Transcription of the interleukin 4 gene is regulated by multiple promoter elements

Are allergic multimorbidities and IgE polysensitization associated with the persistence or re-occurrence of foetal type 2 signalling? The MeDALL hypothesis

Allergic diseases [asthma, rhinitis and atopic dermatitis (AD)] are complex. They are associated with allergen-specific IgE and nonallergic mechanisms that may coexist in the same patient. In addition, these diseases tend to cluster and patients present concomitant or consecutive diseases (multimorbidity). IgE sensitization should be considered as a quantitative trait. Important clinical and immunological differences exist between mono- and polysensitized subjects. Multimorbidities of allergic diseases share common causal mechanisms that are only partly IgE-mediated. Persistence of allergic diseases over time is associated with multimorbidity and/or IgE polysensitization. The importance of the family history of allergy may decrease with age. This review puts forward the hypothesis that allergic multimorbidities and IgE polysensitization are associated and related to the persistence or re-occurrence of foetal type 2 signalling. Asthma, rhinitis and AD are manifestations of a common systemic immune imbalance (mesodermal origin) with specific patterns of remodelling (ectodermal or endodermal origin). This study proposes a new classification of IgE-mediated allergic diseases that allows the definition of novel phenotypes to (i) better understand genetic and epigenetic mechanisms, (ii) better stratify allergic preschool children for prognosis and (iii) propose novel strategies of treatment and prevention.

Oct-1 is responsible for the C-33T polymorphism effect in the IL-4 promoter

IL-4 is a pleiotropic immunoregulatory cytokine secreted by Th2 subset of CD4(+) Th cells. Several transcription factors (TFs) have been determined with various degrees of certainty to bind the IL-4 promoter and to regulate its expression in human. To investigate the mechanisms responsible for phenotypic effects of the C-33T IL-4 promoter polymorphism, we performed a search of TFs binding to this promoter locus and discriminating the -33C and -33T alleles. In silico searches suggest few factors bind this region. Using an electromobility shift assay we found that Jurkat T cells contained proteins which specifically interacted with oligonucleotide probes, corresponding to the -33 region. Considerable binding differences between C and T alleles were demonstrated using competitive conditions, the proteins bound predominantly with -33C allele. We found that the transcription factor Oct-1 produced the major shifted complex. The binding of Oct-1 was not improved using activated nuclear extracts; however, we observed increases in other shifted complexes upon cell activation. We suppose that Oct-1 occupancy may compete for binding of activator proteins to closely or overlapped binding sites. Our findings suggest that the interplay between Oct-1 and unknown TFs may be responsible for the C-33T polymorphism effects.

Phosphoinositide-dependent kinase 1 targets protein kinase A in a pathway that regulates interleukin 4

CD28 plays a critical role in T cell immune responses. Although the kinase Akt has been shown to act downstream of CD28 in T helper (Th)1 cytokine induction, it does not induce Th2 cytokines such as interleukin 4 (IL-4). We recently reported that phosphoinositide-dependent kinase 1 (PDK1) partially corrects the defect in IL-4 production present in CD28-deficient T cells, suggesting that PDK1 regulates IL-4 independently of Akt. We now describe a signaling pathway in which PDK1 targets IL-4 in the murine Th2 cell line D10. PDK1-mediated activation of this pathway is dependent on protein kinase A (PKA) and the nuclear factor of activated T cells (NFAT) P1 transcriptional element in the IL-4 promoter. PDK1 localizes to the immune synapse in a phosphatidylinositol 3-kinase–dependent manner, partially colocalizes with PKA at the synapse, and physically interacts with PKA. In RNA interference knockdown experiments, PDK1 is necessary for phosphorylation of PKA in T cells, as well as for activation of the IL-4 NFAT P1 element by the T cell receptor (TCR) and CD28. Phosphorylation of the critical PKA threonine residue is stimulated by engagement of TCR/CD28 via a PDK1-dependent mechanism. These findings together define a pathway linking the kinases PDK1 and PKA in the induction of the Th2 cytokine IL-4.

Signals from OX40 regulate nuclear factor of activated T cells c1 and T cell helper 2 lineage commitment

T cell helper type 2 (Th2) differentiation is driven by a source of IL-4 receptor (IL-4R) that mobilizes IL-4R signaling pathways and the transcription factor GATA-3. Naïve CD4 cells can secrete IL-4 independently of IL-4R signals, but how this secretion is regulated is not understood. Here we demonstrate that costimulation through the tumor necrosis factor receptor family molecule OX40, in synergy with CD28, is essential for high levels of nuclear factor of activated T cells c1 to accumulate in the nucleus of a recently activated naïve T cell. This action is not dependent on either IL-4R or IL-2R signals and results in OX40 controlling initial naïve T cell IL-4 transcription. OX40 signals subsequently enhance nuclear GATA-3 accumulation through an IL-4R-dependent action, leading to Th2 differentiation. These data show that, in the absence of an exogenous source of IL-4, OX40 provides a critical synergistic and temporal signal with other noncytokine receptors to modulate nuclear factor of activated T cells c1 and to promote optimal Th2 generation.

A distal region in the interferon-gamma gene is a site of epigenetic remodeling and transcriptional regulation by interleukin-2

Interferon-gamma (IFN-gamma) is a multifunctional cytokine that defines the development of Th1 cells and is critical for host defense against intracellular pathogens. IL-2 is another key immunoregulatory cytokine that is involved in T helper differentiation and is known to induce IFN-gamma expression in natural killer (NK) and T cells. Despite concerted efforts to identify the one or more transcriptional control mechanisms by which IL-2 induces IFN-gamma mRNA expression, no such genomic regulatory regions have been described. We have identified a DNase I hypersensitivity site approximately 3.5-4.0 kb upstream of the transcriptional start site. Using chromatin immunoprecipitation assays we found constitutive histone H3 acetylation in this distal region in primary human NK cells, which is enhanced by IL-2 treatment. This distal region is also preferentially acetylated on histones H3 and H4 in primary Th1 cells as compared with Th2 cells. Within this distal region we found a Stat5-like motif, and in vitro DNA binding assays as well as in vivo chromosomal immunoprecipitation assays showed IL-2-induced binding of both Stat5a and Stat5b to this distal element in the IFNG gene. We examined the function of this Stat5-binding motif by transfecting human peripheral blood mononuclear cells with -3.6 kb of IFNG-luciferase constructs and found that phorbol 12-myristate 13-acetate/ionomycin-induced transcription was augmented by IL-2 treatment. The effect of IL-2 was lost when the Stat5 motif was disrupted. These data led us to conclude that this distal region serves as both a target of chromatin remodeling in the IFNG locus as well as an IL-2-induced transcriptional enhancer that binds Stat5 proteins.

Nuclear factor of activated T cells c is a target of p38 mitogen-activated protein kinase in T cells

p38 mitogen activated protein kinase (MAPK) is essential for T-cell activation. Here we demonstrated that nuclear factor of activated T cells (NFAT) is a direct target of p38 MAPK. Inhibition of p38 MAPK led to selective inactivation of NFAT in T cells. We further linked a strict requirement of p38 MAPK to activation of NFATc. A stimulatory effect of p38 MAPK on at least four other stages of NFATc activation was found. First, the p38 MAPK cascade activated the NFATc promoter and induced the transcription of NFATc mRNA. Second, p38 MAPK mildly increased the mRNA stability of NFATc. Third, p38 MAPK enhanced the translation of NFATc mRNA. Fourth, p38 MAPK promoted the interaction of NFATc with the coactivator CREB-binding protein. In contrast, p38 MAPK moderately enhanced the expulsion of NFATc from the nucleus in T cells. Therefore, p38 MAPK has opposite effects on different stages of NFATc activation. All together, the overall effect of p38 MAPK on NFATc in T cells is clear activation.

Chromatin structure and gene regulation in the immune system

The development of the immune system and the host response to microbial infection rely on the activation and silencing of numerous, differentially expressed genes. Since the mid-1980s, a primary goal has been to identify transcription factors that regulate specific genes and specific immunological processes. More recently, there has been a growing appreciation of the role of chromatin structure in gene regulation. Before most activators of a gene access their binding sites, a transition from a condensed to a decondensed chromatin structure appears to take place. The activation of transcription is then accompanied by the remodeling of specific nucleosomes. Conversely, the acquisition of a more condensed chromatin structure is often associated with gene silencing. Chromatin structure is a particularly significant contributor to gene regulation because it is likely to be a major determinant of cell identity and cell memory. That is, the propagation of decondensed chromatin at specific loci through DNA replication and cell division helps a cell remember which genes are expressed constitutively in that cell type or are poised for expression upon exposure to a stimulus. Here we review recent progress toward understanding the role of chromatin in the immune system. The interleukin-4 gene serves as a primary model for exploring the events involved in the acquisition and heritable maintenance of a decondensed chromatin structure. Studies of the interleukin-12 p40 and interferon-beta genes are then reviewed for insight into the mechanisms by which the remodeling of specific nucleosomes in the vicinity of a promoter can contribute to rapid activation following cell stimulation. Finally, basic principles of gene silencing are discussed.

Interferon regulatory factor 4 (IRF4) interacts with NFATc2 to modulate interleukin 4 gene expression

Proteins of the nuclear factor of activated T cells (NFAT) family of transcription factors are critical for lymphocyte activation in the immune system. In particular, NFATs are important regulators of inducible IL-4 gene expression. Interferon regulatory factor 4 (IRF4) is an immune system-restricted interferon regulatory factor that is required for lymphocyte activation, but its molecular functions in the T lineage remain to be elucidated. We demonstrate that IRF4 potently synergizes with NFATc2 to specifically enhance NFATc2-driven transcriptional activation of the IL-4 promoter. This function is dependent on the physical interaction of IRF4 with NFATc2. IRF4 synergizes with NFATc2 and the IL-4-inducing transcription factor, c-maf, to augment IL-4 promoter activity as well as to elicit significant levels of endogenous IL-4 production. Furthermore, naïve T helper cells from mice lacking IRF4 are compromised severely for the production of IL-4 and other Th2 cytokines. The identification of IRF4 as a partner for NFATc2 in IL-4 gene regulation provides an important molecular function for IRF4 in T helper cell differentiation.

Transcription: tantalizing times for T cells

The T helper lymphocyte is responsible for orchestrating an appropriate immune response to pathogens. To do so, it has evolved into two specialized subsets that direct type 1 and type 2 immunity. Here, we discuss the genetic programs that control lineage commitment of progenitor T helper cells along each of these pathways.

Histone deacetylation inhibits IL4 gene expression in T cells

BACKGROUND

Dysregulated expression of IL-4 has been linked with allergic diseases. IL-4 expression is controlled at the level of gene transcription by the coordinated action of multiple factors that bind regulatory promoter elements. In addition, alterations in chromatin structure are thought to play a role in regulating the expression of cytokines in the T(H)2 gene cluster, although the biochemical basis for these alterations in human T cells is not well understood.

OBJECTIVE

We sought to define the role of histone acetylation in the regulation of IL4 gene expression in human T cells.

METHODS

IL-4 protein production was measured by means of ELISA. IL-4 promoter activity was measured with luciferase-based reporter constructs transiently transfected into Jurkat T cells. The acetylation status of histones associated with the IL4 gene was analyzed with chromatin immunoprecipitation assays.

RESULTS

IL-4 production from activated peripheral blood T cells was enhanced by the histone deacetylase inhibitor trichostatin A. Overexpression of the type 1 histone deacetylases 1, 2, and 3 inhibited transcription driven by the IL-4 promoter in Jurkat T cells, whereas cotransfection of the histone acetyltransferase CREB-binding protein potentiated IL-4 promoter activity. Using chromatin immunoprecipitation assays, we show that nucleosomes in the proximal IL-4 promoter are acetylated on T-cell activation.

CONCLUSION

Our results demonstrate that the acetylation state of histones associated with the IL-4 promoter is a key regulator of IL4 gene expression.

The IL-4 production capability of different strains of naive CD4(+) T cells controls the direction of the T(h) cell response

The qualitative nature of an immune response raised against infectious pathogens depends upon the phenotypes of T(h) cell subsets, which secrete distinct types of cytokines. Genetic background is known to greatly influence the nature of the T(h) cell response. However, the precise nature of this influence still remains unclear. In the present study, we demonstrate that CD62L(+), CD44(low) and CD4(+) naive T cells from BALB/c mice are capable of producing significant amounts of IL-4, while naive T cells from B10.D2 mice exhibit no IL-4 production. The addition of exogenous IL-4 into the B10.D2 induction culture recovered T(h)2 development, thereby indicating that the potential of naive T cells to secrete IL-4 at primary activation is likely to substantially influence development of T(h)2. Regulation of the IL-4 gene in naive T cells differs from that in cells committed towards becoming T(h)2 cells, based on the observation that naive T cells from STAT6-deficient mice having a BALB/c background produce detectable amounts of IL-4. The IL-4 promoter region was found to be equally histone acetylated in both BALB/c and B10.D2 naive T cells by primary TCR activation. Interestingly, the expression levels of transcription factors NF-AT and GATA-3, which regulate promoter activity, differ between BALB/c and B10.D2 cells. These results suggest that the differences in expression level between the two transcriptional factors may affect the potential of naive T cells to secrete IL-4, which may subsequently influence the development of T(h) cell phenotypes.

Yin-Yang 1 activates interleukin-4 gene expression in T cells

Interleukin-4 (IL-4) is a multifunctional cytokine that plays an important role in immune and inflammatory responses. Expression of the IL-4 gene is tightly controlled at the level of gene transcription by both positive and negative regulatory elements in the IL-4 promoter. Several constitutive nuclear factors have been identified that can interact with IL-4 promoter elements in DNA binding assays. Here we report that the zinc-finger protein YY-1 (Yin-Yang 1) can bind to multiple elements within the human IL-4 promoter. Cotransfection of Jurkat T cells with different IL-4 promoter/reporter constructs together with expression vectors encoding antisense, wild-type, or zinc finger-deleted mutant YY-1 suggested that YY-1 enhanced IL-4 promoter activity in a DNA-binding domain-dependent manner. Site-directed mutagenesis revealed that a proximal YY-1-binding site, termed Y0 ((-59)TCATTTT(-53)), was essential for YY-1-driven IL-4 promoter activity. In addition, cotransfected YY-1 enhanced both IL-4 promoter activity and endogenous IL-4 gene expression in nontransformed peripheral blood T cells. Thus, YY-1 positively regulates IL-4 gene expression in lymphocytes.

Deletion of a coordinate regulator of type 2 cytokine expression in mice

Mechanisms that underlie the patterning of cytokine expression in T helper (T(H)) cell subsets remain incompletely defined. An evolutionarily conserved approximately 400-bp noncoding sequence in the intergenic region between the genes Il4 and Il13, designated conserved noncoding sequence 1 (CNS-1), was deleted in mice. The capacity to develop T(H)2 cells was compromised in vitro and in vivo in the absence of CNS-1. Despite the profound effect in T cells, mast cells from CNS-1(-/-) mice maintained their capacity to produce interleukin 4. A T cell-specific element critical for the optimal expression of type 2 cytokines may represent the evolution of a regulatory sequence exploited by adaptive immunity.

CD28 co-stimulation restores T cell responsiveness in NOD mice by overcoming deficiencies in Rac-1/p38 mitogen-activated protein kinase signaling and IL-2 and IL-4 gene transcription

Previously, we reported that T cell hyporesponsiveness induced by TCR ligation is causal to autoimmune diabetes in NOD mice. Neonatal CD28 co-stimulation reverses T cell hyporesponsiveness and protects NOD mice from diabetes by an IL-4-mediated mechanism, indicating that a deficiency in TCR signaling may be overcome by CD28/B7-2 co-stimulation in NOD T cells. To investigate which co-stimulation-induced signaling events mediate this protection, we analyzed the activity of Ras, Rac-1, mitogen-activated protein kinases (MAPK) and several transcription factors in TCR-activated NOD T cells in the presence or absence of CD28 co-stimulation. We show that CD28 co-stimulation restores normal TCR-induced activation of Rac-1 and p38 MAPK in NOD T cells. Deficiencies in TCR-induced nuclear expression of activating protein (AP)-1 binding proteins as well as activation of AP-1 and NF-AT in the IL-2 and IL-4 P1 promoters are also corrected by CD28 co-stimulation. Thus, CD28 co-stimulation reverses NOD T cell hyporesponsiveness by restoring TCR signaling leading to the activation of AP-1 and NF-AT during IL-2 and IL-4 gene transcription. Our findings provide additional evidence that CD28 co-stimulation amplifies signals delivered by the TCR and further explain the mechanism by which CD28 co-stimulation may protect against autoimmune diabetes.

Enhancement of T helper2 response in the absence of interleukin (IL-)6; an inhibition of IL-4-mediated T helper2 cell differentiation by IL-6

Functional roles of interleukin (IL-)6 in T cell response were investigated. Mice deficient in IL-6 and wild mice were immunized with antigens (myelin oligodendrocyte glycoprotein or methylated BSA) and production of IL-4 and interferon (IFN)-gamma by regional lymph nodes was measured. IL-6 deficiency led to an enhancement of IL-4 and an inhibition of IFN-gamma production. Moreover, polyclonal stimulation of spleen T cells from unimmunized IL-6-deficient mice with anti-CD3 plus anti-CD28 antibodies (Abs) demonstrated an enhancement of T helper (Th)(2)responses. The presence of IL-6, however, augmented IL-4 production but it inhibited IFN-gamma expression by spleen T cells in response to polyclonal stimulation and by antigen-primed spleen T cells in response to re-challenge with the antigen. In contrast, the induction of spleen CD4-positive T cells into Th(2)cells in vitro by the anti-CD3 plus IL-4 was completely suppressed by exogenously added IL-6, whereas Th(1)differentiation of T cells by the anti-CD3 plus IL-12 was not inhibited by the presence of IL-6. Thus, these results indicate that IL-6 physiologically could modulate qualitative T cell response and suggest that it augments Th(1)responses partly through its inhibitory capability of IL-4-induced Th(2)differentiation of naive T cells.

Interleukin-15 induces rapid tyrosine phosphorylation of STAT6 and the expression of interleukin-4 in mouse mast cells

Interleukin (IL)-4 plays an important role in the differentiation of naive T helper (Th) cells into Th2. Mast cells can produce a significant amount of IL-4 and have been proposed to play a major role in the induction of Th2 responses. Recently, it has been reported that mast cells have a distinct IL-15 receptor system different from that of T or natural killer cells. In the present study, we demonstrated that IL-15 induced IL-4 production from a mouse mast cell line, MC/9, and bone marrow-derived mast cells. IL-4 mRNA expression was increased by IL-15, suggesting that IL-15 promotes IL-4 expression at the transcriptional level. In these mast cells, signal transducer and activator of transcription (STAT) 6 were rapidly tyrosine-phosphorylated in response to IL-15. In MC/9 cells, the expression of a C-terminally truncated dominant negative form of STAT6 significantly suppressed the IL-4 mRNA up-regulation by IL-15, suggesting that STAT6 activation is essential for the IL-15-mediated IL-4 production. Additionally, tyrosine phosphorylation of Tyk2 was rapidly increased by IL-15 treatment in this cell line. Altogether, our results suggest that IL-15 plays an important role in stimulating early IL-4 production in mast cells that may be responsible for the initiation of Th2 response.

Y-24180, an antagonist of platelet-activating factor, suppresses interleukin 5 production in cultured murine th(2)cells and human peripheral blood mononuclear cells

Interleukin (IL)-5 has been shown to play an essential role in the pathogenesis of airway inflammation. We investigated the effect of 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6, 9-dimethyl-6 H -thieno[3,2- f ][1,2,4]triazolo[4,3- a][1,4]diazepine (Y-24180), an antagonist of platelet-activating factor (PAF), on the production of IL-5 in cultured D10.G4.1 cells, a murine Th(2)clone, and human peripheral blood mononuclear cells (PBMC). As a result, Y-24180 was found to suppress both the mRNA expression of IL-5 and the subsequent secretion of this cytokine in antigen-stimulated D10.G4.1 cells. Y-24180 also suppressed the production of IL-4, another Th(2)type cytokine, at the level of mRNA expression, however, it hardly affected the mRNA expression for IL-6 or IL-10, thus indicating it to have a selective action against IL-5 and IL-4. The suppressive effect of Y-24180 on the secretion of IL-5 by human PBMC was more potent than that of WEB2086, which is another PAF-antagonist. These results suggest that Y-24180 suppresses IL-5 production through a common pathway which also affects the production of IL-4, even though the mechanism remains to be elucidated as to whether the PAF-antagonistic actions are involved or not.

Characterization of P5, a novel NFAT/AP-1 site in the human IL-4 promoter

Interleukin 4 (IL-4) gene expression is controlled at the level of transcription by the complex interactions of multiple factors that bind to a proximal promoter region. Nuclear factor of activated T cells (NFAT) can bind up to five purine-rich sequences in the IL-4 promoter termed the P elements (P0-P4). In this paper, we characterize a novel P element in the upstream region of the human IL-4 promoter that we term P5. P5 shares a core NFAT motif ((-353)GGAAA(-357)) and additional sequence similarity with the other P elements and supported strong interactions between the NFATp DNA-binding domain (DBD) and the AP-1 proteins cFos and cJun in DNA-binding assays. Inducibility of the IL-4 promoter was significantly impaired in a reporter construct in which the P5 element was mutated in the context of the full-length promoter. We conclude that P5 represents a novel IL-4 promoter P element that contributes to IL-4 promoter inducibility.

Vav synergizes with protein kinase C theta to mediate IL-4 gene expression in response to CD28 costimulation in T cells

The secretion of IL-4, which displays many important immunoregulatory functions, is restricted to cells of the Th2 subtype. In this study, we investigated the early signaling events leading to the activation of IL-4 transcription. Vav, the protein kinase C (PKC) isoform theta, and the adaptor protein SLP76 (SH2-domain-containing leukocyte protein of 76 kDa), induced transcription from the IL-4 promoter. Vav and PKC theta synergistically activated human IL-4 promoter transcription and IL-4 mRNA production and were found to be constitutively associated in vivo. CD3/CD28-induced IL-4 transcription was inhibited upon coexpression of dominant negative forms of Vav, the adaptor proteins LAT (linker for activation of T cells) and SLP76, PKC theta, and components of the pathways leading to the activation of c-Jun N-terminal kinase (mitogen-activated protein kinase kinase 7 (MKK7), mixed lineage kinase 3 (MLK3)) and NF-kappa B (I kappa B kinase alpha and I kappa B kinase beta). The Vav/PKC theta-mediated synergistic activation of IL-4 transcription was not inhibited by cyclosporin A. Three independent experimental approaches revealed that Vav/PKC theta-derived signals selectively target the P1 and positive regulatory element (PRE)-I elements contained within the human IL-4 promoter. Vav/PKC theta strongly activated a luciferase reporter construct controlled by trimerized P1 or PRE-I elements and furthermore stimulated DNA binding of nuclear proteins to the P1 and PRE-I elements. Vav/PKC theta-induced transcription from the IL-4 promoter was almost completely abrogated by mutation of either the P1 or the PRE-I element within the entire IL-4 promoter.

Characterization of a novel negative regulatory element in the human interleukin 4 promoter

Interleukin 4 (IL-4) is a multifunctional cytokine that plays an important role in hematopoiesis, tumor cell growth, and cellular immune responses. Expression of the IL-4 gene is tightly controlled at the level of gene transcription, and many positive regulatory cis-elements have been identified in the proximal IL-4 promoter region. Relatively little is known about factors that downregulate IL-4 transcription. We performed a detailed deletional analysis of the proximal human IL-4 promoter and studied reporter gene activity in transiently transfected Jurkat T lymphoblasts. In this report, we characterize a novel negative regulatory element (termed P2 NRE) that is adjacent to a binding site for nuclear factor of activated T cells. Mutation of P2 NRE significantly enhanced the activity of a 175 base pair IL-4 promoter construct in transiently transfected Jurkat T lymphoblasts. Using nuclear extracts from Jurkat cells, we identify a candidate factor (termed Rep-1) that binds uniquely to the P2 NRE in DNA-binding assays. Rep-1 is not related to other factors previously shown to interact with the IL-4 promoter, and by UV cross-linking and SDS-PAGE analysis, we found that it migrates with a molecular mass of approximately 150 kDa. Characterizing the molecular mechanisms responsible for downregulating the IL-4 promoter should enhance our understanding of IL-4-gene dysregulation in disease states.

Binding of octamer factors to a novel 3'-positive regulatory element in the mouse interleukin-5 gene

The development of eosinophilia is regulated by interleukin (IL)-5. The biological specificity of eosinophilia suggests a tight and independent regulation of IL-5 expression. A number of regulatory regions in the 5'-end of the IL-5 gene have been described; many of them are involved in the regulation of other genes, and it is not clear how the specific expression of IL-5 is regulated. In this study, we report the finding of a novel 3'-regulatory element. Data base analysis of a 2-kilobase fragment of the 3'-end of the mouse IL-5 gene revealed the presence of a 40-base pair-long repetitive sequence that consists of four direct repeats of ATGAATGA distributed in a symmetrical manner. This sequence, named mouse downstream regulatory element-1 (mDRE1), was shown to be protected in DNase I footprinting assays in vitro. Electrophoretic mobility shift assays using specific antibodies identified the transcription factors Oct-1 and Oct-2 as responsible for the formation of the specific complexes with mDRE1 and nuclear extracts from both EL4 and primary T-cells. Competition electrophoretic mobility shift assays with oligonucleotides containing different numbers of ATGAATGA repeats showed that Oct-1 and Oct-2 bind to different motifs in the mDRE1 sequence. Deletion of mDRE1 from a 9.5-kilobase IL-5 gene construct significantly decreased the expression of the luciferase reporter gene, suggesting that it plays a positive role in the expression of the IL-5 gene.

Glucocorticoids inhibit calcium- and calcineurin-dependent activation of the human IL-4 promoter

The mechanism by which glucocorticoids (GC) inhibit IL-4 gene expression is currently unknown. In T lymphocytes, IL-4 gene expression is regulated at the level of transcription by increases in intracellular calcium concentration and by the calcium-activated phosphatase calcineurin. In this paper we report that dexamethasone (Dex) inhibits calcium ionophore-induced activation of the human IL-4 promoter in transiently transfected Jurkat T cells. Inhibition of the promoter by Dex is dependent on expression of the GC receptor (GR), because it does not occur in GR-deficient cells. Dex also represses activation of the promoter induced by cotransfecting cells with a constitutively active mutant of calcineurin. Using a series of deletion constructs, we show that the proximal 95 bp of the IL-4 promoter contain a Dex-sensitive regulatory element. This region contains the P1 sequence, a proximal binding site for NF-AT. A calcium-induced but Dex-inhibited nuclear complex containing NF-AT binds to the P1 element in EMSA. Using immunoprecipitation under nondenaturing conditions, we found that the GRalpha isoform coprecipitates with NF-ATc in nuclear extracts of calcium ionophore- and Dex-treated cells. Taken together, our results show that GC inhibit IL-4 gene expression by interfering with NF-AT-dependent transactivation of the proximal human IL-4 promoter.

Role of nuclear factor of activated T cells (NFAT) in the expression of interleukin-5 and other cytokines involved in the regulation of hemopoetic cells

NFAT (nuclear factor of activated T cells) is a transcription factor that plays a role in the regulation of various cytokines, including those involved in the regulation of hemopoetic cells such as granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-4 (IL4), interleukin-3 (IL3), interleukin-13 (IL13) and interleukin-5 (IL5). In this report we provide a summary of the various locations in the promoters of each of these cytokines where NFAT has been shown or suggested to bind, and at which sites NFAT has been shown to be involved in transcriptional regulation. We also provide experimental data to show that the binding of NFAT to the nucleotides GAA at positions -113 to -111 of the human IL5 promoter is associated with functional activity in human T cells.

Potential role of calcineurin for brain ischemia and traumatic injury

Calcineurin belongs to the family of Ca2+/calmodulin-dependent protein phosphatase, protein phosphatase 2B. Calcineurin is the only protein phosphatase which is regulated by a second messenger, Ca2+. Furthermore, calcineurin is highly localized in the central nervous system, especially in those neurons vulnerable to ischemic and traumatic insults. For these reasons, calcineurin is considered to play important roles in neuron-specific functions. Recently, on the basis of the finding that FK506 and cyclosporin A serve as calcineurin-specific inhibitors, this enzyme has become the subject of much study. It is clear that calcineurin is involved in many neuronal (or non-neuronal) functions such as neurotransmitter release, regulation of receptor functions, signal transduction systems, neurite outgrowth, gene expression and neuronal cell death. In this review, we describe the calcineurin functions, functions of the substrates, and the pathogenesis of traumatic and ischemic insults, and we discuss the potential role of calcineurin. There are many similarities in traumatic and ischemic pathogenesis of the brain in which the release of excessive glutamate is followed by an intracellular Ca2+ increase. However, the intracellular cascade which leads to neuronal cell death after the release of excess Ca2+ is unclear. Although calcineurin is thought to be a key toxic enzyme on the basis of studies using immunosuppressants (FK506 or cyclosporin A), many of the functions of the substrates for calcineurin protect against neuronal cell death. We concluded that calcineurin is a bi-directional enzyme for neuronal cell death, having protective and toxic actions, and the balance of the bi-directional effects may be important in ischemic and traumatic pathogenesis.

A novel role for the major histocompatibility complex class II transactivator CIITA in the repression of IL-4 production

Class II transactivator (CIITA) is known as a coactivator for MHC class II gene expression in antigen-presenting cells. Surprisingly, when CIITA-/- CD4 T cells were stimulated in the presence of IL-12, they produced not only IFNgamma but also high levels of IL-4. The IL-4 production is due to the accumulation of IL-4 gene transcripts in Th1 cells. This transcriptional control is observed in T cells differentiating to the Th1 but not Th2 lineage, consistent with induction of expression of the CIITA gene in T cells by IFNgamma. Thus, in addition to its role in transactivation of genes involved in antigen presentation, CIITA plays a critical role during the T cell differentiation by negatively regulating the IL-4 gene transcription.

T Cell Priming Enhances IL-4 Gene Expression by Increasing Nuclear Factor of Activated T Cells

The repetitive activation of T cells (priming) enhances the expression of many cytokines, such as IL-4, but not others, such as IL-2. Molecular mechanisms underlying selective expression of cytokines by T cells remain poorly understood. Here we show that priming of CD4 T cells selectively enhances IL-4 expression relative to IL-2 expression by a transcriptional mechanism involving nuclear factor of activated T cells (NFAT) proteins. As detected by in vivo footprinting, priming markedly increases the activation-dependent engagement of the P0 and P1 NFAT-binding elements of the IL-4 promoter. Moreover, each proximal P element is essential for optimal IL-4 promoter activity. Activated primed CD4 T cells contain more NFAT1 and support greater NFAT-directed transcription than unprimed CD4 T cells, while activator protein 1 binding and activator protein 1-mediated transcription by both cell types is similar. Increased expression of wild-type NFAT1 substantially increases IL-4 promoter activity in unprimed CD4 T cells, suggesting NFAT1 may be limiting for IL-4 gene expression in this cell type. Furthermore, a truncated form of NFAT1 acts as a dominant-negative, reducing IL-4 promoter activity in primed CD4 T cells and confirming the importance of endogenous NFAT to increased IL-4 gene expression by effector T cells. NFAT1 appears to be the major NFAT family member responsible for the initial increased expression of IL-4 by primed CD4 T cells.

Regulation of IL-4 expression by the transcription factor JunB during T helper cell differentiation

The molecular basis for restricted cytokine expression by T helper 1 (Th1) and T helper 2 (Th2) cells is unclear. Previous studies found that P1, an element of the interleukin 4 (IL-4) promoter that binds AP-1, is important for Th2-restricted IL-4 expression. Here we show that JunB, but not the other Jun family members, was selectively induced in Th2 cells and not in Th1 cells during differentiation. JunB has previously been considered to be a negative regulator of transcription. However, we show that JunB binds directly to the P1 site and synergizes with c-Maf to activate an IL-4 luciferase reporter gene. JunB-control of IL-4 expression is mediated by the phosphorylation of JunB at Thr102 and -104 by JNK MAP kinase. The synergy between c-Maf and JunB can be attributed to cooperative DNA binding, which is facilitated by JunB phosphorylation. In transgenic mice, elevated JunB levels caused increased expression of several Th2 cytokines in developing Th1 cells. JunB also upregulated IL-4 expression in response to immunization. Thus, the early increase of JunB protein in Th2 cells can provide the specificity for c-Maf in IL-4 expression during T cell development and directs thereby Th2 differentiation.

Th2-Specific Protein/DNA Interactions at the Proximal Nuclear Factor-AT Site Contribute to the Functional Activity of the Human IL-4 Promoter

IL-4 is a pleiotropic immunoregulatory cytokine secreted by activated Th2, but not Th1, cells. The proximal IL-4 promoter contains MARE, C/EBP, P0, octamer-like, P1, and activating protein-1 elements. The half c-Maf binding site (MARE), P0, and P1 sites were previously shown to be involved in Th2-specific transcriptional activity. Except the MARE and P1 site, the molecular basis for Th2 specificity of the P0 site has not been analyzed. Here, we provide the first detailed analysis of the P0 binding factors and show that in Th2, but not in Th1, cells, NF-AT and proteins of the activating protein-1 family are involved in cooperative binding to the P0 and the adjacent octamer-like site. In the mouse Th2 D10 cells, Oct-1/Oct-2 are also found to participate in formation of the P0-binding complexes. Mutation, deletion, and methylation interference analysis demonstrate that both the P0 and the octamer-like sequence are required for inducible binding. Furthermore, we provide the first report of the functional relevance of each site in the human IL-4 promoter by mutagenesis/transfection analysis and demonstrate that the octamer-like, P0 and P1 sites are important for the biologic function of the IL-4 promoter. The MARE site, although it was shown to be critical for the function of the murine IL-4 promoter, does not appear essential for human IL-4 promoter activity in Jurkat T cells. These findings suggest that besides c-Maf, another Th2-specific factor(s) may be involved in tissue-specific expression of the IL-4 gene.

Transient transfection of primary T helper cells by particle-mediated gene transfer

The study of the molecular basis of normal CD4+ T cell function, such as the control of commitment to the TH1 or TH2 phenotypes has been difficult due to the resistance of these cells to transfection by conventional methods. We used antibodies specific to T cell surface molecules to immobilize these cells and optimized conditions for transiently transfecting them by means of particle-mediated gene transfer. Using this technique, a construct encompassing - 577 to +1 of the IL-4 promoter allowed transcription of a luciferase reporter gene in recently-differentiated TH2 cells stimulated by anti-CD3, consistent with regulation of endogenous IL-4 gene expression.

Impaired interleukin 4 signaling in T helper type 1 cells

Cluster of differentation (CD)4+ T helper cells (Th)1s fail to produce interleukin (IL)-4. Even if restimulated in the presence of IL-4, a condition that induces IL-4-producing capacity in naive CD4+ T cells, Th1s fail to become IL-4 producers. We report that Th1 cells have a major impairment in IL-4 signaling. When compared to both Th2s and naive T cells, they display a striking diminution in phosphorylation of Stat6. They also show reduced phosphorylation of Janus kinase (JAK)-3 and insulin receptor substrate (IRS)-2 when compared to Th2s. Stat6 and JAK-3 are present in equivalent amounts in Th1s and Th2s, but IRS-2 protein levels are much lower in Th1s than in Th2s. Altered sensitivity to IL-4, the major inducer of the Th2 phenotype, may explain the stability of the Th1 state.

Characterization of cis-Regulatory Elements and Nuclear Factors Conferring Th2-Specific Expression of the IL-5 Gene: A Role for a GATA-Binding Protein

Expression of the IL-5 gene is restricted to the Th2 subset of helper T cells. We have previously defined four cis-regulatory elements of the IL-5 promoter responding to PMA and cAMP in EL-4 cells. We now report that the 1.2-kb region of the IL-5 promoter directs expression of the IL-5 gene in a Th2 clone but not a Th1 clone, indicating that transcription from the IL-5 promoter is Th2 specific. For the functioning of the IL-5 promoter in a Th2 clone, IL-5C and IL-5CLE0 were critical. IL-5CLE0 interacted with both constitutive and inducible nuclear factors (designated NFIL-5CLE0), which existed in both Th1 and Th2 clones, whereas IL-5C interacted with a constitutive nuclear factor (designated NFIL-5C), which was found only in Th2 but not in Th1 clones. Th2 specificity of NFIL-5C was also confirmed using in vitro-differentiated Th1 and Th2 cells derived from TCR-transgenic mice. The sequence for NFIL-5C binding bears homology with GATA-binding sites. The NFIL-5C complex was supershifted by an anti-GATA-3 Ab and inhibited by an oligonucleotide containing GATA-binding sites. We showed preferential expression of GATA-3 in Th2 cells. Finally, we demonstrated that in vitro-translated GATA-3 bound to IL-5C and overexpression of GATA-3 augmented stimulation-dependent IL-5 promoter activity in EL-4 cells. Taken together, our results provide evidence that GATA-related factors may be involved in Th2-specific expression of the IL-5 gene.

The TH1/TH2 paradigm in allergy

Recent evidence has been accumulated to suggest that allergen-reactive type 2 helper T cells (Th2) play a triggering role in the activation and/or recruitment of IgE antibody-producing B cells, mast cells and eosinophils, i.e. the cellular triad involved in the allergic inflammation. Interleukin (IL)-4 production by a still unknown cell type (T cell subset, mast cell/basophil?) at the time of antigen presentation to the Th cell is critical for the development of Th2 cells. Other cytokines, such as IL-1 and IL-10, and hormones, such as calcitriol and progesterone, also play a favoring role. In contrast, cytokines such as interferon (IFN-alpha, IFN-gamma, IL-12 and transforming growth factor (TGF)-beta, and hormones, play a negative regulatory role on the development of Th2 cells. However, the mechanisms underlying the preferential activation by environmental allergens of Th2 cells in atopic individuals still remain obscure. Some gene products selectively expressed in Th2 cells or selectively controlling the expression of IL-4 have recently been described. Moreover, cytokines and other gene products that dampen the production of IL-4, as well as the development and/or the function of Th2 cells, have been identified. These findings allow us to suggest that the up-regulation of genes controlling IL-4 expression and/or abnormalities of regulatory mechanisms of Th2 development and/or function may be responsible for Th2 responses against common environmental allergens in atopic people. The new insights in the pathophysiology of T cell responses in atopic diseases provide exciting opportunities for the development of novel immunotherapeutic strategies. They include the induction of nonresponsiveness in allergen-specific Th2 cells by allergen peptides or redirection of allergen-specific Th2 responses by Th1-inducing cytokines, altered peptide ligands, allergens incorporated into recombinant microorganisms or bound to appropriate adjuvants, and plasmid DNA vaccination. In severe atopic patients, the possibility of nonallergen-specific immunotherapeutic regimens designed to target Th2 cells or Th2-dependent effector molecules, such as specific IL-4 transcription factors, IL-4, IL-5 and IgE, may also be suggested.

HgCl2-induced interleukin-4 gene expression in T cells involves a protein kinase C-dependent calcium influx through L-type calcium channels

Mercuric chloride (HgCl2) induces T helper 2 (Th2) autoreactive anti-class II T cells in Brown Norway rats. These cells produce interleukin (IL)-4 and induce a B cell polyclonal activation that is responsible for autoimmune disease. In Brown Norway rats, HgCl2 triggers early IL-4 mRNA expression both in vivo and in vitro by T cells, which may explain why autoreactive anti-class II T cells acquire a Th2 phenotype. The aim of this study was to explore the transduction pathways by which this chemical operates. By using two murine T cell hybridomas that express IL-4 mRNA upon stimulation with HgCl2, we demonstrate that: 1) HgCl2 acts at the transcriptional level without requiring de novo protein synthesis; 2) HgCl2 induces a protein kinase C-dependent Ca2+ influx through L-type calcium channels; 3) calcium/calcineurin-dependent pathway and protein kinase C activation are both implicated in HgCl2-induced IL-4 gene expression; and 4) HgCl2 can activate directly protein kinase C, which might be one of the main intracellular target for HgCl2. These data are in agreement with an effect of HgCl2 which is independent of antigen-specific recognition. It may explain the T cell polyclonal activation in the mercury model and the expansion of pathogenic autoreactive anti-class II Th2 cells in this context.

Identification of a Stat-6-responsive element in the promoter of the human interleukin-4 gene

Interleukin (IL)-4 is an immunomodulatory cytokine produced by a number of cell types including T cells, basophils, and mast cells. This pleiotropic cytokine has a number of immunoregulatory functions; however, the molecular mechanisms controlling the transcription of this gene are not yet completely understood. Several studies have implicated a possible autoregulatory mechanism for its own expression. Here, we have identified a Stat-6-responsive element (Stat-6RE) in the promoter of the human IL-4 gene. Utilizing electrophoretic mobility shift analysis, we have demonstrated the presence of two specific IL-4-responsive DNA-protein complexes in nuclear extracts of both human Th1 and Th2 clones. Phytohemagglutinin-blasted peripheral blood T cells also generated an inducible complex in response to stimulation with IL-4 and the IL-4-like cytokine IL-13. Transient transfection of the murine pre-B cell line BA/F3 stably transfected with the full-length human IL-4 receptor alpha chain demonstrated the ability of multicopy Stat-6RE to initiate transcription from a heterologous promoter upon IL-4 or IL-13 stimulation. These results indicate a possible autocrine mechanism for the regulation of IL-4 gene transcription through the Stat-6RE as well as a possible mechanism for IL-13 regulation of the human IL-4 promoter.

Transcription factors in immune-mediated disease

A large amount of detailed information about the intracellular proteins regulating NF-kappa B activation and the cellular response to NF-kappa B activation has emerged recently. Several small molecules, an antisense oligonucleotide, and gene therapeutic agents that inhibit NF-kappa b activation have been described. Despite this, there are still significant gaps in our understanding of this process and its consequences. In contrast, the characterization of transcription factors selectively regulating cytokine production by CD4+ T cell subsets is at a very early stage. Three interacting proteins have recently been shown to contribute to subset-restricted expression of the IL-4 gene. There are other elements regulating IL-4 gene expression, however, and the relative importance of these recently identified proteins has yet to be determined.

Consistent transient transfection of DNA into non-transformed human and murine T-lymphocytes

The ability to analyze transcriptional regulation in non-transformed T-cells has been hampered by the inability to reproducibly transiently transfect these cells with DNA constructs. We have previously demonstrated that normal human whole mononuclear and CD4 T-cells can be consistently transiently transfected with plasmid DNA. Human cells were most receptive to plasmid DNA uptake between 19.5 and 20 h after prestimulation with a submitogenic dose of the polyclonal T-cell activator, PHA. Here we report an alteration and optimization of this protocol for non-transformed murine splenic T-cells, using concanavalin A instead of PHA as the preactivation stimulus. When coupled with the high sensitivity of luciferase reporter gene constructs, this protocol facilitates the analysis of a variety of T-cell-specific promoters in non-transformed T-cells. In addition, we directly demonstrate that murine T-cells are specifically transiently transfected among a population of whole mononuclear cells by using an expression vector for green fluorescent protein.

T-cell subset-specific expression of the IL-4 gene is regulated by a silencer element and STAT6

During development of CD4+ T lymphocytes in the periphery, differential expression of cytokine genes, such as those of interleukin (IL)-2 and IL-4, occurs in distinct T-cell subsets. IL-4 is a cytokine produced by T-helper 2 (Th2) cells, and the IL-4 receptor (IL-4R)-mediated signaling pathway is thought to be required for commitment to the Th2 phenotype. However, the molecular basis for development of the Th subset-specific production of IL-4 remains unclear. We demonstrate here that the IL-4 promoter is functional in Th1 and B cells which do not normally form IL-4 transcripts as well as in IL-4-producing T cells. Based on studies of the effect of several different upstream and downstream regions of the IL-4 gene on IL-4 promoter activity, a Th1-specific IL-4 silencer element was identified in the 3'-untranslated region. The silencer region contained a consensus sequence for a transcriptional factor that is normally regulated by the IL-4 R signaling pathway, STAT6. Nuclear expression of STAT6 protein, which was shown to bind to the silencer region, was observed in Th2 cells but not in Th1 cells. Deletion of the STAT6-binding site from the silencer region and inhibition of STAT6 function resulted in the appearance of silencing function even in Th2 cells. These results provide evidence that the silencer element, and the binding of STAT6 to this element, play a permissive role in determining the commitment into Th2 phenotype.

Identification of transcription factor binding sites important in the regulation of the human interleukin-5 gene

This study identifies three regions of the human interleukin (IL)-5 promoter involved in binding nuclear factors from activated T cells. DNase I footprinting and mobility shift assays with nuclear proteins from the human T cell clone, SP-B21, demonstrated protein interactions with each of these response elements (REs), located between positions -79 and -45 (RE-I), -123 and -92 (RE-II), and -170 and -130 (RE-III). Two of these regions, RE-II and RE-III, have not previously been described to regulate IL-5 expression in T cells. The RE-II site was shown to be critical for inducible IL-5 promoter activity in transient transfection assays in D10.G4.1 T cells, while the RE-III site functions as a negative regulatory element. The activity of the RE-II site was specifically inhibited by cyclosporin A, and transfection assays with IL-5 constructs containing mutations in the RE-II site showed greatly reduced reporter gene activity. We have defined the sequence involved in stimulation-dependent transcription and have identified constitutive as well as inducible DNA-binding protein complexes that bind to RE-II. Antibodies against at least two members of the nuclear factor of activated T cells (NFAT) family of transcription factors are capable of binding to the IL-5 RE-II complexes, although they can be distinguished from previously identified NFAT-specific complexes by several characteristics.

The transcription factor GATA-3 is necessary and sufficient for Th2 cytokine gene expression in CD4 T cells

CD4 T cells potentiate the inflammatory or humoral immune response through the action of Th1 and Th2 cells, respectively. The molecular basis of the differentiation of these cells from naive T cell precursors is, however, unclear. We found that GATA-3 was selectively expressed in Th2 cells. GATA-3 is expressed at a high level in naive, freshly activated T cells and Th2 lineage cells, but subsides to a minimal level in Th1 lineage cells as naive cells commit to their Th subset. Antisense GATA-3 inhibited the expression of all Th2 cytokine genes in the Th2 clone D10. GATA-3 directly activated an IL-4 promoter-luciferase reporter gene in M12 cells. In transgenic mice, elevated GATA-3 in CD4 T cells caused Th2 cytokine gene expression in developing Th1 cells. Thus, GATA-3 is necessary and sufficient for Th2 cytokine gene expression.

Characterization of constitutive and inducible transcription factors binding to the P2 NF-AT site in the human interleukin-4 promoter

Interleukin-4 (IL-4) is a pleiotropic immunomodulatory cytokine secreted by T helper 2 cells. The IL-4 promoter contains multiple sites with DNA sequences homologous to the IL-2 NF-AT binding site. One of these sites--the P2 site--located between -173 and -150 was previously found to be flanked by two octamer-like motifs. NF-ATp/c and octamer proteins were suggested to bind to this region and to cooperatively activate the promoter activity (Chuvpilo et al., 1993). To precisely analyze the P2-binding factors we used antibodies against NF-ATp, NF-ATc, Fos, Jun, Oct-1 and Oct-2 in EMSA. We show here that nuclear extracts from T-cells form two P2-binding complexes--a PMA/ionomycin-inducible and a constitutive one. The PMA/ionomycin-inducible complex contains NF-ATp/c, Fos and Jun. No octamer binding factors could be detected in either of the two complexes. Analysis of the precise DNA contact points of the two complexes showed that both complexes are formed in the center of the NF-AT consensus site. No DNA contact points could be detected in the octamer-like motif site. Furthermore, purified recombinant POU domains of Oct-1 and Oct-2 failed to bind to the P2 site, suggesting that this site is not an independent octamer-binding site. Therefore, the DNA sequence at -173 to -150 of the IL-4 promoter is a binding site for NF-ATp/c and AP-1. Octamer proteins are unlikely to cooperate with NF-ATp/c at this site.

Nitric oxide increased interleukin-4 expression in T lymphocytes

Nitric oxide (NO) is a regulator of many biological functions including T helper 1 (Th1)/T helper 2 cells balance. It has been demonstrated that NO inhibits the secretion of interleukin-2 (IL-2) and interferon-gamma on Th1 cells. Here we showed that, in addition to the suppression of IL-2 production, NO-generating agents sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) increased the secretion of IL-4 both in Th2 clones and EL4 T cells. The additive effect was dependent on the dose of SNP and SNAP. Augmentation of IL-4 production was detected with 1 microM SNP, and up to threefold increase in IL-4 secretion could be observed with higher concentrations of SNP/SNAP. NO also weakly increased the activation of IL-4 promoter. In contrast, NO markedly inhibited the induction of IL-2 promoter, which could account for most of the reduction in IL-2 production. Analysis of the transcriptional elements on IL-2 and IL-4 promoters revealed a selective inactivation of NF-kappa B and NF-AT. It is suggested that despite the complex feedback network regulating NO production, the enhanced IL-4 expression would lead to the expansion of Th2 cells once NO is generated.

Transcription mediated by NFAT is highly inducible in effector CD4+ T helper 2 (Th2) cells but not in Th1 cells

Transcriptional factors of the NFAT family play an important role in regulating the expression of several cytokine genes during the immune response, such as the genes for interleukin 2 (IL-2) and IL-4, among others. Upon antigen stimulation, precursor CD4+ T helper (pTh) cells proliferate and differentiate into two populations of effector cells (eTh1 and eTh2), each one expressing a specific pattern of cytokines that distinguishes them from their precursors. eTh2 cells are the major source of IL-4, while gamma interferon is produced by eTh1 cells. Here we have used reporter transgenic mice to show that DNA binding and transcriptional activities of NFAT are transiently induced during the differentiation of pTh cells into either eTh1 or eTh2 cells to mediate the expression of IL-2 as a common growth factor in both pathways. However, although NFAT DNA binding is similarly induced in both eTh1 and eTh2 cells upon antigen stimulation, only the NFAT complexes present in eTh2 cells are able to mediate high-level transcription, and relatively little NFAT transcriptional activity was induced in eTh1 cells. In contrast to activated pTh cells, neither eTh1 nor eTh2 cells produced significant IL-2 upon stimulation, but the high levels of NFAT transcriptional activities directly correlate with the IL-4 production induced in response to antigen stimulation in eTh2 cells. These data suggest that activated NFAT is involved in the effector function of eTh2 cells and that the failure of eTh1 cells to produce IL-4 in response to an antigen is due, at least partially, to a failure to induce high-level transcription of the IL-4 gene by NFAT. Regulation of NFAT could be therefore a critical element in the polarization to eTh1 or eTh2.

Interleukin (IL)-6 directs the differentiation of IL-4-producing CD4+ T cells

Interleukin (IL)-4 is the most potent factor that causes naive CD4+ T cells to differentiate to the T helper cell (Th) 2 phenotype, while IL-12 and interferon gamma trigger the differentiation of Th1 cells. However, the source of the initial polarizing IL-4 remains unclear. Here, we show that IL-6, probably secreted by antigen-presenting cells, is able to polarize naive CD4+ T cells to effector Th2 cells by inducing the initial production of IL-4 in CD4+ T cells. These results show that the nature of the cytokine (IL-12 or IL-6), which is produced by antigen-presenting cells in response to a particular pathogen, is a key factor in determining the nature of the immune response.