A minimal IFN-gamma promoter confers Th1 selective expression

Human T-bet Governs Innate and Innate-like Adaptive IFN-γ Immunity against Mycobacteria

Inborn errors of human interferon gamma (IFN-γ) immunity underlie mycobacterial disease. We report a patient with mycobacterial disease due to inherited deficiency of the transcription factor T-bet. The patient has extremely low counts of circulating Mycobacterium-reactive natural killer (NK), invariant NKT (iNKT), mucosal-associated invariant T (MAIT), and Vδ2+ γδ T lymphocytes, and of Mycobacterium-non reactive classic TH1 lymphocytes, with the residual populations of these cells also producing abnormally small amounts of IFN-γ. Other lymphocyte subsets develop normally but produce low levels of IFN-γ, with the exception of CD8+ αβ T and non-classic CD4+ αβ TH1∗ lymphocytes, which produce IFN-γ normally in response to mycobacterial antigens. Human T-bet deficiency thus underlies mycobacterial disease by preventing the development of innate (NK) and innate-like adaptive lymphocytes (iNKT, MAIT, and Vδ2+ γδ T cells) and IFN-γ production by them, with mycobacterium-specific, IFN-γ-producing, purely adaptive CD8+ αβ T, and CD4+ αβ TH1∗ cells unable to compensate for this deficit.

Glucocorticoid-Induced Leucine Zipper Inhibits Interferon-Gamma Production in B Cells and Suppresses Colitis in Mice

Glucocorticoid-induced leucine zipper (GILZ) is transcriptionally upregulated by glucocorticoids (GCs) and mediates many of the anti-inflammatory effects of GCs. Since B cell activity has been linked to cytokine production and modulation of inflammatory responses, we herein investigated the role of GILZ in B cells during colitis development. B cell-specific gilz knock-out (gilz B cKO) mice exhibited increased production of the pro-inflammatory cytokine IFN-γ in B cells, and consequently CD4⁺ T cell activation. Increased IFN-γ production in B cells was associated with enhanced transcriptional activity of the transcription factor activator protein-1 (AP-1) on the IFN-γ promoter. Moreover, GILZ deficiency in B cells was linked to enhanced susceptibility to experimental colitis in mice, and this was reversed by administering GILZ protein. Interestingly, we observed increased production of IFN-γ in both B and T cells infiltrating the lamina propria (LP) of gilz B cKO mice. Together, these findings indicate that GILZ controls IFN-γ production in B cells, which also affects T cell activity, and increased production of IFN-γ by B and T cells in LP is associated with predisposition to inflammatory colitis in mice.

Influence of TBX21 T-1993C variant on autoimmune hepatitis development by Yin-Yang 1 binding

AIM

To investigated the mechanism of the association between the TBX21 T-1993C promoter polymorphism and autoimmune hepatitis type 1 (AIH-1) development.

METHODS

In vivo, In vivo, and reporter analyses were performed to determine the function of transcription factors binding to the T-1993C element of the TBX21 promoter in human CD4+ T and B cell lines. Flow cytometry and quantitative real-time PCR were used to analyze T-box transcription factor (T-bet) and interferon-γ (IFN-γ) expressions in CD4+ T cells, B cells and monocytes from the peripheral blood of AIH-1 patients including 5-1993TC and 15-1993TT genotype carriers, and healthy controls including 10-1993TC and 25-1993TT genotype carriers. Furthermore, a range of biochemical indices was measured simultaneously in the blood of AIH-1 patients.

RESULTS

TBX21-1993C allele created a strong Yin-Yang 1 (YY1)-binding site and decreased transcriptional activity of TBX21 promoter in human CD4+ T and B cells. Higher levels of T-bet and IFN-γ were detected in the circulating CD4+ T cells and B cells of AIH-1 patients carrying the TBX21-1993 TT genotype compared with the patients carrying the -1993 TC genotype and controls with the -1993 TC genotype. T-bet expression levels of circulating T cells and B cells were positively correlated with AIH-1 disease activity. Knockdown of YY1 with siRNA caused increased expression of T-bet and IFN-γ in peripheral blood mononuclear cells in AIH-1 patients.

CONCLUSION

The repression of TBX21 expression by high-affinity binding of YY1 to the -1993C allele may contribute to a decreased development of AIH-1 via suppression of type 1 immunity.

MAPKAP kinase 3 suppresses Ifng gene expression and attenuates NK cell cytotoxicity and Th1 CD4 T-cell development upon influenza A virus infection

MK2 and MK3 are downstream targets of p38 and ERK1/2. They control the mRNA stability of several inflammatory cytokines, including TNF-α and IL-10. Whereas MK2 is expressed ubiquitously, the expression of MK3 is restricted to muscle, liver, and heart tissues and T and NK cells. Using Mk-deficient and wild-type (WT) mice, we demonstrated an inhibitory effect of MK3, but not of MK2, on interferon (IFN)-γ expression in T and NK lymphocytes. The results provided evidence that the inhibitory effect of MK3 is based on negative feedback phosphorylation of p38 and ERK1/2, which causes decreased binding of Stat4 to the IFN-γ promoter and reduced expression of IFN-γ mRNA and protein. Consequently, all Mk3(-/-) mice challenged with the Th1-inducing influenza A virus (IAV) survived the WT LD50 virus dose. The reduced disease severity in the Mk3(-/-) mice was accompanied by a >10-fold reduction in viral lung titer and an increase in the number of activated NK cells and enhanced Th1 activation of CD4 T cells. Thus, our data describe the protein kinase MK3 as a novel regulator of the innate and adaptive immune responses.-Köther, K., Nordhoff, C., Masemann, D., Varga, G., Bream, J. H., Gaestel, M., Wixler, V., Ludwig, S. MAPKAP kinase 3 suppresses Ifng gene expression and attenuates NK cell cytotoxicity and Th1 CD4 T-cell development upon influenza A virus infection.

Deletion of a conserved cis-element in the Ifng locus highlights the role of acute histone acetylation in modulating inducible gene transcription

Differentiation-dependent regulation of the Ifng cytokine gene locus in T helper (Th) cells has emerged as an excellent model for functional study of distal elements that control lineage-specific gene expression. We previously identified a cis-regulatory element located 22 kb upstream of the Ifng gene (Conserved Non-coding Sequence -22, or CNS-22) that is a site for recruitment of the transcription factors T-bet, Runx3, NF-κB and STAT4, which act to regulate transcription of the Ifng gene in Th1 cells. Here, we report the generation of mice with a conditional deletion of CNS-22 that has enabled us to define the epigenetic and functional consequences of its absence. Deletion of CNS-22 led to a defect in induction of Ifng by the cytokines IL-12 and IL-18, with a more modest effect on induction via T-cell receptor activation. To better understand how CNS-22 and other Ifng CNSs regulated Ifng transcription in response to these distinct stimuli, we examined activation-dependent changes in epigenetic modifications across the extended Ifng locus in CNS-22-deficient T cells. We demonstrate that in response to both cytokine and TCR driven activation signals, CNS-22 and other Ifng CNSs recruit increased activity of histone acetyl transferases (HATs) that transiently enhance levels of histones H3 and H4 acetylation across the extended Ifng locus. We also demonstrate that activation-responsive increases in histone acetylation levels are directly linked to the ability of Ifng CNSs to acutely enhance Pol II recruitment to the Ifng promoter. Finally, we show that impairment in IL-12+IL-18 dependent induction of Ifng stems from the importance of CNS-22 in coordinating locus-wide levels of histone acetylation in response to these cytokines. These findings identify a role for acute histone acetylation in the enhancer function of distal conserved cis-elements that regulate of Ifng gene expression.

Epigenetic control of cytokine gene expression: regulation of the TNF/LT locus and T helper cell differentiation

Epigenetics encompasses transient and heritable modifications to DNA and nucleosomes in the native chromatin context. For example, enzymatic addition of chemical moieties to the N-terminal "tails" of histones, particularly acetylation and methylation of lysine residues in the histone tails of H3 and H4, plays a key role in regulation of gene transcription. The modified histones, which are physically associated with gene regulatory regions that typically occur within conserved noncoding sequences, play a functional role in active, poised, or repressed gene transcription. The "histone code" defined by these modifications, along with the chromatin-binding acetylases, deacetylases, methylases, demethylases, and other enzymes that direct modifications resulting in specific patterns of histone modification, shows considerable evolutionary conservation from yeast to humans. Direct modifications at the DNA level, such as cytosine methylation at CpG motifs that represses promoter activity, are another highly conserved epigenetic mechanism of gene regulation. Furthermore, epigenetic modifications at the nucleosome or DNA level can also be coupled with higher-order intra- or interchromosomal interactions that influence the location of regulatory elements and that can place them in an environment of specific nucleoprotein complexes associated with transcription. In the mammalian immune system, epigenetic gene regulation is a crucial mechanism for a range of physiological processes, including the innate host immune response to pathogens and T cell differentiation driven by specific patterns of cytokine gene expression. Here, we will review current findings regarding epigenetic regulation of cytokine genes important in innate and/or adaptive immune responses, with a special focus upon the tumor necrosis factor/lymphotoxin locus and cytokine-driven CD4+ T cell differentiation into the Th1, Th2, and Th17 lineages.

STAT4 and T-bet are required for the plasticity of IFN-γ expression across Th2 ontogeny and influence changes in Ifng promoter DNA methylation

CD4(+) T cells developing toward a Th2 fate express IL-4, IL-5, and IL-13 while inhibiting production of cytokines associated with other Th types, such as the Th1 cytokine IFN- γ. IL-4-producing Th2 effector cells give rise to a long-lived memory population committed to reactivation of the Th2 cytokine gene expression program. However, reactivation of these effector-derived cells under Th1-skewing conditions leads to production of IFN-γ along with IL-4 in the same cell. We now show that this flexibility ("plasticity") of cytokine expression is preceded by a loss of the repressive DNA methylation of the Ifng promoter acquired during Th2 polarization yet requires STAT4 along with T-box expressed in T cells. Surprisingly, loss of either STAT4 or T-box expressed in T cells increased Ifng promoter CpG methylation in both effector and memory Th2 cells. Taken together, our data suggest a model in which the expression of IFN-γ by Th2-derived memory cells involves attenuation of epigenetic repression in memory Th2 cells, combined with Th1-polarizing signals after their recall activation.

Loss of methylation at the IFNG promoter and CNS-1 is associated with the development of functional IFN-γ memory in human CD4(+) T lymphocytes

Cytokine memory for IFN-γ production by effector/memory Th1 cells plays a key role in both protective and pathological immune responses. To understand the epigenetic mechanism determining the ontogeny of effector/memory Th1 cells characterized by stable effector functions, we identified a T-cell-specific methylation pattern at the IFNG promoter and CNS-1 in ex vivo effector/memory Th1 cells, and investigated methylation dynamics of these regions during the development of effector/memory Th1 cells. During Th1 differentiation, demethylation occurred at both the promoter and CNS-1 regions of IFNG as early as 16 h, and this process was independent of cell proliferation and DNA synthesis. Using an IFN-γ capture assay, we found early IFN-γ-producing cells from 2-day differentiating cultures acquired "permissive" levels of demethylation and developed into effector/memory Th1 cells undergoing progressive demethylation at the IFNG promoter and CNS-1 when induced by IL-12. Methylation levels of these regions in effector/memory Th1 cells of peripheral blood from rheumatoid arthritis patients correlated inversely with reduced frequencies of IFN-γ-producers, coincident with recruitment of effector/memory Th1 cells to the site of inflammation. Thus, after termination of TCR stimulation, IL-12 signaling potentiates the stable functional IFN-γ memory in effector/memory Th1 cells characterized by hypomethylation at the IFNG promoter and CNS-1.

Genetic variation at a Yin-Yang 1 response site regulates the transcription of cyclin-dependent kinase inhibitor p18INK4C transcript in lupus-prone mice

We have previously shown that a novel -74 C-to-T mutation in the promoter of the cyclin-dependent kinase inhibitor p18(Ink4c) (p18) gene was associated with a reduced p18 expression in B cells from mice carrying the Sle2c1 lupus susceptibility locus. To determine the function of the -74 C/T single nucleotide polymorphism, we have characterized the proximal promoter of the mouse p18 gene. Functional analysis of the 5' flanking region by sequential deletions revealed crucial elements between -300 and +1, confirming the in silico prediction that the -74 T allele created a novel Yin-Yang 1 (YY-1) binding site adjacent to an existing one common to both alleles. Moreover, we found that YY-1, E2F1, and Sp-1 can synergistically enhance the activity of the p18 promoter. Mutational inactivation revealed that YY-1 binding regulates the p18 activity in an allele-dependent fashion. EMSAs with splenic B cell extracts directly demonstrated that YY-1 binds to the p18 promoter with differences between the C and the T alleles. We also determined in vivo by chromatin immunoprecipitation that the T allele resulted in increased YY-1 and decreased Nrf-2 binding to the p18 promoter as compared with the C allele in B cells. Thus, YY-1 is a direct regulator of p18 gene expression in an allele-dependent fashion that is consistent with the lupus-associated T allele, inducing a lower p18 transcriptional activity by increasing YY-1 binding. These results establish the p18 -74 C/T mutation as the leading causal variant for the B1a cell expansion that characterizes the NZB and NZM2410 lupus-prone strains.

C6-ceramide enhances Interleukin-12-mediated T helper type 1 cell responses through a cyclooxygenase-2-dependent pathway

Ceramides, lipid molecules located predominantly within the plasma membrane of a cell, can function as second messengers, and have been known to carry out a number of cellular functions. T helper type 1 (Th1) immune responses are known to be involved in the cellular immunity, which is crucial in the cancer and allergy immunotherapy. This study was designed to evaluate the effects of ceramides on T helper cell responses and their underlying mechanisms. We demonstrated that a cell-permeable C6-ceramide (C6) together with IL-12 enhanced Th1 cell differentiation, whereas C6 alone had no effects, as demonstrated by the increased populations of IFN-γ expressing CD4(+) T cells and the up-regulation of IFN-γ production from CD4(+) T cells. In contrast, C2-ceramide and long chain ceramides (C16 and C24) did not affect the Th1 responses. C6 treatment was shown to increase the expression of T-bet, a master transcription factor of Th1 responses, in a dose-dependent fashion. Furthermore, C6 increased the expression of cyclooxygenase-2 (COX-2) in CD4(+) T cells. The C6-mediated increase of IFN-γ production and IFN-γ expressing CD4(+) T cell populations were significantly suppressed by a COX-2 specific inhibitor (NS-398) in a dose-dependent manner. T-bet expression was also decreased by NS-398 treatment, thereby indicating that C6 ceramide enhances Th1 responses via a COX-2 dependent pathway. This result demonstrates that C6 may be utilized in therapies for the treatment of immune diseases such cancer and allergy by enhancing the Th1 activity.

A common promoter variant of TBX21 is associated with allele specific binding to Yin-Yang 1 and reduced gene expression

T-bet is a key regulator for the lineage commitment in CD4 T helper (Th) 1 cells by activating the hallmark production of interferon-γ, and its expression level is linked to autoimmune, infectious, and allergic diseases. A T to C base substitution has been identified at position -1993 in the TBX21 (encoding T-bet) promoter and has been associated with asthma and systemic lupus erythematosus. This study aimed to investigate the molecular mechanisms responsible for the influence of the T-1993C polymorphism on transcription and its functional effect by luciferase reporter, EMSAs, Chromatin immunoprecipitation assay, and flow cytometric analysis of intracellular T-bet, IFN-γ and IL-4 expression in activated CD4(+) T cells. The presence of a -1993T allele obviously increases promoter activity compared with that of a promoter with a -1993C allele. TBX21 promoter carrying -1993C allele possesses significantly stronger binding affinity to the Yin Yang 1 (YY1) transcription factor than that carrying -1993T allele. YY1 overexpression decreased TBX21 promoter function in a T cell line, demonstrating that this element functions as a repressor. The C to T base exchange relieves the repression mediated by YY1. The individuals carrying -1993C allele were determined to have significantly diminished expression of TBX21 and IFN-γ and increased IL-4 production in cells compared with the individuals carrying -1993T allele (P < 0.05). These findings demonstrate that the TBX21 T-1993C polymorphism represses TBX21 expression and Th1 cytokine production through control of YY1, which might result in the imbalance between Th1 and Th2 immune responses in autoimmune or allergic diseases.

T-bet dependent removal of Sin3A-histone deacetylase complexes at the Ifng locus drives Th1 differentiation

Forming and removing epigenetic histone marks at gene loci are central processes in differentiation. Here, we explored mechanisms establishing long-range H4 acetylation marks at the Ifng locus during Th1 lineage commitment. In Th0 cells, histone deacetylase (HDAC)-Sin3A complexes recruited to the Ifng locus actively prevented accumulation of H4 acetylation marks. Th1 differentiation caused loss of HDAC-Sin3A complexes by T-bet-dependent mechanisms and accumulation of H4 acetylation marks. HDAC-Sin3A complexes were absent from the locus in NOD Th0 cells, obviating the need for Th1 differentiation signals to establish histone marks and Th1 differentiation. Thus, Ifng transcription is actively prevented in Th0 cells via epigenetic mechanisms and epigenetic defects allow unregulated Ifng transcription that may contribute to autoimmunity.

At the crossroads of T helper lineage commitment-Epigenetics points the way

The immune system has the capacity to respond to various types of pathogens including bacteria, viruses, tumors and parasites. This requires a flexible immune system, which in part depends on the development of alternative effector T helper cells, with different cytokine repertoires that direct the overall immune response. The reciprocal effects of the T helper subtypes Th1 and Th2 are well documented, but the mechanisms involved in alternative cytokine expression and silencing are less well defined. Introduction of advances within the field of chromatin folding and epigenetic regulation of transcription has begun to explain some of the fundamental principles of T helper cell development. In addition, epigenetic regulation has proven essential also for the more recently discovered T helper cell subtypes; regulatory T cells and the Th17 lineage. As the importance of proper epigenetic regulation becomes evident, attention is also focused on the potential harmfulness of epigenetic dysregulation. Autoimmunity and allergy are two clinical situations that have been implicated as results of imperfect cytokine silencing. This review will address recent advances in the field of epigenetic regulation of T lymphocytes and their maturation from naive cells into different effector T cell lineages. In particular, epigenetic involvement in regulation of key effector cytokines and specific transcription factors determining the CD4(+) T lymphocyte lineage commitment will be discussed.

Epigenetics and T helper 1 differentiation

Naïve T helper cells differentiate into two subsets, T helper 1 and 2, which either transcribe the Ifng gene and silence the Il4 gene or transcribe the Il4 gene and silence the Ifng gene, respectively. This process is an essential feature of the adaptive immune response to a pathogen and the development of long-lasting immunity. The 'histone code' hypothesis proposes that formation of stable epigenetic histone marks at a gene locus that activate or repress transcription is essential for cell fate determinations, such as T helper 1/T helper 2 cell fate decisions. Activation and silencing of the Ifng gene are achieved through the creation of stable epigenetic histone marks spanning a region of genomic DNA over 20 times greater than the gene itself. Key transcription factors that drive the T helper 1 lineage decision, signal transducer and activator 4 (STAT4) and T-box expressed in T cells (T-bet), play direct roles in the formation of activating histone marks at the Ifng locus. Conversely, STAT6 and GATA binding protein 3, transcription factors essential for the T helper 2 cell lineage decision, establish repressive histone marks at the Ifng locus. Functional studies demonstrate that multiple genomic elements up to 50 kilobases from Ifng play critical roles in its proper transcriptional regulation. Studies of three-dimensional chromatin conformation indicate that these distal regulatory elements may loop towards Ifng to regulate its transcription. We speculate that these complex mechanisms have evolved to tightly control levels of interferon-gamma production, given that too little or too much production would be very deleterious to the host.

NF-kappaB activation by the viral oncoprotein StpC enhances IFN-gamma production in T cells

Interferon-gamma (IFN-gamma) is an essential regulator of innate and adaptive immune responses and a hallmark of the Th1 T-cell subset. It is produced at high levels by human T lymphocytes upon transformation with Herpesvirus saimiri, which depends on the expression of the viral oncoproteins saimiri transformation-associated protein of subgroup C (StpC) and tyrosine kinase-interacting protein (Tip). Here, we show that IFN-gamma production was induced by Tip in Jurkat T cells. StpC by itself did not affect IFN-gamma expression, but enhanced the effect of Tip. Our results substantiated the findings that StpC induces NF-kappaB activation and demonstrated that other transcription factors, including NFAT, AP-1 and serum response element regulators, were not activated by StpC in unstimulated T cells. Studies using StpC mutants deficient in NF-kappaB activation, dominant negative IkappaBalpha and constitutively active IKK2, established the importance of NF-kappaB in StpC-mediated upregulation of IFN-gamma production. These observations suggest that NF-kappaB induction by StpC contributes to the Th1-like phenotype of virus-transformed human T cells.

Yin-Yang 1 regulates effector cytokine gene expression and T(H)2 immune responses

BACKGROUND

The transcription factor Yin-Yang 1 (YY-1) binds to the promoter regions of several T-cell cytokine genes, but the expression and contribution of this factor to cytokine gene expression and T-cell activation in vivo is not clear.

OBJECTIVE

We sought to better define the role of YY-1 in T-cell gene regulation and allergic immune responses.

METHODS

We studied cytokine gene expression in T lymphocytes isolated from wild-type mice and heterozygous littermates bearing 1 targeted yy-1 allele (yy-1(+/-) mice). T cells were stimulated with anti-T-cell receptor (anti-TCR) plus CD28 antibodies or with peptide antigen plus antigen-presenting cells by using newly generated yy-1(+/-) TCR transgenic mice. We also studied ovalbumin-driven allergic immune responses in a mouse model of asthma and YY-1 expression in lung tissue from human asthmatic subjects.

RESULTS

CD4(+) T cells from yy-1(+/-) mice secreted significantly less IL-4 and IFN-gamma compared with wild-type littermates after TCR-dependent activation, whereas IL-2 production was not significantly affected. Both airway inflammation and recall splenocyte IL-4 production were inhibited in yy-1(+/-) mice, as was antigen-driven T-cell proliferation. YY-1 expression was higher in airway biopsy specimens from asthmatic compared with control subjects.

CONCLUSION

These data indicate that YY-1 regulates T-cell cytokine gene expression and allergic immune responses in a gene dose-dependent manner.

Unconventional association of the polycomb group proteins with cytokine genes in differentiated T helper cells

The cytokine transcription profiles of developing T helper 1 and T helper 2 cells are imprinted and induced appropriately following stimulation of differentiated cells. Epigenetic regulation combines several mechanisms to ensure the inheritance of transcriptional programs. We found that the expression of the polycomb group proteins, whose role in maintaining gene silencing is well documented, was induced during development in both T helper lineages. Nevertheless, the polycomb proteins, YY1, Mel-18, Ring1A, Ezh2, and Eed, bound to the Il4 and Ifng loci in a differential pattern. In contrast to the prevailing dogma, the binding activity of the polycomb proteins in differentiated T helper cells was associated with cytokine transcription. The polycomb proteins bound to the cytokine genes under resting conditions, and their binding was induced dynamically following stimulation. The recruitment of the polycomb proteins Mel-18 and Ezh2 to the cytokine promoters was inhibited in the presence of cyclosporine A, suggesting the involvement of NFAT. Considering their binding pattern at the cytokine genes and their known function in higher order folding of regulatory elements, we propose a model whereby the polycomb proteins, in some contexts, positively regulate gene expression by mediating long-distance chromosomal interactions.

BOB.1/OBF.1 controls the balance of TH1 and TH2 immune responses

BOB.1/OBF.1 is a transcriptional coactivator essential at several stages of B-cell development. In T cells, BOB.1/OBF.1 expression is inducible by co-stimulation. However, a defined role of BOB.1/OBF.1 for T-cell function had not been discovered so far. Here, we show that BOB.1/OBF.1 is critical for T helper cell function. BOB.1/OBF.1(-/-) mice showed imbalanced immune responses, resulting in increased susceptibility to Leishmania major infection. Functional analyses revealed specific defects in TH1 and TH2 cells. Whereas expression levels of TH1 cytokines were reduced, the secretion of TH2 cytokines was increased. BOB.1/OBF.1 directly contributes to the IFNgamma and IL2 promoter activities. In contrast, increased TH2 cytokine production is controlled indirectly, probably via the transcription factor PU.1, the expression of which is regulated by BOB.1/OBF.1. Thus, BOB.1/OBF.1 regulates the balance of TH1 versus TH2 mediated immunity.

Dynamic changes in histone-methylation 'marks' across the locus encoding interferon-γ during the differentiation of T helper type 2 cells

The 'histone-code' hypothesis proposes that cell fate 'decisions' are achieved through the creation of stable epigenetic histone 'marks' at gene loci. Here we explored the formation of marks of repressive methylation of histone 3 at lysine 9 (H3-K9) and of H3-K27 at the locus encoding interferon-gamma (Ifng locus) during the commitment of naive T cells to the T helper type 1 (TH1) and TH2 lineages. Methylation of H3-K9 across the Ifng locus was rapidly induced in differentiating TH1 and TH2 cells and was sustained in TH1 cells. In contrast, TH2 differentiation caused loss of methylation of H3-K9 and gain of methylation of H3-K27 by mechanisms dependent on the transcription factors GATA-3 and STAT6. Thus, histone-methylation marks at the Ifng locus are highly dynamic, which may ensure higher-order transcriptional regulation during early lineage commitment.

T-box proteins differentially activate the expression of the endogenous interferon γ gene versus transfected reporter genes in non-immune cells

The T-box transcription factor T-bet is expressed in a number of hematopoetic cell types and plays an essential role in the lineage determination of Th1 T-helper cells. In the absence of T-bet, CD4(+) T-cells fail to induce IFNgamma, the cytokine whose expression characterizes Th1 cells. Here we show that, surprisingly, T-bet induces the expression of endogenous IFNgamma in non-immune human cells, including 293 and other cell lines. Thus T-bet can induce IFNgamma expression independently of its role in T-cell lineage determination. In addition, mutations in T-bet, and chimeras of T-bet with other transcription factors including the T-box transcription factor, TBX2, differentially affect the ability of T-bet to activate expression of endogenous IFNgamma versus a T-site regulated reporter gene. A truncated T-betVp16 fusion protein strongly activates the T-site reporter but fails to activate endogenous IFNgamma. Conversely, native T-bet strongly activates endogenous IFNgamma expression but only weakly activates the reporter gene. Fusion of the Vp16 activation domain to full-length T-bet greatly increases its activation of both endogenous IFNgamma and transfected T-site reporter gene expression. In contrast, TBX2Vp16 potently activates the T-site reporter but has a negligible effect on endogenous IFNgamma expression. Butyrate treatment of T-bet expressing cells potentiates the expression of endogenous IFNgamma but weakly represses expression of the T-site reporter gene. These data indicate that induction of endogenous IFNgamma can be uncoupled from differentiation into the Th1 lineage and that the expression of endogenous IFNgamma versus a T-site reporter gene is differentially regulated by T-bet and other T-box proteins.

Favored T helper 1 response in a mouse model of hepatosteatosis is associated with enhanced T cell-mediated hepatitis

Steatohepatitis enhances the severity of liver injury caused by acute inflammation. The purpose of this study was to test the hypothesis that fatty liver due to chronic choline-deficient diet exacerbates concanavalin A (ConA)-induced liver hepatitis, which is predominantly facilitated by T cells. Male C57BL/6 mice were fed either control choline-sufficient diet (CSD) or choline-deficient diet (CDD) for 6 weeks before ConA administration. Mice were sacrificed 3, 9, and 24 hours after ConA injection. Liver injury measured by aspartate aminotransferase (AST), alanine aminotransferase (ALT), pathology, and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) staining was minimal in mice fed either diet before ConA exposure. However, ConA-induced liver injury was significantly greater in CDD-fed mice compared with control-fed mice. Liver cytokines were assessed by quantitative real-time polymerase chain reaction (PCR). The expression of T helper (Th) 1 cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12 (IL-12), and interferon gamma (IFN-gamma) were dramatically elevated after ConA in CDD-fed mice compared with control-fed mice. CDD also enhanced ConA-induced STAT4 activation, but not STAT6. Notably, regulators of T-cell differentiation were strongly shifted toward a predominant Th1 profile. T-bet, regulator of the Th1 response, was up-regulated in CDD-fed mice, whereas Th2 regulator GATA-3 was significantly suppressed in CDD-fed mice after ConA. Moreover, the expression of suppressor of cytokine signaling (SOCS)-1, SOCS-3, and repressor of GATA-3 (ROG) favored a predominant Th1 cytokine response in CDD-fed mice. In conclusion, these data support the hypothesis that hepatosteatosis caused by CDD is associated with more severe ConA-induced hepatitis due to a predominant shift toward Th1 response.

T helper type 1-specific Brg1 recruitment and remodeling of nucleosomes positioned at the IFN-gamma promoter are Stat4 dependent

Transcriptional competence of the interferon-gamma (IFN-gamma) locus is enhanced as Th1 effectors develop from naive CD4 T lymphocytes; conversely, this gene is repressed during Th2 differentiation. We now show that the Switch (Swi)-sucrose nonfermenter (SNF) component Brahma-related gene 1 (Brg1) is recruited, and positioned nucleosomes are remodeled, in a Th1-specific manner that is dependent on the transcription factor Stat4 and calcineurin phosphatase activity. Interference with specific components of mammalian Swi-SNF complexes decreased CD4 T cell differentiation into IFN-gamma-positive Th1 cells. These findings reveal a collaborative mechanism of IFN-gamma gene regulation during Th1 differentiation and suggest that a Th1-specific chromatin structure is created by early recruitment of Swi-SNF complexes and nucleosome remodeling dependent on Stat4 and calcineurin activation.

Characterization of a novel PMA-inducible pathway of interleukin-13 gene expression in T cells

Although interleukin 13 (IL-13) is an important mediator of asthma and allergic diseases, the molecular mechanisms regulating IL-13 gene expression are not well understood. This study was designed to define the molecular mechanisms governing IL-13 gene expression in T cells. IL-13 expression was examined in human peripheral blood T cells and in the EL-4 T-cell line by enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction. An IL-13 promoter deletion analysis was performed using luciferase-based reporter plasmids transiently transfected into EL-4 cells by electroporation. DNA binding factors were investigated using electrophoretic mobility shift assays. In contrast to IL-4 expression, which required concomitant activation of calcium- and protein kinase C- (PKC-) dependent signalling pathways, PKC activation alone was sufficient for IL-13 protein secretion in mitogen-primed (but not resting) peripheral blood T cells, and for IL-13 mRNA expression and promoter activity in EL-4 T cells. Promoter deletion analysis localized a phorbol 12-myristate 13-acetate (PMA)-sensitive element to a proximal promoter region between -109 and -79 base pairs upstream from the IL-13 transcription start site. This promoter region supported the binding of both constitutive and PMA-inducible nuclear factors in gel shift assays.

Histone hyperacetylated domains across the Ifng gene region in natural killer cells and T cells

Local histone acetylation of promoters precedes transcription of many genes. Extended histone hyperacetylation at great distances from coding regions of genes also occurs during active transcription of gene families or individual genes and may reflect developmental processes that mark genes destined for cell-specific transcription, nuclear signaling processes that are required for active transcription, or both. To distinguish between these, we compared long-range histone acetylation patterns across the Ifng gene region in natural killer (NK) cells and T cells that were or were not actively transcribing the Ifng gene. In T cells, long-range histone acetylation depended on stimulation that drives both T helper (Th) 1 differentiation and active transcription, and it depended completely or partially on the presence of Stat4 or T-bet, respectively, two transcription factors that are required for Th1 lineage commitment. In contrast, in the absence of stimulation and active transcription, similar histone hyperacetylated domains were found in NK cells. Additional proximal domains were hyperacetylated after stimulation of transcription. We hypothesize that formation of extended histone hyperacetylated domains across the Ifng gene region represents a developmental mechanism that marks this gene for cell- or stimulus-specific transcription.

Histone hyperacetylated domains across the Ifng gene region in natural killer cells and T cells

Local histone acetylation of promoters precedes transcription of many genes. Extended histone hyperacetylation at great distances from coding regions of genes also occurs during active transcription of gene families or individual genes and may reflect developmental processes that mark genes destined for cell-specific transcription, nuclear signaling processes that are required for active transcription, or both. To distinguish between these, we compared long-range histone acetylation patterns across the Ifng gene region in natural killer (NK) cells and T cells that were or were not actively transcribing the Ifng gene. In T cells, long-range histone acetylation depended on stimulation that drives both T helper (Th) 1 differentiation and active transcription, and it depended completely or partially on the presence of Stat4 or T-bet, respectively, two transcription factors that are required for Th1 lineage commitment. In contrast, in the absence of stimulation and active transcription, similar histone hyperacetylated domains were found in NK cells. Additional proximal domains were hyperacetylated after stimulation of transcription. We hypothesize that formation of extended histone hyperacetylated domains across the Ifng gene region represents a developmental mechanism that marks this gene for cell- or stimulus-specific transcription.

T-bet-dependent expression of osteopontin contributes to T cell polarization

The osteopontin (Opn) glycoprotein has been implicated in diverse physiological processes, including vascularization, bone formation, and inflammatory responses. Studies of its role in immune responses has suggested that Opn can set the early stage of type-1 immune (cell-mediated) responses through differential regulation of IL-12 and IL-10 cytokine gene expression in macrophages. Although Opn has been suggested to play a role in the development of type-1 immunity, little is known about control of Opn gene expression. Here, we report that Opn gene expression in activated T cells, but not macrophages, is regulated by T-bet, a transcription factor that controls CD4+ T helper (Th1) cell lineage commitment. We also find that T-bet-dependent expression of Opn in T cells is essential for efficient skewing of CD4+ T and CD8+ T cells toward the Th1 and type 1 CD8+ T cells (Tc1) pathway, respectively. Taken together, these findings begin to delineate the genetic basis of Opn expression in T cells and further clarify the role of Opn in Th and Tc1 development.

Glucose availability regulates IFN-gamma production and p70S6 kinase activation in CD8+ effector T cells

Differentiation of CD8+ T cells from the naive to the effector state is accompanied by changes in basal gene expression profiles that parallel the acquisition of effector functions. Among these are metabolism genes, and we now show that 2C TCR transgenic effector CD8+ T cells express higher levels of glycolytic enzymes and display greater glucose uptake, a higher glycolytic rate, and increased lactate production compared with naive cells. To determine whether glucose was required for effector T cell functions, we regulated glucose availability in vitro. Glucose deprivation strongly inhibited IFN-gamma gene expression, whereas IL-2 production was little affected. Inhibition correlated with diminished phosphorylation of p70S6 kinase and eIF4E binding protein 1 and a requirement for de novo protein synthesis, whereas other signaling pathways known to regulate IFN-gamma expression were unaffected. Together, our data reveal that optimal induction of IFN-gamma transcription is a glucose-dependent process, indicate that there are undefined factors that influence IFN-gamma expression, and have implications for regulation of the effector phase of CD8+ T cell responses in tissue microenvironments.

Ets-1, a functional cofactor of T-bet, is essential for Th1 inflammatory responses

To mount an effective type 1 immune response, type 1 T helper (Th1) cells must produce inflammatory cytokines and simultaneously suppress the expression of antiinflammatory cytokines. How these two processes are coordinately regulated at the molecular level is still unclear. In this paper, we show that the proto-oncogene E26 transformation-specific-1 (Ets-1) is necessary for T-bet to promote interferon-gamma production and that Ets-1 is essential for mounting effective Th1 inflammatory responses in vivo. In addition, Ets-1-deficient Th1 cells also produce a very high level of interleukin 10. Thus, Ets-1 plays a crucial and unique role in the reciprocal regulation of inflammatory and antiinflammatory Th responses.

A distinct region of the murine IFN-gamma promoter is hypomethylated from early T cell development through mature naive and Th1 cell differentiation, but is hypermethylated in Th2 cells

Reports on the status of DNA methylation of the IFN-gamma gene during T cell development in human and mouse have presented somewhat contradictory results. In this study we demonstrate in the mouse that methylation of the IFN-gamma promoter inhibits its transcriptional activity, and define a small hypomethylated region in T cells that correlates with transcription. The IFN-gamma promoter was also hypomethylated in NK cells, but not in B cells or nonhemopoietic tissues. Surprisingly, unlike the promoters of the IL-2 and IL-4 genes, the IFN-gamma promoter was hypomethylated in naive CD4(+) and CD8(+) T cells, and in this form from very early in T cell development. A population of non-B, non-T, non-NK cells containing the hypomethylated promoter was also found in the bone marrow. The hypomethylated state appears stable until peripheral CD4(+) T cells differentiate in response to Ag and APC. After T cell stimulation in vitro under Th2 conditions, but far less so under Th1 conditions, CD4(+) cells display a more methylated IFN-gamma promoter, which may contribute to the lack of expression of IFN-gamma in these preactivated cells. Our experiments support a new model of IFN-gamma chromatin structural changes in murine T cell development that differs from what has been previously published for human T cells.

Induction and regulation of IFNs during viral infections

Interferons (IFN)s are involved in numerous immune interactions during viral infections and contribute to both induction and regulation of innate and adaptive antiviral mechanisms. IFNs play a pivotal rule in the outcome of a viral infection, as demonstrated by the impaired resistance against different viruses in mice deficient for the receptors IFNAR-2 and IFNGR. During viral infections, IFNs are involved in numerous immune interactions as inducers, regulators, and effectors of both innate and adaptive antiviral mechanisms. IFN-alpha/beta is produced rapidly when viral factors, such as envelope glycoproteins, CpG DNA, or dsRNA, interact with cellular pattern-recognition receptors (PRRs), such as mannose receptors, toll-like receptors (TLRs), and cytosolic receptors. These host-virus interactions signal downstream to activate transcription factors needed to achieve expression from IFN-alpha/beta genes. These include IFN regulatory factor-3 (IRF-3), IRF-5, IRF-7, c-Jun/ATF-2, and NF-kappaB. In contrast, IFN-gamma is induced by receptor-mediated stimulation or in response to early produced cytokines, including interleukin-2 (IL-12), IL-18, and IFN-alpha/beta, or by stimulation through T cell receptors (TCRs) or natural killer (NK) cell receptors. IFNs signal through transmembrane receptors, activating mainly Jak-Stat pathways but also other signal transduction pathways. Cytokine and TCR-induced IFN-gamma expression uses distinct signal transduction pathways involving such transcription factors as NFAT, Stats and NF-kappaB. This results in induction and activation of numerous intrinsic antiviral factors, such as RNA-activated protein kinase (PKR), the 2-5A system, Mx proteins, and several apoptotic pathways. In addition, IFNs modulate distinct aspects of both innate and adaptive immunity. Thus, IFN-alpha/beta and IFN-gamma affect activities of macrophages, NK cells, dendritic cells (DC), and T cells by enhancing antigen presentation, cell trafficking, and cell differentiation and expression profiles, ultimately resulting in enhanced antiviral effector functions. This review focuses on the latest findings regarding induction and regulation of IFNs, primarily during the early phase of an antiviral immune response. Both cellular and molecular aspects are discussed from the perspective of host-virus interactions.

T-bet antagonizes mSin3a recruitment and transactivates a fully methylated IFN-gamma promoter via a conserved T-box half-site

Promoter DNA methylation is a major epigenetic mechanism for silencing genes and establishing commitment in cells differentiating from their precursors. The transcription factor T-bet is a key determinant of IFN-gamma gene expression in helper T cells, but the mechanisms by which it achieves this effect are not clear. It is shown here that T-bet binds to a highly conserved T-box half-site in the IFN-gamma promoter, is recruited to the endogenous IFN-gamma promoter in T lymphoid cells, and transactivates gene expression through this sequence in a manner dependent on consensus T-box residues. This conserved promoter site is methylated in a model T cell line, and enforced T-bet expression did not alter its complete methylation. T-bet transactivated the conserved core promoter in transfection assays and collaborated functionally with C/EBPbeta despite methylation of the conserved element. Importantly, enforced T-bet expression led to dissociation of the mSin3a corepressor from the endogenous, chromatinized IFN-gamma promoter without decreasing loading of the methyl-CpG binding protein MeCP2. These data indicate that T-bet can override repressive epigenetic modification by a mechanism in which this master regulator acts through a T-box half-site to enforce the activation of IFN-gamma gene expression in part by decreased loading of a corepressor on methylated DNA.

Long-range histone acetylation of the Ifng gene is an essential feature of T cell differentiation

Histone acetylation of promoters precedes activation of many genes. In addition, long-range histone acetylation patterns can be established over many kilobases of the chromatin of linked families of genes that are under common transcriptional control. It is not known whether establishment of long-range histone acetylation patterns is limited to gene families or is a common feature of many genes. The Ifng gene is not known to be a member of a gene family but exhibits complex strain-, cell lineage-, and stimulus-dependent regulation. For example, stimulation of naive T cells through their antigen receptor does not initiate Ifng gene transcription. However, stimulation of naive T cells through their antigen and IL-12 receptors initiates differentiation programs that yield effector cells with 100-fold greater rates of transcription of the Ifng gene after stimulation through the antigen receptor. Here, we demonstrate that these differentiation programs establish long-range histone hyperacetylation patterns that extend at least 50 kb in both upstream and downstream directions of the Ifng gene. Establishment of these histone acetylation patterns and Ifng gene expression is relatively IL-12-independent in T cells from autoimmune-prone nonobese diabetic mice. These results indicate that gene expression programs that mediate T cell differentiation are regulated by long-range histone acetylation patterns and that defective control of these patterns may contribute to development of autoimmunity.

Dynamic alterations in the conformation of the Ifng gene region during T helper cell differentiation

Gene expression and silencing in eukaryotic systems can be controlled by regulatory elements acting over a distance. Here, we analyze chromatin conformation of the 24-kb region of the Ifng gene during CD4(+) T helper (Th) cell differentiation. We find that chromatin within this region is a highly flexible structure that undergoes dynamic changes during the course of transcriptional activation and silencing of the Ifng gene. Each Th subset displays a common core conformation in this gene region and unique features that distinguish neutral and effector Th1 and Th2 lineages. This chromatin configuration brings distal regions into close proximity to the gene. Th1 cells that produce high levels of IFN-gamma display the most open conformation. In contrast, IFN-gamma silent Th2 cells have a tightly closed conformation. Therefore, we postulate that there is a direct structure-function relationship between the spatial organization of the chromatin around the Ifng gene and its transcriptional potential.

Cutting edge: distal regulatory elements are required to achieve selective expression of IFN-gamma in Th1/Tc1 effector cells

Using a transgenic approach, we analyzed the contribution of introns located within the IFN-gamma gene and distal regulatory regions to IFN-gamma gene expression. Intron 1 and 3 from the IFN-gamma gene displayed strong enhancer activity. This activity appeared to be dependent upon integration into the genome but resulted in a loss of Th1 selectivity. We also found that distal regulatory elements are not required for high level expression of the human IFN-gamma gene, but rather for cell lineage-specific expression. An 8.6-kb human IFN-gamma transgene was sufficient to yield high level expression but a 191-kb IFN-gamma transgene with approximately 90 kb of flanking 5' and 3' sequence was necessary to achieve both high level and Th1 selective expression of human IFN-gamma.