Regulation of cytokine production in the human thymus: epidermal growth factor and transforming growth factor alpha regulate mRNA levels of interleukin 1 alpha (IL-1 alpha), IL-1 beta, and IL-6 in human thymic epithelial cells at a post-transcriptional level

Obesity-induced thymic involution and cancer risk

Declining thymic functions associated either with old age (i.e., age-related thymic involution), or with acute involution as a result of stress, infectious disease, or cytoreductive therapies (e.g., chemotherapy/radiotherapy), have been associated with cancer development. A key mechanism underlying such increased cancer risk is the thymus-dependent debilitation of adaptive immunity, which is responsible for orchestrating immunoediting mechanisms and tumor immune surveillance. In the past few years, a blooming set of evidence has intriguingly linked obesity with cancer development and progression. The majority of such studies has focused on obesity-driven chronic inflammation, steroid/sex hormone and adipokine production, and hyperinsulinemia, as principal factors affecting the tumor microenvironment and driving the development of primary malignancy. However, experimental observations about the negative impact of obesity on T cell development and maturation have existed for more than half a century. Here, we critically discuss the molecular and cellular mechanisms of obesity-driven thymic involution as a previously underrepresented intermediary pathology leading to cancer development and progression. This knowledge could be especially relevant in the context of childhood obesity, because impaired thymic function in young individuals leads to immune system abnormalities, and predisposes to various pediatric cancers. A thorough understanding behind the molecular and cellular circuitries governing obesity-induced thymic involution could therefore help towards the rationalized development of targeted thymic regeneration strategies for obese individuals at high risk of cancer development.

Thymus Gland: A Double Edge Sword for Coronaviruses

The thymus is the main lymphoid organ that regulates the immune and endocrine systems by controlling thymic cell proliferation and differentiation. The gland is a primary lymphoid organ responsible for generating mature T cells into CD4+ or CD8+ single-positive (SP) T cells, contributing to cellular immunity. Regarding humoral immunity, the thymic plasma cells almost exclusively secrete IgG1 and IgG3, the two main complement-fixing effector IgG subclasses. Deformity in the thymus can lead to inflammatory diseases. Hassall’s corpuscles’ epithelial lining produces thymic stromal lymphopoietin, which induces differentiation of CDs thymocytes into regulatory T cells within the thymus medulla. Thymic B lymphocytes produce immunoglobulins and immunoregulating hormones, including thymosin. Modulation in T cell and naive T cells decrement due to thymus deformity induce alteration in the secretion of various inflammatory factors, resulting in multiple diseases. Influenza virus activates thymic CD4+ CD8+ thymocytes and a large amount of IFNγ. IFNs limit virus spread, enhance macrophages’ phagocytosis, and promote the natural killer cell restriction activity against infected cells. Th2 lymphocytes-produced cytokine IL-4 can bind to antiviral INFγ, decreasing the cell susceptibility and downregulating viral receptors. COVID-19 epitopes (S, M, and N proteins) with ≥90% identity to the SARS-CoV sequence have been predicted. These epitopes trigger immunity for antibodies production. Boosting the immune system by improving thymus function can be a therapeutic strategy for preventing virus-related diseases. This review aims to summarize the endocrine-immunoregulatory functions of the thymus and the underlying mechanisms in the prevention of COVID-19.

Thymus Degeneration and Regeneration

The immune system’s ability to resist the invasion of foreign pathogens and the tolerance to self-antigens are primarily centered on the efficient functions of the various subsets of T lymphocytes. As the primary organ of thymopoiesis, the thymus performs a crucial role in generating a self-tolerant but diverse repertoire of T cell receptors and peripheral T cell pool, with the capacity to recognize a wide variety of antigens and for the surveillance of malignancies. However, cells in the thymus are fragile and sensitive to changes in the external environment and acute insults such as infections, chemo- and radiation-therapy, resulting in thymic injury and degeneration. Though the thymus has the capacity to self-regenerate, it is often insufficient to reconstitute an intact thymic function. Thymic dysfunction leads to an increased risk of opportunistic infections, tumor relapse, autoimmunity, and adverse clinical outcome. Thus, exploiting the mechanism of thymic regeneration would provide new therapeutic options for these settings. This review summarizes the thymus’s development, factors causing thymic injury, and the strategies for improving thymus regeneration.

Plasma cytokines associated with febrile status epilepticus in children: A potential biomarker for acute hippocampal injury

OBJECTIVE

Our aim was to explore the association between plasma cytokines and febrile status epilepticus (FSE) in children, as well as their potential as biomarkers of acute hippocampal injury.

METHODS

Analysis was performed on residual samples of children with FSE (n = 33) as part of the Consequences of Prolonged Febrile Seizures in Childhood study (FEBSTAT) and compared to children with fever (n = 17). Magnetic resonance imaging (MRI) was obtained as part of FEBSTAT within 72 h of FSE. Cytokine levels and ratios of antiinflammatory versus proinflammatory cytokines in children with and without hippocampal T2 hyperintensity were assessed as biomarkers of acute hippocampal injury after FSE.

RESULTS

Levels of interleukin (IL)-8 and epidermal growth factor (EGF) were significantly elevated after FSE in comparison to controls. IL-1β levels trended higher and IL-1RA trended lower following FSE, but did not reach statistical significance. Children with FSE were found to have significantly lower ratios of IL-1RA/IL-1β and IL-1RA/IL-8. Specific levels of any one individual cytokine were not associated with FSE. However, lower ratios of IL-1RA/IL-1β, IL-1RA/1L-6, and IL-1RA/ IL-8 were all associated with FSE. IL-6 and IL-8 levels were significantly higher and ratios of IL-1RA/IL-6 and IL-1RA/IL-8 were significantly lower in children with T2 hippocampal hyperintensity on MRI after FSE in comparison to those without hippocampal signal abnormalities. Neither individual cytokine levels nor ratios of IL-1RA/IL-1β or IL-1RA/IL-8 were predictive of MRI changes. However, a lower ratio of IL-1RA/IL-6 was strongly predictive (odds ratio [OR] 21.5, 95% confidence interval [CI] 1.17-393) of hippocampal T2 hyperintensity after FSE.

SIGNIFICANCE

Our data support involvement of the IL-1 cytokine system, IL-6, and IL-8 in FSE in children. The identification of the IL-1RA/IL-6 ratio as a potential biomarker of acute hippocampal injury following FSE is the most significant finding. If replicated in another study, the IL-1RA/IL-6 ratio could represent a serologic biomarker that offers rapid identification of patients at risk for ultimately developing mesial temporal lobe epilepsy (MTLE).

Expression of RAGE and HMGB1 in thymic epithelial tumors, thymic hyperplasia and regular thymic morphology

Recently, a role of the receptor for advanced glycation endproducts (RAGE) in myasthenia gravis was described. RAGE and its ligand high mobility group box 1 (HMGB1) play key roles in autoimmunity and cancer. To test whether these molecules are involved in patients with thymic abnormalities we applied immunohistochemical analysis in 33 cases of thymic epithelial tumors, comprising 27 thymomas and 6 thymic carcinomas, and 21 nonneoplastic thymuses. Both molecules were detected in neoplastic epithelial cells: RAGE staining was most intense in WHO type B2 thymomas and thymic carcinomas (p<0.001). HMGB1 nuclear staining was strongest in A and AB, and gradually less in B1 = B2>B3>thymic carcinoma (p<0.001). Conversely, HMGB1 cytoplasmic staining intensities were as follows: A and AB (none), B1 (strong), B2 (moderate), B3 and thymic carcinoma (weak); (p<0.001). Fetal thymic tissue showed a distinct expression of RAGE and HMGB1 in subcapsular cortical epithelial cells which was found in 50% of myasthenic patients. Furthermore RAGE and HMGB1 were expressed in thymocytes, macrophages, Hassall's corpuscles, thymic medulla, and germinal center cells in myasthenic patients. Immunohistochemistry results were complemented by systemic measurements (immunosorbent assay): serum levels of soluble RAGE were significantly reduced in patients with epithelial tumors (p = 0.008); and in invasive tumors (p = 0.008). Whereas RAGE was equally reduced in thymic hyperplasia and epithelial tumors (p = 0.003), HMGB1 was only elevated in malignancies (p = 0.036). Results were most pronounced in thymic carcinomas. Thus, RAGE and HMGB1 are involved in the (patho-)physiology of thymus, as evidenced by differentiated thymic and systemic expression patterns that may act as diagnostic or therapeutic targets in autoimmune disease and cancer.

Epidermal growth factor protects squamous cell carcinoma against cisplatin-induced cytotoxicity through increased interleukin-1β expression

The expression of cytokines, such as IL-1β, and the activation of the epidermal growth factor receptor (EGFR) are crucial regulators in the process of carcinogenesis. The correlation between growth factor and activated cytokine signals in the control of tumor development is a critical issue to be clarified. In our study, we found that the IL-1β gene and protein expression were induced by EGF in squamous cell carcinoma. To clarify the mechanism involved in EGF-regulated IL-1β expression, we examined the transcriptional activity and mRNA stability of IL-1β in EGF-treated cells. We found that EGF induced the expression of IL-1β and was mediated through transcriptional activation, but not through mRNA stability. The involvement of Akt and NF-κB signaling pathways in the EGF-induced IL-1β gene expression was confirmed by knockdown of RelA and Akt in cells or treating cells with Akt and NF-κB inhibitors, LY294002 and parthenolide, respectively. The expression of dominant negative IκB also repressed the activation of NF-κB and inhibited EGF-induced IL-1β expression. Using immunofluorescence staining assay, the EGF-stimulated nuclear translocation of NF-κB (p65) was inhibited by pre-treating cells with LY294002 and parthenolide. Furthermore, EGF increased the binding of NF-κB to the NF-κB binding site of the IL-1β promoter through the activation of the Akt/NF-κB pathway, which resulted in activating IL-1β promoter activity. The expression and secretion of IL-1β induced by EGF considerably reduced chemotherapeutic drug cisplatin-induced cell death. These results showed that EGF enhanced the expression of IL-1β, which was mediated by the Akt/NF-κB pathway. The activation of EGF signaling and increase of IL-1β contributed to chemotherapeutic resistance of cancer cells, suggesting that the expression of IL-1β may be used as a biomarker to evaluate successful cancer treatment.

TSLP and immune homeostasis

In an immune system, dendritic cells (DCs) are professional antigen-presenting cells (APCs) as well as powerful sensors of danger signals. When DCs receive signals from infection and tissue stress, they immediately activate and instruct the initiation of appropriate immune responses to T cells. However, it has remained unclear how the tissue microenvironment in a steady state shapes the function of DCs. Recent many works on thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine that has the strong ability to activate DCs, provide evidence that TSLP mediates crosstalk between epithelial cells and DCs, involving in DC-mediated immune homeostasis. Here, we review recent progress made on how TSLP expressed within the thymus and peripheral lymphoid and non-lymphoid tissues regulates DC-mediated T-cell development in the thymus and T-cell homeostasis in the periphery.

Synergistic and multidimensional regulation of plasminogen activator inhibitor type 1 expression by transforming growth factor type β and epidermal growth factor

The major physiological inhibitor of plasminogen activator, type I plasminogen activator inhibitor (PAI-1), controls blood clotting and tissue remodeling events that involve cell migration. Transforming growth factor type β (TGFβ) and epidermal growth factor (EGF) interact synergistically to increase PAI-1 mRNA and protein levels in human HepG2 and mink Mv1Lu cells. Other growth factors that activate tyrosine kinase receptors can substitute for EGF. EGF and TGFβ regulate PAI-1 by synergistically activating transcription, which is further amplified by a decrease in the rate of mRNA degradation, the latter being regulated only by EGF. The combined effect of transcriptional activation and mRNA stabilization results in a rapid 2-order of magnitude increase in the level of PAI-1. TGFβ also increases the sensitivity of the cells to EGF, thereby recruiting the cooperation of EGF at lower than normally effective concentrations. The contribution of EGF to the regulation of PAI-1 involves the MAPK pathway, and the synergistic interface with the TGFβ pathway is downstream of MEK1/2 and involves phosphorylation of neither ERK1/2 nor Smad2/3. Synergism requires the presence of both Smad and AP-1 recognition sites in the promoter. This work demonstrates the existence of a multidimensional cellular mechanism by which EGF and TGFβ are able to promote large and rapid changes in PAI-1 expression.

Regulatory T-cell trafficking: from thymic development to tumor-induced immune suppression

Regulatory T cells (Tregs) have become a priority for many investigators in immunology due to their potent immunosuppressive and tolerogenic effects. While Treg activity is required for normal immune homeostasis, dysregulation of their numbers can induce autoimmunity or aid in the pathogenesis of disease. Therefore, great effort has been made to understand the mechanisms by which Tregs accumulate in different areas of the body. Like other lymphocytes, Tregs migrate in response to a network of chemotactic stimuli involving chemokines, chemokine receptors, integrins, and their corresponding ligands. However, many of these stimuli are exclusive to Tregs, inducing their migration while leaving conventional populations unaffected. It is these selective stimuli that result in increased ratios of Tregs among conventional effector populations, leading to changes in immune suppression and homeostasis. This review explores selective Treg trafficking during thymic Treg development, migration to secondary lymphoid tissues and emigration into the periphery during homeostatic conditions, inflammation, and the tumor microenvironment, placing emphasis on stimuli that selectively recruits Tregs to target locations.

Somatic cell plasticity and Niemann-Pick type C2 protein: fibroblast activation

A growing body of evidence points toward activated fibroblasts, also known as myofibroblasts, as one of the leading mediators in several major human pathologies including proliferative fibrotic disorders, invasive tumor growth, rheumatoid arthritis, and atherosclerosis. Niemann-Pick Type C2 (NPC2) protein has been recently identified as a product of the second gene in NPC disease. It encodes ubiquitous, highly conserved, secretory protein with the poorly defined function. Here we show that NPC2 deficiency in human fibroblasts confers their activation. The activation phenomenon was not limited to fibroblasts as it was also observed in aortic smooth muscle cells upon silencing NPC2 gene by siRNA. More importantly, activated synovial fibroblasts isolated from patients with rheumatoid arthritis were also identified as NPC2-deficient at both the NPC2 mRNA and protein levels. The molecular mechanism responsible for activation of NPC2-null cells was shown to be a sustained phosphorylation of ERK 1/2 mitogen-activated protein kinase (MAPK), which fulfills both the sufficient and necessary fibroblast activation criteria. All of these findings highlight a novel mechanism where NPC2 by negatively regulating ERK 1/2 MAPK phosphorylation may efficiently suppress development of maladaptive tissue remodeling and inflammation.

Evaluation of patulin toxicity in the thymus of growing male rats

Patulin is a mycotoxin produced by several Penicillium, Aspergillus, and Byssachlamys species growing on food products. In this study, we investigated the effects of patulin on the thymus of growing male rats aged five to six weeks. The rats were receiving it orally at a dose of 0.1 mg kg-1 bw a day for either 60 or 90 days. At the end of the experiment, the thymus was examined for histopathology by light microscopy and for epidermal growth factor (EGF) and its receptor (EGFR) by immunolocalisation. For morphometry we used the Bs200prop program to analyse images obtained with the Olympus BX51 light microscope. Cell ultrastructure was studied by electron microscopy. In rats treated with patulin, the thymus showed haemorrhage, plasma cell hyperplasia, a dilation and fibrosis in the cortex, enlarged interstitial tissue between the thymic lobules, enlarged fat tissue, thinning of the cortex, and blurring of the cortico-medullary demarcation. Electron microscopy showed signs of cell destruction, abnormalities of the nucleus and organelles, and loss of mitochondrial cristae. However, no differences were observed in thymus EGF and EGFR immunoreactivity between treated and control rats.

Vitamin-regulated cytokines and growth factors in the CNS and elsewhere

There is a growing awareness that natural vitamins (with the only exception of pantothenic acid) positively or negatively modulate the synthesis of some cytokines and growth factors in the CNS, and various mammalian cells and organs. As natural vitamins are micronutrients in the human diet, studying their effects can be considered a part of nutritional genomics or nutrigenomics. A given vitamin selectively modifies the synthesis of only a few cytokines and/or growth factors, although the same cytokine and/or growth factor may be regulated by more than one vitamin. These effects seem to be independent of the effects of vitamins as coenzymes and/or reducing agents, and seem to occur mainly at genomic and/or epigenetic level, and/or by modulating NF-kappaB activity. Although most of the studies reviewed here have been based on cultured cell lines, but their findings have been confirmed by some key in vivo studies. The CNS seems to be particularly involved and is severely affected by most avitaminoses, especially in the case of vitamin B(12). However, the vitamin-induced changes in cytokine and growth factor synthesis may initiate a cascade of events that can affect the function, differentiation, and morphology of the cells and/or structures not only in the CNS, but also elsewhere because most natural vitamins, cytokines, and growth factors cross the blood-brain barrier. As cytokines are essential to CNS-immune and CNS-hormone system communications, natural vitamins also interact with these circuits. Further studies of such vitamin-mediated effects could lead to vitamins being used for the treatment of diseases which, although not true avitaminoses, involve an imbalance in cytokine and/or growth factor synthesis.

TSLP in epithelial cell and dendritic cell cross talk

Dendritic cells (DCs) are professional antigen-presenting cells that have the ability to sense infection and tissue stress, sample and present antigen to T lymphocytes, and instruct the initiation of different forms of immunity and tolerance. The functional versatility of DCs depends on their remarkable ability to translate collectively the information from the invading microbes, as well as their resident tissue microenvironments. Recent progress in understanding Toll-like receptor (TLR) biology has illuminated the mechanisms by which DCs link innate and adaptive antimicrobial immune responses. However, how tissue microenvironments shape the function of DCs has remained elusive. Recent studies of TSLP (thymic stromal lymphopoietin), an epithelial cell-derived cytokine that strongly activates DCs, provide strong evidence at a molecular level that epithelial cells/tissue microenvironments directly communicate with DCs, the professional antigen-presenting cells of the immune system. We review recent progress on how TSLP expressed within thymus and peripheral lymphoid and nonlymphoid tissues regulates DC-mediated central tolerance, peripheral T cell homeostasis, and inflammatory Th2 responses.

Thymus atrophy during Trypanosoma cruzi infection is caused by an immuno-endocrine imbalance

C57BL/6 mice infected with Trypanosoma cruzi, the causal agent of Chagas' disease, develop severe thymocyte depletion paralleled by an inflammatory syndrome mediated by tumor necrosis factor-alpha (TNF-alpha). The exacerbated inflammatory reaction induces the activation of hypothalamus-pituitary-adrenal (HPA) axis with the consequent release of corticosterone (CT) into the circulation as a protective response. Thymocyte apoptosis has been related to a rise in TNF-alpha and CT levels, and both mediators are increased in T. cruzi-infected C57BL/6 mice. The depletion of immature CD4(+)CD8(+) thymocytes by apoptosis following infection with the parasite was still present in mice defective in both types of TNF-receptors (double knockout). However, thymic atrophy was prevented by adrenalectomy combined with RU486 administration, demonstrating that this is a CT-driven phenomenon. Our results put emphasis on the importance of an appropriated immuno-endocrine balance during T. cruzi infection and show that functional deviations in the immuno-endocrine equilibrium have profound effects on the thymus and disease outcome.

HB-EGF induces delayed STAT3 activation via NF-kappaB mediated IL-6 secretion in vascular smooth muscle cell

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family that binds to and activates EGF receptor, and is expressed in a variety of tissues, predominantly in the lung, heart, brain and skeletal muscle. HB-EGF is known to induce vascular smooth muscle cell (VSMC) proliferation by activating PI3K-Akt and MAPK pathway. However, our preliminary data showed that Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway was also involved in HB-EGF induced VSMC proliferation. More interestingly, HB-EGF (10 ng/ml) induced a biphasic activation of STAT3 (early at 5 min and late at 60-120 min). Therefore, we tried to elucidate the underlying mechanism of this delayed STAT3 activation by HB-EGF in VSMCs. First, we examined the effect of HB-EGF on interleukin-6 (IL-6) mRNA expressions, since IL-6 have been implicated in the regulation of STAT3 activation. According to our data, HB-EGF increased transcription of IL-6, cardiotrophin-1 (CT-1), leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF). The secretion of IL-6 was also increased by HB-EGF. Furthermore, these HB-EGF-mediated up-regulation of IL-6 mRNA expression and secretion were inhibited by NF-kappaB inhibitor Bay117082 (2.5 microM) treatment suggesting involvement of NF-kappaB pathway. Again, the late activation of STAT3 by HB-EGF was abolished by both Bay117082 and IL-6 neutralizing antibody (1 microg/ml) indicating IL-6 is a key molecule in the delayed activation of STAT3 by HB-EGF. In addition, IL-6 neutralizing antibody inhibited both HB-EGF conditioned media induced STAT3 activation and HB-EGF induced VSMC proliferation. In conclusion, IL-6 plays an important role in the delayed activation of STAT3 and VSMC proliferation induced by HB-EGF.

TSLP: an epithelial cell cytokine that regulates T cell differentiation by conditioning dendritic cell maturation

Dendritic cells (DCs) are professional antigen-presenting cells that have the ability to sense infection and tissue stress, sample and present antigen to T lymphocytes, and induce different forms of immunity and tolerance. The functional versatility of DCs depends on their remarkable ability to translate collectively the information from both the invading microbes and their resident tissue microenvironments and then make an appropriate immune response. Recent progress in understanding TLR biology has illuminated the mechanisms by which DCs link innate and adaptive antimicrobial immune responses. However, how tissue microenvironments shape the function of DCs has remained elusive. Recent studies of TSLP (thymic stromal lymphopoietin), an epithelial cell-derived cytokine that strongly activates DCs, provide evidence at a molecular level that epithelial cells/tissue microenvironments directly communicate with DCs. We review recent progress on how TSLP expressed within thymus and peripheral lymphoid and nonlymphoid tissues regulates DC-mediated central tolerance, peripheral T cell homeostasis, and inflammatory Th2 responses.

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.

Reduction of urate crystal-induced inflammation by root extracts from traditional oriental medicinal plants: elevation of prostaglandin D2 levels

Dried roots of the plants Acanthopanax senticosus, Angelica sinensis and Scutellaria baicalensis are used in traditional oriental medicine and reportedly possess anti-inflammatory properties. Using the murine air pouch model of inflammation, we investigated the efficacy and mode of action of an extract from these three plants in crystal-induced inflammation. Air pouches were raised on the backs of 8-week-old BALB/c mice. Mice were fed 100 mg/kg body weight of root extracts (A. senticosus:A. sinensis:S. baicalensis mixed in a ratio of 5:4:1 by weight) or vehicle only on days 3-6. Inflammation was elicited on day 6 by injecting 2 mg of monosodium urate (MSU) crystals into the pouch. Neutrophil density and IL-6 and TNF-alpha mRNA levels were determined in the pouch membrane, and the leukocyte count and IL-6, prostaglandin E2 (PGE2) and prostaglandin D2 (PGD2) levels were determined in the pouch exudate. Treatment with the root extracts led to a reduction in all inflammatory parameters: the leukocyte count in the pouch exudate decreased by 82%; the neutrophil density in the pouch membrane decreased by 68%; IL-6 and TNF-alpha mRNA levels in the pouch membrane decreased by 100%; the IL-6 concentration in the pouch fluid decreased by 50%; and the PGE2 concentration in the pouch fluid decreased by 69%. Remarkably, the concentration of the potentially anti-inflammatory PGD2 rose 5.2-fold in the pouch exudate (p < 0.005), which led to a normalization of the PGD2:PGE2 ratio. A 3.7-fold rise in hematopoietic PGD synthase (h-PGDS) mRNA paralleled this rise in PGD2 (p = 0.01). Thus, the root extracts diminished MSU crystal-induced inflammation by reducing neutrophil recruitment and expression of pro-inflammatory factors and increasing the level of the potentially anti-inflammatory PGD2. These results support a need for further studies of the efficacy of these extracts in the treatment of inflammatory arthropathies and suggest elevation of PGD2 levels as a novel mechanism for an anti-inflammatory agent.

Thymic stromal lymphopoietin in normal and pathogenic T cell development and function

Thymic stromal lymphopoietin, a four helix-bundle cytokine, is expressed mainly by barrier epithelial cells and is a potent activator of several cell types, particularly myeloid dendritic cells. TSLP influences the outcome of interactions between dendritic cells and CD4+ thymocytes and T cells in many situations, such as the regulation of the positive selection of regulatory T cells, maintenance of peripheral CD4+ T cell homeostasis and induction of CD4+ T cell-mediated allergic inflammation.

Hassall's corpuscles instruct dendritic cells to induce CD4+CD25+ regulatory T cells in human thymus

Hassall's corpuscles-first described in the human thymus over 150 years ago-are groups of epithelial cells within the thymic medulla. The physical nature of these structures differs between mammalian species. Although Hassall's corpuscles have been proposed to act in both the removal of apoptotic thymocytes and the maturation of developing thymocytes within the thymus, the function of Hassall's corpuscles has remained an enigma. Here we report that human Hassall's corpuscles express thymic stromal lymphopoietin (TSLP). Human TSLP activates thymic CD11c-positive dendritic cells to express high levels of CD80 and CD86. These TSLP-conditioned dendritic cells are then able to induce the proliferation and differentiation of CD4(+)CD8(-)CD25(-) thymic T cells into CD4(+)CD25(+)FOXP3(+) (forkhead box P3) regulatory T cells. This induction depends on peptide-major histocompatibility complex class II interactions, and the presence of CD80 and CD86, as well as interleukin 2. Immunohistochemistry studies reveal that CD25(+)CTLA4(+) (cytotoxic T-lymphocyte-associated protein 4) regulatory T cells associate in the thymic medulla with activated or mature dendritic cells and TSLP-expressing Hassall's corpuscles. These findings suggest that Hassall's corpuscles have a critical role in dendritic-cell-mediated secondary positive selection of medium-to-high affinity self-reactive T cells, leading to the generation of CD4(+)CD25(+) regulatory T cells within the thymus.

Upregulation of receptor activator of nuclear factor-kappaB ligand expression in the thymic subcapsular, paraseptal, perivascular, and medullary epithelial cells during thymus regeneration

The receptor activator of nuclear factor (NF)-kappaB ligand (RANKL; also termed TRANCE/OPGL/ODF/TNFSF11), a new member of the tumor-necrosis factor (TNF) superfamily, was identified as a key cytokine involved in the differentiation of the immune system and the regulation of immunity as well as in bone metabolism. In particular, RANKL-deficient mice showed defects in the early differentiation of T lymphocytes, suggesting that RANKL is a novel regulator of early thymocyte development. Here, we describe the expression of RANKL during regeneration following acute involution induced by cyclophosphamide in the rat thymus. The present study demonstrates the presence and upregulated expression of the RANKL in thymic subcapsular, paraseptal, perivascular, and medullary epithelial cells during thymus regeneration. Our results suggest that the RANKL expressed in these thymic epithelial cells plays a role in the development of T cells during thymic regeneration.

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.

Upregulation of TrkA neurotrophin receptor expression in the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration

Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. Here, we report upon an examination of the expression of the TrkA neurotrophin receptor, the high affinity receptor for nerve growth factor, during regeneration following acute involution induced by cyclophosphamide in the rat thymus. Light and electron microscopic immunocytochemistry demonstrated enhanced expression of the TrkA receptor in the subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration. In addition, various morphological alterations, suggestive of a hyperfunctional and dynamic state, of the subcapsular, paraseptal, and perivascular epithelial cells were also observed. The presence of TrkA protein in extracts from the control and regenerating rat thymus was confirmed by western blot. Furthermore, RT-PCR analysis supported these results by demonstrating that thymic extracts contain TrkA mRNA at higher levels during thymus regeneration. Thus, our results suggest that the TrkA receptor located on the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells could play a role in the development of new T cells to replace T cells damaged during thymus regeneration.

1 alpha,25-Dihydroxyvitamin D3 inhibits pro-inflammatory cytokine and chemokine expression in human corneal epithelial cells colonized with Pseudomonas aeruginosa

The cytokines IL-1 beta, IL-6 and the chemokine IL-8 are key mediators of host inflammation. 1 alpha,25-Dihydroxyvitamin D3 (VD3) has been shown to regulate host immune responses in vivo and in vitro. The purpose of this study was to investigate whether the addition of VD3 to human corneal epithelial cells colonized with Pseudomonas aeruginosa altered the expression of IL-1 beta, IL-6 and IL-8. An immortalized human corneal epithelial (HCE) cell line was used in this study. After growth to confluency, HCE cells were challenged with P. aeruginosa strain 6294 in the presence or absence of 10-6 mol/L VD3 for 4 h, 8 h and 12 h. Gene expression of IL-1 beta, IL-6 and IL-8 was detected by reverse transcription-PCR (RT-PCR) from total RNA extracted from HCE cells. Protein concentrations of IL-1 beta, IL-6 and IL-8 in culture supernatants were measured by ELISA. Addition of VD3 to HCE cells colonized with P. aeruginosa significantly inhibited the expression of IL-1 beta and IL-8 mRNA and protein (P < 0.05). Although the expression of IL-6 mRNA was stimulated at 12 h post-challenge (P < 0.05), the expression of IL-6 protein was inhibited at all time points after the addition of VD3. In conclusion, this study demonstrated that VD3 inhibited the P. aeruginosa-induced expression of IL-1 beta, IL-6 and IL-8 in HCE cells, suggesting that this vitamin may have the potential to become a novel anti-inflammatory agent in ocular disease.

Cobalamin (vitamin B(12)) positively regulates interleukin-6 levels in rat cerebrospinal fluid

We have previously demonstrated that the repeated intracerebroventricular (i.c.v.) microinjection of interleukin-6 (IL-6) prevented the myelinolytic lesions of cobalamin-deficient (Cbl-D) central neuropathy [or subacute combined degeneration (SCD)] in totally gastrectomized (TGX) rats. We therefore hypothesized that cobalamin (Cbl) may actually regulate IL-6 levels in rat cerebrospinal fluid (CSF). We measured IL-6 levels in the CSF of rats made Cbl-D by means of total gastrectomy (TG) or chronic feeding with a Cbl-D diet and killed at different times from the beginning of the experiment, and found that IL-6 levels significantly and progressively decreased over time. Chronic 2-month Cbl administration started 1 week after surgery prevented the decrease in IL-6 levels and, when it was started 2 months after surgery, it significantly increased IL-6 levels, but not to presurgical values. We also investigated whether IL-6 decrease might be ultimately due to the Cbl-deficiency-linked decrease in epidermal growth factor (EGF) synthesis. Repeated i.c.v. administrations of EGF to TGX rats did not modify CSF IL-6 levels. These results, together with those of a previous study showing the preventive effect of IL-6 treatment on SCD lesions, demonstrate that: (i) Cbl selectively regulates CSF IL-6 levels; and (ii) decreased IL-6 availability plays a role in the pathogenesis of the experimental SCD, in which no evidence of inflammatory and/or immunological reaction has been observed.

Autoimmunization to epidermal growth factor, a component of the immunological homunculus

Epidermal growth factor (EGF) is being tried as a vaccine in cancer immunotherapy with the aim of inducing neutralizing antibodies that might affect EGF-dependent tumors. Here we summarize our experience using the EGF self-molecule as an autoimmunigen. We report here that IgG anti-EGF antibodies are prevalent in healthy people and that augmentation of the response to EGF requires conjugation to an effective carrier and an adjuvant. Paradoxically, the response to EGF immunization could be enhanced by an 'immunosuppressive' treatment with cyclophosphamide, most probably by suppressing active control mechanisms. EGF is expressed in the thymus. Thus, EGF may be added to the immunological homunculus, the class of self-antigens to which there is both natural autoimmunity and natural regulation of the autoimmunity. The results using EGF as a vaccine can teach us about the homunculus and how to activate it.

Cytokine mRNA and protein expression in primary-culture and repeated-passage synovial fibroblasts from patients with rheumatoid arthritis

Constitutive mRNA expression and secretion of proinflammatory and anti-inflammatory cytokines was comparatively analyzed in rheumatoid arthritis (RA) synovial fibroblasts (SFB), isolated from primary culture or derived by repeated passage; normal-skin fibroblasts were used as controls. First-passage RA-SFB (n = 3) secreted large amounts of IL-6 (15,800 +/- 2,110 pg/ml; mean +/- SEM), but only limited amounts of tumor necrosis factor (TNF)-alpha (22.1 +/- 1.1 pg/ml) or IL-10 (35.7 +/- 34.2 pg/ml; only one of three samples was positive). IL-1beta, IL-15, and IL-18 were not detectable at the protein level and showed very low mRNA levels by semiquantitative RT-PCR. In repeated-passage RA-SFB (tenth passage), protein secretion was significantly lower for IL-6 (one-twentieth of the initial level) and TNF-alpha (two-thirds), and markedly reduced for IL-10 (one-quarter, with only one of three samples positive). While the decrease of IL-10 protein from first to tenth passage was paralleled by a corresponding decrease of mRNA, the relative mRNA levels for IL-6 and TNF-alpha were actually increased (20-fold and 300-fold, respectively), indicating post-transcriptional and/or post-translational regulation of these cytokines. Due to highly variable levels among individual patients, however, no significant differences were observed for any cytokine mRNA between primary-culture and repeated-passage RA-SFB (ninth passage). Likewise, no significant differences were detectable between RA-SFB and normal-skin fibroblasts (primary-culture and repeated-passage). By producing high amounts of IL-6 and limited amounts of TNF-alpha, RA-SFB may contribute to the (im)balance of proinflammatory and anti-inflammatory cytokines in the inflamed joint.

The human thymus during aging

The human thymus is required for establishment of a normal T cell repertoire in fetal development, as children born without a thymus (DiGeorge Syndrome) lack thymus-derived (T) and T cell immunity. While the function of the thymus in children for production of new T cells is clear, it has not been obvious that the adult thymus can produce significant numbers of new T cells. Until recently, no assays were available to directly evaluate postnatal thymic function. This paper reviews work on human thymic aging at Duke University School of Medicine and discusses the relevance of this work to devising new strategies for T cell immune reconstitution in man.

The thymus at the crossroad of neuroimmune interactions

The numerous relationships existing between the nervous and the immune systems suggest that the neural networks present in the intrathymic microenvironment may influence T-cell development. We previously reported that thymic neural-crest-derived stromal cells are involved in a neural differentiation pathway and are able to produce neurotrophic factors and neurokines that are in turn able to increase and/or modulate thymic-stromal cell neuronal phenotype. We also showed that EGF promotes a neural phenotype in thymic epithelial cells by enhancing the expression of neuronal-specific markers, neurotransmitters, and neuropoietic cytokines, such as IL-6 and CNTF. More recently we showed that the effect of EGF in directing thymic epithelial cells toward a neural-oriented cell fate is mediated by modulating the expression of genes directly involved in neurotypic differentiation (i.e., thrombospondin-1). EGF-induced regulation of stromal cells may also affect T-cell differentiation, as we observed that an EGF-pretreatment reduces the ability of thymic epithelial cells to sustain thymocyte differentiation in vitro. Finally, we demonstrated that a complex network involving the neurotrophin BDNF and its specific receptors may have a role in sustaining thymocyte precursor survival and supporting the thymocyte differentiation process. All together, our results suggest that the thymus may be the site of integration of different neuroimmune networks that are potentially involved in the regulation of thymocyte survival and/or differentiation.

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.

Human thymic epithelial cells maintain long-term survival of clonogenic myeloid and erythroid progenitor cells in vitro

Precursor cells that migrate into the thymus are still multipotent. Therefore, thymic epithelial cells (TECs) may provide microenvironments not only for T-cell development, but also for maintenance of multipotent precursor cells until they undergo T-cell commitment. In the present study, we performed long-term cultures of CD34+ bone-marrow (BM) cells on TEC lines that were derived from cortical epithelial cells of post-natal thymus, to investigate whether human TECs could maintain long-term nonlymphoid haematopoiesis. Haematopoietic cells maintained in direct contact with established TEC lines were able to generate clonogenic progeny to both myeloid and erythroid cells for periods in excess of 5 weeks. Their abilities to support colony-forming units of granulocytes-macrophages (CFU-GM) and burst-forming units of erythroids (BFU-E) were almost equal to those of BM stromal cells. We observed similar results by using cloned TEC lines derived by limiting dilution, as well as those by using parental TEC lines. Colony-forming activities were maintained even when haematopoietic progenitor cells were physically separated from TEC lines and cultured on microporous membrane. These observations indicate that haematopoiesis maintained in TEC-contact long-term cultures may depend on soluble factors produced by TEC lines. Our results suggest that thymic cortical epithelial cells have the ability to support not only the differentiation of haematopoietic cells, but also long-term survival of clonogenic myeloid/erythroid progenitor cells.

The brain and thymus have much in common: a functional analysis of their microenvironments

Research into the neural and immune systems has begun to converge. Since the first reports that interleukins play important roles in both systems and that lymphocytes secrete neuronal factors, scientists have been surprised by the ever-increasing list of interactions. Here, Rolf Mentlein and Marion Kendall examine the major supporting cells of the brain and thymus - astrocytes and thymic epithelial cells - the similar neuroectodermal origin of which could explain such fundamental analogies.

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.

Dynamic regulation of the proinflammatory cytokine, interleukin-1beta: molecular biology for non-molecular biologists

Interleukin-1beta (IL-1beta) is a key mediator and modulator of a wide array of physiological responses important for survival. It is created by a variety of cell types, including immune cells, glia, and neurons. It is a very potent biological molecule, acting both at the periphery as well as within the central nervous system. The production and release of IL-1beta is tightly regulated by far more complex processes than previously thought. An appreciation of this complexity is necessary for proper interpretation of apparent contradictions in the literature where different aspects of IL-1beta expression are measured. Given that many researchers are not molecular biologists by training, yet need an appreciation of the controls that regulate the function of key proteins such as IL-1beta, this review is aimed at both: (a) clarifying the multiple levels at which IL-1beta production is modulated and (b) using IL-1beta regulation to explain the dynamics of gene regulation to non-molecular biologists. Three major topics will be discussed. First, regulation of IL-1beta production will be examined at every level from extracellular signals that trigger gene activation through release of active protein into the extracellular fluid. Second, regulation of IL-1beta bioavailability and bioactivity will be discussed. This section examines the fact that even after IL-1beta is released, it may or may not be able to exert a biological action due to multiple modulatory factors. Last is the introduction of the idea that IL-1beta regulation is, at times, beyond the direct control of host; that is, when IL-1beta production becomes dysregulated by pathogens.

The human thymus. A chimeric organ comprised of central and peripheral lymphoid components

The human thymus is a lymphoepithelial organ in which T cells develop during fetal life. After maturation and selection in the fetal thymic microenvironment, T cells emigrate to peripheral lymphoid tissues such as the spleen, gut, and lymph nodes, and establish the peripheral T cell repertoire. Although the thymus has enormous regenerative capacity during fetal development, the regenerative capacity of the human postnatal thymus decreases over time. With the advent of intensive chemotherapy regimens for a variety of cancer syndromes, and the discovery that infection with the Human Immunodeficiency Virus (HIV) leads to severe loss of CD4+ T cells, has come the need to understand the role of the human thymus in reconstitution of the immune system in adults. During a recent study of the thymus in HIV infection, we observed many CD8+ T cells in AIDS thymuses that had markers consistent with those of mature effector cytotoxic T cells usually found in peripheral immune tissues, and noted these CD8+ effector T cells were predominantly located in a thymic zone termed the thymic perivascular space. This article reviews our own work on the thymus in HIV-1 infection, and discusses the work of others that, taken together, suggest that the thymus contains peripheral immune cell components not only in the setting of HIV infection, but also in myasthenia gravis, as well as throughout normal life during the process of thymus involution. Thus, the human thymus can be thought of as a chimeric organ comprised of both central and peripheral lymphoid tissues. These observations have led us to postulate that the thymic epithelial atrophy and decrease in thymopoiesis that occurs in myasthenia gravis, HIV-1 infection, and thymic involution may in part derive from cytokines or other factors produced by peripheral immune cells within the thymic perivascular space.

The human thymus. A chimeric organ comprised of central and peripheral lymphoid components

The human thymus is a lymphoepithelial organ in which T cells develop during fetal life. After maturation and selection in the fetal thymic microenvironment, T cells emigrate to peripheral lymphoid tissues such as the spleen, gut, and lymph nodes, and establish the peripheral T cell repertoire. Although the thymus has enormous regenerative capacity during fetal development, the regenerative capacity of the human postnatal thymus decreases over time. With the advent of intensive chemotherapy regimens for a variety of cancer syndromes, and the discovery that infection with the Human Immunodeficiency Virus (HIV) leads to severe loss of CD4+ T cells, has come the need to understand the role of the human thymus in reconstitution of the immune system in adults. During a recent study of the thymus in HIV infection, we observed many CD8+ T cells in AIDS thymuses that had markers consistent with those of mature effector cytotoxic T cells usually found in peripheral immune tissues, and noted these CD8+ effector T cells were predominately located in a thymic zone termed the thymic perivascular space. This article reviews our own work on the thymus in HIV-1 infection, and discusses the work of others that, taken together, suggest that the thymus contains peripheral immune cell components not only in the setting of HIV infection, but also in myasthenia gravis, as well as throughout normal life during the process of thymus involution. Thus, the human thymus can be thought of as a chimeric organ comprised of both central and peripheral lymphoid tissues. These observations have led us to postulate that the thymic epithelial atrophy and decrease in thymopoiesis that occurs in myasthenia gravis, HIV-1 infection, and thymic involution may in part derive from cytokines or other factors produced by peripheral immune cells within the thymic perivascular space.

Epidermal Growth Factor (EGF) Modulates Fetal Thymocyte Growth and Differentiation: Partial Reversal by Insulin, Mimicking by Specific Inhibitors of EGF Receptor Tyrosine Kinase Activity, and Differential Expression of CD45 Phosphatase Isotypes

We have recently reported that epidermal growth factor (EGF) modulates thymocyte development in fetal thymus organ cultures. Exogenously added EGF arrested thymocyte growth and differentiation, acting at the transition from the CD4−CD8− (double-negative (DN)) to the CD4+CD8+ (double-positive (DP)) phenotype. In this study, we further investigate some molecular aspects of this blockade. This inhibitory effect could be mimicked by tyrphostins, which are selective inhibitors of EGF receptor kinase activity. An attempt to use insulin (INS) as a synergizing effector resulted in partial restoration of lobe cellularity, leading to expansion of the CD44−CD25+ DN subset. However, INS did not overcome the EGF-driven blockade of the thymocyte DN → DP transition. Analysis of CD45 phosphatase showed that this transition was preceded by a rise in CD45RB isotype expression. At the end of a 7-day culture, the remaining DN cells from both EGF- and EGF+INS-treated fetal thymus organ cultures showed a CD45RB− phenotype and were negative for the EGF-immunoreactive molecule described previously on the fetal thymocyte surface. This finding implies that neither molecule is related to the growth capability of cells at this early developmental stage; it is more likely that the molecules are related to subsequent events in the thymocyte pathway to the DP phenotype. Thus, our data support the concept that EGF receptor-related circuitry may be relevant in thymus ontogeny. Additionally, evidence is provided for the duality between growth and differentiation at this particular early stage of thymocyte development.

Epidermal growth factor enhances spontaneous sleep in rabbits

Several growth factors are implicated in sleep regulation. Epidermal growth factor (EGF) is found in the brain, and it influences the production of several sleep-promoting substances. We determined, therefore, whether administration of exogenous EGF affected spontaneous sleep in rabbits. Twenty-five rabbits were implanted with electroencephalographic electrodes, a brain thermistor, and an intracerebroventricular guide cannula. Three doses of EGF (0.5, 5, and 25 microg) were used. The animals were injected intracerebroventricularly with saline as control and one dose of EGF on 2 separate days. Five and twenty-five micrograms of EGF enhanced non-rapid eye movement sleep and increased brain temperature. The 25-microg dose of EGF also inhibited rapid eye movement sleep across the 23-h postinjection recording period. Results are consistent with the hypothesis that EGF, like other growth factors, could be involved in sleep regulation.

Transcriptional regulation of interleukin-1beta gene by interleukin-1beta itself is mediated in part by Oct-1 in thymic stromal cells

Interleukin (IL)-1 is involved in many processes, including thymic development. However, control of IL-1 expression in thymic-derived stromal cells (TSC) has not been reported. We found that IL-1beta increased steady-state mRNA levels for IL-1alpha and IL-1beta in TSC-936 and TSC-2C4 cells; stability was not a major determinant of this effect. To study transcriptional regulation of IL-1beta, we functionally characterized 4 kilobase pairs of the 5'-flanking region and first intron of the bovine IL-1beta gene. The -470/+14 fragment was sufficient to confer maximal responsiveness to IL-1beta upon transfection into these cell lines. Progressive 5' deletions identified several IL-1beta-responsive regions, including -308 to -226, which we further characterized. Electrophoretic mobility shift and supershift analyses showed that IL-1beta induced the ability to form multiple protein complexes with -261/-226 and that one of these contained nuclear factor Oct-1. A competitor containing a mutated Oct consensus site failed to compete not only for this complex but others as well, suggesting that this sequence regulates binding of other proteins to this region. Functional analysis confirmed that this element was essential for maximal induction of transcription. These findings document a heretofore undescribed mechanism utilized by TSC for regulation of IL-1beta transcription by IL-1beta itself.

Molecular mechanisms regulating induction of interleukin-6 gene transcription by interferon-gamma

The multifunctional cytokine interleukin-6 (IL-6) plays a central role in host defence mechanisms and hematopoiesis. Furthermore, dysregulation of IL-6 gene expression is associated with the pathogenesis of various immunologically related diseases such as myeloma, systemic lupus erythematosus, rheumatoid arthritis, psoriasis and Kaposi's sarcoma. The regulation of IL-6 gene expression occurs mainly at transcriptional level, although mechanisms of post-transcriptional regulation have also been described. In the present study we demonstrate that in HeLa cells, induction of IL-6 by interferon-gamma (IFN-gamma) is transcriptionally controlled, as shown by run on assays and analysis of the IL-6 mRNA stability. Gel-retardation experiments using antibodies specific for factors of the IRF family identified four protein-DNA complexes, which bind to the interferon regulatory factor (IRF) binding site at position -267 to -254, in nuclear extracts from IFN-gamma treated cells. Furthermore, transient transfection analyses of the 5'-flanking region of IL-6 gene linked to the chloramphenicol acetyltransferase (CAT) reporter gene demonstrated that the -267 to -254 IRF site is necessary for IL-6 induction by IFN-gamma. However, transfection experiments in which IRF-1 and I kappa B alpha were overexpressed show that full-scale transcriptional activation of the IL-6 promoter directing CAT expression requires the co-operation between IRF-1 and NF-kappa B at a low constitutive level.

Thymic epithelial cell culture

Culture of epithelial cells from the thymus of children and laboratory animals has been used for more than two decades to evaluate both the nature of these cells and their importance in the selection and maturation of functional T cells. Especially by the use of serum-free cultures and by establishment of cell lines from cultured thymic epithelial cells (TEC), it has been possible to obtain basic information on morphology of subpopulations of TEC, including surface determinants of importance for interactions with T-cell precursors, and on the repertoire of cytokines secreted by different types of TEC. The available information, obtained by co-culture of pre-T cells and TEC, on the effects of TEC on the fate of pre-T cells suggests that cultured TEC/TEC lines are able both to secrete needed cytokines for T-cell development, and to deliver signals needed for T-cell selection. In vivo results showing cross-talk between TEC and T cells indicate that more careful evaluation of interactions between well-defined subtypes of cultured TEC and co-cultured subpopulations of pre-T cells (as well as macrophages/dendritic cells) will be of importance in evaluation of the function of the thymus.

Regulation of interleukin (IL)-1alpha, IL-1beta, and IL-6 expression by growth hormone and prolactin in bovine thymic stromal cells

Growth hormone (GH) and prolactin (PRL) have been implicated in T-cell development, but relatively little is known about the mechanism(s) of their actions on the multiple cell types in this complex tissue. Here, we investigated the effects of GH and PRL on the expression of interleukin (IL)-1alpha, IL-1beta and IL-6 in thymic stromal cells (TSC). These cytokine mRNAs were increased by GH, PRL and placental lactogen (PL) in primary cultures prepared from mid-gestational fetuses in a dose-dependent manner. IL-1 receptor antagonist (IL-1ra) abolished the hormone-induced IL-6 expression, suggesting that the induction of IL-6 was secondary to IL-1 activity. To examine the effects of these hormones on an individual cell type and develop a system in which signalling mechanisms can be studied, we generated immortalized cell lines using a strategy of conditional transformation. In the cell line, TSC-936, which displayed vimentin-positive staining and morphological characteristics of mesenchymal cells, both GH and PRL increased levels of steady-state mRNAs for IL-1alpha and IL-1beta. Nuclear run-on analysis revealed that the transcription rate of the IL-1beta gene was significantly increased by GH and PRL at 30 and 60 min, respectively, but that for IL-1alpha was not significantly changed, suggesting the possibility of an alternative mechanism mediating this response. These data suggest that modulation of cytokine gene expression is one mechanism by which GH and PRL facilitate thymic development and T-cell maturation.

Vascular Cell Adhesion Molecule-1 Is Expressed by Cortical Thymic Epithelial Cells and Mediates Thymocyte Adhesion. Implications for the Function of α4β1 (VLA4) Integrin in T-Cell Development

T-cell development requires a series of discrete selection and activation signals delivered to maturing progenitors in the thymic cortex and medulla. We have previously shown the constitutive activity of the integrin, α4β1 (VLA4), on a unique subpopulation of immature cortical thymocytes and proposed a role for integrin-mediated adhesion in positive selection by cortical epithelium. In the present report we show that thymic epithelial cell lines express vascular cell adhesion molecule-1 (VCAM-1) a high-affinity ligand for α4β1, and that VCAM-1 mediates thymocyte binding to these lines. Immunohistochemistry and confocal microscopy show that VCAM-1 is selectively expressed in situ by thymic epithelium in the cortex and corticomedullary junction, two locations at which VCAM-1 could determine the interaction between immature thymocytes and selecting elements on epithelial cells. In parallel, we confirmed that fibronectin (FN), the alternative ligand for α4β1, is expressed predominantly in the medulla. These results suggest that VCAM-1 is an adhesive ligand in the thymic cortex for the activated form of α4β1 constitutively expressed during development by immature double positive thymocytes. The structural segregation of the alternative ligand, FN, to the medulla suggests that medullary FN may regulate the migration, development, and export of more mature thymocytes.

Cytokine production by human thymic epithelial cells: control by the immune recognition of the neurohypophysial self-antigen

Oxytocin (OT) has been shown to be the dominant peptide of the neurohypophysial family expressed by thymic epithelial and nurse cells (TEC/TNC) in various species. Thymic OT is not secreted but, after translocation of a hybrid neurophysin/MHC class I protein, is integrated within the plasma membrane of TEC, thus allowing its presentation to pre-T cells. In order to further demonstrate that thymic OT behaves like a membrane antigen, we assessed the effect of mAbs to OT on cytokine productions by cultures enriched in human TEC. 75-85% pure TEC cultures were prepared from human thymic fragments. Using immunofluorescence and confocal microscopy, ir-OT, ir-interleukin-1 beta (IL-1 beta), ir-interleukin-6 (IL-6) and ir-leukemia inhibitory factor (LIF) could be detected in these TEC cultures. ir-OT was restricted to TEC, while some ir-IL-6 and ir-LIF were also seen in occasional fibroblasts. In basal conditions, ir-IL-6 and ir-LIF (but not ir-OT and ir-IL-1 beta) were detected in the supernatants of human TEC cultures. MAbs to OT induced a marked increase of ir-IL-6 and ir-LIF secretion in TEC cultures. No significant effect was observed using mAbs against vasopressin, mouse immunoglobulins, or control ascitic fluid controls. These data show that OT is fully processed and recognized by specific mAbs at the outer surface of TEC plasma membrane. They further support that thymic OT behaves as the self-antigen of the neurohypophysial family.

Nuclear factor kappa B (NF-kappa B), nuclear factor interleukin-6 (NFIL-6 or C/EBP beta) and nuclear factor interleukin-6 beta (NFIL6-beta or C/EBP delta) are not sufficient to activate the endogenous interleukin-6 gene in the human breast carcinoma cell line MCF-7. Comparative analysis with MDA-MB-231 cells, an interleukin-6-expressing human breast carcinoma cell line

A comparative study of the molecular mechanism of interleukin-6 (IL-6) gene induction on two breast-carcinoma-derived cell lines has been performed. MDA-MB-231 cells produce constitutive detectable levels of both secreted IL-6 and mRNA which, as expected, are dramatically enhanced following induction by either IL-1 beta or tumor necrosis factor-alpha (TNF-alpha). The levels of both secreted IL-6 and IL-6 mRNA are significantly higher in response to IL-1 beta in spite of the fact that stimulation by TNF-alpha alone enhances the half life of IL-6 mRNA. The protein synthesis inhibitor cycloheximide is also a fairly strong inducer of IL-6 in these cells. In contrast, MCF-7 cells fail to produce detectable IL-6 protein or mRNA, even after stimulation with proper inducers. Analysis of transcription factors NF-kappa B, NFIL6 and NFIL6 beta, which have been described to be sufficient to activate the IL-6 gene in other cell systems, shows a similar pattern of expression in both MCF-7 and MDA-MB-231 cells. Furthermore, transfection of a recombinant plasmid carrying the IL-6 promoter linked to a luciferase reporter gene shows that both cell lines are able to drive IL-1 beta or TNF-alpha activation of this construction in a very similar manner. Finally, when MCF-7 cells were treated with IL-1 beta or TNF-alpha in the presence of cycloheximide, transcription of IL-6 mRNA from the endogenous IL-6 gene was observed. These data suggest that a mechanism of IL-6 gene repression is active in MCF-7 cells.