Assessment of telomere length in hematopoietic interphase cells using in situ hybridization and digital fluorescence microscopy

Telomeres are G/C-rich repetitive DNA sequences at the end of all eukaryotic chromosomes. The loss of telomeric repeat sequences during cell divisions has been proposed as a possible mechanism for cell senescence. The standard procedure for measurement of telomere length is Southern blot (SB) hybridization with a telomere-specific probe. However, in using this technique no information can be obtained on variation in telomeric fragments due to interchromosomal, intrachromosomal, and intercellular differences. Lansdorp et al. (Hum Mol Genet 5:685-691, 1996) developed a method to measure individual telomeres, using in situ hybridization on metaphase chromosomes, employing peptide nucleic acid (PNA) probes and digital fluorescence microscopy. In this paper we describe a method that can be used to assess telomeric length in interphase cells. An algorithm was developed to measure the total intranuclear fluorescence in situ hybridization (FISH) signal, which features accurate correction for the local autofluorescence. Application of this methodology to samples of fetal liver, umbilical cord blood, and adult bone marrow cells showed a gradual decrease of average telomeric length. Southern blot analysis and PNA FISH measurements on chromosomes in the same samples showed similar results. Advantages of interphase measurements include the possibility of studying nonproliferating cells, thus avoiding selection and cell culturing.

Assessment of telomere length in hematopoietic interphase cells using in situ hybridization and digital fluorescence microscopy

Telomeres are G/C-rich repetitive DNA sequences at the end of all eukaryotic chromosomes. The loss of telomeric repeat sequences during cell divisions has been proposed as a possible mechanism for cell senescence. The standard procedure for measurement of telomere length is Southern blot (SB) hybridization with a telomere-specific probe. However, in using this technique no information can be obtained on variation in telomeric fragments due to interchromosomal, intrachromosomal, and intercellular differences. Lansdorp et al. (Hum Mol Genet 5:685-691, 1996) developed a method to measure individual telomeres, using in situ hybridization on metaphase chromosomes, employing peptide nucleic acid (PNA) probes and digital fluorescence microscopy. In this paper we describe a method that can be used to assess telomeric length in interphase cells. An algorithm was developed to measure the total intranuclear fluorescence in situ hybridization (FISH) signal, which features accurate correction for the local autofluorescence. Application of this methodology to samples of fetal liver, umbilical cord blood, and adult bone marrow cells showed a gradual decrease of average telomeric length. Southern blot analysis and PNA FISH measurements on chromosomes in the same samples showed similar results. Advantages of interphase measurements include the possibility of studying nonproliferating cells, thus avoiding selection and cell culturing.

Interleukin-9 stimulates the proliferation of enriched human erythroid progenitor cells: additive effect with GM-CSF

In the study we report here we investigated the colony-stimulating activities of interleukin-9 (IL-9). In the presence of erythropoietin, IL-9 was found to stimulate the proliferation of relatively early erythroid progenitor cells (BFU-E) from normal human bone marrow cells depleted of mononuclear phagocytes and T lymphocytes. Neutralization experiments demonstrated that the observed BFU-E-stimulating effect was not the result of intermediate production of IL-3 or GM-CSF by residual accessory cells in response to IL-9. Accordingly, the effects of IL-9 were preserved when cell suspensions were further depleted of accessory cells using CD34 enrichment of progenitor cells. Furthermore, IL-9 did not stimulate bone marrow mononuclear cells to express mRNA for IL-3, GM-CSF, EPA (erythroid-promoting activity), or IL-4, as determined by a cDNA-PCR method. IL-9 is likely to act on a subpopulation of IL-3-responsive erythroid progenitor cells that are not stimulated by GM-CSF, since plateau concentration of IL-9 and GM-CSF had additive effects on BFU-E formation, whereas a combination of IL-9 and IL-3 did not. In addition to its burst-promoting activity, IL-9 was found to have a modest stimulatory activity on myeloid progenitor cells (CFU-GM) in some experiments, suggesting that this effect may be donor related.

Human interleukin for DA cells (HILDA) does not affect the proliferation and differentiation of hematopoietic progenitor cells in human long-term bone marrow cultures

Human Interleukin for DA cells (HILDA), a cytokine also known as leukemia inhibitory factor (LIF), induces proliferation without concurrent differentiation of murine embryonic stem cells. Therefore, we investigated the effects of recombinant HILDA/LIF on the proliferation and differentiation of human hematopoietic progenitor cells (HPC) grown in long-term bone marrow cultures (LTBMC). Pre-established stromal cell layers were reinoculated with autologous cryopreserved mononuclear phagocyte- and T-lymphocyte-depleted bone marrow cells in the presence or absence of HILDA/LIF (200 U/ml). At weekly intervals cultures were sacrificed, and the cells in the adherent and the nonadherent cell fractions were counted. The numbers of HPC were determined by culturing these cells in semisolid medium stimulated with phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM), and LTBMC supernatants were assayed in semisolid cultures for the presence of colony-stimulating activity (CSA). The total number of cells, their differential counts, the number of HPC, and the concentrations of CSA in culture supernatants were similar for long-term cultures containing HILDA/LIF and for controls. These data suggest that HILDA/LIF may not play a role in the proliferation and differentiation of normal human (early) HPC in LTBMC. Moreover, HILDA/LIF did not stimulate the proliferation of relatively mature progenitor cells in semisolid cultures, not did it influence the colony formation induced by other colony-stimulating factors (CSF). Finally, using a [3H]thymidine suicide test we could not find an effect of HILDA/LIF on the cell-cycle status of HPC.

In vivo production of interleukin-5, granulocyte-macrophage colony-stimulating factor, macrophages colony-stimulating factor, and interleukin-6 during intravenous administration of high-dose interleukin-2 in cancer patients

Recombinant human interleukin-2 (IL-2), administered to cancer patients by continuous intravenous (IV) infusion (3 x 10(6) U/m2/d), was found to induce the in vivo production of colony-stimulating factors (CSF). Plasma obtained from patients during IL-2 treatment stimulated in vitro colony formation of normal human bone marrow cells, depleted of mononuclear phagocytes and T lymphocytes. This colony-stimulating activity (CSA) was identified as IL-5, granulocyte-macrophage CSF (GM-CSF), and macrophage CSF (M-CSF), by the ability of specific antibodies against these factors to neutralize their effects. The presence of IL-2-induced GM-CSF and M-CSF was also demonstrated by specific radioimmunoassays. During IL-2 treatment, plasma also contained detectable levels of IL-6, which was measured in a bioassay. Using a cDNA-polymerase chain reaction (PCR) with specific primer sets for the various CSF, we showed that IL-2 treatment induced the expression of mRNA for M-CSF, GM-CSF, IL-3, and IL-5, but not for granulocyte CSF (G-CSF) in peripheral blood mononuclear cells, suggesting differential expression of CSF in vivo in response to IL-2. Furthermore, no negative regulators of hematopoiesis, such as interferon gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha), were found in plasma. These data illustrate that in vivo administration of high-dose IL-2 may result in a stimulatory effect on hematopoiesis. The induction of detectable levels of IL-5 and GM-CSF in the circulation may explain the eosinophilia and neutrophilia observed in these patients.

Increased numbers of circulating haematopoietic progenitor cells after treatment with high-dose interleukin-2 in cancer patients

Immunotherapy with recombinant interleukin-2 (IL-2) and lymphokine-activated killer (LAK) cells has been applied to patients with metastatic cancers for its antitumour activity. In the present study we investigated the effects of in vivo administration of IL-2 (3 x 10(6) U/m2/d, continuously i.v.) on haematopoiesis. Six patients with disseminated renal cell carcinoma, treated with IL-2 and LAK cells, were monitored for the numbers of white blood cells and circulating haematopoietic progenitor cells (HPC). During IL-2 treatment lymphopenia developed, followed by lymphocytosis after discontinuation of IL-2 infusions. IL-2 administration also resulted in neutrophilia and eosinophilia. Absolute numbers of circulating HPC declined markedly during IL-2 treatment. However, after completing IL-2 infusions, the numbers of circulating erythroid (BFU-E), myeloid (CFU-GM) and multipotential progenitor cells (CFU-GEMM) strongly increased, reaching a maximum after 5 d (day 10 from the start of IL-2 treatment). This increase did not result from repeated leucaphereses, since patients treated with IL-2 alone showed a similar response. In comparison with pretreatment levels the pool of circulating HPC expanded about 20-fold. This study illustrates that IL-2 treatment has a biphasic effect on the frequency of circulating BFU-E, CFU-GM and CFU-GEMM, causing a decrease during IL-2 infusion, followed by an increase after IL-2 administration. The total number of progenitor cells harvested by four consecutive leucaphereses is in the range that is commonly used for peripheral blood stem cell autografting.

Interleukin-6 is not involved in the interleukin-1-induced production of colony-stimulating factors by human bone marrow stromal cells and fibroblasts

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a role in regulation of hematopoiesis. Because IL-6 is coinduced with colony-stimulating factors (CSFs) by various cell types in response to stimulation with IL-1, we investigated whether IL-6 is involved in the IL-1-induced production of CSF by human bone marrow (BM) cells in long-term culture or human fibroblasts. We showed that IL-6 does not induce CSF production by these cells. Neither addition of exogenous IL-6 nor neutralization of endogenous production of IL-6 by an anti-IL-6 monoclonal antibody (MoAb) diminished the IL-1-induced colony-stimulating activity (CSA), indicating that IL-6 did not act synergistically with IL-1. Finally, IL-6 did not influence the kinetics of IL-1-induced CSA production by human fibroblasts. We conclude that IL-6, either alone or in combination with IL-1, does not induce CSF production by human BM stromal cells or fibroblasts.

Interleukin-1 synergizes with granulocyte-macrophage colony-stimulating factor on granulocytic colony formation by intermediate production of granulocyte colony-stimulating factor

Interleukin-1 (IL-1) was found to act synergistically with granulocyte-macrophage colony-stimulating factor (GM-CSF) on granulocytic colony growth of normal human bone marrow cells, depleted of mononuclear phagocytes and T lymphocytes. Using CD34/HLA-DR-enriched bone marrow cells we demonstrated that this activity of IL-1 was not a direct action on hematopoietic progenitor cells, but an effect of an intermediate factor produced by residual accessory cells in response to IL-1. Neutralization experiments using an anti-IL-6 antiserum showed that IL-1-induced IL-6 did not contribute to the observed synergy. Furthermore, IL-6 by itself had neither a direct stimulatory effect on CFU-GM colony growth, nor did it act synergistically with GM-CSF on granulocytic or monocytic colony formation. Neutralization experiments with an anti-G-CSF monoclonal antibody showed that IL-1-induced G-CSF production was responsible for the synergy with GM-CSF. Using combinations of G-CSF and GM-CSF this synergistic activity could be detected at concentrations of G-CSF as low as 0.1 ng/mL (10 U/mL). Our results indicate that IL-1, but not IL-6, stimulates the GM-CSF-dependent proliferation of relatively mature myeloid progenitor cells in the presence of small numbers of accessory cells.

Interleukin 1 and poly(rI).poly(rC) induce production of granulocyte CSF, macrophage CSF, and granulocyte-macrophage CSF by human endothelial cells

Electrophoretically pure human interleukin 1 (IL-1) beta was found to stimulate human endothelial cells in monolayer culture to elaborate colony-stimulating activity (CSA). Supernatant fluids from cultures stimulated with increasing concentrations of IL-1 were found to stimulate colony formation of myeloid (CFU-GM), erythroid (BFU-E), and multipotent (CFU-GEMM) progenitor cells in a dose-dependent fashion. The effect on mixed colony formation, however, was less than on CFU-GM and BFU-E growth. Similar to IL-1, the double-stranded RNA polyriboinosinic-polyribocytidilic acid (poly[rI].poly[rC]) also stimulated release of CSA by endothelial cells in a dose-dependent manner. The kinetics of IL-1-induced CSA release as opposed to poly(rI).poly(rC)-induced release were found to be different, in that poly(rI).poly(rC)-induced CSA production occurred more slowly. An anti-IL-1 beta antiserum was able to completely neutralize the IL-1-induced CSA release, but had no effect on poly(rI).poly(rC)-dependent CSA production, indicating that the latter effect was mediated by other mechanisms than intermediate production of IL-1 beta. Using specific immunologic assays, IL-1- as well as poly(rI).poly(rC)-inducible production of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF, and macrophage CSF was found. The release of CSF from endothelial cells in response to IL-1 may be a mechanism for stimulating production of neutrophils and mononuclear phagocytes, and for attracting and activating these cells at sites of inflammation.

Colony growth of normal and neoplastic cells in various concentrations of methylcellulose

To assess the semisolid character of methylcellulose (MC) and its ability to prevent cell migration and aggregation in clonogenic assays, we studied the influence of various concentrations of MC (0.7%-1.26%) on colony growth of neoplastic cell lines, normal bone marrow cells, and hairy cell leukemia (HCL). All cell lines (K562, HL-60, JOK-1, Daudi, and BB3, an IgM-kappa B-cell line) showed a prominent decrease in colony numbers and remarkable changes in colony morphology at rising MC concentrations, whereas no such influence could be demonstrated for HCL, mixed lineage colony-forming units (CFU-GEMM), granulocyte-macrophage CFU (CFU-GM), erythroid burst-forming units (BFU-E), and erythroid CFU (CFU-E). Despite a decrease in colony numbers at high MC concentrations, some cell lines showed a sustained proliferation as measured by growth index calculations and bromodeoxyuridine (BrdUrd) incorporation. This indicates that at certain MC concentrations colony formation is not always a reflection of proliferation. BrdUrd incorporation yielded an extremely low proliferation capacity for HCL. It is likely that HCL cells, which strongly aggregate, formed pseudo-colonies in spite of high MC concentrations.

Factors influencing release of granulocyte-macrophage colony-stimulating activity from human mononuclear phagocytes

Mononuclear phagocytes play an important role in the regulation of hematopoiesis, not only by producing regulatory monokines such as prostaglandins, tumor necrosis factor and interleukin-1 (IL-1), but also by the production of colony-stimulating activity (CSA). Previously, we have demonstrated that granulocyte-macrophage CSA (GM-CSA) production by mononuclear phagocytes can be induced by IL-1. In the present study, the influence of culture conditions on the production of GM-CSA was studied. It was found that both human sera and fetal bovine sera contain constituents - at present undefined - that induce GM-CSA production. These factors are distinct from IL-1 and lipopolysaccharide. In selected experiments, no GM-CSA-inducing effect of serum was found, suggesting that the effect may be donor-related. GM-CSA release in the presence of serum could be reduced by 40% after incubation of mononuclear phagocytes at low cell concentrations in methylcellulose, indicating that intimate cell-cell contact is an additional factor that enhances GM-CSA release.

Human fibroblasts produce granulocyte-CSF, macrophage-CSF, and granulocyte-macrophage-CSF following stimulation by interleukin-1 and poly(rI).poly(rC)

Electrophoretically pure human interleukin-1 (IL-1) beta was found to stimulate human fibroblasts in a monolayer culture to elaborate colony-stimulating activity (CSA). Supernatant fluids from cultures induced with increasing concentrations of IL-1 were found to stimulate colony formation of myeloid (CFU-GM), erythroid (BFU-E), and multipotent (CFU-GEMM) progenitor cells in a dose-dependent fashion. The effect on mixed colony formation, however, was less than on CFU-GM and BFU-E growth. Similar to IL-1, the synthetical double-stranded RNA poly(rI).poly(rC) also stimulated release of CSA by fibroblasts. The kinetics of IL-1- and poly(rI).poly(rC)-induced CSA release were found to be different, in that poly(rI).poly(rC)-induced CSA production occurred more slowly. Anti-IL-1 antiserum was able to completely neutralize the IL-1-induced CSA release, but had no effect on poly(rI).poly(rC)-induced CSF production, suggesting that the latter effect was mediated by other mechanisms than IL-1 in supernatant. By the use of specific immunologic assays, G-CSF, M-CSF, and GM-CSF could be identified in media conditioned by fibroblasts treated with IL-1 or poly(rI).poly(rC). Poly(rI).poly(rC) appeared to be a better inducer for M-CSF than IL-1.

Interleukin-1 (22-K factor) induces release of granulocyte-macrophage colony-stimulating activity from human mononuclear phagocytes

An electrophoretically pure preparation of natural human interleukin-1 (IL-1) was shown to stimulate in vitro colony formation in human bone marrow cultures. Day 4 myeloid cluster-forming cells (CFC), as well as early (day 7) and late (day 10) granulocyte-macrophage colony-forming units (CFU-GM) were stimulated in a dose-dependent fashion. At optimal concentrations of IL-1, the number of day 4 CFC reached 72%, the number of day 7 CFU-GM reached 32%, and the number of day 10 CFU-GM reached 80% of the respective numbers of colonies obtained by addition of crude leukocyte-conditioned medium (LCM). The IL-1-induced stimulatory effect on CFU-GM growth could be completely neutralized by a rabbit anti-IL-1 antiserum. Colony growth was abrogated by depleting the marrow cell suspensions of phagocytic cells prior to IL-1 addition. Conversely, the effect could be reintroduced by addition of marrow-derived adherent cells to bone marrow cell suspensions that had been depleted of both phagocytic and E rosetting T cells. Furthermore, media conditioned by bone marrow-derived adherent cells or by peripheral blood mononuclear phagocytes in the presence but not in the absence of IL-1, stimulated in vitro colony growth of phagocyte-depleted bone marrow cell suspensions. These results indicate that IL-1 induces release of granulocyte-macrophage colony-stimulating activity (GM-CSA) from human mononuclear phagocytes.

Expression of CD11, CDw15, and transferrin receptor antigens on human hematopoietic progenitor cells

The expression of transferrin receptor-associated antigens and of CD11 and CDw15 antigens was investigated on myeloid committed progenitor cells (CFU-GM day 10, CFU-GM day 7, and cluster-forming cells [CFC] day 4), on erythroid committed progenitor cells (BFU-E and CFU-E), and on multilineage progenitor cells (CFU-GEMM). Both complement-dependent cytotoxicity and fluorescence-activated cell-sorting assays were performed. Complement-dependent cytotoxicity appeared to be the more sensitive assay. Transferrin receptor-associated antigens appeared to be clearly present on all myeloid and erythroid committed progenitor cells, but were found to be only weakly expressed on CFU-GEMM. CD11 antigens appeared to be strongly expressed only on mature granulocytes, monocytes, and certain lymphocytes, but not significantly on myeloid committed precursor cells. Surprisingly, CD11 antigens were weakly, but significantly, present on CFU-E. CDw15 antigens appeared to be restricted to myeloid differentiation and were increasingly expressed from CFU-GM day 10 to CFC day 4. Thus, antitransferrin receptor, CD11, and CDw15 antibodies can be used to separate hematopoietic progenitor cells and may be useful tools in the study of hematopoietic differentiation.