Tumor necrosis factor alpha is a potent synergistic factor for the proliferation of primitive human hematopoietic progenitor cells and induces resistance to transforming growth factor beta but not to interferon gamma

Delivery of antigen to porcine dendritic cells by fusing antigen with porcine dendritic cells targeting peptide

Dendritic cells (DCs) are professional antigen-presenting cells that can recognize, capture, and process antigens. Fusing molecules targeting DCs with antigens can effectively improve the efficiency with which antigens are recognized and captured by DCs. This targeting strategy can be used for vaccine development to effectively improve the efficiency of antigen recognition and capture by DCs. The targeting sequence of porcine cytotoxic T-lymphocyte associated protein 4 (CTLA4), which binds porcine DCs, was identified in this study. Recombinant Lactobacillus reuteri (L. reuteri) expressing CTLA4-6aa (LYPPPY) and CTLA4-87aa fused to the porcine epidemic diarrhea virus (PEDV) protective antigen core neutralizing epitope (COE) were used to evaluate the ability of the two targeting motifs to bind the B7 molecule on DCs. Our results demonstrate that CTLA4-6aa could bind porcine DCs, and recombinant Lactobacillus expressing the CTLA4-6aa captured by porcine DCs was more efficient than those expressing CTLA4-87aa. In addition, the expression of DC markers, toll-like receptors, and cytokines was significantly higher in the 6aa-COE/L. reuteri-stimulated porcine DCs compared to DCs treated with 87aa-COE/L. reuteri (p<0.01) and recombinant Lactobacillus expressing CTLA4-6aa enhanced the ability of porcine DCs to activate T-cell proliferation. Our analysis of the protein structure revealed that CTLA4-87aa contains intramolecular hydrogen bonds, which may have weakened the intermolecular force between the residues on porcine CTLA4 and that on B7. In conclusion, recombinant Lactobacillus expressing CTLA4-6aa were more efficiently captured by porcine DCs and had a stronger ability to promote DC maturation and enhance T-cell proliferation. The LYPPPY motif is the optimal sequence for binding to porcine DCs. Piglets immunized with recombinant Lactobacillus showed that recombinant Lactobacillus expressing CTLA4-6aa induced significant levels of anti-PEDV-specific IgG and IgA antibody responses. Our study may promote research on DC-targeting strategies to enhance the effectiveness of porcine vaccines.

Inflammation Regulates Haematopoietic Stem Cells and Their Niche

Haematopoietic stem cells (HSCs) reside in the bone marrow and are supported by the specialised microenvironment, a niche to maintain HSC quiescence. To deal with haematopoietic equilibrium disrupted during inflammation, HSCs are activated from quiescence directly and indirectly to generate more mature immune cells, especially the myeloid lineage cells. In the process of proliferation and differentiation, HSCs gradually lose their self-renewal potential. The extensive inflammation might cause HSC exhaustion/senescence and malignant transformation. Here, we summarise the current understanding of how HSC functions are maintained, damaged, or exhausted during acute, prolonged, and pathological inflammatory conditions. We also highlight the inflammation-altered HSC niche and its impact on escalating the insults on HSCs.

Emerging role of cell-free DNA in kidney transplantation

Monitoring kidney transplants for rejection conventionally includes serum creatinine, immunosuppressive drug levels, proteinuria, and donor-specific antibody (DSA). Serum creatinine is a late marker of allograft injury, and the predictive ability of DSA regarding risk of rejection is variable. Histological analysis of an allograft biopsy is the standard method for diagnosing rejection but is invasive, inconvenient, and carries risk of complications. There has been a long quest to find a perfect biomarker that noninvasively predicts tissue injury caused by rejection at an early stage, so that diagnosis and treatment could be pursued without delay in order to minimize irreversible damage to the allograft. In this review, we discuss relatively novel research on identifying biomarkers of tissue injury, specifically elaborating on donor-derived cell-free DNA, and its clinical utility.

Autocrine TNF-α production supports CML stem and progenitor cell survival and enhances their proliferation

Chronic myeloid leukemia (CML) stem cells are not dependent on BCR-ABL kinase for their survival, suggesting that kinase-independent mechanisms must contribute to their persistence. We observed that CML stem/progenitor cells (SPCs) produce tumor necrosis factor-α (TNF-α) in a kinase-independent fashion and at higher levels relative to their normal counterparts. We therefore investigated the role of TNF-α and found that it supports survival of CML SPCs by promoting nuclear factor κB/p65 pathway activity and expression of the interleukin 3 and granulocyte/macrophage-colony stimulating factor common β-chain receptor. Furthermore, we demonstrate that in CML SPCs, inhibition of autocrine TNF-α signaling via a small-molecule TNF-α inhibitor induces apoptosis. Moreover TNF-α inhibition combined with nilotinib induces significantly more apoptosis relative to either treatment alone and a reduction in the absolute number of primitive quiescent CML stem cells. These results highlight a novel survival mechanism of CML SPCs and suggest a new putative therapeutic target for their eradication.

Ablation of TNF-RI/RII expression in Alzheimer's disease mice leads to an unexpected enhancement of pathology: implications for chronic pan-TNF-α suppressive therapeutic strategies in the brain

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by severe memory loss and cognitive impairment. Neuroinflammation, including the extensive production of pro-inflammatory molecules and the activation of microglia, has been implicated in the disease process. Tumor necrosis factor (TNF)-α, a prototypic pro-inflammatory cytokine, is elevated in AD, is neurotoxic, and colocalizes with amyloid plaques in AD animal models and human brains. We previously demonstrated that the expression of TNF-α is increased in AD mice at ages preceding the development of hallmark amyloid and tau pathological features and that long-term expression of this cytokine in these mice leads to marked neuronal death. Such observations suggest that TNF-α signaling promotes AD pathogenesis and that therapeutics suppressing this cytokine's activity may be beneficial. To dissect TNF-α receptor signaling requirements in AD, we generated triple-transgenic AD mice (3xTg-AD) lacking both TNF-α receptor 1 (TNF-RI) and 2 (TNF-RII), 3xTg-ADxTNF-RI/RII knock out, the cognate receptors of TNF-α. These mice exhibit enhanced amyloid and tau-related pathological features by the age of 15 months, in stark contrast to age-matched 3xTg-AD counterparts. Moreover, 3xTg-ADxTNF-RI/RII knock out-derived primary microglia reveal reduced amyloid-β phagocytic marker expression and phagocytosis activity, indicating that intact TNF-α receptor signaling is critical for microglial-mediated uptake of extracellular amyloid-β peptide pools. Overall, our results demonstrate that globally ablated TNF receptor signaling exacerbates pathogenesis and argues against long-term use of pan-anti-TNF-α inhibitors for the treatment of AD.

The ratio of SRPK1/SRPK1a regulates erythroid differentiation in K562 leukaemic cells

SRPK1, the prototype of the serine/arginine family of kinases, has been implicated in the regulation of multiple cellular processes such as pre-mRNA splicing, chromatin structure, nuclear import and germ cell development. SRPK1a is a much less studied isoform of SRPK1 that contains an extended N-terminal domain and so far has only been detected in human testis. In the present study we show that SRPK1 is the predominant isoform in K562 cells, with the ratio of the two isoforms being critical in determining cell fate. Stable overexpression of SRPK1a induces erythroid differentiation of K562 cells. The induction of globin synthesis was accompanied by a marked decrease in proliferation and a significantly reduced clonogenic potential. Small interfering RNA-mediated down-regulation of SRPK1 in K562 cells results similarly in a decrease in proliferative capacity and induction of globin synthesis. A decreased SRPK1/SRPK1a ratio is also observed upon hemin/DMSO-induced differentiation of K562 cells as well as in normal human erythroid progenitor cells. Mass spectrometric analysis of SRPK1a-associated proteins identified multiple classes of RNA-binding proteins including RNA helicases, heterogeneous nuclear ribonucleoproteins, ribosomal proteins, and mRNA-associated proteins. Several of the SRPK1a-copurifying proteins have been previously identified in ribosomal and pre-ribosomal complexes, thereby suggesting that SRPK1a may play an important role in linking ribosomal assembly and/or function to erythroid differentiation in human leukaemic cells.

Effect of thalidomide and arsenic trioxide on the release of tumor necrosis factor-α and vascular endothelial growth factor from the KG-1a human acute myelogenous leukemia cell line

Studies conducted in our lab have indicated that thalidomide cytotoxicity in the KG-1a human acute myelogenous leukemia (AML) cell line was enhanced by combining it with arsenic trioxide. The current investigation was conducted in order to evaluate the effect of thalidomide either alone or in combination with arsenic trioxide on the release of tumor necrosis factor-α (TNF-α) and vascular endothelial growth factor (VEGF) from this cell line in an attempt to clarify its possible cytotoxic mechanism(s). Human AML cell line KG-1a was used in this study. The cells were cultured for 48 h in the presence or absence of thalidomide (5 mg/l), and or arsenic trioxide (4 μM). The levels of TNF-α and VEGF in the supernatant were determined by ELISA. Results obtained indicate that the levels of TNF-α in the supernatant of KG-1a cell cultures incubated with thalidomide, arsenic trioxide, or combination were statistically lower than those observed in the supernatant of control cells (2.89, 5.07, 4.15 and 16.88 pg/ml, respectively). However, the levels of VEGF in the supernatant of thalidomide-treated cells were statistically higher than those in the supernatant of control cells (69.61 vs. 11.48 pg/l). Arsenic trioxide, whether alone or in combination with thalidomide, did not produce any statistically significant difference in the levels of VEGF as compared to the control or thalidomide-treated cell supernatant. These findings indicate that thalidomide and the arsenic trioxide inhibition of TNF-α production by KG-1a cells may play an important role in their cytotoxic effect.

Mesenchymal stromal cells as supportive cells for hepatocytes

Hepatocytes and hematopoietic stem cells (HSCs) appear to share many of the same requirements for their survival, functionality, and proliferation. This may be due to a shared location during fetal development. Moreover, hepatocytes and HSCs are unable to function, or even survive, without stromal cell support. Bone marrow-derived mesenchymal stromal cells (MSCs) support the proliferation and functionality, not only of HSCs, but also of hepatocytes. Although knowledge of the mechanisms underlying HSCs' support is far more advanced than for hepatocytes, data suggest that many agents important for HSCs also maintain the normal hepatocyte phenotype in vitro. Thus, it is possible that new techniques for the maintenance and expansion of HSCs may also be useful for hepatocytes. Bone marrow-derived MSCs are easily cultured and expanded in vitro, and some data suggest that they are immunoregulatory as well as relatively nonimmunogenic. These observations suggest that allogeneic MSCs may be useful not only in supporting hepatocyte growth and proliferation but also in modulating immune responses such as stellate cell activation.

Cytokine-producing activity of bone marrow erythrokaryocytes and its regulation under normal conditions

We showed that inhibition of cytokine production by bone marrow adherent cells and their soluble products is a mechanism of regulation of cytokine-producing activity of bone marrow erythrokaryocytes under normal conditions.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.

Effector cells derived from host CD8 memory T cells mediate rapid resistance against minor histocompatibility antigen-mismatched allogeneic marrow grafts without participation of perforin, Fas ligand, and the simultaneous inhibition of 3 tumor necrosis factor family effector pathways

Reduced-intensity conditioning regimens for transplant recipients have heightened awareness of immunologic resistance to allogeneic bone marrow transplants (BMT). Although T cell-mediated cytotoxicity has been assumed to play a role in the resistance against donor allogeneic hematopoietic stem and progenitor cell grafts, several studies have reported relatively unimpaired resistance by recipients who lack perforin, Fas ligand (FasL), and other cytotoxic mediators. This study compared the early kinetics of T cell-mediated resistance in B6 (H2b) cytotoxically normal versus deficient recipients after transplantation with major histocompatibility complex-matched, minor histocompatibility antigen (MiHA)-mismatched allogeneic marrow grafts. Wild-type B6 or cytotoxic double-deficient perforin-/-/gld+/+ (B6-cdd) mice were sensitized against major histocompatibility complex-matched BALB.B or C3H.SW (H2b) MiHA and transplanted with a high dose (1 x 10(7)) of T cell-depleted bone marrow. CD8 T memory cells were shown to be present in recipients before BMT, and anti-CD8 monoclonal antibody infusion abolished resistance, thus demonstrating that CD8 T cells are the host effector population. Donor-committed and high proliferative potential progenitor numbers were markedly diminished by 48 hours after transplantation in both wild-type B6 and B6-cdd anti-donor MiHA-sensitized recipients. These observations indicate that the resistance pathway used in the cytotoxic deficient mice was both potent and rapidly induced--consistent with a CD8 memory T-cell response. To examine the role of Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)- and TL1A-mediated cytotoxicity in this strong resistance, newly generated monoclonal antibodies specific for these ligands were administered to B6-cdd recipients sensitized to donor antigens. Recipients of syngeneic B6-gfp bone marrow exhibited significant donor colony-forming unit numbers after BMT. In contrast, low or absent colony-forming unit levels were detected in allogeneic recipients, including those that lacked perforin and FasL and that received anti-TWEAK, anti-tumor necrosis factor-related apoptosis-inducing ligand, and anti-TL1A monoclonal antibodies. These findings extend previous observations by demonstrating the existence of a rapidly effected resistance pathway mediated by memory CD8 effector T cells independent of the 2 major pathways of cytotoxicity. Together with previous findings, these results support the notion that effector cells derived from memory CD8 T-cell populations can mediate strong resistance against donor allogeneic MiHA-disparate hematopoietic engraftment by using a mechanism that is independent of the contribution of perforin, FasL, and the known death ligand receptor pathways.

Transforming growth factor-beta1 to the bone

TGF-beta1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-beta1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-beta1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-beta1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-beta1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.

FLRG, member of the follistatin family, a new player in hematopoiesis

Several years ago, we cloned and characterized from a B cell leukemia a new secreted protein which, on the basis of its high degree of structural homology with follistatin, was defined as a member of the follistatin family and accordingly named follistatin-related gene (FLRG). However, follistatin and FLRG revealed non-overlapping patterns of expression in various tissues thereby indicating the existence of non-redundant functional roles for these proteins throughout the organism. As known for a long time, follistatin is a biological regulator of activin and bone morphogenetic protein (BMP) function in various cellular systems: in particular, it inhibits the effects of activin on hematopoiesis. We therefore investigated the expression and effects of FLRG during human hematopoiesis with particular focus on the effect of this soluble glycoprotein in the regulation of erythropoiesis. For this purpose, we have for the first time, compared the role of Activin A, BMP2 and BMP4 during erythropoiesis, in primary human cells. Our results indicate that, BMP2 acts on early erythroid cells while Activin A acts on a more differentiated population. We report the induction by Activin A and BMP2 of cell commitment towards erythropoiesis in the absence of EPO. This induction involves two key events: increase of EPO-R and the decrease of GATA2 expression. Our results indicate that despite their high structural homology, follistatin and FLRG do not regulate the same signaling targets, therefore highlighting distinct functions and mechanisms for these two proteins in the human hematopoietic system. We thus propose a working model for the regulation of activin or BMP-induced human erythropoiesis by follistatin/FLRG.

Erythropoietin-dependent autocrine secretion of tumor necrosis factor-alpha in hematopoietic cells modulates proliferation via MAP kinase–ERK-1/2 and does not require tyrosine docking sites in the EPO receptor

Primary erythroid cells and erythroid cell lines may synthesize and secrete tumor necrosis factor-alpha (TNF-alpha) following stimulation with erythropoietin (EPO). The effect of triggering TNF-alpha synthesis and secretion was investigated in erythroleukemia and myeloid cell lines: HCD57, DA3-EPOR, and BAF3-EPOR. The EPO-induced, membrane-bound form of autocrine TNF-alpha seemed to enhance proliferation of HCD57 and DA3-EPOR cells; however, the concentration of secreted autocrine/paracrine TNF-alpha was never sufficient to have an effect. Autocrine TNF-alpha acts through TNFRII receptors to stimulate proliferation. Modulation of mitogen-activated protein kinase (MAPK)/extracellular signal-related kinase (ERK-1/2) activity by the membrane-bound form of autocrine TNF-alpha apparently played a central role in the control of EPO-dependent proliferation of HCD57 and DA3-EPOR cells. Primary erythroid cells and DA3-EPOR cells were found to express similar, high levels of both TNFRI and TNFRII, showing that differential expression of TNF-alpha receptors does not explain why primary cells are inhibited and DA3-EPOR cells are stimulated by autocrine TNF-alpha. BAF3 cells expressing a mutant EPOR with no cytoplasmic tyrosine residues were capable of triggering EPO-dependent TNF-alpha synthesis and secretion, indicating that tyrosine-docking sites in the EPOR were not required for EPO-dependent TNF-alpha secretion.

TIAF1 participates in the transforming growth factor beta1--mediated growth regulation

TGF-beta induces growth suppression and apoptosis of various types of cells, but supports fibroblast growth. We previously isolated TIAF1 (TGF-beta1-induced antiapoptotic factor 1), which protects murine L929 fibroblasts from TNF cytotoxicity. Here, we show that TIAF1 induced growth inhibition and apoptosis of monocytic U937 and other types of cells. In contrast, like TGF-beta1, TIAF1 supported transforming growth of L929 fibroblasts. TIAF1 increased the expression of p53, Cip1/p21, and Smad proteins; suppressed ERK phosphorylation; and altered TGF-beta1-mediated Smad2/3 phosphorylation in U937 cells. Antisense TIAF1 mRNA significantly enhanced the proliferation of mink lung Mv1Lu epithelial cells. Together, these observations indicate that TIAF1 participates in the TGF-beta-mediated growth regulation.

Lack of tumor necrosis factor alpha induces impaired proliferation of hepatitis B virus-specific cytotoxic T lymphocytes

Recent studies have shown that tumor necrosis factor alpha (TNF-alpha) plays critical roles in not only viral clearance but also lymphoid tissue development and stem cell differentiation. In this study, we attempted to induce hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTLs) by immunization of TNF-alpha knockout (TNF-alpha(-/-)) mice with HBsAg-encoding plasmid DNA. An immunization with the HBV plasmid failed to induce CTL responses in TNF-alpha(-/-) mice, although CTLs were readily induced in wild-type mice by the same protocol. Weak CTL responses were produced in TNF-alpha(-/-) mice after two sessions of immunization with the HBV plasmid; however, TNF-alpha was required to maintain the responses of these CTL lines to in vitro stimulation and, even then, the responses were lost after 3 weeks. Interestingly, a limiting dilution of a CTL line showed that HBV-specific CTL clones with high specific cytotoxicity were present in TNF-alpha(-/-) mice, but these clones again failed to proliferate for more than 3 weeks. Furthermore, since exogenously added TNF-alpha enhanced the proliferation of a TNF-alpha(-/-) clone but suppressed that of a TNF-alpha(+/+) clone in vitro, TNF-alpha also has a direct effect on the proliferation of CTLs. In conclusion, TNF-alpha is essential rather than important for the proliferation of HBV-specific CTLs both in vivo and in vitro and this effect is not only due to the activation of dendritic cells but is also induced by the direct effect on CTLs.

Regulation of human erythropoiesis by activin A, BMP2, and BMP4, members of the TGFbeta family

Activin A, BMP2, and BMP4, members of the TGFbeta family, have been implicated in the regulation of hematopoiesis. Here we explore and compare, for the first time in human primary cells, the role of activin A, BMP2, and BMP4 during erythropoiesis. Using in vitro erythroid differentiation of CD34(+) primary cells, we obtained the main stages of early erythropoiesis, characterized at the molecular, biochemical, and functional levels. Our results indicate that BMP2 acts on early erythroid cells and activin A on a more differentiated population. We report an insight into the mechanism of commitment of erythropoiesis by activin A and BMP2 involving two key events, increase in EPO-R and decrease in GATA2 expression. Simultaneous addition of activin A with BMP molecules suggests that BMP2 and BMP4 differently affect activin A induction of erythropoiesis. Follistatin and FLRG proteins downmodulate the effects of activin A and BMP2 on erythroid maturation.

Tumor necrosis factor-alpha expressed constitutively in erythroid cells or induced by erythropoietin has negative and stimulatory roles in normal erythropoiesis and erythroleukemia

Binding of erythropoietin (EPO) to its receptor (EPOR) on erythroid cells induces the activation of numerous signal transduction pathways, including the mitogen-activated protein kinase Jun-N-terminal kinase (JNK). In an effort to understand the regulation of EPO-induced proliferation and JNK activation, we have examined the role of potential autocrine factors in the proliferation of the murine erythroleukemia cell line HCD57. We report here that treatment of these cells with EPO induced the expression and secretion of tumor necrosis factor alpha (TNF-alpha). EPO-dependent proliferation was reduced by the addition of neutralizing antibodies to TNF-alpha, and exogenously added TNF-alpha induced proliferation of HCD57 cells. EPO also could induce TNF-alpha expression in BAF3 and DA3 myeloid cells ectopically expressing EPOR. Addition of TNF-alpha activated JNK in HCD57 cells, and the activity of JNK was partially inhibited by addition of a TNF-alpha neutralizing antibody. Primary human and murine erythroid progenitors expressed TNF-alpha in either an EPO-dependent or constitutive manner. However, TNF-alpha had an inhibitory effect on both immature primary human and murine cells, suggestive that the proliferative effects of TNF-alpha may be limited to erythroleukemic cells. This study suggests a novel role for autocrine TNF-alpha expression in the proliferation of erythroleukemia cells that is distinct from the effect of TNF-alpha in normal erythropoiesis.

Hypoplastic myelodysplastic syndromes can be distinguished from acquired aplastic anaemia by bone marrow stem cell expression of the tumour necrosis factor receptor

It is often difficult to distinguish hypoplastic myelodysplastic syndrome (h-MDS) from acquired aplastic anaemia (AA), because of the considerable clinical, cytological and histological similarities between these two disorders. The distinction between AA and h-MDS is important because there is a higher risk of progression to acute leukaemia in patients with h-MDS compared with AA. Recent studies suggest that tumour necrosis factor-alpha (TNF-alpha) plays an important role in the development of AA. In order to determine the potential importance of TNF-alpha in the differential diagnosis of hypoplastic bone marrow (BM) disorders, we examined whether analysis ofTNF-receptor expression could be used as a tool to differentiate AA from h-MDS. Flow cytometric analysis revealed that BM stem cells (CD34+) from AA patients have markedly greater TNF receptor (R) 1 and TNFR2 expression than those from patients with MDS and h-MDS. We suggest that the BM stem cells with a high expression of TNFR in patients with AA may be potently sensitive to TNF-alpha stimulation of differentiation. Thus, we propose that quantification of TNFR expression in BM stem cellsmay be a useful method to distinguish AA from h-MDS.

The soluble Notch ligand, Jagged-1, inhibits proliferation of CD34+ macrophage progenitors

The Notch/Notch ligand system controls diverse cellular processes. The proteolytic cleavage generates transmembrane and soluble forms of Notch ligands. We examined the effect of a soluble Notch ligand, human Jagged-1, on human cord blood (CB) CD34+ cells, under serum-deprived conditions, using soluble human Jagged-1-immunoglobulin G1 chimera protein (hJagged-1). Soluble hJagged-1 inhibited myeloid colony formation but not erythroid-mix or erythroid colony formation, in the presence of stem cell factor (SCF), interleukin-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, thrombopoietin, and erythropoietin. Cytological analysis revealed that the decrease in myeloid colonies resulted mainly from the inhibition of macrophage colony formation. Furthermore, soluble hJagged-1 led to the inhibition of macrophage colony formation supported by M-CSF plus SCF and GM-CSF plus SCF. Delayed-addition experiments and the analysis of colony sizes demonstrated that soluble hJagged-l inhibited the growth of macrophage progenitors by acting in the early stage of macrophage development. The direct action of hJagged-1 was confirmed by the enhanced expression of the HES-1 (hairy enhancer of the split-1) gene. These results suggest that soluble hJagged-1 may regulate human hematopoiesis in the monocyte/macrophage lineage.

Porcine hematopoiesis on primate stroma in long-term cultures: enhanced growth with neutralizing tumor necrosis factor-alpha and tumor growth factor-beta antibodies

BACKGROUND

Donor hematopoiesis is at a competitive disadvantage when bone marrow transplantation is across species barriers. This could present major limitations to xenogeneic stem cell transplantation as an approach to tolerance induction. An in vitro model of xenogeneic engraftment was established to identify inhibitors of porcine hematopoiesis in a primate environment.

METHODS

Porcine bone marrow cells (BMC), in the presence or absence of primate CD34+ positive cells, were cultured for 4-6 weeks on primate stroma with porcine cytokines. Cellularity and growth of colony-forming cells were indicators of hematopoietic growth. Effects of soluble factors were determined by using Transwell inserts to separate porcine cells from stroma. Neutralizing antibodies for human transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha) were added to cultures.

RESULTS

Porcine hematopoiesis can be maintained in long-term cultures on primate stroma with pig cytokines. Adding BMC to the stroma below Transwell-containing porcine cells dramatically inhibited porcine hematopoiesis, showing an inhibitory role for soluble factors. Neutralizing antibodies against TNF-alpha or TGF-beta caused a modest enhancement of porcine hematopoiesis; however, the combination of both led to a substantial increase. Inhibitory effects of these cytokines were confirmed by adding TNF-alpha and TGF-beta to porcine cultures.

CONCLUSIONS

Porcine cells may be more sensitive to inhibitory effects of TNF-alpha and TGF-beta than primate cells and are at a disadvantage when in a primate environment. Potential implications of this observation are discussed in the context of establishing specific immune tolerance via mixed chimerism to facilitate xenotransplantation.

Expression of FLRG, a novel activin A ligand, is regulated by TGF-beta and during hematopoiesis [corrected]

OBJECTIVE

The human gene FLRG, identified from a B-cell chronic lymphocytic leukemia bearing a t(11;19) translocation, encodes a secreted glycoprotein highly homologous with follistatin. Activin A is a TGF-beta family member involved in the regulation of growth and differentiation of various types of cells, such as those of the hematopoietic system. Its biological activity is antagonized by binding with follistatin. We investigated the binding of FLRG to activin A and the expression pattern of FLRG, follistatin, and activin A during hematopoiesis.

MATERIALS AND METHODS

The binding of FLRG with activin A was investigated by immunoprecipitation and Far-Western blot analysis. Gene expression was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) and Northern Blot in purified hematopoietic populations.

RESULTS

We demonstrate that FLRG, like follistatin, is able to bind to activin A. In bone marrow stromal cells, both mRNA and protein FLRG levels were found to be dramatically increased by TGF-beta. FLRG and activin A are expressed in the same cells, with a higher level of expression in the myeloid cells compared with the erythroid and megakaryocytic cells. FLRG and follistatin expression were different in the hematopoietic subpopulations tested. Moreover, we observed that FLRG and activin A expression was up-regulated during hematopoiesis.

CONCLUSION

FLRG and activin A are expressed in the same hematopoietic cells and regulated by TGF-beta. Moreover, FLRG interacts with activin A, suggesting that FLRG, like follistatin, participates in the diverse regulatory functions of activin A, such as those in hematopoiesis.

Transforming growth factor: signal transduction pathways, cell cycle mediation, and effects on hematopoiesis

Transforming growth factor-beta (TGF-beta) is a potent growth inhibitor of various cell types including hematopoietic cells. Two receptors, TGFbetaRI and TGFbetaRII, govern the interaction between the cell and the TGF-beta ligand. Primary binding of the ligand occurs with the RII receptor, promoting formation of a heterodimer with RI and activation of signaling. This induces transient association of Smad proteins with the receptors. Smad 3 and 4 may be involved in the TGF-beta-induced G(1) arrest. TGF-beta(1) down-regulates G(1) and G(2) cyclin-dependent kinases (cdks) and cyclins in terms of both kinase activity and protein amount. TGF- beta (1) also inhibits phosphorylation of the product of the retinoblastoma tumor suppressor gene (pRb) at multiple serine and threonine residues in human myeloid leukemia cells. The underphosphorylated pRb associates with transcription factor E2F-4 in G(1) phase, whereas the phosphorylated pRb mainly binds to E2F-1 and E2F-3. Because TGF-beta(1) up-regulates p130(pRb family member)/E2F-4 complex formation and down-regulates p107(pRb family member)/E2F-4 complex formation, with E2F-4 levels remaining constant, these results suggest that E2F-4 is switched from p107 to pRb and p130 when cells exit from the cell cycle and arrest in G(1) by the action of TGF-beta(1). The "cdk inhibitor" p27 is both a positive and a negative regulator of TGF-beta(1)-mediated cell cycle control. Although TGF-beta(1) has been reported to be a selected inhibitor of normal primitive hematopoietic stem cells, TGF-beta inhibits both primitive and more differentiated myeloid leukemia cell lines.

Phosphatidylcholine-specific phospholipase C and phospholipase D are respectively implicated in mitogen-activated protein kinase and nuclear factor kappaB activation in tumour-necrosis-factor-alpha-treated immature acute-myeloid-leukaemia cells

Tumour necrosis factor-alpha (TNFalpha) has been reported to induce potent growth inhibition of committed myeloid progenitor cells, whereas it is a potential growth stimulator of human CD34(+)CD38(-) multipotent haematopoietic cells. The present study was aimed at evaluating the respective role of two phospholipases, phosphatidylcholine-specific phospholipase C (PC-PLC) and phospholipase D (PLD) in the response of the CD34(+) CD38(-) KG1a cells to TNFalpha. In these cells TNFalpha triggered phosphoinositide 3-kinase (PI3K)-dependent PC hydrolysis within 4-8 min with concomitant production of both diacylglycerol (DAG) and phosphocholine (P-chol). DAG and P-chol production was accompanied by extracellular-signal-related protein kinase-1 ('ERK-1') activation and DNA-synthesis stimulation. PC-PLC stimulation was followed by PI3K-independent PLD activation with concomitant phosphatidic acid (PA) production followed by PA-derived DAG accumulation and sustained nuclear factor kappaB (NF-kappaB) activation. PLD/NF-kappaB signalling activation played no role in the TNFalpha proliferative effect and conferred no consistent protection of KG1a cells towards antileukaemic agents. Altogether these results suggest that, in KG1a cells, TNFalpha can stimulate in parallel PC-PLC and PLD, whose lipid products activate in turn mitogen-activated protein kinase (MAP kinase) and NF-kappaB signalling respectively. Finally, our study suggests that PC-PLC, but not PLD, plays a role in the TNFalpha proliferative effect in immature myeloid cells.

Cell cycle and transcriptional control of human myeloid leukemic cells by transforming growth factor beta

TGFbeta1 is a potent growth inhibitor of both primitive and more differentiated human myeloid leukemic cells. The extent of the growth inhibitory response to TGFbeta varies with cell type, and is not linked to stages of differentiation of cell lines. Downregulation of multiple cell cycle-regulatory molecules is a dominant event in TGFbeta1-mediated growth inhibition of human MV4-11 myeloid leukemia cells. Both G1-phase and G2-phase cyclins and cdks participate in the regulation of TGFbeta1-mediated growth inhibition of MV4-11 cells. By both depressing cdk2 synthesis and up-regulating cyclin E-associated p27, TGFbeta1 may magnify its inhibitory efficiency. TGFbeta1 also rapidly inhibits phosphorylation of pRb at several serine and threonine residues. The underphosphorylated pRb associates with E2F-4 in G1 phase, whereas the phosphorylated pRb mainly binds to E2F-1 and E2F-3 in proliferating MV4-11 cells. Since TGFbeta1 upregulates p130/E2F-4 complex formation and downregulates p107/E2F-4 complex formation, with E2F-4 levels remaining constant, our results suggest that E2F-4 is switched from p107 to pRb and p130 when cells exit from the cell cycle and arrest in G1 by TGFbeta1. In summary, TGFbeta1 inhibits growth of human myeloid leukemic cells through multiple pathways, whereas the "cdk inhibitor" p27 is both a positive and negative regulator.

Changes in the hemopoietic system of mice deficient for tumor necrosis factor or lymphotoxin-alpha

Hemopoietic and stromal precursor cells were studied in mice deficient for tumor necrosis factor or lymphotoxin-alpha. In normal hemopoiesis the main characteristics of hemopoiesis in knockout mice did not differ from those in wild-type mice. Implantation of bone marrow cells from mice deficient for tumor necrosis factor onto irradiated sublayer of a long-living bone marrow culture led to a notable increase in the number of mature cells and granulocytic-macrophage precursor cells. This can be due to the fact that tumor necrosis factor inhibits proliferation of hemopoietic precursor cells, while in the absence of this factor precursor cells actively proliferate. On the other hand, cell composition and number of colony-forming units of granulocytes-macrophages are significantly decreased in cultures onto which bone marrow cells from lymphotoxin-alpha-deficient mice were implanted. This can be explained by impaired expression of adhesion molecules in these animals. In addition, the number of stromal precursor cells was changed in mice deficient by genes of the tumor necrosis factor cluster.

Tumor necrosis factor-alpha and TNF-beta inhibit clonogenicity of mobilized human hematopoietic progenitors

We studied the effect of tumor necrosis factors (TNF-alpha and TNF-beta) on the clonogenicity of peripheral blood progenitor cells (PBPC) mobilized by granulocyte colony-stimulating factor (G-CSF). The cells were obtained by nine leukaphereses in patients with malignancies undergoing peripheral blood stem cell transplantation (PBSCT). Flow cytometry was performed to evaluate the number of CD34+ cells in peripheral blood and leukapheresis products. PBPC were grown in semisolid medium supplemented with human growth factors in the absence or presence of TNF at concentrations ranging from 0.1 to 10 ng/ml. Colonies were scored on day 14. TNF-alpha and TNF-beta suppressed colony formation in all cases studied. TNF-alpha inhibited the growth of colony-forming units-granulocyte-macrophage (CFU-GM) at 1 and 10 ng/ml and burst-forming units-erythroid (BFU-E) at 10 ng/ml (p < 0.05), and TNF-beta inhibited the growth of CFU-GM and BFU-E at 1 and 10 ng/ml (p < 0.05). Thus, G-CSF-mobilized hematopoietic PBPC are highly sensitive to both TNF-alpha and TNF-beta. This finding should be taken in account when PBPC are handled ex vivo.

Generation of T cells from adult human hematopoietic stem cells and progenitors in a fetal thymic organ culture system: stimulation by tumor necrosis factor-α

To investigate the T-lymphopoietic capacity of human adult bone marrow (ABM) hematopoietic progenitor cells, CD34+Lin−, CD34+CD38+, and CD34++CD38− cells were cultured in a severe combined immunodeficient (SCID) mouse fetal thymic organ culture (FTOC). Direct seeding of these progenitors resulted in a moderate to severe cell loss, particularly for the CD34++CD38− cell fraction, and T cells could only be generated from the CD34+Lin− fraction. Preincubation for 36 hours with interleukin-3 (IL-3) and stem cell factor (SCF) led to an improved cell survival and proliferation, although T-cell development was seen only in the CD34+Lin− fraction. Addition of tumor necrosis factor (TNF)- to IL-3 + SCF-supplemented preincubation medium resulted in optimal cell survival, cell proliferation. and T-cell generation of all 3 cell fractions. The TNF- effect resulted in an up-regulation of CD127 (ie, the IL-7 receptor -chain) in a small subset of the CD34+ cells. No evidence could be generated to support the possibility that TNF- inhibits a cell population that suppresses T-cell differentiation. A quantitatively different T-cell generation potency was still seen between the 3 subpopulations: CD34+Lin− (100% success rate) &gt; CD34+CD38+ (66%) &gt; CD34++CD38− (25%). These data contrast with our previous findings using fetal liver and cord blood progenitors, which readily differentiate into T-lymphocytes in FTOC, even without prestimulation with cytokines. Our results demonstrate that adult CD34++CD38− cells, known to contain hematopoietic stem cells, can differentiate into T-lymphocytes and that a significant difference exists in T-lymphopoietic activity of stem cells derived from ontogenetically different sources.

A mechanism of suppression of TGF-beta/SMAD signaling by NF-kappa B/RelA

A number of pathogenic and proinflammatory stimuli, and the transforming growth factor-beta (TGF-beta) exert opposing activities in cellular and immune responses. Here we show that the RelA subunit of nuclear factor kappaB (NF-kappaB/RelA) is necessary for the inhibition of TGF-beta-induced phosphorylation, nuclear translocation, and DNA binding of SMAD signaling complexes by tumor necrosis factor-alpha (TNF-alpha). The antagonism is mediated through up-regulation of Smad7 synthesis and induction of stable associations between ligand-activated TGF-beta receptors and inhibitory Smad7. Down-regulation of endogenous Smad7 by expression of antisense mRNA releases TGF-beta/SMAD-induced transcriptional responses from suppression by cytokine-activated NF-kappaB/RelA. Following stimulation with bacterial lipopolysaccharide (LPS), or the proinflammatory cytokines TNF-alpha and interleukin-1beta (IL-1beta, NF-kappaB/RelA induces Smad7 synthesis through activation of Smad7 gene transcription. These results suggest a mechanism of suppression of TGF-beta/SMAD signaling by opposing stimuli mediated through the activation of inhibitory Smad7 by NF-kappaB/RelA.

A mechanism of suppression of TGF–β/SMAD signaling by NF-κB/RelA

A number of pathogenic and proinflammatory stimuli, and the transforming growth factor-β (TGF-β) exert opposing activities in cellular and immune responses. Here we show that the RelA subunit of nuclear factor κB (NF-κB/RelA) is necessary for the inhibition of TGF-β-induced phosphorylation, nuclear translocation, and DNA binding of SMAD signaling complexes by tumor necrosis factor-α (TNF-α). The antagonism is mediated through up-regulation of Smad7 synthesis and induction of stable associations between ligand-activated TGF-β receptors and inhibitory Smad7. Down-regulation of endogenous Smad7 by expression of antisense mRNA releases TGF-β/SMAD-induced transcriptional responses from suppression by cytokine-activated NF-κB/RelA. Following stimulation with bacterial lipopolysaccharide (LPS), or the proinflammatory cytokines TNF-α and interleukin-1β (IL-1β, NF-κB/RelA induces Smad7 synthesis through activation of Smad7 gene transcription. These results suggest a mechanism of suppression of TGF-β/SMAD signaling by opposing stimuli mediated through the activation of inhibitory Smad7 by NF-κB/RelA.

TGF-beta1 regulation of dendritic cells

Dendritic cells (DCs) represent antigen-presenting cell (APC) populations in lymphoid and nonlymphoid organs which are considered to play key roles in the initiation of antigen-specific T-cell proliferation. According to current knowledge, the net outcome of T-cell immune responses seems to be significantly influenced by the activation stage of antigen-presenting DCs. Several studies have shown that transforming growth factor-beta 1 (TGF-beta1) inhibits in vitro activation and maturation of DCs. TGF-beta1 inhibits upregulation of critical T-cell costimulatory molecules on the surface of DCs and reduces the antigen-presenting capacity of DCs. Thus, in addition to direct inhibitory effects of TGF-beta1 on effector T lymphocytes, inhibitory effects of TGF-beta1 at the level of APCs may critically contribute to previously characterized immunosuppressive effects of TGF-beta1. In contrast to these negative regulatory effects of TGF-beta1 on function and maturation of lymphoid tissue type DCs, certain subpopulations of immature DCs in nonlymphoid tissues are positively regulated by TGF-beta1 signaling. In particular, epithelial-associated DC populations seem to critically require TGF-beta1 stimulation for development and function. Recent studies established that TGF-beta1 stimulation is absolutely required for the development of epithelial Langerhans cells (LCs) in vitro and in vivo. Furthermore, TGF-beta1 seems to enhance antigen processing and costimulatory functions of epithelial LCs.

Essential role for the p55 tumor necrosis factor receptor in regulating hematopoiesis at a stem cell level

Hematopoietic stem cell (HSC) self-renewal is a complicated process, and its regulatory mechanisms are poorly understood. Previous studies have identified tumor necrosis factor (TNF)-alpha as a pleiotropic cytokine, which, among other actions, prevents various hematopoietic progenitor cells from proliferating and differentiating in vitro. However, its role in regulating long-term repopulating HSCs in vivo has not been investigated. In this study, mice deficient for the p55 or the p75 subunit of the TNF receptor were analyzed in a variety of hematopoietic progenitor and stem cell assays. In older p55(-/-) mice (>6 mo), we identified significant differences in their hematopoietic system compared with age-matched p75(-/-) or wild-type counterparts. Increased marrow cellularity and increased numbers of myeloid and erythroid colony-forming progenitor cells (CFCs), paralleled by elevated peripheral blood cell counts, were found in p55-deficient mice. In contrast to the increased myeloid compartment, pre-B CFCs were deficient in older p55(-/-) mice. In addition, a fourfold decrease in the number of HSCs could be demonstrated in a competitive repopulating assay. Secondary transplantations of marrow cells from primary recipients of p55(-/-) marrow revealed impaired self-renewal ability of p55-deficient HSCs. These data show that, in vivo, signaling through the p55 subunit of the TNF receptor is essential for regulating hematopoiesis at the stem cell level.

TNF-α-Induced Growth Suppression of CD34+ Myeloid Leukemic Cell Lines Signals Through TNF Receptor Type I and Is Associated with NF-κB Activation

Conflicting results have been reported regarding the effect of TNF-α on the growth of human primitive hemopoietic cells. In this study, we have examined the effect of TNF-α on the proliferation of several CD34+/CD38+ (KG-1, TF-1) and CD34+/CD38− (KG-1a, TF-1a) myeloid leukemic progenitor cell lines. Our data show that TNF-α markedly inhibits the growth of these cells in both liquid and soft agar cultures. Addition of GM-CSF or IL-3 does not prevent TNF-α-induced growth inhibition. Flow cytometry analyses of propidium iodide-stained cells demonstrated cell death of all four cell lines, as judged by the presence of cells with hypodiploid DNA content after exposure of cells to TNF-α for 4 days. Annexin V assays detected apoptosis in TF-1, but not in TF-1a, KG-1, and KG-1a cells in terms of translocation of phosphatidylserine shortly after TNF-α treatment. Neutralizing anti-TNF receptor type I (TNFR-I; p55) Ab almost completely reversed TNF-α-induced growth inhibition in both liquid and soft agar cultures, whereas anti-TNFR-II (p75) Ab had only a marginal effect. TNF-α rapidly induced marked activation of nuclear transcription factor NF-κB in all 4 cell lines. The majority of this effect was abolished by the type I receptor Ab, whereas the type II receptor neutralizing Ab had no effect. Our data also show that TNF-α is incapable of inducing activation of the mitogen-activated protein kinase pathway in these leukemic cell lines.

Transforming growth factor beta inhibits growth of more differentiated myeloid leukemia cells and retinoblastoma protein phosphorylation at serine 795

Transforming growth factor beta (TGF-beta) has been shown to be a specific inhibitor of early human myeloid progenitors. We show here that TGF-beta1 potentially inhibited not only the growth of primitive but also more mature myeloid leukemic cells. Surprisingly, those apparently more mature progenitor cells, such as MV4-11 and Mo7e cells, are very sensitive to the action of TGF-beta. The addition of TGF-beta1 to liquid cultures of these cells significantly inhibited their proliferation, with as much as 72% inhibition of growth of MV4-11 cells. The suppressive effect by TGF-beta1 was not reversed or prevented by granulocyte-macrophage colony-stimulating factor or interleukin 3 used to promote cell growth in TF-1a and MV4-11 cells. TGF-beta1 completely abolished the clonal growth of MV4-11 cells in soft agar and inhibited Mo7e, KG-1, K562, TF-1, and TF-1a colony growth by 99%, 90%, 63%, 53%, and 43%, respectively. The cells treated with TGF-beta1 showed progressive accumulation in the G1 phase of cell cycle. Maximal G1 arrest (93%) was observed in MV4-11 cells. Using anti-retinoblastoma protein (pRb) and anti-specific phosphorylated-pRb antibodies, we demonstrated that TGF-beta1 greatly inhibited pRb phosphorylation at serine 795 in MV4-11 and Mo7e cells. Taken together, our data suggest that the sensitivity of myeloid leukemic progenitor cells to growth inhibition by TGF-beta may not be inversely correlated with their maturation stage, and the inhibition of the cells appeared to be linked to the suppression of pRb phosphorylation at serine 795.

Neuroendocrine-induced synthesis of bone marrow-derived cytokines with inflammatory immunomodulating properties

Although cytokines and other soluble regulators of immunity are known to be involved in hematopoiesis, little is known about the signals that induce the synthesis of those mediators locally. Based on recent studies linking the neuroendocrine hormone thyrotropin [thyroid-stimulating hormone (TSH)] to immune cell function in other tissues, we investigated the capacity of TSH to activate cytokine responses from bone marrow cells. These studies reveal that stimulation of the TSH receptor on bone marrow cells-using highly purified or recombinant TSH or by direct stimulation with anti-TSH receptor antibodies-rapidly induces the synthesis of cytokines from bone marrow cells that are classically used in the regulation of inflammatory responses. Of 13 cytokines screened for activity by ELISA or by RNase protection assays for gene expression, IL-6, IFN-beta, TNFalpha, TNFbeta, TGFbeta2, and lymphotoxin-beta responses were reproducibly induced by TSH within 2-3 h of stimulation. Intracellularly, TSH stimulation of bone marrow cells caused rapid increases in cAMP levels and induced the phosphorylation of the Jak2 protein kinase, thereby defining a novel G-protein-coupled receptor/cytokine synthesis pathway. These findings demonstrate that TSH can serve as a primary inductive signal of cytokine production by bone marrow cells.

Characterization of a unique factor-independent variant derived from human factor-dependent TF-1 cells: a transformed event

A factor-independent variant (TF-1a) has been isolated from the factor-dependent TF-1 cell line. The subline has been grown continuously in culture for > 1.5 years without added cytokines. The cells retain the ability to respond to multicytokines, with a different response pattern from its parental cell line. The TF-1 cells appeared singly in liquid culture. In contrast. TF-1a cells formed aggregates which increased markedly in size and in number upon TGFbeta1 treatment and showed a diminished TGFbeta-mediated growth inhibition. TF-1a, but not TF-1 cells, formed colonies in soft agar culture in the absence of any added growth factors, and developed the capacity to generate an invasive tumor(s) in nude mice. There was a constitutive activation of MAPK and MEK in TF-1a but not in TF-1 cells, which may be one of the mechanisms leading to factor-independent growth of TF-1a cells. Phenotypically, TF-1 cells were CD34+ /CD38+, whereas TF-1a cells were CD34+ /CD38-. This suggests that TF-1a may represent a less mature hematopoietic cell than TF-1. In conclusion, TF-1a is different from TF-1 in many important aspects which are associated with neoplastic transformation. The variant appears to be an excellent model for studying the process of progressive malignant transformation of myeloid cells and for studying signal pathways involved in the spontaneous and factor-induced growth of the cells.

Epidermal Langerhans cell development and differentiation

Epidermal Langerhans cells (LC) play a critical role in host defense. Still we know rather little about the development and functional specialization of these bone marrow-derived dendritic cells (DC) located in the most peripheral ectodermal tissue of the mammalian organism. How LC develop from their primitive progenitors in bone marrow and to what extent LC are related in their development to other lineages of the hemopoietic system is still under debate. There are currently 3 major areas of debate: 1) which are the signals required for LC development and differentiation to occur, 2) what are the (molecular) characteristics of the intermediate stages of LC differentiation, and 3) how are LC related in their development and/or function to other cells of the hemopoietic system? A better understanding of LC development and answers to these questions can be expected from recently developed technologies which allow the in vitro generation of DC with the typical molecular, morphological and functional features of LC from purified CD34+ progenitor cells under defined serum-free culture conditions. TGF-beta 1 was found to be an absolute requirement for in vitro LC development under serum-free conditions upon stimulation with the classical DC growth and differentiation factors GM-CSF, TNF-alpha and SCF. The recently identified cytokine FLT3 ligand further dramatically enhanced in vitro LC development and even allowed efficient in vitro generation of LC colonies from serum-free single cell cultures of CD34+ hemopoietic progenitor cells.

Thermal injury induces the development of inflammatory macrophages from nonadherent bone marrow cells

The normal course of hematopoiesis is controlled by growth factors and cytokines and, therefore, should be susceptible to alterations induced by systemic mediator release such as that seen following thermal injury. We hypothesized that a brief exposure of developing macrophages to the postthermal injury state would result in functionally altered progeny. We measured the production of inflammatory mediators by rat, bone-marrow macrophage precursors harvested 24 h following a 30% TBSA burn after subsequent maturation in a controlled, in vitro environment. Interleukin (IL)-6, tumor necrosis factor (TNF), and prostaglandin (PG) E2 levels in response to 24 h stimulation with lipopolysaccharide (LPS) were measured following 4 or 8 days of incubation with IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), or both. Flow cytometric analysis showed that bone marrow cells harvested from burn and sham animals cultured in GM-CSF developed principally into macrophages (His48+, R21A6A+, CD11b+. Unstimulated cells produced negligent levels of cytokines and PGE2. Stimulated burn-derived cells released greater amounts of IL-6 and TNF at 4 or 8 days of culture depending on the conditions. Elevated PGE2 release was noted in all GM-CSF containing cultures, with burn-derived cells showing a trend towards reduced prostaglandin release. Detection of mRNA for cytokines after LPS stimulation showed no change in IL-6 or TNF transcripts. A short exposure to the systemic effects of thermal injury preprogramed macrophage progenitor cells with the propensity to develop into inflammatory macrophages, secreting higher levels of TNF and IL-6. This shift towards proinflammatory functions in these cells suggests they could be a source of enhanced inflammatory mediator release at 4 or more days post thermal injury.

Effects of cryopreservation of immune responses. XI. Heightened secretion of tumor necrosis factor-alpha by frozen human peripheral blood mononuclear cells

In view of the wide usage of frozen PBMCs as stem cell support following high-dose chemo- and/or radiotherapy, and the pleiotropic activities of tumor necrosis factor-alpha (TNF-alpha), the influences of freezing and radiation on LPS-induced TNF-alpha production by human peripheral blood mononuclear cells (PBMCs) were studied. Frozen PBMCs secreted significantly larger quantities of TNF-alpha than fresh cells. Blocking of endogenous IL-10 by neutralization with anti-IL-10 monoclonal antibody resulted in further augmented and prolonged secretion of TNF-alpha by both the fresh and frozen cells. In contrast, addition of exogenous IL-10 to LPS-stimulated cultures inhibited TNF-alpha secretion. In vitro irradiation had an inconsistent effect on TNF-alpha production by the fresh PBMCs. Taken together, these results suggest that the endogenously hypersecreted TNF-alpha is indirectly responsible for the previously reported elevated IL-1-, IL-6-, and IL-10-secreting capabilities of frozen PBMCs. They also indicate that the TNF-alpha induced IL-10 and then down-regulates the monocytes from further TNF-alpha secretion. Considering the vital role played by TNF-alpha in antimicrobial and antitumor activities, in the immune system, and in the pathogenesis of many acute and chronic diseases, the abilities of frozen cells to produce large quantities of TNF-alpha in response to infectious agents could have profound impact on patients receiving such frozen PBMCs as stem cell support following myeloablative therapies.