Autoimmunity associated with TGF-beta1-deficiency in mice is dependent on MHC class II antigen expression

TGF-beta1 down-regulates induced expression of both class II MHC and B7-1 on primary murine renal tubular epithelial cells

BACKGROUND

We examined the immunomodulatory effects of transforming growth factor-beta1 (TGF-beta1) on the regulation of class II MHC and costimulatory molecule expression in a primary renal tubular epithelial cell line, called F1K.

METHODS

Class II major histocompatibility complex (MHC), class II transactivator, B7-1, intercellular adhesion molecule-1 (ICAM-1) and interferon-gamma (IFN-gamma) receptor beta chain were evaluated in untreated and cytokine-treated F1K by Northern hybridization analysis and flow cytometry. T cell activation studies were performed to assess TGF-beta1-mediated effects on antigen presenting cell function of F1K.

RESULTS

Pretreatment of F1K with TGF-beta1 markedly inhibited IFN-gamma-induced class II MHC expression, by both FACS and Northern analysis. Total class II transactivator mRNA levels were also diminished by TGF-beta1, indicating that class II MHC modulation in F1K results from inhibition of this intermediate protein. As previous studies demonstrated that cotreatment of F1K cells with IFN-gamma + lipopolysaccharide (LPS) induces B7-1, we evaluated the potential regulatory effects of TGF-beta1 exposure on B7-1 expression. Our studies revealed that B7-1 mRNA and cell-surface expression in IFN-gamma + LPS-treated F1K were decreased by TGF-beta1 pretreatment. Functional studies evaluating TGF-beta1-mediated effects were performed with IFN-gamma + LPS-treated F1K and MR1.3, a nephritogenic CD4+ Th2 clone derived from kidneys of animals with autoimmune glomerulonephritis. Interleukin (IL)-4 production assays demonstrated activation of MR1. 3 by IFN-gamma + LPS-treated cells, but not by IFN-gamma + LPS-treated cells previously exposed to TGF-beta1, indicating that TGF-beta1-mediated inhibition of class II MHC and B7-1 expression alters the antigen presenting cell function of F1K.

CONCLUSIONS

These studies describe the proscriptive influence of TGF-beta1 on class II MHC and B7-1 expression in renal tubular epithelial cells. Such findings indicate that TGF-beta1 alters the antigen presenting cell function of renal tubular epithelial cells in vitro, and suggest a potential mechanism for immunosuppression of T cell-mediated renal immune responses in vivo.

TGF-beta inhibits lipopolysaccharide-stimulated activity of c-Jun N-terminal kinase in mouse macrophages

Transforming growth factor-beta (TGF-beta) is a potent anti-inflammatory cytokine. Although this cytokine inhibits lipopolysaccharide (LPS)-mediated septic shock, the molecular mechanism of TGF-beta is not well known. Since recent studies showed that c-Jun N-terminal kinase (JNK), one of the mitogen-activated protein kinases, plays an important role in LPS signalling, we focused here on the inhibitory action of TGF-beta1 on LPS-stimulated JNK activity in mouse macrophages. TGF-beta1 inhibited LPS-stimulation of phosphorylated JNK1 and JNK2 and consequently of JNK activity in the cells. This JNK activity resulted in a decreased level of phosphorylated c-Jun protein. Using Western blotting, we also observed TGF-beta1 inhibition of newly synthesized c-Jun protein in LPS-stimulated cells. These results demonstrate that TGF-beta1 inhibits LPS-stimulated JNK activity in mouse macrophages. Also, our present study suggests a possible inhibitory mechanism of TGF-beta in signalling of LPS-induced inflammatory responses.

Transforming Growth Factor-β1 Polarizes Murine Hematopoietic Progenitor Cells to Generate Langerhans Cell-Like Dendritic Cells Through a Monocyte/Macrophage Differentiation Pathway

We have recently demonstrated that CD11b−/dullCD11c+ and CD11b+hiCD11c+ dendritic cell (DC) precursor subsets represent two distinct DC differentiation pathways from murine bone marrow lineage-phenotype negative (Lin−)c-kit+ hematopoietic progenitor cells (HPCs) stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + tumor necrosis factor  (TNF). We show here that transforming growth factor-β1 (TGF-β1) significantly inhibits the generation of these CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors. Phenotypically, this inhibitory effect was accompanied by markedly suppressed expression of Ia and CD86 antigens as well as major histocompatibility complex (MHC) class II transactivator (CIITA) and CC-chemokine receptor 7 (CCR7) mRNAs in Lin−c-kit+ HPC cultures stimulated with GM-CSF + SCF + TNF at day 6. TGF-β1 could also suppress mature DC differentiation from CD11b+hiCD11c+ DC precursors, but not the differentiation from CD11b−/dullCD11c+ DC precursors. In the absence of TNF, TGF-β1 markedly suppressed the expression of CIITA and CCR7 mRNAs in GM-CSF + SCF-stimulated Lin−c-kit+ HPCs at either day 6 or day 12 and induced the differentiation solely into monocytes/macrophages as evident in morphology, active phagocytic, and endocytic activities. These cells expressed high levels of F4/80 and E-cadherin antigens, but low or undetectable levels of Ia, CD86, and CD40 molecules. However, upon the stimulation with TNF + GM-CSF, these cells could further differentiate into mature DCs expressing high levels of Ia and E-cadherin, characteristics for Langerhans cells (LCs), and gained the capacity of enhancing allogenic MLR. Taken together, all of these findings suggest that TGF-β1 polarizes murine HPCs to generate LC-like DCs through a monocyte/macrophage differentiation pathway.

Transforming Growth Factor-β1 Polarizes Murine Hematopoietic Progenitor Cells to Generate Langerhans Cell-Like Dendritic Cells Through a Monocyte/Macrophage Differentiation Pathway

We have recently demonstrated that CD11b−/dullCD11c+ and CD11b+hiCD11c+ dendritic cell (DC) precursor subsets represent two distinct DC differentiation pathways from murine bone marrow lineage-phenotype negative (Lin−)c-kit+ hematopoietic progenitor cells (HPCs) stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + tumor necrosis factor  (TNF). We show here that transforming growth factor-β1 (TGF-β1) significantly inhibits the generation of these CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors. Phenotypically, this inhibitory effect was accompanied by markedly suppressed expression of Ia and CD86 antigens as well as major histocompatibility complex (MHC) class II transactivator (CIITA) and CC-chemokine receptor 7 (CCR7) mRNAs in Lin−c-kit+ HPC cultures stimulated with GM-CSF + SCF + TNF at day 6. TGF-β1 could also suppress mature DC differentiation from CD11b+hiCD11c+ DC precursors, but not the differentiation from CD11b−/dullCD11c+ DC precursors. In the absence of TNF, TGF-β1 markedly suppressed the expression of CIITA and CCR7 mRNAs in GM-CSF + SCF-stimulated Lin−c-kit+ HPCs at either day 6 or day 12 and induced the differentiation solely into monocytes/macrophages as evident in morphology, active phagocytic, and endocytic activities. These cells expressed high levels of F4/80 and E-cadherin antigens, but low or undetectable levels of Ia, CD86, and CD40 molecules. However, upon the stimulation with TNF + GM-CSF, these cells could further differentiate into mature DCs expressing high levels of Ia and E-cadherin, characteristics for Langerhans cells (LCs), and gained the capacity of enhancing allogenic MLR. Taken together, all of these findings suggest that TGF-β1 polarizes murine HPCs to generate LC-like DCs through a monocyte/macrophage differentiation pathway.

Two distinct gamma interferon-inducible promoters of the major histocompatibility complex class II transactivator gene are differentially regulated by STAT1, interferon regulatory factor 1, and transforming growth factor beta

The major histocompatibility complex (MHC) class II transactivator (CIITA) is the master regulatory factor required for appropriate expression of class II MHC genes. Understanding the expression of CIITA is key to understanding the regulation of class II MHC genes. This report describes the independent regulation of two distinct CIITA promoters by cytokines with opposing functions, gamma interferon (IFN-gamma) and transforming growth factor beta (TGF-beta). A functional analysis of deletion mutations of the upstream promoter (promoter III) identified an IFN-gamma-responsive region located approximately 5 kb from the transcriptional start site. An in vivo DNase I hypersensitivity analysis detected a hypersensitive site in this area which supports the relevance of this region. When the downstream promoter (promoter IV) was studied by in vivo genomic footprinting, IFN-gamma-induced changes at putative binding sites for STAT1, interferon regulatory factor 1 (IRF-1), and E-box proteins were seen. Gel shift and supershift analyses for IRF-1 confirmed the in vivo footprint results. The role of the IFN-gamma-inducible transcription factor STAT1 was examined functionally. Although both promoters were controlled by STAT1, promoter-specific regulation was exhibited. The IFN-gamma response of promoter III was completely dependent on STAT1 and not IRF-1, while promoter IV was partially activated by IRF-1 in the total absence of STAT1 expression. While both promoters were affected by TGF-beta, activation of promoter III by IFN-gamma was more severely diminished by TGF-beta treatment. The differential control of CIITA promoters by TGF-beta, IRF-1, and STAT1 may be important in refining regulation of class II MHC genes in different cell types and under different stimulatory conditions.

Chronic rejection and chronic cyclosporin toxicity in renal allografts

Recent evidence indicates that growth factors are critically important in both chronic rejection and chronic cyclosporin A toxicity, suggesting that these two entities share a common pathophysiological pathway, leading to progressive allograft failure. Here, Manuel Pascual and colleagues discuss the relevance of growth factors to chronic allograft nephropathy, and the implications for therapy in view of the great choice of immunosuppressive drugs now available.

Transforming growth factor-beta levels in maternal milk and expression in postnatal rat duodenum and ileum

After birth, the gastrointestinal tract of the neonate is exposed to food and bacterial and environmental antigens. Maternal milk components may play a role in regulation of mucosal immune activity to luminal antigens. In this study we determine the ontogeny of transforming growth factor (TGF)-beta1-producing cells in the rat pup small intestine and assess maternal milk concentrations of TGF-beta. Intestinal tissue samples of duodenum and ileum were collected, processed, and stained for TGF-beta1, and in situ hybridization for TGF-beta1 mRNA was also performed on the duodenum. TGF-beta levels in milk were assayed by ELISA. TGF-beta2 levels in milk were high at d 6, and declined thereafter at d 10 and 19. TGF-beta1 was not detected. In contrast, the cell number and intensity of staining of TGF-beta1 peptide in the small intestine was low in 3- and 10-d-old rats and increased markedly by 19 d of life. In the duodenum mRNA levels mirrored this trend. TGF-beta1 expression in the lamina propria was absent before d 19, and increased progressively over time. Maternal milk TGF-beta2 levels are high in early milk and decrease during the weaning period. In contrast, endogenous TGF-beta production in the small intestine increases during the weaning period.

Absence of MHC class II antigen expression in trophoblast cells results from a lack of class II transactivator (CIITA) gene expression

Although the mechanism(s) underlying the failure of the maternal immune system to reject the semiallogeneic fetus have not been clearly defined, the absence of MHC class II antigen expression by fetal trophoblast cells very likely plays a critical role in the maintenance of normal pregnancy. However, the regulation of class II antigen expression in trophoblast cells is poorly understood. Class II transactivator (CIITA) is a transacting factor that is required for both constitutive and IFN-gamma-inducible class II gene transcription. In this report we demonstrate that the inability of trophoblast cells to express class II antigens is due to a lack of CIITA gene expression. Trophoblast cell lines derived from human, mouse, and rat do not express CIITA, and expression is not inducible by IFN-gamma. The absence of CIITA gene expression in trophoblasts treated with IFN-gamma does not result from a defect in the IFN-gamma receptor or the JAK/STAT pathway, because the classical IFN-gamma inducible gene encoding the guanylate-binding protein is expressed. Transfection of CIITA expression vectors into trophoblast cells results in activation of class II promoters, endogenous class II mRNA expression, and subsequent expression of class II antigens on the cell surface. In contrast, class I mRNA is not expressed in human trophoblast cells transfected with CIITA expression vectors. Thus, trophoblast cells contain all of the DNA binding factors necessary for class II transcription, and ectopic expression of CIITA is sufficient to activate class II, but not class I expression. The failure of trophoblast cells to express CIITA, and therefore class II antigens, provides a potential mechanism by which the fetus is protected from the maternal immune system during pregnancy.

Low Dose TGF-β Attenuates IL-12 Responsiveness in Murine Th Cells

Expression of IL-12Rs is one important checkpoint for Th1 development. BALB/c DO11.10 CD4+ T cells stimulated by Ag in neutral conditions lose expression of the IL-12R β2 subunit and become unresponsive to IL-12. In contrast, B10.D2 or F1 (BALB/c × B10.D2) DO11.10 CD4+ T cells maintain IL-12Rβ2 expression when stimulated similarly. Here we show that the loss of IL-12 responsiveness by BALB/c T cells involves the action of endogenous TGF-β. BALB/c T cells stimulated in the presence of anti-TGF-β specifically maintain IL-12 responsiveness, express IL-12Rβ2 mRNA, and can stimulate nitric oxide production in peritoneal exudate cells. Low concentrations of TGF-β added exogenously during primary activation of B10.D2 or F1 T cells significantly inhibit their development of IL-12 responsiveness. These effects of anti-TGF-β are dependent on endogenous IFN-γ and are inhibited by exogenously added IL-4. Thus, at least one effect of TGF-β on Th1/Th2 development may be the attenuation of IL-12Rβ2 expression.

Decreased bone mass and bone elasticity in mice lacking the transforming growth factor-beta1 gene

Transforming growth factor-beta1 (TGF-beta1) knockout (TGF-beta1(-/-)) mice were used to investigate the role of TGF-beta1 in postnatal bone development. Volumetric bone mineral density (BMD) and mineral content (BMC) in these mice and in their normal (TGF-beta1(+/+)) and heterozygous (TGF-beta1(+/-)) littermates were analyzed by quantitative computed tomography (pQCT). Analysis of the proximal tibial metaphysis showed a significant decrease in the BMC of the TGF-beta1(-/-) mice compared to TGF-beta1(+/+) or TGF-beta1(+/-) mice; however, no significant difference was observed in BMD between the groups of mice. pQCT analysis of the tibial midshaft diaphysis showed no difference in the BMD or BMC of cortical bone between the groups. Histomorphometry revealed no significant difference in trabecular connectivity or in trabecular bone volume, number, or thickness. However, the width of the tibial growth plate and the longitudinal growth rate were significantly decreased in the TGF-beta1(-/-) mice, resulting in shorter tibia. Acoustic velocity measurements showed significant differences between the groups of mice with an apparent dosage effect of TGF-beta1 expression on the anisotropic properties of the bone. These data show that longitudinal growth and total mineral content are affected in mice lacking TGF-beta1, as well as the elastic properties of the bone, consistent with an important role for TGF-beta1 in bone modeling and bone quality.

TGF-beta: a balancing act

Regulation of developmental processes as well as host defense and repair mechanisms requires the maintenance of a delicate balance of positive and negative regulatory signals. TGF-beta, a molecule known for its many diverse activities, can promote or inhibit cell growth and function. Disruption of the balance between these opposing activities can contribute to aberrant development, malignancy, or pathogenic immune and inflammatory responses. TGF-beta transgenic mouse studies highlight the essential function(s) of TGF-beta and its receptors and provide insight to potential therapeutic approaches to manipulate TGF-beta expression.

Regulation of immune responses by TGF-beta

The transforming growth factor beta (TGF-beta) family of proteins are a set of pleiotropic secreted signaling molecules with unique and potent immunoregulatory properties. TGF-beta 1 is produced by every leukocyte lineage, including lymphocytes, macrophages, and dendritic cells, and its expression serves in both autocrine and paracrine modes to control the differentiation, proliferation, and state of activation of these immune cells. TGF-beta can modulate expression of adhesion molecules, provide a chemotactic gradient for leukocytes and other cells participating in an inflammatory response, and inhibit them once they have become activated. Increased production and activation of latent TGF-beta have been linked to immune defects associated with malignancy and autoimmune disorders, to susceptibility to opportunistic infection, and to the fibrotic complications associated with chronic inflammatory conditions. In addition to these roles in disease pathogenesis, TGF-beta is now established as a principal mediator of oral tolerance and can be recognized as the sine qua non of a unique subset of effector cells that are induced in this process. The accumulated knowledge gained through extensive in vitro functional analyses and from in vivo animal models, including newly established TGF-beta gene knockout and transgenic mice, supports the concept that clinical therapies based on modulation of this cytokine represent an important new approach to the treatment of disorders of immune function.

Consistent loss of functional transforming growth factor beta receptor expression in murine plasmacytomas

Murine plasmacytomas are tumors of Ig-secreting plasma cells that can be induced in genetically susceptible BALB/c mice. The deregulation of the c-myc protooncogene is a critical oncogenic event in the development of plasmacytomas (PCTs) although it is not sufficient for their malignant transformation. We have demonstrated that PCTs produce active transforming growth factor beta (TGF-beta) in vitro. Because TGF-beta is a potent negative regulator of the proliferation and differentiation of B lymphocytes, we examined its role in plasmacytomagenesis by comparing responsiveness to TGF-beta of nonneoplastic plasma cells and PCTs. The nontransformed plasma cells that accumulate in interleukin 6 transgenic mice undergo accelerated apoptosis upon treatment with TGF-beta, but the 15 PCTs studied, including primary and transplanted tumors as well as established cell lines, were refractory to TGF-beta-mediated growth inhibition and apoptosis. Although PCTs lack functional TGF-beta receptors as demonstrated by chemical crosslinking to radiolabeled TGF-beta1, they nonetheless contain mRNA and protein for both type I and II TGF-beta receptors, suggesting a potential defect in receptor trafficking or processing. The results clearly show the consistent inactivation of TGF-beta receptors in plasmacytoma cells, demonstrating for the first time that interruption of a tumor suppressor pathway contributes to plasmacytomagenesis.

Lacrimal gland inflammation is responsible for ocular pathology in TGF-beta 1 null mice

Mice homozygous for a nonfunctional transforming growth factor-beta 1 gene develop rampant inflammation in vital organs that contributes to a shortened life span. The presence of circulating anti-nuclear anti-bodies, immune deposits in tissues, leukocyte infiltration, and increased major histocompatibility complex antigen expression resembles an autoimmune-like syndrome. One of the overt symptoms that appears in these mice lacking transforming growth factor-beta 1 is the development of dry crusty eyes that close persistently as their health declines. Histologically, the eyes appear normal with little or no inflammation. However, inflammatory lesions, predominantly lymphocytic, develop in the lacrimal glands, disrupting their structure and function and severely limiting their ability to generate tears. This histopathology and aberrant function mimic that of Sjögren's syndrome, a human autoimmune disease characterized by dry eyes and dry mouth. Impeding the leukocyte infiltration into the glands with synthetic fibronectin peptides, which block adhesion, not only prevents the inflammatory pathology but also prevents the persistent eye closure characteristic of these mice.

Biology of TGF-beta in knockout and transgenic mouse models

This paper reviews the basic biology and biochemistry of the TGF-beta isoforms including their unique serine-threonine receptors and signaling intermediates. Dysregulation of TGF-beta expression and/or receptor/signaling function have been implicated in a wide variety of pathologies. We will discuss mechanisms underlying some of these disease processes as gained from study of transgenic mice in which expression of TGF-beta 1 has either been lost by targeted deletion of its gene, is overexpressed in a tissue-specific manner, or blocked by its latency associated peptide.