Synergism of BSF-2/interleukin 6 and interleukin 3 on development of multipotential hemopoietic progenitors in serum-free culture

Interleukin 6 Antagonists in Severe COVID-19 Disease: Cardiovascular and Respiratory Outcomes

BACKGROUND

Inhibitors of interleukin 6 [IL-6] have been utilized to treat severe COVID-19 disease. Their immunosuppressive or immunomodulating impact may be beneficial in COVID-19.

OBJECTIVES

To discuss the role of IL-6 inhibitors and assess various trials conducted to evaluate the efficacy of IL-6 inhibitors in COVID-19 disease.

SUMMARY

Two of the most common causes of mortality in COVID-19-infected critically ill individuals are acute respiratory distress syndrome (ARDS) and multiorgan failure. Increased levels of inflammatory cytokines suggest that a cytokine storm, also known as cytokine release syndrome (CRS), is involved in the etiology of COVID-19. Most tissue damage, sepsis, and pulmonary and cardiovascular problems are caused mainly by the host defense system. Therefore, regulating this inflammatory cascade using immunomodulators is a prudent strategy. Although corticosteroids, as immunomodulators, are routinely used in COVID-19 management, interleukin (IL) inhibitors, especially IL-6 inhibitors, are also tested in many trials. Many studies have demonstrated that IL-6 inhibitors improve disease outcomes and decrease mortality, whereas others have shown that they are ineffective. In this paper, we briefly examined the role of IL-6 in COVID-19 pathogenesis and trials that support or refute the use of IL-6 inhibitors in treating COVID-19 disease.

RESULTS

Though mixed results are coming from trials regarding the adjuvant use of IL-6 inhibitors and standard anti-viral therapy with dexamethasone, a consensus favors using IL-6 inhibitors in severely ill COVID-19 patients regardless of the outcome.

Monocyte-derived IL-6 programs microglia to rebuild damaged brain vasculature

Cerebrovascular injury (CVI) is a common pathology caused by infections, injury, stroke, neurodegeneration and autoimmune disease. Rapid resolution of a CVI requires a coordinated innate immune response. In the present study, we sought mechanistic insights into how central nervous system-infiltrating monocytes program resident microglia to mediate angiogenesis and cerebrovascular repair after an intracerebral hemorrhage. In the penumbrae of human stroke brain lesions, we identified a subpopulation of microglia that express vascular endothelial growth factor A. These cells, termed 'repair-associated microglia' (RAMs), were also observed in a rodent model of CVI and coexpressed interleukin (IL)-6Ra. Cerebrovascular repair did not occur in IL-6 knockouts or in mice lacking microglial IL-6Ra expression and single-cell transcriptomic analyses revealed faulty RAM programming in the absence of IL-6 signaling. Infiltrating CCR2+ monocytes were the primary source of IL-6 after a CVI and were required to endow microglia with proliferative and proangiogenic properties. Faulty RAM programming in the absence of IL-6 or inflammatory monocytes resulted in poor cerebrovascular repair, neuronal destruction and sustained neurological deficits that were all restored via exogenous IL-6 administration. These data provide a molecular and cellular basis for how monocytes instruct microglia to repair damaged brain vasculature and promote functional recovery after injury.

Anti-inflammatory effects of Stephania tetrandra S. Moore on interleukin-6 production and experimental inflammatory disease models

Deregulation of interleukin-6 (IL-6) expression caused the synthesis and release of many inflammatory mediators. It is involved in chronic inflammation, autoimmune diseases, and malignancy. Stephania tetrandra S. Moore is a Chinese medicinal herb which has been used traditionary as a remedy for neuralgia and arthritis in China. To investigate the anti-inflammatory effects of S. tetrandra S. Moore in vitro and in vivo, its effects on the production of IL-6 and inflammatory mediators were analysed. When human monocytes/macrophages stimulated with silica were treated with 0.1–10 μg/ml S. tetranda S. Moore, the production of IL-6 was inhibited up to 50%. At these concentrations, it had no cytotoxicity effect on these cells. It also suppressed the production of IL-6 by alveolar macrophages stimulated with silica. In addition, it inhibited the release of superoxide anion and hydrogen peroxide from human monocytes/macrophages. To assess the anti-fibrosis effects of S. tetrandra S. Moore, its effects on in vivo experimental inflammatory models were evaluated. In the experimental silicosis model, IL-6 activities in the sera and in the culture supernatants of pulmonary fibroblasts were also inhibited by it. In vitro and in vivo treatment of S. tetrandra S. Moore reduced collagen production by rat lung fibroblasts and lung tissue. Also, S. tetrandra S. Moore reduced the levels of serum GOT and GPT in the rat cirrhosis model induced by CCL₄, and it was effective in reducing hepatic fibrosis and nodular formation. Taken together, these data indicate that it has a potent anti-inflammatory and antifibrosis effect by reducing IL-6 production.

Tocilizumab in the treatment of systemic juvenile idiopathic arthritis

Systemic juvenile idiopathic arthritis is one of the common rheumatic diseases in childhood and characterized by spiking fever, evanescent skin rash, lymphadenopathy, hepatosplenomegaly, and serositis, in addition to arthritis. Children with systemic juvenile idiopathic arthritis often show growth retardation and developmental abnormality, as well as macrophage activation syndrome, a life-threatening complication. Overproduction of interleukin-6 is pathologically responsible for the systemic inflammatory manifestations and abnormal laboratory results with systemic juvenile idiopathic arthritis. Thus, tocilizumab, a humanized antihuman interleukin-6 receptor antibody, has been developed as a therapeutic agent for the disease. A series of clinical studies have demonstrated the excellent efficacy and safety of tocilizumab for patients with active disease. Tocilizumab was approved for systemic juvenile idiopathic arthritis in Japan in 2008 and in the European Union and the United States in 2011.

Interleukin-6 (IL-6) and low O2 concentration (1%) synergize to improve the maintenance of hematopoietic stem cells (pre-CFC)

Low O(2) concentration (1%) favors the self-renewal of hematopoietic stem cells and inhibits committed progenitors (CFC). Since IL-6 influences both stem cells and committed progenitors at 20% O(2), we studied its effects in cultures at 1% O(2). The pre-CFC activity in Lin- population of mouse bone marrow was analyzed following 10 days of serum-free culture in medium (LC1) supplemented with IL-3 with and without IL-6, at 20 and 1% O(2) and phenotypic differentiation and proliferative history monitored. The IL-6 receptor expression and initiation of VEGF-A synthesis were also investigated. At 20% O(2), the effects of IL-6 on pre-CFC were negligible but effects on CFC were apparent; conversely, at 1% O(2), the IL-6 enhances activity of pre-CFC but not of CFC. Unlike at 20% O(2), at 1% O(2) a subpopulation of cells remained Lin- in spite of extensive proliferation. However, the absolute number of Lin- cells, did not correlate with pre-CFC activity. A relative increase in VEGF transcripts at 1% O(2) in presence of IL-3 alone was enhanced by the addition of IL-6. IL-6 enhanced pre-CFC activity at 1% O(2) and this was correlated to the induction of VEGF. These data reinforce the concept that physiologically low oxygenation of bone marrow is a regulator of stem cell maintenance. Since the 20% O(2) does not exist in tissues in vivo, further studies in vitro at lower O(2) concentrations should revise our knowledge relating to cytokine effects on stem and progenitor cells.

Preferential expression of the vasoactive intestinal peptide (VIP) receptor VPAC1 in human cord blood-derived CD34+CD38- cells: possible role of VIP as a growth-promoting factor for hematopoietic stem/progenitor cells

Primitive hematopoietic progenitor cells such as severe combined immunodeficiency- repopulating cells and long-term culture-initiating cells are enriched in CD34+CD38- cells derived from various stem cell sources. In this study, to elucidate the features of such primitive cells at the molecular level, we tried to isolate genes that were preferentially expressed in umbilical cord blood (CB)-derived CD34+CD38- cells by subtractive hybridization. The gene for VPAC1 receptor, a receptor for the neuropeptide vasoactive intestinal peptide (VIP), was thereby isolated and it was shown that this gene was expressed in both CD34+CD38- and CD34+CD38+ CB cells and that the expression levels were higher in CD34+CD38- CB cells. Next, we assessed the effects of VIP on the proliferation of CD34+ CB cells using in vitro culture systems. In serum-free single-cell suspension culture, VIP enhanced clonal growth of CD34+ CB cells in synergy with FLT3 ligand (FL), stem cell factor (SCF), and thrombopoietin (TPO). In serum-free clonogenic assays, VIP promoted myeloid (colony-forming unit-granulocyte/macrophage (CFU-GM)) and mixed (CFU-Mix) colony formations. Furthermore, in Dexter-type long-term cultures, VIP increased colony-forming cells at week 5 of culture. These results suggest that VIP functions as a growth-promoting factor of CB-derived hematopoetic progenitor cells.

Mechanisms associated with IL-6-induced up-regulation of Jak3 and its role in monocytic differentiation

We report here that Janus kinase 3 (Jak3) is a primary response gene for interleukin-6 (IL-6) in macrophage differentiation, and ectopic overexpression of Jak3 accelerates monocytic differentiation of normal mouse bone marrow cells stimulated with cytokines. Furthermore, we show that incubation of normal mouse bone marrow cells with a JAK3-specific inhibitor results in profound inhibition of myeloid colony formation in response to granulocyte-macrophage colony-stimulating factor or the combination of stem cell factor, IL-3, and IL-6. In addition, mutagenesis of the Jak3 promoter has revealed that Sp1 binding sites within a -67 to -85 element and a signal transducer and activator of transcription (Stat) binding site at position -44 to -53 are critical for activation of Jak3 transcription in murine M1 myeloid leukemia cells stimulated with IL-6. Electrophoretic mobility shift assay (EMSA) analysis has demonstrated that Sp1 can bind to the -67 to -85 element and Stat3 can bind to the -44 to -53 STAT site in IL-6-stimulated M1 cells. Additionally, ectopic overexpression of Stat3 enhanced Jak3 promoter activity in M1 cells. This mechanism of activation of the murine Jak3 promoter in myeloid cells is distinct from a recently reported mechanism of activation of the human JAK3 promoter in activated T cells.

STI571 inhibits growth and adhesion of human mast cells in culture

Stem cell factor (SCF)/c-kit system is critical for human mast cell development. We thus examined the effects of STI571, an inhibitor of the c-kit tyrosine kinase receptor, on the proliferation and function of human mast cells. STI571 at concentrations of 10(-6) M or higher almost completely abolished the SCF-dependent progeny generation from cord blood-derived cultured mast cells through an inhibition of the tyrosine phosphorylation of c-kit. The compound also suppressed the early phase of mast cell development. The extinction of mast cell growth induced by STI571 may be due largely to apoptosis according to the flow cytometric analysis and gel electrophoresis. Two-hour exposure to STI571 that failed to influence the total viable cell number suppressed adhesion of the cells to fibronectin in the presence of SCF without altering the expressions of integrin molecules. Our results may provide a fundamental insight for the clinical application of STI571 in allergic disorders.

Serum inhibitors for human mast cell growth: possible role of retinol

BACKGROUND

In vitro culture systems have been used to study the physiological and pathological characteristics of human mast cells. However, there are some differences in proliferation and maturation of mast cells between fetal bovine serum (FBS)-containing and serum-deprived cultures. Accordingly, we attempted to identify circulating factor(s) affecting the development of human mast cells.

METHODS

We measured the serum levels of retinol and several cytokines. To elucidate the antiproliferative effects of the serum, a retinoic acid receptor (RARalpha) antagonist and neutralizing antibodies against cytokines were used.

RESULTS

Similar to FBS, human serum dose-dependently suppressed the growth of tryptase+ cells from CD34+ cord blood cells or 20-week cultured mast cells under stimulation with stem cell factor (SCF). The serum-mediated inhibition might be based on a decline in proliferation rate. Among inhibitors for mast cell growth, retinol and transforming growth factor (TGF)-beta1 were present at high levels in human serum. In contrast with anti-TGF-beta1 antibody, an RARalpha antagonist counteracted the serum-induced suppression of human mast cell proliferation.

CONCLUSIONS

Our results suggest that retinol and its derivatives act as a circulating regulator for human mast cell growth. The RARalpha antagonist may be a useful tool to obtain higher numbers of mast cells in FBS-containing cultures.

IL-6 enhances IgE-dependent histamine release from human peripheral blood-derived cultured mast cells

We examined whether interleukin (IL)-6 exerts the stimulatory effects on the secretion of histamine from human mast cells triggered by crosslinking of the high affinity IgE receptor (FcepsilonRI) with IgE and anti-IgE. As target cells, we used peripheral blood-derived cultured mast cells grown with SCF, because they were superior in FcepsilonRIalpha expression to cord blood-derived mast cells. Incubation with SCF+IL-6 for 1 week increased the IgE-dependent release as well as intracellular content of histamine in the cultured mast cells, as compared with the values obtained by incubation with SCF alone. The magnitude of these increases was higher than that for priming with SCF+IL-4. A striking difference was also found in the expression of FcepsilonRIalpha between the two-factor combinations. The addition of IL-6 during FcepsilonRI crosslinking with IgE/anti-IgE in the presence of SCF did not influence histamine secretion. When SCF, IL-6 and IL-4 were used together, a further increase was observed in the anti-IgE-dependent liberation of histamine from the cultured mast cells, compared with the two-factor combinations. These results suggest that IL-6 functions as a secretagogue for the inflammatory mediator of human mast cells in the presence of SCF.

The paradigm of IL-6: from basic science to medicine

IL-6 is a pleiotropic cytokine with a wide range of biological activities in immune regulation, hematopoiesis, inflammation, and oncogenesis. Its activities are shared by IL-6-related cytokines such as leukemia inhibitory factor and oncostatin M. The pleiotropy and redundancy of IL-6 functions have been identified by using a unique receptor system comprising two functional proteins: an IL-6 receptor (IL-6R) and gp130, the common signal transducer of cytokines related to IL-6. Signal transduction through gp130 is mediated by two pathways: the JAK-STAT (Janus family tyrosine kinase-signal transducer and activator of transcription) pathway and the Ras mitogen-activated protein kinase pathway. The negative regulators of IL-6 signaling have also been identified, although the physiological roles of the molecules are not yet fully understood. The pathological roles of IL-6 have also been clarified in various disease conditions, such as inflammatory, autoimmune, and malignant diseases. On the basis of the findings, a new therapeutic approach to block the IL-6 signal using humanized anti-IL-6R antibody for rheumatoid arthritis, Castleman's disease, and multiple myeloma has been attempted.

Generation of definitive hematopoietic stem cells from murine early yolk sac and paraaortic splanchnopleures by aorta-gonad-mesonephros region-derived stromal cells

There is controversy as to whether murine definitive hematopoiesis originates from yolk sac (YS) or the intraembryonic region. This study reports the generation of definitive hematopoietic stem cells (HSCs) from both early YS and intraembryonic paraaortic splanchnopleures (P-Sp) on AGM-S3 stromal cells derived from the aorta-gonad-mesonephros (AGM) region at 10.5 days post coitum (dpc). YS and P-Sp cells at 8.5 dpc generated no definitive hematopoiesis-derived colony-forming cells in cocultures with AGM-S3 cells, but spleen colony-forming cells and HSCs capable of reconstituting definitive hematopoiesis in adult mice simultaneously appeared on day 4 of coculture. Precursors for definitive HSCs were present in YS and P-Sp at 8.0 dpc, a time when YS and embryo were not connected by blood vessels. It is proposed that precursors with the potential to generate definitive HSCs appear independently in YS and intraembryonic P-Sp and that the P-Sp or AGM region affords the microenvironment that facilitates generation of definitive hematopoiesis from precursors.

CD34 expression on long-term repopulating hematopoietic stem cells changes during developmental stages

The CD34 antigen serves as an important marker for primitive hematopoietic cells in therapeutic transplantation of hematopoietic stem cells (HSC) and gene therapy, but it has remained an open question as to whether or not most HSC express CD34. Using a competitive long-term reconstitution assay, the results of this study confirm developmental changes in CD34 expression on murine HSC. In fetuses and neonates, CD34 was expressed on Lin(-)c-Kit(+) long-term repopulating HSC of bone marrow (BM), liver, and spleen. However, CD34 expression on HSC decreased with aging, and in mice older than 10 weeks, HSC were most enriched in the Lin(-)c-Kit(+)CD34(-) marrow cell fraction. A second transplantation was performed from primary recipients who were transplanted with neonatal Lin(-)c-Kit(+) CD34(high) HSC marrow. Although donor-type HSC resided in CD34-expressing cell fraction in BM cells of the first recipients 4 weeks after the first transplantation, the stem cell activity had shifted to Lin(-)c-Kit(+)CD34(-) cells after 16 weeks, indicating that adult Lin(-)c-Kit(+)CD34(-) HSC are the progeny of neonatal CD34-expresssing HSC. Assays for colony-forming cells showed that hematopoietic progenitor cells, unlike HSC, continue to express CD34 throughout murine development. The present findings are important because the clinical application of HSC can be extended, in particular as related to CD34-enriched HSC and umbilical cord blood HSC.

Anti-interleukin 6 receptor antibody treatment in rheumatic disease

Interleukin 6 (IL6) is a pleiotropic cytokine with a wide range of biological activities. IL6 transgene into mice gives rise to the abnormalities such as hypergammaglobulinaemia, thrombocytosis, infiltration of inflammatory cells into the tissues, mesangial cell proliferation of the kidney as well as splenomegaly and lymphadenopathy, which are predictable by the biological functions of IL6 shown in vitro. Continuous overproduction of IL6 is observed in patients with some immune-inflammatory diseases such as Castleman's disease and rheumatoid arthritis that are frequently associated with similar abnormalities to those of IL6 transgenic mice, strongly suggesting the involvement of IL6 in the human diseases. Successful treatment of the model animals for immune-inflammatory diseases with anti-IL6 receptor (IL6R) antibody thus indicates the possible application of IL6 blocking agents to treat the IL6 related immune-inflammatory diseases of humans. In this review, the new therapeutic strategy for Castleman's disease and RA using humanized antibody to human IL6 receptor, MRA, is discussed.

Adiponectin, a new member of the family of soluble defense collagens, negatively regulates the growth of myelomonocytic progenitors and the functions of macrophages

We investigated the functions of adiponectin, an adipocyte-specific secretory protein and a new member of the family of soluble defense collagens, in hematopoiesis and immune responses. Adiponectin suppressed colony formation from colony-forming units (CFU)—granulocyte-macrophage, CFU-macrophage, and CFU-granulocyte, whereas it had no effect on that of burst-forming units—erythroid or mixed erythroid-myeloid CFU. In addition, adiponectin inhibited proliferation of 4 of 9 myeloid cell lines but did not suppress proliferation of erythroid or lymphoid cell lines except for one cell line. These results suggest that adiponectin predominantly inhibits proliferation of myelomonocytic lineage cells. At least one mechanism of the growth inhibition is induction of apoptosis because treatment of acute myelomonocytic leukemia lines with adiponectin induced the appearance of subdiploid peaks and oligonucleosomal DNA fragmentation. Aside from inhibiting growth of myelomonocytic progenitors, adiponectin suppressed mature macrophage functions. Treatment of cultured macrophages with adiponectin significantly inhibited their phagocytic activity and their lipopolysaccharide-induced production of tumor necrosis factor α. Suppression of phagocytosis by adiponectin is mediated by one of the complement C1q receptors, C1qRp, because this function was completely abrogated by the addition of an anti-C1qRp monoclonal antibody. These observations suggest that adiponectin is an important negative regulator in hematopoiesis and immune systems and raise the possibility that it may be involved in ending inflammatory responses through its inhibitory functions.

Adiponectin, a new member of the family of soluble defense collagens, negatively regulates the growth of myelomonocytic progenitors and the functions of macrophages

We investigated the functions of adiponectin, an adipocyte-specific secretory protein and a new member of the family of soluble defense collagens, in hematopoiesis and immune responses. Adiponectin suppressed colony formation from colony-forming units (CFU)—granulocyte-macrophage, CFU-macrophage, and CFU-granulocyte, whereas it had no effect on that of burst-forming units—erythroid or mixed erythroid-myeloid CFU. In addition, adiponectin inhibited proliferation of 4 of 9 myeloid cell lines but did not suppress proliferation of erythroid or lymphoid cell lines except for one cell line. These results suggest that adiponectin predominantly inhibits proliferation of myelomonocytic lineage cells. At least one mechanism of the growth inhibition is induction of apoptosis because treatment of acute myelomonocytic leukemia lines with adiponectin induced the appearance of subdiploid peaks and oligonucleosomal DNA fragmentation. Aside from inhibiting growth of myelomonocytic progenitors, adiponectin suppressed mature macrophage functions. Treatment of cultured macrophages with adiponectin significantly inhibited their phagocytic activity and their lipopolysaccharide-induced production of tumor necrosis factor α. Suppression of phagocytosis by adiponectin is mediated by one of the complement C1q receptors, C1qRp, because this function was completely abrogated by the addition of an anti-C1qRp monoclonal antibody. These observations suggest that adiponectin is an important negative regulator in hematopoiesis and immune systems and raise the possibility that it may be involved in ending inflammatory responses through its inhibitory functions.

Retinoic acid is a negative regulator for the differentiation of cord blood-derived human mast cell progenitors

We examined the effects of retinoids on the human mast cell development using a serum-deprived culture system. When 10-week cultured mast cells derived from CD34+ cord blood cells were used as target cells, both all-trans retinoic acid (ATRA) and 9-cis RA inhibited the progeny generation under stimulation with stem cell factor (SCF) in a dose-dependent manner (the number of progeny grown by SCF plus RA at 10−7 mol/L was one tenth of the value obtained by SCF alone). The early steps in mast cell development appear to be less sensitive to RA according to the single CD34+c-kit+ cord blood cell culture study. The optimal concentration of RAs also reduced the histamine concentration in the cultured mast cells (3.00 ± 0.47 pg per cell in SCF alone, 1.44 ± 0.18 pg per cell in SCF+ATRA, and 1.41 ± 0.10 pg per cell in SCF+9-cis RA). RT-PCR analyses showed the expression of RAR, RARβ, RXR, and RXRβ messenger ribonucleic acid (mRNA) in 10-week cultured mast cells. The addition of an RAR-selective agonist at 10−10 mol/L to 10−7 mol/L decreased the number of mast cells grown in SCF, whereas an RXR-selective agonist at up to 10−8 mol/L was inactive. Among RAR subtype selective retinoids used at 10−9 mol/L to 10−7 mol/L, only the RAR agonist was equivalent to ATRA at 10−7 mol/L in its ability to inhibit mast cell growth. Conversely, the addition of excess concentrations of a RAR antagonist profoundly counteracted the retinoid-mediated suppressive effects. These results suggest that RA inhibits SCF-dependent differentiation of human mast cell progenitors through a specific receptor.

Quantitative and qualitative differences in thrombopoietin-dependent hematopoietic progenitor development between cord blood and bone marrow

BACKGROUND

To assess the clinical application of thrombopoietin (TPO) for thrombocytopenia of patients receiving cord blood (CB) or bone marrow (BM) transplants, we examined whether various types of hematopoietic progenitors including megakaryocyte (MK) progenitors from CB and BM exerted different proliferative and differentiative potential in the presence of TPO.

METHODS

The development of MK, granulocyte-macrophage, and erythroid/mixed erythroid (E/Mix) progenitors in a serum-deprived liquid culture medium supplemented with TPO was compared between CD34+ CB and BM cells.

RESULTS

The CD34+ CB cells generated 30-fold more MKs than the CD34+ BM cells, but the CB-derived MKs were more immature. A single-cell culture study showed that CB CD34+CD38- cells as well as CD34+CD38+ cells proliferated in response to TPO, whereas the two subpopulations of CD34+ BM cells showed little multiplication. In short-term liquid cultures containing CD34+ CB or BM cells, TPO significantly increased the absolute numbers of various types of colony-forming cells, compared with the input values. In particular, MK progenitors and E/Mix progenitors in CB were amplified to a substantially greater extent than in BM. The superior response of CD34+ CB cells to TPO observed in this study may be due in part to the use of cryopreserved cells.

CONCLUSIONS

Our results suggest that TPO alone cannot only stimulate megakaryocytopoiesis but also increase the numbers of various types of hematopoietic progenitors, and that quantitative and qualitative differences in TPO-dependent hematopoietic progenitor development exist between CB and BM.

Chimeric cytokine receptor can transduce expansion signals in interleukin 6 receptor alpha (IL-6Ralpha)-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors

We generated transgenic mice expressing chimeric receptors, which comprise extracellular domains of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) receptor and transmembrane and cytoplasmic domains of the mouse leukemia inhibitory factor receptor. In suspension cultures of lineage-negative (Lin(-)), 5-fluorouracil-resistant bone marrow cells of the transgenic mice, a combination of hGM-CSF and stem cell factor (SCF) induced exponential expansions of mixed colony-forming unit. The combination of hGM-CSF and SCF was effective on enriched, Lin(-)Sca-1(+)c-kit(+) progenitors and increased either mixed colony-forming unit or cobblestone area-forming cells. In case of stimulation with hGM-CSF and SCF, interleukin-6 (IL-6) and SCF, or IL-11 and SCF, the most efficient expansion was achieved with hGM-CSF and SCF. When Lin(-)Sca-1(+)c-kit(+)CD34(-) further enriched progenitors were clone sorted and individually incubated in the presence of SCF, hGM-CSF stimulated a larger number of cells than did IL-6, IL-6 and soluble IL-6 receptor (IL-6R), or IL-11. These data suggest the presence of IL-6Ralpha-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors. Such primitive progenitors are equipped with signal transduction molecules and can expand when these chimeric receptors are genetically introduced into the cells and stimulated with hGM-CSF in the presence of SCF.

Differential Effects of Human Granulocyte Colony-Stimulating Factor (hG-CSF) and Thrombopoietin on Megakaryopoiesis and Platelet Function in hG-CSF Receptor-Transgenic Mice

Granulocyte-colony stimulating factor (G-CSF) has been found to act on the neutrophilic lineage. We recently showed that human G-CSF (hG-CSF) has effects similar to early-acting cytokines such as interleukin-3 (IL-3) in the development of multipotential hematopoietic progenitors in transgenic (Tg) mice expressing receptors (R) for hG-CSF. In the present study, we examined the effects of hG-CSF on more mature hematopoietic cells committed to megakaryocytic lineage in these Tg mice. The administration of hG-CSF to the Tg mice increased the numbers of both platelets in peripheral blood and megakaryocytes in the spleen, indicating that hG-CSF stimulates megakaryopoiesis in the Tg mice in vivo. The stimulatory effect of hG-CSF was also supported by the results of studies in vitro. hG-CSF supported megakaryocyte colony formation in a dose-dependent fashion in clonal cultures of bone marrow cells derived from the Tg mice. Direct effects of hG-CSF on megakaryocytic progenitors in the Tg mice were confirmed by culture of single-cell sorted from bone marrow cells. hG-CSF showed a stronger effect on maturation of megakaryocytes in the Tg mice than that of IL-3 alone, but weaker than that of TPO alone. In addition, hG-CSF induced phosphorylation of STAT3 but not Jak2 or STAT5, while TPO induced phosphorylation of both. In contrast to TPO, hG-CSF did not enhance ADP-induced aggregation. Thus, hG-CSF has a wide variety of functions in megakaryopoiesis of hG-CSFR-Tg mice, as compared with other megakaryopoietic cytokines, but the activity of hG-CSF in megakaryocytes and platelets does not stand up to a comparison with that of TPO. Specific signals may be required for the full maturation and activation of platelets.

Megakaryocyte induced fibroblast proliferation is enhanced by costimulation with IL-6/IL-3 and dependent on secretory and adhesion events

Experimental data are in keeping with the finding that megakaryocytes isolated from normal human bone marrow may promote fibroblast growth. This effect can be significantly enhanced by interleukin (IL)-3. In this context it has been demonstrated that IL-3 induces the release of platelet-derived growth factor (PDGF) and transforming growth factor beta1 (TGFbeta1) from megakaryocytes, factors known to enhance fibroblast proliferation. The present in vitro study was performed to elucidate the action of several other cytokines which are able to influence the different steps of megakaryocyte maturation and function like stem cell factor (SCF), IL-6, and leukemia inhibitory factor (LIF) as well. Following an appropriate experimental design we were able to show that none of the mentioned cytokines enhanced megakaryocyte dependent fibroblast proliferation in the coculture assays. On the other hand, IL-6 in combination with IL-3 surpassed the IL-3 dependent action significantly. However, the combined IL-3/IL-6 effect was not explainable by an increased PDGF/TGF-beta secretion of the megakaryocytes. In transwell experiments the inhibition of cell-to-cell contact via tissue culture inserts generated a conspicuous impairment of fibroblast growth in the IL-3/IL-6 treated cocultures. This reversal surpassed even the effect on the untreated and IL-3 stimulated cocultures. Hence, a direct contact of both cell types probably inducing adhesion phenomenons and warranting a certain threshold of local PDGF/TGF-beta concentration is a prerequisite for the proliferative effect on fibroblasts in the costimulation experiments. These results are of special interest regarding the evolution of myelofibrosis in chronic myeloproliferative disorders (CMPDs) because (1) various progenitor cells including the megakaryocytic lineage are hypersensitive towards IL-3 and (2) an abnormal secretion of IL-6 is described for megakaryocytes in these disorders.

Interleukin-6 Directly Modulates Stem Cell Factor-Dependent Development of Human Mast Cells Derived From CD34+Cord Blood Cells

In the present study, we attempted to clarify the effects of interleukin-6 (IL-6) on the growth and properties of human mast cells using cultured mast cells selectively generated by stem cell factor (SCF) from CD34+ cord blood cells. The addition of IL-6 to cultures containing mast cells resulted in a substantial reduction of the number of progenies grown by SCF in the liquid culture. This IL-6–mediated inhibition of mast cell growth may be due in part to the suppression at the precursor level, according to the results of a clonal cell culture assay. Moreover, a flow cytometric analysis showed that the cultured mast cells grown in the presence of SCF+IL-6 had decreased c-kit expression. The exposure of cultured mast cells to SCF+IL-6 also caused substantial increases in the cell size, frequency of chymase-positive cells, and intracellular histamine level compared with the values obtained with SCF alone. The flow cytometric analysis showed low but significant levels of expression of IL-6 receptor (IL-6R) and gp130 on the cultured mast cells grown with SCF. The addition of either anti–IL-6R antibody or anti-gp130 antibody abrogated the biological functions of IL-6. Although IL-4 exerted an effect similar to that of IL-6 on the cultured mast cells under stimulation with SCF, the results of comparative experiments suggest that the two cytokines use different regulatory mechanisms. Taken together, the present findings suggest that IL-6 modulates SCF-dependent human mast cell development directly via an IL-6R-gp130 system.

Interleukin-6 Directly Modulates Stem Cell Factor-Dependent Development of Human Mast Cells Derived From CD34+Cord Blood Cells

In the present study, we attempted to clarify the effects of interleukin-6 (IL-6) on the growth and properties of human mast cells using cultured mast cells selectively generated by stem cell factor (SCF) from CD34+ cord blood cells. The addition of IL-6 to cultures containing mast cells resulted in a substantial reduction of the number of progenies grown by SCF in the liquid culture. This IL-6–mediated inhibition of mast cell growth may be due in part to the suppression at the precursor level, according to the results of a clonal cell culture assay. Moreover, a flow cytometric analysis showed that the cultured mast cells grown in the presence of SCF+IL-6 had decreased c-kit expression. The exposure of cultured mast cells to SCF+IL-6 also caused substantial increases in the cell size, frequency of chymase-positive cells, and intracellular histamine level compared with the values obtained with SCF alone. The flow cytometric analysis showed low but significant levels of expression of IL-6 receptor (IL-6R) and gp130 on the cultured mast cells grown with SCF. The addition of either anti–IL-6R antibody or anti-gp130 antibody abrogated the biological functions of IL-6. Although IL-4 exerted an effect similar to that of IL-6 on the cultured mast cells under stimulation with SCF, the results of comparative experiments suggest that the two cytokines use different regulatory mechanisms. Taken together, the present findings suggest that IL-6 modulates SCF-dependent human mast cell development directly via an IL-6R-gp130 system.

Enhancement of hematopoietic reconstitution with recombinant cytokines: effect of rhIL-6 in combination with rhGM-CSF and rhIL-3 on unmodified or T cell-depleted bone marrow

We have investigated the response of unmanipulated and lymphocyte-depleted BM cells (BMC), pretreated with monoclonal rat antihuman lymphocyte (CD52) antibody (Campath-1G) used for prevention of GvHD, to incubation with rhIL-6 alone or in combination with rhGM-CSF, rhIL-3, or both. We investigated optimal conditions needed for incubation of human BMC under conditions that can be upscaled for clinical application prior to autologous (auto-BMT) and allogeneic blood or BM transplantation (allo-BMT). When used as a single agent, rhIL-6 showed no or a minimal effect in enhancing in vitro CFU-GM colony formation of human BMC. A potent additive effect was obtained when rhIL-6 was added to rhGM-CSF, rhIL-3, or a combination of both. Binding of the mAb Campath-1G, which is used for in vivo and in vitro depletion of immunocompetent lymphocytes to BMC, did not reduce the enhancing effect of a combination of rhGM-CSF and rhIL-3 on CFU-GM in the presence or absence of rhIL-6. Our present and previously published observations suggest that enhancement of hematopoiesis by rhIL-6 and other hematopoietic growth factors is T cell independent. Based on the present observations, pilot clinical studies to determine the potential benefit of in vitro activation of BMC prior to BMT with various cytokine combinations, including rhIL-6, seems justified. Our goal is to enhance hematopoietic reconstitution in vivo, focusing on possible enhancement of platelet reconstitution in vivo toward safer auto-BMT and more effective allo-BMT with better engraftment of T cell-depleted allografts while avoiding GvHD.

Apoptosis of erythroid precursors under stimulation with thrombopoietin: contribution to megakaryocytic lineage choice

Although the effect of thrombopoietin (TPO) on megakaryocyte production is well established, its role in the commitment of multipotential hematopoietic progenitors to the megakaryocytic lineage remains to be determined. In the present study, we attempted to clarify the determination process of megakaryocytic lineage as a terminal differentiation pathway under stimulation with TPO. Day 7 cultured cells grown by TPO derived from cord blood CD34+ cells were divided into four subpopulations on the basis of CD34 and CD41 expression. The CD34-/CD41- cells showed the labeling pattern of anti-CD42b and anti-CD9 antibodies closer to that of the CD34+/CD41- cells than the CD34+/CD41+ cells. Replating experiments revealed that approximately 40% of the CD34-/CD41- cells proliferated in response to a combination of growth factors, and more than 80% of them were pure erythroid precursors. However, this subpopulation failed to grow/survive and fell into apoptosis in the presence of TPO alone. In contrast, the CD34+/CD41+ cells, which predominantly contained megakaryocytic precursors, exerted a low but significant proliferative potential in the presence of TPO. The insufficient response to TPO of the CD34-/CD41- cells may result from the apparently low expression of c-MpI, as determined by flow cytometric analysis and reverse transcription-polymerase chain reaction analysis. Therefore, these results suggest that the apoptosis of hematopoietic precursors other than megakaryocytic precursors is related to the determination of the terminal differentiation under the influence of TPO.

Soluble Interleukin-6 (IL-6) Receptor With IL-6 Stimulates Megakaryopoiesis From Human CD34+ Cells Through Glycoprotein (gp)130 Signaling

We have recently shown that stimulation of glycoprotein (gp) 130, the membrane-anchored signal transducing receptor component of IL-6, by a complex of human soluble interleukin-6 receptor (sIL-6R) and IL-6 (sIL-6R/IL-6), potently stimulates the ex vivo expansion as well as erythropoiesis of human stem/progenitor cells in the presence of stem cell factor (SCF). Here we show that sIL-6R dose-dependently enhanced the generation of megakaryocytes (Mks) (IIbIIIa-positive cells) from human CD34+ cells in serum-free suspension culture supplemented with IL-6 and SCF. The sIL-6R/IL-6 complex also synergistically acted with IL-3 and thrombopoietin (TPO) on the generation of Mks from CD34+ cells, whereas the synergy of IL-6 alone with TPO was barely detectable. Accordingly, the addition of sIL-6R to the combination of SCF + IL-6 also supported a substantial number of Mk colonies from CD34+ cells in serum-free methylcellulose culture, whereas SCF + IL-6 in the absence of sIL-6R rarely induced Mk colonies. The addition of monoclonal antibodies against gp130 to the suspension and clonal cultures completely abrogated the megakaryopoiesis induced by sIL-6R/IL-6 in the presence of SCF, whereas an anti-TPO antibody did not, indicating that the observed megakaryopoiesis by sIL-6R/IL-6 is a response to gp130 signaling and independent of TPO. Furthermore, human CD34+ cells were subfractionated into two populations of IL-6R–negative (CD34+ IL-6R−) and IL-6R–positive (CD34+ IL-6R+) cells by fluorescence-activated cell sorting. The CD34+IL-6R− cells produced a number of Mks as well as Mk colonies in cultures supplemented with sIL-6R/IL-6 or TPO in the presence of SCF. In contrast, CD34+ IL-6R+cells generated much less Mks and lacked Mk colony forming activity under the same conditions. Collectively, the present results indicate that most of the human Mk progenitors do not express IL-6R, and that sIL-6R confers the responsiveness of human Mk progenitors to IL-6. Together with the presence of functional sIL-6R in human serum and relative unresponsiveness of human Mk progenitors to IL-6 in vitro, current results suggest that the role of IL-6 may be mainly mediated by sIL-6R, and that the gp130 signaling initiated by the sIL-6R/ IL-6 complex is involved in human megakaryopoiesis in vivo.

Soluble Interleukin-6 (IL-6) Receptor With IL-6 Stimulates Megakaryopoiesis From Human CD34+ Cells Through Glycoprotein (gp)130 Signaling

We have recently shown that stimulation of glycoprotein (gp) 130, the membrane-anchored signal transducing receptor component of IL-6, by a complex of human soluble interleukin-6 receptor (sIL-6R) and IL-6 (sIL-6R/IL-6), potently stimulates the ex vivo expansion as well as erythropoiesis of human stem/progenitor cells in the presence of stem cell factor (SCF). Here we show that sIL-6R dose-dependently enhanced the generation of megakaryocytes (Mks) (IIbIIIa-positive cells) from human CD34+ cells in serum-free suspension culture supplemented with IL-6 and SCF. The sIL-6R/IL-6 complex also synergistically acted with IL-3 and thrombopoietin (TPO) on the generation of Mks from CD34+ cells, whereas the synergy of IL-6 alone with TPO was barely detectable. Accordingly, the addition of sIL-6R to the combination of SCF + IL-6 also supported a substantial number of Mk colonies from CD34+ cells in serum-free methylcellulose culture, whereas SCF + IL-6 in the absence of sIL-6R rarely induced Mk colonies. The addition of monoclonal antibodies against gp130 to the suspension and clonal cultures completely abrogated the megakaryopoiesis induced by sIL-6R/IL-6 in the presence of SCF, whereas an anti-TPO antibody did not, indicating that the observed megakaryopoiesis by sIL-6R/IL-6 is a response to gp130 signaling and independent of TPO. Furthermore, human CD34+ cells were subfractionated into two populations of IL-6R–negative (CD34+ IL-6R−) and IL-6R–positive (CD34+ IL-6R+) cells by fluorescence-activated cell sorting. The CD34+IL-6R− cells produced a number of Mks as well as Mk colonies in cultures supplemented with sIL-6R/IL-6 or TPO in the presence of SCF. In contrast, CD34+ IL-6R+cells generated much less Mks and lacked Mk colony forming activity under the same conditions. Collectively, the present results indicate that most of the human Mk progenitors do not express IL-6R, and that sIL-6R confers the responsiveness of human Mk progenitors to IL-6. Together with the presence of functional sIL-6R in human serum and relative unresponsiveness of human Mk progenitors to IL-6 in vitro, current results suggest that the role of IL-6 may be mainly mediated by sIL-6R, and that the gp130 signaling initiated by the sIL-6R/ IL-6 complex is involved in human megakaryopoiesis in vivo.

Neutrophilic Cell Production by Combination of Stem Cell Factor and Thrombopoietin From CD34+ Cord Blood Cells in Long-Term Serum-Deprived Liquid Culture

In the present study, we investigated the effects of stem cell factor (SCF) and/or thrombopoietin (TPO) on the cell production by cord blood CD34+ cells using a serum-deprived liquid culture system. Although SCF alone supported a modest production of neutrophilic cells and a remarkable generation of mast cells, the addition of TPO to the culture containing SCF caused an apparent generation of neutrophilic cells, identified by immunocytochemical staining and flow cytometric analysis. The significant production of neutrophilic cells by SCF and TPO was persistently observed from 2 weeks to 2 to 3 months of culture. The interaction between SCF and TPO on the neutrophilic cell generation was greater than the combined effects of SCF with granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF). The addition of neutralizing antibody against G-CSF or GM-CSF did not influence the SCF + TPO-dependent neutrophilic cell production. A single-cell culture study showed that not only CD34+CD38+ c-kit+ cells but also CD34+CD38−c-kit+ cells were responsible for the neutrophilic cell generation. In clonal cell cultures, GM progenitors as well as erythroid progenitors and multipotential progenitors expanded in the cultures supplemented with SCF and TPO. The neutrophilic cells grown by SCF + TPO were at myeloblast to band cell stages, and scarcely matured to segmented neutrophils. In addition, the cells generated by SCF + TPO were stained with monoclonal antibodies against myeloperoxidase, elastase, lactoferrin, and CD11b, but they had negligible levels of alkaline phosphatase (ALP) and CD35. The replating of the CD34−c-kit−/low CD15+ cells grown by SCF + TPO into a culture containing SCF + G-CSF permitted both the terminal maturation into segmented cells and the appearance of ALP and CD35. These results indicate the existence of a G-CSF/GM-CSF–independent system of neutrophilic cell production.

Neutrophilic Cell Production by Combination of Stem Cell Factor and Thrombopoietin From CD34+ Cord Blood Cells in Long-Term Serum-Deprived Liquid Culture

In the present study, we investigated the effects of stem cell factor (SCF) and/or thrombopoietin (TPO) on the cell production by cord blood CD34+ cells using a serum-deprived liquid culture system. Although SCF alone supported a modest production of neutrophilic cells and a remarkable generation of mast cells, the addition of TPO to the culture containing SCF caused an apparent generation of neutrophilic cells, identified by immunocytochemical staining and flow cytometric analysis. The significant production of neutrophilic cells by SCF and TPO was persistently observed from 2 weeks to 2 to 3 months of culture. The interaction between SCF and TPO on the neutrophilic cell generation was greater than the combined effects of SCF with granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF). The addition of neutralizing antibody against G-CSF or GM-CSF did not influence the SCF + TPO-dependent neutrophilic cell production. A single-cell culture study showed that not only CD34+CD38+ c-kit+ cells but also CD34+CD38−c-kit+ cells were responsible for the neutrophilic cell generation. In clonal cell cultures, GM progenitors as well as erythroid progenitors and multipotential progenitors expanded in the cultures supplemented with SCF and TPO. The neutrophilic cells grown by SCF + TPO were at myeloblast to band cell stages, and scarcely matured to segmented neutrophils. In addition, the cells generated by SCF + TPO were stained with monoclonal antibodies against myeloperoxidase, elastase, lactoferrin, and CD11b, but they had negligible levels of alkaline phosphatase (ALP) and CD35. The replating of the CD34−c-kit−/low CD15+ cells grown by SCF + TPO into a culture containing SCF + G-CSF permitted both the terminal maturation into segmented cells and the appearance of ALP and CD35. These results indicate the existence of a G-CSF/GM-CSF–independent system of neutrophilic cell production.

Human Granulocyte Colony-Stimulating Factor (G-CSF) Stimulates the In Vitro and In Vivo Development But Not Commitment of Primitive Multipotential Progenitors From Transgenic Mice Expressing the Human G-CSF Receptor

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and restricted differentiation of hematopoietic progenitors into neutrophils. To clarify the effects of G-CSF on hematopoietic progenitors, we generated transgenic (Tg) mice that had ubiquitous expression of the human G-CSF receptor (hG-CSFR). In clonal cultures of bone marrow and spleen cells obtained from these mice, hG-CSF supported the growth of myelocytic as well as megakaryocytic, mast cell, mixed, and blast cell colonies. Single-cell cultures of lineage-negative (Lin−)c-Kit+Sca-1+ or Sca-1− cells obtained from the Tg mice confirmed the direct effects of hG-CSF on the proliferation and differentiation of various progenitors. hG-CSF also had stimulatory effects on the formation of blast cell colonies in cultures using 5-fluorouracil–resistant hematopoietic progenitors and clone-sorted Lin−c-Kit+Sca-1+ primitive hematopoietic cells. These colonies contained different progenitors in proportions similar to those obtained when mouse interleukin-3 was used in place of hG-CSF. Administration of hG-CSF to Tg mice led to significant increases in spleen colony-forming and mixed/blast cell colony-forming cells in bone marrow and spleen, but did not alter the proportion of myeloid progenitors in total clonogenic cells. These results show that, when functional G-CSFR is present on the cell surface, hG-CSF stimulates the development of primitive multipotential progenitors both in vitro and in vivo, but does not induce exclusive commitment to the myeloid lineage.

Human Granulocyte Colony-Stimulating Factor (G-CSF) Stimulates the In Vitro and In Vivo Development But Not Commitment of Primitive Multipotential Progenitors From Transgenic Mice Expressing the Human G-CSF Receptor

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and restricted differentiation of hematopoietic progenitors into neutrophils. To clarify the effects of G-CSF on hematopoietic progenitors, we generated transgenic (Tg) mice that had ubiquitous expression of the human G-CSF receptor (hG-CSFR). In clonal cultures of bone marrow and spleen cells obtained from these mice, hG-CSF supported the growth of myelocytic as well as megakaryocytic, mast cell, mixed, and blast cell colonies. Single-cell cultures of lineage-negative (Lin−)c-Kit+Sca-1+ or Sca-1− cells obtained from the Tg mice confirmed the direct effects of hG-CSF on the proliferation and differentiation of various progenitors. hG-CSF also had stimulatory effects on the formation of blast cell colonies in cultures using 5-fluorouracil–resistant hematopoietic progenitors and clone-sorted Lin−c-Kit+Sca-1+ primitive hematopoietic cells. These colonies contained different progenitors in proportions similar to those obtained when mouse interleukin-3 was used in place of hG-CSF. Administration of hG-CSF to Tg mice led to significant increases in spleen colony-forming and mixed/blast cell colony-forming cells in bone marrow and spleen, but did not alter the proportion of myeloid progenitors in total clonogenic cells. These results show that, when functional G-CSFR is present on the cell surface, hG-CSF stimulates the development of primitive multipotential progenitors both in vitro and in vivo, but does not induce exclusive commitment to the myeloid lineage.

Alternatives to animal sera for human bone marrow cell expansion: human serum and serum-free media

The increasing use of cultured human cells in clinical trials is highlighting the need for alternatives to media containing animal sera that are typically used to support these cultures. Perfused cultures of BM mononuclear cells (MNC) were used to evaluate animal sera alternatives with respect to the output of primitive, progenitor, and stromal cells. A serum level of 20% was optimal, and this could be provided by FBS alone or by a mixture of horse serum (HoS) and FBS, but not by HoS alone. Allogeneic human plasma (20%) supported half the level of cell, CFU-GM, and LTC-IC output as compared with animal sera-containing control. Significant donor-to-donor variability in human plasma was observed, but this was mitigated by pooling of plasma samples. Autologous and allogeneic human plasma performed equivalently. The use of autologous or allogeneic human serum was found to be equivalent to the use of human plasma, but all were inferior to animal sera. Animal sera supported typical stroma and cobblestone formation, whereas stroma in human serum cultures was less dense. Eight commercial serum-free media were tested and found to support MNC expansion to varying degrees, but none approached the performance of the animal serum-containing control, particularly with respect to stromal (i.e., CFU-F) support. In fact, when MNC were cultured in parallel with CD34-enriched cells, output (from MNC) was higher only in control medium, apparently because serum-free media reduced accessory cell effects. Because of these results, a new serum-free medium was developed for MNC cultures. This formulation outperformed all commercial serum-free media, resulting in cell and LTC-IC output equivalent to that of control. However, CFU-GM and CFU-F output were 66% and 9% of control, respectively. Precoating the culture surface with collagen increased CFU-F (and Thy-1+ cell) output to control levels, although CFU-GM output was still lower than control. The addition of either fibronectin or PDGF had no measurable effect, nor did the use of 5-100-fold greater concentrations of growth factor supplementation. The serum-free medium also increased CD41+ and CD61+ cell output to 150%-220% of control levels. The development of this new serum-free medium has potential for use in the perfused BM MNC culture systems currently in clinical trials to test the efficacy of expanded cells after cytoablative chemotherapy.

Production and effects of interleukin-6 and other cytokines in patients with non-Hodgkin's lymphoma

Cytokines are regulatory molecules that are produced by a variety of cell types and are characterized by numerous biologic functions involved in the regulation of the immune system and hematopoiesis. This review summarizes the functions and regulation of cytokines in lymphomas and discusses the effect of a specific cytokine, interleukin-6 (IL-6), in B-cell lymphomas. IL-6 is a multipotent cytokine that can mediate the differentiation of B-cells into immunoglobulin-secreting cells, stimulate the autocrine or paracrine growth of myeloma cells, induce acute-phase proteins in liver cells, and may influence the pathogenesis of several diseases by autocrine or paracrine mechanisms. Patients with non-Hodgkin's lymphoma (NHL) have increased serum concentrations of IL-6; increased IL-6 levels can be associated with the presence of B-symptoms. Data presented in this review indicate that neoplastic cells from patients with NHL contained high concentrations of IL-6. Thus, elevated serum levels of IL-6 appear to originate from the lymphoma cells in patients with B-cell NHL, suggesting that the neoplastic cells may modulate the general status of patients with B-cell NHL. The inhibition or modification of the production of IL-6 in lymphoma cells may lead to a more effective control of the general status of patients with B-cell NHL.

Regulated Production of Type I Collagen and Inflammatory Cytokines by Peripheral Blood Fibrocytes

We recently described a novel population of blood-borne cells, termed fibrocytes, that display a distinct cell surface phenotype (collagen+/CD13+/CD34+/CD45+), rapidly enter sites of tissue injury, and contribute to scar formation. To further characterize the role of these cells in vivo, we examined the expression of type I collagen and cytokine mRNAs by cells isolated from wound chambers implanted into mice. Five days after chamber implantation, CD34+ fibrocytes but not CD14+ monocytes or CD90+ T cells expressed mRNA for type I collagen. Fibrocytes purified from wound chambers also were found to express mRNA for IL-1β, IL-10, TNF-α, JE/MCP, MIP-1α, MIP-1β, MIP-2, PDGF-A, TGF-β1, and M-CSF. The addition of IL-1β (1–100 ng/ml), a critical mediator in wound healing, to fibrocytes isolated from human peripheral blood induced the secretion of chemokines (MIP-1α, MIP-1β, MCP-1, IL-8, and GROα), hemopoietic growth factors (IL-6, IL-10, and macrophage-CSF), and the fibrogenic cytokine TNF-α. By contrast, IL-1β decreased the constitutive secretion of type I collagen as measured by ELISA. Additional evidence for a role for fibrocytes in collagen production in vivo was obtained in studies of livers obtained from Schistosoma japonicum-infected mice. Mouse fibrocytes localized to areas of granuloma formation and connective matrix deposition. We conclude that fibrocytes are an important source of cytokines and type I collagen during both the inflammatory and the repair phase of the wound healing response. Furthermore, IL-1β may act on fibrocytes to effect a phenotypic transition between a repair/remodeling and a proinflammatory mode.

An increase in peripheral blood progenitor cells in primates by coadministration of recombinant human interleukin 6 and recombinant human granulocyte colony-stimulating factor

BACKGROUND

We recently demonstrated that coadministration of recombinant human interleukin 6 (rhIL-6) and recombinant human granulocyte colony-stimulating factor (rhG-CSF) in mice synergistically increases peripheral blood stem cells (PBSC), which can rescue lethally irradiated recipient mice. However, there is little information about the effect of coadministration of rhIL-6 and rhG-CSF on PBSC in a primate system.

METHODS

In cynomolgus monkeys, rhG-CSF (5 microg/kg day) alone was administered for 5 days (first cycle). After the wash-out period, rhIL-6 (0, 10, or 20 microg/kg/day) and rhG-CSF were coadministered for 5 days (second cycle).

RESULTS

Total peripheral colony-forming cells levels were increased earlier by coadministration of rhIL-6 and rhG-CSF than by the administration of rhG-CSF alone. The maximum level in the coadministration cycle was obtained on day 5, and a high level was obtained for a further 3 days after cessation. The maximum number of peripheral total colony-forming cells in the coadministration cycle was a mean of 2.12-fold (range 1.38 to 3.35) higher than that in the rhG-CSF alone cycle. Coadministration also increased the peripheral mixed colony-forming units by a mean of 3.62-fold (range 1.02 to 5.52). Interestingly, monkeys that showed a low response to the administration of rhG-CSF alone also had a higher response to the coadministration. No significant difference was observed between the two cycles of administration of rhG-CSF alone.

CONCLUSIONS

These findings suggest that coadministration of rhIL-6 and rhG-CSF may be useful for clinical PBSC collection.

Leptin Stimulates the Proliferation of Murine Myelocytic and Primitive Hematopoietic Progenitor Cells

Leptin, the product of obese gene, was originally identified as a factor regulating body-weight homeostasis and energy balance. The present study has shown that leptin acts on murine hematopoiesis in vitro. In the culture of bone marrow cells (BMC) of normal mice, leptin induced only granulocyte-macrophage (GM) colony formation in a dose-dependent manner, and no other types of colonies were detected even in the presence of erythropoietin (Epo). Leptin also induced GM colony formation from BMC of db/db mutant mice whose leptin receptors were incomplete, but the responsiveness was significantly reduced. The effect of leptin on GM colony formation from BMC of normal mice was also observed in serum-free culture, and comparable with that of GM-colony–stimulating factor (CSF ). Although leptin alone supported few colonies from BMC of 5-fluorouracil (5-FU)–treated mice in serum-free culture, remarkable synergism between leptin and stem cell factor (SCF ) was obtained in the colony formation. The addition of leptin to SCF enhanced the SCF-dependent GM colony formation and induced the generation of a number of multilineage colonies in the presence of Epo. When lineage (Lin)−Sca-1+ cells sorted from BMC of 5-FU–treated mice were incubated in serum-free culture, leptin synergized with SCF in the formation of blast cell colonies, which efficiently produced secondary colonies including a large proportion of multilineage colonies in the replating experiment. In serum-free cultures of clone-sorted Lin−c-Kit+Sca-1+ and Lin−c-Kit+Sca-1− cells, although synergism of leptin and SCF was observed in the colony formation from both cells, leptin alone induced the colony formation from Lin−c-Kit+Sca-1−, but not Lin−c-Kit+Sca-1+ cells. These results have shown that leptin stimulates the proliferation of murine myelocytic progenitor cells and synergizes with SCF in the proliferation of primitive hematopoietic progenitors in vitro.

The role of mel-18, a mammalian Polycomb group gene, during IL-7-dependent proliferation of lymphocyte precursors

mel-18 is a mammalian homolog of Drosophila melanogaster Polycomb group genes. Mice lacking the mel-18 gene show a posterior transformation of the axial skeleton, severe combined immunodeficiency, and a food-passing disturbance in the lower intestine due to hypertrophy of the smooth muscle layer. In this study, the severe combined immunodeficiency observed in mel-18 mutant mice is correlated with the impaired mitotic response of lymphocyte precursors upon interleukin-7 stimulation. Strikingly, the axial skeleton and lymphoid phenotypes are identical in both mel-18 and bmi-1 mutants, indicating that the Mel-18 and Bmi-1 gene products might act in the same genetic cascade. These results suggest that mammalian Polycomb group gene products are involved in cell cycle progression in the immune system.

Role of glucocorticoid on interleukin-6-induced cellular functions in the mouse macrophage cell line (Mm 1)

To discover a role of glucocorticoid on interleukin-6 (IL-6)-induced responses of a macrophage, we investigated the effect of IL-6 and/or dexamethasone (Dex) on cellular functions of a mouse macrophage cell line (Mm1 cells). The results obtained were as follows. (1) Dex decreased the accumulation of tumor necrosis factor-alpha induced by IL-6, whereas nitric oxide production was enhanced by Dex. Moreover, the enhancement of nitric oxide production could be demonstrated to be associated with stimulation of iNOS mRNA expression by the Dex treatment. (2) Cytotoxic activity of Mm1 cells on mouse B16 melanoma cells was much more enhanced by the co-treatment of IL-6 with Dex than IL-6 treatment alone. (3) Dex promoted further the suppression of proliferation induced by IL-6. (4) DNA fragmentation, introduced by the treatment of cells with IL-6, was further enhanced in the presence of Dex.

Tiazofurin-induced autosecretion of IL-6 and hemoglobin production in K562 human leukemia cells

Previous reports have established the synthesis of interleukin-6 (IL-6) and IL-6 receptors (IL-6R) in several human leukemia cells and found that IL-6 and the IL-6R could be expressed in cell lines with erythroid/megakaryocytic features. IL-6 is a pleiotropic cytokine involved in megakaryocytic differentiation. The finding that endogenous IL-6 levels in serum increased after 5-fluorouracil (5-FU) treatment suggests that IL-6 may play some role in the recovery of hematopoietic systems. This observation may assist the understanding of erythroid regeneration caused by antineoplastic agents such as tiazofurin. Tiazofurin inhibits the activity of IMP dehydrogenase. Its exposure to K562 cells at 10 microM tiazofurin stimulates erythroid differentiation. Stimulation of cells with tiazofurin gave a significant increase in IL-6 production. Its levels were quadrupled after 2 days of culture. Tiazofurin also caused a trivial reduction in the percentage of cells with the IL-6R. This evidence implies that tiazofurin produced no significant effect on the IL-6R. Tiazofurin also increased the percentage of benzidine-positive cells representing hemoglobin production, confirmed by GpA expression. We concluded that IL-6 is rate limiting in regard to hemoglobin production and that IL-3 could be used for clinical benefit to stimulate erythropoiesis and synergize with tiazofurin.

Analysis of interleukin 6 receptor and gp130 expressions and proliferative capability of human CD34+ cells

We recently demonstrated that stimulation of gp130 by a combination of soluble interleukin 6 receptor (sIL-6R) and IL-6 but not IL-6 alone significantly stimulates the ex vivo expansion of primitive hematopoietic progenitors and the generation of erythroid cells from human CD34+ cells in the presence of stem cell factor (SCF). Here, we show that gp130 is found low positively on most CD34+ cells, whereas IL-6R is expressed on only 30-50% of these cells. Although most of the colonies generated from FACS-sorted CD34+IL-6R+ cells were granulocyte/macrophage (GM) colonies, CD34+IL-6R- cells gave rise to various types of colonies, including erythroid bursts, GM, megakaryocytes, and mixed colonies in methylcellulose culture with a combination of IL-6, sIL-6R, and SCF. Similar results were obtained in culture supplemented with a combination of IL-3, IL-6, SCF, granulocyte colony-stimulating factor, erythropoietin, and thrombopoietin. A limiting dilution analysis of long-term culture-initiating cells (LTC-IC) showed that the CD34+IL-6R- cells contained a larger number of LTC-IC than did the CD34+IL-6R+ cells. In a serum-free suspension of CD34+IL-6R- cells, the addition of sIL-6R to the combination of IL-6 and SCF dramatically increased the total and multipotential progenitors, whereas CD34+IL-6R+ cells failed to do so under the same conditions. These results indicate that most of the erythroid, megakaryocytic, and primitive human hematopoietic progenitors are included in the IL-6R- populations, and the activation of gp130 on these progenitors can be achieved by a complex of IL-6-sIL-6R, but not by IL-6 alone. The present culture system using IL-6, sIL-6R, and SCF may provide a novel approach for ex vivo expansion of human primitive hematopoietic progenitors.

Inhibition by dexamethasone of the lipopolysaccharide-induced increase in IL-6 mRNA abundance and IL-6 production in human polymorphonuclear leukocytes

Interleukin-6 (IL-6) is a key inflammatory cytokine that is produced by various cell types including polymorphonuclear leukocytes (PMNs). However, the pathophysiological roles of IL-6 produced by human PMNs are unclear. Bacterial lipopolysaccharide (LPS) induced marked increase in IL-6 production, determined by enzyme-linked immunosorbent assay, and IL-6 mRNA abundance determined by reverse transcription-polymerase chain reaction analysis, in purified human PMNs. Both effects of LPS were inhibited in a dose-dependent manner by dexamethasone (10(-6) to 10(-8) M). IL-6 receptor mRNA was constitutively present in PMNs and its abundance was not affected by either LPS or dexamethasone. These results indicate that PMNs are an important source of IL-6 in acute inflammatory reactions, and that the anti-inflammatory actions of dexamethasone is attributable in part to inhibition of IL-6 production by these cells. The constitutive presence of IL-6 receptor mRNA in PMNs suggests that IL-6 may exert pathophysiological effects on these cells.

Enhanced platelet recovery in myelosuppressed mice treated with interleukin-1 and macrophage colony-stimulating factor: potential interactions with cytokines having megakaryocyte colony-stimulating activity

Studies were carried out to determine whether the combination of IL-1 + M-CSF, similar to the effect of these cytokines on neutropenia, was able to reduce the duration of thrombocytopenia in the 5-fluorouracil (5-FU)-myelosuppressed mouse. In addition, comparisons were made between the in vivo effects of IL-1 + M-CSF and other "thrombopoietic" cytokines (e.g., IL-3, IL-6, and GM-CSF) that demonstrate some form of megakaryocytopoietic activity in vitro. Of the five cytokines studied, only IL-1 and IL-6, by themselves, were able to effect thrombopoietic recovery in the myelosuppressed mouse. IL-1, either when acting alone or interacting synergistically with M-CSF, was able to reduce significantly the period of thrombocytopenia, but the effects of IL-6 were restricted to enhancing platelet production during the period of rebound thrombocytopenia without altering the kinetics of thrombopoietic recovery. Moreover, none of the cytokine combinations studied were found to interact to reduce further the duration of thrombocytopenia beyond that observed with IL-1 + M-CSF. Nonetheless, IL-3, IL-6, and, to a lesser extent, GM-CSF were each able to interact with IL-1 + M-CSF to extend further the period of enhanced platelet production in the animal. However, scheduling studies suggested that these thrombopoietic cytokines interacted in sequence, rather than in concert, with IL-1 + M-CSF to enhance platelet production during thrombopoietic recovery. Furthermore, the data presented are consistent with the hypothesis that IL-1 + M-CSF initially acts on a multilineage, 5-FU-resistant target cell and that IL-6 (and possibly IL-3 and GM-CSF) serves as a secondary cytokine further to enhance platelet production during rebound thrombopoiesis in the 5-FU-treated mouse.

Erythropoietin-independent erythrocyte production: signals through gp130 and c-kit dramatically promote erythropoiesis from human CD34+ cells

Erythropoietin (EPO) is the primary humoral regulator of erythropoiesis and no other factor has previously been reported to support proliferation and terminal maturation of erythroid cells from hemopoietic stem cells. Here we show that stimulation of glycoprotein (gp130) by a combination of recombinant human soluble interleukin 6 receptor (sIL-6R) and IL-6 but not sIL-6R or IL-6 alone can support proliferation, differentiation, and terminal maturation of erythroid cells in the absence of EPO from purified human CD34+ cells in suspension culture containing stem cell factor (SCF). A number of erythroid bursts and mixed erythroid colonies also developed in methylcellulose culture under the same combination. The addition of anti-gp130 monoclonal antibodies but not anti-EPO antibody to the same culture completely abrogated the generation of erythroid cells. These results clearly demonstrate that mature erythroid cells can be emerged from hemopoietic progenitors without EPO in vitro. Together with the previous reports that human sera contain detectable levels of sIL-6R, IL-6, and SCF, current data suggest that gp130 signaling in association with c-kit activation may play a role in human erythropoiesis in vivo.

IL-6 cytokine family and signal transduction: a model of the cytokine system

The interleukin 6 (IL-6) cytokine family, which includes IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), IL-11 and cardiotrophin-1 (CT-1), exhibits pleiotropy and redundancy in biological activities. The IL-6 family cytokines exhibit a helical structure. Their receptors belong to the type 1 cytokine receptor family. The receptors of the IL-6 family cytokines share a receptor subunit, which explains one of the mechanisms of functional redundancy. In this review, we describe the general features of the IL-6 cytokine family and its signal transduction mechanisms. Many functional properties of the IL-6 family of cytokines and their receptors are general features of the cytokine system.