TGF-beta and IL-6 signals modulate chromatin binding and promoter occupancy by acetylated FOXP3

Distinct inflammatory signals have physiologically divergent effects on epigenetic regulation of Foxp3 expression and Treg function

Foxp3 expression in regulatory T cells (Treg) is required for their development and suppressive function. How different inflammatory signals affect Foxp3 chromatin structure, expression and Tregs plasticity are not completely known. In the present study, the Toll-like receptor 2 (TLR2) ligand peptidoglycan inhibited Foxp3 expression in both natural Treg (nTreg) and TGFβ-driven adaptive Treg (aTreg). Inhibition was independent of paracrine Th1, Th2 and Th17 cytokines. PGN-induced T cell-intrinsic TLR2-Myd88-dependent IFR1 expression and induced IRF1 bound to IRF1 response elements (IRF-E) in the Foxp3 promoter and intronic enhancers, and negatively regulated Foxp3 expression. Inflammatory IL-6 and TLR2 signals induced divergent chromatin changes at the Foxp3 locus and regulated Treg suppressor function, and in an islet transplant model resulted in differences in their ability to prolong graft survival. These findings are important for understanding how different inflammatory signals can affect the transplantation tolerance and immunity.

Oral administration of ginsenoside Rh1 inhibits the development of atopic dermatitis-like skin lesions induced by oxazolone in hairless mice

In the present study, we examined the inhibitive effect of ginsenoside Rh1 on oxazolone-induced atopic dermatitis-like skin lesions in hairless mice. Oral administration of ginsenoside Rh1 improved clinical symptoms, and it was confirmed by histophathological analysis. In ginsenoside Rh1 (20mg/kg) group, ear swellings and ear weights were significantly lower than the control group. Moreover, elevation of IL-6 and total IgE levels in serum were suppressed by ginsenoside Rh1 (20mg/kg). In addition, ginsenoside Rh1 (20mg/kg) significantly increased mRNA expression of IFNγ and Foxp3, and slightly decreased IL-4 expression in draining lymph nodes. The results suggest that ginsenoside Rh1 can alleviate inflammatory symptoms in atopic dermatitis (AD) by reduction of IgE and IL-6 levels in peripheral blood, increase of Foxp3 expression in draining lymph nodes and suppression of inflammation in skin regions. Indeed, ginsenoside Rh1 exhibited therapeutic possibility in immune disorders.

Synergistic and combinatorial control of T cell activation and differentiation by transcription factors

Naïve CD4(+) T cells are educated in the thymus to survey the periphery for cognate antigen while ignoring self or commensal antigens. T cell antigen receptor (TCR) cross-linking initiates signaling cascades that integrate information from co-stimulatory receptors and locally available cytokines to chart the course of inflammation. The dynamic composition of transcription factors acting within a given T cell drive clonal expansion and specify differentiation into a growing array of effector and regulatory T cell subsets. The classical gamma-interferon (IFNgamma)-secreting T helper type (Th)-1 and IL-4-producing Th2 cell subsets utilize T-bet or GATA3 as master lineage regulators. It is now understood that naïve T cells also differentiate into pro-inflammatory Th17 or tissue-protective inducible T regulatory (iTreg) cells under the respective guidance of RORgammat or FOXP3. Emerging data highlight the reoccurring theme that these Th17 and iTreg master regulators prescribe T cell lineage commitment through interactions with each other, as well as with a broader network of auxiliary transcription factors.

Histone acetyltransferase mediated regulation of FOXP3 acetylation and Treg function

Regulatory T cells (Tregs) are required for the maintenance of immune homeostasis as first clearly described by Herman Waldmann's laboratory. Dysfunction of Treg cells also leads to fatal autoimmunity in humans and mice. Conversely, the activation of different classes of Tregs operative systemically and within the cancer microenvironment can suppress host anti-tumor immune responses and promote tumor progression. Therefore, the development of new therapeutic approaches to regulate the activity of Treg cells may have considerable clinical potential. FOXP3 is the key transcriptional regulator of Treg development and function. The activity of FOXP3 is regulated by acetylation, a process catalyzed by distinct types of histone/protein acetyltransferases (HATs) that regulate the functions of many transcription factors, independently of FOXP3, as well as non-histone proteins, in addition to their effects on chromatin accessibility. Interactions between FOXP3 and these enzymes determine the suppressive function of FOXP3. Clearly, small molecules targeting these enzymes are candidates for the regulation of Treg function in vaccines and tumor therapies.

Reciprocal functional modulation of the activation of T lymphocytes and fibroblasts derived from human solid tumors

Fibroblasts are a dominant cell type in most human solid tumors. The possibility that fibroblasts have the capacity to interact with and modulate the function of tumor-associated T lymphocytes makes them a potential therapeutic target. To address this question, primary cultures of fibroblasts derived from human lung tumors were established and cultured with T cells derived from the same tumor. The tumor fibroblasts significantly enhance the production of IFN-gamma and IL-17A by the tumor-associated T cells following a CD3/CD28-induced activation of the T cells. This enhancement was fibroblast cell dose-dependent and did not require direct contact between the two cell types. Tumor-associated fibroblast-conditioned media similarly enhanced both IFN-gamma and IL-17A in activated T cells, and this enhancement was significantly reduced by Abs to IL-6. Conditioned media derived from activated lymphocyte cultures significantly enhanced IL-6 production by tumor fibroblasts. A similar enhancement of IFN-gamma and IL-17A was observed when activated T cells from a normal donor were cultivated with skin fibroblasts derived from the same donor. These results establish that fibroblasts and autologous lymphocytes, whether derived from the tumor microenvironment or from nonmalignant tissues, have the capacity to reciprocally interact and modulate function. In contrast to other reports, fibroblasts are shown to have an immunostimulatory effect upon activated T lymphocytes. The ability of fibroblasts to enhance two T cell cytokines known to have an impact upon tumor progression suggests that fibroblasts play an important role in tumor pathogenesis that could be exploited therapeutically.

Genome-wide identification of human FOXP3 target genes in natural regulatory T cells

The transcription factor FOXP3 is essential for the formation and function of regulatory T cells (Tregs), and Tregs are essential for maintaining immune homeostasis and tolerance. This is demonstrated by a lethal autoimmune defect in mice lacking Foxp3 and in immunodysregulation polyendocrinopathy enteropathy X-linked syndrome patients. However, little is known about the molecular basis of human FOXP3 function or the relationship between direct and indirect targets of FOXP3 in human Tregs. To investigate this, we have performed a comprehensive genome-wide analysis for human FOXP3 target genes from cord blood Tregs using chromatin immunoprecipitation array profiling and expression profiling. We have identified 5579 human FOXP3 target genes and derived a core Treg gene signature conserved across species using mouse chromatin immunoprecipitation data sets. A total of 739 of the 5579 FOXP3 target genes were differentially regulated in Tregs compared with Th cells, thus allowing the identification of a number of pathways and biological functions overrepresented in Tregs. We have identified gene families including cell surface molecules and microRNAs that are differentially expressed in FOXP3(+) Tregs. In particular, we have identified a novel role for peptidase inhibitor 16, which is expressed on the cell surface of >80% of resting human CD25(+)FOXP3(+) Tregs, suggesting that in conjunction with CD25 peptidase inhibitor 16 may be a surrogate surface marker for Tregs with potential clinical application.

Treating arthritis by immunomodulation: is there a role for regulatory T cells?

The discovery of regulatory T cells almost 15 years ago initiated a new and exciting research area. The growing evidence for a critical role of these cells in controlling autoimmune responses has raised expectations for therapeutic application of regulatory T cells in patients with autoimmune arthritis. Here, we review recent studies investigating the presence, phenotype and function of these cells in patients with RA and juvenile idiopathic arthritis (JIA) and consider their therapeutic potential. Both direct and indirect methods to target these cells will be discussed. Arguably, a therapeutic approach that combines multiple regulatory T-cell-enhancing strategies could be most successful for clinical application.

T lymphocytes: a role in hypertension?

PURPOSE OF REVIEW

Low-grade inflammation has been shown to play a role in cardiovascular disease and specifically in hypertension. Circulating and tissue leukocytes and macrophages are a component of the mechanisms leading to inflammatory responses. Subsets of T lymphocytes have been implicated in the pathogenesis of hypertension and vascular remodeling. This is an area of active research and rapid development in cardiovascular and renal disease which offers great therapeutic potential.

RECENT FINDINGS

Recent data suggest that subsets of T lymphocytes, both effector T cells such as T-helper (Th)1 (interferon-gamma-producing) and Th2 lymphocytes [that produce interleukin (IL)-4], as well as Th17 (that produce IL-17), and T suppressor lymphocytes including regulatory T cells (Treg), which express the transcription factor forkhead box P3 (Foxp3), play critical roles in the development of angiotensin II, deoxycorticosterone salt-sensitive and Dahl salt-sensitive hypertension, and in the progression of vascular remodeling. As well, recent evidence suggests that the inflammatory response involving T lymphocytes may be triggered by oxidative stress in nuclei of the brain and associate with blood pressure elevation.

SUMMARY

These new data implicating T lymphocytes will eventually allow discovery of new therapeutic targets that may improve outcomes in cardiovascular and renal disease in humans.

Immune regulation and vascular inflammation in genetic hypertension

Immune cells have been implicated in the pathogenesis of hypertension. We hypothesized that under the influence of chromosome (chr)2, T lymphocytes contribute to vascular inflammation in genetic salt-sensitive hypertension. Normotensive (Brown Norway), hypertensive (Dahl salt-sensitive), and consomic rats (SSBN2; in which chr2 has been transferred from Brown Norway to Dahl rats) were studied. Systolic blood pressure, measured by tail cuff, and aortic preproendothelin mRNA, measured by quantitative RT-PCR, were elevated in Dahl rats compared with Brown Norway rats and were reduced in SSBN2 rats compared with Dahl rats (P < 0.01). Compared with Brown Norway rats, Dahl rats exhibited increased inflammatory markers and mediators such as nuclear translocation of the aortic p65 subunit of NF-kappaB as well as VCAM-1, ICAM-1, chemokine (C-C motif) receptor 5, and CD4 mRNA, all of which were reduced in SSBN2 rats. Aortic CD8 mRNA was equally increased in Dahl and SSBN2 rats relative to Brown Norway rats. CD4(+) T cell infiltration in the aorta of SSBN2 rats was reduced compared with Dahl rats, whereas the aortic protein expression of Foxp3b and immunosuppressors transforming growth factor (TGF)-beta(1) and IL-10, the three markers associated with the regulatory T cell lineage, were enhanced in SSBN2 rats. Activation in vitro of T cells demonstrated that CD4(+)CD25(+) and CD8(+)CD25(+) cells (Tregs) produce IL-10 in SSBN2 rats. Thus, increased vascular inflammatory responses and hypertension in a genetic salt-sensitive hypertensive rodent model are reduced by transfer of chr2 from a normotensive strain, and this is associated with enhanced levels of immunosuppressive mediators.

Interplay between the TH17 and TReg cell lineages: a (co-)evolutionary perspective

The origins of the adaptive immune system and the basis for its unique association with vertebrate species have been a source of considerable speculation. In light of recent advances in our understanding of the developmental and functional links between the induced regulatory T cell and T helper 17 cell lineages, and their specialized relationship to the gut, we speculate that the co-evolution of these adaptive immune pathways might have given primitive vertebrates a means to benefit from the diversification of their commensal microbiota.

Immunomodulatory effects of deacetylase inhibitors: therapeutic targeting of FOXP3+ regulatory T cells

Classical zinc-dependent histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and also from many non-histone proteins, including the transcription factor FOXP3, a key regulator of the development and function of regulatory T cells. Many HDAC inhibitors are in cancer clinical trials, but a subset of HDAC inhibitors has important anti-inflammatory or immunosuppressive effects that might be of therapeutic benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of HDAC inhibitors to enhance the production and suppressive functions of FOXP3(+) regulatory T cells. Understanding which HDACs contribute to the regulation of the functions of regulatory T cells may further stimulate the development of new class- or subclass-specific HDAC inhibitors with applications beyond oncology.

Epigenetic mechanisms of regulation of Foxp3 expression

Regulatory T cells play important roles in the control of autoimmunity and maintenance of transplantation tolerance. Foxp3, a member of the forkhead/winged-helix family of transcription factors, acts as the master regulator for regulatory T-cell (Treg) development and function. Mutation of the Foxp3 gene causes the scurfy phenotype in mouse and IPEX syndrome (immune dysfunction, polyendocrinopathy, enteropathy, X-linked syndrome) in humans. Epigenetics is defined by regulation of gene expression without altering nucleotide sequence in the genome. Several epigenetic markers, such as histone acetylation and methylation, and cytosine residue methylation in CpG dinucleotides, have been reported at the Foxp3 locus. In particular, CpG dinucleotides at the Foxp3 locus are methylated in naive CD4+CD25- T cells, activated CD4+ T cells, and TGF-beta-induced adaptive Tregs, whereas they are completely demethylated in natural Tregs. The DNA methyltransferases DNMT1 and DNMT3b are associated with the Foxp3 locus in CD4+ T cells. Methylation of CpG residues represses Foxp3 expression, whereas complete demethylation is required for stable Foxp3 expression. In this review, we discuss how different cis-regulatory elements at the Foxp3 locus are subjected to epigenetic modification in different subsets of CD4+ T cells and regulate Foxp3 expression, and how these mechanisms can be exploited to generate efficiently large numbers of suppressive Tregs for therapeutic purposes.

Deacetylase inhibition increases regulatory T cell function and decreases incidence and severity of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an established mouse model of disease with hallmarks of clinical rheumatoid arthritis. Histone/protein deacetylase inhibitors (HDACi) are known to inhibit the pathogenesis of CIA and other models of autoimmune disease, although the mechanisms responsible are unclear. Regulatory T cell (Treg) function is defective in rheumatoid arthritis. FOXP3 proteins in Tregs are present in a dynamic protein complex containing histone acetyltransferase and HDAC enzymes, and FOXP3 itself is acetylated on lysine residues. We therefore investigated the effects of HDACi therapy on regulatory T cell function in the CIA model. Administration of an HDACi, valproic acid (VPA), significantly decreased disease incidence (p<0.005) and severity (p<0.03) in CIA. In addition, VPA treatment increased both the suppressive function of CD4(+)CD25(+) Tregs (p<0.04) and the numbers of CD25(+)FOXP3(+) Tregs in vivo. Hence, clinically approved HDACi such as VPA may limit autoimmune disease in vivo through effects on the production and function of FOXP3(+) Treg cells.

CD4+CD25+Foxp3+ Tregs resolve experimental lung injury in mice and are present in humans with acute lung injury

Acute lung injury (ALI) is characterized by rapid alveolar injury, inflammation, cytokine induction, and neutrophil accumulation. Although early events in the pathogenesis of ALI have been defined, the mechanisms underlying resolution are unknown. As a model of ALI, we administered intratracheal (i.t.) LPS to mice and observed peak lung injury 4 days after the challenge, with resolution by day 10. Numbers of alveolar lymphocytes increased as injury resolved. To examine the role of lymphocytes in this response, lymphocyte-deficient Rag-1-/- and C57BL/6 WT mice were exposed to i.t. LPS. The extent of injury was similar between the groups of mice through day 4, but recovery was markedly impaired in the Rag-1-/- mice. Adoptive transfer studies revealed that infusion of CD4+CD25+Foxp3+ Tregs as late as 24 hours after i.t. LPS normalized resolution in Rag-1-/- mice. Similarly, Treg depletion in WT mice delayed recovery. Treg transfer into i.t. LPS-exposed Rag-1-/- mice also corrected the elevated levels of alveolar proinflammatory cytokines and increased the diminished levels of alveolar TGF-beta and neutrophil apoptosis. Mechanistically, Treg-mediated resolution of lung injury was abrogated by TGF-beta inhibition. Moreover, BAL of patients with ALI revealed dynamic changes in CD3+CD4+CD25hiCD127loFoxp3+ cells. These results indicate that Tregs modify innate immune responses during resolution of lung injury and suggest potential targets for treating ALI, for which there are no specific therapies currently available.

Eos mediates Foxp3-dependent gene silencing in CD4+ regulatory T cells

CD4+ regulatory T cells (Tregs) maintain immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. The core genetic program of Tregs and their ability to suppress pathologic immune responses depends on the transcription factor Foxp3. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. We identified Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Tregs. Eos interacts directly with Foxp3 and induces chromatin modifications that result in gene silencing in Tregs. Silencing of Eos in Tregs abrogates their ability to suppress immune responses and endows them with partial effector function, thus demonstrating the critical role that Eos plays in Treg programming.

The T(reg)/Th17 cell balance: a new paradigm for autoimmunity

Regulatory T cells and T helper 17 cells are two recently described lymphocyte subsets with opposing actions. In this review, we discuss the mechanisms that promote development of these cells from common precursors and the specific factors that impact their cell numbers and function. Altered regulation of this key developmental checkpoint may contribute to the pathophysiology of autoimmune diseases by tipping the balance toward inflammation. We also present recent findings that suggest how the equilibrium between regulatory T cells and proinflammatory T helper subsets might be pharmacologically restored for therapeutic benefit.

Neuroprotection of microglial conditioned medium on 6-hydroxydopamine-induced neuronal death: role of transforming growth factor beta-2

Microglia, the immune cells of the CNS, play essential roles in both physiological and pathological brain states. Here we have used an in vitro model to demonstrate neuroprotection of a 48 h-microglial conditioned medium (MCM) towards cerebellar granule neurons (CGNs) challenged with the neurotoxin 6-hydroxydopamine, which induces a Parkinson-like neurodegeneration, and to identify the protective factor(s). MCM nearly completely protects CGNs from 6-hydroxydopamine neurotoxicity and at least some of the protective factor(s) are peptidic in nature. While the fraction of the medium containing molecules < 30 kDa completely protects CGNs, fractions containing molecules < 10 kDa or > 10 kDa are not neuroprotective. We further demonstrate that microglia release high amounts of transforming growth factor-beta2 (TGF-beta2) and that its exogenous addition to the fraction of the medium not containing it (< 10 kDa) fully restores the neuroprotective action. Moreover, MCM neuroprotection is significantly counteracted by an inhibitor of TGF-beta2 transduction pathway. Our results identify TGF-beta2 as an essential neuroprotective factor released by microglia in its culture medium that requires to be fully effective the concomitant presence of other factor(s) of low molecular weight.

Surveillance of antigen-presenting cells by CD4+ CD25+ regulatory T cells in autoimmunity: immunopathogenesis and therapeutic implications

CD4+CD25+ regulatory T cells (Tregs) play a critical role in preventing immune aggression. One way in which Tregs exert immune surveillance activities is by modifying the function of antigen presenting cells (APCs) such as dendritic cells, macrophages, and B cells. Tregs can induce apoptosis of APCs or inhibit their activation and function, thereby regulating subsequent innate and adaptive immune responses. These actions of Tregs are mediated by both soluble factors (interleukin [IL]-10, transforming growth factor-beta, perforins, granzymes) and cell-associated molecules (cytotoxic T lymphocyte antigen 4, lymphocyte activation gene-3, CD18, neuropilin-1, LFA-1/CD11a, CD39), of which cytotoxic T lymphocyte antigen 4 has a key role. However, in autoimmunity, chronically activated APCs under the influence of intracellular signaling pathways, such as phosphatidyl inositol 3 kinase, JAK-STAT, MAPK, and nuclear factor-kappaB pathways, can escape surveillance by Tregs, leading to the activation of T cells that are refractory to suppression by Tregs. Moreover, APCs and APC-derived inflammatory cytokines such as tumor necrosis factor, IL-6, IL-1beta, and IL-23 can render Tregs defective and can also reciprocally enhance the activity of the IL-17-producing pathogenic Th17 T cell subset. Emerging knowledge of the importance of APC-Treg interactions in maintaining immune tolerance and aberrations in this cross talk in autoimmune diseases provides a rationale for therapeutic approaches specifically targeting this axis of the immune system.

Epigenetic control of FOXP3 expression: the key to a stable regulatory T-cell lineage?

Regulatory T (T(Reg)) cells constitute a unique T-cell lineage that has a crucial role in immunological tolerance. Several years ago, forkhead box P3 (FOXP3) was identified as the transcription factor that was responsible for determining the development and function of these cells. However, the underlying mechanisms that are involved in the regulation of the FOXP3 gene remain unclear and therefore preclude accurate identification and manipulation of T(Reg) cells. In this Progress article, we summarize recent advances in understanding how FOXP3 expression is controlled and highlight evidence suggesting that epigenetic regulation of the FOXP3 locus contributes to its role as a lineage-specification factor.

FOXP3 up-regulates p21 expression by site-specific inhibition of histone deacetylase 2/histone deacetylase 4 association to the locus

p21 loss has been implicated in conferring oncogenic activity to known tumor suppressor gene KLF4 and cancer drug tamoxifen. Regulators of p21, therefore, play critical roles in tumorigenesis. Here, we report that X-linked tumor suppressor FOXP3 is essential for p21 expression in normal epithelia and that lack of FOXP3 is associated with p21 down-regulation in breast cancer samples. A specific FOXP3 binding site in the intron 1 is essential for p21 induction by FOXP3. FOXP3 specifically inhibited binding of histone deacetylase 2 (HDAC2) and HDAC4 to the site and increased local histone H3 acetylation. Short hairpin RNA silencing of either HDAC2 or HDAC4 is sufficient to induce p21 expression. Our data provides a novel mechanism for transcription activation by FOXP3 and a genetic mechanism for lack of p21 in a large proportion of breast cancer.

Prevention of allograft rejection by amplification of Foxp3(+)CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) T cells were identified originally as potent suppressors of autoimmunity and were later termed "natural regulatory T cells" or nTreg cells. Subsequently, a transcription factor called forkhead box protein 3 (Foxp3) was identified to be a critical regulator for Treg differentiation and function. Foxp3(+)CD4(+)CD25(+) Treg cells have been increasingly documented to suppress allograft rejection and to mediate allograft tolerance in transplantation. In this article, the authors review current approaches for amplification of allo-specific Foxp3(+)CD4(+)CD25(+) Treg cells for prevention of allograft rejection and induction of allo-specific transplant tolerance.

Structural aspects of the FOXP3 regulatory complex as an immunopharmacological target

The forkhead family transcription factor FOXP3 plays a fundamental role in immune homeostasis. FOXP3 dysfunction in regulatory T cells (Tregs) contributes to multiple disease processes such as autoimmunity, tumor development, and viral infection. FOXP3 cooperates and associates with a group of other transcriptional factors, co-repressors and co-activators in Tregs to form one or more dynamic regulatory complexes. These ensembles communicate with multiple key signaling pathways to either upregulate or downregulate the expression of downstream target genes such as cytokines and cell surface receptors, which are critical for the control of normal immune responses. Although the details of the underlying mechanism by which FOXP3 operates as a transcriptional repressor or an activator is largely undefined, FOXP3(+) Tregs based cellular therapies have been studied in animal models. Our recent studies concerning the FOXP3 complex ensemble provide structural and biochemical insights into FOXP3 function of Tregs, which are essential to the development of novel immunopharmacological agents for treating human immunological disease.

Using histone deacetylase inhibitors to enhance Foxp3(+) regulatory T-cell function and induce allograft tolerance

The histone/protein deacetylase inhibitor (HDACi), trichostatin A (TsA), increases the production and suppressive function of Foxp3(+) regulatory T cells (T(regs)), at least in part, by promoting the acetylation of Foxp3 protein itself. Acetylation of Foxp3 is required for effective binding of Foxp3 to the promoter of the interleukin-2 (IL-2) gene and the suppression of IL-2 expression. We have sought to identify agents that had similar effects on T(regs), but without the associated toxicity of TsA. This review summarizes the contrasting effects of various HDACis on T(reg) functions in vitro and in vivo. Agents that block primarily class I HDAC had minimal or no effect on T(reg) suppression, whereas multiple inhibitors of both class I and class II HDAC enhanced T(reg) suppression in vitro and in vivo. These data indicate tools for further analysis of T(reg) functions, and point to a critical role of class II HDAC in the regulation of T(regs). Such knowledge has direct implications for the development of in vivo approaches to treat autoimmune and other inflammatory diseases.

FOXP3 and its role in the immune system

FOXP3 is a member of the forkhead transcription factor family. Unlike other members, it is mainly expressed in a subset of CD4+ T-cells that play a suppressive role in the immune system. A function of FOXP3 is to suppress the function of NFAT and NFkappaB and this leads to suppression ofexpression of many genes including IL-2 and effector T-cell cytokines. FOXP3 acts also as a transcription activator for many genes induding CD2S, Cytotoxic T-Lymphocyte Antigen 4 (CTLA4), glucocorticoid-induced TNF receptorfamily gene (GITR) andfolate receptor 4. FOXP3+ T-cells are made in the thymus and periphery. The FOXP3+ T-cells made in the thymus migrate to secondary lymphoid tissues and suppress antigen priming of lymphocytes. Antigen priming of naive FOXP3 T-cdlls and naive FOXP3 T-cells leads to generation of memory FOXP3+ T-cells which are efficient in migration to nonlymphoid tissues. Memory FOXP3+ T-cells are, therefore, effective in suppression of effector T-cell function, while naive FOXP3 T-cells are adept at suppressing the early immune responses in lymphoid tissues. Both naive and memory FOXP3 T-cells are required for effective maintenance of tolerance and prevention of autoimmune diseases throughout the body. Many factors such as cytokines and noncytokine factors regulate the generation of FOXP3 T-cells. For example, retinoic acid, produced by the dendritic cells and epithelial cells in the intestine, works together with TGF-beta1 and promotes generation of small intestine-homing FOXP3 T-cells by upregulating the expression ofFOXP3 and gut homing receptors. FOXP3+ T-cells can be produced in vitro from autologous naive T-cells and, therefore, have great therapeutic potentials in treating a number of inflammatory diseases and grafi rejection.

Regulatory T cells modulate staphylococcal enterotoxin B-induced effector T-cell activation and acceleration of colitis

Oral administration of bacterial superantigen Staphylococcus aureus enterotoxin B (SEB) activates mucosal T cells but does not cause mucosal inflammation. We examined the effect of oral SEB on the development of mucosal inflammation in mice in the absence of regulatory T (Treg) cells. SCID mice were fed SEB 3 and 7 days after reconstitution with CD4(+) CD45RB(high) or CD4(+) CD45RB(high) plus CD4(+) CD45RB(low) T cells. Mice were sacrificed at different time points to examine changes in tissue damage and in T-cell phenotypes. Feeding SEB failed to produce any clinical effect on SCID mice reconstituted with CD4(+) CD45RB(high) and CD4(+) CD45RB(low) T cells, but feeding SEB accelerated the development of colitis in SCID mice reconstituted with CD4(+) CD45RB(high) T cells alone. The latter was associated with an increase in the number of CD4(+) Vbeta8(+) T cells expressing CD69 and a significantly lower number of CD4(+) CD25(+) Foxp3(+) T cells. These changes were not observed in SCID mice reconstituted with both CD45RB(high) and CD45RB(low) T cells. In addition, SEB impaired the development of Treg cells in the SCID mice reconstituted with CD4(+) CD45RB(high) T cells alone but had no direct effect on Treg cells. In the absence of Treg cells, feeding SEB induced activation of mucosal T cells and accelerated the development of colitis. This suggests that Treg cells prevent SEB-induced mucosal inflammation through modulation of SEB-induced T-cell activation.