CD4+CD25+ regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4+CD25−T cells and are potent suppressors of T cell activation in vitro. Their mechanism of suppression remains unknown, but most in vitro studies suggest that it is cell contact–dependent and cytokine independent. The role of TGF-β1 in CD4+CD25+ suppressor function remains unclear. While most studies have failed to reverse suppression with anti–transforming growth factor (TGF)-β1 in vitro, one recent study has reported that CD4+CD25+ T cells express cell surface TGF-β1 and that suppression can be completely abrogated by high concentrations of anti–TGF-β suggesting that cell-associated TGF-β1 was the primary effector of CD4+CD25+-mediated suppression. Here, we have reevaluated the role of TGF-β1 in CD4+CD25+-mediated suppression. Neutralization of TGF-β1 with either monoclonal antibody (mAb) or soluble TGF-βRII-Fc did not reverse in vitro suppression mediated by resting or activated CD4+CD25+ T cells. Responder T cells from Smad3−/− or dominant-negative TGF-β type RII transgenic (DNRIITg) mice, that are both unresponsive to TGF-β1–induced growth arrest, were as susceptible to CD4+CD25+-mediated suppression as T cells from wild-type mice. Furthermore, CD4+CD25+ T cells from neonatal TGF-β1−/− mice were as suppressive as CD4+CD25+ from TGF-β1+/+ mice. Collectively, these results demonstrate that CD4+CD25+ suppressor function can occur independently of TGF-β1.
CD4+ suppressor T cells; autoimmunity; tolerance; immunoregulation; IL-2 receptor
B cells are generally considered to positively regulate immune responses by producing antigen-specific antibodies. B cells are classified into classical CD5- conventional B cells and CD5+ B1 cells. The latter produce multi-specific autoantibodies and are thought to be involved in autoimmune diseases. However, evidence supporting a B cell negative regulatory function has accumulated over the past 30 years. Multiple reports have suggested that absence, or loss, of regulatory B cells exacerbates symptoms of both allergic (including contact hypersensitivity and anaphylaxis) and autoimmune (such as experimental autoimmune encephalomyelitis, chronic colitis, and collagen-induced arthritis) diseases, and in lupus-like models of autoimmunity. Regulatory B cells are characterized by production of the negative regulatory cytokines, IL-10 and TGF-β. IL-10-producing B cells were the first regulatory B cells to be recognized and were termed 'B10' cells. IL-10-producing regulatory B cells are of the CD19+CD5+IgMhiIgDloCD1dhi type. Recently, a TGF-β-producing regulatory B cell subset, Br3, has been shown to be related to immune tolerance in food allergies. Moreover, forkhead box P3 (Foxp3)-expressing B cells have also been identified in humans and may act as regulatory B cells (Bregs). The functional image of regulatory B cells is similar to that of regulatory T cells. Because of the proliferative and apoptotic responses of Br1 and Br3 cells in immune tolerance in non-IgE-mediated food allergy, reciprocal roles and counter-regulatory mechanisms of Br1 and Br3 responses are also suspected. Additionally, different roles for regulatory B and T cells at different time points during initiation and progression of autoimmune disease are described.
Regulatory B cell; allergy; IL-10; TGF-β; CD5+ B; atopic dermatitis; asthma; food allergy; tolerance; counter-regulation
Naturally occurring CD4+CD25+ regulatory T cells mediate immune suppression to limit immunopathogenesis associated with chronic inflammation, persistent infections and autoimmune diseases. Their mode of suppression is contact-dependent, antigen-nonspecific and involves a nonredundant contribution from the cytokine transforming growth factor (TGF)-β. Not only can TGF-β mediate cell–cell suppression between the regulatory T cells and CD4+CD25- or CD8+ T cells, but new evidence also reveals its role in the conversion of CD4+CD25- T cells, together with TCR antigen stimulation, into the regulatory phenotype. Elemental to this conversion process is induction of expression of the forkhead transcription factor, Foxp3. This context-dependent coercion of naive CD4+ T cells into a powerful subset of regulatory cells provides a window into potential manipulation of these cells to orchestrate therapeutic intervention in diseases characterized by inadequate suppression, as well as a promising means of controlling pathologic situations in which excessive suppression dominates.
CD8+ T cells have suppressor effector functions, but the mechanisms involved in the generation of this activity are poorly understood. We report that natural killer (NK) cells have an important role in the acquisition of this function. CD8+ cells induce NK cells to produce transforming growth factor-beta (TGF-beta) which, in turn, stimulates CD8+ T cells to become suppressors of antibody production. Using a monocyte-dependent and -independent method to induce antibody production, we first observed that the addition of NK cells to CD8+ cells was required for optimal suppression. Next, we determined that the interaction of CD8+ T cells with NK cells resulted in a striking increase NK cell TGF-beta mRNA and its production. This cytokine appeared to be involved in the induction of T suppressor cell activity since: (a) anti-TGF-beta 1 completely abrogated the suppression of immunoglobulin G synthesis; (b) TGF-beta 1 could substitute for NK cells in inducing CD8+ T cells to develop suppressor activity; and (c) a short exposure of T cells to TGF-beta 1 in the absence of B cells was sufficient for the generation of suppressor activity by CD8+ T cells. Interferon gamma did not have this property. These studies provide strong evidence that in addition to its suppressive properties, TGF- beta is involved in the generation of CD8+ T suppressor effector cells. Because NK cell function is decreased in many autoimmune diseases, these cells may fail to interact properly with these individuals' CD8+ cells in generating suppressors of aggressive anti-self responses.
The hyperactive interaction between helper T cells and autoimmune B cells in individuals predisposed to systemic lupus erythematosus (SLE) can be interrupted by induction of regulatory and suppressor T cells. Using two strategies—high dose tolerance to an immunoglobulin-derived peptide, and minigene vaccination with DNA encoding T cell epitopes presented by MHC class I molecules—our group has induced at least three types of regulatory/suppressive T cells. They include CD8+ T cells that suppress helper T cells by cytokine secretion, CD8+ T suppressors that kill B cells making anti-DNA antibodies, and peptide-binding CD4+CD25+ regulatory T cells that suppress B cells by direct cell contact. Each of these lymphocyte subsets suppresses anti-DNA antibody production and delays the onset of nephritis in BWF1 lupus-prone mice. Patients with SLE have amino acid sequences similar to those from murine anti-DNA antibodies used in these studies, and at similar locations in the VH regions of anti-DNA immunoglobulins. Therefore, strategies described here might ultimately be useful in therapy of the human disease.
systemic lupus erythematosus; CD8+ T cells; regulatory T cells; suppressor T cells
Immune evasion is now recognized as a key feature of cancer progression. In animal models, the activity of cytotoxic lymphocytes is suppressed in the tumour microenvironment by the immunosuppressive cytokine, Transforming Growth Factor (TGF)-β. Release from TGF-β-mediated inhibition restores anti-tumour immunity, suggesting a therapeutic strategy for human cancer. We demonstrate that human natural killer (NK) cells are inhibited in a TGF-β dependent manner following chronic contact-dependent interactions with tumour cells in vitro. In vivo, NK cell inhibition was localised to the human tumour microenvironment and primary ovarian tumours conferred TGF-β dependent inhibition upon autologous NK cells ex vivo. TGF-β antagonized the interleukin (IL)-15 induced proliferation and gene expression associated with NK cell activation, inhibiting the expression of both NK cell activation receptor molecules and components of the cytotoxic apparatus. Interleukin-15 also promotes NK cell survival and IL-15 excluded the pro-apoptotic transcription factor FOXO3 from the nucleus. However, this IL-15 mediated pathway was unaffected by TGF-β treatment, allowing NK cell survival. This suggested that NK cells in the tumour microenvironment might have their activity restored by TGF-β blockade and both anti-TGF-β antibodies and a small molecule inhibitor of TGF-β signalling restored the effector function of NK cells inhibited by autologous tumour cells. Thus, TGF-β blunts NK cell activation within the human tumour microenvironment but this evasion mechanism can be therapeutically targeted, boosting anti-tumour immunity.
Human immunodeficiency virus (HIV) disease is associated with loss of CD4+ T cells, chronic immune activation, and progressive immune dysfunction. HIV-specific responses, particularly those of CD4+ T cells, become impaired early after infection, before the loss of responses directed against other antigens; the basis for this diminution has not been elucidated fully. The potential role of CD25+CD4+ regulatory T cells (T reg cells), previously shown to inhibit immune responses directed against numerous pathogens, as suppressors of HIV-specific T cell responses was investigated. In the majority of healthy HIV-infected individuals, CD25+CD4+ T cells significantly suppressed cellular proliferation and cytokine production by CD4+ and CD8+ T cells in response to HIV antigens/peptides in vitro; these effects were cell contact dependent and IL-10 and TGF-β independent. Individuals with strong HIV-specific CD25+ T reg cell function in vitro had significantly lower levels of plasma viremia and higher CD4+: CD8+ T cell ratios than did those individuals in whom this activity could not be detected. These in vitro data suggest that CD25+CD4+ T reg cells may contribute to the diminution of HIV-specific T cell immune responses in vivo in the early stages of HIV disease.
cytokine; proliferation; human; suppression; FoxP3
Previous studies suggest that thymus produces a homogenous population of natural regulatory T cells (TR) that express a transcriptional factor Foxp3 and control autoimmunity through a cell contact-dependent mechanism. We found two subsets of Foxp3+ natural TR defined by ICOS-expression in the human thymus and periphery. While the ICOS+Foxp3+ TR use IL-10 to suppress dendritic cell function and TGF-β to suppress T cell function, the ICOS−Foxp3+ TR use TGF-β only. The survival and proliferation of the two subsets of TR are differentially regulated by signaling through ICOS or CD28 respectively. We suggest that the selection of natural TR in thymus is coupled with TR differentiation into two subsets imprinted with different cytokine expression potentials and use both cell-contact-dependent and independent mechanisms for immunosuppression in periphery.
Lupus is an Ab-mediated autoimmune disease. One of the potential contributors to the development of systemic lupus erythematosus is a defect in naturally occurring CD4+CD25+ regulatory T cells. Thus, the generation of inducible regulatory T cells that can control autoantibody responses is a potential avenue for the treatment of systemic lupus erythematosus. We have found that nasal administration of anti-CD3 mAb attenuated lupus development as well as arrested ongoing lupus in two strains of lupus-prone mice. Nasal anti-CD3 induced a CD4+CD25-latency-associated peptide (LAP)+ regulatory T cell that secreted high levels of IL-10 and suppressed disease in vivo via IL-10- and TFG-β-dependent mechanisms. Disease suppression also occurred following adoptive transfer of CD4+CD25-LAP+ regulatory T cells from nasal anti-CD3-treated animals to lupus-prone mice. Animals treated with nasal anti-CD3 had less glomerulonephritis and diminished levels of autoantibodies as measured by both ELISA and autoantigen microarrays. Nasal anti-CD3 affected the function of CD4+ICOS+CXCR5+ follicular helper T cells that are required for autoantibody production. CD4+ICOS+CXCR5+ follicular helper T cells express high levels of IL-17 and IL-21 and these cytokines were down-regulated by nasal anti-CD3. Our results demonstrate that nasal anti-CD3 induces CD4+CD25-LAP+ regulatory T cells that suppress lupus in mice and that it is associated with down-regulation of T cell help for autoantibody production.
Regulatory T cells (T-reg) represent a major roadblock to the induction of anti-tumor immunity through vaccine approaches. TGF-β is a cytokine implicated in the generation and maintenance of T-reg cells, as well as their suppressive function. These experiments examined whether the generation of tumor-sensitized T-reg cells was TGF-β dependent and evaluated whether TGF-β produced by T-reg cells blocked the priming of tumor-specific T cells in vaccinated reconstituted-lymphopenic mice (RLM). We show that tumor-sensitized T-reg cells (CD25+/FoxP3+) obtained from tumor-bearing mice block the generation of tumor-specific T cells in RLM. Strikingly, this suppression is absent if tumor-sensitized T-reg cells are acquired from tumor-bearing mice expressing the dominant-negative TGFβRII in T cells. This loss of suppression was a result of the crucial role of TGF-β in generating tumor-sensitized T-reg cells, and not due to the insensitivity of naïve or tumor-primed effector T cells to the direct suppressive influence of TGF-β. We conclude that blocking TGF-β in a tumor-bearing host can inhibit the induction of highly suppressive tumor-sensitized T-reg. These data suggest that an integrative strategy combining “upfront” T-reg ablation followed by vaccination and TGF-β blockade may limit generation of new tumor-sensitized T-regs and improve the generation of therapeutic immune responses in patients with cancer.
Tumor Immunity; Tolerance/Suppression/Anergy; Cytokines; T Cells; Adoptive immunotherapy
Ample evidence suggests a role of TGF-β in preventing autoimmunity. Multiorgan inflammatory disease, spontaneous activation of self-reactive T cells, and autoantibody production are hallmarks of autoimmune diseases, such as lupus. These features are reminiscent of the immunopathology manifest in TGF-β1-deficient mice. In this study, we show that lupus-prone (New Zealand Black and White)F1 mice have reduced expression of TGF-β1 in lymphoid tissues, and TGF-β1 or TGF-β1-producing T cells suppress autoantibody production. In contrast, the expression of TGF-β1 protein and mRNA and TGF-β signaling proteins (TGF-β receptor type II and phosphorylated SMAD3) increases in the target organs, i.e., kidneys, of these mice as they age and develop progressive organ damage. In fact, the levels of TGF-β1 in kidney tissue and urine correlate with the extent of chronic lesions that represent local tissue fibrosis. In vivo TGF-β blockade by treatment of these mice with an anti-TGF-β Ab selectively inhibits chronic fibrotic lesions without affecting autoantibody production and the inflammatory component of tissue injury. Thus, TGF-β plays a dual, seemingly paradoxical, role in the development of organ damage in multiorgan autoimmune diseases. According to our working model, reduced TGF-β in immune cells predisposes to immune dysregulation and autoantibody production, which causes tissue inflammation that triggers the production of anti-inflammatory cytokines such as TGF-β in target organs to counter inflammation. Enhanced TGF-β in target organs, in turn, can lead to dysregulated tissue repair, progressive fibrogenesis, and eventual end-organ damage.
Activation and proliferation of T cells require a reducing extracellular microenvironment in the immune synapse that is provided by antigen presenting cells especially dendritic cells. Stimulation of dendritic cells by T cells activates the NF-κB pathway in dendritic cells and induces an antioxidant response. It also enhances system xc--dependent cystine uptake, leading to increased glutathione synthesis, export and finally, degradation to cysteine outside the cell. Accumulation of extracellular cysteine supports glutathione synthesis in T cells while also leading to a more reducing redox potential that is needed for T cell proliferation. Naturally occurring regulatory T cells, a suppressor sub-population of T cells, prevent autoimmune diseases and maintain peripheral tolerance by suppressing self-reactive effector T cells. They also suppress beneficial immune responses to parasites, viruses and tumors. However, their mechanism of suppression is still not fully understood. Recently, we have found that inhibition by regulatory T cells of dendritic cell-induced extracellular redox remodeling is a component of the regulatory T cell suppression mechanism. In this review, we describe recent advances in our understanding of redox regulation and signaling in the adaptive immune system with a focus on T cell activation by dendritic cells. The role of regulatory T cells in perturbing redox remodeling by dendritic cells and its implications as a general regulatory T cell suppression mechanism are discussed.
CD4+CD25+ T cells have been identified as a population of immunoregulatory T cells, which mediate suppression of CD4+CD25− T cells by cell–cell contact and not secretion of suppressor cytokines. In this study, we demonstrated that CD4+CD25+ T cells do produce high levels of transforming growth factor (TGF)-β1 and interleukin (IL)-10 compared with CD4+CD25− T cells when stimulated by plate-bound anti-CD3 and soluble anti-CD28 and/or IL-2, and secretion of TGF-β1 (but not other cytokines), is further enhanced by costimulation via cytotoxic T lymphocyte–associated antigen (CTLA)-4. As in prior studies, we found that CD4+CD25+ T cells suppress proliferation of CD4+CD25− T cells; however, we observed here that such suppression is abolished by the presence of anti–TGF-β. In addition, we found that CD4+CD25+ T cells suppress B cell immunoglobulin production and that anti–TGF-β again abolishes such suppression. Finally, we found that stimulated CD4+CD25+ T cells but not CD4+CD25− T cells express high and persistent levels of TGF-β1 on the cell surface. This, plus the fact that we could find no evidence that a soluble factor mediates suppression, strongly suggests that CD4+CD25+ T cells exert immunosuppression by a cell–cell interaction involving cell surface TGF-β1.
T lymphocytes, suppressor-effector; CD4-positive T lymphocytes; receptors, interleukin 2; transforming growth factors; autoimmune diseases
A regulatory role is proposed for the antigen-responsive B cell, as suppressor-inducer of feedback control during the secondary response in vivo. In a double adoptive transfer of memory cells primed to a thymus- dependent antigen from one irradiated host to another, antigen-specific suppressors are generated after a critical time in the primary recipient, able to entirely ablate a secondary anti-hapten response. Positive cell selection in the fluorescence-activated cell sorter confirmed that suppression was mediated by an Lyt-2+ T cell; however, positively selected B cells were also inhibitory and able to induce suppressors in a carrier-specific manner: Bhapten induced suppressors in a carrier-primed population, and Bcarrier induced suppressors in a hapten-carrier population. At the peak of the antibody response in the primary host, memory B cells and their progeny were unable to differentiate further to plasma cells due to their intrinsic suppressor- inducer activity, but this autoregulatory circuit could be severed by adoptive transfer to carrier-primed, X-irradiated recipients.
Interplay between Foxp3+ regulatory T cells (Treg) and dendritic cells (DCs) maintains immunologic tolerance, but the effects of each cell on the other are not well understood. We report that polyclonal CD4+Foxp3+ Treg cells induced ex vivo with transforming growth factor beta (TGFβ) (iTreg) suppress a lupus-like chronic graft-versus-host disease by preventing the expansion of immunogenic DCs and inducing protective DCs that generate additional recipient CD4+Foxp3+ cells. The protective effects of the transferred iTreg cells required both interleukin (IL)-10 and TGFβ, but the tolerogenic effects of the iTreg on DCs, and the immunosuppressive effects of these DCs were exclusively TGFβ-dependent. The iTreg were unable to tolerize Tgfbr2-deficient DCs. These results support the essential role of DCs in ‘infectious tolerance’ and emphasize the central role of TGFβ in protective iTreg/DC interactions in vivo.
regulatory T cells; dendritic cells; TGFβ; graft-versus-host disease
Infectious tolerance is a process whereby one regulatory lymphoid population confers suppressive capacity on another. Diverse immune responses are induced following infection or inflammatory insult that can protect the host, or potentially cause damage if not properly controlled. Thus, the process of infectious tolerance may be critical in vivo for exerting effective immune control and maintaining immune homeostasis by generating specialized regulatory subpopulations with distinct mechanistic capabilities. Foxp3+ regulatory T cells (Tregs) are a central mediator of infectious tolerance through their ability to convert conventional T cells into induced regulatory T cells (iTregs) directly by secretion of the suppressive cytokines TGF-β, IL-10 or IL-35, or indirectly via dendritic cells. In this review we will discuss the mechanisms and cell populations that mediate and contribute to infectious tolerance, with a focus on the intestinal environment, where tolerance induction to foreign material is critical.
Infectious tolerance; regulatory T cell; intestine; helminth; microbiota
One of the major goals for the immunotherapy of autoimmune diseases is the induction of regulatory T cells that mediate immunologic tolerance. Parenteral administration of anti-CD3 monoclonal antibody is an approved therapy for transplantation in humans and is effective in autoimmune diabetes. We have found that oral administration of anti-CD3 monoclonal antibody is biologically active in the gut and suppresses experimental autoimmune encephalomyelitis both prior to disease induction and at the height of disease. Oral anti-CD3 antibody acts by inducing a unique type of regulatory T cell characterized by latency-associated peptide (LAP) on its cell surface that functions in vivo and in vitro via TGF-β dependent mechanism. Orally delivered antibody would not have side effects including cytokine release syndromes, thus oral anti-CD3 antibody is clinically applicable for chronic therapy. These findings identify a novel and powerful immunologic approach that is widely applicable for the treatment of human autoimmune conditions.
regulatory cell; TGF-β; antibody; multiple sclerosis; autoimmunity
The mechanism of alloantigen-activated spleen cell suppression of mixed lymphocyte reaction (MLR) is explored in this report. Activated murine suppressor spleen cells elaborated a soluble noncytotoxic factor which suppressed MLR responses by 55-95%. Generation of suppressor factor required both in vivo alloantigen sensitization and specific in vitro restimulation. Suppressor factor was not produced by activated spleen cells which had been treated with anti-Thy-1.2 serum and complement. Antigenic specificity toward alloantigens of the stimulator cells was not demonstrable. In contrast, suppressor factor effectively inhibited MLR response only of responder cells of those strains that shared the D- end and the I-C subregion of the H-2 complex with the cells producing suppressor factor. Therefore, active suppression appears to require an MHC-directed homology relationship between regulating and responder cells in MLR.
T helper cells that produce IL-17 (Th17 cells) promote autoimmunity in mice and have been implicated in pathogenesis of human inflammatory diseases. At mucosal surfaces Th17 cells are thought to protect the host from infection while regulatory T (Treg) cells control immune responses and inflammation triggered by the resident microflora1–5. Differentiation of both cell types requires TGF-β, but depends on distinct transcription factors, RORγt for Th17 and Foxp3 for Treg cells6-8. How TGF-β regulates the differentiation of T cells with opposing activities has been perplexing. Here, we demonstrate that together with pro-inflammatory cytokines TGF-β orchestrates Th17 cell differentiation in a concentration-dependent manner. At low concentrations, TGF-β synergizes with IL-6 and IL-21 (ref. 9-11) to promote IL-23R expression, favoring Th17 cell differentiation. High concentrations of TGF-β repress IL-23R expression and favor Foxp3+ Treg cells. RORγt and Foxp3 are co-expressed in naïve CD4+ T cells exposed to TGF-β and in a subset of T cells in the small intestinal lamina propria (LP). In vitro, TGF-β-induced Foxp3 inhibits RORγt function at least in part through their interaction. Accordingly, LP T cells that co-express both transcription factors produce less IL-17 than those that express RORγt alone. IL-6, IL-21 and IL-23 relieve Foxp3-mediated inhibition of RORγt, thereby promoting Th17 cell differentiation. Therefore, the decision of antigen-stimulated cells to differentiate into Th17 or Treg cells depends upon the cytokine-regulated balance of RORγt and Foxp3.
Regulatory CD8+ T cells are critical for self-tolerance and restricting excessive immune responses. The variety of immune functions they fulfill, the heterogeneity of their phenotype, and the mechanism of action are still poorly understood. Here we describe that regulatory CD8+ T cells exhibiting immunosuppressive actions in vitro and in vivo are recognized as CD38high T cells and present in naive mice. CD38 is a glycosylated membrane protein with ectonucleotidase properties. CD8+CD38high (CD44+CD122+CD62Lhigh) lymphocytes suppress CD4+ effector T-cell proliferation in an antigen-non specific manner via IFN-γ. While direct cell-to-cell contact is needed for this suppressor activity, it is independent of membrane-bound TGF-β and granzyme B release. IL-15 potentiates the suppressive activity of CD8+CD38high T cells and controls their survival and expansion. In humans CD8+CD38high T cells inhibit CD4+ effector T cell proliferation. In vivo, CD8+CD38high, but not CD8+CD38− T cells mitigate murine experimental autoimmune encephalomyelitis (EAE) by reducing the clinical score and delaying disease occurrence. EAE suppression is enhanced by pre-treatment of CD8+CD38high T cells with IL-15. These findings add evidence that the expression of ectoenzyme receptor family members positively correlates with suppressor functions and identifies CD8+CD38high T cells as potential inhibitors of excessive immune responses.
Colonization with helminthic parasites induces mucosal regulatory cytokines, like IL-10 or TGF-β that are important in suppressing colitis. Helminths induce mucosal T cell IL-10 secretion and regulate lamina propria mononuclear cell Th1 cytokine generation in an IL-10 dependent manner in wild-type mice. Helminths also stimulate mucosal TGF-β release. As TGF-β exerts major regulatory effects on T lymphocytes, we investigated the role of T lymphocyte TGF-β signaling in helminthic modulation of intestinal immunity. T cell TGF-β signaling is interrupted in TGF-βRII DN mice by T cell-specific over-expression of a dominant negative TGF-β receptor II. We studied lamina propria mononuclear cell responses in wild-type and TGF-βRII DN mice that were uninfected or colonized with the nematode, Heligmosomoides polygyrus. Our results indicate an essential role of T cell TGF-β signaling in limiting mucosal Th1 and Th2 responses. Furthermore, we demonstrate that helminthic induction of intestinal T cell IL-10 secretion requires intact T cell TGF-β signaling pathway. Helminths fail to curtail robust, dysregulated intestinal Th1 cytokine production and chronic colitis in TGF-βRII DN mice. Thus, T cell TGF-β signaling is essential for helminthic stimulation of mucosal IL-10 production, helminthic modulation of intestinal interferon-γ generation and H. polygyrus-mediated suppression of chronic colitis.
TGF-β; IL-10; helminths; lamina propria mononuclear cells; regulatory T cells
Tuberculosis (TB) is a disease caused by the chronic and continuous infection of the pathogen Mycobacterium tuberculosis (M. tuberculosis). M. tuberculosis is an intracellular bacterial pathogen and is eliminated mainly through CD4+ effector Th cells. M. tuberculosis induces regulatory T lymphocytes (Tregs) that mediate immune suppression by cell-to-cell contact or by secreting cytokines such as transforming growth factor-β (TGF-β). To understand the role of regulatory T-cells in the pathogenesis of TB, we have measured the in vivo frequency of regulatory T-cells and associated in vivo cytokine production in pulmonary tuberculosis patients.
In this study, we analyzed blood samples from 3 different populations (Group 1: patients with active TB, Group 2: patients recovered from TB and Group 3: healthy controls). We measured natural regulatory T-cell expression in peripheral blood using flow cytometry, and levels of blood serum IFN-γ and TGF-β1 using ELISA. The in vivo function of inductive regulatory T cells was mainly indicated by the expression of IFN-γ, TGF-β1, etc. Frequencyof natural regulatory T cells and inductive regulatory T cells in the peripheral blood samples from Group 1 patients were all significantly higher (P<0.05) than those from Groups 2 and 3.
Our results indicate that frequency of natural regulatory T cells and inductive regulatory T cells are significantly higher in the peripheral blood of patients with active pulmonary tuberculosis. These findings have potential application in improving TB diagnostic methods.
Transforming growth factor beta (TGF-β)- and Interleukin-2 (IL-2)-mediated signaling enables the generation and expansion of induced regulatory T (iTreg) cells that carry high hopes for the treatment of chronic inflammatory and autoimmune diseases. Knowledge about factors stabilizing their lineage commitment and lifespan, however, is limited. Here, we investigated the behavior of iTreg cells, derived from apoptosis-defective mouse mutants, during activated cell autonomous cell death, triggered by cytokine-deprivation, or activation-induced cell death (AICD) after restimulation of the T-cell receptor, and compared these responses with those of effector T cells. We observed that iTreg cells were much more sensitive to IL-2-deprivation but poorly susceptible to AICD. In fact, when apoptosis was compromised, T-cell receptor (TCR)-religation resulted in methylation-independent, ERK- and PI3K/mTOR-mediated loss of Foxp3 expression, impaired suppressive capacity and effector cytokine production. Although iTreg cells prevented colitis induction they rapidly lost Foxp3-GFP expression and gained ability to produce effector cytokines thereby imposing Th1 cell fate on resident effector cells. Surprisingly, iTreg cell conversion itself was limited by TGF-β-mediated Bim/Bcl2L11-dependent apoptosis. Hence, the very same cytokine that drives the generation of iTreg cells can trigger their demise. Our results provide novel insights in iTreg cell biology that will assist optimization of iTreg-based therapy.
activation-induced cell death; activated cell autonomous cell death; TGF-β; regulatory T cells
The pro-inflammatory cytokines play a critical role in the initiation and propagation of autoimmune arthritis and many other disorders resulting from a dysregulated self-directed immune response. These cytokines influence the interplay among the cellular, immunological and biochemical mediators of inflammation at multiple levels. Regulation of the pro-inflammatory activity of these cytokines is generally perceived to be mediated by the anti-inflammatory and immunosuppressive cytokines such as IL-4, IL-10, or TGF-β. However, increasing evidence is accumulating in support of the regulatory attributes of the pro-inflammatory cytokines themselves, in studies conducted in animal models of diabetes, multiple sclerosis, uveitis, and lupus. The results of our recent studies have shown that the pro-inflammatory cytokines, TNF-α and IFN-γ, can suppress arthritic inflammation in rats, and also contribute to resistance against arthritis. These results are of paramount significance not only in fully understanding the pathogenesis of autoimmune arthritis, but also in anticipating the full ramifications of the in vivo neutralization of the pro-inflammatory cytokines, including that for therapeutic purposes.
An early reaction of CD4+ T lymphocytes to antigen is the production of cytokines, notably IL-2. In order to detect cytokine dependent responses, naive antigen-specific T cells were stimulated in vivo and the presence of phosphorylated STAT5 molecules was used to identify the cell populations responding to IL-2. Within hours of T-cell priming, IL-2-dependent STAT5 phosphorylation occurred primarily in Foxp3+ regulatory T cells. In contrast, the antigen-specific T cells received STAT5 signals only after repeated antigen exposure or memory differentiation. Regulatory T cells receiving IL-2 signals proliferated and developed enhanced suppressive activity. These results indicate that one of the earliest events in a T cell response is the activation of endogenous regulatory cells, potentially to prevent autoimmunity.
T-cells; cytokines; cell activation; tolerance/suppression