Expression of LIF in transgenic mice results in altered thymic epithelium and apparent interconversion of thymic and lymph node morphologies

Leukemia inhibitory factor is a therapeutic target for renal interstitial fibrosis

BACKGROUND

The role of the IL6 family members in organ fibrosis, including renal interstitial fibrosis (TIF), has been widely explored. However, few studies have ever simultaneously examined them in the same cohort of patients. Besides, the role of leukemia inhibitory factor (LIF) in TIF remains unclear.

METHODS

RNA-seq data of kidney biopsies from chronic kidney disease (CKD) patients, in both public databases and our assays, were used to analyze transcript levels of IL6 family members. Two TIF mouse models, the unilateral ureteral obstruction (UUO) and the ischemia reperfusion injury (IRI), were employed to validate the finding. To assess the role of LIF in vivo, short hairpin RNA, lenti-GFP-LIF was used to knockdown LIF receptor (LIFR), overexpress LIF, respectively. LIF-neutralizing antibody was used in therapeutic studies. Whether urinary LIF could be used as a promising predictor for CKD progression was investigated in a prospective observation patient cohort.

FINDINGS

Among IL6 family members, LIF is the most upregulated one in both human and mouse renal fibrotic lesions. The mRNA level of LIF negatively correlated with eGFR with the strongest correlation and the smallest P value. Baseline urinary concentrations of LIF in CKD patients predict the risk of CKD progression to end-stage kidney disease by Kaplan-Meier analysis. In mouse TIF models, knockdown of LIFR alleviated TIF; conversely, overexpressing LIF exacerbated TIF. Most encouragingly, visible efficacy against TIF was observed by administering LIF-neutralizing antibodies to mice. Mechanistically, LIF-LIFR-EGR1 axis and Sonic Hedgehog signaling formed a vicious cycle between fibroblasts and proximal tubular cells to augment LIF expression and promote the pro-fibrotic response via ERK and STAT3 activation.

INTERPRETATION

This study discovered that LIF is a noninvasive biomarker for the progression of CKD and a potential therapeutic target of TIF.

FUNDINGS

Stated in the Acknowledgements section of the manuscript.

Endometrial injury concurrent with hysteroscopy increases the expression of Leukaemia inhibitory factor: a preliminary study

OBJECTIVE

It is not known by which mechanism endometrial injury increases pregnancy rates. Leukaemia inhibitory factor (LIF) is a cytokine involved in wound healing and implantation. The aim of this study was to determine the change in endometrial LIF mRNA expression before and after mechanical injury during hysteroscopy.

METHODS

Forty patients with a history of two or more unsuccessful implantations who decided to undergo hysteroscopy in the proliferative phase were divided into two equal groups: one with endometrial injury (scratching group) and the other with noninjury (control group). Endometrial sampling was conducted before injury on the patients in the scratching group, and then injury was performed with monopolar needle forceps. Only diagnostic hysteroscopy was performed on the patients in the control group. Endometrial tissues were collected using a Pipelle catheter between Days 20 and 23 of the mid-luteal phase of the next cycles in both the scratching and control groups. Endometrial LIF mRNA expression was evaluated with the use of reverse-transcription polymerase chain reactions.

RESULTS

Relative changes in mRNA expression levels of the LIF gene in endometrial samples taken before and after injury were calculated using the 2-ΔΔCt method, and the fold changes obtained were compared between and within the groups. Compared with preinjury values, an 11.1-fold increase was found in postinjury LIF mRNA expression in patients with monopolar forceps injury (p < 0.001). There was a 3.9-fold significant increase in postinjury LIF mRNA levels compared with those in the control group (p < 0.02).

CONCLUSIONS

The fertility-promoting effect of hysteroscopy-guided mechanical endometrial injury may be mediated by LIF mRNA.

Emerging roles for IL-6 family cytokines as positive and negative regulators of ectopic lymphoid structures

IL-6 family cytokines display broad effects in haematopoietic and non-haematopoietic cells that regulate immune homeostasis, host defence, haematopoiesis, development, reproduction and wound healing. Dysregulation of these activities places this cytokine family as important mediators of autoimmunity, chronic inflammation and cancer. In this regard, ectopic lymphoid structures (ELS) are a pathological hallmark of many tissues affected by chronic disease. These inducible lymphoid aggregates form compartmentalised T cell and B cell zones, germinal centres, follicular dendritic cell networks and high endothelial venules, which are defining qualities of peripheral lymphoid organs. Accordingly, ELS can support local antigen-specific responses to self-antigens, alloantigens, pathogens and tumours. ELS often correlate with severe disease progression in autoimmune conditions, while tumour-associated ELS are associated with enhanced anti-tumour immunity and a favourable prognosis in cancer. Here, we discuss emerging roles for IL-6 family cytokines as regulators of ELS development, maintenance and activity and consider how modulation of these activities has the potential to aid the successful treatment of autoimmune conditions and cancers where ELS feature.

Coordination of Immune-Stroma Crosstalk by IL-6 Family Cytokines

Stromal cells are a subject of rapidly growing immunological interest based on their ability to influence virtually all aspects of innate and adaptive immunity. Present in every bodily tissue, stromal cells complement the functions of classical immune cells by sensing pathogens and tissue damage, coordinating leukocyte recruitment and function, and promoting immune response resolution and tissue repair. These diverse roles come with a price: like classical immune cells, inappropriate stromal cell behavior can lead to various forms of pathology, including inflammatory disease, tissue fibrosis, and cancer. An important immunological function of stromal cells is to act as information relays, responding to leukocyte-derived signals and instructing leukocyte behavior in kind. In this regard, several members of the interleukin-6 (IL-6) cytokine family, including IL-6, IL-11, oncostatin M (OSM), and leukemia inhibitory factor (LIF), have gained recognition as factors that mediate crosstalk between stromal and immune cells, with diverse roles in numerous inflammatory and homeostatic processes. This review summarizes our current understanding of how IL-6 family cytokines control stromal-immune crosstalk in health and disease, and how these interactions can be leveraged for clinical benefit.

Current Knowledge of IL-6 Cytokine Family Members in Acute and Chronic Kidney Disease

Healthy kidneys are important for the efficient regulation of metabolism. However, there is an ever increasing population of patients suffering from both acute and chronic kidney diseases that disrupt this homeostasis. This review will explore the emerging roles that interleukin 6 (IL-6) cytokine family members play in the pathogenesis of kidney disease. The IL-6 family of cytokines are involved in a diverse range of physiological functions. In relation to kidney disease, their involvement is no less diverse. Evidence from both preclinical and clinical sources show that IL-6 cytokine family members can play either a deleterious or protective role in response to kidney disease. This appears to be dependent on the type of kidney disease in question or the specific cytokine. Current attempts to use or target IL-6 cytokine family members as therapies of kidney diseases will be highlighted throughout this review. Finally, the involvement of IL-6 cytokine family members in kidney disease will be presented in the context of three regularly overlapping conditions: obesity, hypertension and diabetes.

Regulation of T-Cell Signaling by Post-Translational Modifications in Autoimmune Disease

The adaptive immune system involves antigen-specific host defense mechanisms mediated by T and B cells. In particular, CD4⁺ T cells play a central role in the elimination of pathogens. Immunological tolerance in the thymus regulates T lymphocytes to avoid self-components, including induction of cell death in immature T cells expressing the self-reactive T-cell receptor repertoire. In the periphery, mature T cells are also regulated by tolerance, e.g., via induction of anergy or regulatory T cells. Thus, T cells strictly control intrinsic signal transduction to prevent excessive responses or self-reactions. If the inhibitory effects of T cells on these mechanisms are disrupted, T cells may incorrectly attack self-components, which can lead to autoimmune disease. The functions of T cells are supported by post-translational modifications, particularly phosphorylation, of signaling molecules, the proper regulation of which is controlled by endogenous mechanisms within the T cells themselves. In recent years, molecular targeted agents against kinases have been developed for treatment of autoimmune diseases. In this review, we discuss T-cell signal transduction in autoimmune disease and provide an overview of acetylation-mediated regulation of T-cell signaling pathways.

The emerging role of ECM crosslinking in T cell mobility as a hallmark of immunosenescence in humans

Immunosenescence is thought to result from cellular aging and to reflect exposure to environmental stressors and antigens, including cytomegalovirus (CMV). However, not all of the features of immunosenescence are consistent with this view, and this has led to the emergence of the sister theory of "inflammaging". The recently discovered diffuse tissue distribution of resident memory T cells (T_RM) which don't recirculate, calls these theories into question. These cells account for most T cells residing in barrier epithelia which sit in and travel through the extracellular matrix (ECM). With almost all studies to date carried out on peripheral blood, the age-related changes of the ECM and their consequences for T cell mobility, which is crucial for the function of these cells, have been largely ignored. We propose an update of the theoretical framework of immunosenescence, based on a novel hypothesis: the increasing stiffness and cross-linking of the senescent ECM lead to a progressive immunodeficiency due to an age-related decrease in T cell mobility and eventually the death of these cells. A key element of this mechanism is the mechanical stress to which the cell cytoplasm and nucleus are subjected during passage through the ECM. This hypothesis is based on an "evo-devo" perspective bringing together some major characteristics of aging, to create a single interpretive framework for immunosenescence.

Activin A programs the differentiation of human TFH cells

Follicular helper T (T_FH) cells are CD4⁺ T cells specialized in helping B cells and are associated both with protective antibody responses and autoimmune diseases. The promise of targeting T_FH cells therapeutically has been limited by fragmentary understanding of extrinsic signals regulating human T_FH cell differentiation. A screen of a human protein library identified activin A as new regulator of T_FH cell differentiation. Activin A orchestrated expression of multiple T_FH-associated genes, independently or in concert with additional signals. T_FH programming by activin A was antagonized by the cytokine IL-2. Activin A’s capacity to drive T_FH cell differentiation in vitro was conserved for non-human primates but not mice. Finally, activin A-induced T_FH programming was dependent on SMAD2 and SMAD3 signaling and blocked by pharmacological inhibitors.

Proteomic dissection of LPS-inducible, PHF8-dependent secretome reveals novel roles of PHF8 in TLR4-induced acute inflammation and T cell proliferation

Endotoxin (LPS)-induced changes in histone lysine methylation contribute to the gene-specific transcription for control of inflammation. Still unidentified are the chromatin regulators that drive the transition from a transcriptional-repressive to a transcriptional-active chromatin state of pro-inflammatory genes. Here, using combined approaches to analyze LPS-induced changes in both gene-specific transcription and protein secretion to the extracellular compartment, we characterize novel functions of the lysine demethylase PHF8 as a pro-inflammatory, gene-specific chromatin regulator. First, in the LPS-induced, acute-inflamed macrophages, PHF8 knockdown led to both a reduction of pro-inflammatory factors and an increase in a transcriptional-repressive code (H3K9me2) written by the methyltransferase G9a. Through unbiased quantitative secretome screening we discovered that LPS induces the secretion of a cluster of PHF8-dependent, 'tolerizable' proteins that are related to diverse extracellular pathways/processes including those for the activation of adaptive immunity. Specifically, we determined that PHF8 promotes T-cell activation and proliferation, thus providing the first link between the epigenetic regulation of inflammation and adaptive immunity. Further, we found that, in the acute-inflamed macrophages, the acute-active PHF8 opposes the H3K9me1/2-writing activity of G9a to activate specific protein secretions that are suppressed by G9a in the endotoxin-tolerant cells, revealing the inflammatory-phenotypic chromatin drivers that regulate the gene-specific chromatin plasticity.

Phospholipid-binding proteins differ in their capacity to induce autoantibodies and murine systemic lupus erythematosus

We have previously shown that immunization of nonautoimmune mice with the phospholipid-binding protein β2-glycoprotein I (β2GPI), in combination with lipopolysaccharide (LPS), induces a murine model of systemic lupus erythematosus (SLE), with sequential emergence of autoantibodies and glomerulonephritis. Here, we determine whether the paradigm for induction of murine SLE extends to other phospholipid-binding proteins. Mice were immunized with a phospholipid-binding protein (prothrombin (PT), protein S, or β2GPI), or a nonphospholipid-binding protein (glu-plasminogen), in the presence of LPS. The breadth and degree of the autoantibody response, and the frequency of glomerulonephritis, varied among the three proteins, with β2GPI being the most effective in inducing SLE-like disease. The phospholipid-binding proteins also differed in the pattern of serum cytokines they elicited. The most apparent difference between β2GPI and the other phospholipid-binding proteins was in their ability to bind to LPS: β2GPI bound to LPS, while PT and protein S did not. Our data suggest that binding to phospholipid(s) is a necessary, but not sufficient, condition for full induction of murine SLE. We propose that other properties, such as physiologic function, avidity for anionic phospholipids, and degree of interaction with other cell surface and/or circulating molecules (particularly LPS) may determine the range and severity of disease.

Immunotropic effects of hexavalent chromium soluble compounds on the thymus and peripheral blood values in a subacute experiment

Intraperitoneal injections of hexavalent chromium (sodium bichromate) in the concentrations of 0.025 μg/kg (10-fold lower than MAC; group 1) and 2.5 μg/kg (10-fold higher than MAC; group 2) to rats in a subacute experiment caused dose-dependent morphological changes in the thymus: increased the counts of cells in a state of destruction, macrophages, and plasmocytes and impairs interactions between epithelial reticular cells and lymphocytes with formation of cystic cavities. Proliferation of lymphoblasts and large lymphocytes of the glandular cortical matter was detected in groups 1 and 2, of medium-sized and minor lymphocytes in group 1. Lymph node-like zones with Hassall's corpuscles, pigment foci in the cortical matter, and plasmocytes in the medulla were detected throughout the entire study in controls and in group 1 animals and on days 1 and 7 in group 2. Histiocytes, macrophages, cells in a state of destruction, and siderophages were detected in dilated lymph sinuses. Normal tissue of the gland left lobe in group 2 was completely replaced by lymph node-like zones on days 15 and 30, while the right lobe retained the structure characteristic of the gland. A dose-dependent reduction of the peripheral blood erythrocyte and platelet counts and a decrease in hemoglobin level were observed in experimental animals. On day 30 peripheral blood lympho- and leukocytosis developed at the expense of higher counts of B (CD20) and T lymphocytes (CD3) and their subpopulations - T helpers (CD4), T suppressors (CD8), and immature lymphocytes in group 1 and at the expense of higher counts of only B lymphocytes (CD20) and immature lymphocytes in group 2.

Insight into lymphoid tissue morphogenesis

Secondary lymphoid organs (SLO) are crucial structures for immune-surveillance and rapid immune responses allowing resident lymphocytes to encounter antigen-presenting cells that carry antigens from peripheral tissues. These structures develop during embryonic life through a tightly regulated process that involves interactions between haematopoietic and mesenchymal cells. Importantly, this morphogenesis potential is maintained throughout life since in chronic inflammatory conditions novel "tertiary lymphoid organs" can be generated by processes that are reminiscent of embryonic SLO development. In this review we will discuss early events in SLO morphogenesis, focusing on haematopoietic and mesenchymal cell subsets implicated on the development of lymphoid organs.

LIF in the regulation of T-cell fate and as a potential therapeutic

At the heart of lineage commitment within the adaptive immune response is the intrinsic genetic plasticity of the naive peripheral T lymphocyte (T cell). Primary activation by presentation of cognate antigen is coupled to rapid T-cell cycling and progressive epigenetic changes that guide the cell down distinct T-cell lineages, either effector (Th1, Th2, Th17) or tolerogenic (Treg). Fate choice is influenced both by strength of the priming activation signal and by cues from the micro-environment that are integrated with lineage-specific gene expression profiles, eventually becoming hard-wired in the fully differentiated cell. The micro-environmental cues include cytokines, and the discovery that leukaemia inhibitory factor (LIF) and interleukin (IL)-6 counter-regulate development of the Treg and Th17 lineages places LIF within the core regulatory circuitry of T cells. I first summarise current understanding of LIF and the LIF receptor in the context of T cells. Next, the central relevance of the LIF/IL-6 axis in immune-mediated disease is set in the context of (i) a new nano-therapeutic approach for targeted delivery of LIF and (ii) MARCH-7, a novel E3-ligase discovered to have a central mechanistic role in LIF-mediated T-cell biology, functioning as a rheostat-type regulator of endogenous LIF-signalling.

A role for IL-27p28 as an antagonist of gp130-mediated signaling

The heterodimeric cytokine interleukin 27 (IL-27) signals through the IL-27Rα subunit of its receptor, combined with gp130, a common receptor chain used by several cytokines, including IL-6. Notably, the IL-27 subunits p28 (IL-27p28) and EBI3 are not always expressed together, which suggests that they may have unique functions. Here we show that IL-27p28, independently of EBI3, antagonized cytokine signaling through gp130 and IL-6-mediated production of IL-17 and IL-10. Similarly, the ability to generate antibody responses was dependent on the activity of gp130-signaling cytokines. Mice transgenic for expression of IL-27p28 showed a substantial defect in the formation of germinal centers and antibody production. Thus, IL-27p28, as a natural antagonist of gp130-mediated signaling, may be useful as a therapeutic for managing inflammation mediated by cytokines that signal through gp130.

Therapeutic potential of LIF in multiple sclerosis

Therapies for multiple sclerosis (MS) reduce the relapse rate but are unable to stop neurological decline. Here, we evaluate the potential of leukemia inhibitory factor (LIF) as a novel therapeutic in diseases with a neurodegenerative and inflammatory component, such as MS. LIF, which can be a proinflammatory cytokine, can also modulate the immune response in a beneficial way. Recent evidence demonstrates a crucial role of LIF in neuroprotection and axonal regeneration as well as the prevention of demyelination. Finally, LIF is an important survival factor for stem cells and neuronal precursors. Therefore, we propose that LIF is a potential therapeutic candidate for MS.

Mice overexpressing murine oncostatin M (OSM) exhibit changes in hematopoietic and other organs that are distinct from those of mice overexpressing human OSM or bovine OSM

Oncostatin M (OSM) and leukemia inhibitory factor (LIF) belong to the interleukin-6 family of cytokines. The authors' previous in vitro work demonstrated that in mouse cells mouse OSM (mOSM) signals through a heterodimeric receptor complex incorporating the mOSM-specific receptor mOSMRbeta while human OSM (hOSM) and bovine OSM (bOSM) use the mouse LIF receptor mLIFRbeta rather than mOSMRbeta. These in vitro data suggest that prior studies in mouse systems with hOSM or bOSM (the usual molecules used in early studies) reflect LIF rather than OSM biology. The current work assessed whether or not this divergence in actions among these three OSMs also occurs in vivo in mouse models. Adult female (C57BL/6J x DBA/2J) F(1) mice were engineered to stably overexpress mOSM, hOSM, or bOSM by retrovirus-mediated gene transfer (n = 10 or more per group). After 4 weeks, molecular and hematologic profiles and anatomic phenotypes in multiple organs were assessed by standard techniques. Animals overexpressing either hOSM or bOSM had an identical phenotype resembling that associated with LIF activation, including significant hematologic abnormalities (anemia, neutrophilia, lymphopenia, eosinopenia, and thrombocytosis); weight loss; profound enlargement (lymph node, spleen) and/or structural reorganization (lymph node, spleen, thymus) of lymphoid organs; and severe osteosclerosis. In contrast, mice overexpressing mOSM did not develop hematologic changes, weight loss, or osteosclerosis and exhibited more modest and anatomically distinct restructuring of lymphoid organs. These data indicate that activities imputed to OSM and the mOSMRbeta signaling pathway using in vitro and in vivo mouse experimental systems are unique to mOSM.

Cytokines, leptin, and stress-induced thymic atrophy

Thymopoiesis is essential for development and maintenance of a robust and healthy immune system. Acute thymic atrophy is a complication of many infections, environmental stressors, clinical preparative regimens, and cancer treatments used today. This undesirable sequela can decrease host ability to reconstitute the peripheral T cell repertoire and respond to new antigens. Currently, there are no treatments available to protect against acute thymic atrophy or accelerate recovery, thus leaving the immune system compromised during acute stress events. Several useful murine models are available for mechanistic studies of acute thymic atrophy, including a sepsis model of endotoxin-induced thymic involution. We have identified the IL-6 cytokine gene family members (i.e., leukemia inhibitory factor, IL-6, and oncostatin M) as thymosuppressive agents by the observation that they can acutely involute the thymus when injected into a young, healthy mouse. We have gone on to explore the role of thymosuppressive cytokines and specifically defined a corticosteroid-dependent mechanism of action for the leukemia inhibitory factor in acute thymic atrophy. We also have identified leptin as a novel, thymostimulatory agent that can protect against endotoxin-induced acute thymic atrophy. This review will highlight mechanisms of stress-induced thymic involution and focus on thymosuppressive agents involved in atrophy induction and thymostimulatory agents that may be exploited for therapeutic use.

Interleukin-27 directly induces differentiation in hematopoietic stem cells

Interleukin (IL)-27, one of the most recently discovered IL-6 family cytokines, activates both the signal transducer and activator of transcription (STAT)1 and STAT3, and plays multiple roles in pro- and anti-inflammatory immune responses. IL-27 acts on various types of cells including T, B, and macrophage through the common signal-transducing receptor gp130 and its specific receptor WSX-1, but the effect of IL-27 on hematopoietic stem cells (HSCs) remains unknown. Here, we show that IL-27 together with stem cell factor (SCF) directly acts on HSCs and supports their early differentiation in vitro and in vivo. CD34(-/low)c-Kit(+)Sca-1(+)lineage marker(-) (CD34(-)KSL) cells, a population highly enriched in mouse HSCs, were found to express both IL-27 receptor subunits. In vitro cultures of CD34(-)KSL cells with IL-27 and SCF resulted in an expansion of progenitors including short-term repopulating cells, while some of their long-term repopulating activity also was maintained. To examine its in vivo effect, transgenic mice expressing IL-27 were generated. These mice exhibited enhanced myelopoiesis and impaired B lymphopoiesis in the bone marrow with extramedullary hematopoiesis in the spleen. Moreover, IL-27 similarly acted on human CD34(+) cells. These results suggest that IL-27 is one of the limited cytokines that play a role in HSC regulation.

Extrathymic rearrangement of alphabetaT-lymphocyte antigen receptor genes during pregnancy

The existence of alphabetaT-lymphocyte differentiation processes have been demonstrated in mouse peripheral lymphoid organs during pregnancy. Study of pregnant Swiss mice has shown that the development of the second half of gestation is accompanied by expression of RAG-1 recombinase mRNA and unrearranged TCR alpha-chain (pre-TCRalpha) preferentially in T-lymphocytes of lymph nodes involved in uterine drainage (para-aortal lymph nodes), and to a lesser extent in other lymph nodes (mainly from axillary lymph nodes). The data suggest that during pregnancy the differentiation of alphabetaT lymphocytes may occur not only in central (thymus) but also in peripheral lymphoid organs.

Evidence for functional inter-relationships between FOXP3, leukaemia inhibitory factor, and axotrophin/MARCH-7 in transplantation tolerance

In an ex vivo mouse model, regulatory transplantation tolerance is not only linked to Foxp3, but also to release of leukaemia inhibitory factor (LIF) and to expression of axotrophin (also known as MARCH-7), a putative ubiquitin E3 ligase associated with feedback control of T cell activation and of T cell-derived LIF. Given this coordinate correlation with tolerance, we now ask if Foxp3 expression is influenced by LIF or by axotrophin. In spleen cells from allo-rejected mice we found that exogenous LIF reduced interferon gamma release in response to donor antigen by 50%, but LIF had no direct effect on levels of Foxp3 protein in allo-primed cells that were either tolerant, or aggressive, for donor antigen. However, we did find an effect of axotrophin on Foxp3: in the axotrophin null mouse, thymic Foxp3 transcripts were reduced compared to axotrophin wildtype littermates. To test whether these findings in the mouse were of potential significance in man we measured transcript levels of axotrophin and LIF in peripheral blood cell samples collected for a recently published clinical study concerning haematopoietic stem cell recipients. In controls, human peripheral blood CD4+CD25+cells contained significantly more FOXP3 and axotrophin than CD4+CD25-cells. In bone marrow autograft recipients, where peripheral blood cell samples directly represent both the grafted tissue and the immune response, both FOXP3 and axotrophin negatively correlated with graft versus host disease (GVHD). These data suggest that (i) thymic Foxp3+T cell development is influenced by axotrophin; and (ii) clinical auto-GVHD inversely correlates with axotrophin transcript expression as has been previously reported for FOXP3.

T-cell development: an extrathymic perspective

The lymph nodes (LNs) harbor a cryptic T-lymphopoietic pathway that is dramatically amplified by oncostatin M (OM). OM-transgenic mice generate massive amounts of T lymphocytes in the absence of Lin(-)c-Kit(hi)IL-7Ralpha- lymphoid progenitors and of reticular epithelial cells. Extrathymic T cells that develop along the OM-dependent LN pathway originate from Lin(-)c-Kit(lo)IL-7Ralpha+ lymphoid progenitors and are different from classic T cells in terms of turnover kinetics and function. Positive selection does not obey the same rules in the thymus and the LNs, where positive selection of developing T cells is supported primarily by epithelial and hematopoietic cells, respectively. Extrathymic T cells undergo enhanced homeostatic proliferation and thereby acquire some properties of memory T cells. Following antigen encounter, extrathymic T-cells initiate proliferation and cytokine secretion more readily than classic T cells, but their accumulation is limited by an exquisite susceptibility to apoptosis. Studies on in vitro and in vivo extrathymic T-cell development have yielded novel insights into the essence of a primary T-lymphoid organ. Furthermore, comparison of the thymic and OM-dependent extrathymic pathways shows how the division of labor between primary and secondary lymphoid organs influences the repertoire and homeostasis of T lymphocytes.

Cyclical mobilization and gated importation of thymocyte progenitors in the adult mouse: evidence for a thymus-bone marrow feedback loop

It has recently been observed, as in the fetal thymus, that the importation of hematogenous thymocyte progenitors by the adult thymus is a gated phenomenon, whereby saturating numbers of progenitors periodically enter the thymus and occupy a finite number of intrathymic niches. In addition, the mobilization of thymocyte progenitors from the bone marrow appears to be a cyclical process that coincides temporally with the periods of thymic receptivity (open gate). It is proposed that these events are coordinated by a thymus-bone marrow feedback loop in which a wave of developing triple negative (CD3- CD4- CD8-) thymocytes interacts with stromal cells in the stratified regions of the thymus cortex to sequentially induce the release of diffusible cytokines that regulate the production, mobilization, and recruitment of thymocyte progenitors. The likely components of this feedback loop are described here, as are the properties of the intrathymic vascular gates and niches for thymocyte progenitors. The cyclical production and release of thymocyte progenitors from the bone marrow is placed in the context of a general phenomenon of oscillatory feedback regulation involving all lymphohemopoietic cell lineages. Lastly, the question of whether the gated (as opposed to the continuous) entry of thymocyte progenitors is essential for normal thymocytopoiesis in adult life is discussed.

Stem Cells in Aging: Influence of Ontogenic, Genetic and Environmental Factors

Aging is a genetically programmed decline in the functional effectiveness of the organism. It is manifested by a collective group of changes in cells or organs that occur over the course of a lifespan, limiting the duration of life. Longevity usually refers to long-lived members of a population within species. Organs develop and can involute according to specific timetables. Such timetables correlate with a preordained proliferative capacity of cells mediated by cell and organ clocks. In this review, we discuss different aspects related to genetic and environmental factors that are involved in determining life span. We discuss the influence of ontogenic, genetic and environmental factors in aging. The genetic factors can be studied in embryonic stem cells (ESC) and in niches (microenvironments) of stem cells (SC) using cellular or experimental animal models. We discuss molecular mechanisms involving genes and proteins associated with death pathways, niches, or hubs, on longevity. Moreover, we also discuss genes and proteins, associated with death pathways, on longevity. Unraveling these mechanisms may further our understanding of human aging leading to development of therapeutic interventions with the potential of prolonging life.

T-cell generation by lymph node resident progenitor cells

In the thymus, 2 types of Lin–Sca-1+ (lineage-negative stem cell antigen-1–positive) progenitors can generate T-lineage cells: c-Kithi interleukin-7 receptor α–negative (c-KithiIL-7Rα–) and c-KitloIL-7Rα+. While c-KithiIL-7Rα– progenitors are absent, c-KitloIL-7Rα+ progenitors are abundant in the lymph nodes (LNs). c-KitloIL-7Rα+ progenitors undergo abortive T-cell commitment in the LNs and become arrested in the G1 phase of the cell cycle because they fail both to up-regulate c-myb, c-myc, and cyclin D2 and to repress junB, p16INK4a, and p21Cip1/WAF. As a result, development of LN c-KitloIL-7Rα+ progenitors is blocked at an intermediate CD44+CD25lo development stage in vivo, and LN-derived progenitors fail to generate mature T cells when cultured with OP9-DL1 stromal cells. LN stroma can provide key signals for T-cell development including IL-7, Kit ligand, and Delta-like–1 but lacks Wnt4 and Wnt7b transcripts. LN c-KitloIL-7Rα+ progenitors are able to generate mature T cells when cultured with stromal cells producing wingless-related MMTV integration site 4 (Wnt4) or upon in vivo exposure to oncostatin M whose signaling pathway intersects with Wnt. Thus, supplying Wnt signals to c-KitloIL-7Rα+ progenitors may be sufficient to transform the LN into a primary T-lymphoid organ. These data provide unique insights into the essence of a primary T-lymphoid organ and into how a cryptic extrathymic T-cell development pathway can be amplified.

Insights into thymic aging and regeneration

The deterioration of the immune system with progressive aging is believed to contribute to morbidity and mortality in elderly humans due to the increased incidence of infection, autoimmunity, and cancer. Dysregulation of T-cell function is thought to play a critical part in these processes. One of the consequences of an aging immune system is the process termed thymic involution, where the thymus undergoes a progressive reduction in size due to profound changes in its anatomy associated with loss of thymic epithelial cells and a decrease in thymopoiesis. This decline in the output of newly developed T cells results in diminished numbers of circulating naive T cells and impaired cell-mediated immunity. A number of theories have been forwarded to explain this 'thymic menopause' including the possible loss of thymic progenitors or epithelial cells, a diminished capacity to rearrange T-cell receptor genes and alterations in the production of growth factors and hormones. Although to date no interventions fully restore thymic function in the aging host, systemic administration of various cytokines and hormones or bone marrow transplantation have resulted in increased thymic activity and T-cell output with age. In this review, we shall examine the current literature on thymic involution and discuss several interventional strategies currently being explored to restore thymic function in elderly subjects.

The threshold of gp130-dependent STAT3 signaling is critical for normal regulation of hematopoiesis

The interleukin-6 (IL-6) cytokine family plays an important role in regulating cellular responses during hematopoiesis. We report here that mice homozygous for a knock-in mutation in the IL-6 cytokine family receptor signaling subunit glycoprotein (gp) 130 (gp130(Y757F/Y757F)) that leads to gp130-dependent signal transducers and activators of transcription (STAT) 1/3 hyperactivation develop a broad spectrum of hematopoietic abnormalities, including splenomegaly, lymphadenopathy, and thrombocytosis. To determine whether STAT3 hyperactivation was responsible for the perturbed hematopoiesis in gp130(Y757F/Y757F) mice, we generated gp130(Y757F/Y757F) mice on a Stat3 heterozygous (Stat3(+/-)) background to specifically reduce gp130-dependent activation of STAT3, but not STAT1. Normal hematopoiesis was observed in gp130(Y757F/Y757F):Stat3(+/-) bone marrow and spleen, with no evidence of the splenomegaly and thrombocytosis displayed by gp130(Y757F/Y757F) mice. The perturbed cellular composition of thymus and lymph nodes in gp130(Y757F/Y757F) mice was also alleviated in gp130(Y757F/Y757F): Stat3(+/-) mice. Furthermore, we show that hematopoietic cells from gp130(Y757F/Y757F) mice exhibited increased survival and proliferation in response to IL-6 family cytokines. Collectively, these data provide genetic evidence that gp130-dependent STAT3 hyperactivation during hematopoiesis has pathological consequences affecting multiple organs, and therefore identify the threshold of STAT3 signaling elicited by IL-6 family cytokines as a critical determinant for hematopoietic homeostasis.

Identification of the leukemia inhibitory factor cell targets within the rat testis

Leukemia inhibitory factor (LIF), a pleiotropic cytokine, is expressed in the rat testis and produced predominantly by peritubular myoid cells. The aims of this study were to characterize the testicular cell targets of LIF and to identify the role of LIF in the testis. The LIF receptor (LIF-R)/gp190 transcript was detected by reverse transcription-polymerase chain reaction (RT-PCR) in the rat testis from Day 13.5 postcoitum until adulthood. Seven highly purified testicular cell populations, representative of the major testicular constituents, were studied at transcriptional and protein levels by, respectively, RT-PCR and flow cytometry with biotinylated-LIF. Spermatogonia and, to a lesser extent, the somatic cells, exhibited specific LIF-binding sites. These results were strengthened by in situ analysis, showing predominant LIF-R immunoreactivity in spermatogonia at all ages studied. In addition to the 190-kDa LIF-R, Western blot analysis revealed the presence of a 50- to 60-kDa C-terminal gp190 isoform. This truncated form, which is unable to bind LIF, was the only form expressed in meiotic germ cells, suggesting an original down-regulation process of LIF-R expression during spermatogenesis. Finally, we showed that LIF increased [3H]-thymidine incorporation in spermatogonia in microdissected, cultured seminiferous tubules. Taken together, our results strongly suggest that LIF has a role in the regulation of the spermatogonial cell compartment.

IL-6 signal transduction and its physiological roles: the signal orchestration model

Interleukin (IL)-6 is a pleiotropic cytokine that not only affects the immune system, but also acts in other biological systems and many physiological events in various organs. In a target cell, IL-6 can simultaneously generate functionally distinct or sometimes contradictory signals through its receptor complex, IL-6Ralpha and gp130. One good illustration is derived from the in vitro observations that IL-6 promotes the growth arrest and differentiation of M1 cells through gp130-mediated STAT3 activation, whereas the Y759/SHP-2-mediated cascade by gp130 stimulation has growth-enhancing effects. The final physiological output can be thought of as a consequence of the orchestration of the diverse signaling pathways generated by a given ligand. This concept, the signal orchestration model, may explain how IL-6 can elicit proinflammatory or anti-inflammatory effects, depending on the in vivo environmental circumstances. Elucidation of the molecular mechanisms underlying this issue is a challenging subject for future research. Intriguingly, recent in vivo studies indicated that the SHP-2-binding site- and YXXQ-mediated pathways through gp130 are not mutually exclusive but affect each other: a mutation at the SHP-2-binding site prolongs STAT3 activation, and a loss of STAT activation by gp130 truncation leads to sustained SHP-2/ERK MAPK phosphorylation. Although IL-6/gp130 signaling is a promising target for drug discovery for many human diseases, the interdependence of each signaling pathway may be an obstacle to the development of a nonpeptide orally active small molecule to inhibit one of these IL-6 signaling cascades, because it would disturb the signal orchestration. In mice, a consequence of the imbalanced signals causes unexpected results such as gastrointestinal disorders, autoimmune diseases, and/or chronic inflammatory proliferative diseases. However, lessons learned from IL-6 KO mice indicate that IL-6 is not essential for vital biological processes, but a significant impact on disease progression in many experimental models for human disorders. Thus, IL-6/gp130 signaling will become a more attractive therapeutic target for human inflammatory diseases when a better understanding of IL-6 signaling, including the identification of the conductor for gp130 signal transduction, is achieved.

Involvement of growth factors in thymic involution

The thymus undergoes an age-dependent degenerative process which is mainly characterized by a progressive loss of lymphoid tissue. Thymic involution is particularly important in relation to immunosenescence and its various associated diseases; this fact has prompted many studies aimed at understanding the causes and mechanisms of thymic degeneration which may, ultimately, lead to the possibility of manipulating it. In this sense, one of the aspects which has deserved most attention is the thymic microenvironment, and more precisely, the many growth factors to which the cells present in the organ are exposed. Thus, the levels of several of such factors have been reported to undergo age-dependent changes in the thymus, which may point at an influence on the regression of the organ. In this article we consider which growth factors and growth factor receptors occur in the vertebrate thymus. Then, focusing on those whose influences are better documented, i.e., neurotrophins, cytokines and IGFs, we discuss their potential role in the organ and the possibility of their being involved in thymic involution.

Gated Importation of Prothymocytes by Adult Mouse Thymus Is Coordinated with Their Periodic Mobilization from Bone Marrow

The wavelike pattern of fetal T cell neogenesis is largely determined by the intermittent generation and exportation of waves of prothymocytes by the hemopoietic tissues in coordination with their gated importation by the thymus. Having previously shown that the importation of prothymocytes by the adult mouse thymus is also gated and that thymocytopoiesis proceeds in discrete (albeit overlapping) waves, we now demonstrate that prothymocytes are periodically exported in saturating numbers from the adult mouse bone marrow. Experiments in normal, radioablated, and parabiotic mice document the cyclical accumulation (3-5 wk) of prothymocytes in both the steady state and regenerating bone marrow, followed by their release into the blood approximately 1 wk before intrathymic gate opening. The results also show that circulating donor-origin thymocyte precursors can transiently ( approximately 1 wk) establish high level chimerism in the bone marrow after the mobilization of endogenous prothymocytes, presumably by occupying vacated microenvironmental niches. Hence, by analogy with the fetal state, we posit the existence of a feedback loop whereby diffusible chemokines of thymic origin regulate the production and/or release of bone marrow prothymocytes during each period of thymic receptivity. Because each resulting wave of thymocytopoiesis is accompanied by a wave of intrathymic dendritic cell formation, these coordinated events may help to optimize thymocyte selection as well as production.

The unsolved enigmas of leukemia inhibitory factor

Leukemia inhibitory factor (LIF) is a polyfunctional glycoprotein cytokine whose inducible production can occur in many, perhaps all, tissues. LIF acts on responding cells by binding to a heterodimeric membrane receptor composed of a low-affinity LIF-specific receptor and the gp130 receptor chain also used as the receptor for interleukin-6, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. LIF is essential for blastocyst implantation and the normal development of hippocampal and olfactory receptor neurons. LIF is used extensively in experimental biology because of its key ability to induce embryonic stem cells to retain their totipotentiality. LIF has a wide array of actions, including acting as a stimulus for platelet formation, proliferation of some hematopoietic cells, bone formation, adipocyte lipid transport, adrenocorticotropic hormone production, neuronal survival and formation, muscle satellite cell proliferation, and acute phase production by hepatocytes. Unwanted actions of LIF can be minimized by circulating soluble LIF receptors and by intracellular suppression by suppressors of cytokine-signaling family members. However, the outstanding problems remain of how the induction of LIF is mediated in response to demands from such a heterogeneity of target tissues and why it makes design sense to use LIF in the regulation of such a diverse and unrelated series of biological processes.

Changes in the lymph node microenvironment induced by oncostatin M

Oncostatin M (OM) transforms the lymph node (LN) into a "super lymphoid organ" with 2 striking features: massive thymus-independent T-cell development and major expansion of the memory T-cell pool. We report that T-cell development in the LckOM LN is regulated by a cyclooxygenase-2 (COX-2)-dependent neoangiogenesis involving high endothelial venules (HEVs). That LN HEVs are particularlyrich in OM-receptor beta-chain provides aplausible explanation for the fact that extrathymic T-cell development in LckOM mice is limited to the LN. Moreover, we found that increased production of the CCL20 chemokine by LN stromal cells was instrumental in the expansion of the memory phenotype CD4 T-cell pool in LckOM mice. The generality of the latter finding was demonstrated by the fact that CCL20/CCR6 interactions increase the basal proliferation rate of CD62L(lo) CD4 T cells irrespective of their thymic (in non-OM-transgenic mice) or extrathymic (in LckOM mice) origin. To our knowledge, CCL20 is the first molecule found to increase the proliferation of memory phenotype CD4 T cells. These findings identify potential targets for the creation of thymic substitutes (LN HEVs) and for expansion of the CD4 memory T-cell compartment (CCL20).

Thymic and extrathymic T cell development pathways follow different rules

Separation between primary and secondary lymphoid organs is a universal feature in jawed vertebrates. Strikingly, oncostatin M (OM)-transgenic mice present massive extrathymic T cell development, localized exclusively in the lymph nodes (LN). According to the prevailing paradigm, the thymus is the main source of T lymphocytes in gnathostomes mainly because thymic epithelial cells have a unique ability to support early steps in T cell development. It is therefore remarkable that productive T cell development occurs in the OM(+) LN, despite the absence of epithelial cells. The present study shows that in the OM(+) LN: 1) MHC class I expression strictly on hemopoietic cells is sufficient to support the development of a diversified repertoire of CD8 T cells; 2) the efficiency of positive selection of specific TCR-transgenic T cells is not the same as in the thymus; 3) negative selection is very effective, despite the lack of an organized thymic-like medulla. Furthermore, our data suggest that extrathymic T lymphocytes developing in the OM(+) LN undergo extensive postselection expansion because they live in the microenvironment in which they were positively selected. This work illustrates how the division of labor between primary and secondary lymphoid organs influences the repertoire and homeostasis of T lymphocytes.

Persistent infection of human thymic epithelial cells by coxsackievirus B4

Persistent replication of coxsackievirus B4 (CVB4) E2 (diabetogenic) and CVB4 JBV (nondiabetogenic) strains in thymic epithelial cell (TEC)-enriched cultures (>or=95%) was proved by detection of positive- and negative-strand viral RNA by reverse transcription-PCR in extracted RNA from cell cultures, VP1 capsid protein detection by immunofluorescence (IF) staining, and release of infectious particles up to 30 days after infection without obvious cytolysis. By double-IF staining, cytokeratin-containing cells were shown to be susceptible to CVB4. The persistence of CVB4 was associated with a significantly increased rate of TEC proliferation (up to 70%) after 20 days of culture and a significantly increased chronic production of immunoreactive interleukin-6 (IL-6), leukemia inhibitory factor, and granulocyte-macrophage colony-stimulating factor in supernatant after 3 days of culture. The CVB4 replication and the release of cytokines were not restricted to the CVB4 E2 diabetogenic strain and did not depend on the genetic background of the host; however, TEC were more responsive to CVB4 E2 than CVB4 JBV as far as the production of cytokines.

The molecular control of hematopoiesis: progress and problems with gene manipulation

The in vitro-based discovery and characterization of hematopoietic regulators were of great value in identifying many of the agents active in controlling hematopoiesis. Subsequent in vivo studies have validated most of the information obtained from the in vitro studies, although the in vitro studies proved to be somewhat misleading in predicting which agents would exhibit the greatest quantitative effects in vivo. Establishing more clearly the actual situation in vivo has required a return to more complex, and often less satisfactory, studies on genetically-manipulated whole animals. Of the two possible general approaches, gene inactivation models have proved more informative than transgenic, overexpression models. Each model has raised multiple questions in need of further resolution and the deletion studies have also indicated that other regulators must exist for various lineages, but have yet to be discovered. Of particular interest is the finding from gene inactivation studies that both G-CSF and thrombopoietin are necessary for the maintenance of normal numbers of progenitor cells in multiple lineages, suggesting that each of these lineage-dominant regulators may have broader actions when operating on cells in the stem cell and progenitor cell compartments.

Human thymic epithelial cells inhibit IL-15- and IL-2-driven differentiation of NK cells from the early human thymic progenitors

T/NK progenitors are present in the thymus; however, the thymus predominantly promotes T cell development. In this study, we demonstrated that human thymic epithelial cells (TEC) inhibit NK cell development. Most ex vivo human thymocytes express CD1a, indicating that thymic progenitors are predominantly committed to the T cell lineage. In contrast, the CD1a(-)CD3(-)CD56(+) NK population comprises only 0.2% (n = 7) of thymocytes. However, we observed increases in the percentage (20- to 25-fold) and absolute number (13- to 71-fold) of NK cells when thymocytes were cultured with mixtures of either IL-2, IL-7, and stem cell factor or IL-15, IL-7, and stem cell factor. TEC, when present in the cultures, inhibited the increases in the percentage (3- to 10-fold) and absolute number (3- to 25-fold) of NK cells. Furthermore, we show that TEC-derived soluble factors inhibit generation of NK-CFU and inhibit IL15- or IL2-driven NK cell differentiation from thymic CD34(+) triple-negative thymocytes. The inhibitory activity was found to be associated with a 8,000- to 30,000 Da fraction. Thus, our data demonstrate that TEC inhibit NK cell development from T/NK CD34(+) triple negative progenitors via soluble factor(s), suggesting that the human thymic microenvironment not only actively promotes T cell maturation but also controls the development of non-T lineage cells such as the NK lineage.

Leukemia inhibitory factor gene improves skin allograft survival in the mouse model

BACKGROUND

Leukemia inhibitory factor (LIF) is a widely expressed cytokine involved in both local and systemic immune response. Furthermore, it has been implicated in various immunological processes including thymic T cell maturation and embryo implantation. We investigated implication of various modalities in the application of prolonged and viable allograft to the wound, using cytokines and growth factors.

MATERIALS

BALB/c and B6D2F1 strains of mice were used either as a skin graft donor or host. LIF cDNA inserted in plasmid vector or the vector alone was injected intradermally in graft skin and observed up to 21 days. LIF, LIF-receptor, gp130, as well as type 1 and 2 T helper cytokine expressions were investigated by reverse transcription polymerasse chain reaction, in situ hybridization, and histological studies.

RESULTS

LIF cDNA-treated groups showed significantly improved graft survival compared to the vector-treated control in 21 days postoperatively for grafting from B6D2F1 to BALB/c and BALB/c to B6D2F1. LIF and LIF receptor mRNA expressions were observed 24 hr and 21 days posttransplantation. The gp130 expression was only observed in LIF-treated B6D2F1 to BALB/c allografting on day 21 posttransplantation. LIF transcripts were strongly present in the epidermal, dermal, and subdermal tissues as determined by an in situ hybridization of LIF-treated grafting.

CONCLUSIONS

These results suggest that LIF cDNA treatment is an effective and beneficial adjuvant for the skin allograft survival. Improved skin allograft modulation by cytokine gene transfer is a potentially promising therapy for temporary large skin coverage.

gp130 Cytokine family and bone cells

Bone tissue is continually being remodelled according to physiological circumstances. Two main cell populations (osteoblasts and osteoclasts) are involved in this process, and cellular activities (including cell differentiation) are modulated by hormones, cytokines and growth factors. Within the last 20 years, many factors involved in bone tissue metabolism have been found to be closely related to the inflammatory process. More recently, a cytokine family sharing a common signal transducer (gp130) had been identified, which appears to be a key factor in bone remodelling. This family includes interleukin 6, interleukin 11, oncostatin M, leukaemia inhibitory factor, ciliary neurotrophic factor and cardiotrophin-1. This paper provides an exhaustive review of recent knowledge on the involvement of gp130 cytokine family in bone cell (osteoblast, osteoclast, etc.) differentiation/activation and in osteoarticular pathologies.

Radiation-associated loss of heterozygosity at the Znfn1a1 (Ikaros) locus on chromosome 11 in murine thymic lymphomas

Although information on the molecular pathways in radiation carcinogenesis is accumulating, the data are still relatively scanty. To find the tumor suppressor locus associated with radiation carcinogenesis, we determined the frequency and distribution of loss of heterozygosity (LOH) of X-ray-induced thymic lymphomas of B6C3F(1) mice using 58 microsatellite markers and compared the results with those for spontaneous lymphomas and N-ethylnitrosourea (ENU)-induced lymphomas. Based on the results, we describe a unique locus with frequent LOH in the centromeric region of chromosome 11 of X-ray-induced lymphomas. This locus has never been observed to be altered similarly in either ENU-induced or spontaneous lymphomas, suggesting radiation-specific molecular alteration. The LOH patterns of individual thymic lymphomas indicated that the common region of LOH was located within 1.6 cM between D11Mit62 and D11Mit204, a region syntenic to human chromosome 7p13. Linkage analysis revealed that the markers of the common LOH region were genetically linked to Ikaros (now known as Znfn1a1), a master gene of lymphopoiesis. Although the presence of radiation-associated LOH in other loci cannot be ruled out, these results suggest a novel molecular pathway in induction of thymic lymphomas by ionizing radiation.

The role of the thymus in immune reconstitution in aging, bone marrow transplantation, and HIV-1 infection

The human thymus is a complex chimeric organ comprised of central (thymic epithelial space) and peripheral (perivascular space) components that functions well into adult life to produce naive T lymphocytes. Recent advances in identifying thymic emigrants and development of safe methods to study thymic function in vivo in adults have provided new opportunities to understand the role that the human thymus plays in immune reconstitution in aging, in bone marrow transplantation, and in HIV-1 infection. The emerging concept is that there are age-dependent contributions of thymic emigrants and proliferation of postthymic T cells to maintain the peripheral T cell pool and to contribute to T cell regeneration, with the thymus contributing more at younger ages and peripheral T cell expansion contributing more in older subjects. New studies have revealed a dynamic interplay between postnatal thymus output and peripheral T cell pool proliferation, which play important roles in determining the nature of immune reconstitution in congenital immunodeficiency diseases, in bone marrow transplantation, and in HIV-1 infection. In this paper, we review recent data on human postnatal thymus function that, taken together, support the notion that the human thymus is functional well into the sixth decade and plays a role throughout life to optimize human immune system function.

Renal synthesis of leukaemia inhibitory factor (LIF), under normal and inflammatory conditions

Leukaemia inhibitory factor (LIF) is a pleiotropic cytokine that is particularly involved in nephrogenesis and repair of the extracellular matrix. Transgenic mice overexpressing LIF have mesangial proliferative glomerulonephritis. Also, during local inflammatory reactions, such as kidney graft rejection or urinary tract infections, urinary LIF excretion is enhanced. The aim of the study therefore was to study LIF production by normal and inflammatory diseased kidneys (glomerulonephritis or graft rejection), maintained in short cultures. To determine the responsibility of the kidney itself in LIF synthesis, we measured LIF secretion into the culture supernatants of human mesangial or renal tubular epithelial cells. Fragments from diseased kidneys, whether grafts or not, released more LIF than normal human kidney fragments, mesangial or renal tubular epithelial cells. However, LIF production was delayed in renal transplants compared to glomerulonephritic samples taken from untreated patients. In every case, LIF production was enhanced by interleukin 1beta (IL-1beta) and inhibited by IL-4 or dexamethasone, except in two severe rejection episodes. So, LIF appeared to respond to pro- and anti-inflammatory stimuli, in vitro and in vivo. Considering its biological effects, LIF could play a role in inflammatory renal diseases.

Leukemia inhibitory factor expression and regulation within the testis

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine known to control the proliferation and survival of stem cells including primordial germ cells and gonocytes. This led us to study the origin and regulation of testicular LIF. The LIF transcript was detected in the rat testis by RT-PCR from 13.5 days postcoitum until adulthood. LIF expression was investigated further in vitro in seven different highly purified testicular cell populations using RT-PCR and bioassays combined with neutralization experiments. LIF was found to be produced by peritubular cells and, to a much lesser extent, by the other testicular somatic cell types. No LIF was detected in meiotic and postmeiotic germ cell-conditioned medium, and only low levels of LIF were detected in spermatogonia-conditioned medium. Large amounts of bioactive LIF were measured in testicular lymph. While LIF production was greatly enhanced in presence of serum, lipopolysaccharide, and TNFalpha further increased this production in peritubular and Sertoli cells, and human CG enhanced Leydig cell LIF production. In conclusion, peritubular cells are the principal source of testicular LIF, probably accounting for its high concentration in the lymph. Given the proliferative effect of LIF on immature germ cells, we suggest that peritubular LIF plays an important role in the regulation of testicular function.

Leukemia inhibitory factor, oncostatin M, IL-6, and stem cell factor mRNA expression in human thymus increases with age and is associated with thymic atrophy

The roles that thymus cytokines might play in regulating thymic atrophy are not known. Reversing thymic atrophy is important for immune reconstitution in adults. We have studied cytokine mRNA steady-state levels in 45 normal human (aged 3 days to 78 years) and 34 myasthenia gravis thymuses (aged 4 to 75 years) during aging, and correlated cytokine mRNA levels with thymic signal joint (sj) TCR delta excision circle (TREC) levels, a molecular marker for active thymopoiesis. LIF, oncostatin M (OSM), IL-6, M-CSF, and stem cell factor (SCF) mRNA were elevated in normal and myasthenia gravis-aged thymuses, and correlated with decreased levels of thymopoiesis, as determined by either decreased keratin-positive thymic epithelial space or decreased thymic sjTRECs. IL-7 is a key cytokine required during the early stages of thymocyte development. Interestingly, IL-7 mRNA expression did not fall with aging in either normal or myasthenia gravis thymuses. In vivo administration of LIF, OSM, IL-6, or SCF, but not M-CSF, i.p. to mice over 3 days induced thymic atrophy with loss of CD4+, CD8+ cortical thymocytes. Taken together, these data suggest a role for thymic cytokines in the process of thymic atrophy.

The oncostatin M signalling pathway: reversing the neoplastic phenotype?

Oncostatin M (OSM) is a member of the interleukin 6 (IL-6) family of cytokines and was originally identified by its ability to inhibit proliferation of melanoma cells but augment the growth of normal fibroblasts. OSM has pleiotropic effects on many different cell types, but here we focus on its ability to inhibit the proliferation of cell lines derived from several tumour types, including breast carcinoma, ovarian cancer, melanoma, glioma and lung carcinoma. The inhibition of proliferation of several cancer cell lines by OSM is associated with alterations in cellular morphology and with phenotypic changes that are consistent with the induction of differentiation of these cells. These observations raise the possibility that OSM could have therapeutic potential.