic cell proliferation of progenitor and stem cells rather than depleting cells of the bone marrow microenvironment.

Ethanol and Acetaldehyde Inhibit the Formation of Early Osteoblast Progenitors in Murine and Human Bone Marrow Cultures

Alcohol abuse is commonly associated with reduced bone mass and osteoporosis as a consequence of both systemic and direct cellular effects. To clarify some of the pathways by which alcohol exerts its actions directly on bone cells, we investigated the formation of early osteoblast progenitors (colony-forming units for fibroblasts; CFU-F) in long-term murine and human bone marrow cultures exposed to ethanol and to its main metabolite, acetaldehyde. In murine bone marrow cultures, obtained from Swiss female mice, ethanol inhibited CFU-F formation (maximal reduction +/- SEM: 50 +/- 2%; p < 0.01) at concentrations ranging from 0.04% to 0.6% that are similar to those reached in vivo in alcoholics. Acetaldehyde strongly reduced CFU-F formation at concentrations of 0.004% and 0.02%, and completely abolished it at the dose of 0.06%. Similarly, ethanol (at concentrations > or =0.02%) and acetaldehyde (from 0.004% to 0.06%) significantly decreased the number of CFU-F in human bone marrow cultures; the mean reduction observed with ethanol was 63 +/- 12% (p < 0.05), whereas acetaldehyde completely prevented CFU-F formation at the concentration of 0.06%. These in vitro observations were confirmed by the in vivo findings that the CFU-F formation in bone marrow cultures from nine young, chronic, noncirrhotic alcoholics was significantly reduced (70 +/- 15%), compared with seven age-matched normal subjects (p < 0.01). In addition, acetaldehyde inhibited cell proliferation in human osteoblastic cells (MG-63 and HOBIT cell lines), whereas ethanol reduced proliferation only in MG-63 cells. Our results indicate that ethanol and acetaldehyde may directly inhibit the osteoblastogenic potential of the bone marrow, and this effect may contribute to the decreased bone formation observed in alcoholics.

The pivotal role of interleukin 6 in formation and function of hematopoietically active murine long-term bone marrow cultures.

The multifunctional cytokine interleukin 6 (IL-6) is involved in the regulation of inflammatory and immune responses, and influences many bone and bone marrow functions. In this report we show high concentrations of IL-6 in the supernatant of murine long-term bone marrow cultures (LTBMC). The concentration increases following medium change peaking 12 h later. IL-6 plays a critical role in the generation and maintenance of myelopoiesis in LTBMC. The addition of monoclonal anti-IL-6 antibody to culture significantly suppresses myeloid cell production. IL-6 is also necessary for stromal layer development and the initiation of myelopoiesis in LTBMC. Horse sera (HS) containing low concentrations of IL-6 did not support LTBMC stromal layer development or myeloid cell production, whereas those with high concentrations did. LTBMC initially set up with horse serum containing high IL-6 concentration produced higher concentrations of colony-stimulating activity and IL-6 at the fifth week after culture initiation than those with low concentrations. The ability of a deficient serum to support myelopoiesis could be improved by the addition of recombinant IL-6 to culture. Similarly, the addition of an anti-IL-6 antibody to culture impaired the ability of a HS to initiate and support myelopoiesis in LTBMC. These results suggest that IL-6 is one of the factors that play an essential role in the formation and function of hematopoietically active LTBMC.

Production of human and murine eosinophils in vitro and assay for eosinophil differentiation factors.

Bone marrow cells from a number of animal species have been used extensively in liquid and semisolid cultures to study hemopoiesis and to produce functional mature cells and factor-dependent cell lines (for review see ref. ). Neutrophils and macrophages are produced without added growth factors from murine long-term bone marrow cultures (), whereas lymphoid cells (,) and megakaryocytes (reviewed in ref. ) can be induced under certain conditions.

Murine marrow stromal response to myelotoxic agents in vitro.

Previous studies have shown that the haemopoietically active murine long-term bone marrow culture (LTBMC) is a useful model for studying drug-induced suppression and recovery of myelopoiesis. We studied the effects on stromal morphology and stromal progenitors, assessed as colony forming unit-fibroblasts (CFU-F), of the addition of either the antimetabolite methotrexate (MTX) or the betalactam ceftazidime (CEF) to LTBMC. The examination of 500 micrograms/ml CEF-treated cultures revealed a stroma that appeared empty, with modest reduction in total stromal counts, and significant decreases in fat-containing and endothelial cells. In contrast, treatment with 1 microM MTX for 1 week initially caused minimal morphologic stromal changes, thereafter total stromal cell count as well as fibroblastoid, endothelial, fat containing and macrophage cells significantly increased. Haemopoiesis and the stroma recovered. Both CEF and MTX reversibly suppressed stromal progenitor cells in LTBMC. When added directly to CFU-F cultures, the concentrations resulting in a 50% colony growth inhibition were 214 micrograms/ml for CEF and 375 nM for MTX. These results suggest that CEF, but not MTX, has direct toxic effects on the stroma of established LTBMC. Stromal cell increase following MTX treatment probably indicates a stromal response that may contribute to haemopoietic cell recovery.

Requirement for CD44 in proliferation and homing of hematopoietic precursor cells.

The hematopoietic form of the adhesion molecule CD44 is known to be involved in lymphocyte maturation and homing. To define lineage and stage of maturation, which requires expression of CD44, murine long-term bone marrow cultures were established. Stroma formation and proliferation of early as well as committed erythroid, myeloid, and lymphoid progenitors were evaluated under the influence of monoclonal anti-CD44 antibodies. Although the formation of stromal elements was not affected, formation of cobblestone areas was completely abolished. [3H]thymidine suicide confirmed that anti-CD44 treatment interfered with the proliferation of early and committed hematopoietic progenitor cells. In addition, homing and seeding of bone marrow cells was impaired by anti-CD44. The data are indicative of a dual functional mode of CD44 in adhesion and proliferation of hematopoietic progenitors and confirm an essential requirement for the molecule in early stages of hematopoiesis.

Long-Term Protection of Hematopoiesis Against the Cytotoxic Effects of Multiple Doses of Nitrosourea by Retrovirus-Mediated Expression of Human O -Alkylguanine-DNA-Alkyltransferase

A human O6-alkylguanine-DNA-alkyltransferase (ATase) cDNA-containing retrovirus was used to infect murine long-term primary bone marrow cultures. High levels of ATase expression were obtained, and colony-forming cells of the granulocyte-macrophage lineage from the cultures transduced with the human ATase retrovirus were three times more resistant to the alkylating agent, N-methyl-N-nitrosourea (MNU), than control cultures. Furthermore, expression of the human ATase protected long-term hematopoiesis, measured as the output of progenitor cells to the nonadherent fraction of the culture, against the cytotoxic effects of repeated exposures to MNU. These results clearly show that a human ATase cDNA-containing retrovirus can be used to infect long-term primary bone marrow cultures and that this attenuates their sensitivity to nitrosoureas.

Long-term protection of hematopoiesis against the cytotoxic effects of multiple doses of nitrosourea by retrovirus-mediated expression of human O6-alkylguanine-DNA-alkyltransferase

A human O6-alkylguanine-DNA-alkyltransferase (ATase) cDNA-containing retrovirus was used to infect murine long-term primary bone marrow cultures. High levels of ATase expression were obtained, and colony- forming cells of the granulocyte-macrophage lineage from the cultures transduced with the human ATase retrovirus were three times more resistant to the alkylating agent, N-methyl-N-nitrosourea (MNU), than control cultures. Furthermore, expression of the human ATase protected long-term hematopoiesis, measured as the output of progenitor cells to the nonadherent fraction of the culture, against the cytotoxic effects of repeated exposures to MNU. These results clearly show that a human ATase cDNA-containing retrovirus can be used to infect long-term primary bone marrow cultures and that this attenuates their sensitivity to nitrosoureas.

Mofarotene (Ro 40-8757) Inhibits Hematopoiesis In Vitro by Preventing Maturation From Primitive Progenitor Cells

AbstractThe effect of the arotinoid mofarotene (Ro 40-8757; 4-[2-[p-[(E)-2(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-propenyl]phenoxy]ethyl]morpholine) on stromal cell-mediated hematopoiesis was examined in murine long-term bone marrow cultures. Whether added at week 2 to regenerating cultures or at week 4 to plateau-phase cultures, mofarotene strongly inhibited total cell production in a dose-dependent manner. Progenitor cell production was also inhibited, but to a lesser extent. When added at the initiation of culture, 1 μmol/L mofarotene did not affect formation of the adherent layer, but production of total nucleated cells and progenitors was inhibited over the next 10 weeks by 95% and 96%, respectively. However, after mofarotene treatment ceased, progenitor cell levels began increasing immediately, and cell production reached plateau levels comparable with those of control cultures within 4 weeks. Hematopoiesis was maintained for 14 more weeks, indicating that long-term culture-initiating cells survived the treatment. Assays of spleen colony-forming units (CFU-S) in the adherent layers showed an enrichment of day-13 CFU-S relative to the more mature day-9 CFU-S. Mofarotene did not inhibit colony formation by bone marrow cells stimulated by exogenous growth factors and did not decrease production of growth factors by stromal cells in the cultures, as determined by functional assays and by mRNA levels. These results suggest that mofarotene blocks differentiation of very primitive progenitors, inhibiting production of more mature hematopoietic elements.

Interleukin-11 Stimulates Multilineage Progenitors, But Not Stem Cells, in Murine and Human Long-Term Marrow Cultures

Interleukin-11 (IL-11) is a bone marrow microenvironment-derived growth factor with pleiotropic effects on a variety of hematopoietic cells. To more accurately assess the effects of IL-11 on stem and progenitor compartments within the hematopoietic microenvironment (HM), we added recombinant human (rh) IL-11 to human and murine long-term bone marrow cultures (LTMC) and analyzed primitive (high proliferative potential-colony forming cells [HPP-CFC], long-term culture-initiating cells [LTC-IC], and long-term reconstituting stem cells) and progenitor (day 12 colony forming unit-spleen [CFU-S12], colony forming unit-megakaryocyte [CFU-Mk] and colony forming unit-granulocyte/macrophage [CFU-GM]) compartments throughout the duration of the cultures. rhIL-11 (100 ng/mL) added twice weekly resulted in significantly increased nonadherent (NA) cellularity, CFU-GM, and CFU-Mk production in human LTMC. Addition of rhIL-11 to murine LTMC was associated with a 5- to 40-fold increase in CFU-GM and a four- to 20-fold increase in day 12 CFU-S in NA cells. However, IL-11 had no significant effect on total HPP-CFC concentration and decreased the size of the more primitive stem/progenitor compartment as evidenced by both decreased LTC-IC frequency in human LTMC and decreased frequency of long-term reconstituting stem cells in murine LTMC. These data suggest that IL-11 may increase commitment of stem cells into a multipotential progenitor compartment.

Morphological characterization of stromal cell types in hematopoietically active long-term murine bone marrow cultures.

Accurate histological evaluation of stromal morphology is very difficult in cultures incubated in plastic flasks. Employing glass flasketts, we were able to characterize the morphology and immunocytochemistry of four marrow stromal cell types in a functionally intact microenvironment of murine long-term bone marrow cultures (LTBMCs). Fibroblastoid cells stained positively for collagen Type I and III, negatively for von Willebrand factor (vWf), the mouse macrophage F4/80 antigen, and the Bandeiraea simplicifolia lectin I isolectin B4 (BSL I-B4). Endothelial cells stained positively for vWf antigen and lectin BSL I-B4 but negatively for collagen Types I and III and for F4/80 antigen. Fat-containing cells had a dense, ovaloid, indented nucleus and fat-containing vacuoles. Macrophages were strongly positive for the F4/80 antigen and stained weakly with BSL I-B4. Between the fourth and ninth weeks after culture initiation, fibroblastoid and endothelial cells remained constant, between 21 +/- 2% and 24 +/- 2% and between 3 +/- 0.3% and 4 +/- 0.4%, respectively, of the total stromal cell population. By contrast, the percentage of fat-containing cells decreased significantly from 26 +/- 3% at Week 4 to 17 +/- 2% at Week 9, and macrophages increased significantly from 49 +/- 1% at Week 4 to 57 +/- 1% at Week 9. This characterization of the stromal cell types in functionally intact LTBMCs should assist in the study of the complex interactions among the marrow stroma, cytokine production, and hematopoiesis.

AM5, a protein-associated polysaccharide, stimulates hematopoiesis and modulates the expression of endogenous hematopoietic growth factors in murine long-term bone marrow cultures.

We have investigated the mechanism behind the hematopoietic stimulation mediated by AM5, a protein-associated polysaccharide that stimulates in vivo the murine hematopoietic system. A dose-dependent increase in hematopoietic progenitors was observed in long-term bone marrow cultures (LTBMCs) treated in vitro with AM5. The stimulatory effect was more marked in colony-forming units-granulocyte-macrophage (CFU-GM) than in CFU-spleen (CFU-S) progenitors and also more significant in the supernatant than in the adherent layer. This stimulatory effect was reversible, and continuous stimulation with high doses of AM5 was conductive to a progressive exhaustion of the culture. The analysis of the CFU-GM stimulating activity present in the supernatant of AM5-treated cultures revealed a dose-dependent induction of granulocyte-macrophage colony-stimulating activity (GM-CSA), in contrast with control cultures in which no CSA was detected. Northern blots of LTBMC-adherent layers obtained after in vitro treatment with AM5 revealed a significant mRNA expression for interleukin 1 alpha (IL-1 alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage CSF (M-CSF) and granulocyte CSF (G-CSF), in contrast with adherent layers from untreated cultures which only expressed, in detectable levels, M-CSF and stem cell factor (SCF). The SCF expression was down-modulated in AM5-treated cultures. Our results strongly suggest that the hematopoietic stimulation induced by AM5 is mediated by the modulated expression of endogenous hematopoietic growth factors.

Osteocalcin promotes differentiation of osteoclast progenitors from murine long-term bone marrow cultures.

Murine long-term bone marrow cultures (LTBMCs) were used to generate hematopoietic cells free from marrow stromal cells. These progenitor cells were treated with GM-CSF (5 U/ml) with or without rat bone osteocalcin or rat serum albumin in either alpha-MEM with 2% heat-inactivated horse serum alone (alpha) or supplemented with 10% L-cell-conditioned medium (as a source of M-CSF) (L10). Few substrate-attached cells survived in basal alpha medium, but when treated with L10 medium or GM-CSF, they survived and proliferated. Osteocalcin did not significantly affect survival or proliferation. Subcultures of cells treated with GM-CSF had large numbers of multinucleated cells, more than half of which were tartrate-resistant acid phosphatase-positive (TRAP). Osteocalcin further promoted the development of TRAP-positive multinucleated cells; a dose of 0.7 microgram/ml osteocalcin promoted osteoclastic differentiation by 60%. Using a novel microphotometric assay, we detected significantly more tartrate-resistant acid phosphatase activity in the osteocalcin plus GM-CSF group (75.6 +/- 14.2) than in GM-CSF alone (53.3 +/- 7.3). In the absence of M-CSF, GM-CSF stimulated tartrate-resistant acid phosphatase activity, but osteocalcin did not have an additional effect. These studies indicate that osteocalcin promotes osteoclastic differentiation of a stromal-free subpopulation of hematopoietic progenitors in the presence of GM-CSF and L-cell-conditioned medium. These results are consistent with the hypothesis that this bone-matrix constituent plays a role in bone resorption.

Effects of ceftazidime, a betalactam antibiotic, on murine haemopoiesis in vitro

Agranulocytosis has been reported in 5-15% of patients treated with high-dose betalactam antibiotics (BLA). We investigated the toxic effect of ceftazidime (CEF) as a representative of these antibiotics on colony-forming unit-granulocyte/macrophage (CFU-GM), on burst-forming unit-erythroid (BFU-E) colony growth and on myelopoiesis in murine long-term bone marrow culture (mLTBMC). The CEF concentration resulting in a 50% inhibition of growth was 146 micrograms/ml (267 microM) for CFU-GM, 132 micrograms/ml (241 microM) for BFU-E and 180 micrograms/ml (329 microM) for myeloid cell production in the supernatant of mLTBMC. Following addition of CEF to mLTBMC, CFU-GM remained low for 1 week and total myeloid cell production remained low for 2 weeks after removal of CEF from culture. Thereafter the values returned to control levels. The myeloid differential counts in the supernatant and adherent layers demonstrated a 'maturation arrest', which could be overcome by simultaneously adding all-trans retinoic acid to culture. These results demonstrate that CEF has reversible inhibitory effects on myelopoiesis and highlight the utility of in vitro haemopoietic assays as models to examine drug-induced haemopoietic dyscrasias.

Effects of rIL-7 on Murine Bone Marrow NK Precursor Cells

We recently demonstrated that functional NK cells are produced from their precursors in murine long-term bone marrow cultures without the addition of exogenous growth factors. Because IL-7 is known to be produced by bone marrow stromal cells and is a proliferation factor for some immature cells of the B and T cell lineages, we tested whether rIL-7 could support the proliferation or maturation of NK precursor cells. By itself, rIL-7 did not induce NK lytic activity in cultures of unseparated bone marrow cells (BMC), but it did augment the response of unseparated BMC to 50 U rIL-2/ml, with a maximal enhancement at 10 ng IL-7/ml. Depletion experiments demonstrated that the IL-7-induced increase in cytotoxicity was not due to NK precursors, however, but to mature T and NK cells. IL-7 preferentially increased the number of CD8 + cells. Preculture of NK 1.1-depleted BMC with IL-7 did not increase the total number of NK 1.1 + cells or the lytic activity generated from NK precursor cells. However, IL-2-responsive NK lineage cells survived better in IL-7-supplemented medium than in medium alone. Thus, soluble rIL-7 did not expand the NK precursor cell population in vitro but it maintained the viability and subsequent responsiveness to IL-2 of NK precursors.