Requirement for TNF-alpha and IL-1 alpha in fetal thymocyte commitment and differentiation

ANRIL regulating the secretion of Muc5ac induced by atmospheric PM2.5 via NF-κB pathway in Beas-2B cells

PM2.5 can cause airway inflammation and promote the excessive secretion of mucin 5ac (Muc5ac), which can further induce many respiratory diseases. Antisense non-coding RNA in the INK4 locus (ANRIL) might regulate the inflammatory responses mediated by nuclear factor kappa-B (NF-κB) signaling pathway. Beas-2B cells were used to clarify the role of ANRIL in the secretion of Muc5ac induced by PM2.5 . The siRNA was used to silence ANRIL expression. Normal and gene silenced Beas-2B cells were respectively exposed to different doses of PM2.5 for 6, 12, and 24 h. The survival rate of Beas-2B cells was detected by methyl thiazolyl tetrazolium (MTT) assay. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and Muc5ac levels were determined by enzyme linked immunosorbent assay (ELISA). The expression levels of NF-κB family genes and ANRIL were detected by real time polymerase chain reaction (PCR). The levels of NF-κB family proteins and NF-κB family phosphorylated proteins were determined using Western blot. Immunofluorescence experiments were performed to observe the nuclear transposition of RelA. PM2.5 exposure increased the levels of Muc5ac, IL-1β and TNF-α, and ANRIL gene expression (p < .05). With the dose and time of PM2.5 exposure increasing, the protein levels of inhibitory subunit of nuclear factor kappa-B alpha (IκB-α), RelA, and NF-κB1 decreased, the protein levels of phosphorylated RelA (p-RelA) and phosphorylated NF-κB1 (p-NF-κB1) increased, and RelA nuclear translocation increased, which indicated that the NF-κB signaling pathway was activated (p < .05). Silencing ANRIL could decrease the levels of Muc5ac, IL-1β, TNF-α, decrease NF-κB family genes expression, inhibit the degradation of IκB-α and the activation of NF-κB pathway (p < .05). ANRIL played a regulatory role in the secretion of Muc5ac and the inflammation induced by atmospheric PM2.5 via NF-κB pathway in Beas-2B cells. ANRIL could be a target for prevention and treatment of the respiratory diseases caused by PM2.5 .

Multi-objective optimization reveals time- and dose-dependent inflammatory cytokine-mediated regulation of human stem cell derived T-cell development

The generation of T-cells from stem cells in vitro could provide an alternative source of cells for immunotherapies. T-cell development from hematopoietic stem and progenitor cells (HSPCs) is tightly regulated through Notch pathway activation by Delta-like (DL) ligands 1 and 4. Other molecules, such as stem cell factor (SCF) and interleukin (IL)-7, play a supportive role in regulating the survival, differentiation, and proliferation of developing T-cells. Numerous other signaling molecules influence T-lineage development in vivo, but little work has been done to understand and optimize their use for T-cell production. Using a defined engineered thymic niche system, we undertook a multi-stage statistical learning-based optimization campaign and identified IL-3 and tumor necrosis factor α (TNFα) as a stage- and dose-specific enhancers of cell proliferation and T-lineage differentiation. We used this information to construct an efficient three-stage process for generating conventional TCRαβ⁺CD8⁺ T-cells expressing a diverse TCR repertoire from blood stem cells. Our work provides new insight into T-cell development and a robust system for generating T-cells to enable clinical therapies for treating cancer and immune disorders.

Tumor Necrosis Factor Alpha Signaling and Organogenesis

Tumor necrosis factor alpha (TNF-α) plays important roles in processes such as immunomodulation, fever, inflammatory response, inhibition of tumor formation, and inhibition of viral replication. TNF-α and its receptors are ubiquitously expressed in developing organs and they regulate the survival, proliferation, and apoptosis of embryonic stem cells (ESCs) and progenitor cells. TNF-α is an important inflammatory factor that also regulates the inflammatory response during organogenesis, and its cytotoxic effects can interfere with normal developmental processes, even leading to the onset of diseases. This review summarizes the various roles of TNF-α in organogenesis in terms of its secreting pattern, concentration-dependent activities, and interactions with other signaling pathways. We also explored new potential functions of TNF-α.

VSIG4(+) peritoneal macrophages induce apoptosis of double-positive thymocyte via the secretion of TNF-α in a CLP-induced sepsis model resulting in thymic atrophy

Thymic atrophy in sepsis is a critical disadvantage because it induces immunosuppression and increases the mortality rate as the disease progresses. However, the exact mechanism of thymic atrophy has not been fully elucidated. In this study, we discovered a novel role for VSIG4-positive peritoneal macrophages (V4(+) cells) as the principal cells that induce thymic atrophy and thymocyte apoptosis. In CLP-induced mice, V4(+) cells were activated after ingestion of invading microbes, and the majority of these cells migrated into the thymus. Furthermore, these cells underwent a phenotypic shift from V4(+) to V4(−) and from MHC II(low) to MHC II(+). In coculture with thymocytes, V4(+) cells mainly induced apoptosis in DP thymocytes via the secretion of TNF-α. However, there was little effect on CD4 or CD8 SP and DN thymocytes. V4(−) cells showed low levels of activity compared to V4(+) cells. Thymic atrophy in CLP-induced V4(KO) mice was much less severe than that in CLP-induced wild-type mice. In addition, V4(KO) peritoneal macrophages also showed similar activity to V4(−) cells. Taken together, the current study demonstrates that V4(+) cells play important roles in inducing immunosuppression via thymic atrophy in the context of severe infection. These data also suggest that controlling the function of V4(+) cells may play a crucial role in the development of new therapies to prevent thymocyte apoptosis in sepsis.

Thymic function in the regulation of T cells, and molecular mechanisms underlying the modulation of cytokines and stress signaling (Review)

The thymus is critical in establishing and maintaining the appropriate microenvironment for promoting the development and selection of T cells. The function and structure of the thymus gland has been extensively studied, particularly as the thymus serves an important physiological role in the lymphatic system. Numerous studies have investigated the morphological features of thymic involution. Recently, research attention has increasingly been focused on thymic proteins as targets for drug intervention. Omics approaches have yielded novel insights into the thymus and possible drug targets. The present review addresses the signaling and transcriptional functions of the thymus, including the molecular mechanisms underlying the regulatory functions of T cells and their role in the immune system. In addition, the levels of cytokines secreted in the thymus have a significant effect on thymic functions, including thymocyte migration and development, thymic atrophy and thymic recovery. Furthermore, the regulation and molecular mechanisms of stress-mediated thymic atrophy and involution were investigated, with particular emphasis on thymic function as a potential target for drug development and discovery using proteomics.

Cadmium-induced endoplasmic reticulum stress in chicken neutrophils is alleviated by selenium

Cadmium (Cd) decreases immune function and induces apoptosis of immune cells. Selenium (Se) can antagonize some metal element toxicity including Cd. To evaluate the cytotoxicity of Cd and the chemoprotective role of Se on bird neutrophils in vitro, we incubated chicken neutrophils cells with Cadmium chloride (CdCl₂) (10^-6M), Sodium selenite (Na₂SeO₃) (10^-7M), and with a mixture of Na₂SeO₃ (10^-7M) and CdCl₂ (10^-6M) for 12, 24, 36, and 48h. We found that Interleukin 1β (IL-1β), Interleukin 10 (IL-10), and interferon gamma (IFN-γ) increased and interleukin 17 (IL-17), interleukin 4 (IL-4) decreased significantly in the chicken neutrophils of the Cd treatment groups. Cd significantly increased the mRNA expression levels of nuclear factor kappaB (NF-κB), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor (TNF-α), and prostaglandin E2 (PGE₂) and the nitric oxide (NO) content. In addition, we demonstrated that Cd induced the apoptosis of chicken neutrophils and increased mRNA level of Bak, Cysteine-aspartic protease (Caspase)-3, Caspase-9, Caspase-12, glucose-regulated protein 78 (GRP78) and activating transcription factor 6 (ATF6), decreased mRNA level of Bcl-xl, and Ca/calmodulin-dependent protein (CaM). Moreover, the expression of NF-κB and Caspase-12 protein increased significantly in the Cd treatment groups. Se pretreatment significantly protected neutrophils against Cd-caused alterations. Our work suggested that Cd-induced immune suppression, inflammatory response, and apoptosis via endoplasmic reticulum stress (ERS). Moreover, these factors played critical roles in Se-mediated chemoprevention against Cd-induced immunotoxicity.

TNF-alpha and Notch signaling regulates the expression of HOXB4 and GATA3 during early T lymphopoiesis

During the early thymus colonization, Notch signaling activation on hematopoietic progenitor cells (HPCs) drives proliferation and T cell commitment. Although these processes are driven by transcription factors such as HOXB4 and GATA3, there is no evidence that Notch directly regulates their transcription. To evaluate the role of NOTCH and TNF signaling in this process, human CD34⁺ HPCs were cocultured with OP9-DL1 cells, in the presence or absence of TNF. The use of a Notch signaling inhibitor and a protein synthesis inhibitor allowed us to distinguish primary effects, mediated by direct signaling downstream Notch and TNF, from secondary effects, mediated by de novo synthesized proteins. A low and physiologically relevant concentration of TNF promoted T lymphopoiesis in OP9-DL1 cocultures. TNF positively modulated the expression of both transcripts in a Notch-dependent manner; however, GATA3 induction was mediated by a direct mechanism, while HOXB4 induction was indirect. Induction of both transcripts was repressed by a GSK3β inhibitor, indicating that activation of canonical Wnt signaling inhibits rather than induces their expression. Our study provides novel evidences of the mechanisms integrating Notch and TNF-alpha signaling in the transcriptional induction of GATA3 and HOXB4. This mechanism has direct implications in the control of self-renewal, proliferation, commitment, and T cell differentiation.

Cucurbitacin E suppresses cytokine expression in human Jurkat T cells through down-regulating the NF-κB signaling

Cucurbitacin E (CucE), a triterpenoid isolated from Cucurbitaceae plants, has been shown to possess an anti-inflammatory or immunosuppressive activity in vitro and in vivo, yet the underlying mechanism has been incompletely understood. The aim of the present study was to explore its effect on cytokine expression and the underlying mechanism in human Jurkat T cells as a cellular model. The results showed that CucE significantly inhibited the production of interleukin-2, tumor necrosis factor-α, and interferon-γ in culture medium of cells treated with phorbol 12,13-dibutyrate (PDB) plus ionomycin (Ion). Furthermore, the mRNA levels of these cytokines in activated Jurkat T cells were also decreased upon CucE treatment, suggesting a potential modulatory effect on the critical signaling pathways for cytokine expression, including nuclear factor-κB (NF-κB) or mitogen-activated protein kinases (MAPKs). In support of its effect on the NF-κB signaling pathway, CucE decreased the phosphorylation levels of inhibitor of κB (IκB) and NF-κB/p65 in PDB + Ion-stimulated cells. Further supporting this, the nuclear translocation of NF-κB/p65 was significantly suppressed in response to PDB plus Ion stimulation in the presence of CucE. The phosphorylation of p38MAPK, c-Jun N-terminal kinase (JNK), and Erk1/2, however, was not decreased or slightly increased at some time points by CucE treatment. Collectively, these data suggest that CucE may exhibit immunosuppressive effect by attenuating critical cytokine expression through down-regulating the NF-κB signaling pathway.

Regulation of mu opioid receptor expression in developing T cells

We have previously reported that functionally active μ-opioid receptors (MOR) are constitutively expressed at relatively low levels by developing T cells in the thymus. However, very little is known about the regulation of MOR expression by immature T cells. In this report, we first attempted to determine the effect of T cell receptor-induced T cell activation on the expression of MOR. We activated T cells with either the combination of anti-CD3 and CD28, or with superantigen, and observed a substantial increase in MOR transcript expression. We also chose to examine the effect of cytokine-mediated T cell activation on the expression of this opioid receptor. We selected certain cytokines that play a role in T cell development and are known to be present at functional levels in the thymus gland. Our results show that interferon γ (IFNγ), IL-1β, and IL-2, and in particular transforming growth factor-β (TGFβ), all induced significant increases in MOR transcript expression. On the other hand, both TNFα and IL-7 exhibited much weaker effects on MOR expression. These results show that MOR expression by developing T cells is strongly regulated by several cytokines involved in T cell development in the thymus gland.

Acute inducible ablation of GRP78 reveals its role in hematopoietic stem cell survival, lymphogenesis and regulation of stress signaling

GRP78, a master regulator of the unfolded protein response (UPR) and cell signaling, is required for inner cell mass survival during early embryonic development. However, little is known about its role in adult hematopoietic stem cells (HSCs) and hematopoiesis. Here we generated a conditional knockout mouse model that acutely deletes Grp78 in the adult hematopoietic system. Acute GRP78 ablation resulted in a significant reduction of HSCs, common lymphoid and myeloid progenitors, and lymphoid cell populations in the mutant mice. The GRP78-null induced reduction of the HSC pool could be attributed to increased apoptosis. Chimeric mice with Grp78 deletion only in the hematopoietic cells also showed a loss of HSCs and lymphopenia, suggesting a cell intrinsic effect. Analysis of GRP78 deficient bone marrow (BM) cells showed constitutive activation of all the major UPR signaling pathways, including activation of eIF2α, ATF6, xbp-1 splicing, as well as caspase activation. A multiplex cytokine assay further revealed alteration in select cytokine and chemokine serum levels in the mutant mice. Collectively, these studies demonstrate that GRP78 plays a pleiotropic role in BM cells and contributes to HSC survival and the maintenance of the lymphoid lineage.

Virus Distribution and Role of Thymic Macrophages During Experimental Infection With Noncytopathogenic Bovine Viral Diarrhea Virus Type 1

Thymic depletion, presence of viral antigen, and changes in distribution and cytokine production of thymic macrophages were investigated in calves experimentally infected with a noncytopathogenic bovine viral diarrhea virus type (BVDV) 1 strain. Ten clinically healthy colostrum-deprived calves were used. Eight calves were inoculated with the virus and two were used as uninfected controls. Calves were sedated and euthanized in batches between 3 and 14 days postinoculation. At necropsy, thymus samples were collected for structural, immunohistochemical, and ultrastructural study and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling). From 6 days postinoculation, the thymic cortex was multifocally depleted with increased frequency of pyknosis and karyorrhexis, suggestive of apoptosis and confirmed by the TUNEL technique. Although the onset of lymphoid depletion was coincident with the detection of viral antigen by immunohistochemistry, the number of infected lymphocytes was very low through the experiment. There was an increase in number of macrophages in cortex and medulla, accompanied by ultrastructural changes indicative of phagocyte activation, and a decrease in cells expressing tumor necrosis factor-alpha (TNF-α) and IL-1α. These results suggest that the increase in number of these cells could be related to phagocytosis of cell debris and apoptotic lymphocytes. Furthermore, the results imply that, in contrast to the situation with classical swine fever virus, the lymphocyte apoptosis resulting from bovine viral diarrhea virus infection is not mediated by TNF-α or interleukin-1 alpha (IL-1α) production by virus-infected macrophages. This is the first study that describes this decrease in the number of thymic cells expressing TNF-α and IL-1α in cattle experimentally infected with bovine viral diarrhea virus type 1.

Immunoendocrinology of the thymus in Chagas disease

During immune response to infectious agents, the host develops an inflammatory response which could fail to eliminate the pathogen or may become dysregulated. In this case, the ongoing response acquires a new status and turns out to be detrimental. The same elements taking part in the establishment and regulation of the inflammatory response (cytokines, chemokines, regulatory T cells and counteracting compounds like glucocorticoids) may also mediate harmful effects. Thymic disturbances seen during Trypanosoma cruzi (T. cruzi) infection fit well with this conceptual framework. After infection, this organ suffers a severe atrophy due to apoptosis-induced thymocyte exhaustion, mainly affecting the immature double-positive (DP) CD4+CD8+ population. Thymus cellularity depletion, which occurs in the absence of main immunological mediators involved in anti-T. cruzi defense, seems to be linked to a systemic cytokine/hormonal imbalance, involving a dysregulated increase in Tumor Necrosis Factor alpha (TNF-α) and corticosterone hormone levels. Additionally, we have found an anomalous exit of potentially autoimmune DP cells to the periphery, in parallel to a shrinkage in the compartment of natural regulatory T cells. In this context, our data clearly point to the view that the thymus is a target organ of T. cruzi infection. Preserved thymus may be essential for the development of an effective immune response against T. cruzi, but this organ is severely affected by a dysregulated circuit of proinflammatory cytokines and glucocorticoids. Also, the alterations observed in the DP population might have potential implications for the autoimmune component of human Chagas disease.

Maturation-dependent licensing of naive T cells for rapid TNF production

The peripheral naïve T cell pool is comprised of a heterogeneous population of cells at various stages of development, which is a process that begins in the thymus and is completed after a post-thymic maturation phase in the periphery. One hallmark of naïve T cells in secondary lymphoid organs is their unique ability to produce TNF rapidly after activation and prior to acquiring other effector functions. To determine how maturation influences the licensing of naïve T cells to produce TNF, we compared cytokine profiles of CD4⁺ and CD8⁺ single positive (SP) thymocytes, recent thymic emigrants (RTEs) and mature-naïve (MN) T cells during TCR activation. SP thymocytes exhibited a poor ability to produce TNF when compared to splenic T cells despite expressing similar TCR levels and possessing comparable activation kinetics (upregulation of CD25 and CD69). Provision of optimal antigen presenting cells from the spleen did not fully enable SP thymocytes to produce TNF, suggesting an intrinsic defect in their ability to produce TNF efficiently. Using a thymocyte adoptive transfer model, we demonstrate that the ability of T cells to produce TNF increases progressively with time in the periphery as a function of their maturation state. RTEs that were identified in NG-BAC transgenic mice by the expression of GFP showed a significantly enhanced ability to express TNF relative to SP thymocytes but not to the extent of fully MN T cells. Together, these findings suggest that TNF expression by naïve T cells is regulated via a gradual licensing process that requires functional maturation in peripheral lymphoid organs.

TNF receptor 2 pathway: drug target for autoimmune diseases

Although drug development has advanced for autoimmune diseases, many current therapies are hampered by adverse effects and the frequent destruction or inactivation of healthy cells in addition to pathological cells. Targeted autoimmune therapies capable of eradicating the rare autoreactive immune cells that are responsible for the attack on the body's own cells are yet to be identified. This Review presents a new emerging approach aimed at selectively destroying autoreactive immune cells by specific activation of tumour necrosis factor receptor 2 (TNFR2), which is found on autoreactive and normal T lymphocytes, with the potential of avoiding or reducing the toxicity observed with existing therapies.

A genetic model of chronic rhinosinusitis-associated olfactory inflammation reveals reversible functional impairment and dramatic neuroepithelial reorganization

Inflammatory sinus and nasal disease is a common cause of human olfactory loss. To explore the mechanisms underlying rhinosinusitis-associated olfactory loss, we have generated a transgenic mouse model of olfactory inflammation, in which tumor necrosis factor alpha (TNF-alpha) expression is induced in a temporally controlled manner specifically within the olfactory epithelium (OE). Like the human disease, TNF-alpha expression leads to a progressive infiltration of inflammatory cells into the OE. Using this model, we have defined specific phases of the pathologic process. An initial loss of sensation without significant disruption is observed, followed by a striking reorganization of the sensory neuroepithelium. An inflamed and disrupted state is sustained chronically by continued induction of cytokine expression. After prolonged maintenance in a deficient state, there is a dramatic recovery of function and a normal histologic appearance when TNF-alpha expression is extinguished. Although obstruction of airflow is also a contributing factor in human rhinosinusitis, this in vivo model demonstrates for the first time that direct effects of inflammation on OE structure and function are important mechanisms of olfactory dysfunction. These features mimic essential aspects of chronic rhinosinusitis-associated olfactory loss, and illuminate underlying cellular and molecular aspects of the disease. This manipulable model also serves as a platform for developing novel therapeutic interventions.

Disruption of thymopoiesis in ST6Gal I-deficient mice

Thymocyte development is accompanied by sequential changes in cell surface glycosylation. For example, medullary thymocytes have increased levels of alpha2,3-linked sialic acid and a loss of asialo core 1 O-glycans as compared to cortical thymocytes. Some of these changes have been linked to fine tuning of the T cell receptor avidity. We analyzed ST6Gal I transcript abundance and levels of alpha2,6-linked sialic acid across thymocyte subsets. We found that ST6Gal I transcript levels increased following T cell receptor beta-selection suggesting that this sialyltransferase may influence the development of early thymocyte populations. Indeed, low levels of alpha2,6-linked sialic acid were found in the earliest T lineage cells, and then increased in T cell receptor beta-selected cells. To determine whether ST6Gal I influences T cell development, we analyzed ST6Gal I-deficient mice for disruptions in thymocyte populations. We found reduced thymic cellularity in the ST6Gal I-deficient mice starting in the early thymocyte compartments.

Mouse models with human immunity and their application in biomedical research

Biomedical research in human beings is largely restricted to in vitro studies that lack complexity of a living organism. To overcome this limitation, humanized mouse models are developed based on immunodeficient characteristics of severe combined immunodeficiency (SCID) or recombination activating gene (Rag)(null) mice, which can accept xenografts. Peripheral constitution of human immunity in SCID or Rag(null) mice has been achieved by transplantation of mature human immune cells, foetal human thymus, bone marrow, liver tissues, lymph nodes or a combination of these, although efficiency needs to be improved. These mouse models with constituted human immunity (defined as humanized mice in the present text) have been widely used to investigate the basic principles of human immunobiology as well as complex pathomechanisms and potential therapies of human diseases. Here, elements of an ideal humanized mouse model are highlighted including genetic and non-genetic modification of recipient mice, transplantation strategies and proposals to improve engraftments. The applications of the humanized mice to study the development and response of human immune cells, human autoimmune diseases, virus infections, transplantation biology and tumour biology are reviewed as well.

The Thymus as an Inductive Site for T Lymphopoiesis

Like all hematopoietic cells, T lymphocytes are derived from bone-marrow-resident stem cells. However, whereas most blood lineages are generated within the marrow, the majority of T cell development occurs in a specialized organ, the thymus. This distinction underscores the unique capacity of the thymic microenvironment to support T lineage restriction and differentiation. Although the identity of many of the contributing thymus-derived signals is well established and rooted in highly conserved pathways involving Notch, morphogenetic, and protein tyrosine kinase signals, the manner in which the ensuing cascades are integrated to orchestrate the underlying processes of T cell development remains under investigation. This review focuses on the current definition of the early stages of T cell lymphopoiesis, with an emphasis on the nature of thymus-derived signals delivered to T cell progenitors that support the commitment and differentiation of T cells toward the alphabeta and gammadelta T cell lineages.

Tumor necrosis factor promotes T-cell at the expense of B-cell lymphoid development from cultured human CD34+ cord blood cells

OBJECTIVE

Human CD34+ cord blood (CB) cells are hematopoietic progenitors useful for stem cell transplantation, even after ex vivo expansion. We investigated the effect of tumor necrosis factor (TNF) on lymphoid development from cultured CD34+ CB cells.

MATERIALS AND METHODS

Human CD34+ CB cells were cultured in cytokine mixes with or without TNF. Preculture during 60 hours was followed by in vitro differentiation assays, including fetal thymus organ culture and coculture on murine stromal MS-5 cells. In a next step, experiments were extended to CD34+CD38- and CD34+CD38+ CB cells and prolonged preculture.

RESULTS

Preculture in the presence of TNF improved differentiation into T cells and diminished the ability to generate B cells, while NK potential and myeloid development were unaffected. Sorted CD34+CD38- CB cells were more potent T-cell precursors after preculture in TNF, compared to CD34+CD38+ CB cells. In precultured CD34+CD38- CB cells, TNF increased GATA3 but decreased EBF1 expression, in line with the skewed lymphoid differentiation induced by TNF. However, when preculture in the presence of TNF was extended to 1 week, T-cell precursors were lost.

CONCLUSION

After short-term culture of CD34+ CB cells in the presence of TNF, T-cell generation is stimulated at the expense of B-cell generation. T-cell progenitors are enriched in the CD34+CD38- fraction. These results have implications on the culture conditions to be used for CB CD34+ cells prior to transplantation.

Ex vivo characterization of human thymic dendritic cell subsets

Interactions between thymic dendritic cells (DC) and thymocytes are critical for proper development of T-cells. We identified human thymic DC populations on the basis of CD123, CD11c and CD14 expression. High levels of CD123 (IL-3R) and CD45RA defined the plasmacytoid DC (pDC) subset. Human thymic CD11c(+) DC expressed CD45RO and myeloid-related markers (CD13, CD33 and CD11b). CD11c(+) DC could be separated into two main subsets based on differential expression of CD14: CD11c(+) CD14(-) and CD11c(+) CD14(+) cells. Spontaneous production of IL-10 and IFNgamma without exogenous stimulation, was observed in the three DC subsets. Important phenotype modifications were observed in pDC cultures supplemented with IL-3. A down-regulation of CD123 and appearance of myeloid markers such as CD11b and CD11c on CD45RA(+) cells was noticed within the first 48h; at a later time there was a shift from CD45RA to CD45RO expression, as well as appearance of CD14 expression. CD11c(+) cells emerging in pDC culture did not express high levels of HLA-DR, CD83 and co-stimulatory molecules. This suggests an in vitro evolution of human thymic pDC toward a myeloid phenotype found in the CD11c(+) subset of thymic DC.

Thymus organogenesis and development of the thymic stroma

T-cell development occurs principally in the thymus. Here, immature progenitor cells are guided through the differentiation and selection steps required to generate a complex T-cell repertoire that is both self-tolerant and has propensity to bind self major histocompatibility complex. These processes depend on an array of functionally distinct epithelial cell types within the thymic stroma, which have a common developmental origin in the pharyngeal endoderm. Here, we describe the structural and phenotypic attributes of the thymic stroma, and review current cellular and molecular understanding of thymus organogenesis.

Higher expression of transcription targets and components of the nuclear factor-kappaB pathway is a distinctive feature of umbilical cord blood CD34+ precursors

Delayed engraftment, better reconstitution of progenitors, higher thymic function, and a lower incidence of the graft-versus-host disease are characteristics associated with umbilical cord blood (UCB) transplants, compared with bone marrow (BM). To understand the molecular mechanisms causing these intrinsic differences, we analyzed the differentially expressed genes between BM and UCB hematopoietic stem and progenitor cells (HSPCs). The expressions of approximately 10,000 genes were compared by serial analysis of gene expression of magnetically sorted CD34(+) cells from BM and UCB. Differential expression of selected genes was evaluated by real-time polymerase chain reaction on additional CD34(+) samples from BM (n = 22), UCB (n = 9), and granulocyte colony stimulating factor-mobilized peripheral blood (n = 6). The overrepresentation of nuclear factor-kappaB (NF-kappaB) pathway components and targets was found to be a major characteristic of UCB HSPCs. Additional promoter analysis of 41 UCB-overrepresented genes revealed a significantly higher number of NF-kappaB cis-regulatory elements (present in 22 genes) than would be expected by chance. Our results point to an important role of the NF-kappaB pathway on the molecular and functional differences observed between BM and UCB HSPCs. Our study forms the basis for future studies and potentially for new strategies to stem cell graft manipulation, by specific NF-kappaB pathway modulation on stem cells, prior to transplant.

Regulation of intrathymic T-cell development by Lunatic Fringe- Notch1 interactions

Intrathymic Notch1 signaling critically regulates T-lineage specification and commitment as well as T-cell progenitor survival and differentiation. Notch1 activation is continuously required during progression of early CD4/CD8-double-negative thymocytes to the CD4/CD8-double-positive stage. This developmental transition occurs as thymocytes migrate from the corticomedullary junction (CMJ) to the outer subcapsular zone (SCZ) of the thymus. Members of two families of structurally distinct Notch ligands, Delta-like 1 and Jagged-1, are expressed by cortical thymic epithelial cells, but it is not known which ligands are functionally required within the CMJ and SCZ microenvironmental niches. Our laboratory has investigated this question by genetically manipulating thymocyte expression of Lunatic Fringe (L-Fng), a glycosyltransferase that enhances sensitivity of Notch receptors to Delta-like ligands. This approach has revealed that low-threshold intrathymic Notch1 signals instruct multipotent thymus-seeding progenitors to suppress their B-cell potential and choose the T-cell fate. This strategy has also revealed that Delta-like Notch ligands are functionally limiting in both the CMJ and SCZ microenvironmental niches. Finally, we discuss our recent demonstration that L-Fng-mediated competition for Delta-like ligands is an important mechanism for regulating thymus size.

Tumor necrosis factor promotes human T-cell development in nonobese diabetic/severe combined immunodeficient mice

A major problem after clinical hematopoietic stem cell transplantations is poor T-cell reconstitution. Studying the mechanisms underlying this concern is hampered, because experimental transplantation of human stem and progenitor cells into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice usually results in low T-lymphocyte reconstitution. Because tumor necrosis factor alpha (TNFalpha) has been proposed to play a role in T-lineage commitment and differentiation in vitro, we investigated its potential to augment human T-cell development in vivo. Administration of TNF to irradiated NOD/SCID mice before transplantation of human mononuclear cells from either cord blood or adult G-CSF-mobilized peripheral blood (MPBL) led 2-3 weeks after transplantation to the emergence of human immature CD4(+)CD8(+) double-positive T-cells in the bone marrow (BM), spleen, and thymus, and in this organ, the human cells also express CD1a marker. One to 2 weeks later, single-positive CD4(+) and CD8(+) cells expressing heterogenous T-cell receptor alpha beta were detected in all three organs. These cells were also capable of migrating through the blood circulation. Interestingly, human T-cell development in these mice was associated with a significant reduction in immature lymphoid human CD19(+) B cells and natural killer progenitors in the murine BM. The human T cells were mostly derived from the transplanted immature CD34(+) cells. This study demonstrates the potential of TNF to rapidly augment human T lymphopoiesis in vivo and also provides clinically relevant evidence for this process with adult MPBL progenitors.

Maintenance of T cell specification and differentiation requires recurrent notch receptor-ligand interactions

Notch signaling has been shown to play a pivotal role in inducing T lineage commitment. However, T cell progenitors are known to retain other lineage potential long after the first point at which Notch signaling is required. Thus, additional requirements for Notch signals and the timing of these events relative to intrathymic differentiation remain unknown. Here, we address this issue by culturing subsets of CD4 CD8 double negative (DN) thymocytes on control stromal cells or stromal cells expressing Delta-like 1 (Dll1). All DN subsets were found to require Notch signals to differentiate into CD4+ CD8+ T cells. Using clonal analyses, we show that CD44+ CD25+ (DN2) cells, which appeared committed to the T cell lineage when cultured on Dll1-expressing stromal cells, nonetheless gave rise to natural killer cells with a progenitor frequency similar to that of CD44+ CD25- (DN1) thymocytes when Notch signaling was absent. These data, together with the observation that Dll1 is expressed on stromal cells throughout the thymic cortex, indicates that Notch receptor-ligand interactions are necessary for induction and maintenance of T cell lineage specification at both the DN1 and DN2 stages of T cell development, suggesting that the Notch-induced repression of the B cell fate is temporally separate from Notch-induced commitment to the T lineage.

Reconstitution of the cellular immune response by lactoferrin in cyclophosphamide-treated mice is correlated with renewal of T cell compartment

Cyclophosphamide is an alkylating agent used to treat both malignant and non-malignant immune-mediated inflammatory disorders in humans. It is also known as a potent immunosuppressive drug in humans and experimental animals. The aim of this study was to evaluate the effects of oral administration of lactoferrin (LF) on cellular responses and reconstruction of the lymphocyte pool in mice treated with cyclophosphamide (CP). Twelve week-old CBA mice were given a single intraperitoneal (i.p.) dose of CP (400 mg/kg body weight), then were treated per os with seven doses of LF (1 mg/dose) on alternate days. We demonstrated that the magnitude of delayed type hypersensitivity to ovalbumin, strongly diminished by CP action, was reconstituted by LF. Oral LF treatment also resulted in partial recovery of Concanavalin A-induced splenocyte proliferation. Blood profile analysis revealed elevation of leukocytosis by LF in CP-treated mice (from 64.9 to 84.76% of the control value). LF also caused substantial restoration of the percentage of the lymphocyte population in circulating blood (from 43.4 to 60.2% of the control values). LF alone had no effect on the neutrophil/lymphocyte ratio in normal mice, however, the total number of leukocytes decreased by 23.25%. Furthermore, we showed that LF increased the cellularity of spleens isolated from CP-treated mice (from 53.2 to 78.8%) and the content of peritoneal and alveolar macrophages (elevations from 50.6 to 67.3% and from 65.2 to 83.6%, respectively). Lastly, using panning technique, we demonstrated that LF strongly elevated the pool of CD3+ T cells in normal and CP-immunocompromised mice and CD4+ T cell content. In conclusion, we showed for the first time that lactoferrin, given orally to CP-immunosuppressed mice, could reconstitute a T-cell mediated immune response by renewal of the T cell pool.

T-cell developmental blockage by tachykinin antagonists and the role of hemokinin 1 in T lymphopoiesis

Hemokinin 1 (HK-1) is a new member of the tachykinin peptide family that is expressed in hematopoietic cells. Recent reports studying mouse, rat, and human orthologs of HK-1 demonstrate a broader distribution than originally reported. Our previous studies demonstrated that HK-1, by promoting proliferation, survival, and possibly maturation of B-cell precursors, plays an important role in B lymphopoiesis. Here we present data showing that HK-1 also influences T-cell development at a similar stage of differentiation. This peptide enhanced the proliferation of T-cell precursors and increased the number of thymocytes in fetal thymus organ cultures (FTOCs). Tachykinin antagonists, on the other hand, greatly reduced the cellularity of thymi both in vivo and in vitro. The major reduction occurred in the CD4/CD8 double-positive (DP) cells and the CD44-CD25+ subset of the CD4/CD8 double-negative (DN) cells. Of note, these populations also express HK-1, raising the possibility of autocrine or paracrine pathways influencing T-cell development as we previously reported for B-cell development. Consistent with this, the detrimental effect of tachykinin antagonists could be partially overcome with exogenous HK-1 peptide.

The origin and development of the immune system with a view to stem cell therapy

Careful study of the phylogeny and ontogeny of the three components of the immune system reveals that the macrophage, lymphatic, and hematopoietic systems originate independently of each other. Chronologically, the most ancient is the macrophage system, which arises in the coelomic cavity as mesenchymal ameboid cells having the properties to recognize self from non-self and to ingest foreign particles. The lymphatic system later develops from the endoderm of pharyngeal pouches, where the thymic anlage differentiates. The lymphocytes that originate here seed all lymphatic organs and retain the ability to divide and thereby form multiple colonies (lymphatic nodules) in the respiratory and digestive tract; further diversification of lymphocytes follows after confrontation with antigens. The last component of the immune system to appear is the hematopoietic system, which originates from the splanchnic mesoderm of the yolk sac as hematogenic tissue, containing hemangioblasts. The hematogenic tissue remains attached to the outer wall of the vitelline vessels, which provides an efficient mechanism for introducing the hematogenic tissue into the embryo. In an appropriate microenvironment, the hemangioblasts give rise to sinusoidal endothelium and to hemocytoblasts - the bone marrow stem cells for erythrocytes, myeloid cells, and megakaryocytes. The facts and opinions presented in this article are not in agreement with the currently accepted dogma that a common "hematolymphatic stem cell" localized in the marrow generates all of the cellular components of blood and the immune system.

Hierarchical interactions control CD4 gene expression during thymocyte development

CD4 gene regulation provides an ideal model for understanding the molecular events that drive T cell development. In this paper we use a transgenic approach to identify a CD4 LCR containing a stage-specific thymocyte enhancer (TE) and a region that protects against position effect variegation. Surprisingly, the TE acts indirectly through the previously defined proximal enhancer and is strongly induced upon commitment to the T cell lineage. We also describe a complex series of hierarchical control element interactions that orchestrate CD4 expression throughout thymopoiesis. These data provide a framework for understanding how CD4 gene expression is regulated in response to lineage commitment decisions.

Stromal cells provide the matrix for migration of early lymphoid progenitors through the thymic cortex

During steady state lymphopoiesis in the postnatal thymus, migration of precursors outward from the deep cortex toward the capsule is required for normal differentiation. Such migration requires, at a minimum, expression of adhesive receptors on the migrating lymphoid cells, as well as a stable matrix of their ligands persisting throughout the region of migration. In this study, we address the nature of this adhesive matrix. Although some precursor stages bound efficiently to extracellular matrix ligands, a specific requirement for the cell surface ligand VCAM-1 was also found. In situ analysis revealed that early precursors are found in intimate contact with a matrix formed by stromal cells in the cortex, a proportion of which expresses VCAM-1. In vivo administration of an anti-VCAM-1 Ab resulted in decreased thymic size and altered distribution of early precursors within the cortex. These results indicate that precursors migrating outward through the cortex may use a cellular, rather than extracellular, matrix for adhesion, and suggest that the VCAM-1(+) subset of cortical stroma may play a crucial role in supporting the migration of early precursors in the steady state thymus.

The developmentally regulated expression of Twisted gastrulation reveals a role for bone morphogenetic proteins in the control of T cell development

The evolutionarily conserved, secreted protein Twisted gastrulation (Tsg) modulates morphogenetic effects of decapentaplegic (dpp) and its orthologs, the bone morphogenetic proteins 2 and 4 (BMP2/4), in early Drosophila and vertebrate embryos. We have uncovered a role for Tsg at a much later stage of mammalian development, during T cell differentiation in the thymus. BMP4 is expressed by thymic stroma and inhibits the proliferation of CD4(-)CD8(-) double-negative (DN) thymocytes and their differentiation to the CD4(+)CD8(+) double-positive (DP) stage in vitro. Tsg is expressed by thymocytes and up-regulated after T cell receptor signaling at two developmental checkpoints, the transition from the DN to the DP and from the DP to the CD4(+) or CD8(+) single-positive stage. Tsg can synergize with the BMP inhibitor chordin to block the BMP4-mediated inhibition of thymocyte proliferation and differentiation. These data suggest that the developmentally regulated expression of Tsg may allow thymocytes to temporarily withdraw from inhibitory BMP signals.

The death domain kinase RIP protects thymocytes from tumor necrosis factor receptor type 2-induced cell death

Fas and the tumor necrosis factor receptor (TNFR)1 regulate the programmed cell death of lymphocytes. The death domain kinase, receptor interacting protein (rip), is recruited to the TNFR1 upon receptor activation. In vitro, rip-/- fibroblasts are sensitive to TNF-induced cell death due to an impaired nuclear factor kappaB response. Because rip-/- mice die at birth, we were unable to examine the effects of a targeted rip mutation on lymphocyte survival. To address the contribution of RIP to immune homeostasis, we examined lethally irradiated mice reconstituted with rip-/- hematopoietic precursors. We observed a decrease in rip-/- thymocytes and T cells in both wild-type C57BL/6 and recombination activating gene 1-/- irradiated hosts. In contrast, the B cell and myeloid lineages are unaffected by the absence of rip. Thus, the death domain kinase rip is required for T cell development. Unlike Fas-associated death domain, rip does not regulate T cell proliferation, as rip-/- T cells respond to polyclonal activators. However, rip-deficient mice contain few viable CD4+ and CD8+ thymocytes, and rip-/- thymocytes are sensitive to TNF-induced cell death. Surprisingly, the rip-associated thymocyte apoptosis was not rescued by the absence of TNFR1, but appears to be rescued by an absence of TNFR2. Taken together, this study implicates RIP and TNFR2 in thymocyte survival.

A defective NF-kappa B/RelB pathway in autoimmune-prone New Zealand black mice is associated with inefficient expansion of thymocyte and dendritic cells

New Zeland Black (NZB) mice develop an autoimmune disease involving an abnormal B cell response to peripheral self Ags. This disease is associated with defects in other cell types and thymic stromal organization. We present evidence that NZB cells of various lineages, including thymocytes, fibroblasts, and dendritic precursor cells, show impaired proliferation and enhanced cell death in culture upon stimulation compared with non-autoimmune-prone mice such as C57BL/6. This phenotype explains the reduced efficiency of maturation of bone marrow-derived dendritic cells and the loss of TNF- or IL-1-dependent thymocyte costimulation. Upon TNF-induced activation of NZB thymocytes, nuclear translocation and DNA binding of RelA- and RelB-dependent NF-kappaB heterodimers are significantly reduced. This phenotype has a transcriptional signature, since the NZB, but not the nonobese diabetic, thymic transcriptome shows striking similarities with that of RelB-deficient thymuses. This partial NF-kappaB deficiency detected upon activation by proinflammatory cytokines could explain the disorganization of thymic microenvironments in NZB mice. These combined effects might reduce the efficiency of central tolerance and expose apoptotic debris generated during inflammatory processes to self recognition.

Inflammatory and anti-inflammatory cytokines regulate the recovery from sublethal X irradiation in rat thymus

We investigated the regeneration of rat thymus after sublethal X irradiation (6 Gy). The number of thymocytes was much lower on day 3 after irradiation, and many apoptotic cells were observed. However, by day 5, there had been a rapid proliferation of thymocytes. Since cytokines are considered to be important regulatory factors in postirradiation recovery, we performed in vivo cytokine assays using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and found serial changes in the cytokine message. The messenger RNA (mRNA) expression of the pro-inflammatory cytokines interleukin 1 beta (Il1b), Il6 and tumor necrosis factor alpha (Tnf) was higher than normal on day 3, lower on day 5, and higher again on day 7. In particular, Tnf was completely absent on day 5 and was expressed again on day 7. Of the anti-inflammatory cytokines Il4, transforming growth factor beta (Tgfb) and Il10, only the Il10 message changed substantially. Il10 expression was very high on day 5 but was completely absent on day 7. Thus the Tnf and Il10 messages were expressed alternately. The changes in the distribution of macrophages detected by the immunohistochemical analysis may be related to the changes in the cytokines. Analysis of cytokine messages in the regenerating thymus in vivo may provide new insights into potential therapies for radiation-induced damage.

Lymphoid apoptosis and myeloid hyperplasia in CCAAT displacement protein mutant mice

CCAAT displacement protein (cux/CDP) is an atypical homeodomain protein that represses expression of several developmentally regulated lymphoid and myeloid genes in vitro, including gp91-phox, immunoglobulin heavy chain, the T-cell receptor beta and gamma chains, and CD8. To determine how this activity affects cell development in vivo, a hypomorphic allele of cux/CDP was created by gene targeting. Homozygous mutant mice (cux/CDP(Delta HD/Delta HD)) demonstrated a partial neonatal lethality phenotype. Surviving animals suffered from a wasting disease, which usually resulted in death between 2 and 3 weeks of age. Analysis of T lymphopoiesis demonstrated that cux/CDP(Delta HD/Delta HD) mice had dramatically reduced thymic cellularity due to enhanced apoptosis, with a preferential loss of CD4(+)CD8(+) thymocytes. Ectopic CD25 expression was also observed in maturing thymocytes. B lymphopoiesis was also perturbed, with a 2- to 3-fold reduction in total bone marrow B-lineage cells and a preferential loss of cells in transition from pro-B/pre-BI to pre-BII stages due to enhanced apoptosis. These lymphoid abnormalities were independent of effects related to antigen receptor rearrangement. In contrast to the lymphoid demise, cux/CDP(Delta HD/Delta HD) mice demonstrated myeloid hyperplasia. Bone marrow reconstitution experiments identified that many of the hematopoietic defects were linked to microenvironmental effects, suggesting that underexpression of survival factors or overexpression of death-inducing factors accounted for the phenotypes observed. Tumor necrosis factor (TNF) levels were elevated in several tissues, especially thymus, suggesting that TNF may be a target gene for cux/CDP-mediated repression. These data suggest that cux/CDP regulates normal hematopoiesis, in part, by modulating the levels of survival and/or apoptosis factors expressed by the microenvironment.

Subversion of the T/B lineage decision in the thymus by lunatic fringe-mediated inhibition of Notch-1

Notch-1 signaling is essential for lymphoid progenitors to undergo T cell commitment, but the mechanism has not been defined. Here we show that thymocytes ectopically expressing Lunatic Fringe, a modifier of Notch-1 signaling, induce lymphoid progenitors to develop into B cells in the thymus. This cell fate switch resulted from Lunatic Fringe-mediated inhibition of Notch-1 function, as revealed by experiments utilizing lymphoid progenitors in which Notch-1 activity was genetically manipulated. These data identify Lunatic Fringe as a potent regulator of Notch-1 during the T/B lineage decision and show that an important function of Notch-1 in T cell commitment is to suppress B cell development in the thymus.

IkappaB kinase-dependent chronic activation of NF-kappaB is necessary for p21(WAF1/Cip1) inhibition of differentiation-induced apoptosis of monocytes

The molecular mechanisms regulating monocyte differentiation to macrophages remain unknown. Although the transcription factor NF-kappaB participates in multiple cell functions, its role in cell differentiation is ill defined. Since differentiated macrophages, in contrast to cycling monocytes, contain significant levels of NF-kappaB in the nuclei, we questioned whether this transcription factor is involved in macrophage differentiation. Phorbol 12-myristate 13-acetate (PMA)-induced differentiation of the promonocytic cell line U937 leads to persistent NF-kappaB nuclear translocation. We demonstrate here that an increased and persistent IKK activity correlates with monocyte differentiation leading to persistent NF-kappaB activation secondary to increased IkappaBalpha degradation via the IkappaB signal response domain (SRD). Promonocytic cells stably overexpressing an IkappaBalpha transgene containing SRD mutations fail to activate NF-kappaB and subsequently fail to survive the PMA-induced macrophage differentiation program. The differentiation-induced apoptosis was found to be dependent on tumor necrosis factor alpha. The protective effect of NF-kappaB is mediated through p21(WAF1/Cip1), since this protein was found to be regulated in an NF-kappaB-dependent manner and to confer survival features during macrophage differentiation. Therefore, NF-kappaB plays a key role in cell differentiation by conferring cell survival that in the case of macrophages is mediated through p21(WAF1/Cip1).

Progression of T cell lineage restriction in the earliest subpopulation of murine adult thymus visualized by the expression of lck proximal promoter activity

The proximal promoter of lck directs gene expression exclusively in T cells. To investigate the developmental regulation of the lck proximal promoter activity and its relationship to T cell lineage commitment, a green fluorescence protein (GFP) transgenic (Tg) mouse in which the GFP expression is under the control of the proximal promoter of lck was created. In the adult GFP-Tg mice, >90% of CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes, and the majority of CD4(-)CD8(+) and CD4(-)CD8(-) [double-negative (DN)] thymocytes were highly positive for GFP. Slightly lower but substantial levels of expression of GFP was also observed in mature splenic T cells. No GFP(+) cells was detected in non-T lineage subsets, including mature and immature B cells, CD5(+) B cells, and NK cells, indicating a preserved tissue specificity of the promoter. The earliest GFP(+) cells detected were found in the CD44(+)CD25(-) DN thymocyte subpopulation. The developmental potential of GFP(-) and GFP(+) cells in the CD44(+)CD25(-) DN fraction was examined using in vitro culture systems. The generation of substantial numbers of alphabeta and gammadelta T cells as well as NK cells was demonstrated from both GFP(-) and GFP(+) cells. However, no development of B cells or dendritic cells was detected from GFP(+) CD44(+)CD25(-) DN thymocytes. These results suggest that the progenitors expressing lck proximal promoter activity in the CD44(+)CD25(-) DN thymocyte subset have lost most of the progenitor potential for the B and dendritic cell lineage. Thus, progression of T cell lineage restriction in the earliest thymic population can be visualized by lck proximal promoter activity, suggesting a potential role of Lck in the T cell lineage commitment.

TNF regulates thymocyte production by apoptosis and proliferation of the triple negative (CD3-CD4-CD8-) subset

TNF is a proinflammatory cytokine with opposing death/no-death effects in vivo and in vitro. Our studies showed that TNF regulates mouse thymocyte production, inducing both apoptosis and proliferation of the most immature CD3(-)CD4(-)CD8(-) triple negative (TN) subset within a broad range of dosages (10(1)-10(5) pg/ml) in the presence of IL-7. TNF apoptosis affected only the TN3 (CD44(-)CD25(+)) and TN4 (CD44(-)CD25(-)) subsets that expressed both TNFR-p55 and -p75. Although each TNFR alone could mediate TNF apoptosis, maximal apoptosis was seen in C57BL/6J wild type, which expressed both TNFRs. TNF also induced proliferation of TN3 cells at higher doses (10(4)-10(5) pg/ml) mediated only by TNFR-p75. Both anti-TNFR-p55 and -TNFR-p75 mAb inhibited apoptosis but only anti-p75 inhibited proliferation. TNF also regulated TN proliferation to IL-7 because TNFR knockout (KO), TNF KO, and TNF/lymphotoxin alpha and beta triple KO mice showed 2- to 3-fold increased responses not seen in C57BL/6J wild type. In vivo, TNFR KO mice showed thymic hypertrophy with a 60% increase in total thymocytes, with no effect on the CD4/CD8 subsets. We conclude that TNF maintains homeostatic control of total thymocyte production by negative selection of TN3 and TN4 prothymocytes and down-regulation of their proliferation to endogenous IL-7.

Development of natural killer cells from lymphohematopoietic progenitors of murine fetal liver

We established a clonal culture system which supports the growth of murine immature natural killer (NK) cells. When we plated day 14 fetal thymocytes in methylcellulose media containing interleukin 2 (IL-2), IL-7 and steel factor (SF), we observed diffuse colonies which could not be classified into known colony types. Cells in the colonies were blast-like and expressed Thy-1 and CD25 but not lineage-specific markers. Cells in the colonies developed into NK1.1+ cells in fetal thymus organ culture indicating that the colonies consist of immature NK cells. We then examined the colony-forming ability of fetal liver cells. The combination of IL-2, IL-7 and SF with or without IL-11 supported formation of few immature NK cell colonies from purified progenitors. Interestingly, addition of IL-11 to the culture stimulated formation of mixed colonies consisting of immature NK cells, B cells, macrophages and/or mast cells. The clonal origin of the mixed NK cell colonies was confirmed by micromanipulation of the colony-forming cells. This culture assay should facilitate the analysis of the pathway and cytokine regulation of NK cell development.

A profound deficiency in thymic progenitor cells in mice lacking Jak3

Humans and mice with genetic deficiencies that lead to loss of signaling through common gamma-chain (gammac)-containing cytokine receptors have severe defects in B and T lymphocytes. In humans, these deficiencies lead to a complete absence of T cells, whereas in mice, small thymuses give rise to normal numbers of peripheral T cells. We have examined the first wave of developing T cells in Jak3-/-, IL-7-/-, and IL-7Ralpha-/- fetal mice, and have found a near absence of thymic progenitor cells. This deficiency is highlighted by the complete inability of Jak3-/- progenitor cells to reconstitute T cell development in the presence of competing wild-type cells. These data clearly demonstrate a strong common basis for the T cell deficiencies in mice and humans lacking gammac/Jak3 signaling pathways.

The fas antigen is involved in thymic T-cell development as a costimulatory molecule, but not in the deletion of neglected thymocytes

To determine whether the Fas antigen (Fas) is involved in thymic T-cell development, we introduced the lymphoproliferation (lpr) mutation into a T-cell receptor-alphabeta transgenic mouse (DO10 mouse) and generated 4 genotypes of T-cell receptor transgenic mice homozygous or heterozygous for the lpr mutation with selecting or nonselecting H-2 haplotype. Unexpectedly, we found that the homozygous Fas mutation (lpr/lpr) induced a marked reduction in CD4(+)CD8(+) double-positive (DP) thymocytes in mice with nonselecting background and that the thymus showed severe cortical atrophy. We also found that the homozygous Fas mutation inhibited the activation of DP thymocytes in the process of positive selection, as indicated by the lower levels of CD5 and CD69 expressions on DP thymocytes in lpr/lpr mice with both selecting and nonselecting background than those of lpr/+ mice. Furthermore, we found a significant skewing from CD4(+) to CD8(+) single-positive thymocytes in lpr/lpr mice with nonselecting background compared with that in the corresponding lpr/+ mice. Taken together, these results indicate that Fas is involved in thymic T-cell development, DP thymocyte generation and positive selection, as a costimulatory molecule but is not involved in the deletion of neglected thymocytes.

Preferential proliferation and differentiation of double-positive thymocytes into CD8(+) single-positive thymocytes in a novel cell culture medium

The identification of factors that regulate the proliferation and differentiation of double-positive (DP) into CD4(+) and CD8(+) single-positive (SP) thymocytes has proven difficult due to the inability of DP thymocytes to proliferate, expand, and differentiate into SP thymocytes in available cell culture media. Here we report on the ability of DP thymocytes to differentiate in a novel conditioned medium, termed XLCM, derived from the supernatant of mitogen activated human cord blood mononuclear cells. During a 5-day culture in XLCM in the absence of thymic stromal cells, DP thymocytes from normal mice and MHC double knockout mice (lack SP thymocytes) proliferate, expand, and differentiate into several (alphabetaTCR(+), NK1.1(+)alphabetaTCR(+), and gammadeltaTCR(+)) subsets of CD4(+) and predominantly CD8(+) SP thymocytes. These studies suggest that the use of XLCM may aid in the characterization of factors that regulate the differentiation of DP thymocytes into CD8(+) SP thymocytes.

Protective role of interleukin-1 in mycobacterial infection in IL-1 alpha/beta double-knockout mice

To understand the role of the proinflammatory cytokine interleukin-1 (IL-1) in mycobacterial inflammation, IL-1 alpha/beta double-knockout (KO) mice were produced. These mice were infected with either Mycobacterium tuberculosis H37Rv by the airborne route using an airborne infection apparatus, and their capacities to control mycobacterial growth, granuloma formation, cytokine, and nitric oxide (NO) production were examined. The IL-1 alpha/beta mice developed significantly larger (p < 0.01) granulomatous, but not necrotic, lesions in their lungs than wild-type (WT) mice after infection with H37Rv. Inflammatory lesions, but not granulomas, were observed in spleen and liver tissues from both IL-1 alpha/beta KO and wild-type mice. Granulomatous lesion development in IL-1 alpha/beta KO mice was not significantly inhibited by treatment with exogenous recombinant IL-1 alpha/beta. Compared with wild-type mice, splenic IFN-gamma and IL-12 levels were within the normal range. NO production by cultured alveolar macrophages from IL-1 alpha/beta KO mice was lower than in wild-type mice but were increased by the addition of recombinant IL-1 alpha/beta. Our data clearly indicate that IL-1 is important for the generation of early-phase protective immunity against mycobacterial infection.

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.

Clonal characterization of a bipotent T cell and NK cell progenitor in the mouse fetal thymus

We recently described a population of fetal thymocytes with a CD117+NK1.1+CD90lowCD25- phenotype, which were shown to contain committed T cell and NK cell progenitors. However, the characterization of a single cell with a restricted T and NK cell precursor potential was lacking. Here, using an in vitro model for T and NK cell differentiation, we provide conclusive evidence demonstrating the existence of a clonal lineage-restricted T and NK cell progenitor. These results establish that fetal thymocytes with a CD117+NK1.1+CD90lowCD25- phenotype represent bipotent T and NK cell progenitors.

Activation of the p38 mitogen-activated protein kinase pathway arrests cell cycle progression and differentiation of immature thymocytes in vivo

The development of T cells in the thymus is coordinated by cell-specific gene expression programs that involve multiple transcription factors and signaling pathways. Here, we show that the p38 mitogen-activated protein (MAP) kinase signaling pathway is strictly regulated during the differentiation of CD4(-)CD8(-) thymocytes. Persistent activation of p38 MAP kinase blocks fetal thymocyte development at the CD25(+)CD44(-) stage in vivo, and results in the lack of T cells in the peripheral immune system of adult mice. Inactivation of p38 MAP kinase is required for further differentiation of these cells into CD4(+)CD8(+) thymocytes. The arrest of cell cycle in mitosis is partially responsible for the blockade of differentiation. Therefore, the p38 MAP kinase pathway is a critical regulatory element of differentiation and proliferation during the early stages of in vivo thymocyte development.

Commitment of common T/Natural killer (NK) progenitors to unipotent T and NK progenitors in the murine fetal thymus revealed by a single progenitor assay

We have established a new clonal assay system that can evenly support the development of T and natural killer (NK) cells. With this system, we show that all T cell progenitors in the earliest CD44(+)CD25(-)FcgammaRII/III(-) fetal thymus (FT) cell population retain NK potential, and that the NK lineage-committed progenitors (p-NK) also exist in this population. T cell lineage-committed progenitors (p-T), which are unable to generate NK cells, first appear at the CD44(+)CD25(-) FcgammaRII/III(+) stage in day 12 FT. The proportion of p-T markedly increases during the transition from the CD44(+)CD25(-) stage to the CD44(+)CD25(+) stage in day 14 FT. On the other hand, p-NK preferentially increase in number at the CD44(+)CD25(-) stage between days 12 and 14 of gestation. The production of p-NK continues up to the CD44(+)CD25(+) stage, but ceases before the rearrangement of T cell receptor beta chain genes. It was further shown that the CD44(+)CD25(-) CD122(+) population of day 14 FT exclusively contains p-NK. These results indicate that the earliest T cell progenitor migrating into the FT is T/NK bipotent, and strongly suggest that the bipotent progenitor continuously produces p-NK and p-T until the CD44(+)CD25(+) stage.