'Yin-Yang' functions of transforming growth factor-beta and T regulatory cells in immune regulation

Increased ΤGF-β3 in primary biliary cirrhosis: an abnormality related to pathogenesis?

AIM

To investigate the transforming growth factor-β (TGF-β) isoforms in the peripheral and hepatic venous blood of primary biliary cirrhosis (PBC) patients.

METHODS

We examined TGF-β1, TGF-β2 and TGF-β3 (enzyme-linked immunosorbent assay), in 27 stage IV PBC patients (27 peripheral and 15 hepatic vein sera), 35 early (I-II) PBC and 60 healthy controls. As disease controls 28 hepatitis C virus (HCV) cirrhosis (28 peripheral and 17 hepatic vein serum), 44 chronic HCV hepatitis and 38 HCV-related hepatocellular carcinomas were included. We also tested liver tissue by immunohistochemistry to identify localization of TGF isoforms.

RESULTS

TGF-β1 was significantly decreased in all cirrhotics (PBC III-IV: median 13.4 ng/mL; range, 7.4-26.2, HCV cirrhosis: 11.6 ng/mL; range, 5.0-33.8), compared to controls (30.9 ng/mL; range, 20.9-37.8). TGF-β2 was increased in viral cirrhosis but not in PBC and chronic hepatitis. TGF-β3 (47.2 pg/mL; range, 27.0-79.7 in healthy controls) was increased in early and late PBC (I-II: 94.3 pg/mL; range, 41.5-358.6; III-IV: 152.8 pg/mL; range, 60.4-361.2; P < 0.001) and decreased in viral cirrhosis (37.4 pg/mL; range, 13.3-84.0; P < 0.05). Hepatic vein TGF-β levels were analogous to those in peripheral blood. Immunohistochemistry identified all isoforms in portal tract lymphocytes, sinusoidal cells and cholangiocytes. TGF-β3 was additionally overexpressed in hepatocytes in PBC patients.

CONCLUSION

The serum profile of TGF-β isoforms is different in cirrhotics. Increased TGF-β3 is characteristic of PBC. These findings may be related to the immunological abnormalities of PBC.

IL-2 and IL-4 stimulate MEK1 expression and contribute to T cell resistance against suppression by TGF-beta and IL-10 in asthma

The T cell-driven airway inflammation in chronic asthma is uninhibited and sustained. We examined the resistance of T cells from asthmatic patients against suppression by TGF-β, IL-10 and glucocorticoids and explored its signaling mechanism. CD4(+)CD25(-) T cells from allergic asthmatic subjects demonstrated increased TCR-stimulated proliferation as compared with healthy and chronic obstructive pulmonary disease controls. This proliferation was resistant to inhibition by TGF-β, IL-10, and dexamethasone and to anergy induction. CD4 T cells from asthmatic patients, but not chronic obstructive pulmonary disease, allergic rhinitis, and healthy subjects, showed increased expression of MEK1, heightened phosphorylation of ERK1/2, and increased levels of c-Fos. IL-2 and IL-4 stimulated the expression of MEK1 and c-Fos and induced T cell resistance. The inhibition of MEK1 reversed, whereas induced expression of c-Fos and JunB promoted T cell resistance against TGF-β- and IL-10-mediated suppression. We have uncovered an IL-2- and IL-4-driven MEK1 induction mechanism that results in heightened ERK1/2 activation in asthmatic T cells and make them resistant to certain inhibitory mechanisms.

Brain ingress of regulatory T cells in a murine model of HIV-1 encephalitis

CD4+CD25+ regulatory T cells (Treg) transform the HIV-1 infected macrophage from a neurotoxic to a neuroprotective phenotype. This was demonstrated previously in a murine model of HIV-1 encephalitis induced by intracranial injection of HIV-1/vesicular stomatitis virus-infected bone marrow macrophages. In this report, relationships between Treg ingress of end organ tissues, notably the brain, and neuroprotection were investigated. Treg from EGFP-transgenic donor mice were expanded, labeled with indium-111, and adoptively transferred. Treg distribution was assayed by single photon emission computed tomography and immunohistochemistry. Treg readily migrated across the blood brain barrier and were retained within virus-induced neuroinflammatory sites. In non-inflamed peripheral tissues (liver and spleen) Treg were depleted. These observations demonstrate that Treg migrate to sites of inflammation where they modulate immune responses.

Improved regulatory T-cell activity in patients with chronic immune thrombocytopenia treated with thrombopoietic agents

Immune thrombocytopenia (ITP) is an autoantibody-mediated bleeding disorder with both accelerated platelet destruction and impaired platelet production. We and others have described impaired regulatory CD4(+)CD25(hi) T cells (Treg) numbers and/or suppressive function in ITP patients. Clinical trials using thrombopoietic agents to stimulate platelet production have shown favorable outcomes in ITP patients, but information on the immunologic responses of treated patients are lacking. We studied the immunologic profile of chronic ITP patients before (n = 10) and during treatment with thrombopoietin receptor (TPO-R) agonists (n = 9). Treg activity, as measured by suppression of proliferation of autologous CD4(+) CD25(-) cells, was improved in patients on treatment (P < .05), and the improvement correlated with reduction in interleukin-2-producing CD4(+) cells, consistent with dampening of immune responses. There was a concomitant increase in total circulating transforming growth factor-β1 (TGF-β1) levels (P = .002) in patients on treatment, and the levels of TGF-β1 correlated with the degree of improvement in platelet counts (r = .8, P = .0002). This suggests that platelets in patients on TPO-R treatment may play a role in improving Treg function, either directly or indirectly by enhanced release of TGF-β1 as a result of greater platelet turnover. In conclusion, our findings suggest that thrombopoietic agents in patients with ITP have profound effects to restore immune tolerance.

Cellular and molecular basis for the regulation of inflammation by TGF-beta

Transforming growth factor-beta (TGF-beta) has been shown to play an essential role in the suppression of inflammation, yet recent studies have revealed the positive roles of TGF-beta in inflammatory responses. For example, TGF-beta induces Foxp3-positive regulatory T cells (iTregs) in the presence of interleukin-2 (IL-2), while in the presence of IL-6, it induces pathogenic IL-17 producing Th17 cells. TGF-beta inhibits the proliferation of immune cells as well as cytokine production via Foxp3-dependent and -independent mechanisms. Little is known about molecular mechanisms involved in immune suppression via TGF-beta; however, Smad2/3 have been shown to play essential roles in Foxp3 induction as well as in IL-2 and IFN-gamma suppression, whereas Th17 differentiation is promoted via the Smad-independent pathway. Interaction between TGF-beta and other cytokine signaling is important in establishing the balance of immunity and tolerance.

Bipolar properties of red seabream (Pagrus major) transforming growth factor-beta in induction of the leucocytes migration

TGF-beta is one of the pleiotropic cytokines and plays a pivotal role in immune regulation and orchestrating the subsequent healing response. Recombinant red seabream TGF-beta (rTGF-beta) mature peptide was expressed and purified under native conditions in vitro. Bio-assay showed that the rTGF-beta could significantly induce head kidney (HK) and peripheral blood (PB) leucocytes migration in a dose dependent manner, whereas the rTGF-beta suppressed HK and PB leucocyte migration when the leucocytes was activated by primed with lipopolysaccharide (LPS). Both enhancing and suppressing roles of rTGF-beta on the HKL and PBL chemotactic activity indicated that the fish TGF-beta shared the similar bipolar nature with mammalian TGF-beta. Furthermore, the results indicated that the activity of TGF-beta induction of leucocyte migration appears not to be an innate feature but function by regulation the chemokines activity. This is the first time we reported that fish TGF-beta has innate bipolar property in regulation of fish immune function.

Potential role of multiple members of the kallikrein-related peptidase family of serine proteases in activating latent TGF beta 1 in semen

Transforming growth factor beta1 (TGF beta 1) has been implicated as a key contributor of immunosuppression in seminal plasma. The biochemical mechanisms that lead to production of active seminal TGF beta 1 are not fully understood. It is plausible that TGF beta 1 activation is partly induced simultaneously with the release of motile spermatozoa following liquefaction of the semen coagulum. Several members of the kallikrein-related peptidase (KLK) family are involved in the regulation of semen liquefaction. This study examines the involvement of these KLKs in TGF beta 1 activation in vitro and ex vivo, in seminal plasma. Latent TGF beta 1 was rapidly activated by KLK14. The latency-associated propeptide (LAP) was shown to be cleaved by KLK14 into small peptide fragments, providing a possible mechanism for TGF beta 1 activation. KLK14 also cleaved the latent TGFbeta binding protein 1 (LTBP1). KLK1, 2, and 5 might also contribute to TGF beta 1 activation by nicking the LAP motif and inducing conformational changes that aid in subsequent processing of LAP or through LTBP1 cleavage. Our study provides strong evidence for the involvement of multiple members of the seminal KLK cascade in activation of latent TGF beta 1 in seminal plasma. These findings might have clinical implications in infertility treatment of cases with concurrent delayed liquefaction and TGF beta 1-related semen antigenicity.

Smad3 differentially regulates the induction of regulatory and inflammatory T cell differentiation

Transforming growth factor beta (TGF-beta) is a crucial cytokine with pleiotropic functions on immune cells. In CD4(+) T cells, TGF-beta is required for induction of both regulatory T and Th17 cells. However, the molecular mechanism underlying this differential T cell fate decision remains unclear. In this study, we have evaluated the role of Smad3 in the development of Th17 and regulatory T cells. Smad3 was found to be dispensable for natural regulatory T cell function. However, induction of Foxp3 expression by TGF-beta in naive T cells was significantly reduced in the absence of this molecule. On the contrary, Smad3 deficiency led to enhanced Th17 differentiation in vitro and in vivo. Moreover, Smad3 was found to interact with retinoid acid receptor-related orphan receptor gammat (RORgammat) and decrease its transcriptional activity. These results demonstrate that Smad3 is differentially involved in the reciprocal regulatory and inflammatory T cell generation.

The role of regulatory T cells in cancer

There has been an explosion of literature focusing on the role of regulatory T (Treg) cells in cancer immunity. It is becoming increasingly clear that Treg cells play an active and significant role in the progression of cancer, and have an important role in suppressing tumor-specific immunity. Thus, there is a clear rationale for developing clinical strategies to diminish their regulatory influences, with the ultimate goal of augmenting antitimor immunity. Therefore, manipulation of Treg cells represent new strategies for cancer treatment. In this Review, I will summarize and review the explosive recent studies demonstrating that Treg cells are increased in patients with malignancies and restoration of antitumor immunity in mice and humans by depletion or reduction of Treg cells. In addition, I will discuss both the prognostic value of Treg cells in tumor progression in tumor-bearing hosts and the rationale for strategies for therapeutic vaccination and immunotherapeutic targeting of Treg cells with drugs and microRNA.

Transforming Growth Factor type beta and Smad family signaling in stem cell function

Ligands of the Transforming Growth Factor type beta (TGFbeta) family exert multiple and sometimes opposite effects on most cell types in vivo depending on cellular context, which mainly includes the stage of the target cell, the local environment of this cell or niche, and the identity and the dosage of the ligand. Significant progress has been made in the molecular dissection of the regulation of the activity of the ligands and their intracellular signal transduction pathways, including via the canonical Smad pathway where Smads interact with many transcription factors. This knowledge together with results from functional studies within the embryology and stem cell research fields is giving us insight in the role of individual ligands and other components of this signaling system and where and how it regulates many properties of embryonic and adult stem/progenitor cells, which is anticipated to contribute to successful cell-based therapy in the future. We review and discuss recent progress on the effects of Nodal/Activin and Bone Morphogenetic Proteins (BMPs) and their canonical signaling in cells with stem cell properties. We focus on embryonic stem cells and their maintenance and pluripotency, and conversion into selected cell types of neuroectoderm, mesoderm and endoderm, on induced pluripotent cells and on neurogenic cells in the adult brain.

Transforming growth factor-beta1 and incident type 2 diabetes: results from the MONICA/KORA case-cohort study, 1984-2002

OBJECTIVE

Subclinical inflammation leads to insulin resistance and beta-cell dysfunction. This study aimed to assess whether levels of circulating transforming growth factor-beta1 (TGF-beta1)-a central, mainly immunosuppressive, and anti-inflammatory cytokine-were associated with incident type 2 diabetes.

RESEARCH DESIGN AND METHODS

We measured serum levels of TGF-beta1 from 460 individuals with and 1,474 individuals without incident type 2 diabetes in a prospective case-cohort study within the population-based MONICA (MONItoring of Trends and Determinants in CArdiovascular Disease)/KORA (Cooperative Health Research in the Region of Augsburg) cohort.

RESULTS

Elevated TGF-beta1 concentrations were associated with higher, not lower, risk for type 2 diabetes (age-, sex-, and survey-adjusted hazard ratios [95% CI] for increasing TGF-beta1 tertiles: 1.0, 1.08 [0.83-1.42], and 1.41 [1.08-1.83]; P(for) (trend) = 0.012). Adjustment for BMI and metabolic and lifestyle factors had virtually no impact on the effect size.

CONCLUSIONS

Elevated serum concentrations of the cytokine TGF-beta1 indicate an increased risk for type 2 diabetes. TGF-beta1 may be upregulated to counterbalance metabolic and immunological disturbances preceding type 2 diabetes.

Conveying glycan information into T-cell homeostatic programs: a challenging role for galectin-1 in inflammatory and tumor microenvironments

The immune system has evolved sophisticated mechanisms composed of several checkpoints and fail-safe processes that enable it to orchestrate innate and adaptive immunity, while at the same time limiting aberrant or unfaithful T-cell function. These multiple regulatory pathways take place during the entire life-span of T cells including T-cell development, homing, activation, and differentiation. Galectin-1, an endogenous glycan-binding protein widely expressed at sites of inflammation and tumor growth, controls a diversity of immune cell processes, acting either extracellularly through specific binding to cell surface glycan structures or intracellularly through modulation of pathways that remain largely unexplored. In this review, we highlight the discoveries that have led to our current understanding of the role of galectin-1 in distinct immune cell process, particularly those associated with T-cell homeostasis. Also, we emphasize findings emerging from the study of experimental models of autoimmunity, chronic inflammation, fetomaternal tolerance, and tumor growth, which have provided fundamental insights into the critical role of galectin-1 and its specific saccharide ligands in immunoregulation. Challenges for the future will embrace the rational manipulation of galectin-1-glycan interactions both towards attenuating immune responses in autoimmune diseases, graft rejection, and recurrent fetal loss, while at the same overcoming immune tolerance in chronic infections and cancer.

Systemic effects of local radiotherapy

Radiotherapy is generally used to treat a localised target that includes cancer. Increasingly, evidence indicates that radiotherapy recruits biological effectors outside the treatment field and has systemic effects. We discuss the implications of such effects and the role of the immune system in standard cytotoxic treatments. Because the effects of chemotherapy and radiotherapy are sensed by the immune system, their combination with immunotherapy presents a new therapeutic opportunity. Radiotherapy directly interferes with the primary tumour and possibly reverses some immunosuppressive barriers within the tumour microenvironment-ideally, recovering the role of the primary tumour as an immunogenic hub. Local radiation also triggers systemic effects that can be used in combination with immunotherapy to induce responses outside the radiation field.

The emerging role of TGF-beta superfamily coreceptors in cancer

The transforming growth factor beta (TGF-beta) signaling pathway plays a key role in different physiological processes such as development, cellular proliferation, extracellular matrix synthesis, angiogenesis or immune responses and its deregulation may result in tumor development. The TGF-beta coreceptors endoglin and betaglycan are emerging as modulators of the TGF-beta response with important roles in cancer. Endoglin is highly expressed in the tumor-associated vascular endothelium with prognostic significance in selected neoplasias and with potential to be a prime vascular target for antiangiogenic cancer therapy. On the other hand, the expression of endoglin and betaglycan in tumor cells themselves appears to play an important role in the progression of cancer, influencing cell proliferation, motility, invasiveness and tumorigenicity. In addition, experiments in vitro and in vivo in which endoglin or betaglycan expression is modulated have provided evidence that they act as tumor suppressors. The purpose of this review was to highlight the potential of membrane and soluble forms of the endoglin and betaglycan proteins as molecular targets in cancer diagnosis and therapy.

Differential regulation of Foxp3 and IL-17 expression in CD4 T helper cells by IRAK-1

Host immune responses are finely regulated by the opposing effects of Th17 and T regulatory (Treg) cells. Treg cells help to dampen inflammatory processes and Th17 cells facilitate various aspects of immune activation. The differentiation of Th cells depends on a unique combination of stimulants and subsequent activation of diverse transcription factors. In particular, cooperative activation of NFAT and Smad3 leads to the induction of Treg cells, and cooperation among STAT3 and Smad3 switches to the induction of Th17 cells. We have previously shown that the IL-1 receptor associated kinase 1 (IRAK-1) selectively activates STAT3 and inactivates NFAT. Physiological studies have shown that IRAK-1(-/-) mice are protected from developing various inflammatory diseases, including experimental autoimmune encephalomyelitis and atherosclerosis with unknown mechanism. In this study, we demonstrate that IRAK-1 plays a critical modulatory role in the differentiation of Th17 and Treg cells. Following stimulation with TCR agonists and TGFbeta, IRAK-1(-/-) CD4 Th cells display elevated nuclear NFATc2 levels and increased interaction of NFATc2 and Smad3, resulting in increased expression of Foxp3, a key marker for Treg cells. IRAK-1(-/-) mice have constitutively higher populations of Treg cells. In contrast, when stimulated with TCR agonists together with IL-6 and TGF-beta, IRAK-1(-/-) CD4 Th cells exhibit attenuated STAT3 Ser727 phosphorylation and reduced expression of IL-17 and RORgamma t compared with wild-type cells. Correspondingly, IRAK-1 deletion results in decreased IL-17 expression and dampened inflammatory responses in acute and chronic inflammatory mice models. Our data provides mechanistic explanation for the anti-inflammatory phenotypes of IRAK-1(-/-) mice.

Components of the mitogen-activated protein kinase cascade are activated in hepatic cells by Echinococcus multilocularis metacestode

AIM: To explore the effect of Echinococcus multilocularis (E. multilocularis) on the activation of mitogen-activated protein kinase (MAPK) signaling pathways and on liver cell proliferation.

METHODS: Changes in the phosphorylation of MAPKs and proliferating cell nuclear antigen (PCNA) expression were measured in the liver of patients with alveolar echinococcosis (AE). MAPKs, MEK1/2 [MAPK/extracellular signal-regulated protein kinase (ERK) kinase] and ribosomal S6 kinase (RSK) phosphorylation were detected in primary cultures of rat hepatocytes in contact in vitro with (1) E. multilocularis vesicle fluid (EmF), (2) E. multilocularis-conditioned medium (EmCM).

RESULTS: In the liver of AE patients, ERK 1/2 and p38 MAPK were activated and PCNA expression was increased, especially in the vicinity of the metacestode. Upon exposure to EmF, p38, c-Jun N-terminal kinase (JNK) and ERK1/2 were also activated in hepatocytes in vitro, as well as MEK1/2 and RSK, in the absence of any toxic effect. Upon exposure to EmCM, only JNK was up-regulated.

CONCLUSION: Previous studies have demonstrated an influence of the host on the MAPK cascade in E. multilocularis. Our data suggest that the reverse, i.e. parasite-derived signals efficiently acting on MAPK signaling pathways in host liver cells, is actually operating.

Increased blood plasma concentrations of TGF-beta1 and TGF-beta2 after treatment with intravenous immunoglobulins in childhood autoimmune diseases

Transforming growth factor-beta (TGF-beta), a multifunctional, immunosuppressive cytokine, is shown to be present in substantial amounts in commercially available intravenous immunoglobulin (IVIG) preparations. To assess whether TGF-beta isoforms are changed in the plasma of paediatric patients with childhood autoimmune diseases after IVIG infusion, 17 patients who received over a period of 12 months overall 56 IVIG infusions (Endobulin) were enrolled in a study. High levels of TGF-beta1 (16.95 +/- 8.16 ng/ml) as well as TGF-beta2 (62.71 +/- 9.50 ng/ml) were detected in the used 56 IVIG probes. TGF-beta1 and TGF-beta2 plasma concentrations were measured prior and 120 min after IVIG infusions by specific TGF-beta ELISA. Interestingly, significant increased TGF-beta1 and TGF-beta2 plasma levels were found in patients after treatment with IVIG. This data suggest that a TGF-beta-mediated mechanism of action may accompany other molecular effects of IVIG therapy. The amount of the potent anti-inflammatory TGF-beta isoforms within the IVIG preparations may exert a differentiated view regarding the manifold indications of IVIG therapy.

Inflammatory skin disease in K5.hTGF-beta1 transgenic mice is not dependent on the IL-23/Th17 inflammatory pathway

In the presence of IL-6, transforming growth factor (TGF)-beta1 induces differentiation of T helper (Th) 17 cells in mice. Interleukin (IL)-23, a heterodimeric cytokine composed of IL-23p19 and IL-12/23p40 subunits, stimulates the growth and expansion of Th17 cells, and has been implicated in psoriasis pathogenesis. To study the associations between TGF-beta1, the IL-23/Th17 inflammatory pathway, and psoriasis, we investigated inflammatory skin disease in transgenic mice that constitutively overexpress human TGF-beta1 in basal keratinocytes (K5.hTGF-beta1 transgenic mice); these mice had previously been reported as having a psoriasis-like disease. K5.hTGF-beta1 transgenic mice had high levels of TGF-beta1 mRNA and protein in both skin and serum. Levels of cytokines involved in IL-23/Th17-mediated inflammation were not elevated in lesional skin compared with those in non-lesional and wild-type skin. It is noteworthy that IL-4 and IgE were markedly elevated in inflamed skin and serum, respectively, of transgenic mice. Monoclonal antibodies (mAbs) specifically directed against IL-23p19 or IL-12/23p40 had no clinical effect on established inflammatory skin disease in K5.hTGF-beta1 transgenic mice, whereas the same mAbs were able to block the development of murine experimental autoimmune encephalomyelitis, an IL-23/Th17-mediated disease. In summary, the IL-23/Th17 inflammatory pathway is not responsible for the maintenance of inflammatory skin disease in K5.hTGF-beta1 transgenic mice.

CD4 T-cell differentiation and inflammatory bowel disease

Differentiation of naïve T cells leads to the generation of T-cell subsets, each possessing distinct cytokine expression profiles for serving different immune functions. Through the activation of separate signaling pathways, this process results in both differentiated helper T (Th) cells, termed Th1, Th2 and Th17, and induced regulatory T cells, which suppress Th cells. These different cells are important for combating infectious diseases and cancers; however, when aberrant, they can be responsible for chronic inflammatory diseases. One such disease is inflammatory bowel disease (IBD), in which each T-cell subset can have a role in disease. New studies highlight the importance of the recently identified Th17 subset in IBD. Therapeutics targeting these aberrant Th responses are already under development and hold promise for treating IBD and other chronic inflammatory diseases.

T cell sensitivity to TGF-beta is required for the effector function but not the generation of splenic CD8+ regulatory T cells induced via the injection of antigen into the anterior chamber

The introduction of antigen into the anterior chamber (AC) of the eye induces the production of antigen-specific splenic CD8⁺ regulatory T cells (AC-SPL cells) that suppress a delayed-type hypersensitivity (DTH) reaction in immunized mice. Because the generation of these regulatory T cells is also induced by exposure to transforming growth factor (TGF)-β and antigen or F4/80⁺ cells exposed to TGF-β and antigen in vitro, we investigated (i) whether these cells are produced in dominant negative receptor for transforming growth factor β receptor type II (dnTGFβRII) or Cbl-b^−/− mice whose T cells are resistant to TGF-β, (ii) whether DTH is suppressed by wild type (WT) CD8⁺ AC-SPL cells in Cbl-b^−/− and dnTGFβRII mice and (iii) the effect of antibodies to TGF-β on the suppression of DTH by CD8⁺ AC-SPL cells. DnTGFβRII immunized and Cbl-b^−/− mice produced splenic CD8⁺ regulatory cells after the intracameral injection of antigen and immunization. The suppression of a DTH reaction by CD8⁺ AC-SPL cells in WT mice was blocked by the local inclusion of antibodies to TGF-β when WT splenic CD8⁺ AC-SPL cells were injected into the DTH reaction site. Moreover, the DTH reaction in immunized dnTGFβRII and Cbl-b^−/− mice was not suppressed by the transfer of WT CD8⁺ AC-SPL cells to the site challenged with antigen. In aggregate, these observations suggest that T cell sensitivity to TGF-β is not an obligate requirement for the in vivo induction of CD8⁺ AC-SPL T cells but the suppression of an in vivo DTH reaction by CD8⁺ AC-SPL cells is dependent on TGF-β.

Mice that lack activity of alphavbeta6- and alphavbeta8-integrins reproduce the abnormalities of Tgfb1- and Tgfb3-null mice

The arginine-glycine-aspartate (RGD)-binding integrins alphavbeta6 and alphavbeta8 activate latent TGFbeta1 and TGFbeta3 in vivo, but it is uncertain whether other RGD-binding integrins such as integrins alphavbeta5 and alphavbeta3 activate these TGFbeta isoforms. To define the combined role of alphavbeta6- and alphavbeta8-integrin in TGFbeta activation, we analyzed mice lacking function of both integrins by means of gene deletion and/or pharmacologic inhibition. Most Itgb6-/-;Itgb8-/- embryos die at mid-gestation; those that survive develop cleft palate-as observed in Tgfb3-/- mice. Itgb8-/- mice treated with an anti-alphavbeta6-integrin antibody develop severe autoimmunity and lack Langerhans cells-similar to Tgfb1-null mice. These results support a model in which TGFbeta3-mediated palate fusion and TGFbeta1-mediated suppression of autoimmunity and generation of Langerhans cells require integrins alphavbeta6 and alphavbeta8 but not other RGD-binding integrins as TGFbeta activators.

IL-17-producing human peripheral regulatory T cells retain suppressive function

Although implicated in antagonistic functions, both regulatory T cells (Tregs) and Th17 effector cells play an important role in controlling autoimmune pathogenesis. Paradoxically, recent studies indicate that Tregs have the capacity to produce interleukin-17 (IL-17), although the ability of these cells to retain their suppressive function remains unknown. Here we report that human Tregs within the CD4(+)CD45RA(-)CD25(high)CCR6(+)HLA-DR(-)FoxP3(+) population produce IL-17 when activated in the presence of the proinflammatory cytokines IL-1beta and IL-6, whereas IL-17 secretion was inhibited by TGFbeta. To assess the ability of a single Treg to secrete IL-17 and to suppress in vitro immune function, we isolated clones from this population. We found that IL-17(+)/FoxP3(+) Treg clones retain suppressive function and exhibit the plasticity to secrete IL-17 or suppress depending on the nature of the stimulus provided. IL-17 production by these Treg clones was accompanied by sustained FoxP3 expression and concomitant, but reversible, loss of suppressive activity. Our data demonstrate that at the single cell level a subset of in vitro suppressive FoxP3(+) cells can be driven to secrete IL-17 under inflammatory conditions. These findings suggest a new mechanism by which inflammation can drive Tregs to secrete IL-17, thereby dampening suppression and promoting an inflammatory milieu.

Polymorphism of the TGFB1 gene is not associated with bronchial allergic asthma in a Polish population

Allergic asthma is a complex genetic disorder that involves interactions between genetic and environmental factors. Some studies have indicated that transforming growth factor beta(1) (TGF-beta(1)), a pleiotropic cytokine regulating inflammatory reactions and airway remodeling, may participate in the pathogenesis of asthma. Several polymorphisms have been described in the TGFB1 gene; some were tested in allergic asthma, with conflicting results. The aim of this study was to investigate the possible associations of four TGFB1 gene polymorphisms (-800G>A, -509C>T, 869T>C, and 915G>C) with allergic asthma in a Polish population. These four single nucleotide polymorphisms were genotyped in 247 asthmatic patients (including 207 atopic individuals) and 287 unrelated healthy volunteers by means of the polymerase chain reaction-restriction fragment length polymorphism method. No significant differences between patients and controls in allele, genotype, and haplotype frequencies were reported. Logistic regression analysis of genotype distribution and allele positivity adjusted for age and sex did not reveal any significant differences between all patients or patients selected for atopy and controls. Thus, no evidence was reported for a contribution of the TGFB1 gene to allergic asthma in a Polish population. The results are discussed in the context of similar studies in other populations.

IL-10 and TGF-beta redundantly protect against severe liver injury and mortality during acute schistosomiasis

The cytokines IL-10 and TGF-beta regulate immunity and inflammation. IL-10 is known to suppress the extent of hepatic damage caused by parasite ova during natural infection with Schistosoma mansoni, but the role of TGF-beta is less clear. Cytokine blockade studies in mice revealed that anti-IL-10R mAb treatment during acute infection modestly increased cytokine production and liver damage, whereas selective anti-TGF-beta mAb treatment had marginal effects. In contrast, mice administered both mAbs developed severe hepatic inflammation, with enlarged, necrotic liver granulomas, cachexia, and >80% mortality by 8 wk postinfection, despite increased numbers of CD4(+)CD25(+)Foxp3(+) T regulatory cells. Blocking both IL-10 and TGF-beta at the onset of egg production also significantly increased IL-4, IL-6, TNF, IFN-gamma, and IL-17 production and markedly increased hepatic, peritoneal, and splenic neutrophilia. In contrast, coadministration of anti-IL-10R and TGF-beta mAbs had little effect upon parasite ova-induced intestinal pathology or development of alternatively activated macrophages, which are required to suppress intestinal pathology. This suggests that inflammation is controlled during acute S. mansoni infection by two distinct, organ-specific mechanisms: TGF-beta and IL-10 redundantly suppress hepatic inflammation while intestinal inflammation is regulated by alternatively activated macrophages.

Regulatory T cells in inflammatory bowel disease

PURPOSE OF REVIEW

The intestinal immune system must orchestrate a complex balance between proinflammatory and anti-inflammatory responses to luminal antigens, and disruptions in this balance can result in inflammatory bowel disease (IBD). This review explores recent data that elucidate the role of regulatory T cells (Tregs) in the pathogenesis of IBD in mice and humans.

RECENT FINDINGS

Data from murine models of colitis implicate several novel mechanisms critical to Treg function and generation including the inhibitory cytokine interleukin-35, pericellular adenosine generation and cytokine deprivation-induced apoptosis. Although Tregs are essential in mice for the maintenance of intestinal homeostasis, their role in human IBD remains unclear. Patients with IBD appear to have relatively reduced numbers of Tregs in the blood and colon; however, Tregs from these patients are functional in vitro.

SUMMARY

Tregs are important for the maintenance of intestinal self-tolerance and will likely prove to be an important avenue for therapeutic manipulation in IBD.

Transforming growth factor-beta signaling: emerging stem cell target in metastatic breast cancer?

In most human breast cancers, lowering of TGFbeta receptor- or Smad gene expression combined with increased levels of TGFbetas in the tumor microenvironment is sufficient to abrogate TGFbetas tumor suppressive effects and to induce a mesenchymal, motile and invasive phenotype. In genetic mouse models, TGFbeta signaling suppresses de novo mammary cancer formation but promotes metastasis of tumors that have broken through TGFbeta tumor suppression. In mouse models of "triple-negative" or basal-like breast cancer, treatment with TGFbeta neutralizing antibodies or receptor kinase inhibitors strongly inhibits development of lung- and bone metastases. These TGFbeta antagonists do not significantly affect tumor cell proliferation or apoptosis. Rather, they de-repress anti-tumor immunity, inhibit angiogenesis and reverse the mesenchymal, motile, invasive phenotype characteristic of basal-like and HER2-positive breast cancer cells. Patterns of TGFbeta target genes upregulation in human breast cancers suggest that TGFbeta may drive tumor progression in estrogen-independent cancer, while it mediates a suppressive host cell response in estrogen-dependent luminal cancers. In addition, TGFbeta appears to play a key role in maintaining the mammary epithelial (cancer) stem cell pool, in part by inducing a mesenchymal phenotype, while differentiated, estrogen receptor-positive, luminal cells are unresponsive to TGFbeta because the TGFBR2 receptor gene is transcriptionally silent. These same cells respond to estrogen by downregulating TGFbeta, while antiestrogens act by upregulating TGFbeta. This model predicts that inhibiting TGFbeta signaling should drive the differentiation of mammary stem cells into ductal cells. Consequently, TGFbeta antagonists may convert basal-like or HER2-positive cancers to a more epithelioid, non-proliferating (and, perhaps, non-metastatic) phenotype. Conversely, these agents might antagonize the therapeutic effects of anti-estrogens in estrogen-dependent luminal cancers. These predictions need to be addressed prospectively in clinical trials and should inform the selection of patient populations most likely to benefit from this novel anti-metastatic therapeutic approach.

Experimental expansion of the regulatory T cell population increases resistance to African trypanosomiasis

Inflammatory responses mounted to eliminate parasites can be lethal if not counterbalanced by regulatory responses protecting the host from collateral tissue damage. Here, we show that the maintained inflammation associated with tissue damage, anemia, and reduced survival of Trypanosoma brucei-infected mice correlates with the absence of the expansion of the regulatory T (T(reg)) cell population. Induction of T(reg) cell expansion via CD28 superagonist antibody treatment in these mice down-regulated interferon-gamma production by T cells and tumor necrosis factor-alpha and reactive oxygen species production by classically activated macrophages, triggered the development of alternatively activated macrophages, delayed the onset of liver injury, diminished the anemia burden, and prolonged the survival of infected animals. Thus, triggering the expansion of the T(reg) cell population coupled with the induction of alternatively activated macrophages can restore the balance between pro- and anti-inflammatory signals and thereby limit the pathogenicity of African trypanosomiasis.

Review of the activation of TGF-beta in immunity

The evolutionarily conserved TGF-beta proteins are distributed ubiquitously throughout the body and have a role in almost every biological process. In immunity, TGF-beta has an important role in modulating immunity. Much is understood about the process of TGF-beta production as a latent molecule and of the consequences and the intercellular signaling of active TGF-beta binding to its receptors; however, there is little discussed between the production and activation of TGF-beta. This review focuses on what is understood about the biochemical and physiological processes of TGF-beta activation and identifies the gaps in understanding immune cell activation of TGF-beta. A mechanistic understanding of the process activating TGF-beta can lead to regulating multiple biological systems by enhancing or inhibiting TGF-beta activation.

Reprogrammed FoxP3+ T regulatory cells become IL-17+ antigen-specific autoimmune effectors in vitro and in vivo

Lymphocyte differentiation from naive CD4(+) T cells into mature Th1, Th2, Th17, or T regulatory cell (Treg) phenotypes has been considered end stage in character. In this study, we demonstrate that dendritic cells (DCs) activated with a novel immune modulator B7-DC XAb (DC(XAb)) can reprogram Tregs into T effector cells. Down-regulation of FoxP3 expression after either in vitro or in vivo Treg-DC(XAb) interaction is Ag-specific, IL-6-dependent, and results in the functional reprogramming of the mature T cell phenotype. The reprogrammed Tregs cease to express IL-10 and TGFbeta, fail to suppress T cell responses, and gain the ability to produce IFN-gamma, IL-17, and TNF-alpha. The ability of IL-6(+) DC(XAb) and the inability of IL-6(-/-) DC(XAb) vaccines to protect animals from lethal melanoma suggest that exogenously modulated DC can reprogram host Tregs. In support of this hypothesis and as a test for Ag specificity, transfer of DC(XAb) into RIP-OVA mice causes a break in immune tolerance, inducing diabetes. Conversely, adoptive transfer of reprogrammed Tregs but not similarly treated CD25(-) T cells into naive RIP-OVA mice is also sufficient to cause autoimmune diabetes. Yet, treatment of normal mice with B7-DC XAb fails to elicit generalized autoimmunity. The finding that mature Tregs can be reprogrammed into competent effector cells provides new insights into the plasticity of T cell lineage, underscores the importance of DC-T cell interaction in balancing immunity with tolerance, points to Tregs as a reservoir of autoimmune effectors, and defines a new approach for breaking tolerance to self Ags as a strategy for cancer immunotherapy.

Chronic inflammation in asthma: a contest of persistence vs resolution

Recent investigations have highlighted that endogenous anti-inflammatory mediators and immune regulating mechanisms are important for the resolution of inflammatory processes. A disruption of these mechanisms can be causally related not only to the initiation of unnecessary inflammation, but also to the persistence of several chronic inflammatory diseases. In asthma, chronic Th-2 driven eosinophilic inflammation of the airways is one of the central abnormalities. To date, elucidating the role of the different pro-inflammatory mediators involved in orchestrating the inflammatory processes in asthma has been the subject of intense research in both humans and animal models. However, the counter-regulatory mechanisms that co-determine the outcome in the contest of resolution vs persistence of the eosinophilic airway inflammation remain poorly understood. These are currently being investigated in animal models of chronic asthma. Elucidating these mechanisms is of relevance, since it can give rise to a new therapeutic approach in the treatment of chronic airway inflammation in asthmatics. This novel concept of treatment involves the stimulation of endogenous anti-inflammatory pathways, rather than solely antagonising the various pro-inflammatory mediators. Here, we review and discuss the current knowledge about these endogenous anti-inflammatory mediators in clinical and experimental asthma.

TGF-beta promotes thyroid epithelial cell hyperplasia and fibrosis in IFN-gamma-deficient NOD.H-2h4 mice

IFN-gamma(-/-)NOD.H-2h4 mice given 0.05% NaI in their water develop severe thyroid epithelial cell (thyrocyte) hyperplasia and proliferation (TEC H/P) and fibrosis. Proliferating thyrocytes of IFN-gamma(-/-) mice with TEC H/P produce TGF-beta as demonstrated by immunohistochemical staining and in situ hybridization. Strong expression of activating phosphorylated Smad-2/3 and weak expression of inhibitory Smad-7 by proliferating thyrocytes correlate with the severity of TEC H/P. Splenocytes from IFN-gamma(-/-) mice with severe TEC H/P transfer severe TEC H/P to IFN-gamma(-/-)NOD.H-2h4.SCID mice. Mice given anti-TGF-beta had markedly reduced thyrocyte proliferation and decreased fibrosis compared with mouse Ig-treated controls, suggesting that TGF-beta plays an important role in development of TEC H/P induced by activated splenocytes. Moreover, transgenic IFN-gamma(-/-)NOD.H-2h4 mice expressing TGF-beta on thyrocytes all develop fibrosis and moderate to severe TEC H/P with accelerated kinetics, directly demonstrating a role for TGF-beta in severe TEC H/P and fibrosis.

Treatment strategies for allergy and asthma

Allergic diseases have reached epidemic proportions worldwide. An understanding of the cellular and soluble mediators that are involved in allergic inflammatory responses not only helps in understanding the mechanisms of current treatments, but is also important for the identification of new targets that are amenable to both small-molecule and biological interventions. There is now considerable optimism with regards to tackling the allergy epidemic in light of improvements in systemic and mucosal allergen-specific immunotherapy, the identification of key cytokines and their receptors that drive T-helper-2-cell polarization, a clearer understanding of the pathways of leukocyte recruitment and the signalling pathways that are involved in cell activation and mediator secretion, and new approaches to vaccine development.