Circulating colony stimulating factor-1 and breast cancer risk

Colony stimulating factor-1 (CSF1) and its receptor (CSF1-R) are important in mammary gland development and have been implicated in breast carcinogenesis. In a nested case-control study in the Nurses' Heath Study of 726 breast cancer cases diagnosed between June 1, 1992, and June 1, 1998, and 734 matched controls, we prospectively evaluated whether circulating levels of CSF1 (assessed in 1989-1990) are associated with breast cancer risk. The association varied by menopausal status (P(heterogeneity) = 0.009). CSF1 levels in the highest quartile (versus lowest) were associated with an 85% reduced risk of premenopausal breast cancer [relative risk (RR), 0.15; 95% confidence interval (95% CI), 0.03-0.85; P(trend) = 0.02]. In contrast, CSF1 levels in the highest quartile conferred a 33% increased risk of postmenopausal breast cancer (RR, 1.33; 95% CI, 0.96-1.86; P(trend) = 0.11), with greatest risk for invasive (RR, 1.45; 95% CI, 1.02-2.07; P(trend) = 0.06) and ER+/PR+ tumors (RR, 1.72; 95% CI, 1.11-2.66; P(trend) = 0.04). Thus, the association of circulating CSF1 levels and breast cancer varies by menopausal status.

Enucleation of primitive erythroid cells generates a transient population of "pyrenocytes" in the mammalian fetus

Enucleation is the hallmark of erythropoiesis in mammals. Previously, we determined that yolk sac-derived primitive erythroblasts mature in the bloodstream and enucleate between embryonic day (E)14.5 and E16.5 of mouse gestation. While definitive erythroblasts enucleate by nuclear extrusion, generating reticulocytes and small, nucleated cells with a thin rim of cytoplasm ("pyrenocytes"), it is unclear by what mechanism primitive erythroblasts enucleate. Immunohistochemical examination of fetal blood revealed primitive pyrenocytes that were confirmed by multispectral imaging flow cytometry to constitute a distinct, transient cell population. The frequency of primitive erythroblasts was higher in the liver than the bloodstream, suggesting that they enucleate in the liver, a possibility supported by their proximity to liver macrophages and the isolation of erythroblast islands containing primitive erythroblasts. Furthermore, primitive erythroblasts can reconstitute erythroblast islands in vitro by attaching to fetal liver-derived macrophages, an association mediated in part by alpha4 integrin. Late-stage primitive erythroblasts fail to enucleate in vitro unless cocultured with macrophage cells. Our studies indicate that primitive erythroblasts enucleate by nuclear extrusion to generate erythrocytes and pyrenocytes and suggest this occurs in the fetal liver in association with macrophages. Continued studies comparing primitive and definitive erythropoiesis will lead to an improved understanding of terminal erythroid maturation.

Human epidermal Langerhans cells express the tight junction protein claudin-1 and are present in human genetic claudin-1 deficiency (NISCH syndrome)

Claudin-1 (CLDN1) is a structural tight junction (TJ) protein and is expressed in differentiating keratinocytes and Langerhans cells in the epidermis. Our objective was to identify immunoreactive CLDN1 in human epidermal Langerhans cells and to examine the pattern of epidermal Langerhans cells in genetic human CLDN1 deficiency [neonatal ichthyosis, sclerosing cholangitis (NISCH) syndrome]. Epidermal cells from healthy human skin labelled with CLDN1-specific antibodies were analysed by confocal laser immunofluorescence microscopy and flow cytometry. Skin biopsy sections of two patients with NISCH syndrome were stained with an antibody to CD1a expressed on epidermal Langerhans cells. Epidermal Langerhans cells and a subpopulation of keratinocytes from healthy skin were positive for CLDN1. The gross number and distribution of epidermal Langerhans cells of two patients with molecularly confirmed NISCH syndrome, however, was not grossly altered. Therefore, CLDN1 is unlikely to play a critical role in migration of Langerhans cells (or their precursors) to the epidermis or their positioning within the epidermis. Our findings do not exclude a role of this TJ molecule once Langerhans cells have left the epidermis for draining lymph nodes.

Rb intrinsically promotes erythropoiesis by coupling cell cycle exit with mitochondrial biogenesis

Regulation of the cell cycle is intimately linked to erythroid differentiation, yet how these processes are coupled is not well understood. To gain insight into this coordinate regulation, we examined the role that the retinoblastoma protein (Rb), a central regulator of the cell cycle, plays in erythropoiesis. We found that Rb serves a cell-intrinsic role and its absence causes ineffective erythropoiesis, with a differentiation block at the transition from early to late erythroblasts. Unexpectedly, in addition to a failure to properly exit the cell cycle, mitochondrial biogenesis fails to be up-regulated concomitantly, contributing to this differentiation block. The link between erythropoiesis and mitochondrial function was validated by inhibition of mitochondrial biogenesis. Erythropoiesis in the absence of Rb resembles the human myelodysplastic syndromes, where defects in cell cycle regulation and mitochondrial function frequently occur. Our work demonstrates how these seemingly disparate pathways play a role in coordinately regulating cellular differentiation.

Ox-LDL induces monocyte-to-macrophage differentiation in vivo: Possible role for the macrophage colony stimulating factor receptor (M-CSF-R)

Monocyte-to-macrophage differentiation and LDL oxidation play a pivotal role in early atherogenesis. We thus questioned possible mechanisms for oxidized LDL (Ox-LDL)-induced monocyte-to-macrophage differentiation in vivo. Mouse peritoneal mononuclear cells, that were isolated 1, 2, or 3 days after Ox-LDL intraperitoneal injection, gradually exhibited the characteristic macrophage morphology, along with the expression of the cell-surface antigen CD11b. Molecular mechanisms involved in Ox-LDL-induced differentiation were further investigated in vitro using the THP-1 monocytic cell line. THP-1 cells incubated with Ox-LDL in the presence of as low as 1 ng/ml of PMA differentiated into macrophages, as evidenced by morphologic, phenotypic, and functional properties. Stimulation of monocyte-to-macrophage differentiation was selective to Ox-LDL (and not native LDL), was dependent on the extent of LDL oxidation, and required Ox-LDL internalization by the cells. These effects of Ox-LDL could be attributed to its major oxysterols, 7-ketocholesterol and 7beta-hydroxycholesterol. Finally, the stimulation of monocyte differentiation to macrophages by Ox-LDL was shown to require the M-CSF-receptor, since blocking the binding to the receptor abolished Ox-LDL/7beta-hydroxycholesterol-induced differentiation. Furthermore, Ox-LDL/7beta-hydroxycholesterol elicited tyrosine phosphorylation and activation of the M-CSF-R. We thus conclude that Ox-LDL induces monocyte differentiation to macrophages in vivo and this phenomenon involves activation of the M-CSF-receptor.

Antigen presentation by monocytes and monocyte-derived cells

Monocytes are circulating mononuclear phagocytes with a fundamental capacity to differentiate into macrophages. This differentiation can, in the presence of the right environmental cues, be re-directed instead to dendritic cells (DCs). Recent advances have been made in understanding the role of monocytes and their derivatives in presenting antigen to drive immune responses, and we review this topic herein. We briefly discuss the heterogeneity of monocytes in the blood and subsequently raise the possibility that one of the major monocyte phenotypes in the blood corresponds with a population of 'blood DCs' previously proposed to drive T-independent antibody reactions in the spleen. Then we evaluate the role of monocytes in T-dependent immunity, considering their role in acquiring antigens for presentation before exiting the bloodstream and their ability to differentiate into macrophages versus antigen-presenting DCs. Finally, we review recent literature on the role of monocyte-derived cells in cross-presentation and discuss the possibility that monocyte-derived cells participate critically in processing antigen for cross-priming, even if they do not present that antigen to T cells themselves.

Towards a better understanding and new therapeutics of osteopetrosis

Lack of or dysfunction in osteoclasts result in osteopetrosis, a group of rare but often severe, genetic disorders affecting skeletal tissue. Increase in bone mass results in skeletal malformation and bone marrow failure that may be fatal. Many of the underlying defects have lately been characterized in humans and in animal models of the disease. In humans, these defects often involve mutations in genes expressing proteins involved in the acidification of the osteoclast resorption compartment, a process necessary for proper bone degradation. So far, the only cure for children with severe osteopetrosis is allogeneic hematopoietic stem cell (HSC) transplantation but without a matching donor this form of therapy is far from optimal. The characterization of the genetic defects opens up the possibility for gene replacement therapy as an alternative. Accordingly, HSC-targeted gene therapy in a mouse model of infantile malignant osteopetrosis was recently shown to correct many aspects of the disease.

[Dendritic cells of mucosa and skin: "recruited for vaccination"]

Mucosae and skin are exposed to environmental antigens and are natural entry routes for most infectious agents. To maintain immunological tolerance and ensure protective immunity against pathogens, epithelial surfaces are surveyed permanently by antigen-presenting dendritic cells (DCs). Many DC subsets have been described in epithelial tissues, depending on the inflammatory state and the type of epithelium. Identification of the DC subset able to induce cytotoxic CD8+ T cells against antigens delivered via mucosae or skin, is a major issue for the development of efficient anti-infectious and anti-tumoral vaccines. Until recently, it was commonly accepted that Langerhans cells (LC), the prototype of immature DCs residing in skin and certain mucosae, can capture and process antigens and, in response to danger signals, undergo a maturation program allowing their migration to the draining lymph nodes for priming of naïve T cells. This concept likely needs to be revisited. Recent evidence from animal models revealed that resident epithelial tissue DCs, including LCs, do not play a direct role in T cell priming, but may contribute to maintenance of peripheral tolerance. Alternatively, DCs newly recruited into muco-cutaneous tissues exposed to pro-inflammatory stimuli are responsible for efficient priming and differentiation of CD8+ T cells into cytolytic effectors. These DC originate from blood monocytes and can cross-present protein antigens to CD8+ T cells, which subsequently give rise to specific CTL effectors. Remarkably, components derived from bacteria, virus and chemicals capable to enhance CCL20 production in epithelia, promote CCR6-dependent DC recruitment and behave as adjuvants allowing for cross-primed CD8+ CTL. These advances in the dynamic and function of epithelial tissue DC provide a rationale for the screening of novel CD8+ T cell adjuvants and the design of novel mucosal and skin vaccines.

Transcriptional diversity during monocyte to macrophage differentiation

Monocytes recruited into tissues from peripheral blood differentiate into macrophages, which are critical in the pathogenesis of many diseases. There is limited data concerning the global changes in the expression of genes during monocyte to macrophage differentiation, and how the patterns of change identify the mechanism contributing to macrophage differentiation or function. Employing microarray technology, we examined the transcriptional profile of in vitro adherence-induced differentiation of primary human monocytes into macrophages. We found the significant up regulation of genes contributing to the functions of macrophages, including those regulating to immunity and defense; lipid, fatty acid and steroid metabolism; cell adhesion, carbohydrate metabolism; amino acid metabolism and endocytosis. In contrast, the vast majority of transcription factors affected were down regulated during monocyte to macrophage differentiation, suggesting that transcriptional repression may be important for the transition from monocytes to macrophages. However, a limited number of transcription factors were up regulated, among these was C/EBPalpha, which may contribute to differentiation by regulating down stream genes, which are a characteristic of differentiated macrophages. These observations suggest that examination of the transcriptional profile in monocytes and macrophages in patients may identify relevant therapeutic targets in diseases mediated by macrophages.

Dendritic cell-induced memory T cell activation in nonlymphoid tissues

Secondary lymphoid organs are dominant sites of T cell activation, although many T cells are subsequently retained within peripheral tissues. Currently, these nonlymphoid compartments are viewed as sites only of effector T cell function, without the involvement of renewed induction of immunity via the interactions with professional antigen-presenting cells. We describe a method of reactivation of herpes simplex virus to examine the stimulation of tissue-resident T cells during secondary challenge. The results revealed that memory CD8+ T cell responses can be initiated within peripheral tissues through a tripartite interaction that includes CD4+ T cells and recruited dendritic cells. These findings lend evidence for the existence of a sophisticated T cell response mechanism in extra-lymphoid tissues that can act to control localized infection.

CtBP is an essential corepressor for BCL6 autoregulation

The transcription repressor BCL6 plays an essential role in the formation and function of germinal centers (GCs). While normal B cells promptly shut off BCL6 when they exit the GC, many GC-derived B-cell lymphomas sustain BCL6 expression through chromosomal translocations and activating mutations. We have previously shown that a common effect of lymphoma-associated BCL6 gene alterations is to bypass a negative autoregulatory loop that controls its transcription. In this study, we report that BCL6 autoregulation is independent of several known corepressor complexes including silencing mediator for retinoid and thyroid hormone receptors, nuclear receptor coreceptor, BCL6 corepressor, and MTA3/NuRD. Furthermore, we show that BCL6 can interact with the CtBP (C-terminal binding protein) corepressor both in vitro and in vivo and that CtBP is recruited by BCL6 to its 5' regulatory region. In lymphoma cell lines carrying BCL6 translocations, small interfering RNA-mediated CtBP knock-down selectively relieved the previously silenced wild-type BCL6 allele but not the translocated alleles, which are driven by heterologous promoters. These results demonstrate that CtBP is a novel BCL6 corepressor and suggest that a unique corepressor requirement for BCL6 autoregulation may allow GC B cells to differentially control the expression of BCL6 and other BCL6 target genes in response to environmental stimuli during the GC stage of B cell development.

Hematopoietic cytokines

The production of hematopoietic cells is under the tight control of a group of hematopoietic cytokines. Each cytokine has multiple actions mediated by receptors whose cytoplasmic domains contain specialized regions initiating the various responses-survival, proliferation, differentiation commitment, maturation, and functional activation. Individual cytokines can be lineage specific or can regulate cells in multiple lineages, and for some cell types, such as stem cells or megakaryocyte progenitors, the simultaneous action of multiple cytokines is required for proliferative responses. The same cytokines control basal and emergency hematopoietic cell proliferation. Three cytokines, erythropoietin, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor, have now been in routine clinical use to stimulate cell production and in total have been used in the management of many millions of patients. In this little review, discussion will be restricted to those cytokines well established as influencing the production of hematopoietic cells and will exclude newer candidate regulators and those active on lymphoid cells. As requested, this account will describe the cytokines in a historical manner, using a sequential format of discovery, understanding, validation, and puzzlement, a sequence that reflects the evolving views on these cytokines over the past 50 years.

Phenotypic characterisation of intestinal dendritic cells in sheep

The present study was undertaken to identify dendritic cells (DCs) in the ileum and rectum of lambs and adult sheep. The distribution of these cells in four different intestinal compartments, i.e. lamina propria, lymphoid follicles, domes and interfollicular areas was assessed, and the presence of these cells in lambs and adult sheep was compared. Specimens were examined by using a number of potential DC markers (CD11c, CD205, MHC class II (MHCII), CD1b and CD209) in immunohistochemical and multicolour immunofluorescent procedures. The ovine ileal and rectal mucosa contain many CD11c+/CD205+ cells with a dendritic morphology, and the majority of these cells co-expressed MHCII. These double-positive cells were also labelled with the CD209 antibody in the lamina propria and interfollicular regions. Only very few cells expressed CD1b. In conclusion, a major DC population in ileum and rectum of sheep co-expressed the CD11c, CD205 and MHCII molecules. The CD209 antibody appeared to be a novel marker for a subpopulation of ovine intestinal DCs.

Alendronate treatment promotes bone formation with a less anisotropic microstructure during intramembranous ossification in rats

There are safety concerns regarding administration of bisphosphonates to children. Little is known about the effects of bisphosphonates on bone matrix organization during bone modeling. The present study examined the effects of alendronate (ALN) on bone matrices formed by intramembranous ossification in the appendicular growing skeleton. ALN was administered to 1-week-old Sprague-Dawley rats at a dose of 0, 35, or 350 microg/kg/week for 4 or 8 weeks. The position of femoral diaphysis formed exclusively by intramembranous ossification was identified, and cross sections of cortical bone at this position were analyzed. Bone mineral density (BMD) and geometric parameters were evaluated using peripheral quantitative computed tomography. The preferential orientation degree of biological apatite (BAp) crystals in the bone longitudinal direction, which shows the degree of bone matrix anisotropy, was evaluated using microbeam X-ray diffraction analysis. We analyzed bone histomorphometrical parameters and performed bone nanomechanical tests to examine the material properties of newly developing cortical bone. The preferential orientation degree of BAp crystals significantly decreased in 35 microg/kg/week ALN-treated groups compared with vehicle-treated groups, although there were no significant differences in BMD between the two groups. The periosteal mineral apposition rate significantly increased in the 35 microg/kg/week ALN-treated group. We found a high negative correlation between bone matrix anisotropy and the regional periosteal mineral apposition rate (r = -0.862, P < 0.001). Nanomechanical tests revealed that 35 microg/kg/week ALN administration caused deterioration of the material properties of the bone microstructure. These new findings suggest that alendronate affects bone matrix organization and promotes bone formation with a less anisotropic microstructure during intramembranous ossification.

The erythroblastic island

Erythroblastic islands are specialized microenvironmental compartments within which definitive mammalian erythroblasts proliferate and differentiate. These islands consist of a central macrophage that extends cytoplasmic protrusions to a ring of surrounding erythroblasts. The interaction of cells within the erythroblastic island is essential for both early and late stages of erythroid maturation. It has been proposed that early in erythroid maturation the macrophages provide nutrients, proliferative and survival signals to the erythroblasts, and phagocytose extruded erythroblast nuclei at the conclusion of erythroid maturation. There is also accumulating evidence for the role of macrophages in promoting enucleation itself. The central macrophages are identified by their unique immunophenotypic signature. Their pronounced adhesive properties, ability for avid endocytosis, lack of respiratory bursts, and consequent release of toxic oxidative species, make them perfectly adapted to function as nurse cells. Both macrophages and erythroblasts display adhesive interactions that maintain island integrity, and elucidating these details is an area of intense interest and investigation. Such interactions enable regulatory feedback within islands via cross talk between cells and also trigger intracellular signaling pathways that regulate gene expression. An additional control mechanism for cellular growth within the erythroblastic islands is through the modulation of apoptosis via feedback loops between mature and immature erythroblasts and between macrophages and immature erythroblasts. The focus of this chapter is to outline the mechanisms by which erythroblastic islands aid erythropoiesis, review the historical data surrounding their discovery, and highlight important unanswered questions.

Macrophage colony-stimulating factor in the pathogenesis of HIV infection: potential target for therapeutic intervention

Macrophage colony stimulating factor (M-CSF) appears to play a major role in promoting and maintaining reservoirs of human immunodeficiency virus type 1 (HIV-1) in infected individuals. HIV-1 infection induces production of M-CSF by macrophages, which in turn promotes further infection of macrophages via increases in CD4 and CCR5 receptors, as well as increases in virus gene expression. M-CSF promotes the ontogeny and survival of macrophages, contributing to both the number and longevity of these infected cells. M-CSF dysregulation promotes the differentiation of monocytes toward macrophages and osteoclasts and at the same time may inhibit differentiation toward dendritic cells, resulting in immune impairment. The potential role of M-CSF in HIV-associated end organ diseases including HIV-associated dementia, HIV-associated nephropathy, and osteoporosis is discussed. This review emphasizes the need for developing M-CSF antagonists for treatment of HIV-1-infected patients.

Cell surface colony-stimulating factor 1 can be cleaved by TNF-alpha converting enzyme or endocytosed in a clathrin-dependent manner

CSF-1 is a hemopoietic growth factor, which plays an essential role in macrophage and osteoclast development. Alternative splice variants of CSF-1 are synthesized as soluble or membrane-anchored molecules, although membrane CSF-1 (mCSF-1) can be cleaved from the cell membrane to become soluble CSF-1. The activities involved in this proteolytic processing, also referred to as ectodomain shedding, remain poorly characterized. In the present study, we examined the properties of the mCSF-1 sheddase in cell-based assays. Shedding of mCSF-1 was up-regulated by phorbol ester treatment and was inhibited by the metalloprotease inhibitors GM6001 and tissue inhibitor of metalloproteases 3. Moreover, the stimulated shedding of mCSF-1 was abrogated in fibroblasts lacking the TNF-alpha converting enzyme (TACE, also known as a disintegrin and metalloprotease 17) and was rescued by expression of wild-type TACE in these cells, strongly suggesting that the stimulated shedding is TACE dependent. Additionally, we observed that mCSF-1 is predominantly localized to intracellular membrane compartments and is efficiently internalized in a clathrin-dependent manner. These results indicate that the local availability of mCSF-1 is actively regulated by ectodomain shedding and endocytosis. This mechanism may have important implications for the development and survival of monocyte lineage cells.

Identification of a novel population of Langerin+ dendritic cells

Langerhans cells (LCs) are antigen-presenting cells that reside in the epidermis of the skin and traffic to lymph nodes (LNs). The general role of these cells in skin immune responses is not clear because distinct models of LC depletion resulted in opposite conclusions about their role in contact hypersensitivity (CHS) responses. While comparing these models, we discovered a novel population of LCs that resides in the dermis and does not represent migrating epidermal LCs, as previously thought. Unlike epidermal LCs, dermal Langerin(+) dendritic cells (DCs) were radiosensitive and displayed a distinct cell surface phenotype. Dermal Langerin(+) DCs migrate from the skin to the LNs after inflammation and in the steady state, and represent the majority of Langerin(+) DCs in skin draining LNs. Both epidermal and dermal Langerin(+) DCs were depleted by treatment with diphtheria toxin in Lang-DTREGFP knock-in mice. In contrast, transgenic hLang-DTA mice lack epidermal LCs, but have normal numbers of dermal Langerin(+) DCs. CHS responses were abrogated upon depletion of both epidermal and dermal LCs, but were unaffected in the absence of only epidermal LCs. This suggests that dermal LCs can mediate CHS and provides an explanation for previous differences observed in the two-model systems.

Blood-derived dermal langerin+ dendritic cells survey the skin in the steady state

Langerin is a C-type lectin receptor that recognizes glycosylated patterns on pathogens. Langerin is used to identify human and mouse epidermal Langerhans cells (LCs), as well as migratory LCs in the dermis and the skin draining lymph nodes (DLNs). Using a mouse model that allows conditional ablation of langerin⁺ cells in vivo, together with congenic bone marrow chimeras and parabiotic mice as tools to differentiate LC- and blood-derived dendritic cells (DCs), we have revisited the origin of langerin⁺ DCs in the skin DLNs. Our results show that in contrast to the current view, langerin⁺CD8⁻ DCs in the skin DLNs do not derive exclusively from migratory LCs, but also include blood-borne langerin⁺ DCs that transit through the dermis before reaching the DLN. The recruitment of circulating langerin⁺ DCs to the skin is dependent on endothelial selectins and CCR2, whereas their recruitment to the skin DLNs requires CCR7 and is independent of CD62L. We also show that circulating langerin⁺ DCs patrol the dermis in the steady state and migrate to the skin DLNs charged with skin antigens. We propose that this is an important and previously unappreciated element of immunosurveillance that needs to be taken into account in the design of novel vaccine strategies.

The dermis contains langerin+ dendritic cells that develop and function independently of epidermal Langerhans cells

Langerhans cells (LCs) constitute a subset of dendritic cells (DCs) that express the lectin langerin and that reside in their immature state in epidermis. Paradoxically, in mice permitting diphtheria toxin (DT)–mediated ablation of LCs, epidermal LCs reappeared with kinetics that lagged behind that of their putative progeny found in lymph nodes (LNs). Using bone marrow (BM) chimeras, we showed that a major fraction of the langerin⁺, skin-derived DCs found in LNs originates from a developmental pathway that is independent from that of epidermal LCs. This pathway, the existence of which was unexpected, originates in the dermis and gives rise to langerin⁺ dermal DCs (DDCs) that should not be confused with epidermal LCs en route to LNs. It explains that after DT treatment, some langerin⁺, skin-derived DCs reappear in LNs long before LC-derived DCs. Using CD45 expression and BrdU-labeling kinetics, both LCs and langerin⁺ DDCs were found to coexist in wild-type mice. Moreover, DT-mediated ablation of epidermal LCs opened otherwise filled niches and permitted repopulation of adult noninflammatory epidermis with BM-derived LCs. Our results stress that the langerin⁺ DC network is more complex than originally thought and have implications for the development of transcutaneous vaccines and the improvement of humanized mouse models.

DC homeostasis in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation is an important experimental tool and therapeutic modality. Its efficacy and toxicity are both linked to a GvH reaction that is initiated by donor T cells recognizing recipient APC, of which DC are the most potent. In most tissues recipient DC are replaced after transplantation because they turnover rapidly from BM-derived precursors. However, in a number of sites, notably the skin, recipient DC may persist and even self-renew for many months after transplantation. Understanding the homeostasis of different APC populations and how they are related to the induction of alloreactivity may help to improve the therapeutic benefit of transplantation.

Human CD34+ CD11b- cord blood stem cells generate in vitro a CD34- CD11b+ subset that is enriched in langerin+ Langerhans dendritic cell precursors

OBJECTIVE

We investigated whether the expression of CD11b on precursors derived in vitro from CD34+ hematopoietic stem cells was related to their ability to generate CD11b- and CD11b+ Langerhans dendritic cells (LC).

METHODS

Human CD34+ cells purified from cord blood were cultured with FLT3 ligand, thrombopoietin, and stem cell factor (FTS) for 2 weeks, analyzed, and sorted by FACS. Sorted fractions were cultured as above, or differentiated into LC with GM-CSF, IL-4, and TGF-beta1 (G4-TGF) for 6 days. The capacity of LC to internalize langerin and dextran was assessed.

RESULTS

Ex vivo, human CD34+ cells were CD11b- and mostly CLA+. After 2 weeks of culture with FTS, CD34- CLA- CD11b- and CD34- CLA- CD11b+ cells emerged. CD11b- cells were the most ancestral because they were the only ones to proliferate with FTS, and constantly generated CD11b+ cells. Both CD11b- and CD11b+ sorted cells generated E-cadherin+ langerin+ LC after incubation with G4-TGF. The former fraction contained 46% +/- 15% of E-cadherin+ and 10% +/- 5% of langerin+ cells, whereas in the latter fraction these values reached respectively 66% +/- 23% and 30% +/- 16% (mean +/- SD, n = 7, p < 0.056). Looking at functional properties, CD11b- and CD11b+ LC were similar in terms of langerin and dextran endocytosis. By contrast, only CD11b+ LC internalized fluorescent LPS.

CONCLUSION

Human CD34+ CD11b- cells differentiate in FTS culture into a CD34- CD11b- precursor that in turn generates CD34- CD11b+ cells. These cells are enriched in LC precursors compared to CD34- CD11b- cells. Both CD11b- and CD11b+ LC are generated in vitro, and each fraction may assume different functions in inflammatory situations.

The BCL6-associated transcriptional co-repressor, MTA3, is selectively expressed by germinal centre B cells and lymphomas of putative germinal centre derivation

Metastasis-associated protein 3 (MTA3) is a recently described cell-type specific component of the Mi-2-NURD transcriptional co-repressor complex that is expressed in breast epithelia and germinal centre B cells. In model B cell lines, MTA3 physically interacts with BCL6 and appears to be instrumental in maintenance of the germinal centre B cell transcriptional programme that precludes premature plasmacytic differentiation. Here, we report selective, in situ cell-type specific expression of MTA3 among lymphoid cells largely confined to the germinal centre B cell compartment. Centroblasts display greater expression than smaller, less proliferative centrocytes, with undetectable expression in quiescent plasma cells. Among B cell neoplasms, germinal centre B cell-like lymphomas likewise exhibit selective expression that generally escalates with increasing proliferative capacity. MTA3 protein expression was, in accord, highly predictive of the germinal centre B cell-like gene expression profile for diffuse large B cell lymphomas. Lastly, relative repression of a subset of known BCL6 targets, including BLIMP1 and p27kip1, was highest in diffuse large B cell lymphomas that co-expressed both MTA3 and BCL6 protein. Together, these novel data suggest a role for MTA3 in BCL6-mediated lymphomagenesis in germinal centre B cell-like neoplasms.

Cytokine knockouts in reproduction: the use of gene ablation to dissect roles of cytokines in reproductive biology

Cytokines play many diverse and important roles in reproductive biology, and dissecting the complex interactions between these proteins and the different reproductive organs is a difficult task. One approach is to use gene ablation, or 'knockout', to analyse the effect of deletion of a single cytokine on mouse reproductive function. This review summarizes the essential roles of cytokines in reproductive biology that have been revealed by gene knockout studies, including development and regulation of the hypothalamo-pituitary-gondal axis, ovarian folliculogenesis, implantation and immune system modulation during pregnancy. However, successful utilization of this approach must consider the caveats associated with gene ablation studies, e.g. embryonic lethality, systemic effects of cytokine ablation on local reproductive processes and the limited exposure to pathogens in mice housed in laboratory conditions. New sophisticated technology that temporally or spatially regulates gene ablation can overcome some of these limitations. Discoveries on the roles of cytokines in reproductive function uncovered by gene ablation studies can now be applied to improve in vitro fertilization for infertile couples and in the development of contraceptive therapies.

Macrophage colony stimulating factor expression in human cardiac cells is upregulated by tumor necrosis factor-alpha via an NF-kappaB dependent mechanism

INTRODUCTION

Macrophage colony stimulating factor (M-CSF) is a key factor for monocyte and macrophage survival and proliferation. M-CSF has been implicated in cardiac healing and repair after myocardial infarction.

METHODS AND RESULTS

We show by immunohistochemistry and Western blotting analysis that M-CSF protein is present in human heart tissue. Cultured human adult cardiac myocytes (HACM) and human adult cardiac fibroblasts (HACF) isolated from human myocardial tissue constitutively express M-CSF. When HACM and HACF were treated with tumor necrosis factor-alpha (TNF-alpha) M-CSF protein production and M-CSF mRNA expression, determined by ELISA or by using RT-PCR, respectively, was significantly increased. To determine a possible role of nuclear factor kappaB (NF-kappaB) and activating protein 1 (AP-1) in M-CSF regulation, blockers to both pathways and an adenovirus overexpressing a dominant negative (dn) form of IkappaB kinase 2 (IKK2) were used. Only the NF-kappaB blocker dimethylfumarate and the dn IKK2, but not januskinase inhibitor-1 (JNK-I), were able to block the TNF-alpha-induced increase in M-CSF production in these cells, suggesting that the induction of M-CSF through TNF-alpha is mainly dependent on the activation of the NF-kappaB pathway. The monocyte activation marker CD11b was significantly increased after incubating U937 cells with conditioned medium from HACM or HACF as determined by FACS analysis.

CONCLUSIONS

Our in vitro data taken together with our immunohistochemistry data suggest that human cardiac cells constitutively express M-CSF. This expression of M-CSF in the human heart and its upregulation by TNF-alpha might contribute to monocyte and macrophage survival and differentiation.

The retinoblastoma tumor suppressor is a critical intrinsic regulator for hematopoietic stem and progenitor cells under stress

The retinoblastoma tumor suppressor protein (RB) plays important roles in the control of the cell division cycle. It is estimated that RB is dysfunctional/inactivated in up to 40% of human leukemias. The consequences of loss of RB on hematopoietic stem and progenitor cell (HSPC) function in vivo are incompletely understood. Here, we report that mice genetically deficient in Rb in all hematopoietic cells (Vav-Cre Rb knockout [KO] animals) showed altered contribution of distinct hematopoietic cell lineages to peripheral blood, bone marrow, and spleen; significantly increased extramedullary hematopoiesis in the spleen; and a 2-fold increase in the frequency of hematopoietic progenitor cells in peripheral blood. Upon competitive transplantation, HSPCs from Vav-Cre Rb KO mice contributed with an at least 4- to 6-fold less efficiency to hematopoiesis compared with control cells. HSPCs deficient in Rb presented with impaired cell-cycle exit upon stress-induced proliferation, which correlated with impaired function. In summary, Rb is critical for hematopoietic stem and progenitor cell function, localization, and differentiation.

In vivo transformation of mouse conventional CD8alpha+ dendritic cells leads to progressive multisystem histiocytosis

Division and proliferation of dendritic cells (DCs) have been proposed to contribute to homeostasis and to prolonged antigen presentation. Whether abnormal proliferation of dendritic cells causes Langerhans cell histiocytosis (LCH) is a highly debated topic. Transgenic expression of simian virus 40 (SV40) T antigens in mature DCs allowed their transformation in vivo while maintaining their phenotype, function, and maturation capacity. The transformed cells were differentiated splenic CD8 alpha-positive conventional dendritic cells with increased Langerin expression. Their selective transformation was correlated with higher steady-state cycling compared with CD8 alpha-negative DCs in wild-type and transgenic mice. Mice developed a DC disease involving the spleen, liver, bone marrow, thymus, and mesenteric lymph node. Surprisingly, lesions displayed key immunohistologic features of Langerhans cell histiocytosis, including expression of Langerin and absence of the abnormal mitoses observed in Langerhans cell sarcomas. Our results demonstrate that a transgenic mouse model with striking similarities to aggressive forms of multisystem histiocytosis, such as the Letterer-Siwe syndrome, can be obtained by transformation of conventional DCs. These findings suggest that conventional DCs may cause some human multisystem LCH. They can reveal shared molecular pathways for human histiocytosis between humans and mice.

Vaginal epithelial dendritic cells renew from bone marrow precursors

Dendritic cells (DCs) represent key professional antigen-presenting cells capable of initiating primary immune responses. A specialized subset of DCs, the Langerhans cells (LCs), are located in the stratified squamous epithelial layer of the skin and within the mucosal epithelial lining of the vaginal and oral cavities. The vaginal mucosa undergoes cyclic changes under the control of sex hormones, and the renewal characteristics of the vaginal epithelial DCs (VEDCs) remain unknown. Here, we examined the origin of VEDCs. In contrast to the skin epidermal LCs, the DCs in the epithelium of the vagina were found to be repopulated mainly by nonmonocyte bone-marrow-derived precursors, with a half-life of 13 days under steady-state conditions. Upon infection with HSV-2, the Gr-1(hi) monocytes were found to give rise to VEDCs. Furthermore, flow cytometric analysis of the VEDCs revealed the presence of at least three distinct populations, namely, CD11b(+)F4/80(hi), CD11b(+)F4/80(int), and CD11b(-)F4/80(-). Importantly, these VEDC populations expressed CD207 at low levels and had a constitutively more activated phenotype compared with the skin LCs. Collectively, our results revealed mucosa-specific features of the VEDCs with respect to their phenotype, activation status, and homeostatic renewal potential.

Extracellular branched-chain amino acids, especially valine, regulate maturation and function of monocyte-derived dendritic cells

The functions of dendritic cells (DCs) are impaired in patients with liver cirrhosis. It is well-known that cirrhotic patients show decreased levels of plasma branched-chain amino acids (BCAA). Although amino acids are associated with maintaining the cell structure and function in many organs, limited data are available regarding the role of amino acids including BCAA in the immune system. We aimed to investigate the roles of BCAA in the function of human monocyte-derived DCs (MoDC). CD14-positive monocytes (CD14 (+)) were isolated from PBMC from healthy volunteers and hepatitis C virus (HCV) cirrhotic patients. In medium deprived of BCAA or valine, monocytes were able to differentiate into immature, but not into mature, DCs and showed weak expression of CD83. The deprivation of leucine or isoleucine did not affect this process. The MoDC allostimulatory capacity was significantly decreased in medium deprived of BCAA or valine (p = 0.017, p = 0.012, Bonferroni's analysis, respectively). Annexin V(FITC)/propidium iodide staining showed that the DC yield and viability were not significantly different under any medium. Immunoblotting demonstrated that depletion of valine or leucine decreased phospho-S6 kinase expression. Valine increased dose-dependently the allostimulatory capacity and IL-12 production of MoDC from both healthy volunteers and HCV cirrhotic patients. An elevated extracellular concentration of valine could improve the DC function in cirrhotic patients. These data provide a rationale for nutrition therapy that could be beneficial to patients with cirrhosis.

Constitutively activated STAT3 promotes cell proliferation and survival in the activated B-cell subtype of diffuse large B-cell lymphomas

Diffuse large B-cell lymphoma (DLBCL) consists of at least 2 phenotypic subtypes; that is, the germinal center B-cell-like (GCB-DLBCL) and the activated B-cell-like (ABC-DLBCL) groups. It has been shown that GCB-DLBCL responds favorably to chemotherapy and expresses high levels of BCL6, a transcription repressor known to play a causative role in lymphomagenesis. In comparison, ABC-DLBCL has lower levels of BCL6, constitutively activated nuclear factor-kappaB, and tends to be refractory to chemotherapy. Here, we report that the STAT3 gene is a transcriptional target of BCL6. As a result, high-level STAT3 expression and activation are preferentially detected in ABC-DLBCL and BCL6-negative normal germinal center B cells. Most importantly, inactivating STAT3 by either AG490 or small interference RNA in ABC-DLBCL cells inhibits cell proliferation and triggers apoptosis. These phenotypes are accompanied by decreased expression of several known STAT3 target genes, including c-Myc, JunB, and Mcl-1, and increased expression of the cell- cycle inhibitor p27. In addition to identifying STAT3 as a novel BCL6 target gene, our results define a second oncogenic pathway, STAT3 activation, which operates in ABC-DLBCL, suggesting that STAT3 may be a new therapeutic target in these aggressive lymphomas.

Autocrine/paracrine TGFbeta1 is required for the development of epidermal Langerhans cells

Langerhans cells (LCs) are bone marrow (BM)–derived epidermal dendritic cells (DCs) that develop from precursors found in the dermis. Epidermal LCs are absent in transforming growth factor (TGF) β1-deficient mice. It is not clear whether TGFβ1 acts directly on LC precursors to promote maturation or whether it acts on accessory cells, which in turn affect LC precursors. In addition, the physiologic source of TGFβ1 is uncertain because BM chimera experiments showed that neither hematopoietic nor nonhematopoietic-derived TGFβ1 is required for LC development. To address these issues, we created mice transgenic for a bacterial artificial chromosome (BAC) containing the gene for human Langerin into which Cre recombinase had been inserted by homologous recombination (Langerin-Cre). These mice express Cre selectively in LCs, and they were bred to floxed TGFβRII and TGFβ1 mice, thereby generating mice with LCs that either cannot respond to or generate TGFβ1, respectively. Langerin-Cre TGFβRII mice had substantially reduced numbers of epidermal LCs, demonstrating that TGFβ1 acts directly on LCs in vivo. Interestingly, Langerin-Cre TGFβ1 mice also had very few LCs both in the steady state and after BM transplantation. Thus, TGFβ1 derived from LCs acts directly on LCs through an autocrine/paracrine loop, and it is required for LC development and/or survival.

Unique functions of splenic CD8alpha+ dendritic cells during infection with intracellular pathogens

Deciphering the prerequisites for the induction of protective cytotoxic T cell responses is essential for future development of more effective CD8(+) T cell-based vaccines against infectious diseases and cancer. Since crucial events for CD8(+) T cell priming and differentiation occur during the first contacts of naïve T cells with distinct antigen-presenting cells (APCs), the identification and therapeutic targeting of these 'master' APCs has become a major quest in the field. A decade ago, dendritic cells (DCs) were discovered as potent APCs, as they combine all major features for the initiation of T cell responses: (1) naïve DCs demonstrate high endocytic activity and scan continuously their environment in strategic positions throughout the whole body; (2) after activation (e.g. during pathogen invasion), DCs migrate into T cell zones of their draining lymphatic compartments, meanwhile processing captured antigen and maturing in order to stimulate encountered antigen-specific T cells. During the last years, different subsets of DCs that can be distinguished by specific surface marker expression and effector functions have been identified in mice. Their distinct functional capabilities have led to the concept of work-sharing; "migrating" DCs primarily transport antigens to the lymph node, where a specialized subset of "resident" DCs, defined by the expression of the CD8alphaalpha homodimer (CD8alpha(+) DCs), primes CD8(+) T cells upon antigen cross-presentation. Accordingly, CD8alpha(+) DCs have been found to prime CD8(+) T cells against different viruses as well as intracellular bacteria such as Listeria monocytogenes (L.m.). Recently, L.m. was found to survive specifically in splenic CD8alpha(+) DCs shortly after intravenous infection. Further experiments revealed a more generalized sampling activity of CD8alpha(+) DCs for blood-borne particles. These findings indicate that splenic CD8alpha(+) DCs might unite efficacious antigen-trapping with the licence to prime CD8(+) T cells. This new aspect of DC function could have evolved to guarantee a more rapid antigen-specific response against generalized infections.

Development of plasmacytoid and conventional dendritic cell subtypes from single precursor cells derived in vitro and in vivo

The development of functionally specialized subtypes of dendritic cells (DCs) can be modeled through the culture of bone marrow with the ligand for the cytokine receptor Flt3. Such cultures produce DCs resembling spleen plasmacytoid DCs (pDCs), CD8(+) conventional DCs (cDCs) and CD8(-) cDCs. Here we isolated two sequential DC-committed precursor cells from such cultures: dividing 'pro-DCs', which gave rise to transitional 'pre-DCs' en route to differentiating into the three distinct DC subtypes (pDCs, CD8(+) cDCs and CD8(-) cDCs). We also isolated an in vivo equivalent of the DC-committed pro-DC precursor cell, which also gave rise to the three DC subtypes. Clonal analysis of the progeny of individual pro-DC precursors demonstrated that some pro-DC precursors gave rise to all three DC subtypes, some produced cDCs but not pDCs, and some were fully committed to a single DC subtype. Thus, commitment to particular DC subtypes begins mainly at this pro-DC stage.

Identification of clonogenic common Flt3+M-CSFR+ plasmacytoid and conventional dendritic cell progenitors in mouse bone marrow

Lymphoid tissue plasmacytoid and conventional dendritic cells (DCs) are continuously regenerated from hematopoietic stem cells. The cytokine dependence and biology of plasmacytoid and conventional DCs suggest that regeneration might proceed through common DC-restricted developmental intermediates. By selecting for cytokine receptor expression relevant to DC development, we identify here highly cycling Lin(-)c-Kit(int)Flt3(+)M-CSFR(+) cells with a distinct gene-expression profile in mouse bone marrow that, on a clonal level in vitro and as a population both in vitro and in vivo, efficiently generated plasmacytoid and conventional DCs but no other lineages, which increased in number after in vivo injection of the cytokine Flt3 ligand. These clonogenic common DC progenitors thus define a cytokine-regulated DC developmental pathway that ensures the supply of various DC populations.

Dendritic cells in the kidney

Dendritic cells (DC) in nonlymphoid organs function at the crossroads of innate and adaptive immunity, self-tolerance, and tissue homeostasis. This review provides an overview of the study of DC in the kidney, tracing its history leading to the current knowledge of the origins, migration, and function of renal DC. Together, these studies suggest that renal DC play a critical role in the health and disease of the kidney, opening the way to direct targeting of renal DC for therapeutic benefit.

Initiation of primary anti-vaccinia virus immunity in vivo

The primary focus of our work is the initiation of an antiviral immune response. While we employ many experimental systems to address this fundamental issue, much of our work revolves around the use of vaccinia virus. Concerns over the negative effects of vaccination have prevented the return of the smallpox immunization program to the general population and underscored the importance of understanding the primary immune response to vaccinia virus. This response is comprised of a complex symphony of immune system components employing a variety of different mechanisms. In this review, we will both highlight the roles of many of these components and touch on the applications of vaccinia virus in the laboratory and the clinic.

The endless complexity of lymphocyte differentiation and lymphomagenesis: IRF-4 downregulates BCL6 expression

The BCL6 gene is a key factor necessary for formation of germinal centers and is implicated in pathogenesis of diffuse large B cell lymphoma (DLBCL). In this issue of Cancer Cell, Saito and colleagues explore regulation of BCL6 gene expression by CD40-NF-kappaB signaling pathway and show that the IRF4 transcriptional factor, induced by the NF-kappaB canonical pathway, directly downregulates BCL6 expression. The authors further demonstrate that this negative regulatory mechanism may be disturbed in DLBCLs harboring BCL6 gene translocations or mutations. These finding suggest that IRF4 may function as a key regulator of germinal center reaction and a guardian of lymphomagenesis.

Long slender cytoplasmic extensions: a common feature of neuroendocrine cells?

We have recently developed a new method for visualisation of gut mucosal cells and demonstrated that enterochromaffin (EC) and enterochromaffin-like (ECL) cells possess cytoplasmic extensions. The aim of the present study was to characterise the morphology of D- and G-cells. The D-cells in the stomach differed morphologically from intestinal D-cells, suggesting two distinct subpopulations of D-cells. Some D-cells appeared to be interconnected. No cell-to-cell contact between parietal and D-cells was found. Both D- and G-cells possessed long cytoplasmic extensions corresponding with our previous descriptions of EC and ECL cells. We propose that all neuroendocrine cells have the ability to develop cytoplasmic extensions, enabling them to signal to their target cells in a neurocrine manner.

Dendritic cells: ontogeny

Dendritic cells (DC) play key rolls in various aspects of immunity. The functions of DC depend on the subsets as well as their location or activation status. Understanding developmental lineages, precursors and inducing factors for various DC subsets would help their clinical application, but despite extensive efforts, the precise ontogeny of various DC, remain unclear and complex. Because of their many functional similarities to macrophages, DC were originally thought to be of myeloid-lineage, an idea supported by many in vitro studies where monocytes or GM-CSF (a key myeloid growth factor) has been extensively used for generating DC. However, there has been considerable evidence which suggests the existence of lymphoid-lineage DC. After the confusion of myeloid-/lymphoid-DC concept regarding DC surface markers, we have now reached a consensus that each DC subset can differentiate through both myeloid- and lymphoid-lineages. The identification of committed populations (such as common myeloid- and lymphoid progenitors) as precursors for every DC subsets and findings from various knockout (KO) mice that have selected lymphoid- or myeloid-lineage deficiency appear to indicate flexibility of DC development rather than their lineage restriction. Why is DC development so flexible unlike other hematopoitic cells? It might be because there is developmental redundancy to maintain such important populations in any occasions, or such developmental flexibility would be advantageous for DC to be able to differentiate from any "available" precursors in situ irrespective of their lineages. This review will cover ontogeny of conventional (CD8 +/- DC) DC, plasmacytoid DC and skin Langerhans cells, and recently-identified many Pre-DC (immediate DC precursor) populations, in addition to monocytes and plasmacytoid DC, will also be discussed.

Monocyte-derived dendritic cells from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile

BACKGROUND

Chronic hepatitis C virus (HCV) infection is characterized by an insufficient immune response, possibly owing to impaired function of antigen-presenting cells such as myeloid dendritic cells (DCs). Therapeutic vaccination with in vitro generated DCs may enhance the immune response. Subsets of DCs can originate from monocytes, but the presence of HCV in monocytes that develop into DCs in vitro may impair DC function. Therefore, we studied the presence of HCV RNA in monocytes and monocyte-derived DCs from chronic HCV patients.

METHODS

Monocytes were cultured with granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) for 6 days, and then with GM-CSF, IL-4, tumour necrosis factor-alpha (TNF-alpha), prostaglandin E2, IL-1beta and IL-6 for 2 days to generate mature DCs. HCV RNA was assessed by polymerase chain reaction. Surface molecules were assessed by flow cytometry. Cytokine production was assessed by cytokine bead array.

RESULTS

HCV RNA was present in monocytes in 11 of 13 patients, but undetectable in mature DCs in 13 of 13 patients. The morphology of patient DCs was comparable with DCs from healthy controls, but the percentage of cells expressing surface molecules CD83 (P=0.001), CD86 (P=0.023) and human leucocyte antigen-DR (P=0.028) was lower in HCV patients. Compared with control DCs, patient DCs produced enhanced levels of IL-10 (P=0.0079) and IL-8 (P=0.0079), and lower levels of TNF-alpha (P=0.032), IL-6 (P=NS) and IL-1beta (P=0.0079). Patient and control DCs did not produce IL-12.

CONCLUSIONS

Monocyte-derived DCs from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile.

Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment

Hematopoiesis is maintained by stem cells (HSCs) that undergo fate decisions by integrating intrinsic and extrinsic signals, with the latter derived from the bone marrow (BM) microenvironment. Cell-cycle regulation can modulate stem cell fate, but it is unknown whether this represents an intrinsic or extrinsic effector of fate decisions. We have investigated the role of the retinoblastoma protein (RB), a central regulator of the cell cycle, in hematopoiesis. Widespread inactivation of RB in the murine hematopoietic system resulted in profound myeloproliferation. HSCs were lost from the BM due to mobilization to extramedullary sites and differentiation. This phenotype was not intrinsic to HSCs, but, rather, was the consequence of an RB-dependent interaction between myeloid-derived cells and the microenvironment. These findings demonstrate that myeloproliferation may result from perturbed interactions between hematopoietic cells and the niche. Therefore, RB extrinsically regulates HSCs by maintaining the capacity of the BM to support normal hematopoiesis and HSCs.