IFN Regulatory Factor-2 Deficiency Revealed a Novel Checkpoint Critical for the Generation of Peripheral NK Cells

Deletion of the mRNA endonuclease Regnase-1 promotes NK cell anti-tumor activity via OCT2-dependent transcription of Ifng

Limited infiltration and activity of natural killer (NK) and T cells within the tumor microenvironment (TME) correlate with poor immunotherapy responses. Here, we examined the role of the endonuclease Regnase-1 on NK cell anti-tumor activity. NK cell-specific deletion of Regnase-1 (Reg1ΔNK) augmented cytolytic activity and interferon-gamma (IFN-γ) production in vitro and increased intra-tumoral accumulation of Reg1ΔNK-NK cells in vivo, reducing tumor growth dependent on IFN-γ. Transcriptional changes in Reg1ΔNK-NK cells included elevated IFN-γ expression, cytolytic effectors, and the chemokine receptor CXCR6. IFN-γ induced expression of the CXCR6 ligand CXCL16 on myeloid cells, promoting further recruitment of Reg1ΔNK-NK cells. Mechanistically, Regnase-1 deletion increased its targets, the transcriptional regulators OCT2 and IκBζ, following interleukin (IL)-12 and IL-18 stimulation, and the resulting OCT2-IκBζ-NF-κB complex induced Ifng transcription. Silencing Regnase-1 in human NK cells increased the expression of IFNG and POU2F2. Our findings highlight NK cell dysfunction in the TME and propose that targeting Regnase-1 could augment active NK cell persistence for cancer immunotherapy.

Characterization and expression analysis of the interferon regulatory factor (IRF) gene family in zig-zag eel (Mastacembelus armatus) against Aeromonas veronii infection

Interferon regulatory factors (IRFs) play an important role in innate and adaptive immune system. However, in teleosts, the data on IRFs is still scarce. Here, for the first time, we identified 11 members of IRFs from the zig-zag eel Mastacembelus armatus (MarIRF1-10). The deduced protein sequences are highly conserved among different fish species especially in DBD and IAD domain. Phylogenetic analysis indicated that MarIRFs preferentially grouped with fish species in Synbranchiformes or Perciformes. Expression analysis showed that MarIRFs were expressed in all nine tissues including spleen, gill, muscle and intestine. After infected by Aeromonas veronii, expression of MarIRF2, MaIRF4b and MaIRF5 were significantly upregulated in spleen, MarIRF1, MarIRF2 were significantly upregulated in kidney, but in liver, nearly all MarIRFs were downregulated. Taken together, this study first reported molecular characterization and expression patterns of 11 IRFs in the zig-zag eel. All these results will contribute a lot to better understanding the antibacterial mechanism of IRFs in teleosts.

IRF2 is required for development and functional maturation of human NK cells

Natural killer (NK) cells are cytotoxic and cytokine-producing lymphocytes that play an important role in the first line of defense against malignant or virus-infected cells. A better understanding of the transcriptional regulation of human NK cell differentiation is crucial to improve the efficacy of NK cell-mediated immunotherapy for cancer treatment. Here, we studied the role of the transcription factor interferon regulatory factor (IRF) 2 in human NK cell differentiation by stable knockdown or overexpression in cord blood hematopoietic stem cells and investigated its effect on development and function of the NK cell progeny. IRF2 overexpression had limited effects in these processes, indicating that endogenous IRF2 expression levels are sufficient. However, IRF2 knockdown greatly reduced the cell numbers of all early differentiation stages, resulting in decimated NK cell numbers. This was not caused by increased apoptosis, but by decreased proliferation. Expression of IRF2 is also required for functional maturation of NK cells, as the remaining NK cells after silencing of IRF2 had a less mature phenotype and showed decreased cytotoxic potential, as well as a greatly reduced cytokine secretion. Thus, IRF2 plays an important role during development and functional maturation of human NK cells.

Heavy oil exposure suppresses antiviral activities in Japanese flounder Paralichthys olivaceus infected with viral hemorrhagic septicemia virus (VHSV)

A combined treatment of heavy oil (HO) exposure and virus infection induces increased mortality in Japanese flounder (Paralichthys olivaceus). In this study, we addressed how HO exposure affects the immune system, especially antiviral activities, in Japanese flounder. The fish were infected with viral hemorrhagic septicemia virus (VHSV), followed by exposure to HO. We analyzed virus titers in the heart and mRNA expression in the kidney of surviving fish. The virus titers in fish exposed to heavy oil were higher than the threshold for onset. The results suggest that HO exposure may allow the replication of VHSV, leading to higher mortality in the co-treated group. Gene-expression profiling demonstrated that the expression of antiviral-activity-related genes, such as those for interferon and apoptosis induction, were lower in the co-treated group than in the group with VHSV infection only. These results helped explain the high virus titers in fish treated with both stressors. Thus, interferon production in the virus-infected cells and apoptosis induction by natural killer cells worked normally in the VHSV-infected fish without HO exposure, but these antiviral activities were slightly suppressed by HO exposure, possibly leading to extensive viral replication in the host cells and the occurrence of VHS.

Landscape and Dynamics of the Transcriptional Regulatory Network During Natural Killer Cell Differentiation

Natural killer (NK) cells are essential in controlling cancer and infection. However, little is known about the dynamics of the transcriptional regulatory machinery during NK cell differentiation. In this study, we applied the assay of transposase accessible chromatin with sequencing (ATAC-seq) technique in a home-developed in vitro NK cell differentiation system. Analysis of ATAC-seq data illustrated two distinct transcription factor (TF) clusters that dynamically regulate NK cell differentiation. Moreover, two TFs from the second cluster, FOS-like 2 (FOSL2) and early growth response 2 (EGR2), were identified as novel essential TFs that control NK cell maturation and function. Knocking down either of these two TFs significantly impacted NK cell differentiation. Finally, we constructed a genome-wide transcriptional regulatory network that provides a better understanding of the regulatory dynamics during NK cell differentiation.

Effects of caloric restriction on immunosurveillance, microbiota and cancer cell phenotype: Possible implications for cancer treatment

Fasting, caloric restriction and foods or compounds mimicking the biological effects of caloric restriction, known as caloric restriction mimetics, have been associated with a lower risk of age-related diseases, including cardiovascular diseases, cancer and cognitive decline, and a longer lifespan. Reduced calorie intake has been shown to stimulate cancer immunosurveillance, reducing the migration of immunosuppressive regulatory T cells towards the tumor bulk. Autophagy stimulation via reduction of lysine acetylation, increased sensitivity to chemo- and immunotherapy, along with a reduction of insulin-like growth factor 1 and reactive oxygen species have been described as some of the major effects triggered by caloric restriction. Fasting and caloric restriction have also been shown to beneficially influence gut microbiota composition, modify host metabolism, reduce total cholesterol and triglyceride levels, lower diastolic blood pressure and elevate morning cortisol level, with beneficial modulatory effects on cardiopulmonary fitness, body fat and weight, fatigue and weakness, and general quality of life. Moreover, caloric restriction may reduce the carcinogenic and metastatic potential of cancer stem cells, which are generally considered responsible of tumor formation and relapse. Here, we reviewed in vitro and in vivo studies describing the effects of fasting, caloric restriction and some caloric restriction mimetics on immunosurveillance, gut microbiota, metabolism, and cancer stem cell growth, highlighting the molecular and cellular mechanisms underlying these effects. Additionally, studies on caloric restriction interventions in cancer patients or cancer risk subjects are discussed. Considering the promising effects associated with caloric restriction and caloric restriction mimetics, we think that controlled-randomized large clinical trials are warranted to evaluate the inclusion of these non-pharmacological approaches in clinical practice.

NK Cell Development in Times of Innate Lymphoid Cell Diversity

After being described in the 1970s as cytotoxic cells that do not require MHC-dependent pre-activation, natural killer (NK) cells remained the sole member of innate lymphocytes for decades until lymphoid tissue-inducer cells in the 1990s and helper-like innate lymphoid lineages from 2008 onward completed the picture of innate lymphoid cell (ILC) diversity. Since some of the ILC members, such as ILC1s and CCR6^- ILC3s, share specific markers previously used to identify NK cells, these findings provoked the question of how to delineate the development of NK cell and helper-like ILCs and how to properly identify and genetically interfere with NK cells. The description of eomesodermin (EOMES) as a lineage-specifying transcription factor of NK cells provided a candidate that may serve as a selective marker for the genetic targeting and identification of NK cells. Unlike helper-like ILCs, NK cell activation is, to a large degree, regulated by the engagement of activating and inhibitory surface receptors. NK cell research has revealed some elegant mechanisms of immunosurveillance, coined "missing-self" and "induced-self" recognition, thus complementing "non-self recognition", which is predominantly utilized by adaptive lymphocytes and myeloid cells. Notably, the balance of activating and inhibitory signals perceived by surface receptors can be therapeutically harnessed for anti-tumor immunity mediated by NK cells. This review aims to summarize the similarities and the differences in development, function, localization, and phenotype of NK cells and helper-like ILCs, with the purpose to highlight the unique feature of NK cell development and regulation.

SRC-3 Functions as a Coactivator of T-bet by Regulating the Maturation and Antitumor Activity of Natural Killer Cells

Natural killer (NK)-cell development and maturation is a well-organized process. The steroid receptor coactivator 3 (SRC-3) is a regulator of the hematopoietic and immune systems; however, its role in NK cells is poorly understood. Here, SRC-3 displayed increased nuclear translocation in NK cells during terminal differentiation and upon inflammatory cytokine stimulation. Targeted deletion of SRC-3 altered normal NK-cell distribution and compromised NK-cell maturation. SRC-3 deficiency led to significantly impaired NK-cell functions, especially their antitumor activity. The expression of several critical T-bet target genes, including Zeb2, Prdm1, and S1pr5, but not T-bet itself, was markedly decreased in NK cells in the absence of SRC-3. There was a physiologic interaction between SRC-3 and T-bet proteins, where SRC-3 was recruited by T-bet to regulate the transcription of the aforementioned genes. Collectively, our findings unmask a previously unrecognized role of SRC-3 as a coactivator of T-bet in NK-cell biology and indicate that targeting SRC-3 may be a promising strategy to increase the tumor surveillance function of NK cells.

Transcriptional Regulation of Natural Killer Cell Development and Functions

Natural killer (NK) cells are the major lymphocyte subset of the innate immune system. Their ability to mediate anti-tumor cytotoxicity and produce cytokines is well-established. However, the molecular mechanisms associated with the development of human or murine NK cells are not fully understood. Knowledge is being gained about the environmental cues, the receptors that sense the cues, signaling pathways, and the transcriptional programs responsible for the development of NK cells. Specifically, a complex network of transcription factors (TFs) following microenvironmental stimuli coordinate the development and maturation of NK cells. Multiple TFs are involved in the development of NK cells in a stage-specific manner. In this review, we summarize the recent advances in the understandings of TFs involved in the regulation of NK cell development, maturation, and effector function, in the aspects of their mechanisms, potential targets, and functions.

Generation of a common innate lymphoid cell progenitor requires interferon regulatory factor 2

Innate lymphoid cells (ILCs), composed of heterogeneous populations of lymphoid cells, contribute critically to immune surveillance at mucosal surfaces. ILC subsets develop from common lymphoid progenitors through stepwise lineage specification. However, the composition and temporal regulation of the transcription factor network governing such a process remain incompletely understood. Here, we report that deletion of the transcription factor interferon regulatory factor 2 (IRF-2), known also for its importance in the maturation of conventional NK cells, resulted in an impaired generation of ILC1, ILC2 and ILC3 subsets with lymphoid tissue inducer (LTi)-like cells hardly affected. In IRF-2-deficient mice, PD-1hi ILC precursors (ILCPs) that generate these three ILCs but not LTi-like cells were present at normal frequency, while their sub-population expressing high amounts of PLZF, another marker for ILCPs, was severely reduced. Notably, these IRF-2-deficient ILCPs contained normal quantities of PLZF-encoding Zbtb16 messages, and PLZF expression in developing invariant NKT cells within the thymus was unaffected in these mutant mice. These results point to a unique, cell-type selective role for IRF-2 in ILC development, acting at a discrete step critical for the generation of functionally competent ILCPs.

Transcriptional control of natural killer cell differentiation

Natural killer (NK) cells are highly specialized cytotoxic lymphocytes that provide protection against pathogens and malignant cells. They develop from common lymphoid progenitors via a multi-stage lineage commitment and differentiation process that gives rise to mature NK cells with potent cytotoxic functionality. Although generally considered cells of the innate immune system, recent studies have demonstrated that NK cells have the capacity to mount immune responses with features of adaptive immunity, including robust antigen-specific clonal-like expansion and the generation of long-lived memory cells that mediate enhanced recall responses. Here, we discuss specific transcription factors that have been shown to commonly and uniquely regulate NK cell development and effector and memory responses in experimental mouse models.

Loss of Canonical Notch Signaling Affects Multiple Steps in NK Cell Development in Mice

Within the hematopoietic system, the Notch pathway is critical for promoting thymic T cell development and suppressing the B and myeloid lineage fates; however, its impact on NK lymphopoiesis is less understood. To study the role of Notch during NK cell development in vivo, we investigated different NK cell compartments and function in Rbp-Jk^fl/flVav-Cre^tg/+ mice, in which Rbp-Jk, the major transcriptional effector of canonical Notch signaling, was specifically deleted in all hematopoietic cells. Peripheral conventional cytotoxic NK cells in Rbp-Jk-deleted mice were significantly reduced and had an activated phenotype. Furthermore, the pool of early NK cell progenitors in the bone marrow was decreased, whereas immature NK cells were increased, leading to a block in NK cell maturation. These changes were cell intrinsic as the hematopoietic chimeras generated after transplantation of Rbp-Jk-deficient bone marrow cells had the same NK cell phenotype as the Rbp-Jk-deleted donor mice, whereas the wild-type competitors did not. The expression of several crucial NK cell regulatory pathways was significantly altered after Rbp-Jk deletion. Together, these results demonstrate the involvement of canonical Notch signaling in regulation of multiple stages of NK cell development.

Transcriptional regulation of murine natural killer cell development, differentiation and maturation

Natural killer (NK) cells are innate cytotoxic effector cells that play important protective roles against certain pathogens as well as against pathogen-infected and transformed host cells. NK cells continuously arise from adult bone marrow-resident haematopoietic progenitors. Their generation can be sub-divided into three phases. The early NK cell development phase from multipotent common lymphoid progenitors occurs at least in part in common with that of additional members of a family of innate lymphoid cells, for which NK cells are the founding member. An intermediate phase of NK cell differentiation is characterized by the acquisition of IL-15 responsiveness and lineage-defining properties such as the transcription of genes coding for cytotoxic effector molecules. This is followed by a late maturation phase during which NK cells lose homeostatic expansion and increase effector capacity. These three phases are regulated by multiple stage-specific but not NK cell-specific transcription factors. This review summarizes the NK cell developmental and maturation processes and their transcriptional regulation with an emphasis on data derived from genetically modified mouse models.

Combination of Asiatic Acid and Naringenin Modulates NK Cell Anti-cancer Immunity by Rebalancing Smad3/Smad7 Signaling

Transforming growth factor β1 (TGF-β1) plays a promoting role in tumor growth via a mechanism associated with hyperactive Smad3 and suppressed Smad7 signaling in the tumor microenvironment. We report that retrieving the balance between Smad3 and Smad7 signaling with asiatic acid (AA, a Smad7 inducer) and naringenin (NG, a Smad3 inhibitor) effectively inhibited tumor progression in mouse models of invasive melanoma (B16F10) and lung carcinoma (LLC) by promoting natural killer (NK) cell development and cytotoxicity against cancer. Mechanistically, we found that Smad3 physically bound Id2 and IRF2 to suppress NK cell production and NK cell-mediated cytotoxicity against cancer. Treatment with AA and NG greatly inhibited Smad3 translation and phosphorylation while it restored Smad7 expression, and, therefore, it largely promoted NK cell differentiation, maturation, and cytotoxicity against cancer via Id2/IRF2-associated mechanisms. In contrast, silencing Id2 or IRF2 blunted the protective effects of AA and NG on NK cell-dependent anti-cancer activities. Thus, treatment with AA and NG produced an additive effect on inactivating TGF-β1/Smad3 signaling, and, therefore, it suppressed melanoma and lung carcinoma growth by promoting NK cell immunity against cancer via a mechanism associated with Id2 and IRF2.

Transcription Factor IRF8 Orchestrates the Adaptive Natural Killer Cell Response

Natural killer (NK) cells are innate lymphocytes that display features of adaptive immunity during viral infection. Biallelic mutations in IRF8 have been reported to cause familial NK cell deficiency and susceptibility to severe viral infection in humans; however, the precise role of this transcription factor in regulating NK cell function remains unknown. Here, we show that cell-intrinsic IRF8 was required for NK-cell-mediated protection against mouse cytomegalovirus infection. During viral exposure, NK cells upregulated IRF8 through interleukin-12 (IL-12) signaling and the transcription factor STAT4, which promoted epigenetic remodeling of the Irf8 locus. Moreover, IRF8 facilitated the proliferative burst of virus-specific NK cells by promoting expression of cell-cycle genes and directly controlling Zbtb32, a master regulator of virus-driven NK cell proliferation. These findings identify the function and cell-type-specific regulation of IRF8 in NK-cell-mediated antiviral immunity and provide a mechanistic understanding of viral susceptibility in patients with IRF8 mutations.

Critical functions for STAT5 tetramers in the maturation and survival of natural killer cells

Interleukin-15 (IL-15) is essential for the development and maintenance of natural killer (NK) cells. IL-15 activates STAT5 proteins, which can form dimers or tetramers. We previously found that NK cell numbers are decreased in Stat5a-Stat5b tetramer-deficient double knockin (DKI) mice, but the mechanism was not investigated. Here we show that STAT5 dimers are sufficient for NK cell development, whereas STAT5 tetramers mediate NK cell maturation and the expression of maturation-associated genes. Unlike the defective proliferation of Stat5 DKI CD8⁺ T cells, Stat5 DKI NK cells have normal proliferation to IL-15 but are susceptible to death upon cytokine withdrawal, with lower Bcl2 and increased active caspases. These findings underscore the importance of STAT5 tetramers in maintaining NK cell homoeostasis. Moreover, defective STAT5 tetramer formation could represent a cause of NK cell immunodeficiency, and interrupting STAT5 tetramer formation might serve to control NK leukaemia.

Regulation of Murine Natural Killer Cell Development

Natural killer (NK) cells are effector lymphocytes of the innate immune system that are known for their ability to kill transformed and virus-infected cells. NK cells originate from hematopoietic stem cells in the bone marrow, and studies on mouse models have revealed that NK cell development is a complex, yet tightly regulated process, which is dependent on both intrinsic and extrinsic factors. The development of NK cells can be broadly categorized into two phases: lineage commitment and maturation. Efforts to better define the developmental framework of NK cells have led to the identification of several murine NK progenitor populations and mature NK cell subsets, each defined by a varied set of cell surface markers. Nevertheless, the relationship between some of these NK cell subsets remains to be determined. The classical approach to studying both NK cell development and function is to identify the transcription factors involved and elucidate the mechanistic action of each transcription factor. In this regard, recent studies have provided further insight into the mechanisms by which transcription factors, such as ID2, FOXO1, Kruppel-like factor 2, and GATA-binding protein 3 regulate various aspects of NK cell biology. It is also becoming evident that the biology of NK cells is not only transcriptionally regulated but also determined by epigenetic alterations and posttranscriptional regulation of gene expression by microRNAs. This review summarizes recent progress made in NK development, focusing primarily on transcriptional regulators and their mechanistic actions.

Interferon regulatory factor 2 protects mice from lethal viral neuroinvasion

Li et al. describe a novel role for IRF2, previously known as a negative regulator of type I IFN signaling, in protection of mice from lethal viral neuroinvasion by facilitating the proper localization of B cells and antibodies to the central nervous system.

The host responds to virus infection by activating type I interferon (IFN) signaling leading to expression of IFN-stimulated genes (ISGs). Dysregulation of the IFN response results in inflammatory diseases and chronic infections. In this study, we demonstrate that IFN regulatory factor 2 (IRF2), an ISG and a negative regulator of IFN signaling, influences alphavirus neuroinvasion and pathogenesis. A Sindbis virus strain that in wild-type (WT) mice only causes disease when injected into the brain leads to lethal encephalitis in Irf2^−/− mice after peripheral inoculation. Irf2^−/− mice fail to control virus replication and recruit immune infiltrates into the brain. Reduced B cells and virus-specific IgG are observed in the Irf2^−/− mouse brains despite the presence of peripheral neutralizing antibodies, suggesting a defect in B cell trafficking to the central nervous system (CNS). B cell–deficient μMT mice are significantly more susceptible to viral infection, yet WT B cells and serum are unable to rescue the Irf2^−/− mice. Collectively, our data demonstrate that proper localization of B cells and local production of antibodies in the CNS are required for protection. The work advances our understanding of host mechanisms that affect viral neuroinvasion and their contribution to immunity against CNS infections.

Biallelic mutations in IRF8 impair human NK cell maturation and function

Human NK cell deficiencies are rare yet result in severe and often fatal disease, particularly as a result of viral susceptibility. NK cells develop from hematopoietic stem cells, and few monogenic errors that specifically interrupt NK cell development have been reported. Here we have described biallelic mutations in IRF8, which encodes an interferon regulatory factor, as a cause of familial NK cell deficiency that results in fatal and severe viral disease. Compound heterozygous or homozygous mutations in IRF8 in 3 unrelated families resulted in a paucity of mature CD56dim NK cells and an increase in the frequency of the immature CD56bright NK cells, and this impairment in terminal maturation was also observed in Irf8-/-, but not Irf8+/-, mice. We then determined that impaired maturation was NK cell intrinsic, and gene expression analysis of human NK cell developmental subsets showed that multiple genes were dysregulated by IRF8 mutation. The phenotype was accompanied by deficient NK cell function and was stable over time. Together, these data indicate that human NK cells require IRF8 for development and functional maturation and that dysregulation of this function results in severe human disease, thereby emphasizing a critical role for NK cells in human antiviral defense.

Development and maturation of natural killer cells

Natural killer (NK) cells are innate lymphocytes that are critical for host protection against pathogens and cancer due to their ability to rapidly release inflammatory cytokines and kill infected or transformed cells. In the 40 years since their initial discovery, much has been learned about how this important cellular lineage develops and functions. We now know that NK cells are the founding members of an expanded family of lymphocyte known as innate lymphoid cells (ILC). Furthermore, we have recently discovered that NK cells can possess features of adaptive immunity such as antigen specificity and long-lived memory responses. Here we will review our current understanding of the molecular mechanisms driving development of NK cells from the common lymphoid progenitor (CLP) to mature NK cells, and from activated effectors to long-lived memory NK cells.

Transcriptional and post-transcriptional regulation of NK cell development and function

Natural killer (NK) cells are specialized innate lymphoid cells that survey against viral infections and malignancy. Numerous advances have improved our understanding of the molecular mechanisms that control NK cell development and function over the past decade. These include both studies on the regulatory effects of transcription factors and translational repression via microRNAs. In this review, we summarize our current knowledge of DNA-binding transcription factors that regulate gene expression and thereby orchestrate NK cell development and activation, with an emphasis on recent discoveries. Additionally, we highlight our understanding of how RNA-binding microRNAs fine tune the NK cell molecular program. We also underscore the large number of open questions in the field that are now being addressed using new technological approaches and genetically engineered model organisms. Ultimately, a deeper understanding of the basic molecular biology of NK cells will facilitate new strategies to manipulate NK cells for the treatment of human disease.

gga-miR-9* inhibits IFN production in antiviral innate immunity by targeting interferon regulatory factor 2 to promote IBDV replication

MicroRNAs (miRNAs) are small non-coding RNAs that contribute to the repertoire of host-pathogen interactions during viral infections. In the current study, miRNA analysis showed that a panel of microRNAs, including gga-miR-9*, were markedly upregulated in specific-pathogen-free (SPF) chickens upon infection with infectious bursal disease virus (IBDV); however, the biological function of gga-miR-9* during viral infection remains unknown. Using a TCID50 assay, it was found that ectopic expression of gga-miR-9* significantly promoted IBDV replication. In turn, gga-miR-9* negatively regulated IBDV-triggered type I IFN production, thus promoting IBDV replication in DF-1 cells. Bioinformatics analysis indicates that the 3' untranslated region (UTR) of interferon regulatory factor 2 (IRF2) has two putative binding sites for gga-miR-9*. Targeting of IRF2 3'UTR by gga-miR-9* was determined by luciferase assay. Functional overexpression of gga-miR-9*, using gga-miR-9* mimics, inhibited IRF2 mRNA and protein expression. Transfection of the gga-miR-9* inhibitor abolished the suppression of IRF2 protein expression. Furthermore, IRF2 knockdown mediated the enhancing effect of gga-miR-9* on the type I IFN-mediated antiviral response. These findings indicate that inducible gga-miR-9* feedback negatively regulates the host antiviral innate immune response by suppressing type I IFN production via targeting IRF2.

Molecular characterization and expression analysis of eleven interferon regulatory factors in half-smooth tongue sole, Cynoglossus semilaevis

Interferon regulatory factors (IRFs) act as transcription mediators in virus-, bacteria-, and interferon (IFN)-induced signaling pathways and play diverse functions in antimicrobial defense, immune modulation, hematopoietic differentiation, and cell apoptosis. In this study, we described for the first time eleven IRFs (IRF1, IRF1L, IRF2X1, IRF3, IRF4a, IRF4b, IRF5, IRF6, IRF7, IRF8, and IRF9) from half-smooth tongue sole (Cynoglossus semilaevis) and examined their tissue distributions and expression patterns under different conditions. The deduced protein sequences of these IRFs (except IRF1) share high identities (71.8-86.6%) with other corresponding IRFs in other teleosts, whereas the sequence identity of IRF1 with the corresponding IRF1 in other teleosts is only 58.1%. A conserved N-terminal DNA binding domain (DBD), which is characterized by a winged type helix-loop-helix motif with four to six tryptophan repeats, is present in all IRFs. Another conserved IRF associated domain (IAD), which mediates the interactions in the C-terminal part of the protein, is present in all IRFs except IRF1 and IRF2X1, which instead contain the IAD2 domain. Several special domains also were found, including a serine-rich domain (SRD) in IRF3, IRF4a, IRF4b, and IRF7; a proline-rich domain (PRD) in IRF9; nuclear localization signals (NLSs) in IRF5, IRF8, and IRF9; and a virus activated domain (VAD) in IRF5. Quantitative real time RT-PCR (qRT-PCR) analysis showed that expression of all IRFs occurred in multiple tissues. IRF1, IRF2X1, IRF4a, IRF5, IRF7, and IRF8 exhibited relatively high levels of expression in immune organs, whereas the other five IRFs displayed high levels of expression in non-immune organs. Infection with extracellular and intracellular bacterial pathogens and virus upregulated the expression of IRFs in a manner that depended on tissue type, pathogen, and infection stage. Specifically, IRF1 and IRF2X1 were highly induced by bacterial and viral pathogens; IRF1L and IRF6 responded mainly to extracellular and intracellular bacterial pathogens; IRF3, IRF5, IRF7, IRF8, and IRF9 were markedly induced by intracellular bacterial pathogen and virus; IRF4a and IRF4b were mainly induced by virus and intracellular bacterial pathogen respectively. These results indicate that the IRFs of C. semilaevis can be categorized into several groups which exhibit different expression patterns in response to the infection of different microbial pathogens. These results provide new insights into the roles of teleost IRFs in antimicrobial immunity.

Transcriptional control of NK cell differentiation and function

Natural killer (NK) cells are crucial to mounting an effective immune response. They have a significant role in cancer immunosurveillance and function as a bridge between innate and adaptive immunity. However, until recently, surprisingly little was known about the molecular basis of NK cell development as compared to the impressive body of knowledge on B- and T-cell development. Here we outline the key transcription factors known to influence NK cell development and at what stages they function. The recent progress in understanding allows us to speculate on the nature of the network of interactions between transcription factors that ultimately facilitate the production of mature functional NK cells.

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

The family of interferon regulatory factors (IRFs) consists of nine members (IRF1-IRF9) in mammals. They act as transcription factors for the interferons and thus exert essential regulatory functions in the immune system and in oncogenesis. Recent clinical and experimental studies have identified critically important roles of the IRFs in cardiovascular diseases, arising from their participation in divergent and overlapping molecular programmes beyond the immune response. Here we review the current knowledge of the regulatory effects and mechanisms of IRFs on the immune system. The role of IRFs and their potential molecular mechanisms as novel stress sensors and mediators of cardiovascular diseases are highlighted.

Transcriptional Control of NK Cells

Natural killer (NK) cells are innate lymphocytes that survey the environment and protect the host from infected and cancerous cells. As their name implies, NK cells represent an early line of defense during pathogen invasion by directly killing infected cells and secreting inflammatory cytokines. Although the function of NK cells was first described more than four decades ago, the development of this cytotoxic lineage is not well understood. In recent years, we have begun to identify specific transcription factors that control each stage of development and maturation, from ontogeny of the NK cell progenitor to the effector functions of activated NK cells in peripheral organs. This chapter highlights the transcription factors that are unique to NK cells, or shared between NK cells and other hematopoietic cell lineages, but govern the biology of this cytolytic lymphocyte.

Disease resistance and immune-relevant gene expression in golden mandarin fish, Siniperca scherzeri Steindachner, infected with infectious spleen and kidney necrosis virus-like agent

Infectious spleen and kidney necrosis virus (ISKNV), family Iridoviridae, genus Megalocytivirus, may cause high mortality rates such as those seen in mandarin fish, Siniperca chuatsi. ISKNV has attracted much attention due to the possible environmental threat and economic losses it poses on both cultured and wild populations. We have investigated the pathogenicity of ISKNV-like agent Megalocytivirus, isolated from infected pearl gourami, in golden mandarin fish, Siniperca scherzeri - a member of the Percichthyidae family - and in another Percichthyidae species, S. chuatsi. Fish were challenged with four different doses of ISKNV-like agent Megalocytivirus (1, 10, 100 or 1000 μg per fish) over a 30-day period, and cumulative fish mortalities were calculated for each group. No significant mortality was observed for fish challenged with the lowest dose (1 μg per fish) relative to a control group. However, all other challenged groups showed 100% mortality over a 30-day period in proportion to the challenge dose. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune-related genes in golden mandarin fish following ISKNV-like agent challenge. mRNA expression levels for IRF1, Mx, viperin and interleukin 8 significantly increased, while mRNA levels for IRF2 and IRF7 remained constant or declined during the challenge period.

Dysregulation of interferon regulatory factors impairs the expression of immunostimulatory molecules in hepatitis C virus genotype 1-infected hepatocytes

BACKGROUND

IL-7 and IL-15 are produced by hepatocytes and are critical for the expansion and function of CD8 T cells. IL-15 needs to be presented by IL-15Rα for efficient stimulation of CD8 T cells.

METHODS

We analysed the hepatic levels of IL-7, IL-15, IL-15Rα and interferon regulatory factors (IRF) in patients with chronic hepatitis C (CHC) (78% genotype 1) and the role of IRF1 and IRF2 on IL-7 and IL-15Rα expression in Huh7 cells with or without hepatitis C virus (HCV) replicon.

RESULTS

Hepatic expression of both IL-7 and IL-15Rα, but not of IL-15, was reduced in CHC. These patients exhibited decreased hepatic IRF2 messenger RNA levels and diminished IRF2 staining in hepatocyte nuclei. We found that IRF2 controls basal expression of both IL-7 and IL-15Rα in Huh7 cells. IRF2, but not IRF1, is downregulated in cells with HCV genotype 1b replicon and this was accompanied by decreased expression of IL-7 and IL-15Rα, a defect reversed by overexpressing IRF2. Treating Huh7 cells with IFNα plus oncostatin M increased IL-7 and IL-15Rα mRNA more intensely than either cytokine alone. This effect was mediated by strong upregulation of IRF1 triggered by the combined treatment. Induction of IRF1, IL-7 and IL-15Rα by IFNα plus oncostatin M was dampened in replicon cells but the combination was more effective than either cytokine alone.

CONCLUSIONS

HCV genotype 1 infection downregulates IRF2 in hepatocytes attenuating hepatocellular expression of IL-7 and IL-15Rα. Our data reveal a new mechanism by which HCV abrogates specific T-cell responses and point to a novel therapeutic approach to stimulate anti-HCV immunity.

The transcription factor E4bp4/Nfil3 controls commitment to the NK lineage and directly regulates Eomes and Id2 expression

E4bp4 is required for commitment to the NK lineage and promotes NK development by directly regulating the expression of Eomes and Id2.

The transcription factor E4bp4 (Nfil3) is essential for natural killer (NK) cell production. Here, we show that E4bp4 is required at the NK lineage commitment point when NK progenitors develop from common lymphoid progenitors (CLPs) and that E4bp4 must be expressed at the CLP stage for differentiation toward the NK lineage to occur. To elucidate the mechanism by which E4bp4 promotes NK development, we identified a central core of transcription factors that can rescue NK production from E4bp4^−/− progenitors, suggesting that they act downstream of E4bp4. Among these were Eomes and Id2, which are expressed later in development than E4bp4. E4bp4 binds directly to the regulatory regions of both Eomes and Id2, promoting their transcription. We propose that E4bp4 is required for commitment to the NK lineage and promotes NK development by directly regulating the expression of the downstream transcription factors Eomes and Id2.

Frozen cord blood hematopoietic stem cells differentiate into higher numbers of functional natural killer cells in vitro than mobilized hematopoietic stem cells or freshly isolated cord blood hematopoietic stem cells

Adoptive natural killer (NK) cell therapy relies on the acquisition of large numbers of NK cells that are cytotoxic but not exhausted. NK cell differentiation from hematopoietic stem cells (HSC) has become an alluring option for NK cell therapy, with umbilical cord blood (UCB) and mobilized peripheral blood (PBCD34⁺) being the most accessible HSC sources as collection procedures are less invasive. In this study we compared the capacity of frozen or freshly isolated UCB hematopoietic stem cells (CBCD34⁺) and frozen PBCD34⁺ to generate NK cells in vitro. By modifying a previously published protocol, we showed that frozen CBCD34⁺ cultures generated higher NK cell numbers without loss of function compared to fresh CBCD34⁺ cultures. NK cells generated from CBCD34⁺ and PBCD34⁺ expressed low levels of killer-cell immunoglobulin-like receptors but high levels of activating receptors and of the myeloid marker CD33. However, blocking studies showed that CD33 expression did not impact on the functions of the generated cells. CBCD34⁺-NK cells exhibited increased capacity to secrete IFN-γ and kill K562 in vitro and in vivo as compared to PBCD34⁺-NK cells. Moreover, K562 killing by the generated NK cells could be further enhanced by IL-12 stimulation. Our data indicate that the use of frozen CBCD34⁺ for the production of NK cells in vitro results in higher cell numbers than PBCD34⁺, without jeopardizing their functionality, rendering them suitable for NK cell immunotherapy. The results presented here provide an optimal strategy to generate NK cells in vitro for immunotherapy that exhibit enhanced effector function when compared to alternate sources of HSC.

Tissue-specific effector functions of innate lymphoid cells

Innate lymphoid cells (ILCs) is the collective term for a group of related innate lymphocytes, including natural killer (NK) cells and the more recently discovered non-NK ILCs, which all lack rearranged antigen receptors such as those expressed by T and B cells. Similar to NK cells, the newly discovered ILCs depend on the transcription factor Id2 and the common γ-chain of the interleukin-2 receptor for development. However, in contrast to NK cells, non-NK ILCs also require interleukin-7. In addition to the cytotoxic functions of NK cells, assuring protection against tumour development and viruses, new data indicate that ILCs contribute to a wide range of homeostatic and pathophysiological conditions in various organs via specialized cytokine production capabilities. Here we summarize current knowledge on ILCs with a particular emphasis on their tissue-specific effector functions, in the gut, liver, lungs and uterus. When possible, we try to highlight the role that these cells play in humans.

NK cell maturation and function in C57BL/6 mice are altered by caloric restriction

NK cells are a heterogenous population of innate lymphocytes with diverse functional attributes critical for early protection from viral infections. We have previously reported a decrease in influenza-induced NK cell cytotoxicity in 6-mo-old C57BL/6 calorically restricted (CR) mice. In the current study, we extend our findings on the influence of CR on NK cell phenotype and function in the absence of infection. We demonstrate that reduced mature NK cell subsets result in increased frequencies of CD127(+) NK cells in CR mice, skewing the function of the total NK cell pool. NK cells from CR mice produced TNF-α and GM-CSF at a higher level, whereas IFN-γ production was impaired following IL-2 plus IL-12 or anti-NK1.1 stimulation. NK cells from CR mice were highly responsive to stimulation with YAC-1 cells such that CD27(-)CD11b(+) NK cells from CR mice produced granzyme B and degranulated at a higher frequency than CD27(-)CD11b(+) NK cells from ad libitum fed mice. CR has been shown to be a potent dietary intervention, yet the mechanisms by which the CR increases life span have yet to be fully understood. To our knowledge, these findings are the first in-depth analysis of the effects of caloric intake on NK cell phenotype and function and provide important implications regarding potential ways in which CR alters NK cell function prior to infection or cancer.

Cryptotanshinone and tanshinone IIA enhance IL-15-induced natural killer cell differentiation

Natural killer (NK) cells are a subset of lymphocytes crucial for innate and adaptive immune responses. Here we show a stimulatory effect of cryptotanshinone (CTS) and tanshinone IIA (TS), isolated from Salvia miltiorrhiza Bunge, on the differentiation of NK cells. In the presence of IL-15, tanshinones increased NK cell maturation, NK cell differentiation and the expression of several transcription factors, including Id2, GATA3, T-bet, and Ets-1. Additionally, tanshinones increased p38 MAPK phosphorylation during NK cell differentiation. Furthermore, the p38 inhibitor SB203580 blocked the developmental effects of the tanshinones and suppressed Id2, T-bet, and Ets-1 expression during NK cell differentiation. These results suggest that tanshinones significantly increased IL-15-induced NK cell differentiation via enhancing the p38 phosphorylation and the expression of transcription factors.

TGF-β is responsible for NK cell immaturity during ontogeny and increased susceptibility to infection during mouse infancy

A major gap in our understanding of infant immunity is why natural killer (NK) cellresponses are deficient, making infants more prone to viral infection. Here we demonstrate that transforming growth factor-β (TGF-β) was responsible for NK cell immaturity during infancy. Higher numbers of fully mature NK cells were found in CD11c^dnR mice, whose NK cells lack TGF-βR signaling. Importantly, ontogenic maturation of NK cells progressed faster in the absence of TGF-β signaling, resulting in the formation of mature NK cell pool early in life. As a consequence, infant CD11c^dnR mice efficiently controlled viral infections. These data thus demonstrate an unprecedented role for TGF-β in ontogeny that can explain why NK cell responses are deficient early in life.

IRF7 regulates TLR2-mediated activation of splenic CD11c(hi) dendritic cells

Members of the Interferon Regulatory Factor (IRF) family of transcription factors play an essential role in the development and function of the immune system. Here we investigated the role of IRF7 in the functional activation of conventional CD11c(hi) splenic dendritic cells (cDCs) in vitro and in vivo. Using mice deficient in IRF7, we found that this transcription factor was dispensable for the in vivo development of cDC subsets in the spleen. However, IRF7-deficient cDCs showed enhanced activation in response to microbial stimuli, characterised by exaggerated expression of CD80, CD86 and MHCII upon TLR2 ligation in vitro. The hyper-responsiveness of Irf7(-/-) cDC to TLR ligation could not be reversed with exogenous IFNα, nor by co-culture with wild-type cDCs, suggesting an intrinsic defect due to IRF7-deficiency. Irf7(-/-) cDCs also had impaired capacity to produce IL-12p70 when stimulated ex vivo, instead producing elevated levels of IL-10 that impaired their capacity to drive Th1 responses. Finally, analysis of bone marrow microchimeric mice revealed that cDCs deficient in IRF7 were also hyper-responsive to TLR2-mediated activation in vivo. Our data suggest a previously unknown function for IRF7 as a component of the regulatory network associated with cDC activation and adds to the wide variety of situations in which these transcription factors play a role.

IRF-2 regulates B-cell proliferation and antibody production through distinct mechanisms

Interferon regulatory factor (IRF)-2 is a transcription factor involved in type I (IFN- α/β) signaling. It has been reported that IRF-2 deficiency results in various immune dysfunctions. However, the role of IRF-2 in B-cell functions needs to be elucidated. Unlike wild-type (WT) B cells, IRF-2(-/-) B2 cells were refractory to anti-IgM, but not LPS. Such a defect in proliferation was dependent on IFN- α/β receptor (IFNAR). Marginal zone B cells increased in the proportion relative to B2 cells in IRF-2(-/-) mice produced IgM normally to LPS stimulation. However, IRF-2(-/-) B2 cells were defective in IgM production in an IFNAR-independent manner, although both B-cell subsets differentiated phenotypically to plasma cells at elevated efficiencies. Class switch recombination of IRF-2(-/-) B2 cells by LPS plus IL-4 was also impaired. Their reduced IgM production was conceivably due to an inefficient up-regulation of Blimp-1. Consistent with these in vitro observations, specific antibody production in vivo to a T-dependent antigen by B2 cells was severely impaired in IRF-2(-/- )mice. However, a low, but significant, level of IgG was detected at a late time point, and this IgG exhibited comparable binding affinity to that in WT mice. Follicular helper T-cell development and germinal center formation were normal. A similar tendency was observed when µ chain(-/-) mice were reconstituted with IRF-2(-/- )B cells. These results revealed a multi-faceted role of IRF-2 in the function of B cells, particularly B2 cells, through regulating proliferation in an IFNAR-dependent manner and antibody production via up-regulation of Blimp-1.

Genetic regulation on ex vivo differentiated natural killer cells from human umbilical cord blood CD34+ cells

Natural killer (NK)-cells are a lymphocyte population playing a critical role in the immune surveillance against tumors and virally infected cells. The development of human hematopoietic stem cells (hHSC) into fully differentiated NK-cells pass through discrete stages of differentiation involving a variety of factors such as cytokines, membrane factors, and transcription factors (TFs). Because there is lack of studies in this field, we decided to perform an extended analysis of TFs during in vitro differentiation of NK-cells. At several points of differentiation, cells were characterized by their mRNA expression either for NK-cell cell markers, for a number of mature NK-cell receptors or a large panel of TFs. Our data suggests that some TFs (ID2, EGR-2 and T-BET) play a role in NK-cell commitment, differentiation and maturation. Although delayed on its expression, BLIMP1 also seems to be involved in differentiation and maturation of NK cells, but not in NK-cell commitment. E4BP4 and TOX are more related with initial stages of NK-cell commitment. PU.1, MEF, Ikaros, EGR-1, BCL11B and IRF-2 revealed less involvement in maturation and were more associated with NK-cell commitment and pNK cell production. GATA-3 showed a differential role during the ontogeny of NK-cells. We show that assessment of the transcripts present in the differentiating NK-cells demonstrated, a pattern of preserved and differential gene expression remarkably similar to that seen in mice except for E4BP4 that showed constant downregulation throughout the culture period. A thorough understanding of NK-cell developmental mechanisms is important as it may enable future therapeutic manipulation.

Differential requirements for IRF-2 in generation of CD1d-independent T cells bearing NK cell receptors

NK cell receptors (NKRs) such as NK1.1, NKG2D, and Ly49s are expressed on subsets of CD1d-independent memory phenotype CD8(+) and CD4(-)CD8(-) T cells. However, the mechanism for the generation and functions of these NKR(+) T cells remained elusive. In this study, we found that CD1d-independent Ly49(+) T cells were reduced severely in the spleen, bone marrow, and liver, but not thymus, in mice doubly deficient for IFN regulatory factor-2 (IRF-2) and CD1d, in which the overall memory phenotype T cell population was contrastingly enlarged. Because a large fraction of Ly49(+) T cells coexpressed NK1.1 or NKG2D, the reduction of Ly49(+) T cells resulted indirectly in underrepresentation of NK1.1(+) or NKG2D(+) cells. Ly49(+) T cell deficiency was observed in IRF-2(-/-) mice additionally lacking IFN-α/βR α-chain (IFNAR1) as severely as in IRF-2(-/-) mice, arguing against the involvement of the accelerated IFN-α/β signals due to IRF-2 deficiency. Rather, mice lacking IFN-α/βR alone also exhibited relatively milder Ly49(+) T cell reduction, and IL-2 could expand Ly49(+) T cells from IFNAR1(-/-), but not from IRF-2(-/-), spleen cells in vitro. These results together indicated that IRF-2 acted in Ly49(+) T cell development in a manner distinct from that of IFN-α/β signals. The influence of IRF-2 deficiency on Ly49(+) memory phenotype T cells observed in this study suggested a unique transcriptional program for this T cell population among other NKR(+) T and memory phenotype T cells.

Kruppel-like factor 4 (KLF4) promotes the survival of natural killer cells and maintains the number of conventional dendritic cells in the spleen

The development and survival of NK cells rely on a complex, spatiotemporal gene expression pattern regulated by specific transcription factors in NK cells and tissue-specific microenvironments supported by hematopoietic cells. Here, we show that somatic deletion of the KLF4 gene, using inducible and lineage-specific cre-transgenic mice, leads to a significant reduction of NK cells (NK1.1(+) TCR-β(-)) in the blood and spleen but not in the BM, liver, or LNs. Functional and immunophenotypic analyses revealed increased apoptosis of CD27(+/-) CD11b(+) NK cells in the spleen of KLF4-deficient mice, although remaining NK cells were able to lyse tumor target cells and produce IFN-γ. A normal recovery of adoptively transferred KLF4-deficient NK cells in WT hosts suggested that the survival defect was not intrinsic of NK cells. However, BM chimeras using KLF4-deficient mice as donors indicated that reduced survival of NK cells depended on BM-derived hematopoietic cells in the spleen. The number of CD11c(hi) DCs, which are known to support NK cell survival, was reduced significantly in the spleen of KLF4-deficient mice, likely a result of a lower number of precDC progenitor cells in this tissue. Taken together, our data suggest that the pluripotency-associated gene KLF4 is required for the maintenance of DCs in the spleen and consequently, survival of differentiated NK cells in this tissue.

Molecular cloning and characterization of interferon regulatory factor 1 (IRF-1), IRF-2 and IRF-5 in the chondrostean paddlefish Polyodon spathula and their phylogenetic importance in the Osteichthyes

The interferon regulatory factor (IRF) with its 10 members is a very important gene family related to innate immunity. Currently, most fish IRFs reported are from bony fish (teleosts). Cloning and sequencing of IRFs from chondrosteans, the so-called "ancient fish" including sturgeon, paddlefish, bichir and gar, are absent from the literature. In this study, three IRF genes PsIRF-1, PsIRF-2 and PsIRF-5, were cloned and characterized from the paddlefish (Polyodon spathula). PsIRF-1 includes an open reading frame (ORF) of 972 bp that encodes a putative protein of 324 amino acids; PsIRF-2 includes an ORF of 1023 bp encoding 341 amino acids and PsIRF-5 includes an ORF of 1491 bp that encodes 497 amino acids. The PsIRF-5 gene structure is similar to those in mammals but differs from those in teleosts in the first and second exons. Phylogenetic studies of the putative amino acid sequences of PsIRF-1, PsIRF-2 and PsIRF-5 based on the neighbor-joining and Bayesian inference method for Osteichthyes found widely accepted inter-relationships among actinopterygians and tetrapods. Reverse Transcription Polymerase Chain Reaction (RT-PCR) analysis of PsIRF-1, PsIRF-2 and PsIRF-5 in different paddlefish tissues shows higher levels of expression in gill, spleen and head kidney. Poly (I: C) (polyinosinic-polycytidylic acid) stimulation in vivo up-regulated PsIRF-1 and PsIRF-2 expression, while PsIRF-5 gene expression did not respond to the challenge of Poly (I: C).

A gammaherpesvirus cooperates with interferon-alpha/beta-induced IRF2 to halt viral replication, control reactivation, and minimize host lethality

The gammaherpesviruses, including Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV), establish latency in memory B lymphocytes and promote lymphoproliferative disease in immunocompromised individuals. The precise immune mechanisms that prevent gammaherpesvirus reactivation and tumorigenesis are poorly defined. Murine gammaherpesvirus 68 (MHV68) is closely related to EBV and KSHV, and type I (alpha/beta) interferons (IFNαβ) regulate MHV68 reactivation from both B cells and macrophages by unknown mechanisms. Here we demonstrate that IFNβ is highly upregulated during latent infection, in the absence of detectable MHV68 replication. We identify an interferon-stimulated response element (ISRE) in the MHV68 M2 gene promoter that is bound by the IFNαβ-induced transcriptional repressor IRF2 during latency in vivo. The M2 protein regulates B cell signaling to promote establishment of latency and reactivation. Virus lacking the M2 ISRE (ISREΔ) overexpresses M2 mRNA and displays uncontrolled acute replication in vivo, higher latent viral load, and aberrantly high reactivation from latency. These phenotypes of the ISREΔ mutant are B-cell-specific, require IRF2, and correlate with a significant increase in virulence in a model of acute viral pneumonia. We therefore identify a mechanism by which a gammaherpesvirus subverts host IFNαβ signaling in a surprisingly cooperative manner, to directly repress viral replication and reactivation and enforce latency, thereby minimizing acute host disease. Since we find ISREs 5′ to the major lymphocyte latency genes of multiple rodent, primate, and human gammaherpesviruses, we propose that cooperative subversion of IFNαβ-induced IRFs to promote latent infection is an ancient strategy that ensures a stable, minimally-pathogenic virus-host relationship.

Herpesviruses establish life-long infection in a non-replicating state termed latency. During immune compromise, herpesviruses can reactivate and cause severe disease, including cancer. We investigated mechanisms by which interferons alpha/beta (IFNαβ), a family of antiviral immune genes, inhibit reactivation of murine gammaherpesvirus 68 (MHV68). MHV68 is related to Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, human gammaherpesviruses associated with multiple cancers. We made the surprising discovery that during latency, MHV68 cooperates with IFNαβ to inhibit its own replication. Specifically, a viral gene required for reactivation has evolved to be directly repressed by an IFNαβ-induced transcription factor, IRF2. Once virus replication has triggered sufficient IFNαβ production, expression of this viral gene is reduced and reactivation efficiency decreases. This strategy safeguards the health of the host, since a mutant virus that cannot respond to IRF2 replicates uncontrollably and is more virulent. Viral sensing of IFNαβ is also potentially subversive, since it allows MHV68 to detect periods of localized immune quiescence during which it can reactivate and spread to a new host. Thus, we highlight a novel path of virus-host coevolution, toward cooperative subversion of the antiviral immune response. These observations may illuminate new targets for drugs to inhibit herpesvirus reactivation or eliminate herpesvirus-associated tumors.

Transcriptional control of natural killer cell differentiation and function

Gene expression can be modulated depending on physiological and developmental requirements. A multitude of regulatory genes, which are organized in interdependent networks, guide development and eventually generate specific phenotypes. Transcription factors (TF) are a key element in the regulatory cascade controlling cell fate and effector functions. In this review, we discuss recent data on the diversity of TF that determine natural killer (NK) cell fate and NK cell function.

IL-15-high-responder developing NK cells bearing Ly49 receptors in IL-15-/- mice

In mice lacking IL-15, NK cell development is arrested at immature stages, providing an opportunity to investigate the earliest developing NK cells that would respond to IL-15. We show in this study that immature NK cells were present in the spleen as well as bone marrow (BM) and contained IL-15-high-responder cells. Thus, mature NK cells were generated more efficiently from IL-15(-/-) than from control donor cells in radiation BM chimeras, and the rate of IL-15-induced cell division in vitro was higher in NK cells in the spleen and BM from IL-15(-/-) mice than in those from wild-type mice. Phenotypically, NK cells developed in IL-15(-/-) mice up to the minor but discrete CD11b(-)CD27(+)DX5(hi)CD51(dull)CD127(dull)CD122(hi) stage, which contained the majority of Ly49G2(+) and D(+) NK cells both in the spleen and BM. Even among wild-type splenic NK cells, IL-15-induced proliferation was most prominent in CD11b(-)DX5(hi) cells. Notably, IL-15-mediated preferential expansion (but not conversion from Ly49(-) cells) of Ly49(+) NK cells was observed in vitro only for NK cells in the spleen. These observations indicated the uneven distribution of NK cells of different developing stages with variable IL-15 responsiveness in these lymphoid organs. Immature NK cells in the spleen may contribute, as auxiliaries to those in BM, to the mature NK cell compartment through IL-15-driven extramarrow expansion under steady-state or inflammatory conditions.

Interferon regulatory factors: beyond the antiviral response and their link to the development of autoimmune pathology

Abnormal production of interferon type I has been widely related to multiple autoimmune diseases, particularly systemic lupus erythematosus (SLE). It has been considered the molecular signature characterized by the overexpression of type I Interferon related genes in SLE patients. Among these, are the interferon regulatory factors (IRF). These transcription factors have been involved in the innate immune response, mainly the one related to the defense against viral infections; the development of immune cells and carcinogenesis. The role of IRF in autoimmune pathology has been addressed in diverse murine models. However, evidence in humans is quite scant. This review will focus on the evidence that supports the role of IRF in the development or susceptibility to autoimmune diseases. Specific emphasis will be made over the role of IRF-5 and IRF-7, since evidence of its association to the development of pathology, particularly systemic lupus erythematosus is the strongest.

A role for Blimp1 in the transcriptional network controlling natural killer cell maturation

Natural killer (NK) cells are innate lymphocytes capable of immediate effector functions including cytokine production and cytotoxicity. Compared with B and T cells, the factors that control the peripheral maturation of NK cells are poorly understood. We show that Blimp1, a transcriptional repressor required for the differentiation of plasma cells and short-lived effector T cells, is expressed by NK cells throughout their development. Interleukin 15 (IL-15) is required for the early induction of Blimp1 in NK cells, with expression increasing in the most mature subsets of mouse and human NK cells. We show that Blimp1 is required for NK-cell maturation and homeostasis and for regulating their proliferative potential. It is also essential for high granzyme B expression, but not for most cytokine production and cytotoxicity. Surprisingly, interferon regulatory factor 4 (IRF4) and B-cell lymphoma 6 (Bcl6), 2 transcription factors crucial for the regulation of Blimp1 in B and T cells, are largely dispensable for Blimp1 expression in NK cells. T-bet deficiency, however, leads to attenuated Blimp1 expression. We have identified NK cells as the first hematopoietic cell type in which the IRF4-Blimp1-Bcl6 regulatory axis is not in operation, highlighting the distinct nature of the NK-cell gene-regulatory network.

Transcriptional control of natural killer cell development and function

Natural killer (NK) cells play an important role in host defense against tumors and viruses and other infectious diseases. NK cell development is regulated by mechanisms that are both shared with and separate from other hematopoietic cell lineages. Functionally, NK cells use activating and inhibitory receptors to recognize both healthy and altered cells such as transformed or infected cells. Upon activation, NK cells produce cytokines and cytotoxic granules using mechanisms similar to other hematopoietic cell lineages especially cytotoxic T cells. Here we review the transcription factors that control NK cell development and function. Although many of these transcription factors are shared with other hematopoietic cell lineages, they control unexpected and unique aspects of NK cell biology. We review the mechanisms and target genes by which these transcriptional regulators control NK cell development and functional activity.

Innate immune processes are sufficient for driving silicosis in mice

The lung is constantly exposed to potentially pathogenic particles and microorganisms. It has become evident recently that not only innate but also adaptive immune responses to particulates, such as SiO(2) entering the respiratory tract, are complex and dynamic events. Although the cellular mechanisms and anatomical consequences involved in the development of silicosis have been studied extensively, they still remain poorly understood. Based on their capacity for immune regulation, lymphocytes may play a key role in the respiratory response to environmental challenge by SiO(2). The objective of this study was to characterize the impact of SiO(2) exposure on respiratory immune processes, with particular emphasis on evaluating the importance of lymphocytes in the murine silicosis model. Therefore, lymphopenic mice, including NK-deficient, Rag1(-/-), or a combination (Rag1(-/-) NK-depleted), were used and demonstrated that SiO(2)-induced fibrosis and inflammation can occur independently of T, B, NK T, and NK cells. Studies in Rag1(-/-) mice suggest further that lymphocytes may participate in the regulation of SiO(2)-induced inflammation through modulation of the Nalp3 inflammasome. This observation may have clinical relevance in the treatment of inflammatory and fibrotic lung diseases that are refractory or respond suboptimally to current therapeutics.