Cutting Edge: Innate production of IFN-gamma by NK cells is independent of epigenetic modification of the IFN-gamma promoter

The molecular perspective on the melanoma and genome engineering of T-cells in targeting therapy

Melanoma, an aggressive malignant tumor originating from melanocytes in humans, is on the rise globally, with limited non-surgical treatment options available. Recent advances in understanding the molecular and cellular mechanisms underlying immune escape, tumorigenesis, drug resistance, and cancer metastasis have paved the way for innovative therapeutic strategies. Combination therapy targeting multiple pathways simultaneously has been shown to be promising in treating melanoma, eliciting favorable responses in most melanoma patients. CAR T-cells, engineered to overcome the limitations of human leukocyte antigen (HLA)-dependent tumor cell detection associated with T-cell receptors, offer an alternative approach. By genetically modifying apheresis-collected allogeneic or autologous T-cells to express chimeric antigen receptors, CAR T-cells can appreciate antigens on cell surfaces independently of major histocompatibility complex (MHC), providing a significant cancer cell detection advantage. However, identifying the most effective target antigen is the initial step, as it helps mitigate the risk of toxicity due to "on-target, off-tumor" and establishes a targeted therapeutic strategy. Furthermore, evaluating signaling pathways and critical molecules involved in melanoma pathogenesis remains insufficient. This study emphasizes the novel approaches of CAR T-cell immunoediting and presents new insights into the molecular signaling pathways associated with melanoma.

IL-15 Priming Alters IFN-γ Regulation in Murine NK Cells

NK effector functions can be triggered by inflammatory cytokines and engagement of activating receptors. NK cell production of IFN-γ, an important immunoregulatory cytokine, exhibits activation-specific IFN-γ regulation. Resting murine NK cells exhibit activation-specific metabolic requirements for IFN-γ production, which are reversed for activating receptor-mediated stimulation following IL-15 priming. Although both cytokine and activating receptor stimulation leads to similar IFN-γ protein production, only cytokine stimulation upregulates Ifng transcript, suggesting that protein production is translationally regulated after receptor stimulation. Based on these differences in IFN-γ regulation, we hypothesized that ex vivo IL-15 priming of murine NK cells allows a switch to IFN-γ transcription upon activating receptor engagement. Transcriptional analysis of primed NK cells compared with naive cells or cells cultured with low-dose IL-15 demonstrated that primed cells strongly upregulated Ifng transcript following activating receptor stimulation. This was not due to chromatin accessibility changes in the Ifng locus or changes in ITAM signaling, but was associated with a distinct transcriptional signature induced by ITAM stimulation of primed compared with naive NK cells. Transcriptional analyses identified a common signature of c-Myc (Myc) targets associated with Ifng transcription. Although Myc marked NK cells capable of Ifng transcription, Myc itself was not required for Ifng transcription using a genetic model of Myc deletion. This work highlights altered regulatory networks in IL-15-primed cells, resulting in distinct gene expression patterns and IFN-γ regulation in response to activating receptor stimulation.

Clonal haematopoiesis and dysregulation of the immune system

Age-related diseases are frequently linked to pathological immune dysfunction, including excessive inflammation, autoreactivity and immunodeficiency. Recent analyses of human genetic data have revealed that somatic mutations and mosaic chromosomal alterations in blood cells - a condition known as clonal haematopoiesis (CH) - are associated with ageing and pathological immune dysfunction. Indeed, large-scale epidemiological studies and experimental mouse models have demonstrated that CH can promote cardiovascular disease, chronic obstructive pulmonary disease, chronic liver disease, osteoporosis and gout. The genes most frequently mutated in CH, the epigenetic regulators TET2 and DNMT3A, implicate increased chemokine expression and inflammasome hyperactivation in myeloid cells as a possible mechanistic connection between CH and age-related diseases. In addition, TET2 and DNMT3A mutations in lymphoid cells have been shown to drive methylation-dependent alterations in differentiation and function. Here we review the observational and mechanistic studies describing the connection between CH and pathological immune dysfunction, the effects of CH-associated genetic alterations on the function of myeloid and lymphoid cells, and the clinical and therapeutic implications of CH as a target for immunomodulation.

25KDa branched polyethylenimine increases interferon-γ production in natural killer cells via improving translation efficiency

BACKGROUND

Ex vivo cultivation is a promising strategy for increasing the number of NK cells and enhancing their antitumor activity prior to clinical application. Recent studies show that stimulation with 25KDa branched polyethylenimine (25KbPEI) generates NK cells with enhanced antitumor activity. To better understand how 25KbPEI primes NK cells, we explored the mechanism underlying increase in production of IFN-γ.

METHODS

Chemical priming was performed on NK-92MI cells by incubating them with 5 μg/ml of 25KbPEI. The production of IFN-γ was evaluated by RT-qPCR, ELISA, and Flow cytometry. By evaluating the effect of pharmacological inhibition of ERK/mTOR-eIF4E signaling pathways on IFN-γ translation, the function of these signaling pathways in IFN-γ translation was examined. To comprehend the level of 25KbPEI activity on immune-related components in NK cells, RNA sequencing and proteomics analyses were conducted.

RESULTS

25KbPEI enhances the production of IFN-γ by NK cells without transcriptional activation. Activation of ERK and mTOR signaling pathways was found to be associated with 25KbPEI-mediated calcium influx in NK cells. The activation of ERK/mTOR signaling was linked to the phosphorylation of 4E-BP1, which resulted in the activation of translation initiation complex and subsequent IFN-γ translation. Analysis of RNA sequencing and proteomics data revealed that the activity of 25KbPEI to improve translation efficiency in NK cells could be extended to additional immune-related molecules.

CONCLUSIONS

This study provides substantial insight into the process by which 25KbPEI primes NK cells. Our data demonstrated that the 25KbPEI mediated activation of ERK/mTOR signaling and subsequent stimulation of eIF4E is the primary mechanism by which the chemical stimulates translation of IFN-γ in NK cells. Video abstract.

IL-15 priming alters IFN-γ regulation in murine NK cells

Natural killer (NK) effector functions can be triggered by inflammatory cytokines and engagement of activating receptors. NK cell production of IFN-γ, an important immunoregulatory cytokine, exhibits activation-specific IFN-γ regulation. Resting murine NK cells exhibit activation-specific metabolic requirements for IFN-γ production, which are reversed for activating receptor-mediated stimulation following IL-15 priming. While both cytokine and activating receptor stimulation leads to similar IFN-γ protein production, only cytokine stimulation upregulates Ifng transcript, suggesting that protein production is translationally regulated after receptor stimulation. Based on these differences in IFN-γ regulation, we hypothesized that ex vivo IL-15 priming of murine NK cells allows a switch to IFN-γ transcription upon activating receptor engagement. Transcriptional analysis of primed NK cells compared to naïve cells or cells cultured with low-dose IL-15 demonstrated that primed cells strongly upregulated Ifng transcript following activating receptor stimulation. This was not due to chromatin accessibility changes in the Ifng locus or changes in ITAM signaling, but was associated with a distinct transcriptional signature induced by ITAM stimulation of primed compared to naïve NK cells. Transcriptional analyses identified a common signature of c-Myc (Myc) targets associated with Ifng transcription. While Myc marked NK cells capable of Ifng transcription, Myc itself was not required for Ifng transcription using a genetic model of Myc deletion. This work highlights altered regulatory networks in IL-15 primed cells, resulting in distinct gene expression patterns and IFN-γ regulation in response to activating receptor stimulation.

TGF-β/IFN-γ Antagonism in Subversion and Self-Defense of Phase II Coxiella burnetii-Infected Dendritic Cells

Dendritic cells (DCs) belong to the first line of innate defense and come into early contact with invading pathogens, including the zoonotic bacterium Coxiella burnetii, the causative agent of Q fever. However, the pathogen-host cell interactions in C. burnetii-infected DCs, particularly the role of mechanisms of immune subversion beyond virulent phase I lipopolysaccharide (LPS), as well as the contribution of cellular self-defense strategies, are not understood. Using phase II Coxiella-infected DCs, we show that impairment of DC maturation and MHC I downregulation is caused by autocrine release and action of immunosuppressive transforming growth factor-β (TGF-β). Our study demonstrates that IFN-γ reverses TGF-β impairment of maturation/MHC I presentation in infected DCs and activates bacterial elimination, predominantly by inducing iNOS/NO. Induced NO synthesis strongly affects bacterial growth and infectivity. Moreover, our studies hint that Coxiella-infected DCs might be able to protect themselves from mitotoxic NO by switching from oxidative phosphorylation to glycolysis, thus ensuring survival in self-defense against C. burnetii. Our results provide new insights into DC subversion by Coxiella and the IFN-γ-mediated targeting of C. burnetii during early steps in the innate immune response.

The unique role of innate lymphoid cells in cancer and the hepatic microenvironment

Cancer is a complex disease, and despite incredible progress over the last decade, it remains the leading cause of death worldwide. Liver cancers, including hepatocellular carcinoma (HCC), and liver metastases are distinct from other cancers in that they typically emerge as a consequence of long-term low-grade inflammation. Understanding the mechanisms that underpin inflammation-driven tissue remodeling of the hepatic immune environment is likely to provide new insights into much needed treatments for this devastating disease. Group 1 innate lymphoid cells (ILCs), which include natural killer (NK) cells and ILC1s, are particularly enriched in the liver and thought to contribute to the pathogenesis of a number of liver diseases, including cancer. NK cells are an attractive, but underexplored, therapeutic target in hepatic disease due to their role in immunosurveillance and their ability to recognize and eliminate malignant cells. ILC1s are closely related to and share many phenotypic features with NK cells but are less well studied. Thus, their utility in immunotherapeutic approaches is not yet well understood. Here, we review our current understanding of ILCs in cancer with a particular focus on liver and liver-related diseases.

TLR-4 Agonist Induces IFN-γ Production Selectively in Proinflammatory Human M1 Macrophages through the PI3K-mTOR- and JNK-MAPK-Activated p70S6K Pathway

IFN-γ, a proinflammatory cytokine produced primarily by T cells and NK cells, activates macrophages and engages mechanisms to control pathogens. Although there is evidence of IFN-γ production by murine macrophages, IFN-γ production by normal human macrophages and their subsets remains unknown. Herein, we show that human M1 macrophages generated by IFN-γ and IL-12- and IL-18-stimulated monocyte-derived macrophages (M0) produce significant levels of IFN-γ. Further stimulation of IL-12/IL-18-primed macrophages or M1 macrophages with agonists for TLR-2, TLR-3, or TLR-4 significantly enhanced IFN-γ production in contrast to the similarly stimulated M0, M2a, M2b, and M2c macrophages. Similarly, M1 macrophages generated from COVID-19-infected patients' macrophages produced IFN-γ that was enhanced following LPS stimulation. The inhibition of M1 differentiation by Jak inhibitors reversed LPS-induced IFN-γ production, suggesting that differentiation with IFN-γ plays a key role in IFN-γ induction. We subsequently investigated the signaling pathway(s) responsible for TLR-4-induced IFN-γ production in M1 macrophages. Our results show that TLR-4-induced IFN-γ production is regulated by the ribosomal protein S6 kinase (p70S6K) through the activation of PI3K, the mammalian target of rapamycin complex 1/2 (mTORC1/2), and the JNK MAPK pathways. These results suggest that M1-derived IFN-γ may play a key role in inflammation that may be augmented following bacterial/viral infections. Moreover, blocking the mTORC1/2, PI3K, and JNK MAPKs in macrophages may be of potential translational significance in preventing macrophage-mediated inflammatory diseases.

Targeting NK Cells to Enhance Melanoma Response to Immunotherapies

Natural killer (NK) cells are a key component of an innate immune system. They are important not only in initiating, but also in augmenting adaptive immune responses. NK cell activation is mediated by a carefully orchestrated balance between the signals from inhibitory and activating NK cell receptors. NK cells are potent producers of proinflammatory cytokines and are also able to elicit strong antitumor responses through secretion of perforin and granzyme B. Tumors can develop many mechanisms to evade NK cell antitumor responses, such as upregulating ligands for inhibitory receptors, secreting anti-inflammatory cytokines and recruiting immunosuppressive cells. Enhancing NK cell responses will likely augment the effectiveness of immunotherapies, and strategies to accomplish this are currently being evaluated in clinical trials. A comprehensive understanding of NK cell biology will likely provide additional opportunities to further leverage the antitumor effects of NK cells. In this review, we therefore sought to highlight NK cell biology, tumor evasion of NK cells and clinical trials that target NK cells.

Coxiella burnetii-Infected NK Cells Release Infectious Bacteria by Degranulation

Natural killer (NK) cells are critically involved in the early immune response against various intracellular pathogens, including Coxiella burnetii and Chlamydia psittaci Chlamydia-infected NK cells functionally mature, induce cellular immunity, and protect themselves by killing the bacteria in secreted granules. Here, we report that infected NK cells do not allow intracellular multiday growth of Coxiella, as is usually observed in other host cell types. C. burnetii-infected NK cells display maturation and gamma interferon (IFN-γ) secretion, as well as the release of Coxiella-containing lytic granules. Thus, NK cells possess a potent program to restrain and expel different types of invading bacteria via degranulation. Strikingly, though, in contrast to Chlamydia, expulsed Coxiella organisms largely retain their infectivity and, hence, escape the cell-autonomous self-defense mechanism in NK cells.

Rapid Enhancer Remodeling and Transcription Factor Repurposing Enable High Magnitude Gene Induction upon Acute Activation of NK Cells

Innate immune responses rely on rapid and precise gene regulation mediated by accessibility of regulatory regions to transcription factors (TFs). In natural killer (NK) cells and other innate lymphoid cells, competent enhancers are primed during lineage acquisition, and formation of de novo enhancers characterizes the acquisition of innate memory in activated NK cells and macrophages. Here, we investigated how primed and de novo enhancers coordinate to facilitate high-magnitude gene induction during acute activation. Epigenomic and transcriptomic analyses of regions near highly induced genes (HIGs) in NK cells both in vitro and in a model of Toxoplasma gondii infection revealed de novo chromatin accessibility and enhancer remodeling controlled by signal-regulated TFs STATs. Acute NK cell activation redeployed the lineage-determining TF T-bet to de novo enhancers, independent of DNA-sequence-specific motif recognition. Thus, acute stimulation reshapes enhancer function through the combinatorial usage and repurposing of both lineage-determining and signal-regulated TFs to ensure an effective response.

Induction of Rabies Virus Infection in Mice Brain may Up and Down Regulate Type II Interferon gamma via epigenetic modifications

As feared and deadly human diseases globally, Rabies virus contrived mechanisms to escape early immune recognition via suppression of the interferon response. This study, preliminarily investigated whether Rabies virus employs epigenetic mechanism for the suppression of the interferon using the Challenge virus standard (CVS) strain and Nigerian street Rabies virus (SRV) strain. Mice were challenged with Rabies virus (RABV) infection, and presence of RABV antigen was assessed by direct fluorescent antibody test (DFAT). A real time quantitative Polymerase chain reaction (qRT-PCR) was used to measure the expression of type II interferon gamma (IFNG) and methylation specific quantitative PCR for methylation analysis of 1FNG promoter region. Accordingly, DNA methyltransferase (DNMT) and histone acetyltransferase (HAT) enzymes activities were determined. RABV antigen was detected in all infected samples. A statistically significant increase (p < 0.05) in mRNA level of IFNG was observed at the onset of the disease and a decrease as the disease progressed. An increase in methylation in the test groups from the control group was observed, with a fluctuation in methylation as the disease progressed. DNMT and HAT activities also agree with methylation as there was an observed increase activity in test group compared with control group. Similar fluctuation pattern was observed in both CVS and SRV groups as the disease progressed with HAT, being the most active proportionally. This study suggests that epigenetic modification via DNA methylation and histone acetylation may have played a role in the expression of type II interferon gamma in Rabies virus infection. Graphical abstract.

Bromodomain inhibitor JQ1 reversibly blocks IFN-γ production

As a class, ‘BET’ inhibitors disrupt binding of bromodomain and extra-terminal motif (BET) proteins, BRD2, BRD3, BRD4 and BRDT, to acetylated histones preventing recruitment of RNA polymerase 2 to enhancers and promoters, especially super-enhancers, to inhibit gene transcription. As such, BET inhibitors may be useful therapeutics for treatment of cancer and inflammatory disease. For example, the small molecule BET inhibitor, JQ1, selectively represses MYC, an important oncogene regulated by a super-enhancer. IFN-γ, a critical cytokine for both innate and adaptive immune responses, is also regulated by a super-enhancer. Here, we show that JQ1 represses IFN-γ expression in TH1 polarized PBMC cultures, CD4+ memory T cells, and NK cells. JQ1 treatment does not reduce activating chromatin marks at the IFNG locus, but displaces RNA polymerase II from the locus. Further, IFN-γ expression recovers in polarized TH1 cultures following removal of JQ1. Our results show that JQ1 abrogates IFN-γ expression, but repression is reversible. Thus, BET inhibitors may disrupt the normal functions of the innate and adaptive immune response.

Gene expression analysis delineates the potential roles of multiple interferons in systemic lupus erythematosus

A role for interferon (IFN) in systemic lupus erythematosus (SLE) pathogenesis is inferred from the prominent IFN gene signature (IGS), but the major IFN species and its relationship to disease activity are unknown. A bioinformatic approach employing individual IFN species gene signatures to interrogate SLE microarray datasets demonstrates a putative role for numerous IFN species, with prominent expression of IFNB1 and IFNW signatures. In contrast with other SLE-affected organs, the IGS is less prominent in lupus nephritis. SLE patients with active and inactive disease have readily detectable IGS and the IGS changes synchronously with a monocyte signature but not disease activity, and is significantly related to monocyte transcripts. Monocyte over-expression of three times as many IGS transcripts as T and B cells and IGS retention in monocytes, but not T and B cells from inactive SLE patients contribute to the lack of correlation between the IGS and SLE disease activity.

Metabolic Regulation of Natural Killer Cell IFN-γ Production

Metabolism is critical for a host of cellular functions and provides a source of intracellular energy. It has been recognized recently that metabolism also regulates differentiation and effector functions of immune cells. Although initial work in this field has focused largely on T lymphocytes, recent studies have demonstrated metabolic control of innate immune cells, including natural killer (NK) cells. Here, we review what is known regarding the metabolic requirements for NK cell activation, focusing on NK cell production of interferon-gamma (IFN-γ). NK cells are innate immune lymphocytes that are poised for rapid activation during the early immune response. Although their basal metabolic rates do not change with short-term activation, they exhibit specific metabolic requirements for activation depending upon the stimulus received. These metabolic requirements for NK cell activation are altered by culturing NK cells with interleukin-15, which increases NK cell metabolic rates at baseline and shifts them toward aerobic glycolysis. We discuss the metabolic pathways important for NK cell production of IFN-γ protein and potential mechanisms whereby metabolism regulates NK cell function.

Epigenomic Views of Innate Lymphoid Cells

The discovery of innate lymphoid cells (ILCs) with selective production of cytokines typically attributed to subsets of T helper cells forces immunologists to reassess the mechanisms by which selective effector functions arise. The parallelism between ILCs and T cells extends beyond these two cell types and comprises other innate-like T lymphocytes. Beyond the recognition of specialized effector functionalities in diverse lymphocytes, features typical of T cells, such as plasticity and memory, are also relevant for innate lymphocytes. Herein, we review what we have learned in terms of the molecular mechanisms underlying these shared functions, focusing on insights provided by next generation sequencing technologies. We review data on the role of lineage-defining- and signal-dependent transcription factors (TFs). ILC regulomes emerge developmentally whereas the much of the open chromatin regions of T cells are generated acutely, in an activation-dependent manner. And yet, these regions of open chromatin in T cells and ILCs have remarkable overlaps, suggesting that though accessibility is acquired by distinct modes, the end result is that convergent signaling pathways may be involved. Although much is left to be learned, substantial progress has been made in understanding how TFs and epigenomic status contribute to ILC biology in terms of differentiation, specification, and plasticity.

Adoptively transferred natural killer cells maintain long-term antitumor activity by epigenetic imprinting and CD4+ T cell help

Natural killer (NK) cell infusions can induce remissions in subsets of patients with different types of cancer. The optimal strategies for NK cell activation prior to infusion are still under debate. There is recent evidence that NK cells can acquire long-term functional competence by preactivation with the cytokines IL-12/15/18. The mechanisms supporting the maintenance of long-term NK cell antitumor activity are incompletely under-stood. Here, we show that NK cells preactivated in vitro with IL-12/15/18, but not with IL-15 alone, maintained high antitumor activity even 1 mo after transfer into lymphopenic RAG-2^-/-γc^-/- mice. The NK cell intrinsic ability for IFNγ production coincided with demethylation of the conserved non-coding sequence (CNS) 1 in the Ifng locus, previously shown to enhance transcription of Ifng. In a xenograft melanoma mouse model, human IL-12/15/18-preactivated NK cells rejected tumors more efficiently. In RAG-2^-/-γc^-/- mice, co-transfer of CD4⁺ T cells further improved the long-term competence of NK cells for IFNγ production that was dependent on IL-2. CD4⁺ T cell activation during homeostatic proliferation required macrophages and further promoted the long-term NK cell antitumor activity. Thus, NK cells can "remember" a previous exposure to cytokines by epigenetic imprinting resulting in a remarkable stability of the IFNγ-producing phenotype after adoptive transfer. In addition, our results support combination of cytokine-preactivated NK cells with CD4⁺ T cell activation upon lymphopenic conditioning to achieve long-term NK cell effector function for cancer immunotherapy.

H3K4me3 Demethylase Kdm5a Is Required for NK Cell Activation by Associating with p50 to Suppress SOCS1

The H3K4me3 demethylase Kdm5a regulates gene transcription and is implicated in carcinogenesis. However, the role of Kdm5a in innate immune response remains poorly understood. Here, we demonstrate that Kdm5a deficiency impairs activation of natural killer (NK) cells, with decreased IFN-γ production. Accordingly, Kdm5a(-/-) mice are highly susceptible to Listeria monocytogenes (Lm) infection. During NK cell activation, loss of Kdm5a profoundly impairs phosphorylation and nuclear localization of STAT4, along with increased expression of suppressor of cytokine signaling 1 (SOCS1). Mechanistic studies reveal that Kdm5a associates with p50 and binds to the Socs1 promoter region in resting NK cells, leading to a substantial decrease in H3K4me3 modification and repressive chromatin configuration at the Socs1 promoter. Thus, Kdm5a is required for priming activation of NK cells by suppressing the suppressor, SOCS1. Our study provides insights into the epigenetic regulation of innate immune response of NK cells.

The DNA methylation profile of activated human natural killer cells

Natural killer (NK) cells are now recognized to exhibit characteristics akin to cells of the adaptive immune system. The generation of adaptive memory is linked to epigenetic reprogramming including alterations in DNA methylation. The study herein found reproducible genome wide DNA methylation changes associated with human NK cell activation. Activation led predominately to CpG hypomethylation (81% of significant loci). Bioinformatics analysis confirmed that non-coding and gene-associated differentially methylated sites (DMS) are enriched for immune related functions (i.e., immune cell activation). Known DNA methylation-regulated immune loci were also identified in activated NK cells (e.g., TNFA, LTA, IL13, CSF2). Twenty-one loci were designated high priority and further investigated as potential markers of NK activation. BHLHE40 was identified as a viable candidate for which a droplet digital PCR assay for demethylation was developed. The assay revealed high demethylation in activated NK cells and low demethylation in naïve NK, T- and B-cells. We conclude the NK cell methylome is plastic with potential for remodeling. The differentially methylated region signature of activated NKs revealed similarities with T cell activation, but also provided unique biomarker candidates of NK activation, which could be useful in epigenome-wide association studies to interrogate the role of NK subtypes in global methylation changes associated with exposures and/or disease states.

The natural killer cell response and tumor debulking are associated with prolonged survival in recurrent glioblastoma patients receiving dendritic cells loaded with autologous tumor lysates

Recurrent glioblastomas (GBs) are highly aggressive tumors associated with a 6–8 mo survival rate. In this study, we evaluated the possible benefits of an immunotherapeutic strategy based on mature dendritic cells (DCs) loaded with autologous tumor-cell lysates in 15 patients affected by recurrent GB. The median progression-free survival (PFS) of this patient cohort was 4.4 mo, and the median overall survival (OS) was 8.0 mo. Patients with small tumors at the time of the first vaccination (< 20 cm³; n = 8) had significantly longer PFS and OS than the other patients (6.0 vs. 3.0 mo, p = 0.01; and 16.5 vs. 7.0 mo, p = 0.003, respectively). CD8⁺ T cells, CD56⁺ natural killer (NK) cells and other immune parameters, such as the levels of transforming growth factor β, vascular endothelial growth factor, interleukin-12 and interferon γ (IFNγ), were measured in the peripheral blood and serum of patients before and after immunization, which enabled us to obtain a vaccination/baseline ratio (V/B ratio). An increased V/B ratio for NK cells, but not CD8⁺ T cells, was significantly associated with prolonged PFS and OS. Patients exhibiting NK-cell responses were characterized by high levels of circulating IFNγ and E4BP4, an NK-cell transcription factor. Furthermore, the NK cell V/B ratio was inversely correlated with the TGFβ2 and VEGF V/B ratios. These results suggest that tumor-loaded DCs may increase the survival rate of patients with recurrent GB after effective tumor debulking, and emphasize the role of the NK-cell response in this therapeutic setting.

Human cytomegalovirus drives epigenetic imprinting of the IFNG locus in NKG2Chi natural killer cells

Memory type 1 T helper (T(H)1) cells are characterized by the stable expression of interferon (IFN)-γ as well as by the epigenetic imprinting of the IFNG locus. Among innate cells, NK cells play a crucial role in the defense against cytomegalovirus (CMV) and represent the main source of IFN-γ. Recently, it was shown that memory-like features can be observed in NK cell subsets after CMV infection. However, the molecular mechanisms underlying NK cell adaptive properties have not been completely defined. In the present study, we demonstrated that only NKG2Chi NK cells expanded in human CMV (HCMV) seropositive individuals underwent epigenetic remodeling of the IFNG conserved non-coding sequence (CNS) 1, similar to memory CD8(+) T cells or T(H)1 cells. The accessibility of the CNS1 was required to enhance IFN-γ transcriptional activity in response to NKG2C and 2B4 engagement, which led to consistent IFN-γ production in NKG2C(hi) NK cells. Thus, our data identify epigenetic imprinting of the IFNG locus as selective hallmark and crucial mechanism driving strong and stable IFN-γ expression in HCMV-specific NK cell expansions, providing a molecular basis for the regulation of adaptive features in innate cells.

Soypeptide lunasin in cytokine immunotherapy for lymphoma

Immunostimulatory cytokines can enhance anti-tumor immunity and are part of the therapeutic armamentarium for cancer treatment. We have previously reported that post-transplant lymphoma patients have an acquired deficiency of signal transducer and activator of transcription 4, which results in defective IFNγ production during clinical immunotherapy. With the goal of further improving cytokine-based immunotherapy, we examined the effects of a soybean peptide called lunasin that synergistically works with cytokines on natural killer (NK) cells. Peripheral blood mononuclear cells of healthy donors and post-transplant lymphoma patients were stimulated with or without lunasin in the presence of IL-12 or IL-2. NK activation was evaluated, and its tumoricidal activity was assessed using in vitro and in vivo tumor models. Chromatin immunoprecipitation assay was performed to evaluate the histone modification of gene loci that are regulated by lunasin and cytokine. Adding lunasin to IL-12- or IL-2-stimulated NK cells demonstrated synergistic effects in the induction of IFNG and GZMB involved in cytotoxicity. The combination of lunasin and cytokines (IL-12 plus IL-2) was capable of restoring IFNγ production by NK cells from post-transplant lymphoma patients. In addition, NK cells stimulated with lunasin plus cytokines displayed higher tumoricidal activity than those stimulated with cytokines alone using in vitro and in vivo tumor models. The underlying mechanism responsible for the effects of lunasin on NK cells is likely due to epigenetic modulation on target gene loci. Lunasin represents a different class of immune modulating agent that may augment the therapeutic responses mediated by cytokine-based immunotherapy.

Epigenetic Activation and Silencing of the Gene that Encodes IFN-γ

Transcriptional activation and repression of genes that are developmentally regulated or exhibit cell-type specific expression patterns is largely achieved by modifying the chromatin template at a gene locus. Complex formation of stable epigenetic histone marks, loss or gain of DNA methylation, alterations in chromosome conformation, and specific utilization of both proximal and distal transcriptional enhancers and repressors all contribute to this process. In addition, long non-coding RNAs are a new species of regulatory RNAs that either positively or negatively regulate transcription of target gene loci. IFN-γ is a pro-inflammatory cytokine with critical functions in both innate and adaptive arms of the immune system. This review focuses on our current understanding of how the chromatin template is modified at the IFNG locus during developmental processes leading to its transcriptional activation and silencing.

DNA methylation dynamics in blood after hematopoietic cell transplant

Epigenetic deregulation is considered a common hallmark of cancer. Nevertheless, recent publications have demonstrated its association with a large array of human diseases. Here, we explore the DNA methylation dynamics in blood samples during hematopoietic cell transplant and how they are affected by pathophysiological events during transplant evolution. We analyzed global DNA methylation in a cohort of 47 patients with allogenic transplant up to 12 months post-transplant. Recipients stably maintained the donor’s global methylation levels after transplant. Nonetheless, global methylation is affected by chimerism status. Methylation analysis of promoters revealed that methylation in more than 200 genes is altered 1 month post-transplant when compared with non-pathological methylation levels in the donor. This number decreased by 6 months post-transplant. Finally, we analyzed methylation in IFN-γ, FASL, IL-10, and PRF1 and found association with the severity of the acute graft-versus-host disease. Our results provide strong evidence that methylation changes in blood are linked to underlying physiological events and demonstrate that DNA methylation analysis is a viable strategy for the study of transplantation and for development of biomarkers.

A CD8α(-) subpopulation of macaque circulatory natural killer cells can mediate both antibody-dependent and antibody-independent cytotoxic activities

Natural killer (NK) cells are important components of the innate immune system that mediate effector and regulatory functions. As effector cells, NK cells help control virus-infected cells through cell-mediated antibody-dependent mechanisms such as antibody-dependent cellular cytotoxicity (ADCC). Although macaques are an important and reliable animal model for the study of retrovirus-induced human diseases, and despite the crucial role played by NK cells in innate and adaptive immune responses against simian immunodeficiency virus (SIV), only a few studies have attempted to characterize different macaque NK cell subpopulations. In the present study, we identified a subpopulation of circulatory CD8α(-) macaque NK cells that express NK lineage markers and exhibit cytotoxic potential. CD8α(-) NK cells were phenotypically characterized as CD3(-) CD14(-) CD20(-) CD8α(-) cells that express NK cell markers including CD16, CD56, granzyme B, perforin, NKG2D and KIR2D. Based on their CD56/CD16 expression patterns, cells within the CD8α(-) gate can be divided into four subpopulations: CD56(dim) CD16(bright) , CD56(dim) CD16(-) , CD56(bright) CD16(-) , and CD56(-) CD16(-) cells. In contrast, CD8α(+) NK cells are 95% CD56(dim) CD16(bright) , which correlates with their high cytotoxic potential. Upon interleukin-15 activation, CD8α(-) cells up-regulated CD69 expression and produced low levels of interferon-γ and tumour necrosis factor-α. Sorted CD8α(-) NK cells were capable of killing MHC-I-devoid target cells and mediated ADCC responses against SIV gp120-coated target cells in the presence of macaque anti-gp120 antibodies. Taking into account CD8α(-) myeloid dendritic cells, we show that about 35% of macaque CD8α(-) cells represent a novel, functional population of circulatory NK cells that possesses cytotoxic potential and is capable of mediating anti-viral immune responses.

Memory-like responses of natural killer cells

Natural killer (NK) cells are lymphocytes with the capacity to produce cytokines and kill target cells upon activation. NK cells have long been categorized as members of the innate immune system and as such have been thought to follow the 'rules' of innate immunity, including the principle that they have no immunologic memory, a property thought to be strictly limited to adaptive immunity. However, recent studies have suggested that NK cells have the capacity to alter their behavior based on prior activation. This property is analogous to adaptive immune memory; however, some NK cell memory-like functions are not strictly antigen dependent and can be demonstrated following cytokine stimulation. Here, we discuss the recent evidence that NK cells can exhibit properties of immunologic memory, focusing on the ability of cytokines to non-specifically induce memory-like NK cells with enhanced responses to restimulation.

Memory-like responses of natural killer cells

Natural killer (NK) cells are lymphocytes with the capacity to produce cytokines and kill target cells upon activation. NK cells have long been categorized as members of the innate immune system and as such have been thought to follow the 'rules' of innate immunity, including the principle that they have no immunologic memory, a property thought to be strictly limited to adaptive immunity. However, recent studies have suggested that NK cells have the capacity to alter their behavior based on prior activation. This property is analogous to adaptive immune memory; however, some NK cell memory-like functions are not strictly antigen dependent and can be demonstrated following cytokine stimulation. Here, we discuss the recent evidence that NK cells can exhibit properties of immunologic memory, focusing on the ability of cytokines to non-specifically induce memory-like NK cells with enhanced responses to restimulation.

Memory-like responses of natural killer cells

Natural killer (NK) cells are lymphocytes with the capacity to produce cytokines and kill target cells upon activation. NK cells have long been categorized as members of the innate immune system and as such have been thought to follow the 'rules' of innate immunity, including the principle that they have no immunologic memory, a property thought to be strictly limited to adaptive immunity. However, recent studies have suggested that NK cells have the capacity to alter their behavior based on prior activation. This property is analogous to adaptive immune memory; however, some NK cell memory-like functions are not strictly antigen dependent and can be demonstrated following cytokine stimulation. Here, we discuss the recent evidence that NK cells can exhibit properties of immunologic memory, focusing on the ability of cytokines to non-specifically induce memory-like NK cells with enhanced responses to restimulation.

Distinct Methylation of IFNG in the Gut

Mucosal expression of proinflammatory cytokines plays a pivotal role in inflammatory bowel disease (IBD) pathogenesis. Epigenetic remodeling of chromatin via DNA methylation regulates gene expression. In this study, IFNG DNA methylation was analyzed within the mucosal compartment in both normal and IBD populations and compared to its peripheral counterparts. Overall IFNG methylation (across eight CpG sites) was significantly lower in lamina propria (LP) T cells compared to peripheral blood (PB) T cells. No methylation differences were detected when comparing PB T derived from normal to IBD patients. However, LP T-cell DNA derived from IBD patients displayed different levels of IFNG methylation of the upstream regulatory regions compared to DNA from normal controls. In fact, IFNG DNA promoter methylation levels functionally correlate with IFNG mRNA expression in unstimulated T cells, using quantitative real-time PCR. A 5% decrease in promoter methylation status is associated with nearly a 3-fold increase in IFNG expression. Likewise, methylation of the single -54 bp IFNG SnaB1 site strongly inhibited IFNG promoter expression. These results suggest that the epigenetic methylation status of IFNG may play a mechanistic role in the modulation of cytokine secretion in the mucosa.

Biochemical signaling pathways for memory T cell recall

Memory T cells exhibit low activation thresholds and rapid effector responses following antigen stimulation, contrasting naive T cells with high activation thresholds and no effector responses. Signaling mechanisms for the distinct properties of naive and memory T cells remain poorly understood. Here, I will discuss new results on signal transduction in naive and memory T cells that suggest proximal control of activation threshold and a distinct biochemical pathway to rapid recall. The signaling and transcriptional pathways controlling immediate effector function in memory T cells closely resemble pathways for rapid effector cytokine production in innate immune cells, suggesting memory T cells use innate pathways for efficacious responses.

Interferon gamma in successful pregnancies

Interferon gamma (IFNG) is a proinflammatory cytokine secreted in the uterus during early pregnancy. It is abundantly produced by uterine natural killer cells in maternal endometrium but also by trophoblasts in some species. In normal pregnancies of mice, IFNG plays critical roles that include initiation of endometrial vasculature remodeling, angiogenesis at implantation sites, and maintenance of the decidual (maternal) component of the placenta. In livestock and in humans, deviations in these processes are thought to contribute to serious gestational complications, such as fetal loss or preeclampsia. Interferon gamma has broader roles in activation of innate and adaptive immune responses to viruses and tumors, in part through upregulating transcription of genes involved in cell cycle regulation, apoptosis, and antigen processing/presentation. Despite this, rodent and human trophoblast cells show dampened responses to IFNG that reflect the resistance of these cells to IFNG-mediated activation of major histocompatibility complex (MHC) class II transplantation antigen expression. Lack of MHC class II antigens on trophoblasts is thought to facilitate survival of the semiallogeneic conceptus in the presence of maternal lymphocytes. This review describes the dynamic roles of IFNG in successful pregnancy and briefly summarizes data on IFNG in gestational pathologies.

Self-antigen prevents CD8 T cell effector differentiation by CD134 and CD137 dual costimulation

We compared how CD4 vs CD8 cells attain the capacity to express the effector cytokine IFN-gamma under both immunogenic and tolerogenic conditions. Although the Ifng gene locus was epigenetically repressed in naive Ag-inexperienced CD4 cells, it had already undergone partial remodeling toward a transcriptionally competent configuration in naive CD8 cells. After TCR stimulation, CD8 cells fully remodeled the Ifng locus and gained the capacity to express high levels of IFN-gamma more rapidly than CD4 cells. Enforced dual costimulation through OX40 and 4-1BB redirected CD8 cells encountering soluble exogenous peptide to expand and differentiate into IFN-gamma and TNF-alpha double-producing effectors rather than becoming tolerant. Despite this and the stronger tendency of CD8 compared with CD4 cells to differentiate into IFN-gamma-expressing effectors, when parenchymal self-Ag was the source of tolerizing Ag, enforced dual costimulation selectively boosted expansion but did not push effector differentiation in CD8 cells while both expansion and effector differentiation were dramatically boosted in CD4 cells. Notably, enforced dual costimulation was able to push effector differentiation in CD8 cells encountering cognate parenchymal self-Ag when CD4 cells were simultaneously engaged. Thus, the ability of enforced OX40 plus 4-1BB dual costimulation to redirect CD8 cells to undergo effector differentiation was unexpectedly influenced by the source of tolerizing Ag and help was selectively required to facilitate CD8 cell effector differentiation when the tolerizing Ag derived from self.

KIR2DL4 differentially signals downstream functions in human NK cells through distinct structural modules

KIR2DL4 (2DL4) is a member of the killer cell Ig-like receptor (KIR) family in human NK cells. It can stimulate potent cytokine production and weak cytolytic activity in resting NK cells, but the mechanism for 2DL4-mediated signaling remains unclear. In this study we characterized the signaling pathways stimulated by 2DL4 engagement. In a human NK-like cell line, KHYG-1, cross-linking of 2DL4 activated MAPKs including JNK, ERK, and p38. Furthermore, 2DL4 cross-linking resulted in phosphorylation of IkappaB kinase beta (IKKbeta) and the phosphorylation and degradation of IkappaBalpha, which indicate activation of the classical NF-kappaB pathway. Engagement of 2DL4 was also shown to activate the transcription and translation of a variety of cytokine genes, including TNF-alpha, IFN-gamma, MIP1alpha, MIP1beta, and IL-8. Pharmacological inhibitors of JNK, MEK1/2 and p38, blocked IFN-gamma, IL-8, and MIP1alpha production, suggesting that MAPKs are regulating 2DL4-mediated cytokine production in a nonredundant manner. Activation of both p38 and ERK appear to be upstream of the stimulation of NF-kappaB. Mutation of a transmembrane arginine in 2DL4 to glycine (R/G mutant) abrogated FcepsilonRI-gamma association, as well as receptor-mediated cytolytic activity and calcium responses. Surprisingly, the R/G mutant still activated MAPKs and the NF-kappaB pathway and selectively stimulated the production of MIP1alpha, but not that of IFN-gamma or IL-8. In conclusion, we provide evidence that the activating functions of 2DL4 can be compartmentalized into two distinct structural modules: 1) through transmembrane association with FcepsilonRI-gamma; and 2) through another receptor domain independent of the transmembrane arginine.

Differential effects of ifosfamide on dendritic cell-mediated stimulation of T cell interleukin-2 production, natural killer cell cytotoxicity and interferon-gamma production

Ifosfamide is a DNA-alkylating agent used frequently in chemotherapy of human malignancies. Ifosfamide and its major decomposition products deplete intracellular glutathione (GSH). Glutathione is the major intracellular thiol reductant that protects cells against oxidative injury. Ifosfamide depletion of intracellular GSH in human dendritic cells (DC), T cells and natural killer (NK) cells impairs their functional activity which can be restored by reconstituting GSH. Here we assessed the effect of ifosfamide on DC-mediated stimulation of NK cell proliferation via T cells and on direct DC stimulation of NK cell cytotoxicity and interferon (IFN)-gamma production. Indirect DC stimulation of NK cell proliferation via T cells and T cell-derived interleukin (IL)-2 were reduced by ifosfamide treatment of DC and reconstitution of GSH in DC restored both responses. When DC and NK cells were treated with ifosfamide, DC could overcome the negative effect of ifosfamide on NK cytotoxic function whereas NK cell IFN-gamma production was less efficiently restored. The ability of IL-2 activated NK cells to kill autologous immature DC or to induce DC maturation was reduced moderately by treatment of both cell types with ifosfamide. Overall, our results suggest that DC may stimulate anti-tumour effector cells in patients even if they had received treatment with chemotherapeutic agents such as ifosfamide.

ATF3 regulates MCMV infection in mice by modulating IFN-gamma expression in natural killer cells

Activating transcription factor 3 (ATF3) is a negative regulator of proinflammatory cytokine expression in macrophages, and ATF3-deficient mice are more susceptible to endotoxic shock. Here, we demonstrate that ATF3 interacts with a cis-regulatory element of the IFN-gamma gene in natural killer (NK) cells, and that ATF3null NK cells show increased transcription and secretion of IFN-gamma. NK cell-derived IFN-gamma has previously been demonstrated to be protective against murine cytomegalovirus (MCMV) infection, and we show here that ATF3null mice exhibit decreased hepatic viral load and reduced liver histopathology upon challenge with MCMV. Reconstitution of NK-deficient mice with ATF3null NK cells more effectively controlled MCMV infection than mice reconstituted with WT cells, indicating that ATF3 acts within NK cells to regulate antiviral responses.

Regulation of interferon-gamma during innate and adaptive immune responses

Interferon-gamma (IFN-gamma) is crucial for immunity against intracellular pathogens and for tumor control. However, aberrant IFN-gamma expression has been associated with a number of autoinflammatory and autoimmune diseases. This cytokine is produced predominantly by natural killer (NK) and natural killer T (NKT) cells as part of the innate immune response, and by Th1 CD4 and CD8 cytotoxic T lymphocyte (CTL) effector T cells once antigen-specific immunity develops. Herein, we briefly review the functions of IFN-gamma, the cells that produce it, the cell extrinsic signals that induce its production and influence the differentiation of naïve T cells into IFN-gamma-producing effector T cells, and the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine. We then review and discuss recent insights regarding the molecular regulation of IFN-gamma, focusing on work that has led to the identification and characterization of distal regulatory elements and epigenetic modifications with the IFN-gamma locus (Ifng) that govern its expression. The epigenetic modifications and three-dimensional structure of the Ifng locus in naive CD4 T cells, and the modifications they undergo as these cells differentiate into effector T cells, suggest a model whereby the chromatin architecture of Ifng is poised to facilitate either rapid opening or silencing during Th1 or Th2 differentiation, respectively.

Epigenetic regulation of tumor necrosis factor alpha

Tumor necrosis factor alpha (TNF-alpha) is a potent cytokine which regulates inflammation via the induction of adhesion molecules and chemokine expression. Its expression is known to be regulated in a complex manner with transcription, message turnover, message splicing, translation, and protein cleavage from the cell surface all being independently regulated. This study examined both cell lines and primary cells to understand the developmental regulation of epigenetic changes at the TNF-alpha locus. We demonstrate that epigenetic modifications of the TNF-alpha locus occur both developmentally and in response to acute stimulation and, importantly, that they actively regulate expression. DNA demethylates early in development, beginning with the hematopoietic stem cell. The TNF-alpha locus migrates from heterochromatin to euchromatin in a progressive fashion, reaching euchromatin slightly later in differentiation. Finally, histone modifications characteristic of a transcriptionally competent gene occur with myeloid differentiation and progress with differentiation. Additional histone modifications characteristic of active gene expression are acquired with stimulation. In each case, manipulation of these epigenetic variables altered the ability of the cell to express TNF-alpha. These studies demonstrate the importance of epigenetic regulation in the control of TNF-alpha expression. These findings may have relevance for inflammatory disorders in which TNF-alpha is overproduced.

Epigenetic and transcriptional programs lead to default IFN-gamma production by gammadelta T cells

Gammadelta T cells have unique features and functions compared with alphabeta T cells and have been proposed to bridge the innate and adaptive immune responses. Our earlier studies demonstrated that splenic gammadelta T cells predominantly produce IFN-gamma upon activation in vitro, which is partially due to the expression of the Th1-specific transcription factor T-bet. In this study we have explored the epigenetic and transcriptional programs that underlie default IFN-gamma production by gammadelta T cells. We show that the kinetics of IFN-gamma transcription is faster in gammadelta T cells compared with CD4(+) and CD8(+) T cells and that gammadelta T cells produce significantly greater amounts of IFN-gamma in a proliferation-independent manner when compared with other T cell subsets. By analyzing the methylation pattern of intron 1 of the ifn-gamma locus, we demonstrate that this region in naive gammadelta T cells is hypomethylated relative to the same element in naive CD4(+) and CD8(+) T cells. Furthermore, naive gammadelta T cells constitutively express eomesodermin (Eomes), a transcription factor important for IFN-gamma production in CD8(+) T cells, and Eomes expression levels are enhanced upon activation. Retroviral transduction of activated gammadelta T cells from both wild-type and T-bet-deficient mice with a dominant negative form of Eomes significantly reduced IFN-gamma production, indicating a critical role for this transcription factor in mediating IFN-gamma production by gammadelta T cells in a T-bet-independent manner. Our results demonstrate that both epigenetic and transcriptional programs contribute to the early vigorous IFN-gamma production by gammadelta T cells.

Zygotically activated genes are suppressed in mouse nuclear transferred embryos

Mammalian oocytes have the ability to confer totipotency to terminally differentiated somatic cell nuclei. Viable cloned animals have been produced by somatic cell nuclear transfer (NT) into oocytes in many mammalian species including mouse. However, the success rates of the production were quite low in all species. Many studies have measured differences in gene expression between NT and fertilized embryos in relatively advanced stages of development such as pre- and post-natal stages or the blastocyst stage. In the present study, we compared gene expression patterns using differential display RT-PCR (DDRT-PCR) between the NT and IVF embryos at the 2-cell stage to detect some abnormalities affecting later development of NT embryos. Aberrant gene expression was detected in NT embryos compared with IVF embryos, and MuERV-L and Dnaja2 genes were down-regulated and Inpp5b and Chst12 genes were up-regulated in the NT embryos. Further analysis showed that the expression of zygotically activated genes such as Interferon-gamma, Dub-1, Spz1, DD2106 (unknown gene), and DD2111 (unknown gene) were suppressed in NT embryos, suggesting that the cellular process involved in the nuclear reprogramming of somatic nucleus is not appropriately regulated.

NK cell-derived IFN-gamma differentially regulates innate resistance and neutrophil response in T cell-deficient hosts infected with Mycobacterium tuberculosis

Although it is known that IFN-gamma-secreting T cells are critical for control of Mycobacterium tuberculosis infection, the contribution of IFN-gamma produced by NK cells to host resistance to the pathogen is less well understood. By using T cell-deficient RAG(-/-) mice, we showed that M. tuberculosis stimulates NK cell-dependent IFN-gamma production in naive splenic cultures and in lungs of infected animals. More importantly, common cytokine receptor gamma-chain(-/-)RAG(-/-) animals deficient in NK cells, p40(-/-)RAG(-/-), or anti-IFN-gamma mAb-treated RAG(-/-) mice displayed significantly increased susceptibility to M. tuberculosis infection compared with untreated NK-sufficient RAG(-/-) controls. Studies comparing IL-12 p40- and p35-deficient RAG(-/-) mice indicated that IL-12 plays a more critical role in the induction of IFN-gamma-mediated antimycobacterial effector functions than IL-23 or other p40-containing IL-12 family members. The increased susceptibility of IL-12-deficient or anti-IFN-gamma mAb-treated RAG(-/-) mice was associated not only with elevated bacterial loads, but also with the development of granulocyte-enriched foci in lungs. This tissue response correlated with increased expression of the granulocyte chemotactic chemokines KC and MIP-2 in NK as well as other leukocyte populations. Interestingly, depletion of granulocytes further increased bacterial burdens and exacerbated pulmonary pathology in these animals, revealing a compensatory function for neutrophils in the absence of IFN-gamma. The above observations indicate that NK cell-derived IFN-gamma differentially regulates T-independent resistance and granulocyte function in M. tuberculosis infection and suggest that this response could serve as an important barrier in AIDS patients or other individuals with compromised CD4+ T cell function.

Impaired interferon-gamma production in response to live bacteria and Toll-like receptor agonists in patients with ataxia telangiectasia

Ataxia telangiectasia (AT) is a pleiotropic autosomal recessive neurodegenerative disorder with associated immunodeficiency and cancer predisposition, caused by mutational inactivation of the ATM gene. Early death usually results from lymphoreticular malignancy or recurrent, chronic respiratory infections. Immune deficiency of AT patients is heterogeneous and involves both humoral and cellular responses. Reports on the number and integrity of immunocompetent cells in AT are conflicting. In the early phase of infection, the interleukin (IL)-12/interferon (IFN)-gamma axis plays a crucial role in first-line defence against pathogens. In a whole blood assay we studied the IL-12/IFN-gamma axis in the immune response of AT cells to the Toll-like receptor agonists lipopolysaccharide and heat-killed Staphylococcus aureus, as well as whole live M. bovis bacille Calmette-Guérin (BCG). The function of AT antigen-presenting cells was normal in terms of IL-12 production, while IFN-gamma production by T and natural killer (NK) cells was severely impaired, even in the presence of adequate co-stimulation by exogenous IL-12.

Rapid Demethylation of the IFN-γ Gene Occurs in Memory but Not Naive CD8 T Cells

DNA methylation is an epigenetic mechanism of gene regulation. We have determined that specific modifications in DNA methylation at the IFN-gamma locus occur during memory CD8 T cell differentiation in vivo. Expression of the antiviral cytokine IFN-gamma in CD8 T cells is highly developmental stage specific. Most naive cells must divide before they express IFN-gamma, while memory cells vigorously express IFN-gamma before cell division. Ag-specific CD8 T cells were obtained during viral infection of mice and examined directly ex vivo. Naive cells had an IFN-gamma locus with extensive methylation at three specific CpG sites. An inhibitor of methylation increased the amount of IFN-gamma in naive cells, indicating that methylation contributes to the slow and meager production of IFN-gamma. Effectors were unmethylated and produced large amounts of IFN-gamma. Interestingly, while memory cells were also able to produce large amounts of IFN-gamma, the gene was partially methylated at the three CpG sites. Within 5 h of antigenic stimulation, however, the gene was rapidly demethylated in memory cells. This was independent of DNA synthesis and cell division, suggesting a yet unidentified demethylase. Rapid demethylation of the IFN-gamma promoter by an enzymatic factor only in memory cells would be a novel mechanism of differential gene regulation. This differentiation stage-specific mechanism reflects a basic immunologic principle: naive cells need to expand before becoming an effective defense factor, whereas memory cells with already increased precursor frequency can rapidly mount effector functions to eliminate reinfecting pathogens in a strictly Ag-dependent fashion.

Natural killer cell behavior in lymph nodes revealed by static and real-time imaging

Natural killer (NK) cells promote dendritic cell (DC) maturation and influence T cell differentiation in vitro. To better understand the nature of the putative interactions among these cells in vivo during the early phases of an adaptive immune response, we have used immunohistochemical analysis and dynamic intravital imaging to study NK cell localization and behavior in lymph nodes (LNs) in the steady state and shortly after infection with Leishmania major. In the LNs of naive mice, NK cells reside in the medulla and the paracortex, where they closely associate with DCs. In contrast to T cells, intravital microscopy revealed that NK cells in the superficial regions of LNs were slowly motile and maintained their interactions with DCs over extended times in the presence or absence of immune-activating signals. L. major induced NK cells to secrete interferon-γ and to be recruited to the paracortex, where concomitant CD4 T cell activation occurred. Therefore, NK cells form a reactive but low mobile network in a strategic area of the LN where they can receive inflammatory signals, interact with DCs, and regulate colocalized T cell responses.

Opposing roles of NF-kappaB family members in the regulation of NK cell proliferation and production of IFN-gamma

It is well established that the nuclear factor-kappaB (NF-kappaB) family of transcription factors participates in the regulation of many aspects of innate and adaptive immunity. The majority of these reports have focused on the role of NF-kappaB in accessory cell and T or B cell function, but less is known about the role of NF-kappaB in NK cells. However, several studies have demonstrated that these transcription factors are required for NK cell production of IFN-gamma and proliferation. The studies presented here examine the role of two NF-kappaB members, c-Rel and p50, in NK cell function. In vitro data revealed that in the absence of c-Rel, NK cells have a defect in their ability to secrete IFN-gamma, but remain unaffected in their capacity to proliferate. In contrast, p50-/- NK cells have enhanced proliferative and IFN-gamma responses compared with wild-type NK cells. The latter findings suggest a role for p50 as a negative regulator of NK cell production of IFN-gamma and chromatin immunoprecipitation assays demonstrated the association of p50 with the IFN-gamma promoter of resting NK cells. Consistent with the in vitro studies, in vivo studies with NF-kappaB gene-deficient mice infected with Toxoplasma gondii revealed that the absence of p50 leads to enhanced NK cell proliferation and production of IFN-gamma. Together, these studies define distinct roles for c-Rel and p50 in the function of NK cells.

T-bet concomitantly controls migration, survival, and effector functions during the development of Valpha14i NKT cells

Valpha14i natural killer T (NKT)-cell function has been implicated in a number of disease conditions. The molecular events that drive Valpha14i NKT-cell development remain elusive. We recently showed that T-bet is required for the terminal maturation of these cells. Here we identify some of the genetic targets of T-bet during Valpha14i NKT-cell lineage development. Microarray gene-expression analyses on developing Valpha14i NKT cells were performed and provide a molecular framework to study these maturation events. In vitro ectopic expression of T-bet in immature Valpha14i NKT cells, which do not yet express T-bet, was sufficient to promote Valpha14i NKT-cell maturation, driving the expression of multiple genes, including those that participate in migration, survival, and effector functions. By regulating the expression of T-helper 1 (Th1)-associated cytokines, chemokines, chemokine receptors, and molecules involved in cytolysis, T-bet defines the unique lineage attributes of mature Valpha14i NKT cells and acts to link these attributes to a developmental process.

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

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

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

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

LNFPIII/LeX-stimulated macrophages activate natural killer cells via CD40-CD40L interaction

Lacto-N-fucopentaose III (LNFPIII) is a human milk sugar containing the biologically active Lewis X (LeX) trisaccharide. LNFPIII/LeX is also expressed by immunosuppressive helminth parasites, by bacteria, and on a number of tumor/cancer cells. In this report, we first demonstrate that LNFPIII activates macrophages in vitro as indicated by upregulation of Gr-1 expression on F4/80(+) cells. Further, we investigated the effect of LNFPIII-activated macrophages on NK cell activity. We found that LNFPIII-stimulated F4/80(+) cells were able to activate NK cells, inducing upregulation of CD69 expression and gamma interferon (IFN-gamma) production. The experiments show that NK cell activation is macrophage dependent, since NK cells alone did not secrete IFN-gamma in response to LNFPIII. Furthermore, we found that activation of NK cells by glycan-stimulated macrophages required cell-cell contact. As part of the cell-cell contact mechanism, we determined that CD40-CD40L interaction was critical for IFN-gamma secretion by NK cells, as the addition of anti-CD40L antibodies to the coculture blocked IFN-gamma production. We also demonstrated that LNFPIII-stimulated macrophages secrete prostaglandin E(2), interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-alpha) but a very low level of IL-12. Interestingly, addition of anti-TNF-alpha, anti-IL-10, or anti-IL-12 monoclonal antibodies did not significantly alter NK cell activity. Our data show that these soluble mediators are not critical for LNFPIII-stimulated macrophage activation of NK cells and provide further evidence for the importance of cell-cell contact and CD40-CD40L interactions between macrophages and NK cells.

Intracellular bacteria differentially regulated endothelial cytokine release by MAPK-dependent histone modification

Epigenetic histone modifications contribute to the regulation of eukaryotic gene transcription. The role of epigenetic regulation in immunity to intracellular pathogens is poorly understood. We tested the hypothesis that epigenetic histone modifications influence cytokine expression by intracellular bacteria. Intracellular Listeria monocytogenes, but not noninvasive Listeria innocua, induced release of distinct CC and CXC chemokines, as well as Th1 and Th2 cytokines and growth factors by endothelial cells. Cytokine expression was in part dependent on p38 MAPK and MEK1. We analyzed global histone modification and modifications in detail at the gene promoter of IL-8, which depended on both kinase pathways, and of IFN-gamma, which was not blocked by kinase inhibition. Intracellular Listeria induced time-dependent acetylation (lysine 8) of histone H4 and phosphorylation/acetylation (serine 10/lysine 14) of histone H3 globally and at the il8 promoter in HUVEC, as well as recruitment of the histone acetylase CREB-binding protein. Inhibitors of p38 MAPK and MEK1 reduced lysine 8 acetylation of histone H4 and serine 10/lysine 14 phosphorylation/acetylation of histone H3 in Listeria-infected endothelial cells and disappearance of histone deacetylase 1 at the il8 promoter in HUVEC. In contrast, IFN-gamma gene transcription was activated by Listeria monocytogenes independent of p38 MAPK and MEK1, and histone phosphorylation/acetylation remained unchanged in infected cells at the IFN-gamma promoter. Specific inhibition of histone deacetylases by trichostatin A increased Listeria-induced expression of IL-8, but not of IFN-gamma, underlining the specific physiological impact of histone acetylation. In conclusion, MAPK-dependent epigenetic modifications differentially contributed to L. monocytogenes-induced cytokine expression by human endothelial cells.