Roles of transcription factors and epigenetic modifications in differentiation and maintenance of regulatory T cells

HIC1 interacts with FOXP3 multi protein complex: Novel pleiotropic mechanisms to regulate human regulatory T cell differentiation and function

Transcriptional repressor, hypermethylated in cancer 1 (HIC1) participates in a range of important biological processes, such as tumor repression, immune suppression, embryonic development and epigenetic gene regulation. Further to these, we previously demonstrated that HIC1 provides a significant contribution to the function and development of regulatory T (Treg) cells. However, the mechanism by which it regulates these processes was not apparent. To address this question, we used affinity-purification mass spectrometry to characterize the HIC1 interactome in human Treg cells. Altogether 61 high-confidence interactors were identified, including IKZF3, which is a key transcription factor in the development of Treg cells. The biological processes associated with these interacting proteins include protein transport, mRNA processing, non-coding (ncRNA) transcription and RNA metabolism. The results revealed that HIC1 is part of a FOXP3-RUNX1-CBFB protein complex that regulates Treg signature genes thus improving our understanding of HIC1 function during early Treg cell differentiation.

Regulatory T cells in rheumatoid arthritis: functions, development, regulation, and therapeutic potential

Rheumatoid arthritis (RA) is an autoimmune disease that mainly affects the joints but also leads to systemic inflammation. Auto-reactivity and dysregulation of self-tolerance are thought to play a vital role in disease onset. In the pathogenesis of autoimmune diseases, disturbed immunosuppressive properties of regulatory T cells contribute to the dysregulation of immune homeostasis. In RA patients, the functions of Treg cells and their frequency are reduced. Therefore, focusing on the re-establishment of self-tolerance by increasing Treg cell frequencies and preventing a loss of function is a promising strategy for the treatment of RA. This approach could be especially beneficial for those patients who do not respond well to current therapies. In this review, we summarize and discuss the current knowledge about the function, differentiation and regulation of Treg cells in RA patients and in animal models of autoimmune arthritis. In addition, we highlight the therapeutic potential as well as the challenges of Treg cell targeting treatment strategies.

Long Noncoding RNAs as Orchestrators of CD4+ T-Cell Fate

CD4⁺ T cells differentiate towards different subpopulations through the regulation of lineage-specific cytokines and transcription factors, which flexibly respond to various immune challenges. However, considerable work has demonstrated that the CD4⁺ T-cell differentiation mechanism is complex and not limited to transcription factors and cytokines. Long noncoding RNAs (lncRNAs) are RNA molecules with lengths exceeding 200 base pairs that regulate various biological processes and genes. LncRNAs have been found to conciliate the plasticity of CD4⁺ T-cell differentiation. Then, we focused on lncRNAs involved in CD4⁺ T-cell differentiation and enlisted some molecular thought into the plasticity and functional heterogeneity of CD4⁺ T cells. Furthermore, elucidating how lncRNAs modulate CD4⁺ T-cell differentiation in disparate immune diseases may provide a basis for the pathological mechanism of immune-mediated diseases.

Comparison Between Nr4a Transcription Factor Regulation and Function in Lymphoid and Tumor Treg Cells

Although the “lymphoid” function of regulatory T (Treg) cells is crucial for organismal homeostasis, these cells are also known to suppress the antitumor immune response in the tumor microenvironments. Thus, a detailed understanding of Treg cell maintenance and function in both lymphoid organs and tumor environments may help to establish novel methods for the reactivating antitumor immunity, while retaining necessary immune tolerance towards self and non-hazardous antigens. Previous studies have hypothesized that Treg cells behave similarly in lymphoid organs and in tumor environments; however, few studies have been conducted specifically researching Treg cell activity in tumor environments. In addition, several recent studies identified a novel mechanism regulating Treg cell function in tumor environments. Our group has previously described the critical roles of the Nr4a family of nuclear orphan receptors, comprising Nr4a1, Nr4a2, and Nr4a3, in the differentiation and maintenance of Treg cells in lymphoid organs. Subsequently, it was found that Nr4a factors help to maintain Treg cell function in tumor environments, thereby playing a suppressive role against T cell antitumor immunity. Importantly, there were some differences between the activities of these Nr4a factors under these conditions, including the specific function of the COX/PGE2 axis in tumor environments. This review was designed to investigate the role of Nr4a factors in the regulation of Treg cell activities both in the lymphoid organs and tumor environments, highlighting the commonalities and differences in their behaviors between Treg cells in these two different environments.

NR4A nuclear receptors in T and B lymphocytes: Gatekeepers of immune tolerance. Immunol Rev 2022;307:116-133. [PMID: 35174510 DOI: 10.1111/imr.13072]

Random VDJ recombination early in T and B cell development enables the adaptive immune system to recognize a vast array of evolving pathogens via antigen receptors. However, the potential of such randomly generated TCRs and BCRs to recognize and respond to self-antigens requires layers of tolerance mechanisms to mitigate the risk of life-threatening autoimmunity. Since they were originally cloned more than three decades ago, the NR4A family of nuclear hormone receptors have been implicated in many critical aspects of immune tolerance, including negative selection of thymocytes, peripheral T cell tolerance, regulatory T cells (Treg), and most recently in peripheral B cell tolerance. In this review, we discuss important insights from many laboratories as well as our own group into the function and mechanisms by which this small class of primary response genes promotes self-tolerance and immune homeostasis to balance the need for host defense against the inherent risks posed by the adaptive immune system.

Functional Diversities of Regulatory T Cells in the Context of Cancer Immunotherapy

Regulatory T cells (Tregs) are a subset of CD4+ T cells with their immunosuppressive activities to block abnormal or excessive immune responses to self and non-autoantigens. Tregs express the transcription factor Foxp3, maintain the immune homeostasis, and prevent the initiation of anti-tumor immune effects in various ways as their mechanisms to modulate tumor development. Recognition of different phenotypes and functions of intratumoral Tregs has offered the possibilities to develop therapeutic strategies by selectively targeting Tregs in cancers with the aim of alleviating their immunosuppressive activities from anti-tumor immune responses. Several Treg-based immunotherapeutic approaches have emerged to target cytotoxic T lymphocyte antigen-4, glucocorticoid-induced tumor necrosis factor receptor, CD25, indoleamine-2, 3-dioxygenase-1, and cytokines. These immunotherapies have yielded encouraging outcomes from preclinical studies and early-phase clinical trials. Further, dual therapy or combined therapy has been approved to be better choices than single immunotherapy, radiotherapy, or chemotherapy. In this short review article, we discuss our current understanding of the immunologic characteristics of Tregs, including Treg differentiation, development, therapeutic efficacy, and future potential of Treg-related therapies among the general cancer therapy.

Measurements of Treg Cell Induction by Candida albicans DNA Using Flow Cytometry

Microbiota and their metabolites in the human gut regulate a variety of immune cells including regulatory T cells (Treg cells) and cytokine production. The T helper 17 (Th17)/Treg ratio biomarker (Th17/Treg), for example, has been linked to the development and progression of certain inflammatory diseases, insulin resistance, and systemic lupus erythematosus (SLE). Candida albicans is an opportunistic fungal pathogen that also colonizes the gut. T cell reactivity through T helper cells play critical roles in fungal clearance by the host through the secretion of proinflammatory cytokines. While these cytokines are mainly produced by the Th1 and Th17 subsets of T cells, another subset of T cells, the Treg cells, are also induced by antigenic ligands from pathogens that inhibit the responses of other effector T cells during the inflammation. The antigenic ligands for Treg induction have been found to include microbial cell wall polysaccharides (PSA), metabolites like short chain fatty acids (SCFA), or even microbial DNA.

Dynamics and epigenetic signature of regulatory T-cells following antiretroviral therapy initiation in acute HIV infection

BACKGROUND

HIV infection promotes the expansion of immunosuppressive regulatory T-cells (Tregs), contributing to immune dysfunction, tissue fibrosis and disease progression. Early antiretroviral treatment (ART) upon HIV infection improves CD4 count and decreases immune activation. However, Treg dynamics and their epigenetic regulation following early ART initiation remain understudied.

METHODS

Treg subsets were characterized by flow cytometry in 103 individuals, including untreated HIV-infected participants in acute and chronic phases, ART-treated in early infection, elite controllers (ECs), immunological controllers (ICs), and HIV-uninfected controls. The methylation status of six regulatory regions of the foxp3 gene was assessed using MiSeq technology.

FINDINGS

Total Treg frequency increased overtime during HIV infection, which was normalized in early ART recipients. Tregs in untreated individuals expressed higher levels of activation and immunosuppressive markers (CD39, and LAP(TGF-β1)), which remained unchanged following early ART. Expression of gut migration markers (CCR9, Integrin-β7) by Tregs was elevated during untreated HIV infection, while they declined with the duration of ART but not upon early ART initiation. Notably, gut-homing Tregs expressing LAP(TGF-β1) and CD39 remained higher despite early treatment. Additionally, the increase in LAP(TGF-β1)⁺ Tregs overtime were consistent with higher demethylation of conserved non-coding sequence (CNS)-1 in the foxp3 gene. Remarkably, LAP(TGF-β1)-expressing Tregs in ECs were significantly higher than in uninfected subjects, while the markers of Treg activation and gut migration were not different.

INTERPRETATION

Early ART initiation was unable to control the levels of immunosuppressive Treg subsets and their gut migration potential, which could ultimately contribute to gut tissue fibrosis and HIV disease progression.

FUNDING

This study was funded by the Canadian Institutes of Health Research (CIHR, grant MOP 142294) and in part by the AIDS and Infectious Diseases Network of the Réseau SIDA et maladies infectieuses du Fonds de recherche du Québec-Santé (FRQ-S).

Function and Role of Regulatory T Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic and heterogeneous autoimmune disease with symmetrical polyarthritis as its critical clinical manifestation. The basic cause of autoimmune diseases is the loss of tolerance to self or harmless antigens. The loss or functional deficiency of key immune cells, regulatory T (Treg) cells, has been confirmed in human autoimmune diseases. The pathogenesis of RA is complex, and the dysfunction of Tregs is one of the proposed mechanisms underlying the breakdown of self-tolerance leading to the progression of RA. Treg cells are a vital component of peripheral immune tolerance, and the transcription factor Foxp3 plays a major immunosuppressive role. Clinical treatment for RA mainly utilizes drugs to alleviate the progression of disease and relieve disease activity, and the ideal treatment strategy should be to re-induce self-tolerance before obvious tissue injury. Treg cells are one of the ideal options. This review will introduce the classification, mechanism of action, and characteristics of Treg cells in RA, which provides insights into clinical RA treatment.

Treg Cells and Epigenetic Regulation

The discovery of the epigenetic regulation of Treg cells, a cell population with fundamental immunoregulatory properties, has shed considerable insights into an understanding of the role of these cells in health and disease. Research over the past several years has shown that the interaction of Treg cells with the gut microbiota are critical not only for the development of Treg function in health but also for abnormalities of Treg function that play a critical role in the pathogenesis of human diseases such as the allergic diseases, the autoimmune disorders, and cancer. The equilibrium between phenotypic plasticity and stability of Treg cells is defined by the fine-tuned transcriptional and epigenetic events required to ensure stable expression of Foxp3 in Treg cells. In this chapter, we discuss the molecular events that control Foxp3 gene expression and address the importance of DNA methylation as an important molecular switch that regulates the genetic expression of Treg induction and the possible implications of these findings for the treatment of human diseases characterized by abnormalities of Treg cell function.

Molecular Mechanisms Controlling Foxp3 Expression in Health and Autoimmunity: From Epigenetic to Post-translational Regulation

The discovery of the transcription factor Forkhead box-p3 (Foxp3) has shed fundamental insights into the understanding of the molecular determinants leading to generation and maintenance of T regulatory (Treg) cells, a cell population with a key immunoregulatory role. Work over the past few years has shown that fine-tuned transcriptional and epigenetic events are required to ensure stable expression of Foxp3 in Treg cells. The equilibrium between phenotypic plasticity and stability of Treg cells is controlled at the molecular level by networks of transcription factors that bind regulatory sequences, such as enhancers and promoters, to regulate Foxp3 expression. Recent reports have suggested that specific modifications of DNA and histones are required for the establishment of the chromatin structure in conventional CD4⁺ T (Tconv) cells for their future differentiation into the Treg cell lineage. In this review, we discuss the molecular events that control Foxp3 gene expression and address the associated alterations observed in human diseases. Also, we explore how Foxp3 influences the gene expression programs in Treg cells and how unique properties of Treg cell subsets are defined by other transcription factors.

Treg Heterogeneity, Function, and Homeostasis

T-regulatory cells (Tregs) represent a unique subpopulation of helper T-cells by maintaining immune equilibrium using various mechanisms. The role of T-cell receptors (TCR) in providing homeostasis and activation of conventional T-cells is well-known; however, for Tregs, this area is understudied. In the last two decades, evidence has accumulated to confirm the importance of the TCR in Treg homeostasis and antigen-specific immune response regulation. In this review, we describe the current view of Treg subset heterogeneity, homeostasis and function in the context of TCR involvement. Recent studies of the TCR repertoire of Tregs, combined with single-cell gene expression analysis, revealed the importance of TCR specificity in shaping Treg phenotype diversity, their functions and homeostatic maintenance in various tissues. We propose that Tregs, like conventional T-helper cells, act to a great extent in an antigen-specific manner, which is provided by a specific distribution of Tregs in niches.

A Two-Way Proteome Microarray Strategy to Identify Novel Mycobacterium tuberculosis-Human Interactors

Tuberculosis (TB) is still a serious threat to human health which is caused by mycobacterium tuberculosis (Mtb). The main reason for failure to eliminate TB is lack of clearly understanding the molecular mechanism of Mtb pathogenesis. Determining human Mtb-interacting proteins enables us to characterize the mechanism and identify potential molecular targets for TB diagnosis and treatment. However, experimentally systematic Mtb interactors are not readily available. In this study, we performed an unbiased, comprehensive two-way proteome microarray based approach to systematically screen global human Mtb interactors and determine the binding partners of Mtb effectors. Our results, for the first time, screened 84 potential human Mtb interactors. Bioinformatic analysis further highlighted these protein candidates might engage in a wide range of cellular functions such as activation of DNA endogenous promoters, transcription of DNA/RNA and necrosis, as well as immune-related signaling pathways. Then, using Mtb proteome microarray followed His tagged pull-down assay and Co-IP, we identified one interacting partner (Rv0577) for the protein candidate NRF1 and three binding partners (Rv0577, Rv2117, Rv2423) for SMAD2, respectively. This study gives new insights into the profile of global Mtb interactors potentially involved in Mtb pathogenesis and demonstrates a powerful strategy in the discovery of Mtb effectors.

Heligmosomoides polygyrus bakeri Infection Decreases Smad7 Expression in Intestinal CD4+ T Cells, Which Allows TGF-β to Induce IL-10-Producing Regulatory T Cells That Block Colitis

Helminthic infections modulate host immunity and may protect their hosts from developing immunological diseases like inflammatory bowel disease. Induction of regulatory T cells (Tregs) may be an important part of this protective process. Heligmosomoides polygyrus bakeri infection also promotes the production of the regulatory cytokines TGF-β and IL-10 in the gut. In the intestines, TGF-β helps induce regulatory T cells. This study used Foxp3/IL-10 double reporter mice to investigate the effect of TGF-β on the differentiation of colon and mesenteric lymph node-derived murine Foxp3^- IL-10^- CD4⁺ T cells into their regulatory phenotypes. Foxp3^- IL-10^- CD4⁺ T cells from H. polygyrus bakeri-infected mice, as opposed to T cells from uninfected animals, cultured in vitro with TGF-β and anti-CD3/CD28 mAb differentiated into Foxp3⁺ and/or IL-10⁺ T cells. The IL-10-producing T cells nearly all displayed CD25. Smad7 is a natural inhibitor of TGF-β signaling. In contrast to gut T cells from uninfected mice, Foxp3^- IL10^- CD4⁺ T cells from H. polygyrus bakeri-infected mice displayed reduced Smad7 expression and responded to TGF-β with Smad2/3 phosphorylation. The TGF-β-induced Tregs that express IL-10 blocked colitis when transferred into the Rag/CD25^- CD4⁺ T cell transfer model of inflammatory bowel disease. TGF-β had a greatly diminished capacity to induce Tregs in H. polygyrus bakeri-infected transgenic mice with constitutively high T cell-specific Smad7 expression. Thus, infection with H. polygyrus bakeri causes down-modulation in Smad7 expression in intestinal CD4⁺ T cells, which allows the TGF-β produced in response to the infection to induce the Tregs that prevent colitis.

Brain regulatory T cells suppress astrogliosis and potentiate neurological recovery

In addition to maintaining immune tolerance, FOXP3⁺ regulatory T (T_reg) cells perform specialized functions in tissue homeostasis and remodelling^1,2. However, the characteristics and functions of brain T_reg cells are not well understood because there is a low number of T_reg cells in the brain under normal conditions. Here we show that there is massive accumulation of T_reg cells in the mouse brain after ischaemic stroke, and this potentiates neurological recovery during the chronic phase of ischaemic brain injury. Although brain T_reg cells are similar to T_reg cells in other tissues such as visceral adipose tissue and muscle^3-5, they are apparently distinct and express unique genes related to the nervous system including Htr7, which encodes the serotonin receptor 5-HT₇. The amplification of brain T_reg cells is dependent on interleukin (IL)-2, IL-33, serotonin and T cell receptor recognition, and infiltration into the brain is driven by the chemokines CCL1 and CCL20. Brain T_reg cells suppress neurotoxic astrogliosis by producing amphiregulin, a low-affinity epidermal growth factor receptor (EGFR) ligand. Stroke is a leading cause of neurological disability, and there are currently few effective recovery methods other than rehabilitation during the chronic phase. Our findings suggest that T_reg cells and their products may provide therapeutic opportunities for neuronal protection against stroke and neuroinflammatory diseases.

Thyrotroph embryonic factor is downregulated in bladder cancer and suppresses proliferation and tumorigenesis via the AKT/FOXOs signalling pathway

Objectives

Thyrotroph embryonic factor (TEF) plays an important role in several different processes in normal human cells; however, its function in malignant cells has not been fully elucidated.

Materials and methods

The mRNA levels of TEF in 408 bladder cancer (BC) samples from the Cancer Genome Atlas (TCGA) database were analysed in depth. Next, the expression of TEF in 7 BC cell lines was compared to that in normal bladder epithelial cells. The cell count, colony formation and anchorage‐independent growth assays as well as a nude mouse xenograft model were utilized to examine the effects of TEF on proliferation and tumorigenesis. Immunofluorescence staining, flow cytometry analysis and treatment with an AKT inhibitor were performed to explore the molecular regulation mechanisms of TEF in BC.

Results

Analysis of TCGA data indicated that TEF mRNA was decreased in BC samples compared to that in normal bladder epithelial cells and correlated with the poor survival of BC patients. Additional experiments verified that the mRNA and protein expression of TEF were significantly decreased in BC cells compared to that in normal bladder epithelial cells. Upregulation of TEF expression significantly retarded BC cell growth by inhibiting the G1/S transition via regulating AKT/FOXOs signalling.

Conclusion

Our results suggest that TEF might play an important role in suppressing BC cells proliferation and tumorigenesis.

Development and Functional Modulation of Regulatory T Cells by Transcription Factors and Epigenetics

Regulatory T cells (Tregs) are essential for the maintenance of immune homeostasis. Studies of Treg are not only necessary for understanding the mechanism of immune homeostasis but also extremely useful for the development of treatments of various immune diseases. Forkhead box P3 (Foxp3) was identified as the master gene responsible for the immune-suppressing activity of Tregs. The promoter region and several intronic enhancers, designated conserved noncoding sequence (CNS) 0, 1, 2, and 3, at the Foxp3 gene locus have important roles in Foxp3 expression and Treg development. We demonstrated that transcription factors Nr4a and Smad2/3 are required for development of thymic Tregs and induced Tregs, respectively. In addition to transcription factors, Treg-specific DNA demethylation has been shown to be important for Treg stability. In particular, DNA demethylation of CNS2 was implicated in Treg stability, and members of the ten-eleven translocation family of demethylation factors were recently demonstrated to have important roles in 5'-C-phosphate-G-3' demethylation at CNS2. This article summarizes recent findings regarding the roles of transcription factors and epigenetic modifications in the differentiation, maintenance, and function of Tregs. This review will facilitate clinical application of Tregs to diseases in the field of ophthalmology, including uveitis and age-related macular degeneration.

Negative Regulation of Cytokine Signaling in Immunity

Cytokines are key modulators of immunity. Most cytokines use the Janus kinase and signal transducers and activators of transcription (JAK-STAT) pathway to promote gene transcriptional regulation, but their signals must be attenuated by multiple mechanisms. These include the suppressors of cytokine signaling (SOCS) family of proteins, which represent a main negative regulation mechanism for the JAK-STAT pathway. Cytokine-inducible Src homology 2 (SH2)-containing protein (CIS), SOCS1, and SOCS3 proteins regulate cytokine signals that control the polarization of CD4+ T cells and the maturation of CD8+ T cells. SOCS proteins also regulate innate immune cells and are involved in tumorigenesis. This review summarizes recent progress on CIS, SOCS1, and SOCS3 in T cells and tumor immunity.

Improvement of Foxp3 stability through CNS2 demethylation by TET enzyme induction and activation

Since induced regulatory T cells (iTregs) can be produced in a large quantity in vitro, these cells are expected to be clinically useful to induce immunological tolerance in various immunological diseases. Foxp3 (Forkhead box P3) expression in iTregs is, however, unstable due to the lack of demethylation of the CpG island in the conserved non-coding sequence 2 (CNS2) of the Foxp3 locus. To facilitate the demethylation of CNS2, we over-expressed the catalytic domain (CD) of the ten-eleven translocation (TET) protein, which catalyzes the steps of the iterative demethylation of 5-methylcytosine. TET-CD over-expression in iTregs resulted in partial demethylation of CNS2 and stable Foxp3 expression. We also discovered that TET expression was enhanced under low oxygen (5%) culture conditions, which facilitated CNS2 DNA demethylation and stabilization of Foxp3 expression in a TET2- and TET3-dependent manner. In combination with vitamin C treatment, which has been reported to enhance TET catalytic activity, iTregs generated under low oxygen conditions retained more stable Foxp3 expression in vitro and in vivo and exhibited stronger suppression activity in a colitis model compared with untreated iTregs. Our data indicate that the induction and activation of TET enzymes in iTregs would be an effective method for Treg-mediated adoptive immunotherapy.

Inhibition of Nr4a Receptors Enhances Antitumor Immunity by Breaking Treg-Mediated Immune Tolerance

Enhanced infiltration of regulatory T cells (Treg) into tumor tissue is detrimental to patients with cancer and is closely associated with poor prognosis as they create an immunosuppressive state that suppresses antitumor immune responses. Therefore, breaking Treg-mediated immune tolerance is important when considering cancer immunotherapy. Here, we show that the Nr4a nuclear receptors, key transcription factors maintaining Treg genetic programs, contribute to Treg-mediated suppression of antitumor immunity in the tumor microenvironment. Mice lacking Nr4a1 and Nr4a2 genes specifically in Tregs showed resistance to tumor growth in transplantation models without exhibiting any severe systemic autoimmunity. The chemotherapeutic agent camptothecin and a common cyclooxygenase-2 inhibitor were found to inhibit transcriptional activity and induction of Nr4a factors, and they synergistically exerted antitumor effects. Genetic inactivation or pharmacologic inhibition of Nr4a factors unleashed effector activities of CD8⁺ cytotoxic T cells and evoked potent antitumor immune responses. These findings demonstrate that inactivation of Nr4a in Tregs breaks immune tolerance toward cancer, and pharmacologic modulation of Nr4a activity may be a novel cancer treatment strategy targeting the immunosuppressive tumor microenvironment.Significance: This study reveals the role of Nr4a transcription factors in Treg-mediated tolerance to antitumor immunity, with possible therapeutic implications for developing effective anticancer therapies. Cancer Res; 78(11); 3027-40. ©2018 AACR.

Nur77 Is Upregulated in B-1a Cells by Chronic Self-Antigen Stimulation and Limits Generation of Natural IgM Plasma Cells

B-1a cells are a unique population of innate-like B cells with a highly restricted and self-reactive BCR repertoire. Preimmune "natural" IgM produced by B-1a-derived plasma cells is essential for homeostatic clearance of cellular debris and forms a primary layer of protection against infection. In this study, we take advantage of a fluorescent reporter of BCR signaling to show that expression of the orphan nuclear hormone receptor Nur77 is upregulated under steady-state conditions in self-reactive B-1a cells in response to chronic Ag stimulation. Nur77-deficient mice exhibit elevated natural serum IgM (but not IgG) and marked expansion of IgM plasma cells of B-1a origin. Moreover, we show that Nur77 restrains the turnover of B-1a cells and the accumulation of immature IgM plasma cells. Thus, we identify a new critical negative-regulatory pathway that serves to maintain B-1a cells in a quiescent state in the face of chronic endogenous Ag stimulation.

Induction and maintenance of regulatory T cells by transcription factors and epigenetic modifications

Regulatory T cells (Tregs) are an essential cell subset for the maintenance of immune homeostasis. Foxp3 (Forkhead box P3) is the Treg master gene which is essential for immune suppressing activity. In addition, Tregs are characterized by a distinct pattern of gene expression, including upregulation of immune-suppressive genes and silencing of inflammatory genes. The molecular mechanisms of Treg development and maintenance have been intensively investigated. Tregs are characterized by expression of the transcription factor Foxp3. Several intronic enhancers and a promoter at the Foxp3 gene locus were shown to play important roles in Treg differentiation. The enhancers have been designated as conserved non-coding sequences (CNSs) 0, 1, 2, and 3. We showed that the transcription factors Nr4a and Smad2/3 are essential for the development of thymic Tregs and induced Tregs, respectively. Recently, Treg-specific DNA demethylation has been shown to play an important role in Treg stability. DNA demethylation of CNS2 has been implicated in Treg stability, and recent reports have revealed that the ten-eleven translocation (Tet) family of demethylation factor plays an important role in CpG demethylation at CNS2. This article reviews the recent progress on the roles of transcription factors and epigenetic modifications in the differentiation, maintenance, and function of Tregs.

Milk's Role as an Epigenetic Regulator in Health and Disease

It is the intention of this review to characterize milk's role as an epigenetic regulator in health and disease. Based on translational research, we identify milk as a major epigenetic modulator of gene expression of the milk recipient. Milk is presented as an epigenetic "doping system" of mammalian development. Milk exosome-derived micro-ribonucleic acids (miRNAs) that target DNA methyltransferases are implicated to play the key role in the upregulation of developmental genes such as FTO, INS, and IGF1. In contrast to miRNA-deficient infant formula, breastfeeding via physiological miRNA transfer provides the appropriate signals for adequate epigenetic programming of the newborn infant. Whereas breastfeeding is restricted to the lactation period, continued consumption of cow's milk results in persistent epigenetic upregulation of genes critically involved in the development of diseases of civilization such as diabesity, neurodegeneration, and cancer. We hypothesize that the same miRNAs that epigenetically increase lactation, upregulate gene expression of the milk recipient via milk-derived miRNAs. It is of critical concern that persistent consumption of pasteurized cow's milk contaminates the human food chain with bovine miRNAs, that are identical to their human analogs. Commercial interest to enhance dairy lactation performance may further increase the epigenetic miRNA burden for the milk consumer.