TGF beta 1 inhibits Ca2+-calcineurin-mediated activation in thymocytes

Regulatory T Cell Plasticity and Stability and Autoimmune Diseases

CD4⁺CD25⁺ regulatory T cells (Tregs) are a class of CD4⁺ T cells with immunosuppressive functions that play a critical role in maintaining immune homeostasis. However, in certain disease settings, Tregs demonstrate plastic differentiation, and the stability of these Tregs, which is characterized by the stable expression or protective epigenetic modifications of the transcription factor Foxp3, becomes abnormal. Plastic Tregs have some features of helper T (Th) cells, such as the secretion of Th-related cytokines and the expression of specific transcription factors in Th cells, but also still retain the expression of Foxp3, a feature of Tregs. Although such Th-like Tregs can secrete pro-inflammatory cytokines, they still possess a strong ability to inhibit specific Th cell responses. Therefore, the plastic differentiation of Tregs not only increases the complexity of the immune circumstances under pathological conditions, especially autoimmune diseases, but also shows an association with changes in the stability of Tregs. The plastic differentiation and stability change of Tregs play vital roles in the progression of diseases. This review focuses on the phenotypic characteristics, functions, and formation conditions of several plastic Tregs and also summarizes the changes of Treg stability and their effects on inhibitory function. Additionally, the effects of Treg plasticity and stability on disease prognosis for several autoimmune diseases were also investigated in order to better understand the relationship between Tregs and autoimmune diseases.

Developmental differences in microglia morphology and gene expression during normal brain development and in response to hypoxia-ischemia

BACKGROUND

Neuroinflammation plays an important role in ischemic brain injury and recovery, however the interplay between brain development and the neuroinflammatory response is poorly understood. We previously described age-dependent differences in the microglial response and the effect of microglial inhibition. Here we investigate whether age-dependent microglial responses may be related to pre-injury developmental differences in microglial phenotype.

METHODS

Measures of microglia morphology were quantified using semi-automated software analysis of immunostained sections from postnatal day 2 (P2), P9, P30 and P60 mice using IMARIS. Microglia were isolated from P2, P9, P30 and P60 mice, and expression of markers of classical and alternative microglial activation was assessed, as well as transforming growth factor beta (TGF-β) receptor, Serpine1, Mer Tyrosine Kinase (MerTK), and the suppressor of cytokine signaling (SOCS3). Hypoxia-ischemia (HI) was induced in P9 and P30 mice using unilateral carotid artery ligation and exposure to 10% oxygen for 50 min. Microglia morphology and microglial expression of genes in the TGF-β and MerTK pathways were determined in ipsilateral and contralateral hippocampus.

RESULTS

A progressive and significant increase in microglia branching morphology was seen in all brain regions from P2 to P30. No consistent classical or alternative activation profile was seen in isolated microglia. A clear transition to increased expression of TGF-β and its downstream effector serpine1 was seen between P9 and P30. A similar increase in expression was seen in MerTK and its downstream effector SOCS3. HI resulted in a significant decrease in branching morphology only in the P9 mice, and expression of TGF-β receptor, Serpine1, MerTK, and SOCS3 were elevated in P30 mice compared to P9 post-HI.

CONCLUSION

Microglia maturation is associated with changes in morphology and gene expression, and microglial responses to ischemia in the developing brain differ based on the age at which injury occurs.

Yangyin Qingre Huoxue Method in Traditional Chinese Medicine Ameliorates Atherosclerosis in ApoE-/- Mice Suffering from High-Fat Diet and HSP65 Aggression

Atherosclerosis (AS) is a complicated arterial disease resulting from abnormal lipid deposition and inflammatory injury, which is attributed to Yin deficiency, accumulation of heat materials, and stasis of blood flow in Traditional Chinese Medicine (TCM) theory. Thus, according to TCM theory, the method of nourishing Yin (Yangyin), clearing away heat (Qingre), and promoting blood circulation (Huoxue) is a reasonable strategy, which has achieved remarkable clinical efficacy in the treatment of AS, but the mechanisms remain to be known. In this study, we evaluated the effects of Yangyin Qingre Huoxue Prescription (YQHP) on AS in ApoE^-/- mice suffering from a high-fat diet and heat shock protein (HSP65) attack. YQHP regulated levels of blood lipids and inflammation-linked cytokines as well as Th17/Treg ratio in peripheral blood. Suppressed IL-6-p-STAT3 signaling and restored IL-2-p-STAT5 signaling in the presence of YQHP may partake in the regulation of Th17 and Treg differentiation. Moreover, YQHP modulated transcriptional levels of costimulator CD80 in aortas as well corresponding to the downregulation of GM-CSF in serum and CD3 expression in CD4⁺ T cells, which might indicate the potential of YQHP to regulate antigen presenting cells. All these effects eventually promoted the improvement of atherosclerotic lesions. In addition, YQHP promoted less monocyte infiltration in the liver and lower levels of AST, ALT, and AKP production than simvastatin. Conclusively, lipid-regulating and anti-inflammatory functions mediated by YQHP with lower hepatotoxicity than simvastatin hindered the progression of HSP65 aggravated AS in ApoE^-/- mice, indicating the effectiveness of Yangyin Qingre Huoxue Method in the treatment of AS.

Ion homeostasis and transport are regulated by genes differentially expressed in porcine buccal pouch mucosal cells during long-term culture in vitro – a microarray approach

The oral mucosa is a compound tissue composed of several cells types, including fibroblasts and keratinocytes, that are characterized by different morphology, as well as biochemical and metabolomic properties. The oral mucosal cells are the most important factors mediated between transport and drugs delivery. The changes in cellular ion homeostasis may significantly affect the bioavailability of administrated drugs and their transport across the mucous membrane. Therefore we investigated the expression profile of genes involved in ion transport and homeostasis in porcine buccal pouch mucosal cells.

The oral mucosa was separated surgically and isolated enzymatically. The cells were examined during long-term in vitro culture (IVC). The cultured cells were collected at 7, 15 and 30 days of IVC and subsequently transferred to RNA isolation and next, the gene expression profile was measured using Affymetrix microarray assays.

In the results, we can extract genes belonging to four ontology groups: “ion homeostasis”, “ion transport”, “metal ion transport”, and “inorganic ion homeostasis”. For TGFB1 and CCL2, we observed up-regulation after 7 days of IVC, down-regulation after 15 days of IVC and upregulation again after 30 days of IVC. The ATP13A3, ATP1B1, CCL8, LYN, STEAP1, PDPN, PTGS2, and SLC5A3genes showed high activity after day 7 of IVC, and in the days 15 and 30 of IVC showed low activity.

We showed an expression profile of genes associated with the effects of ion influence on the porcine normal oral mucosal cell development in IVC. These studies may be the starting point for further research into oral diseases and will allow for the comparison of the gene expression profile of normal and disease altered cells.

The Transforming Growth Factor Beta 1/SMAD Signaling Pathway Involved in Human Chronic Myeloid Leukemia

Transforming growth factor beta 1 (TGF-β1) is the prototypic member of a large family of structurally related pleiotropic-secretedcytokines. The TGF-β1/SMAD signaling pathway usually participates in a wide range of cellular processes such as growth, proliferation, differentiation and apoptosis. Upon binding onTGF-β1, the dimerized TGF-β type II receptors recruit and phosphorylate the TGF-β type I receptors, which phosphorylate the receptor-regulated SMAD (SMAD2 and SMAD3) presented by the SMAD anchor for receptor activation.

The phosphorylated receptor-regulated SMAD form heterologous complexes with the common-mediator SMAD (SMAD4) and subsequently translocate into the nucleus, where they interact with other transcription factors to regulate the expression of target genes. This multi-functional signaling pathway modulated by various elements with complex mechanisms at different levels is also inevitably involved in cancer. We herein present data on the role of the TGF-β1/SMAD signaling pathway in human chronic myeloid leukemia and explain the potent biological effects of TGF-β1 on leukemia cells. The paper is based on a review of articles selected from Cancerline and Medline data bases.

The constitutively active tyrosine kinase produced by the specific Bcr-Abl fusion gene on the Philadelphia chromosome can enhance the resistance of malignant cells to TGF-β1-induced growth inhibition and apoptosis, which contributes to enhancement of proteasomal degradation of p27. However, overexpression of the EVI1 gene, which is also caused by Bcr-Abl, can recruit the C-terminal binding protein and histone deacetylase to prevent the MH2 domain on SMAD3. The later is essential for transcription activation on target genes and leads to blockage of the TGF-β1/SMAD signaling pathway.

Some studies have indicated that certain therapeutic agents applied in clinical treatment can inhibit proliferation and promote differentiation of leukemia cells by way of modulation of the TGF-β1/SMAD signal pathway. For example, arsenic trioxide can promote specific degradation of the AML1/MDS1/EVI1 oncoprotein and inhibit the proliferation of leukemia cells. However, specific histone deacetylase inhibitors can interrupt the effect of histone deacetylase to alleviate EVI1-mediated suppression of TGF-β1/SMAD signaling. The tyrosine kinase inhibitor in the target therapy of chronic myeloid leukemia can effectively inhibit the tyrosine kinase activity of Bcr-Abl and induce suppression on the TGF-β1/SMAD signaling pathway.

The TGF-β1/SMAD signaling pathway plays an important role in chronic myeloid leukemia cells and leads the leukemia cells to growth inhibition, differentiation and apoptosis. The positive influence of the TGF-β1/SMAD signaling pathway in chronic myeloid leukemia is fairly significant, and its potential effects in clinical treatment will bring about definite benefits.

Since it is a complex signaling pathway widely involved in many aspects of cellular activities, further study and comprehensive analysis of the TGF-β1/SMAD signaling pathway are imperative and will have a guiding significance in research and clinical applications. It is an exciting area for future research. Free full text available at www.tumorionline.it

TGF-β1 improving abnormal pregnancy outcomes induced by Toxoplasma gondii infection: Regulating NKG2D/DAP10 and killer subset of decidual NK cells

Our current aim was to investigate whether injection of TGF-β1 played an important role in improving abnormal pregnancy outcomes with T. gondii infection and how the TGF-β1 regulated. Results showed that TGF-β1 exhibited improved pregnancy outcomes induced by T. gondii infection. dNK cytotoxicity was increased with T. gondii infection while decreased with TGF-β1 treatment. dNK cytotoxicity related NKG2D/DAP10 expression, perforin, granzyme, IFN-γ and killer subsets were all increased with T. gondii infection while decreased after TGF-β1 treatment. In addition, anti-TGF-β1 antibodies could aggregate the cytotoxicity of dNK cells and the levels of molecules above. These results indicated that TGF-β1 treatment could improve the abnormal pregnancy outcomes with T. gondii infection by decreasing the cytotoxicity of dNK cells mediated by NKG2D/DAP10 pathway and killer subset. These results suggested that TGF-β1 might be a potential immunoprotective method for the treatment of abnormal pregnancy outcomes following T. gondii infection.

TGF-β - an excellent servant but a bad master

The transforming growth factor (TGF-β) family of growth factors controls an immense number of cellular responses and figures prominently in development and homeostasis of most human tissues. Work over the past decades has revealed significant insight into the TGF-β signal transduction network, such as activation of serine/threonine receptors through ligand binding, activation of SMAD proteins through phosphorylation, regulation of target genes expression in association with DNA-binding partners and regulation of SMAD activity and degradation. Disruption of the TGF-β pathway has been implicated in many human diseases, including solid and hematopoietic tumors. As a potent inhibitor of cell proliferation, TGF-β acts as a tumor suppressor; however in tumor cells, TGF-β looses anti-proliferative response and become an oncogenic factor. This article reviews current understanding of TGF-β signaling and different mechanisms that lead to its impairment in various solid tumors and hematological malignancies.

Tiotropium bromide inhibits TGF-β-induced MMP production from lung fibroblasts by interfering with Smad and MAPK pathways in vitro

Background:

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation and structural alterations (ie, tissue remodeling) throughout the conducting airways, parenchyma, and pulmonary vasculature. Matrix metalloproteinases (MMPs) are extracellular degrading enzymes that play a critical role in inflammatory cell infiltration and tissue remodeling, but the influence of the agents that are used for the treatment of COPD on the production of MMPs is not well understood.

Purpose:

The present study aimed to examine the influence of tiotropium bromide hydrate (TBH) on the production of MMPs from lung fibroblasts (LFs) induced by transforming growth factor (TGF)-β in vitro.

Methods:

LFs, at a concentration of 5 × 10⁵ cells·mL⁻¹, were stimulated with TGF-β in the presence of various concentrations of TBH. MMP-1 and MMP-2 levels in culture supernatants were examined by enzyme-linked immunosorbent assay (ELISA), and MMP messenger ribonucleic acid (mRNA) expression was examined by real-time polymerase chain reaction (RT-PCR). The influence of TBH on TGF-β signaling pathways was also analyzed by examining Smad activation and signaling protein phosphorylation by ELISA.

Results:

TBH at more than 15 pg·mL⁻¹ inhibited the production of MMP-1 and MMP-2, but not tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2, from LFs, after TGF-β stimulation. TBH also suppressed MMP mRNA expression through the inhibition of Smad activation and signaling protein, extracellular-signal-regulated kinase (ERK) 1 and 2, and c-Jun N-terminal kinase (JNK), phosphorylation.

Conclusion:

These results may suggest that TBH suppresses MMP production from LFs, through interference of TGF-β-mediated signaling pathways and results in favorable modification of the clinical status of COPD.

Calcineurin deficiency decreases inflammatory lesions in transforming growth factor beta1-deficient mice

Transforming growth factor (TGF) beta1) is an immunoregulatory cytokine involved in self-tolerance and lymphocyte homeostasis. Tgfb1 knock-out (KO) mice develop severe multi-focal autoimmune inflammatory lesions due to [Ca(2+)]i deregulation in T cells, and die within 3 weeks after birth. Because the calcineurin inhibitor FK506 inhibits the hyperresponsiveness of Tgfb1(-/-) thymocytes, and because calcineurin Abeta (CNAbeta)-deficient mice do not reject allogenic tumours, we have generated Tgfb1(-/-) Cnab(-/-) mice to address whether CNAbeta deficiency prevents T cell activation and inflammation in Tgfb1(-/-) mice. Here we show that in Tgfb1(-/-) Cnab(-/-) mice inflammation is reduced significantly relative to that in Tgfb1(-/-) mice. However, both CD4(+) and CD8(+) T cells in double knock-out (DKO) mice are activated, as revealed by up-regulation of CD11a lymphocyte function-associated antigen-1 (LFA-1), CD44 and CD69 and down-regulation of CD62L. These data suggest that deficiency of CNAbeta decreases inflammatory lesions but does not prevent activation of autoreactive T cells. Also Tgfb1(-/-) T cells can undergo activation in the absence of CNAbeta, probably by using the other isoform of calcineurin (CNAalpha) in a compensatory manner. CNAbeta-deficient T cells undergo spontaneous activation in vivo and are activated upon anti-T cell receptor stimulation in vitro. Understanding the role of calcineurin in T cell regulation should open up new therapeutic opportunities for inflammation and cancer.

Generation of mice with a conditional allele for transforming growth factor beta 1 gene

Transforming growth factor beta1 (TGFbeta1) is a multifunctional growth factor involved in wound healing, tissue fibrosis, and in the pathogenesis of many syndromic diseases (e.g., Marfan syndrome, Camurati-Engelmann disease) and muscular, neurological, ophthalmic, cardiovascular and immunological disorders, and cancer. Since the generation of Tgfb1 knockout mice, there has been extraordinary progress in understanding its physiological and pathophysiological function. Here, we report the generation of a conditional knockout allele for Tgfb1 in which its exon 6 is flanked with LoxP sites. As proof of principle, we crossed these mice to LckCre transgenic mice and specifically disrupted Tgfb1 in T cells. The results indicate that T-cell-produced TGFbeta1 is required for normal in vivo regulation of peripheral T-cell activation, maintenance of T-cell homeostasis, and suppression of autoimmunity.

Influence of genetic background on genetically engineered mouse phenotypes

The history of mouse genetics, which involves the study of strain-dependent phenotype variability, makes it clear that the genetic background onto which a gene-targeted allele is placed can cause considerable variation in genetically engineered mouse (GEM) phenotype. This variation can present itself as completely different phenotypes, as variations in penetrance of phenotype, or as variable expressivity of phenotype. In this chapter we provide examples from gene-targeting literature showing each of these types of phenotype variation. We discuss ways in which modifier genes can affect the phenotype of a mouse with a mutant gene, and we give examples of modifier locus identification. We also review approaches to minimize gene polymorphism and flanking gene differences between experimental animals, and between them and their controls. In addition, we discuss the advantages and disadvantages of performing the first analysis of a knockout mouse on a mixed genetic background. We conclude that a mixed background provides the quickest preview of possible strain-dependent phenotypes (1 , 2). Finally, we review recent approaches to improving genetic diversity by generating new inbred strains that encompass a broader range of alleles within the mouse species.

The Critical Role of TGF-beta1 in the Development of Induced Foxp3+ Regulatory T Cells

Foxp3+T regulatory cell (Treg) subsets play a crucial role in the maintenance of immune homeostasis against self-antigen. The lack or dysfunction of these cells is responsible for the pathogenesis and development of many autoimmune diseases. Therefore, manipulation of these cells may provide a novel therapeutic approach to treat autoimmune diseases and prevent allograft rejection during organ transplantation. In the article, we will provide current opinions concerning the classification, developmental and functional characterizations of Treg subsets. A particular emphasis will be focused on transforming cell growth factor beta (TGF-beta) and its role in the differentiation and development of induced regulatory T cells (iTregs) in the periphery. Moreover, the similarity and disparity of iTregs and naturally occurring, thymus-derived CD4+CD25+Foxp3+ regulatory T cells (nTregs) will also be discussed. While proinflammatory cytokine IL-6 can convert nTregs to IL-17-producing cells, peripheral Tregs induced by TGF-beta are resistant to this cytokine. This difference may affect the role of each in the adaptive immune response.

TGFbeta1 deficiency does not affect the generation and maintenance of CD4+CD25+FOXP3+ putative Treg cells, but causes their numerical inadequacy and loss of regulatory function

TGFbeta1 is considered to be required for peripheral maintenance of CD4(+)CD25(+)FOXP3(+) T(reg) cells. However, we demonstrate no reduction in the percentage of such T cells in the spleens and thymi of Tgfb1(-/-) mice. Although putative T(reg) cells, characterized as CD4(+)CD25(+)FOXP3(+)CD62L(+) T cells, are increased in Tgfb1(-/-) mice, they may be inadequate to control activated T cells since the ratio of activated T cells:putative T(reg) cells is several-fold higher in Tgfb1(-/-) mice than in control mice. We further show that whereas Tgfb1(-/-) mice that express a chicken OVA-specific TCR transgene (DO11.10) have an increase in putative T(reg) cells, there are no detectable CD4(+)CD25(+) T cells in the spleens of DO11.10 Rag1(-/-) mice suggesting that T(reg)-cell generation is self-antigen dependent regardless of whether they express Tgfb1. Finally, we demonstrate that Tgfb1(-/-) T cells remain responsive to the suppressive effect of TGFbeta1 in vitro. These data suggest that TGFbeta1 is required for the regulatory function of T(reg) cells to prevent activation of T cells and autoimmunity.

Regulation of the NFAT pathway discriminates CD4+CD25+ regulatory T cells from CD4+CD25- helper T cells

CD4(+)CD25(+) regulatory T cells (Tregs) are potent modulators of immune responses. The transcriptional program distinguishing Tregs from the CD4(+)CD25(-) Th cells is unclear. NFAT, a key transcription factor, is reported to interact with forkhead box p3, allowing inhibitory and activating signals in T cells. In the current study, we hypothesize that distinctive NFAT regulation in Tregs as compared with Th cells, may contribute to specific functions of these cells. Tregs express basal levels of cytoplasmic NFATc1 and NFATc2. In contrast to Th cells, anti-CD3-mediated T cell activation did not induce nuclear translocation of NFATc1 or NFATc2 in Tregs. This effect was associated with altered regulation for NFAT in Tregs that included reduced calcium flux, diminished calcineurin activation, and increased activity of glycogen synthase kinase-3beta, a negative regulatory kinase for NFAT in Tregs relative to Th cells. These data suggested that NFAT inhibition in Th cells may induce regulatory function. Indeed, pharmacologically mediated NFAT inhibition induced Th cells to function as Tregs, an effect that was mediated by induction of membrane-bound TGF-beta on Th cells. Collectively, these data suggest that maintaining NFAT at basal levels is a part of the transcriptional program required for Tregs.

TGFbeta1 and Treg cells: alliance for tolerance

Transforming growth factor beta1 (TGFbeta1), an important pleiotropic, immunoregulatory cytokine, uses distinct signaling mechanisms in lymphocytes to affect T-cell homeostasis, regulatory T (Treg)-cell and effector-cell function and tumorigenesis. Defects in TGFbeta1 expression or its signaling in T cells correlate with the onset of several autoimmune diseases. TGFbeta1 prevents abnormal T-cell activation through the modulation of Ca2+-calcineurin signaling in a Caenorhabditis elegans Sma and Drosophila Mad proteins (SMAD)3 and SMAD4-independent manner; however, in Treg cells, its effects are mediated, at least in part, through SMAD signaling. TGFbeta1 also acts as a pro-inflammatory cytokine and induces interleukin (IL)-17-producing pathogenic T-helper cells (Th IL-17 cells) synergistically during an inflammatory response in which IL-6 is produced. Here, we will review TGFbeta1 and its signaling in T cells with an emphasis on the regulatory arm of immune tolerance.

A key role for TGF-beta signaling to T cells in the long-term acceptance of allografts

TGF-beta is a key immunoregulatory cytokine which supports self-tolerance by signaling to T cells. In this report, we show a crucial role for TGF-beta signaling to T cells in enabling the long-term acceptance of allografts, whether natural or induced therapeutically by coreceptor and costimulation blockade. The requirement for TGF-beta appears most pronounced during the initial exposure to alloantigens. We demonstrate the ability of TGF-beta to direct the development in vitro of regulatory cells that suppress graft rejection in vivo. Such suppression was not affected by anti-TGF-beta treatment of the recipient mice. Despite this, TGF-beta may still have a role in CD4+ cell-mediated suppression of antiallograft responses in vivo, since its neutralization can, in some cases, abrogate suppression. These results show that TGF-beta signaling to T cells is dispensable for mounting destructive responses against skin allografts while appearing to be an essential intermediary in establishing long-term tolerance.

TGF-beta 1 regulates antigen-specific CD4+ T cell responses in the periphery

T cell expansion typically is due to cognate interactions with specific Ag, although T cells can be experimentally activated through bystander mechanisms not involving specific Ag. TGF-beta1 knockout mice exhibit a striking expansion of CD4+ T cells in the liver by 11 days of age, accompanied by CD4+T cell-dependent necroinflammatory liver disease. To examine whether hepatic CD4+T cell expansion in TGF-beta1(-/-) mice is due to cognate TCR-peptide interactions, we used spectratype analysis to examine the diversity in TCR Vbeta repertoires in peripheral CD4+T cells. We reasoned that Ag-nonspecific T cell responses would yield spectratype profiles similar to those derived from control polyclonal T cell populations, whereas Ag-specific T cell responses would yield perturbed spectratype profiles. Spleen and liver CD4+T cells from 11-day-old TGF-beta1(-/-) mice characteristically exhibited highly perturbed nonpolyclonal distributions of TCR Vbeta CDR3 lengths, indicative of Ag-driven T cell responses. We quantitatively assessed spectratype perturbation to derive a spectratype complexity score. Spectratype complexity scores were considerably higher for TGF-beta1(-/-) CD4+ T cells than for TGF-beta1(+/-) CD4+T cells. TCR repertoire perturbations were apparent as early as postnatal day 3 and preceded both hepatic T cell expansion and liver damage. By contrast, TGF-beta1(-/-) CD4+ single-positive thymocytes from 11-day-old mice exhibited normal unbiased spectratype profiles. These results indicate that CD4+ T cells in TGF-beta1(-/-) mice are activated by and respond to self-Ags present in the periphery, and define a key role for TGF-beta1 in the peripheral regulation of Ag-specific CD4+ T cell responses.

The role of TGF-beta superfamily during T cell development: new insights

Members of the transforming growth factor beta (TGF-beta) superfamily are soluble factors that regulate a variety of functional responses including proliferation, differentiation, apoptosis and cell cycle, among others, depending not only on the cell type and its differentiation state, but also on the milieu of cytokines present. All three members of this superfamily: TGF-betas, bone morphogenetic proteins (BMPs) and Activins, have been shown to be expressed in the thymus suggesting their potential role as regulators of the T lymphocyte differentiation process. Although initial reports described the role of TGF-beta in controlling specific checkpoints during thymocyte development, recent data has provided new evidence on the role of BMPs and Activins in this process. This review provides new insights on the function of members of the TGF-beta superfamily at different stages of thymocyte development.

Self-antigen recognition by TGF beta1-deficient T cells causes their activation and systemic inflammation

To investigate whether the multifocal inflammatory disease in TGFbeta1-deficient mice is caused by self-antigen (self-Ag)-specific autoreactive T cells, or whether it is caused by antigen independent, spontaneous hyperactivation of T cells, we have generated Tgfb1(-/-) and Tgfb1(-/-) Rag1(-/-) mice expressing the chicken OVA-specific TCR transgene (DO11.10). On a Rag1-sufficient background, Tgfb1(-/-) DO11.10 mice develop a milder inflammation than do Tgfb1(-/-) mice, and their T cells display a less activated phenotype. The lower level of activation correlates with the expression of hybrid TCR (transgenic TCRbeta and endogenous TCRalpha), which could recognize self-Ag and undergo activation. In the complete absence of self-Ag recognition (Tgfb1(-/-) DO11.10 Rag1(-/-) mice) inflammation and T-cell activation are eliminated, demonstrating that self-Ag recognition is required for the hyper-responsiveness of TGFbeta1-deficient T cells. Thus, TGFbeta1 is required for the prevention of autoimmune disease through its ability to control the activation of autoreactive T cells to self-Ag.

Infectious tolerance and the long-term acceptance of transplanted tissue

Short courses of antibody treatment aimed at blocking the coreceptors CD4 and CD8 and/or costimulatory molecules such as CD40L are able to bring about long-term acceptance and tolerance of allogeneic transplants. This tolerant state is operational, in that potential effector cells remain but are tightly regulated through the induction of antigen-specific CD4+ regulatory T cells (Tregs). CD4+ CD25+ FoxP3+ Tregs appear to play a prominent role, although other categories of Tregs have been documented. Transforming growth factor beta (TGFbeta) has been found to play a major role in the induction of the tolerant state with therapeutic antibodies as well as promoting the induction of FoxP3+ T cells from naïve populations. The observation that Tregs can be found in tolerated grafts has led to the idea that they may interact with the grafted tissue to establish a state of acquired privilege symmetrical with a similar privileged microenvironment around antigen-presenting cells in lymphoid tissues. Dampening of aggressive immune responses by Tregs allows antigen to persist and be presented in an innocuous way to promote tolerance in new cohorts of T cells throughout the life of the tolerated graft. Regulation may operate at many stages of an immune response, even as a censor at the terminal differentiation stages of effector function.

Restriction of the CD4+ T-cell receptor repertoire prevents immune pathology in TGF-beta1 knockout mice

Mice with a targeted deletion in TGF-beta1 spontaneously develop CD4+ T-cell-dependent multifocal inflammatory disease and autoimmune pathology. T cells from TGF-beta1-/- mice are strongly activated, but the mechanisms that lead to T-cell activation and organ pathology are not well understood. Recent work shows that TGF-beta1 raises the threshold for signaling through the TCR, suppressing the response of T cells to mitogenic stimuli. This suggests the possibility that CD4+ T cells in TGF-beta1-/- mice become aberrantly activated and cause damage in response to physiologic inputs that ordinarily are not sufficient for cell activation, such as homeostatic MHC-TCR interactions, cytokines, or adhesion molecules. This model predicts that pathology is largely antigen-independent, and that CD4+ T cells, regardless of antigen specificity, will become activated in TGF-beta1-/- mice, with subsequent organ pathology. To test this model, we crossed BALB/c-TGF-beta1-/- mice with the DO11.10 TCR transgenic mouse. To obviate the possible development of nonclonotypic TCRs, we also bred in a deficiency in RAG-1. Cohorts of highly inbred BALB/c background TGF-beta1-/- mice with an increasingly restricted CD4+ T-cell repertoire (TGF-beta1-/- mice; DO11.10-TGF-beta1-/- mice; DO11.10-RAG-1-/-TGF-beta1-/- mice) were then analyzed for inflammatory organ pathology and T-cell activation. The data show that progressively restricting the CD4+ T-cell repertoire improved survival, ameliorated target organ pathology, and reduced T-cell activation to control levels. Therefore, these results find no support for the involvement of atypical T-cell activation pathways in disease in TGF-beta1-/- mice. Rather, T-cell activation and pathology in TGF-beta1-/- mice appear to be functions of typical TCR activation pathways. This supports the hypothesis that immune pathology in TGF-beta1-/- mice is self-antigen triggered.

Transforming growth factor-beta regulation of immune responses

Transforming growth factor-beta (TGF-beta) is a potent regulatory cytokine with diverse effects on hemopoietic cells. The pivotal function of TGF-beta in the immune system is to maintain tolerance via the regulation of lymphocyte proliferation, differentiation, and survival. In addition, TGF-beta controls the initiation and resolution of inflammatory responses through the regulation of chemotaxis, activation, and survival of lymphocytes, natural killer cells, dendritic cells, macrophages, mast cells, and granulocytes. The regulatory activity of TGF-beta is modulated by the cell differentiation state and by the presence of inflammatory cytokines and costimulatory molecules. Collectively, TGF-beta inhibits the development of immunopathology to self or nonharmful antigens without compromising immune responses to pathogens. This review highlights the findings that have advanced our understanding of TGF-beta in the immune system and in disease.

Regulatory T cells in transplantation

Our ability to harness tolerance mechanisms will have a major impact in organ transplantation. It should enable drug minimization, and eventually, the elimination of all immunosuppressive drugs. An improved understanding of the biology of regulatory T cells will make it possible to replace current induction regimens with those favouring the selective vaccination of T cells that prevent graft rejection. Once regulation is established, the continued supply of graft antigens should empower T cell regulation to become the dominant natural mechanism to prevent graft rejection.

Regulatory T cells in transplantation tolerance

Our ability to harness tolerance mechanisms will have a major impact in organ transplantation if it becomes possible to minimize drug maintenance, or even wean off immunosuppressive drugs. An improved understanding of the biology of regulatory T cells will make it possible to replace current induction regimens with those favouring the vaccination and selection of T cells that prevent graft rejection. Once tolerance is established, the continuous supply of graft antigens should sustain T cell mediated regulation as the dominant mechanism preventing graft rejection.

TGF-beta 1 uses distinct mechanisms to inhibit IFN-gamma expression in CD4+ T cells at priming and at recall: differential involvement of Stat4 and T-bet

TGF-beta1 plays a critical role in restraining pathogenic Th1 autoimmune responses in vivo, but the mechanisms that mediate TGF-beta1's suppressive effects on CD4(+) T cell expression of IFN-gamma expression remain incompletely understood. To evaluate mechanisms by which TGF-beta1 inhibits IFN-gamma expression in CD4(+) T cells, we primed naive wild-type murine BALB/c CD4(+) T cells in vitro under Th1 development conditions in the presence or the absence of added TGF-beta1. We found that the presence of TGF-beta1 during priming of CD4(+) T cells suppressed both IFN-gamma expression during priming as well as the development of Th1 effector cells expressing IFN-gamma at a recall stimulation. TGF-beta1 inhibited the development of IFN-gamma-expressing cells in a dose-dependent fashion and in the absence of APC, indicating that TGF-beta1 can inhibit Th1 development by acting directly on the CD4(+) T cell. During priming, TGF-beta1 strongly inhibited the expression of both T-bet (T box expressed in T cells) and Stat4. We evaluated the importance of these two molecules in the suppression of IFN-gamma expression at the two phases of Th1 responses. Enforced expression of T-bet by retrovirus prevented TGF-beta1's inhibition of Th1 development, but did not prevent TGF-beta1's inhibition of IFN-gamma expression at priming. Conversely, enforced expression of Stat4 partly prevented TGF-beta1's inhibition of IFN-gamma expression during priming, but did not prevent TGF-beta1's inhibition of Th1 development. These data show that TGF-beta1 uses distinct mechanisms to inhibit IFN-gamma expression in CD4(+) T cells at priming and at recall.

Elimination of both CD4+ and CD8+ T cells but not B cells eliminates inflammation and prolongs the survival of TGFbeta1-deficient mice

Transforming growth factor beta1 (TGFbeta1) is a potent negative immunoregulatory molecule. We have previously shown that the autoimmune-mediated weaning-age lethality of Tgfb1-/- mice is reversed upon genetic combination with Scid or Rag null alleles. Here, we show that elimination of T but not B cells is sufficient for the reversal, but elimination of either CD4+ or CD8+ cells is not. Although elimination of B cells does not rescue TGFbeta1-deficient animals from autoimmunity, B cells are hyperresponsive to LPS in the absence of TGFbeta1. TGFbeta1 deficiency leads to activation of CD8+ T cells as suggested by down-modulation of CD8 even in the absence of CD4+ T cells. This study provides evidence that both CD4+ and CD8+ T cells, but not B cells, have the ability to cause inflammation in the absence of TGFbeta1. However, though TGFbeta1-deficient B cells are hyperresponsive to stimulation, alone they are not sufficient to cause inflammation.

Concerted effect of transforming growth factor-β, cyclin inhibitor p21, and c-mycon smooth muscle cell proliferation

Increased aortic smooth muscle cell (SMC) proliferation is a key event in the pathogenesis of atherosclerosis. Transforming growth factor-β (TGF-β) is one of the potent inhibitors of SMC proliferation. The purpose of this study was 1) to explore the effect of TGF-β inhibition on proliferation of SMC and expression of growth regulatory molecules like p21 and c- myc and 2) to determine whether restoration of cell cycle regulatory molecules normalizes the altered proliferation. To test the role of TGF-β in SMC proliferation, using antisense plasmid DNA, we inhibited TGF-β gene from aortic SMC, which resulted in a significant increase ( P < 0.03) in proliferation (studied by quantifying new DNA synthesis with [3H]thymidine uptake assay). In TGF-β-altered SMC (TASMC), the mRNA expression (studied by RT-PCR) of c- myc was increased whereas that of the cyclin inhibitor p21 was completely inhibited. Using p21 sense plasmid DNA, we transfected p21 gene in TASMC, which restored p21 mRNA and protein expression and decreased proliferation ( P < 0.002) in TASMC. Similar treatment with c- myc antisense oligonucleotides significantly ( P < 0.001) decreased the proliferation of TASMC. TASMC also exhibited alteration in morphological changes in SMC but returned to normal with treatment of p21 and TGF-β sense plasmid DNA. Two-dimensional gel electrophoresis analysis of SMC and TASMC demonstrated differential expression of proteins relevant to cellular proliferation and atherosclerosis. This study uniquely analyzes the effect of TGF-β at the molecular level on proliferation of SMC and on cell cycle regulatory molecules, implicating their potential role in the pathogenesis of atherosclerosis.

TGF-beta, T-cell tolerance and anti-CD3 therapy

Recent studies by Chatenoud and co-workers suggest that non-mitogenic F(ab′)2 fragments of anti-CD3 antibodies, which cannot bind the Fc receptor, induce a prolonged period of tolerance and prevent diabetes in nonobese diabetic (NOD) mice. Tolerance is established by regulatory T cells through the production of transforming growth factor-β1 (TGF-β1), but the mechanism by which TGF-β1 confers this activity is unclear. Analysis of mice deficient in TGF-β1 suggests that TGF-β1 raises the threshold at which intracellular calcium activates T cells to a level that prevents an autoimmune response.

Novel approaches to gene expression analysis of active polyarticular juvenile rheumatoid arthritis

Juvenile rheumatoid arthritis (JRA) has a complex, poorly characterized pathophysiology. Modeling of transcriptosome behavior in pathologic specimens using microarrays allows molecular dissection of complex autoimmune diseases. However, conventional analyses rely on identifying statistically significant differences in gene expression distributions between patients and controls. Since the principal aspects of disease pathophysiology vary significantly among patients, these analyses are biased. Genes with highly variable expression, those most likely to regulate and affect pathologic processes, are excluded from selection, as their distribution among healthy and affected individuals may overlap significantly. Here we describe a novel method for analyzing microarray data that assesses statistically significant changes in gene behavior at the population level. This method was applied to expression profiles of peripheral blood leukocytes from a group of children with polyarticular JRA and healthy control subjects. Results from this method are compared with those from a conventional analysis of differential gene expression and shown to identify discrete subsets of functionally related genes relevant to disease pathophysiology. These results reveal the complex action of the innate and adaptive immune responses in patients and specifically underscore the role of IFN-γ in disease pathophysiology. Discriminant function analysis of data from a cohort of patients treated with conventional therapy identified additional subsets of functionally related genes; the results may predict treatment outcomes. While data from only 9 patients and 12 healthy controls was used, this preliminary investigation of the inflammatory genomics of JRA illustrates the significant potential of utilizing complementary sets of bioinformatics tools to maximize the clinical relevance of microarray data from patients with autoimmune disease, even in small cohorts.

Transforming growth factor beta in cardiovascular development and function

Transforming growth factor betas (TGFbetas) are pleiotropic cytokines involved in many biological processes. Genetic engineering and tissue explanation studies have revealed specific non-overlapping roles for TGFbeta ligands and their signaling molecules in development and in normal function of the cardiovascular system in the adult. In the embryo, TGFbetas appear to be involved in epithelial-mesenchymal transformations (EMT) during endocardial cushion formation, and in epicardial epithelial-mesenchymal transformations essential for coronary vasculature, ventricular myocardial development and compaction. In the adult, TGFbetas are involved in cardiac hypertrophy, vascular remodeling and regulation of the renal renin-angiotensin system. The evidence for TGFbeta activities during cardiovascular development and physiologic function will be given and areas which need further investigation will be discussed.

TGF-beta 1 regulates lymphocyte homeostasis by preventing activation and subsequent apoptosis of peripheral lymphocytes

TGF-beta1 plays an important role in the maintenance of immune homeostasis and self-tolerance. To determine the mechanism by which TGF-beta1 prevents autoimmunity we have analyzed T cell activation in splenic lymphocytes from TGF-beta1-deficient mice. Here we demonstrate that unlike wild-type splenic lymphocytes, those from Tgfb1(-/-) mice are hyporesponsive to receptor-mediated mitogenic stimulation, as evidenced by diminished proliferation and reduced IL-2 production. However, they have elevated levels of IFN-gamma and eventually undergo apoptosis. Receptor-independent stimulation of Tgfb1(-/-) T cells by PMA plus ionomycin induces IL-2 production and mitogenic response, and it rescues them from anergy. Tgfb1(-/-) T cells display decreased CD3 expression; increased expression of the activation markers LFA-1, CD69, and CD122; and increased cell size, all of which indicate prior activation. Consistently, mutant CD4(+) T cells have elevated intracellular Ca(2+) levels. However, upon subsequent stimulation in vitro, increases in Ca(2+) levels are less than those in wild-type cells. This is also consistent with the anergic phenotype. Together, these results demonstrate that the ex vivo proliferative hyporesponsiveness of Tgfb1(-/-) splenic lymphocytes is due to prior in vivo activation of T cells resulting from deregulated intracellular Ca(2+) levels.