Regulation of the Il4 gene is independently controlled by proximal and distal 3' enhancers in mast cells and basophils

Diverse innate stimuli activate basophils through pathways involving Syk and IκB kinases

Mature basophils play critical inflammatory roles during helminthic, autoimmune, and allergic diseases through their secretion of histamine and the type 2 cytokines interleukin 4 (IL-4) and IL-13. Basophils are activated typically by allergen-mediated IgE cross-linking but also by endogenous "innate" factors. The aim of this study was to identify the innate stimuli (cytokines, chemokines, growth factors, hormones, neuropeptides, metabolites, and bacterial products) and signaling pathways inducing primary basophil activation. Basophils from naïve mice or helminth-infected mice were cultured with up to 96 distinct stimuli and their influence on basophil survival, activation, degranulation, and IL-4 or IL-13 expression were investigated. Activated basophils show a heterogeneous phenotype and segregate into distinct subsets expressing IL-4, IL-13, activation, or degranulation markers. We find that several innate stimuli including epithelial derived inflammatory cytokines (IL-33, IL-18, TSLP, and GM-CSF), growth factors (IL-3, IL-7, TGFβ, and VEGF), eicosanoids, metabolites, TLR ligands, and type I IFN exert significant direct effects on basophils. Basophil activation mediated by distinct upstream signaling pathways is always sensitive to Syk and IκB kinases-specific inhibitors but not necessarily to NFAT, STAT5, adenylate cyclase, or c-fos/AP-1 inhibitors. Thus, basophils are activated by very diverse mediators, but their activation seem controlled by a core checkpoint involving Syk and IκB kinases.

Characterization of Cytokines and Proliferation Marker Ki67 in Cleft Affected Lip Tissue

Background and objectives: Cleft lip palate takes the second place among all anomalies. The complex appearance of cytokines and proliferation markers has still not been clarified despite their possible crucial role in cleft tissue. Therefore, the aim of work was the detection of appearance of pro- and anti-inflammatory cytokines and proliferation marker Ki67, and their inter-correlations in cleft affected lip (CAL). Materials and Methods: The lip material was obtained from 16 children aged before primary dentition during plastic surgery. Control was obtained from 7 non-CAL oral tissue. Tissues were stained for IL-1, IL-4, IL-6, IL-8, IL-10 and Ki67 immunohistochemically. Non-parametric statistic, Mann-Whitney and Spearman's coefficient were used. Results: All cytokines positive cells were observed more into the epithelium. Statistically significant difference was seen between epithelial IL-1, IL-10, IL-8 and Ki67 positive cells and IL-10-, IL-4-containing connective tissue cells in comparison to the control. Strong positive correlation was detected in CAL epithelium between IL-10 and IL-8, IL-10 and IL-4, IL-10 and IL-1, IL-1 and IL-8, IL-1 and IL-4, IL-4 and IL-8, IL-8 and Ki67, IL-10 and Ki67, but moderate-in connective tissue between IL-1 and IL-10, IL-1 and IL-4. Conclusion: The CAL epithelium is the main source for the interleukins. Rich similar expression of IL-1 and IL-10 suggests the balance between pro-and anti-inflammatory tissue response on basis of dysregulated tissue homeostasis (increase of IL-8). The correlations between the different ILs -1, -4, -8, -10 in CAL epithelium seem to indicate the self-protection compensatory mechanism for intensification of local inflammatory-immune response without involvement of IL-6. The correlations between Ki67 and cytokines indicate the involvement of IL-8 and IL-10 in stimulation of cellular proliferation. IL-4 and IL-10 expression from CAL connective tissue simultaneously to IL-1, IL-4 and IL-10 inter-correlations there suggests the intensification of local immune response regulated probably by main pro-inflammatory cytokine-IL-1.

Stabilization of cytokine mRNAs in iNKT cells requires the serine-threonine kinase IRE1alpha

Activated invariant natural killer T (iNKT) cells rapidly produce large amounts of cytokines, but how cytokine mRNAs are induced, stabilized and mobilized following iNKT activation is still unclear. Here we show that an endoplasmic reticulum stress sensor, inositol-requiring enzyme 1α (IRE1α), links key cellular processes required for iNKT cell effector functions in specific iNKT subsets, in which TCR-dependent activation of IRE1α is associated with downstream activation of p38 MAPK and the stabilization of preformed cytokine mRNAs. Importantly, genetic deletion of IRE1α in iNKT cells reduces cytokine production and protects mice from oxazolone colitis. We therefore propose that an IRE1α-dependent signaling cascade couples constitutive cytokine mRNA expression to the rapid induction of cytokine secretion and effector functions in activated iNKT cells.

Invariant natural killer T (iNKT) cells rapidly enhance cytokine secretion and effector function following activation, but the underlying mechanism is still unclear. Here the authors show that an endoplasmic reticulum stress sensor, inositol-requiring enzyme 1α, activates the p38 kinase to stabilize cytokine mRNA for enhanced iNKT functions.

Innate and adaptive type 2 immunity in lung allergic inflammation

Allergic inflammation is a type 2 immune disorder classically characterized by high levels of immunoglobulin E (IgE) and the development of Th2 cells. Asthma is a pulmonary allergic inflammatory disease resulting in bronchial hyper-reactivity. Atopic asthma is defined by IgE antibody-mediated mast cell degranulation, while in non-atopic asthma there is no allergen-specific IgE and more involvement of innate immune cells, such as basophils, group 2 innate lymphoid cells (ILC2), and eosinophils. Recently, protease allergens were shown to cause asthmatic responses in the absence of Th2 cells, suggesting that an innate cell network (IL-33/TSLP-basophil-ILC2-IL-5/IL-13 axis) can facilitate the sensitization phase of type 2 inflammatory responses. Recent evidence also indicates that in the chronic phase, these innate immune cells directly or indirectly contribute to the adaptive Th2 cell responses. In this review, we discuss the role of Th2 cytokines (IL-4 and IL-13) and innate immune cells (mast cells, basophils, ILC2s, and dendritic cells) in the cross-talk between innate and adaptive inflammatory responses.

Age-Related Changes in DNA Methylation Associated with Shifting Th1/Th2 Balance

This study was conducted in order to explore age-related changes in the production of Th1 and Th2 cytokines and determine the corresponding status of DNA methylation. The plasma IL-4 and IFN-γ levels and expression of Th-related cytokines and transcription factors in CD4+ splenocytes were observed in mice at different weeks of age. The DNA methylation levels of IL-4 and IFN-γ promoters and the related regulatory regions in CD4+ splenocytes of mice at different weeks of age were analyzed. The DNA methyltransferase (DNMT) levels in CD4+ splenocytes of mice were analyzed. Changes in plasma IL-4 and IFN-γ levels after 5-AZA injection were evaluated. Plasma IL-4 and IL-4 expression in CD4+ splenocytes declined with increasing age, while the IFN-γ expression levels increased. Th-related transcription factors showed no differences in mice at different weeks of age. The DNMT1 and DNMT3b mRNA expression did not show significant changes in CD4+ splenocytes, whereas the DNMT3a mRNA expression increased with age. DNA methylation in the IL-4 promoter was increased, while DNA methylation in the IFN-γ promoter was decreased. The methylation of RSH7, CNS-1, and HSV increased significantly with age. Age-related changes in DNA methylation may be associated with the shift in Th1/Th2 balance.

Regulation of IL-4 Expression in Immunity and Diseases

IL-4 was first identified as a T cell-derived growth factor for B cells. Studies over the past several decades have markedly expanded our understanding of its cellular sources and function. In addition to T cells, IL-4 is produced by innate lymphocytes, such as NTK cells, and myeloid cells, such as basophils and mast cells. It is a signature cytokine of type 2 immune response but also has a nonimmune function. Its expression is tightly regulated at several levels, including signaling pathways, transcription factors, epigenetic modifications, microRNA, and long noncoding RNA. This chapter will review in detail the molecular mechanism regulating the cell type-specific expression of IL-4 in physiological and pathological type 2 immune responses.

Notch signaling enhances FcεRI-mediated cytokine production by mast cells through direct and indirect mechanisms

Th2-type cytokines and TNF-α secreted by activated mast cells upon cross-linking of FcεRI contribute to the development and maintenance of Th2 immunity to parasites and allergens. We have previously shown that cytokine secretion by mouse mast cells is enhanced by signaling through Notch receptors. In this study, we investigated the molecular mechanisms by which Notch signaling enhances mast cell cytokine production induced by FcεRI cross-linking. FcεRI-mediated production of cytokines, particularly IL-4, was significantly enhanced in mouse bone marrow-derived mast cells by priming with Notch ligands. Western blot analysis showed that Notch signaling augmented and prolonged FcεRI-mediated phosphorylation of MAPKs, mainly JNK and p38 MAPK, through suppression of the expression of SHIP-1, a master negative regulator of FcεRI signaling, resulting in the enhanced production of multiple cytokines. The enhancing effect of Notch ligand priming on multiple cytokine production was abolished by knockdown of Notch2, but not Notch1, and FcεRI-mediated production of multiple cytokines was enhanced by retroviral transduction with the intracellular domain of Notch2. However, only IL-4 production was enhanced by both Notch1 and Notch2. The enhancing effect of Notch signaling on IL-4 production was lost in bone marrow-derived mast cells from mice lacking conserved noncoding sequence 2, which is located at the distal 3' element of the Il4 gene locus and contains Notch effector RBP-J binding sites. These results indicate that Notch2 signaling indirectly enhances the FcεRI-mediated production of multiple cytokines, and both Notch1 and Notch2 signaling directly enhances IL-4 production through the noncoding sequence 2 enhancer of the Il4 gene.

Approaches for analyzing the roles of mast cells and their proteases in vivo

The roles of mast cells in health and disease remain incompletely understood. While the evidence that mast cells are critical effector cells in IgE-dependent anaphylaxis and other acute IgE-mediated allergic reactions seems unassailable, studies employing various mice deficient in mast cells or mast cell-associated proteases have yielded divergent conclusions about the roles of mast cells or their proteases in certain other immunological responses. Such "controversial" results call into question the relative utility of various older versus newer approaches to ascertain the roles of mast cells and mast cell proteases in vivo. This review discusses how both older and more recent mouse models have been used to investigate the functions of mast cells and their proteases in health and disease. We particularly focus on settings in which divergent conclusions about the importance of mast cells and their proteases have been supported by studies that employed different models of mast cell or mast cell protease deficiency. We think that two major conclusions can be drawn from such findings: (1) no matter which models of mast cell or mast cell protease deficiency one employs, the conclusions drawn from the experiments always should take into account the potential limitations of the models (particularly abnormalities affecting cell types other than mast cells) and (2) even when analyzing a biological response using a single model of mast cell or mast cell protease deficiency, details of experimental design are critical in efforts to define those conditions under which important contributions of mast cells or their proteases can be identified.

Cytokine signaling in the differentiation of innate effector cells

Innate effector cells, including innate effector cells of myeloid and lymphoid lineages, are crucial components of various types of immune responses. Bone marrow progenitors differentiate into many subsets of innate effector cells after receiving instructional signals often provided by cytokines. Signal transducer and activator of transcription (STATs) have been shown to be essential in the differentiation of various types of innate effector cells. In this review, we focus specifically on the differentiation of innate effector cells, particularly the role of cytokine signaling in the differentiation of innate effector cells.

Lymphocyte-based model systems for allergy research: a historic overview

During the last decades, a multitude of studies applying distinct in vitro and in vivo model systems have contributed greatly to our better understanding of the initiation and regulation of inflammatory processes leading to allergic diseases. Over the years, it has become evident that among lymphocytes, not only IgE-producing B cells and allergy-orchestrating CD4(+) helper cells but also cytotoxic CD8(+) T cells, γδ-T cells and innate lymphoid cells, as well as regulatory lymphocytes, might critically shape the immune response towards usually innocuous allergens. In this review, we provide a historic overview of pioneering work leading to the establishment of important lymphocyte-based model systems for allergy research. Moreover, we contrast the original findings with our currently more refined knowledge to appreciate the actual validity of the respective models and to reassess the conclusions obtained from them. Conflicting studies and interpretations are identified and discussed. The tables are intended to provide an easy overview of the field not only for scientists newly entering the field but also for the broader readership interested in updating their knowledge. Along those lines, herein we discuss in vitro and in vivo approaches to the investigation of lymphocyte effector cell activation, polarization and regulation, and describe depletion and adoptive transfer models along with gene knockout and transgenic (tg) methodologies. In addition, novel attempts to establish humanized T cell antigen receptor tg mouse models for allergy research are described and discussed.

Basophils regulate the recruitment of eosinophils in a murine model of irritant contact dermatitis

BACKGROUND

Although eosinophils have been detected in several human skin diseases in the vicinity of basophils, how eosinophils infiltrate the skin and the role of eosinophils in the development of skin inflammation have yet to be examined.

OBJECTIVE

Using murine irritant contact dermatitis (ICD) as a model, we sought to clarify the roles of eosinophils in ICD and the underlying mechanism of eosinophil infiltration of the skin.

METHODS

We induced croton oil-induced ICD in eosinophil-deficient ΔdblGATA mice with or without a reactive oxygen species (ROS) inhibitor. We performed cocultivation with fibroblasts and bone marrow-derived basophils and evaluated eosinophil migration using a chemotaxis assay.

RESULTS

ICD responses were significantly attenuated in the absence of eosinophils or by treatment with the ROS inhibitor. ROS was produced abundantly by eosinophils, and both basophils and eosinophils were detected in human and murine ICD skin lesions. In coculture experiments, basophils attracted eosinophils, especially in the presence of fibroblasts. Moreover, basophils produced IL-4 and TNF-α in contact with fibroblasts and promoted the expression of eotaxin/CCL11 from fibroblasts in vitro.

CONCLUSION

Eosinophils mediated the development of murine ICD, possibly through ROS production. Recruitment of eosinophils into the skin was induced by basophils in cooperation with fibroblasts. Our findings introduce the novel concept that basophils promote the recruitment of eosinophils into the skin through fibroblasts in the development of skin inflammation.

Basophils are required for the induction of Th2 immunity to haptens and peptide antigens

The relative contributions of basophils and dendritic cells in Th2 skewing to foreign antigen exposure remain unclear. Here we report the ability of basophils to induce Th2 polarization upon epicutaneous sensitization with different antigens using basophil conditionally depleted Bas TRECK transgenic mice. Basophils are responsible for Th2 skewing to haptens and peptide antigens, but not protein antigens in vivo. Consistent with this, basophils cannot take up or process ovalbumin protein in significant quantities, but present ovalbumin peptide to T cells for Th2 differentiation via major histocompatibility complex class II. Intriguingly, basophils promote Th2 skewing upon ovalbumin protein exposure in the presence of dendritic cells. Taken together, our results suggest that basophils alone are able to induce Th2 skewing with haptens and peptide antigens but require dendritic cells for the induction of Th2 for protein antigens upon epicutaneous immunization.

Both dendritic cells and basophils have been shown to influence T helper 2 cell induction, however the relative importance of their roles remains unclear. Otsuka et al. find that basophils present hapten and peptide antigens to T cells, but are unable to present protein antigens in the absence of dendritic cells.

GATA-1 regulates the generation and function of basophils

Developmental processes of hematopoietic cells are orchestrated by transcriptional networks. GATA-1, the founding member of the GATA family of transcription factors, has been demonstrated to play crucial roles in the differentiation of erythroid cells, magakaryocytes, eosinophils, and mast cells. However, the role of GATA-1 in basophils remains elusive. Here we show that basophils abundantly express Gata1 mRNAs, and that siRNA-mediated knockdown of Gata1 resulted in impaired production of IL-4 by basophils in response to the stimulation with IgE plus antigens. ΔdblGATA mice that carry the mutated Gata1 promoter and are widely used for functional analysis of eosinophils owing to their selective loss of eosinophils showed a decreased number of basophils with reduced expression of Gata1 mRNAs. The number of basophil progenitors in bone marrow was reduced in these mice, and the generation of basophils from their bone marrow cells in culture with IL-3 or thymic stromal lymphopoietin was impaired. ΔdblGATA basophils responded poorly ex vivo to stimulation with IgE plus antigens compared with wild-type basophils as assessed by degranulation and production of IL-4 and IL-6. Moreover, ΔdblGATA mice showed impaired responses in basophil-mediated protective immunity against intestinal helminth infection. Thus, ΔdblGATA mice showed numerical and functional aberrancy in basophils in addition to the known deficiency of eosinophils. Our findings demonstrate that GATA-1 plays a key role in the generation and function of basophils and underscore the need for careful distinction of the cell lineage responsible for each phenotype observed in ΔdblGATA mice.

Targeted deletion of the antisilencer/enhancer (ASE) element from intron 1 of the myelin proteolipid protein gene (Plp1) in mouse reveals that the element is dispensable for Plp1 expression in brain during development and remyelination

Myelin proteolipid protein gene (Plp1) expression is temporally regulated in brain, which peaks during the active myelination period of CNS development. Previous studies with Plp1-lacZ transgenic mice demonstrated that (mouse) Plp1 intron 1 DNA is required for high levels of expression in oligodendrocytes. Deletion-transfection analysis revealed the intron contains a single positive regulatory element operative in the N20.1 oligodendroglial cell line, which was named ASE (antisilencer/enhancer) based on its functional properties in these cells. To investigate the role of the ASE in vivo, the element was deleted from the native gene in mouse using a Cre/lox strategy. Although removal of the ASE from Plp1-lacZ constructs profoundly decreased expression in transfected oligodendroglial cell lines (N20.1 and Oli-neu), the element was dispensable to achieve normal levels of Plp1 gene expression in mouse during development (except perhaps at postnatal day 15) and throughout the remyelination period following cuprizone-induced (acute) demyelination. Thus, it is possible that the ASE is non-functional in vivo, or that loss of the ASE from the native gene in mouse can be compensated for by the presence of other regulatory elements within the Plp1 gene.

New models for analyzing mast cell functions in vivo

In addition to their well-accepted role as critical effector cells in anaphylaxis and other acute IgE-mediated allergic reactions, mast cells (MCs) have been implicated in a wide variety of processes that contribute to disease or help to maintain health. Although some of these roles were first suggested by analyses of MC products or functions in vitro, it is critical to determine whether, and under which circumstances, such potential roles actually can be performed by MCs in vivo. This review discusses recent advances in the development and analysis of mouse models to investigate the roles of MCs and MC-associated products during biological responses in vivo, and comments on some of the similarities and differences in the results obtained with these newer versus older models of MC deficiency.

Differentiation of innate type-2 effector cells

Type-2 immune responses are the underlying cause of many allergic diseases and provide protection against parasitic infection. Effective type-2 immune responses are generated by type-2 helper CD4(+) T cells (Th2) as well as type-2 innate effector cells. While we have learned a great deal about how CD4(+) Th2 cells regulate their Th2 cytokine gene transcription, we still do not know how type-2 innate effector cells acquire their capacity to express Th2 cytokine genes. Furthermore, it remains poorly understood how Th2 cytokines regulate the differentiation of innate type-2 progenitor cells. In this review, we will focus on (1) the long distance interaction between the sites of allergic inflammation and the site of hematopoiesis in the bone marrow, (2) the characteristics of innate type-2 progenitors, and (3) the molecular mechanisms by which innate type-2 effector cells acquire the capacity to produce type-2 cytokines.

The 3' enhancer CNS2 is a critical regulator of interleukin-4-mediated humoral immunity in follicular helper T cells

A main role for interleukin-4 (IL-4) is in humoral immunity, and follicular helper CD4(+) T (Tfh) cells may be an intrinsic IL-4 source. Here we demonstrate that conserved noncoding sequence 2 (CNS2) is an essential enhancer element for IL-4 expression in Tfh cells but not in Th2 cells. Mice with a CNS2 deletion had a reduction in IgG1 and IgE production and in IL-4 expression in Tfh cells. Tracking of CNS2 activity via a GFP reporter mouse demonstrated that CNS2-active cells expressed several markers of Tfh cells: CXCR5, PD-1, and ICOS; the transcriptional master regulator Bcl6; and the cytokines IL-21 and IL-4. These CNS2-active cells were mainly localized in B cell follicles and germinal centers. The GFP(+) Tfh cells were derived from GFP(-) naive T cells after in vivo systemic immunization. These results indicate that CNS2 is an essential enhancer element required for IL-4 expression in Tfh cells controlling humoral immunity.

Interleukin-4 production by follicular helper T cells requires the conserved Il4 enhancer hypersensitivity site V

Follicular helper T cells (Tfh cells) are the major producers of interleukin-4 (IL-4) in secondary lymphoid organs where humoral immune responses develop. Il4 regulation in Tfh cells appears distinct from the classical T helper 2 (Th2) cell pathway, but the underlying molecular mechanisms remain largely unknown. We found that hypersensitivity site V (HS V; also known as CNS2), a 3' enhancer in the Il4 locus, is essential for IL-4 production by Tfh cells. Mice lacking HS V display marked defects in type 2 humoral immune responses, as evidenced by abrogated IgE and sharply reduced IgG1 production in vivo. In contrast, effector Th2 cells that are involved in tissue responses were far less dependent on HS V. HS V facilitated removal of repressive chromatin marks during Th2 and Tfh cell differentiation and increased accessibility of the Il4 promoter. Thus, Tfh and Th2 cells utilize distinct but overlapping molecular mechanisms to regulate Il4, a finding with important implications for understanding the molecular basis of allergic diseases.

Requirement of interaction between mast cells and skin dendritic cells to establish contact hypersensitivity

The role of mast cells (MCs) in contact hypersensitivity (CHS) remains controversial. This is due in part to the use of the MC-deficient Kit ^W/Wv mouse model, since Kit ^W/Wv mice congenitally lack other types of cells as a result of a point mutation in c-kit. A recent study indicated that the intronic enhancer (IE) for Il4 gene transcription is essential for MCs but not in other cell types. The aim of this study is to re-evaluate the roles of MCs in CHS using mice in which MCs can be conditionally and specifically depleted. Transgenic Mas-TRECK mice in which MCs are depleted conditionally were newly generated using cell-type specific gene regulation by IE. Using this mouse, CHS and FITC-induced cutaneous DC migration were analyzed. Chemotaxis assay and cytoplasmic Ca²⁺ imaging were performed by co-culture of bone marrow-derived MCs (BMMCs) and bone marrow-derived dendritic cells (BMDCs). In Mas-TRECK mice, CHS was attenuated when MCs were depleted during the sensitization phase. In addition, both maturation and migration of skin DCs were abrogated by MC depletion. Consistently, BMMCs enhanced maturation and chemotaxis of BMDC in ICAM-1 and TNF-α dependent manners Furthermore, stimulated BMDCs increased intracellular Ca²⁺ of MC upon direct interaction and up-regulated membrane-bound TNF-α on BMMCs. These results suggest that MCs enhance DC functions by interacting with DCs in the skin to establish the sensitization phase of CHS.

p53 negatively regulates RGS13 protein expression in immune cells

RGS13, a member of the regulator of G protein signaling (RGS) family, inhibits G protein-coupled receptor signaling in B cells and mast cells (MCs) and suppresses IgE-antigen-induced MC degranulation and anaphylaxis. Although RGS13 expression is induced by immune receptor and chemokine receptor stimulation, the molecular regulation of RGS13 transcription is unknown. Here, we investigated the role of two p53 response elements (REs) in the regulation of RGS13 promoter activity and expression. We found that a 1000-bp DNA fragment upstream of the ATG translation start site (TSS) had promoter activity in reporter gene assays, and deletion or mutation of a p53-binding motif nearest the TSS abolished promoter activity. Notably, p53 bound to both REs in the RGS13 promoter in vivo as assessed by chromatin immunoprecipitation, suggesting that the p53 RE most distal to the TSS is physiologically inactive. We detected reduced RGS13 expression in MCs exogenously expressing p53 or treated with doxorubicin, which induces genotoxic stress and leads to p53 accumulation. RNA silencing of p53 up-regulated RGS13 expression in B lymphocytes, and bone marrow-derived MCs from p53(-/-) mice had increased RGS13 expression. Finally, p53-depleted B cells with increased RGS13 expression had reduced Ca(2+) mobilization in response to sphingosine 1-phosphate. These studies indicate that p53 may modulate immune responses through suppression of RGS13 transcription in MCs and B cells.

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is critical for interleukin-4 expression in response to FcepsilonRI receptor cross-linking

Basophils mediate many of their biological functions by producing IL-4. However, it is unknown how the Il4 gene is regulated in basophils. Here, we report that CCAAT/enhancer-binding protein α (C/EBPα), a major myeloid transcription factor, was highly expressed in basophils. We show that C/EBPα selectively activated Il4 promoter-luciferase reporter gene transcription in response to IgE cross-linking, but C/EBPα did not activate other known Th2 or mast cell enhancers. We found that the PI3K pathway and calcineurin were essential in C/EBPα-driven Il4 promoter-luciferase gene transcription. Our mutation analyses revealed that C/EBPα drove Il4 promoter-luciferase activity depending on its DNA binding domain. Mutation of the C/EBPα-binding site in the Il4 promoter region abolished C/EBPα-driven Il4 promoter-luciferase activity. Our results further showed that a mutation in nuclear factor of activated T cells (NFAT)-binding sites in the Il4 promoter also negated C/EBPα-driven Il4 promoter-luciferase activity. Our study demonstrates that C/EBPα, in cooperation with NFAT, directly regulates Il4 gene transcription.

The enhancer HS2 critically regulates GATA-3-mediated Il4 transcription in T(H)2 cells

GATA-3 is a master regulator of T helper type 2 (T(H)2) differentiation. However, the molecular basis of GATA-3-mediated T(H)2 lineage commitment is poorly understood. Here we identify the DNase I-hypersensitive site 2 (HS2) element located in the second intron of the interleukin 4 locus (Il4) as a critical enhancer strictly controlled by GATA-3 binding. Mice lacking HS2 showed substantial impairment in their asthmatic responses and their production of IL-4 but not of other T(H)2 cytokines. Overexpression of Gata3 in HS2-deficient T cells failed to restore Il4 expression. HS2 deletion impaired the trimethylation of histone H3 at Lys4 and acetylation of histone H3 at Lys9 and Lys14 in the Il4 locus. Our results indicate that HS2 is the target of GATA-3 in regulating chromosomal modification of the Il4 locus and is independent of the Il5 and Il13 loci.

Basophils: what they 'can do' versus what they 'actually do'

Basophils, the least abundant granulocytes, have poorly understood functions. They have been linked to the development of T helper type 2 immunity during parasite infection and allergic inflammation. Emerging evidence has not only shown the critical involvement of basophils in the development of T helper type 2 immunity but also provided useful animal models with which basophil functions can be further examined. However, distinctions must be made between what basophils 'can do' after in vitro manipulation and what they 'actually do' during in vivo immune responses; these may be very different. In this review, the functions of basophils determined on the basis of analysis of in vitro and in vivo systems and their potential involvement in clinical settings are discussed.