Regulation of Th2 differentiation and Il4 locus accessibility

The transcription factor PU.1 is required for the development of IL-9-producing T cells and allergic inflammation

CD4⁺ T helper cells acquire effector phenotypes that promote specialized inflammatory responses. We show that the ETS family transcription factor, PU.1 was required for the development of an interleukin 9 (IL-9)-secreting subset of T_H cells. Decreasing PU.1 expression either by conditional deletion in murine T cells or siRNA in human T cells impaired IL-9 production, while ectopic PU.1 expression promoted IL-9 production. Mice with PU.1-deficient T cells developed normal T_H2 responses in vivo, but exhibited attenuated allergic pulmonary inflammation corresponding to decreased Il9 and chemokine expression in peripheral T cells and in lungs as compared to wild-type mice. Together, these data suggest a critical role for PU.1 in generating the T_H9 phenotype and in the development of allergic inflammation.

The transcriptional control of the perforin locus

SUMMARY

Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) use cytotoxic granules containing perforin and granzymes to lyse infected or malignant host cells, thereby providing immunity to intracellular microbes and tumors. Perforin is essential for cytotoxic granule-mediated killing. Perforin expression is regulated transcriptionally and correlates tightly with the development of cells that can exhibit cytotoxic activity. Although a number of genes transcribed by T cells and NK cells have been studied, the cell-specificity of perforin gene expression makes it an ideal model system in which to clarify the transcriptional mechanisms that guide the development and activation of cytotoxic lymphocytes. In this review, we discuss what is known about perforin expression and its regulation, then elaborate on recent studies that utilized chromosome transfer and bacterial artificial chromosome transgenics to define a comprehensive set of cis-regulatory regions that control transcription of the human PRF1 gene in a near-physiologic context. In addition, we compare the human and murine Prf1 loci and discuss how transcription factors known to be important for driving CTL differentiation might also directly regulate the cis-acting domains that control Prf1. Our review emphasizes how studies of PRF1/Prf1 gene transcription can illuminate not only the mechanisms of cytotoxic lymphocyte differentiation but also some basic principles of transcriptional regulation.

Sickness behavior induced by endotoxin can be mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization

Peripheral activation of the immune system by infectious agents triggers the brain-cytokine system causing sickness behaviors which profoundly impact well-being. Dietary fiber is a beneficial foodstuff that, from a gastrointestinal tract perspective, exists in both insoluble and soluble forms. We show that a diet rich in soluble fiber protects mice from endotoxin-induced sickness behavior by polarizing mice Th2 when compared to a diet containing only insoluble fiber. Mice fed soluble fiber became less sick and recovered faster from endotoxin-induced sickness behaviors than mice fed insoluble fiber. In response to intraperitoneal endotoxin, mice fed soluble fiber had up-regulated IL-1RA and reduced IL-1beta and TNF-alpha in the brain as compared to mice fed insoluble fiber. Importantly, mice fed soluble fiber had a basal increase in IL-4 in the ileum and spleen which was absent in MyD88 knockout mice. Con-A stimulated splenocytes from mice fed soluble fiber showed increased IL-4 and IL-5 and decreased IL-2, IL-12 and IFN-gamma when compared to mice fed insoluble fiber. Likewise, endotoxin-stimulated macrophages from mice fed soluble fiber demonstrated decreased IL-1beta, TNF-alpha, IFN-gamma, IL-12 and nitrate and increased IL-1RA, arginase 1 and Ym1 when compared to mice fed insoluble fiber. Finally, the behavioral protection afforded by feeding mice soluble fiber was reduced in IL-4 knockout mice, as was the impact of soluble fiber on Con-A stimulated splenocytes and endotoxin activated macrophages. These data show that a diet rich in soluble fiber protects against endotoxin-induced sickness behavior by polarizing mice Th2 and promoting alternative activation of macrophages.

The transcription factor GATA3 actively represses RUNX3 protein-regulated production of interferon-gamma

The transcription factor GATA3 is crucial for the differentiation of naive CD4(+) T cells into T helper 2 (Th2) cells. Here, we show that deletion of Gata3 allowed the appearance of interferon-gamma (IFN-gamma)-producing cells in the absence of interleukin-12 (IL-12) and IFN-gamma. Such IFN-gamma production was transcription factor T-bet independent. Another T-box-containing transcription factor Eomes, but not T-bet, was induced both in GATA3-deficient CD4(+) T cells differentiated under Th2 cell conditions and in Th2 cells with enforced Runx3 expression, contributing to IFN-gamma production. GATA3 overexpression blocked Runx3-mediated Eomes induction and IFN-gamma production, and GATA3 protein physically interacted with Runx3 protein. Furthermore, we found that Runx3 directly bound to multiple regulatory elements of the Ifng gene and that blocking Runx3 function in either Th1 or GATA3-deficient "Th2" cells results in diminished IFN-gamma production by these cells. Thus, the Runx3-mediated pathway, actively suppressed by GATA3, induces IFN-gamma production in a STAT4- and T-bet-independent manner.

Histone acetylation at the single-cell level: a marker of memory CD8+ T cell differentiation and functionality

Following stimulation, memory T (T(M)) cells rapidly express many effector functions, a hallmark feature that allows them to provide protective immunity. Recent studies suggest that genes involved in this rapid recall response may maintain an open chromatin structure in resting T(M) cells via epigenetic modifications. However, these studies have mostly focused on a few loci, and the techniques used required a large number of cells. We have developed a flow cytometric assay measuring histone modifications in individual murine T cells in combination with lineage-specific markers. In this study, we show that the per-cell level of a marker of open chromatin, diacetylated histone H3 (diAcH3), increases as naive CD8(+) T cells develop into T(M) cells, demonstrating a novel correlation between the differentiation state of a CD8(+) T cell and its abundance of a specific histone modification. Furthermore, our results show that T(M) cells defective in rapid recall ability have less diAcH3 than their fully functional counterparts, indicating that the diAcH3 level of individual T(M) cells is a useful marker for assessing their functionality.

Lck mediates Th2 differentiation through effects on T-bet and GATA-3

The Src family kinase Lck has been shown to be crucial in T cell signaling and development. However, its role in Th effector functions is not well understood. Lck has previously been shown to play a role in the cytokine expression of Th2 cells, but the mechanism by which Lck influences Th2 effector functions is unknown. Using a mouse model, we report that Lck is important in regulating the expression of IL-4 in Th2 skewed cells but is not as necessary for the expression of Th2 cytokines IL-5, IL-10, and IL-13. Furthermore, in the absence of Lck, T-bet and GATA-3 expression is aberrant. Moreover, this atypical expression pattern of T-bet and GATA-3 correlates with increased histone 3 acetylation at the Ifng locus and production of the Th1 cytokine IFN-gamma. We find overexpression of GATA-3 restores IL-4 expression in lck(-/-) Th2 cells; this indicates that the decreased IL-4 expression is due in part to reduced amounts of GATA-3. Taken together, these data imply that Lck mediates Th2 differentiation through effects on T-bet and GATA-3.

Polycomb group gene product Ring1B regulates Th2-driven airway inflammation through the inhibition of Bim-mediated apoptosis of effector Th2 cells in the lung

Polycomb group (PcG) gene products regulate the maintenance of homeobox gene expression in Drosophila and vertebrates. In the immune system, PcG molecules control cell cycle progression of thymocytes, Th2 cell differentiation, and the generation of memory CD4 T cells. In this paper, we extended the study of PcG molecules to the regulation of in vivo Th2 responses, especially allergic airway inflammation, by using conditional Ring1B-deficient mice with a CD4 T cell-specific deletion of the Ring1B gene (Ring1B(-/-) mice). In Ring1B(-/-) mice, CD4 T cell development appeared to be normal, whereas the differentiation of Th2 cells but not Th1 cells was moderately impaired. In an Ag-induced Th2-driven allergic airway inflammation model, eosinophilic inflammation was attenuated in Ring1B(-/-) mice. Interestingly, Ring1B(-/-) effector Th2 cells were highly susceptible to apoptosis in comparison with wild-type effector Th2 cells in vivo and in vitro. The in vitro experiments revealed that the expression of Bim was increased at both the transcriptional and protein levels in Ring1B(-/-) effector Th2 cells, and the enhanced apoptosis in Ring1B(-/-) Th2 cells was rescued by the knockdown of Bim but not the other proapoptotic genes, such as Perp, Noxa, or Bax. The enhanced apoptosis detected in the transferred Ring1B(-/-) Th2 cells in the lung of the recipient mice was also rescued by knockdown of Bim. Therefore, these results indicate that Ring1B plays an important role in Th2-driven allergic airway inflammation through the control of Bim-dependent apoptosis of effector Th2 cells in vivo.

NF45 and NF90 regulate HS4-dependent interleukin-13 transcription in T cells

Expression of the cytokine interleukin-13 (IL13) is critical for Th2 immune responses and Th2-mediated allergic diseases. Activation of human IL13 expression involves chromatin remodeling and formation of multiple DNase I-hypersensitive sites throughout the locus. Among these, HS4 is detected in the distal IL13 promoter in both naive and polarized CD4(+) T cells. We show herein that HS4 acts as a position-independent, orientation-dependent positive regulator of IL13 proximal promoter activity in transiently transfected, activated human CD4(+) Jurkat T cells and primary murine Th2 cells. The 3'-half of HS4 (HS4-3') was responsible for IL13 up-regulation and bound nuclear factor (NF) 90 and NF45, as demonstrated by DNA affinity chromatography coupled with tandem mass spectrometry, chromatin immunoprecipitation, and gel shift analysis. Notably, the CTGTT NF45/NF90-binding motif within HS4-3' was critical for HS4-dependent up-regulation of IL13 expression. Moreover, transfection of HS4-IL13 reporter vectors into primary, in vitro differentiated Th2 cells from wild-type, NF45(+/-), or NF90(+/-) mice showed that HS4 activity was exquisitely dependent on the levels of endogenous NF45 (and to a lesser degree NF90), because HS4-dependent IL13 expression was virtually abrogated in NF45(+/-) cells and reduced in NF90(+/-) cells. Collectively, our results identify NF45 and NF90 as novel regulators of HS4-dependent human IL13 transcription in response to T cell activation.

Epigenomics of T cell activation, differentiation, and memory

Activation of T cells is an essential step in the immunological response to infection. Although activation of naïve T cells results in proliferation and slow differentiation into cytokine-producing effector cells, antigen engagement with memory cells leads to cytokine production immediately. Even though the cell surface signaling events are similar in both the cases, the outcome is different, suggesting that distinct regulatory mechanisms may exist downstream of the activation signals. Recent advances in the understanding of global epigenetic patterns in T cells have resulted in the appreciation of the role of epigenetic mechanisms in processes such as activation and differentiation. In this review we discuss recent data suggesting that naïve T cell activation, differentiation, and lineage commitment result in epigenetic changes and a fine balance between different histone modifications is required. On the other hand, memory T cells are poised and do not require epigenetic changes for short-term activation.

What determines Th2 differentiation, in vitro and in vivo?

We have known since 1991 how to induce naive CD4 T cells to differentiate in vitro into Th2 cells and, over the ensuing years, a comprehensive picture of the molecules involved in this important process has emerged. GATA3 and STAT5 are both essential for in vitro differentiation, stimulating naive cells through a process involving induction, which is T-cell receptor (TCR) dependent but interleukin (IL)-4 independent, and commitment, which is IL-4 dependent. Th2 differentiation in vivo appears more complex. GATA3 and probably STAT5 are required in vivo but, at least for certain helminth infections, the IL-4/IL-4Ra/STAT6 pathway is dispensable. The role of thymic stromal lymphopoietin and of low TCR signal strength and the participation of basophils in establishing a Th2-baising in vivo environment have achieved considerable attention. Here I discuss the major players in Th2 differentiation particularly as they may exert their effects in vivo.

NIP45 controls the magnitude of the type 2 T helper cell response

Nuclear factor of activated T cell (NFAT) transcription factors are key regulators of gene transcription within immune cells. The NFAT-interacting protein, (NIP45), augments NFAT-driven IL-4 expression by a mechanism that relies on arginine methylation. To establish the function of NIP45 in vivo, we generated mice with a targeted deletion of the gene encoding this cofactor. NIP45-deficient T helper cells displayed profound defects in the expression of NFAT-regulated cytokine genes, including IL-4. Whereas NIP45 deficiency does not interfere with T helper cell NFAT activation or lineage-specific transcription-factor expression, NIP45 acts as an enhancer for the assembly of protein arginine methyltransferase 1 and the protein arginine methyltransferase 1-linked histone 4 arginine 3 methylation with the IL-4 promoter. Our study reveals an essential role for NIP45 in promoting robust cytokine expression in vivo, which is required for the efficient handling of parasites. We propose that NIP45 acts as a molecular rheostat serving to amplify the type-2 immune response.

Genetic variation in the IL7RA/IL7 pathway increases multiple sclerosis susceptibility

Multiple sclerosis (MS) is characterized as an autoimmune demyelinating disease. Numerous family studies have confirmed a strong genetic component underlying its etiology. After several decades of frustrating research, the advent and application of affordable genotyping of dense SNP maps in large data sets has ushered in a new era in which rapid progress is being made in our understanding of the genetics underlying many complex traits. For MS, one of the first discoveries to emerge in this new era was the association with rs6897932[T244I] in the interleukin-7 receptor alpha chain (IL7RA) gene (Gregory et al. in Nat Genet 39(9):1083-1091, 2007; International Multiple Sclerosis Genetics Consortium in N Engl J Med 357(9):851-862, 2007; Lundmark in Nat Genet 39(9):1108-1113, 2007), a discovery that was accompanied by functional data that suggest this variant is likely to be causative rather than a surrogate proxy (Gregory et al. in Nat Genet 39(9):1083-1091, 2007). We hypothesized that variations in other genes functionally related to IL7RA might also influence MS. We investigated this hypothesis by examining genes in the extended biological pathway related to IL7RA to identify novel associations. We identified 73 genes with putative functional relationships to IL7RA and subsequently genotyped 7,865 SNPs in and around these genes using an Illumina Infinium BeadChip assay. Using 2,961 case-control data sets, two of the gene regions examined, IL7 and SOCS1, had significantly associated single-nucleotide polymorphisms (SNPs) that further replicated in an independent case-control data set (4,831 samples) with joint p values as high as 8.29 x 10(-6) and 3.48 x 10(-7), respectively, exceeding the threshold for experiment-wise significance. Our results also implicate two additional novel gene regions that are likely to be associated with MS: PRKCE with p values reaching 3.47 x 10(-4), and BCL2 with p values reaching 4.32 x 10(-4). The TYK2 gene, which also emerged in our analysis, has recently been associated with MS (Ban et al. 2009). These results help to further delineate the genetic architecture of MS and validate our pathway approach as an effective method to identify novel associations in a complex disease.

Epigenetics in atherosclerosis and inflammation

Atherosclerosis is a multifactorial disease with a severe burden on western society. Recent insights into the pathogenesis of atherosclerosis underscore the importance of chronic inflammation in both the initiation and progression of vascular remodelling. Expression of immunoregulatory molecules by vascular wall components within the atherosclerotic lesions is accordingly thought to contribute to the ongoing inflammatory process. Besides gene regulatory proteins (transcription factors), epigenetic mechanisms also play an essential and fundamental role in the transcriptional control of gene expression. These epigenetic mechanisms change the accessibility of chromatin by DNA methylation and histone modifications. Epigenetic modulators are thus critically involved in the regulation of vascular, immune and tissue-specific gene expression within the atherosclerotic lesion. Importantly, epigenetic processes are reversible and may provide an excellent therapeutic target. The concept of epigenetic regulation is gradually being recognized as an important factor in the pathogenesis of atherosclerosis. Recent research provides an essential link between inflammation and reprogramming of the epigenome. In this review we therefore discuss the basis of epigenetic regulation – and the contribution thereof in the regulation of inflammatory processes in general and during atherosclerosis in particular. Moreover we highlight potential therapeutic interventions based on epigenetic mechanisms.

NFAT pulls the strings during CD4+ T helper cell effector functions

The Ca(2+) dependent transcription factor family known as nuclear factor of activated T cells (NFAT) has been shown to be important in T-cell immune responses. Because NFAT proteins have a weak DNA-binding capacity, they cooperate with other transcription factors at composite sites within the promoters of target genes. Recently, NFAT was shown to also be important for the induction of specific genetic programs that guide the differentiation and effector or regulatory activities of CD4(+) T helper subsets via the transcriptional regulation of their lineage-specific transcription factors, specifically T-bet (Th1), Gata3 (Th2), RORgammat (Th17), and Foxp3 (iTregs). In addition, the NFAT family governs the transcription of several signature cytokines, including their cytokine receptors. Subsequently, the integration of these complex intracellular signal transduction cascades is considered to critically determine the crosstalk between the T-cell receptor and receptors that are activated by both the adaptive and innate immune systems to determine pathways of T helper cell differentiation and function. Here, we carefully review the critical role of the established transcriptional partners and functional outcomes of these NFAT interactions in regard to the effector responses of these clinically relevant CD4(+) T helper subsets.

Global regulator SATB1 recruits beta-catenin and regulates T(H)2 differentiation in Wnt-dependent manner

Chromatin organizer SATB1 and Wnt transducer β-catenin form a complex and regulate expression of GATA3 and T_H2 cytokines in Wnt-dependent manner and orchestrate T_H2 lineage commitment.

In vertebrates, the conserved Wnt signalling cascade promotes the stabilization and nuclear accumulation of β-catenin, which then associates with the lymphoid enhancer factor/T cell factor proteins (LEF/TCFs) to activate target genes. Wnt/β -catenin signalling is essential for T cell development and differentiation. Here we show that special AT-rich binding protein 1 (SATB1), the T lineage-enriched chromatin organizer and global regulator, interacts with β-catenin and recruits it to SATB1's genomic binding sites. Gene expression profiling revealed that the genes repressed by SATB1 are upregulated upon Wnt signalling. Competition between SATB1 and TCF affects the transcription of TCF-regulated genes upon β-catenin signalling. GATA-3 is a T helper type 2 (T_H2) specific transcription factor that regulates production of T_H2 cytokines and functions as T_H2 lineage determinant. SATB1 positively regulated GATA-3 and siRNA-mediated knockdown of SATB1 downregulated GATA-3 expression in differentiating human CD4⁺ T cells, suggesting that SATB1 influences T_H2 lineage commitment by reprogramming gene expression. In the presence of Dickkopf 1 (Dkk1), an inhibitor of Wnt signalling, GATA-3 is downregulated and the expression of signature T_H2 cytokines such as IL-4, IL-10, and IL-13 is reduced, indicating that Wnt signalling is essential for T_H2 differentiation. Knockdown of β-catenin also produced similar results, confirming the role of Wnt/β-catenin signalling in T_H2 differentiation. Furthermore, chromatin immunoprecipitation analysis revealed that SATB1 recruits β-catenin and p300 acetyltransferase on GATA-3 promoter in differentiating T_H2 cells in a Wnt-dependent manner. SATB1 coordinates T_H2 lineage commitment by reprogramming gene expression. The SATB1:β-catenin complex activates a number of SATB1 regulated genes, and hence this study has potential to find novel Wnt responsive genes. These results demonstrate that SATB1 orchestrates T_H2 lineage commitment by mediating Wnt/β-catenin signalling. This report identifies a new global transcription factor involved in β-catenin signalling that may play a major role in dictating the functional outcomes of this signalling pathway during development, differentiation, and tumorigenesis.

In vertebrates the canonical Wnt signalling culminates in β-catenin moving into the nucleus where it activates transcription of target genes. Wnt/β-catenin signalling is essential for the thymic maturation and differentiation of naïve T cells. Here we show that SATB1, a T cell lineage-enriched chromatin organizer and global regulator, binds to β-catenin and recruits it to SATB1's genomic binding sites so that genes formerly repressed by SATB1 are upregulated by Wnt signalling. Some of the genes known to be regulated by SATB1 (such as genes encoding cytokines and the transcription factor GATA3) are required for differentiation of Th2 cells, an important subset of helper T cells. Specifically we show that siRNA-mediated knockdown of SATB1 downregulated GATA-3 expression in differentiating human CD4⁺ T cells. Inhibiting Wnt signalling led to downregulation of GATA-3 and of signature T_H2 cytokines such as IL-4, IL-10, and IL-13. Knockdown of β-catenin also produced similar results, thus together these data confirm the role of Wnt/β-catenin signalling in T_H2 differentiation. Our data demonstrate that SATB1 orchestrates T_H2 lineage commitment by modulating Wnt/β-catenin signalling.

Interleukin-2 and inflammation induce distinct transcriptional programs that promote the differentiation of effector cytolytic T cells

Interleukin(IL)-2 and inflammation regulate effector and memory cytolytic T-lymphocyte (CTL) generation during infection. We demonstrate a complex interplay between IL-2 and inflammatory signals during CTL differentiation. IL-2 stimulation induced the transcription factor eomesodermin (Eomes), upregulated perforin (Prf1) transcription, and repressed re-expression of memory CTL markers Bcl6 and IL-7Ralpha. Binding of Eomes and STAT5 to Prf1 cis-regulatory regions correlated with transcriptional initiation (increased recruitment of RNA polymerase II to the Prf1 promoter). Inflammation (CpG, IL-12) enhanced expression of IL-2Ralpha and the transcription factor T-bet, but countered late Eomes and perforin induction while preventing IL-7Ralpha repression by IL-2. After infection of mice with lymphocytic choriomeningitis virus, IL-2Ralpha-deficient effector CD8(+) T cells expressed more Bcl6 but less perforin and granzyme B, formed fewer KLRG-1(+) and T-bet-expressing CTL, and killed poorly. Thus, inflammation influences both effector and memory CTL differentiation, whereas persistent IL-2 stimulation promotes effector at the expense of memory CTL development.

Memory Th1/Th2 cell generation controlled by Schnurri-2

Schnurri (Shn) is a large zinc-finger containingprotein, which plays a critical role in cell growth, signal transduction and lymphocyte development. There are three orthologues (Shn-1, Shn-2 and Shn-3) in vertebrates. In Shn-2-deficient mice, the activation of NF-kappaB in CD4 T cells is upregulated and their ability to differentiate into Th2 cells is enhanced in part through the increased expression of GATA3. Shn-2 is found to compete with p50 NF-kappaB for binding to a consensus NF-kappaB motif and inhibit the NF-kappaB-driven promoter activity. In addition, Th2-driven allergic airway inflammation was enhanced in Shn-2-deficient mice. Therefore, Shn-2 appears to negatively control the differentiation of Th2 cells and Th2 responses through the repression of NF-kappaB function. Memory Th1/Th2 cells are not properly generated from Shn-2-deficient effector Th1/Th2 cells. The expression levels of CD69 and the number ofapoptotic cells are selectively increased in Shn-2-deficient Thl/Th2 cells when they are transferred into syngeneic host animals, in which memoryh Th1/Th2 cells are generated within a month. In addition, an increased susceptibility to apoptotic cell death is also observed in vitro accompanied with the increased expression of FasL, one of the NF-kappaB-dependent genes. Th2 effector cells overexpressing the p65 subunit of NF-kappaB demonstrate a decreased cell survival particularly in the lymph node. These results indicate that Shn-2-mediated repression of NF-kappaB is required for cell survival and the successful generation of memory Th1/Th2 cells. This may point to the possibility that after antigen clearance the recovery of the quiescent state in effector Th cells is required for the generation of memory Th cells. A repressor molecule Shn-2 plays an important role in this process.

The many face-lifts of CD4 T helper cells

Recent advances in stem cell research have redefined previous concepts of hematopoietic hierarchy, lineage commitment, and cell fate. The immune system is comprised of several well-defined cell lineages of which many exhibit high levels of plasticity or capacity in changing their phenotype. The CD4 T helper cells provide a peculiar example of apparently defined cell subsets, at times described as lineages, but also highly sensitive to tissue environmental cues that may change their fate. The classical Th1/Th2 CD4 T cell differentiation referred to for many years as the main CD4 T cell fate dichotomy and the later additions of CD4 helper T cell variants, such as T helper 17 (Th17) and induced regulatory T cells (iTreg), have added complexity but also doubts on the accuracy of defining CD4 T cell subsets as fixed T cell lineages.

IRF4 and its regulators: evolving insights into the pathogenesis of inflammatory arthritis?

Accumulating evidence from murine and human studies supports a key role for interleukin-17 (IL-17) and IL-21 in the pathogenesis of inflammatory arthritis. The pathways and molecular mechanisms that underlie the production of IL-17 and IL-21 are being rapidly elucidated. This review focuses on interferon regulatory factor 4 (IRF4), a member of the IRF family of transcription factors, which has emerged as a crucial controller of both IL-17 and IL-21 production. We first outline the complex role of IRF4 in the function of CD4(+) T cells and then discuss recent studies from our laboratory that have revealed a surprising role for components of Rho GTPase-mediated pathways in controlling the activity of IRF4. A better understanding of these novel pathways will hopefully provide new insights into mechanisms responsible for the development of inflammatory arthritis and potentially guide the design of novel therapeutic approaches.

Heterogeneity and plasticity of T helper cells

CD4 T helper (Th) cells play critical roles in adaptive immune responses. They recruit and activate other immune cells including B cells, CD8 T cells, macrophages, mast cells, neutrophils, eosinophils and basophils. Based on their functions, their pattern of cytokine secretion and their expression of specific transcription factors, Th cells, differentiated from naïve CD4 T cells, are classified into four major lineages, Th1, Th2, Th17 and T regulatory (Treg) cells, although other Th lineages may exist. Subsets of the same lineage may express different effector cytokines, reside at different locations or give rise to cells with different fates, whereas cells from different lineages may secrete common cytokines, such as IL-2, IL-9 and IL-10, resulting in massive heterogeneity of the Th cell population. In addition, the pattern of cytokine secretion may switch from that of one lineage toward another under certain circumstances, suggesting that Th cells are plastic. Tregs are also more heterogeneous and plastic than were originally thought. In this review, we summarize recent reports on heterogeneity and plasticity of Th cells, and discuss potential mechanisms and implications of such features that Th cells display.

Differentiation of effector CD4 T cell populations (*)

CD4 T cells play critical roles in mediating adaptive immunity to a variety of pathogens. They are also involved in autoimmunity, asthma, and allergic responses as well as in tumor immunity. During TCR activation in a particular cytokine milieu, naive CD4 T cells may differentiate into one of several lineages of T helper (Th) cells, including Th1, Th2, Th17, and iTreg, as defined by their pattern of cytokine production and function. In this review, we summarize the discovery, functions, and relationships among Th cells; the cytokine and signaling requirements for their development; the networks of transcription factors involved in their differentiation; the epigenetic regulation of their key cytokines and transcription factors; and human diseases involving defective CD4 T cell differentiation.

Myeloid STAT3 inhibits T cell-mediated hepatitis by regulating T helper 1 cytokine and interleukin-17 production

BACKGROUND & AIMS

T cell-mediated hepatitis is a leading cause of acute liver failure; there is no effective treatment, and the mechanisms underlying its pathogenesis are obscure. The aim of this study was to investigate the immune cell-signaling pathways involved-specifically the role of signal transducer and activator of transcription 3 (STAT3)-in T cell-mediated hepatitis in mice.

METHODS

T cell-mediated hepatitis was induced in mice by injection of concanavalin A (Con A). Mice with myeloid cell-specific and T-cell-specific deletion of STAT3 were generated.

RESULTS

STAT3 was activated in myeloid and T cells following Con A injection. Deletion of STAT3 specifically from myeloid cells exacerbated T-cell hepatitis and induced STAT1-dependent production of a T helper cell (Th)1 cytokine (interferon [IFN]-gamma) and to a lesser extent of Th17 cytokines (interleukin [IL]-17 and IL-22) in a STAT1-independent manner. In contrast, deletion of STAT3 in T cells reduced T cell-mediated hepatitis and IL-17 production. Furthermore, deletion of IFN-gamma completely abolished Con A-induced T-cell hepatitis, whereas deletion of IL-17 slightly but significantly reduced such injury. In vitro experiments indicated that IL-17 promoted liver inflammation but inhibited hepatocyte apoptosis.

CONCLUSIONS

Myeloid STAT3 activation inhibits T cell-mediated hepatitis via suppression of a Th1 cytokine (IFN-gamma) in a STAT1-dependent manner, whereas STAT3 activation in T cells promotes T-cell hepatitis to a lesser extent, via induction of IL-17. Therefore, activation of STAT3 in myeloid cells could be a novel therapeutic strategy for patients with T-cell hepatitis.

GATA3 in development and cancer differentiation: cells GATA have it!

There is increasing evidence that the numerous mechanisms that regulate cell differentiation during normal development are also involved in tumorigenesis. In breast cancer, differentiation markers expressed by the primary tumor are routinely profiled to guide clinical decisions. Indeed, numerous studies have shown that the differentiation profile correlates with the metastatic potential of tumors. The transcription factor GATA3 has emerged recently as a strong predictor of clinical outcome in human luminal breast cancer. In the mammary gland, GATA3 is required for luminal epithelial cell differentiation and commitment, and its expression is progressively lost during luminal breast cancer progression as cancer cells acquire a stem cell-like phenotype. Importantly, expression of GATA3 in GATA3-negative, undifferentiated breast carcinoma cells is sufficient to induce tumor differentiation and inhibits tumor dissemination in a mouse model. These findings demonstrate the exquisite ability of a differentiation factor to affect malignant properties, and raise the possibility that GATA3 or its downstream genes could be used in treating luminal breast cancer. This review highlights our recent understanding of GATA3 in both normal mammary development and tumor differentiation.

Ikaros silences T-bet expression and interferon-gamma production during T helper 2 differentiation

CD4+ T cells can be instructed by nonantigen-specific signals to differentiate into functionally distinct lineages with mutually exclusive patterns of cytokine production. The molecular events that drive interferon-gamma (IFN gamma) production during Th1 development are well understood, but mechanisms that silence this cytokine during Th2 polarization are not clear. In this study, we find that the tbx21 gene encoding the Th1 master regulator T-bet is a direct target of the transcriptional repressor Ikaros. In Th2 cells, which do not express T-bet, strong Ikaros binding could be detected at the endogenous tbx21 promoter, whereas this gene was not occupied by Ikaros in T-bet-expressing Th1 cells. Inhibition of Ikaros DNA binding activity during Th2 polarization resulted in loss of Ikaros promoter occupancy, increased T-bet expression, and inappropriate T-bet-dependent production of IFN gamma. Ikaros was also required for epigenetic imprinting of the ifn gamma locus during Th2 polarization, and loss of Ikaros function in vivo led to an inappropriate Th1 response to the parasite Shistosoma mansoni. These studies demonstrate that Ikaros, a factor with an established role in lymphocyte development, also regulates the development of peripheral T helper responses.

A continuous T-bet expression is required to silence the interleukin-4-producing potential in T helper type 1 cells

To develop into committed T helper type 1 (Th1) cells, naive CD4(+) T cells not only need to acquire the capacity to produce interferon-gamma (IFN-gamma), but they also need to gain the ability to silence their interleukin-4 (IL-4) -producing potential. How Th1 cells silence their Th2 cytokine-producing potential is an important yet unresolved issue in Th1 immunity. We found that a lack of IL-4 stimulation was not sufficient to silence the IL-4-producing potential in activated CD4(+) T cells and that Th1-promoting factor was required. Although it has been shown that T-bet is a crucial factor in suppressing Il4 gene expression, it is unclear whether a continuous presence of T-bet is required to silence the Il4 gene in Th1 cells. To address this problem, we used an inducible form of T-bet - a T-bet-oestrogen receptor fusion molecule (T-bet-ER). We found that the activation of T-bet during primary or secondary culture was sufficient to silence IL-4-producing potential. On the other hand, the inactivation of T-bet after naïve CD4(+) T cells had differentiated into Th1 cells resulted in derepression of Il4 gene transcription. Additionally, we found that T-bet is required to maintain Ifng expression. Our data demonstrate that the continuous expression of T-bet is required for Th1 cells to silence their IL-4-producing potential.

Immunomodulatory effect of 5-azacytidine (5-azaC): potential role in the transplantation setting

Cytokine genes are targets of multiple epigenetic mechanisms in T lymphocytes. 5-azacytidine (5-azaC) is a nucleoside-based DNA methyltransferase inhibitor that induces demethylation and gene reactivation. In the current study, we analyzed the effect of 5-azaC in T-cell function and observed that 5-azaC inhibits T-cell proliferation and activation, blocking cell cycle in the G(0) to G(1) phase and decreasing the production of proinflammatory cytokines such as tumor necrosis factor-alpha and interferon-gamma. This effect was not attributable to a proapoptotic effect of the drug but to the down-regulation of genes involved in T-cell cycle progression and activation such as CCNG2, MTCP1, CD58, and ADK and up-regulation of genes that induce cell-growth arrest, such as DCUN1D2, U2AF2, GADD45B, or p53. A longer exposure to the drug leads to demethylation of FOXP3 promoter, overexpression of FOXP3, and expansion of regulatory T cells. Finally, the administration of 5-azaC after transplantation prevented the development of graft-versus-host disease, leading to a significant increase in survival in a fully mismatched bone marrow transplantation mouse model. In conclusion, the current study shows the effect of 5-azaC in T lymphocytes and illustrates its role in the allogeneic transplantation setting as an immunomodulatory drug, describing new pathways that must be explored to prevent graft-versus-host disease.

Neonatal immunity: faulty T-helpers and the shortcomings of dendritic cells

Immunity in the newborn is characterized by minimal T helper (Th)1 function but an excess of Th2 activity. Since Th1 lymphocytes are important to counter microbes and Th2 cells favor allergies, the newborn faces susceptibility to microbial infections and allergic reactions. Delayed maturation of certain dendritic cells leads to limited interleukin (IL)-12 production during the neonatal period. The Th2 cytokine locus of neonatal CD4(+) T cells is poised epigenetically for rapid and robust production of IL-4 and IL-13. Together, these circumstances lead to efficient differentiation of Th2 cells and the expression of an IL-4Ralpha/IL-13Ralpha1 heteroreceptor on Th1 cells. Upon re-challenge, Th2 cells rapidly produce IL-4 which utilizes the heteroreceptor to drive apoptosis of Th1 cells, thus yielding the Th2 bias of neonatal immunity.

CCCTC-binding factor and the transcription factor T-bet orchestrate T helper 1 cell-specific structure and function at the interferon-gamma locus

How cell type-specific differences in chromatin conformation are achieved and their contribution to gene expression are incompletely understood. Here we identify a cryptic upstream orchestrator of interferon-gamma (IFNG) transcription, which is embedded within the human IL26 gene, compromised of a single CCCTC-binding factor (CTCF) binding site and retained in all mammals, even surviving near-complete evolutionary deletion of the equivalent gene encoding IL-26 in rodents. CTCF and cohesins occupy this element in vivo in a cell type-nonspecific manner. This element is juxtaposed to two other sites located within the first intron and downstream of Ifng, where CTCF, cohesins, and the transcription factor T-bet bind in a T helper 1 (Th1) cell-specific manner. These interactions, close proximity of other elements within the locus to each other and to the gene encoding interferon-gamma, and robust murine Ifng expression are dependent on CTCF and T-bet. The results demonstrate that cooperation between architectural (CTCF) and transcriptional enhancing (T-bet) factors and the elements to which they bind is required for proper Th1 cell-specific expression of Ifng.

Th9 and allergic disease

Helper CD4(+) T-cell subsets have improved our understanding of adaptive immunity in humans and in animal models of disease. These include T helper type 1 (Th1), Th2 and the interleukin-17 (IL-17) -producing population 'Th17'. Th2 cells have been described as orchestrating the immune response in allergic disease based on studies with patient samples and animal models. The cytokine IL-9 has largely been regarded as a Th2 cytokine that makes multifocal contributions to allergic disease. Recent data suggest that under certain conditions relevant to chronic disease (IL-4 and transforming growth factor-beta), a distinct population of IL-9-producing 'Th9' helper T cells can exist. The contribution of Th9 cells in allergic disease is currently unknown, and this review will propose a model for how these cells may regulate chronic allergic inflammation.

Intestinal effector T cells in health and disease

Crohn's disease and ulcerative colitis are the two major forms of chronic relapsing inflammatory disorders of the human intestines collectively referred to as inflammatory bowel disease (IBD). Though a complex set of autoinflammatory disorders that can be precipitated by diverse genetic and environmental factors, a feature that appears common to IBD pathogenesis is a dysregulated effector T cell response to the commensal microbiota. Due to the heightened effector T cell activity in IBD, developmental and functional pathways that give rise to these cells are potential targets for therapeutic intervention. In this review, we highlight recent advances in our understanding of effector T cell biology in the context of intestinal immune regulation and speculate on their potential clinical significance.

An allergy-associated polymorphism in a novel regulatory element enhances IL13 expression

IL-13 is a central effector of Th2-mediated allergic inflammation and is critical for the induction of IgE synthesis. Common IL13 variants are associated with allergy phenotypes in populations of distinct ethnic background. We recently demonstrated that IL13 expression by human CD4+ T cells is paralleled by extensive IL13 locus remodeling, which results in the appearance of multiple DNase I hypersensitive sites. Among these, HS4 in the distal promoter is constitutive in both naïve and polarized Th1 and Th2 cells, and spans a common single nucleotide polymorphism, IL13-1512A>C (rs1881457), strongly associated with total serum IgE levels. We recently characterized HS4 as a novel cis-acting element that upregulates IL13 transcription in activated human and murine T cells. Here we show that IL13-1512A>C is a functional polymorphism that significantly enhances HS4-dependent IL13 expression by creating a binding site for the transcription factor Oct-1. Of note, endogenous Oct-1 was preferentially recruited to the IL13-1512C risk allele in primary CD4+ T cells from IL13-1512A>C heterozygous subjects. Moreover, the IL13-1512C allele was overexpressed in transfected Th2 cells from Oct1(+/+) mice, but not from Oct1(+/-) mice, demonstrating that increased activity was exquisitely dependent on physiologic levels of Oct-1. Our results illustrate how a functional variant in a regulatory element enhances transcription of an allergy-associated gene, thereby modulating disease susceptibility.

KLF2 transcription-factor deficiency in T cells results in unrestrained cytokine production and upregulation of bystander chemokine receptors

The transcription factor KLF2 regulates T cell trafficking by promoting expression of the lipid-binding receptor S1P(1) and the selectin CD62L. Recently, it was proposed that KLF2 also represses the expression of chemokine receptors. We confirmed the upregulation of the chemokine receptor CXCR3 on KLF2-deficient T cells. However, we showed that this was a cell-nonautonomous effect, as revealed by CXCR3 upregulation on wild-type bystander cells in mixed bone-marrow chimeras with KLF2-deficient cells. Furthermore, KLF2-deficient T cells overproduced IL-4, leading to the upregulation of CXCR3 through an IL-4-receptor- and eomesodermin-dependent pathway. Consistent with the increased IL-4 production, we found high concentrations of serum IgE in mice with T cell-specific KLF2 deficiency. Our findings support a model where KLF2 regulates T cell trafficking by direct regulation of S1P(1) and CD62L and restrains spontaneous cytokine production in naive T cells.

T cell factor 1 initiates the T helper type 2 fate by inducing the transcription factor GATA-3 and repressing interferon-gamma

The differentiation of activated CD4(+) T cells into the T helper type 1 (T(H)1) or T(H)2 fate is regulated by cytokines and the transcription factors T-bet and GATA-3. Whereas interleukin 12 (IL-12) produced by antigen-presenting cells initiates the T(H)1 fate, signals that initiate the T(H)2 fate are not completely characterized. Here we show that early GATA-3 expression, required for T(H)2 differentiation, was induced by T cell factor 1 (TCF-1) and its cofactor beta-catenin, mainly from the proximal Gata3 promoter upstream of exon 1b. This activity was induced after T cell antigen receptor (TCR) stimulation and was independent of IL-4 receptor signaling through the transcription factor STAT6. Furthermore, TCF-1 blocked T(H)1 fate by negatively regulating interferon-gamma (IFN-gamma) expression independently of beta-catenin. Thus, TCF-1 initiates T(H)2 differentiation of activated CD4(+) T cells by promoting GATA-3 expression and suppressing IFN-gamma expression.

Mechanisms and functions for the duration of intercellular contacts made by lymphocytes

Communication across intercellular contacts is central to establishing appropriate innate and adaptive immune responses. Recent imaging of lymphocyte interactions suggests that a complex orchestration of cell-cell contact times is a key correlate to establishing appropriate immune responses. Here I review the molecular and cellular processes that influence the duration of intercellular contacts, including integrin activation and dynamic changes in membrane morphology. I discuss how these processes can be regulated, for example, by the balance of activating and inhibitory receptor signals, and how they can establish the appropriate outcome for individual cell-cell interactions.

Understanding autoimmune disease: new targets for drug discovery

A more complete understanding of the mechanisms that drive autoimmune diseases has begun to be translated into therapeutic options with significant clinical consequences. A clear example of this is the introduction of biological therapies, which have provided new therapeutic avenues, as well as validated the mediators (TNFalpha, IL-6), mechanisms (T cell costimulation, leukocyte migration), and cellular players (T and B lymphocytes) of the disease process itself. New discoveries into the role of Th17 and regulatory T cells and the epigenetic regulation of cytokine expression may offer novel intervention strategies to satisfy the unmet medical needs that still exist in these diseases.

Fibronectin is a TH1-specific molecule in human subjects

BACKGROUND

T(H)1 cell-mediated immunity is essential for host defense against a variety of intracellular pathogens, such as mycobacteria, salmonella, and Leishmania species. A major T(H)1-mediated effector mechanism involves the IFN-gamma-induced killing of the pathogen by infected macrophages.

OBJECTIVES

The range of known T(H)1-specific effector molecules is limited, especially in human subjects. We sought to identify novel effector molecules that might be involved in T(H)1-mediated pathogen clearance.

METHODS

We performed microarray-based analysis of human T(H)1 and T(H)2 cells to identify T(H)1-specific molecules. These analyses identified the extracellular matrix molecule fibronectin as a highly expressed T(H)1-specific molecule. We examined the expression of fibronectin in a variety of human cell types by using real-time RT-PCR, ELISA, and Western blotting. We also studied the role of fibronectin in modulating monocyte phenotype using in vitro culture.

RESULTS

We show that human T(H)1 cells constitutively express and secrete fibronectin after in vitro differentiation from naive precursors. Furthermore, we demonstrate that ex vivo human T(H)1 cells selectively express fibronectin when compared with T(H)2 cells. The predominant isoform of fibronectin expressed by T(H)1 cells contains additional domains of the protein responsible for alpha4beta1 integrin binding and activation of Toll-like receptor 4. We show that treatment of monocytes with T(H)1 cell-derived fibronectin induces expression of the proinflammatory cytokine IL-6 while inhibiting IL-10 expression.

CONCLUSIONS

Because fibronectin also plays a major role in the attachment and opsonization of numerous intracellular pathogens, we propose that it might be a critical molecule produced by T(H)1 cells involved in pathogen eradication.

Epigenetic regulation of the alternatively activated macrophage phenotype

Alternatively activated (M2) macrophages play critical roles in diverse chronic diseases, including parasite infections, cancer, and allergic responses. However, little is known about the acquisition and maintenance of their phenotype. We report that M2-macrophage marker genes are epigenetically regulated by reciprocal changes in histone H3 lysine-4 (H3K4) and histone H3 lysine-27 (H3K27) methylation; and the latter methylation marks are removed by the H3K27 demethylase Jumonji domain containing 3 (Jmjd3). We found that continuous interleukin-4 (IL-4) treatment leads to decreased H3K27 methylation, at the promoter of M2 marker genes, and a concomitant increase in Jmjd3 expression. Furthermore, we demonstrate that IL-4-dependent Jmjd3 expression is mediated by STAT6, a major transcription factor of IL-4-mediated signaling. After IL-4 stimulation, activated STAT6 is increased and binds to consensus sites at the Jmjd3 promoter. Increased Jmjd3 contributes to the decrease of H3K27 dimethylation and trimethylation (H3K27me2/3) marks as well as the transcriptional activation of specific M2 marker genes. The decrease in H3K27me2/3 and increase in Jmjd3 recruitment were confirmed by in vivo studies using a Schistosoma mansoni egg-challenged mouse model, a well-studied system known to support an M2 phenotype. Collectively, these data indicate that chromatin remodeling is mechanistically important in the acquisition of the M2-macrophage phenotype.

Dll1 haploinsufficiency in adult mice leads to a complex phenotype affecting metabolic and immunological processes

BACKGROUND

The Notch signaling pathway is an evolutionary conserved signal transduction pathway involved in embryonic patterning and regulation of cell fates during development and self-renewal. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, involving as well other signal transduction pathways, and implicated in distinct human diseases. Delta-like 1 (Dll1) is one of the known ligands of the Notch receptors. The role of the Notch ligands is less well understood. Loss-of-function of Dll1 leads to embryonic lethality, but reduction of Delta-like 1 protein levels has not been studied in adult stage.

METHODOLOGY/PRINCIPAL FINDINGS

Here we present the haploinsufficient phenotype of Dll1 and a missense mutant Dll1 allele (Dll1(C413Y)). Haploinsufficiency leads to a complex phenotype with several biological processes altered. These alterations reveal the importance of Dll1 mainly in metabolism, energy balance and in immunology. The animals are smaller, lighter, with altered fat to lean ratio and have increased blood pressure and a slight bradycardia. The animals have reduced cholesterol and triglyceride levels in blood. At the immunological level a subtle phenotype is observed due to the effect and fine-tuning of the signaling network at the different levels of differentiation, proliferation and function of lymphocytes. Moreover, the importance of the proteolytic regulation of the Notch signaling network emphasized.

CONCLUSIONS/SIGNIFICANCE

In conclusion, slight alterations in one player of Notch signaling alter the entire organism, emphasizing the fine-tuning character of this pathway in a high number of processes.

Genomic antagonism between retinoic acid and estrogen signaling in breast cancer

Retinoic acid (RA) triggers antiproliferative effects in tumor cells, and therefore RA and its synthetic analogs have great potential as anticarcinogenic agents. Retinoic acid receptors (RARs) mediate RA effects by directly regulating gene expression. To define the genetic network regulated by RARs in breast cancer, we identified RAR genomic targets using chromatin immunoprecipitation and expression analysis. We found that RAR binding throughout the genome is highly coincident with estrogen receptor alpha (ERalpha) binding, resulting in a widespread crosstalk of RA and estrogen signaling to antagonistically regulate breast cancer-associated genes. ERalpha- and RAR-binding sites appear to be coevolved on a large scale throughout the human genome, often resulting in competitive binding activity at nearby or overlapping cis-regulatory elements. The highly coordinated intersection between these two critical nuclear hormone receptor signaling pathways provides a global mechanism for balancing gene expression output via local regulatory interactions dispersed throughout the genome.

Regulation of DNA demethylation during maturation of CD4+ naive T cells by the conserved noncoding sequence 1

Demethylation of transcriptional regulatory elements and gene coding regions is an important step in the epigenetic regulation of gene expression. Several noncoding conserved regions are required for the efficient transcription of cytokine genes. In this paper, we show that the deletion of one such sequence, conserved noncoding sequence 1 (CNS-1), interferes with the efficient demethylation of Th2 cytokine genes but has little effect on histone modifications in the area. Th2 cells derived from CD4 single-positive (SP) mature thymocytes exhibit more rapid demethylation of CNS-1 and Th2-specific cytokine genes and produce more Th2 cytokines than do Th2 cells derived from CD4-positive peripheral naive T cells. De-repression of the Th1 cytokine IFN-gamma was also detected in Th2-primed CD4 SP thymocytes but not in naive T cells. Our results indicate that susceptibility to demethylation determines the efficiency and kinetics of cytokine gene transcription. The extrathymic maturation step undergone by naive T cells suppresses robust and rapid cytokine expression, whereas mature CD4 SP thymocytes maintain a rapid and less-specific cytokine expression profile. Finally, we detected the methyl cytosine binding protein MBD2 at CNS-1 in mature thymocytes, suggesting that this protein may regulate the demethylation of this region.

SUMO conjugation contributes to immune deviation in nonobese diabetic mice by suppressing c-Maf transactivation of IL-4

It is not clear why the development of protective Th2 cells is poor in type 1 diabetes (T1D). c-Maf transactivates the IL-4 gene promoting Th2 cell development; therefore, abnormalities in c-Maf may contribute to reduced IL-4 production by CD4 cells from nonobese diabetic (NOD) mice. In this study we demonstrate that despite normal expression, c-Maf binds poorly to the IL-4 promoter (IL-4p) in NOD CD4 cells. Immunoblotting demonstrates that c-Maf can be modified at lysine 33 by SUMO-1 (small ubiquitin-like modifier 1). Sumoylation is facilitated by direct interaction with the E2-conjugating enzyme Ubc9 and increases following T cell stimulation. In transfected cells, sumoylation decreases c-Maf transactivation of IL-4p-driven luciferase reporter activity, reduces c-Maf binding to the IL-4p in chromatin immunoprecipitation assays, and enhances c-Maf localization into promyelocytic leukemia nuclear bodies. Sumoylation of c-Maf is increased in NOD CD4 cells as compared with CD4 cells from diabetes-resistant B10.D2 mice, suggesting that increased c-Maf sumoylation contributes to immune deviation in T1D by reducing c-Maf access to and transactivation of the IL-4 gene.

Chromatin structure and DNA methylation of the IL-4 gene in human T(H)2 cells

Human T(H)2 cell differentiation results in the selective demethylation of several specific CpG dinucleotides in the IL-4 and IL-13 genes, which are expressed in activated T(H)2, but not T(H)1, cells. This demethylation is accompanied by the appearance of six DNase I hypersensitive sites within 1.4 kb at the 5'-end of the IL-4 gene. Micrococcal nuclease (MNase) digestion revealed that in both T(H)1 and T(H)2 cells nine nucleosomes with a repeat length of 201 bp are identically positioned around the 5'-end of the IL-4 gene. However, only in T(H)2 cells are six out of the eight intervening linkers exposed to DNase I. This suggests that a major perturbation of the higher-order chromatin structure occurs above the level of the nucleosome in vivo. It is observed in cells that are poised for expression but which are not actively expressing the gene (i.e. resting T(H)2 cells). Notably, all the demethylated CpGs in T(H)2 cells are found in DNA that is accessible to DNase I. This may suggest that the opening of the chromatin structure allows binding of specific trans-acting factors that prevent de novo methylation.