Identification of IFN regulatory factor-1 binding site in IL-12 p40 gene promoter

Atherosclerosis Deteriorates Liver Ischemia/Reperfusion Injury Via Interferon Regulatory Factor-1 Overexpression in a Murine Model

BACKGROUND

Abdominal aortic calcification (AAC) is associated with cardiovascular-related mortality, along with an elevated risk of coronary, cerebrovascular, and cardiovascular events. Notably, AAC is strongly associated with poor overall and recurrence free survival posthepatectomy for hepatocellular carcinoma. Despite the acknowledged significance of atherosclerosis in systemic inflammation, its response to ischemia/reperfusion injury (IRI) remains poorly elucidated. In this study, we aimed to clarify the impact of atherosclerosis on the liver immune system using a warm IRI mouse model.

METHODS

Injury was induced in an atherosclerotic mouse model (ApoE-/-) or C57BL/6J wild-type (WT) mice through 70% clamping for 1 hour and analyzed after 6 hours of reperfusion.

RESULTS

Elevated serum levels of aspartate and alanine aminotransferase, along with histological assessment, indicated considerable damage in the livers of ApoE-/- mice than that in WT mice. This indicates a substantial contribution of atherosclerosis to IRI. Furthermore, T and natural killer (NK) cells in ApoE-/- mouse livers displayed a more inflammatory phenotype than those in WT mouse livers. Reverse transcription-polymerase chain reaction analysis revealed a significant upregulation of interleukin (IL)-15 and its transcriptional regulator, interferon regulatory factor-1 (IRF-1) in ApoE-/- mouse livers compared with that in WT mouse livers.

CONCLUSIONS

These findings suggest that in an atherosclerotic mouse model, atherosclerosis can mirror intrahepatic immunity, particularly activating liver NK and T cells through IL-15 production, thereby exacerbating hepatic damage. The upregulation of IL-15 expression is associated with IRF-1 overexpression.

Alternative splicing in Atlantic salmon head kidney and SHK-1 cell line during the Piscirickettsia salmonis infection: A comparative transcriptome survey

Piscirickettsia salmonis, an intracellular bacterium in salmon aquaculture, is a big challenge because it is responsible for 54.2% of Atlantic salmon mortalities. In recent years, the high relevance of Alternative Splicing (AS) as a molecular mechanism associated with infectious conditions and host-pathogen interaction processes, especially in host immune activation, has been observed. Several studies have highlighted the role of AS in the host's immune response during viral, bacterial, and endoparasite infection. In the present study, we evaluated AS transcriptome profiles during P. salmonis infection in the two most used study models, SHK-1 cell line and salmon head kidney tissue. First, the SHK-1 cell line was exposed to P. salmonis infection at 0-, 7-, and 14-days post-infection (dpi). Following, total RNA was extracted for Illumina sequencing. On the other hand, RNA-Seq datasets of Atlantic salmon head kidney infected with the same P. salmonis strayingwase used. For both study models, the highest number of differentially alternative splicing (DAS) events was observed at 7 dpi, 16,830 DAS events derived from 9213 DAS genes in SHK-1 cells, and 13,820 DAS events from 7684 DAS genes in salmon HK. Alternative first exon (AF) was the most abundant AS type in the three infection times analyzed, representing 31% in SHK-1 cells and 228.6 in salmon HK; meanwhile, mutually exclusive exon (MX) was the least abundant. Notably, functional annotation of DAS genes in SHK-1 cells infected with P. salmonis showed a high presence of genes related to nucleotide metabolism. In contrast, the salmon head kidney exhibited many GO terms associated with immune response. Our findings reported the role of AS during P. salmonis infection in Atlantic salmon. These studies would contribute to a better understanding of the molecular bases that support the pathogen-host interaction, evidencing the contribution of AS regulating the transcriptional host response.

Adipose tissue macrophages and their role in obesity-associated insulin resistance: an overview of the complex dynamics at play

Obesity, a major global health concern, is characterized by serious imbalance between energy intake and expenditure leading to excess accumulation of fat in adipose tissue (AT). A state of chronic low-grade AT inflammation is prevalent during obesity. The adipose tissue macrophages (ATM) with astounding heterogeneity and complex regulation play a decisive role in mediating obesity-induced insulin resistance. Adipose-derived macrophages were broadly classified as proinflammatory M1 and anti-inflammatory M2 subtypes but recent reports have proclaimed several novel and intermediate profiles, which are crucial in understanding the dynamics of macrophage phenotypes during development of obesity. Lipid-laden hypertrophic adipocytes release various chemotactic signals that aggravate macrophage infiltration into AT skewing toward mostly proinflammatory status. The ratio of M1-like to M2-like macrophages is increased substantially resulting in copious secretion of proinflammatory mediators such as TNFα, IL-6, IL-1β, MCP-1, fetuin-A (FetA), etc. further worsening insulin resistance. Several AT-derived factors could influence ATM content and activation. Apart from being detrimental, ATM exerts beneficial effects during obesity. Recent studies have highlighted the prime role of AT-resident macrophage subpopulations in not only effective clearance of excess fat and dying adipocytes but also in controlling vascular integrity, adipocyte secretions, and fibrosis within obese AT. The role of ATM subpopulations as friend or foe is determined by an intricate interplay of such factors arising within hyperlipidemic microenvironment of obese AT. The present review article highlights some of the key research advances in ATM function and regulation, and appreciates the complex dynamics of ATM in the pathophysiologic scenario of obesity-associated insulin resistance.

Dendritic cell functions in vivo: a user's guide to current and next generation mutant mouse models

Dendritic cells (DCs) do not just excel in antigen presentation. They orchestrate information transfer from innate to adaptive immunity, by sensing and integrating a variety of danger signals, and translating them to naïve T cells, to mount specifically tailored immune responses. This is accomplished by distinct DC types specialized in different functions and because each DC is functionally plastic, assuming different activation states depending on the input signals received. Mouse models hold the key to untangle this complexity and determine which DC types and activation states contribute to which functions. Here, we aim to provide comprehensive information for selecting the most appropriate mutant mouse strains to address specific research questions on DCs, considering three in vivo experimental approaches: (i) interrogating the roles of DC types through their depletion; (ii) determining the underlying mechanisms by specific genetic manipulations; (iii) deciphering the spatiotemporal dynamics of DC responses. We summarize the advantages, caveats, suggested use and perspectives for a variety of mutant mouse strains, discussing in more detail the most widely used or accurate models. Finally, we discuss innovative strategies to improve targeting specificity, for the next generation mutant mouse models, and briefly address how humanized mouse models can accelerate translation into the clinic. This article is protected by copyright. All rights reserved.

Interferon Regulatory Factor-1 (IRF1) activates autophagy to promote liver ischemia/reperfusion injury by inhibiting β-catenin in mice

Autophagy is an important factor in liver ischemia-reperfusion injury. In the current study we investigate the function of interferon regulatory factor-1 (IRF1) in regulating autophagy to promote hepatic ischemia reperfusion injury (IR). The high expression of IRF1 during hepatic IR exhibited increased liver damage and was associated with activation of autophagy shown by Western blot markers, as well as immunofluorescent staining for autophagosomes. These effects were diminished by IRF1 deficiency in IRF1 knock out (KO) mice. Moreover, the autophagy inhibitor 3-MA decreased IR-induced liver necrosis and markedly abrogated the rise in liver injury tests (AST/ALT). β-catenin expression decreased during liver IR and was increased in the IRF1 KO mice. Immunoprecipitation assay showed the binding between IRF1 and β-catenin. Overexpression of IRF1 induced autophagy and also inhibited the expression of β-catenin. β-catenin inhibitor increased autophagy while β-catenin agonist suppressed autophagy in primary mouse hepatocytes. These results indicate that IRF1 induced autophagy aggravates hepatic IR injury in part by inhibiting β-catenin and suggests that targeting IRF1 may be an effective strategy in reducing hepatic IR injury.

TLR4 abrogates the Th1 immune response through IRF1 and IFN-β to prevent immunopathology during L. infantum infection

A striking feature of human visceral leishmaniasis (VL) is chronic inflammation in the spleen and liver, and VL patients present increased production levels of multiple inflammatory mediators, which contribute to tissue damage and disease severity. Here, we combined an experimental model with the transcriptional profile of human VL to demonstrate that the TLR4-IFN-β pathway regulates the chronic inflammatory process and is associated with the asymptomatic form of the disease. Tlr4-deficient mice harbored fewer parasites in their spleen and liver than wild-type mice. TLR4 deficiency enhanced the Th1 immune response against the parasite, which was correlated with an increased activation of dendritic cells (DCs). Gene expression analyses demonstrated that IRF1 and IFN-β were expressed downstream of TLR4 after infection. Accordingly, IRF1- and IFNAR-deficient mice harbored fewer parasites in the target organs than wild-type mice due to having an increased Th1 immune response. However, the absence of TLR4 or IFNAR increased the serum transaminase levels in infected mice, indicating the presence of liver damage in these animals. In addition, IFN-β limits IFN-γ production by acting directly on Th1 cells. Using RNA sequencing analysis of human samples, we demonstrated that the transcriptional signature for the TLR4 and type I IFN (IFN-I) pathways was positively modulated in asymptomatic subjects compared with VL patients and thus provide direct evidence demonstrating that the TLR4-IFN-I pathway is related to the nondevelopment of the disease. In conclusion, our results demonstrate that the TLR4-IRF1 pathway culminates in IFN-β production as a mechanism for dampening the chronic inflammatory process and preventing immunopathology development.

Visceral leishmaniasis (VL) is one of the most lethal neglected tropical diseases and is caused by Leishmania parasites. Most subjects infected with Leishmania present subclinical VL symptoms, and their immune response is mediated by Th1 cells and immunoregulatory mechanisms. However, when infection progresses to disease, VL patients present increased levels of inflammatory mediators in the serum which are related to the severity of disease. During infection, Toll-like receptors (TLRs) interact with Leishmania parasites and contribute to the outcome of the disease. Herein, we report that TLR4 signaling hampers the chronic immune response during VL to prevent immunopathology. TLR4 triggers the activation of IRF1 and thus induces the transcription of IFN-β, which in turn acts directly on Th1 cells to limit the production of IFN-γ. In addition, a transcription analysis of human VL samples provides direct evidence demonstrating that the TLR4-IFN-I pathway is related to the asymptomatic form of the disease. Collectively, our findings reveal that TLR4 hampers the Th1 immune response through IRF1 and IFN-β to prevent immunopathology during VL.

An IRF-3-, IRF-5-, and IRF-7-Independent Pathway of Dengue Viral Resistance Utilizes IRF-1 to Stimulate Type I and II Interferon Responses

Interferon-regulatory factors (IRFs) are a family of transcription factors (TFs) that translate viral recognition into antiviral responses, including type I interferon (IFN) production. Dengue virus (DENV) and other clinically important flaviviruses are suppressed by type I IFN. While mice lacking the type I IFN receptor (Ifnar1^-/-) succumb to DENV infection, we found that mice deficient in three transcription factors controlling type I IFN production (Irf3^-/-Irf5^-/-Irf7^-/- triple knockout [TKO]) survive DENV challenge. DENV infection of TKO mice resulted in minimal type I IFN production but a robust type II IFN (IFN-γ) response. Using loss-of-function approaches for various molecules, we demonstrate that the IRF-3-, IRF-5-, IRF-7-independent pathway predominantly utilizes IFN-γ and, to a lesser degree, type I IFNs. This pathway signals via IRF-1 to stimulate interleukin-12 (IL-12) production and IFN-γ response. These results reveal a key antiviral role for IRF-1 by activating both type I and II IFN responses during DENV infection.

Transcriptomic profiles of post-smolt Atlantic salmon challenged with Piscirickettsia salmonis reveal a strategy to evade the adaptive immune response and modify cell-autonomous immunity

Piscirickettsiosis is the main bacterial disease affecting the Chilean salmon farming industry and is responsible for high economic losses. The development of effective strategies to control piscirickettsiosis has been limited in part by insufficient knowledge of the host response. The aim of this study was to use RNA sequencing to describe the transcriptional profiles of the responses of post-smolt Atlantic salmon infected with LF-89-like or EM-90-like Piscirickettsia salmonis. Enrichment and pathway analyses of the differentially expressed genes revealed several central signatures following infection, including positive regulation of DC-SIGN and TLR5 signalling, which converged at the NF-κB level to modulate the pro-inflammatory cytokine response, particularly in the PS-EM-90-infected fish. P. salmonis induced an IFN-inducible response (e.g., IRF-1 and GBP-1) but inhibited the humoral and cell-mediated immune responses. P. salmonis induced significant cytoskeletal reorganization but decreased lysosomal protease activity and caused the degradation of proteins associated with cellular stress. Infection with these isolates also delayed protein transport, antigen processing, vesicle trafficking and autophagy. Both P. salmonis isolates promoted cell survival and proliferation and inhibited apoptosis. Both groups of Trojan fish used similar pathways to modulate the immune response at 5 dpi, but the transcriptomic profiles in the head kidneys of the cohabitant fish infected with PS-LF-89 and PS-MS-90 were relatively different at day 35 post-infection of the Trojan fish, probably due to the different degree of pathogenicity of each isolate. Our study showed the most important biological mechanisms used by P. salmonis, regardless of the isolate, to evade the immune response, maintain the viability of host cells and increase intracellular replication and persistence at the infection site. These results improve the understanding of the mechanisms by which P. salmonis interacts with its host and may serve as a basis for the development of effective strategies for the control of piscirickettsiosis.

The impact of interferon-regulatory factors to macrophage differentiation and polarization into M1 and M2

The mononuclear phagocytes control the body homeostasis through the involvement in resolving tissue injury and further wound healing. Indeed, local tissue microenvironmental changes can significantly influence the functional behavior of monocytes and macrophages. Such microenvironmental changes for example occur in an atherosclerotic plaque during all progression stages. In response to exogenous stimuli, macrophages show a great phenotypic plasticity and heterogeneity. Exposure of monocytes to inflammatory or anti-inflammatory conditions also induces predominant differentiation to proinflammatory (M1) or anti-inflammatory (M2) macrophage subsets and phenotype switch between macrophage subsets. The phenotype transition is accompanied with great changes in the macrophage transcriptome and regulatory networks. Interferon-regulatory factors (IRFs) play a key role in hematopoietic development of monocytes, their differentiation to macrophages, and regulating macrophage maturation, phenotypic polarization, phenotypic switch, and function. Of 9 IRFs, at least 3 (IRF-1, IRF-5, and IRF-8) are involved in the commitment of proinflammatory M1 whereas IRF-3 and IRF-4 control M2 polarization. The role of IRF-2 is context-dependent. The IRF impact on macrophage phenotype plasticity and heterogeneity is complex and involves activating and repressive function in triggering transcription of target genes.

Reovirus infection triggers inflammatory responses to dietary antigens and development of celiac disease

Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (TH1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pTreg) conversion and promoting TH1 immunity to dietary antigen. Initiation of TH1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pTreg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.

An Infectious Disease-Associated Il12b Polymorphism Regulates IL-12/23 p40 Transcription Involving Poly(ADP-Ribose) Polymerase 1

IL-12 and IL-23 are important host defense factors produced by APCs against certain intracellular and extracellular pathogens. Their dysregulation has also been implicated in several autoimmune diseases. The nucleotide polymorphism in the promoter region of Il12b (rs41292470 consisting of the long or short allele) encoding the shared subunit of IL-12 and IL-23, p40, has been reported to associate with susceptibility to infectious diseases and autoimmune disorders. How these genetic variants impact Il12b expression at the molecular level was unclear. We established an Il12b promoter-luciferase reporter system containing the long or short allele driving the reporter gene expression and found that the long allele (infection-resistant) displayed ∼2-fold higher transcriptional activity than the short allele (infection-susceptible), associated with a selective and differential nuclear binding activity to the two alleles in activated macrophages. DNA pull-down assays coupled with mass spectrometry analyses identified the specific DNA binding activity as poly(ADP-ribose) polymerase 1 (PARP-1). Small hairpin RNA-mediated knockdown of the endogenous PARP-1 expression resulted in reduced p40 mRNA expression and Il12b promoter activity. Bone marrow-derived macrophages from PARP-1-deficient mice had decreased p40 expression at both mRNA and protein levels. Furthermore, selective PARP-1 inhibitors resulted in impaired production of IL-12p40 and IL-23 in bone-marrow derived macrophages and PBMCs. Chromatin immunoprecipitation assay revealed that PARP-1 could bind specifically to Il12b in LPS-stimulated macrophages. Our study opens the way for further elucidating the molecular mechanism whereby allele-specific immune responses to foreign and self-antigens mediated by IL-12/IL-23 are controlled in an individually variable manner.

Gene Regulatory Network Inference of Immunoresponsive Gene 1 (IRG1) Identifies Interferon Regulatory Factor 1 (IRF1) as Its Transcriptional Regulator in Mammalian Macrophages

Immunoresponsive gene 1 (IRG1) is one of the highest induced genes in macrophages under pro-inflammatory conditions. Its function has been recently described: it codes for immune-responsive gene 1 protein/cis-aconitic acid decarboxylase (IRG1/CAD), an enzyme catalysing the production of itaconic acid from cis-aconitic acid, a tricarboxylic acid (TCA) cycle intermediate. Itaconic acid possesses specific antimicrobial properties inhibiting isocitrate lyase, the first enzyme of the glyoxylate shunt, an anaplerotic pathway that bypasses the TCA cycle and enables bacteria to survive on limited carbon conditions. To elucidate the mechanisms underlying itaconic acid production through IRG1 induction in macrophages, we examined the transcriptional regulation of IRG1. To this end, we studied IRG1 expression in human immune cells under different inflammatory stimuli, such as TNFα and IFNγ, in addition to lipopolysaccharides. Under these conditions, as previously shown in mouse macrophages, IRG1/CAD accumulates in mitochondria. Furthermore, using literature information and transcription factor prediction models, we re-constructed raw gene regulatory networks (GRNs) for IRG1 in mouse and human macrophages. We further implemented a contextualization algorithm that relies on genome-wide gene expression data to infer putative cell type-specific gene regulatory interactions in mouse and human macrophages, which allowed us to predict potential transcriptional regulators of IRG1. Among the computationally identified regulators, siRNA-mediated gene silencing of interferon regulatory factor 1 (IRF1) in macrophages significantly decreased the expression of IRG1/CAD at the gene and protein level, which correlated with a reduced production of itaconic acid. Using a synergistic approach of both computational and experimental methods, we here shed more light on the transcriptional machinery of IRG1 expression and could pave the way to therapeutic approaches targeting itaconic acid levels.

Regulation of Interleukin-12 Production in Antigen-Presenting Cells

Interleukin-12 is a heterodimeric cytokine produced primarily by pathogen-activated antigen-presenting cells, particularly macrophages and dendritic cells, during encountering with intracellular microbes. IL-12 plays a key role in the activation of natural killer cells and CD4⁺ T helper cells in both innate and adaptive immune responses against infectious agents and immunosurveillance against endogenous malignancies. However, the potency of IL-12 makes it a target for stringent regulation. Indeed, the temporal, spatial, and quantitative expression of IL-12 during an immune response in a microenvironment contributes critically to the determination of the type, extent, and ultimate resolution of the reaction. Breaching of the delicate control and balance involving IL-12 frequently leads to autoimmune inflammatory disorders and pathogenesis. Thus, a better understanding of the regulatory mechanisms in the production and control of this cytokine is both scientifically significant and clinically beneficial. Here we provide an update on the research that has been conducted on this subject particularly in the last 10 years since the publication of a major thesis of this nature.

Regulation of IL-10 and IL-12 production and function in macrophages and dendritic cells

Interleukin-10 and Interleukin-12 are produced primarily by pathogen-activated antigen-presenting cells, particularly macrophages and dendritic cells. IL-10 and IL-12 play very important immunoregulatory roles in host defense and immune homeostasis. Being anti- and pro-inflammatory in nature, respectively, their functions are antagonistically opposing. A comprehensive and in-depth understanding of their immunological properties and signaling mechanisms will help develop better clinical intervention strategies in therapy for a wide range of human disorders. Here, we provide an update on some emerging concepts, controversies, unanswered questions, and opinions regarding the immune signaling of IL-10 and IL-12.

Listeria arpJ gene modifies T helper type 2 subset differentiation

BACKGROUND

Although the T-cell subset differentiation pathway has been characterized extensively from the view of host gene regulation, the effects of genes of the pathogen on T-cell subset differentiation during infection have yet to be elucidated. Especially, the bacterial genes that are responsible for this shift have not yet been determined.

METHODS

Utilizing a single-gene-mutation Listeria panel, we investigated genes involved in the host-pathogen interaction that are required for the initiation of T-cell subset differentiation in the early phase of pathogen infection.

RESULTS

We demonstrate that the induction of T helper types 1 and 2 (Th1 and Th2) subsets are separate phenomena and are mediated by distinct Listeria genes. We identified several candidate Listeria genes that appear to be involved in the host-Listeria interaction. Among them, arpJ is the strongest candidate gene for inhibiting Th2 subset induction. Furthermore, the analysis utilizing arpJ-deficient Listeria monocytogenes (Lm) revealed that the tumor necrosis factor (TNF) superfamily (Tnfsf) 9-TNF receptor superfamily (Tnfrsf) 9 interaction inhibits the Th2 response during Lm infection.

CONCLUSIONS

arpJ is the candidate gene for inhibiting Th2 T-cell subset induction. The arpJ gene product influences the expression of Tnfsf/Tnfrsf on antigen-presenting cells and inhibits the Th2 T-cell subset differentiation during Listeria infection.

Cutting Edge: Synchronization of IRF1, JunB, and C/EBPβ Activities during TLR3-TLR7 Cross-Talk Orchestrates Timely Cytokine Synergy in the Proinflammatory Response

Multiple pathogen-associated molecular pattern-induced TLR pathway cross-talk provokes proinflammatory cytokine synergy in macrophages, which is important for pathogen resistance and immune homeostasis. However, the detailed mechanisms are unclear. In this article, we demonstrate viral RNA analog-induced transcription synergy of Il6 and Il12b via IFN regulatory factor (IRF)1 (TLR3-TIR domain-containing adaptor inducing IFN-β [TRIF] responsive), C/EBPβ (TLR7-MyD88 responsive), and JunB (all responsive). Coactivation of the TLR3 and TLR7 pathways synchronizes the interaction of IRF1, JunB, and C/EBPβ with the Il6 and Il12b promoters, facilitating maximal gene expression. MyD88 pathway activation suppresses TRIF-induced IRF1 in a delayed manner, controlling the magnitude and timing of cytokine expression. Our findings provide novel mechanisms of cooperation of different TLR pathways to achieve optimal immune responses, with the potential for immunomodulatory strategies.

Dual Inhibition of TNFR1 and IFNAR1 in Imiquimod-Induced Psoriasiform Skin Inflammation in Mice

Psoriasis is a chronic inflammatory skin disease affecting 2-3% of the world population and is mainly characterized by epidermal hyperplasia, scaling, and erythema. A prominent role for TNF in the pathogenesis of psoriasis has been shown, and consequently various types of TNF antagonists such as etanercept and infliximab have been used successfully. Recently, increasing amounts of data suggest that type I IFNs are also crucial mediators of psoriasis. To investigate whether blocking their respective receptors would be useful, TNFR1- and IFNAR1-deficient mice were challenged with Aldara, which contains imiquimod, and is used as an experimental model to induce psoriasis-like skin lesions in mice. Both transgenic mice showed partial protection toward Aldara-induced inflammation compared with control groups. Additionally, TNFR1 knockout mice showed sustained type I IFN production in response to Aldara. Double knockout mice lacking both receptors showed superior protection to Aldara in comparison with the single knockout mice and displayed reduced levels of IL-12p40, IL-17F, and S100A8, indicating that the TNF and type I IFN pathways contribute significantly to inflammation upon treatment with Aldara. Our findings reveal that dual inhibition of TNFR1 and IFNAR1 may represent a potential novel strategic treatment of psoriasis.

A novel function of interferon regulatory factor-1: inhibition of Th2 cells by down-regulating the Il4 gene during Listeria infection

Infection with certain pathogens induces a shift of the Th subset balance to a Th1 dominant state. This, in turn, results in the suppression of Th2 responses. We focused on the involvement of interferon regulatory factor-1 (IRF-1) in the suppression of Th2 cells during Listeria infection. We found that the inhibition of IL-4 production by Th2 cells is mediated by a soluble factor (LmSN) produced by Listeria-infected antigen-presenting cells. The inhibition is not observed with T cells from Irf1 gene-targeted mice. IRF-1 suppresses transcription of the Il4 gene in Th2 cells. Under the influence of the LmSN, IRF-1 binds to the 3' untranslated region (UTR) region of the Il4 gene and down-regulates Il4 gene transcription. Finally, we identified IL-1α and IL-1β as the mediator of the LmSN activity. Signaling through IL-1R induces the stabilization and/or nuclear translocation of IRF-1. We propose that IRF-1 functions to induce the T-cell subset shift via a novel mechanism. Under the influence of IL-1, IRF-1 translocates into the nucleus and acts on the 3'UTR region of the Il4 gene, thus inhibiting its transcription in Th2 cells. As a result, the immune system shifts predominantly to a Th1 response during Listeria infection, resulting in effective protection of the host.

Leishmania major inhibits IL-12 in macrophages by signalling through CR3 (CD11b/CD18) and down-regulation of ETS-mediated transcription

Leishmania major is an aetiological agent of cutaneous leishmaniasis. The parasite primarily infects immune sentinel cells, specifically macrophages and dendritic cells, in the mammalian host. Infection is receptor mediated and is known to involve parasite binding to cell surface protein complement receptor 3 (CR3, Mac-1, CD11b/CD18). Engagement of CR3 by various ligands inhibits production of interleukin-12 (IL-12), the cytokine that drives antileishmanial T helper 1-type immune responses. Likewise, L. major infection inhibits IL-12 production and activation of host macrophages. Our data indicate that in the absence of CR3, L. major-infected bone marrow-derived macrophages produce more IL-12 and nitric oxide compared with WT cells upon lipopolysaccharide (LPS) stimulation. We therefore investigated multiple signalling pathways by which L. major may inhibit IL-12 transcription through CR3 ligation. We demonstrate that L. major infection does not elicit significant NFκB p65, MAPK, IRF-1 or IRF-8 activation in WT or CD11b-deficient macrophages. Furthermore, infection neither inhibits LPS-induced MAPK or NFκB activation nor blocks IFN-γ-activated IRF-1 and IRF-8. ETS-mediated transcription, however, is inhibited by L. major infection independently of CR3. Our data indicate that L. major-mediated inhibition of IL-12 occurs through CR3 engagement; however, the mechanism of inhibition is independent of NFκB, MAPK, IRF and ETS.

Tick-borne flaviviruses antagonize both IRF-1 and type I IFN signaling to inhibit dendritic cell function

Tick-borne encephalitis virus (TBEV), a member of the Flaviviridae family, is a leading cause of viral encephalitis in Europe and Asia. Dendritic cells (DCs), as early cellular targets of infection, provide an opportunity for flaviviruses to inhibit innate and adaptive immune responses. Flaviviruses modulate DC function, but the mechanisms underpinning this are not defined. We examined the maturation phenotype and function of murine bone marrow-derived DCs infected with Langat virus (LGTV), a naturally attenuated member of the TBEV serogroup. LGTV infection failed to induce DC maturation or a cytokine response. Treatment with LPS or LPS/IFN-γ, strong inducers of inflammatory cytokines, resulted in enhanced TNF-α and IL-6 production, but suppressed IL-12 production in infected DCs compared with uninfected "bystander" cells or mock-infected controls. LGTV-mediated antagonism of type I IFN (IFN-I) signaling contributed to inhibition of IL-12p40 mRNA expression at late time points after stimulation. However, early suppression was still observed in DCs lacking the IFN-I receptor (Ifnar(-/-)), suggesting that additional mechanisms of antagonism exist. The early IFN-independent inhibition of IL-12p40 was nearly abolished in DCs deficient in IFN regulatory factor-1 (IRF-1), a key transcription factor required for IL-12 production. LGTV infection did not affect Irf-1 mRNA expression, but rather diminished IRF-1 protein levels and nuclear localization. The effect on IRF-1 was also observed in DCs infected with the highly virulent Sofjin strain of TBEV. Thus, antagonism of IRF-1 is a novel mechanism that synergizes with the noted ability of flaviviruses to suppress IFN-α/β receptor-dependent signaling, resulting in the orchestrated evasion of host innate immunity.

Gene trap mice reveal an essential function of dual specificity phosphatase Dusp16/MKP-7 in perinatal survival and regulation of Toll-like receptor (TLR)-induced cytokine production

MAPK activity is negatively regulated by members of the dual specificity phosphatase (Dusp) family, which differ in expression, substrate specificity, and subcellular localization. Here, we investigated the function of Dusp16/MKP-7 in the innate immune system. The Dusp16 isoforms A1 and B1 were inducibly expressed in macrophages and dendritic cells following Toll-like receptor stimulation. A gene trap approach was used to generate Dusp16-deficient mice. Homozygous Dusp16tp/tp mice developed without gross abnormalities but died perinatally. Fetal liver cells from Dusp16tp/tp embryos efficiently reconstituted the lymphoid and myeloid compartments with Dusp16-deficient hematopoietic cells. However, GM-CSF-induced proliferation of bone marrow progenitors in vitro was impaired in the absence of Dusp16. In vivo challenge with Escherichia coli LPS triggered higher production of IL-12p40 in mice with a Dusp16-deficient immune system. In vitro, Dusp16-deficient macrophages, but not dendritic cells, selectively overexpressed a subset of TLR-induced genes, including the cytokine IL-12. Dusp16-deficient fibroblasts showed enhanced activation of p38 and JNK MAPKs. In macrophages, pharmacological inhibition and siRNA knockdown of JNK1/2 normalized IL-12p40 secretion. Production of IL-10 and its inhibitory effect on IL-12 production were unaltered in Dusp16tp/tp macrophages. Altogether, the Dusp16 gene trap mouse model identifies an essential role in perinatal survival and reveals selective control of differentiation and cytokine production of myeloid cells by the MAPK phosphatase Dusp16.

Engagement of CD14 sensitizes primary monocytes to IFN-γ to produce IL-12/23p40 and IL-23 through p38 mitogen-activated protein kinase and independent of the janus kinase/signal transducers and activators of transcription signaling

Interferon (IFN)-γ is a potent stimulator of the IL-12 family Th1 cytokines, including IL-12/23p40 and IL-23, responsible for coordinating the innate and adaptive immune responses. Our results show that IFN-γ induced the production of IL-12/23p40 and IL-23p19 mRNA as well as IL-12p40 and IL-23 proteins in primary human monocytes isolated by positive selection through anti-CD14 microbeads. These results were confirmed by IFN-γ stimulation of CD14-activated monocytes resulting in IL-12/23p40 and IL-23 production. We investigated the signaling pathways governing the regulation of IL-23 and its subunits IL-23p40 and IL-23p19 following IFN-γ stimulation. We observed a differential regulation of IL-23p19, IL-12/23p40, and IL-23 following IFN-γ stimulation. IFN-γ-induced IL-23 and IL-12/23p40 expression was positively regulated by the p38 mitogen-activated protein kinases (MAPKs), independent of the Janus kinase (Jak)/signal transducers and activators of transcription (STAT) signaling. In contrast, IL-12 and IL-23 were negatively regulated by the Jak/STAT, phosphatidylinositol 3-kinase (PI3K), and the c-Jun-N-terminal kinase (JNK) MAPKs in IFN-γ-stimulated monocytes. Overall, our results suggest for the first time a differential positive regulation of IL-12p40 and IL-23 by p38 MAPKs independent of the Jak/STAT pathways and negative regulation by the Jak/STAT, JNK, and PI3K pathways in CD14-activated primary human monocytes stimulated with IFN-γ.

Francisella tularensis SchuS4 and SchuS4 lipids inhibit IL-12p40 in primary human dendritic cells by inhibition of IRF1 and IRF8

Induction of innate immunity is essential for host survival of infection. Evasion and inhibition of innate immunity constitute a strategy used by pathogens, such as the highly virulent bacterium Francisella tularensis, to ensure their replication and transmission. The mechanism and bacterial components responsible for this suppression of innate immunity by F. tularensis are not defined. In this article, we demonstrate that lipids enriched from virulent F. tularensis strain SchuS4, but not attenuated live vaccine strain, inhibit inflammatory responses in vitro and in vivo. Suppression of inflammatory responses is associated with IκBα-independent inhibition of NF-κBp65 activation and selective inhibition of activation of IFN regulatory factors. Interference with NF-κBp65 and IFN regulatory factors is also observed following infection with viable SchuS4. Together these data provide novel insight into how highly virulent bacteria selectively modulate the host to interfere with innate immune responses required for survival of infection.

Regulation of T helper cell differentiation by interferon regulatory factor family members

Interferon regulatory factors (IRFs) consist of a family of transcription factors with diverse functions in the transcriptional regulation of cellular responses in health and diseases. IRFs commonly contain a DNA-binding domain in the N-terminus, with most members also containing a C-terminal IRF-associated domain that mediates protein-protein interactions. Ten IRFs and several virus-encoded IRF homologs have been identified in mammals so far. In response to endogenous and microbial stimuli during an immune response, IRFs are activated, and selectively and cooperatively modulate the expression of key cytokine and transcription factors involved in T helper cell differentiation in T cells and/or antigen-presenting cells. This review focuses on recent advances in the understanding of IRF-mediated transcriptional regulation in T helper cell differentiation and discusses the implications on the development of cellular and humoral immune responses and the pathogenesis of immune disorders.

The expression of interleukin-12 is increased by MAP kinase phosphatase-1 through a mechanism related to interferon regulatory factor 1

Mitogen-activated protein kinase phosphatase-1 (MKP-1) is a nuclear tyrosine/threonine phosphatase that inhibits p38 mitogen-activated protein kinase (MAPK) activity. We and others have shown that MKP-1 deficiency leads to excessive activation of innate immunity and inflammatory gene expression. Surprisingly, the present study shows that MKP-1 is a positive regulator of IL-12 expression in macrophages suggesting a stimulatory effect on Th1 type immune response. In the present study, we found that LPS-induced expression of IL-12p40 was lower in primary mouse peritoneal macrophages (PMs) and bone marrow-derived macrophages from MKP-1 deficient mice than in cells from wild-type mice whereas TNF expression was enhanced as expected. Correspondingly, the inhibition of p38 MAPK by pharmacologic inhibitors BIRB 796 and SB 202190 enhanced LPS-induced IL-12p40 production. Silencing of interferon regulatory factor 1 (IRF1) by siRNA inhibited the expression of IL-12p40 in J774 macrophages, showing that IRF1 is an important factor regulating IL-12p40 expression. BIRB 796 enhanced LPS-induced expression of IRF1 in J774 macrophages and in PMs from wild-type mice, and IRF1 expression was reduced in PMs from MKP-1 deficient mice. In conclusions, our results show that MKP-1 increases and p38 MAPK decreases the expression of IL-12 by enhancing the expression of IRF1. MKP-1, through regulation of IRF1 and IL-12, therefore may be an important factor supporting the development of Th1 type of immune response and anti-microbial defense.

Nfkb1 inhibits LPS-induced IFN-β and IL-12 p40 production in macrophages by distinct mechanisms

Background

Nfkb1-deficient murine macrophages express higher levels of IFN-β and IL-12 p40 following LPS stimulation than control macrophages, but the molecular basis for this phenomenon has not been completely defined. Nfkb1 encodes several gene products including the NF-κB subunit p50 and its precursor p105. p50 is derived from the N-terminal of 105, and p50 homodimers can exhibit suppressive activity when overexpressed. The C-terminal region of p105 is necessary for LPS-induced ERK activation and it has been suggested that ERK activity inhibits both IFN-β and IL-12 p40 following LPS stimulation. However, the contributions of p50 and the C-terminal domain of p105 in regulating endogenous IFN-β(Ifnb) and IL-12 p40 (Il12b) gene expression in macrophages following LPS stimulation have not been directly compared.

Methodology/Principal Findings

We have used recombinant retroviruses to express p105, p50, and the C-terminal domain of p105 (p105ΔN) in Nfkb1-deficient murine bone marrow-derived macrophages at near endogenous levels. We found that both p50 and p105ΔN inhibited expression of Ifnb, and that inhibition of Ifnb by p105ΔN depended on ERK activation, because a mutant of p105ΔN (p105ΔNS930A) that lacks a key serine necessary to support ERK activation failed to inhibit. In contrast, only p105ΔN but not p50 inhibited Il12b expression. Surprisingly, p105ΔNS930A retained inhibitory activity for Il12b, indicating that ERK activation was not necessary for inhibition. The differential effects of p105ΔNS930A on Ifnb and Il12b expression inversely correlated with the function of one of its binding partners, c-Rel. This raised the possibility that p105ΔNS930A influences gene expression by interfering with the function of c-Rel.

Conclusions

These results demonstrate that Nfkb1 exhibits multiple gene-specific inhibitory functions following TLR stimulation of murine macrophages.

Bid regulates the immunological profile of murine microglia and macrophages

Apoptosis is a controlled cell-death process mediated inter alia by proteins of the Bcl-2 family. Some proteins previously shown to promote the apoptotic process were found to have nonapoptotic functions as well. Microglia, the resident immune cells of the central nervous system, respond to brain derangements by becoming activated to contend with the brain damage. Activated microglia can also undergo activation-induced cell death. Previous studies have addressed the role of core apoptotic proteins in the death process, but whether these proteins also play a role or not in the activation process is not been reported. Here we explore the effect of the BH3-only protein Bid on the immunological features of microglia and macrophages. Our results showed that Bid regulates both the phagocytotic activities and the inflammatory profiles of these cells. Deficiency of Bid attenuated the phagocytotic activity of primary microglia and peritoneal macrophages. It also changed the expression profile of distinct inflammation-related genes in lipopolysaccharide-activated microglia and peritoneal macrophages in vitro and in an in vivo sepsis-like paradigm. Notably, similar changes followed downregulation of Bid in the N9 microglial cell line. Cell death could not be detected in any of the systems examined. Our findings demonstrate that Bid can regulate the immunological profiles of activated microglial and macrophages, via a novel nonapoptotic activity. In view of the critical role of these cells in various pathologies, including acute and chronic brain insults, our findings suggest that impairments in Bid expression may contribute to these pathologies also via a nonapoptotic activity.

Enhanced IL-12p40 production by phenylarsine oxide is mediated by cAMP response element in macrophages

Phenylarsine oxide (PAO), a membrane-permeable trivalent arsenical, is widely used as an inhibitor of protein tyrosine phosphatases. It reacts with vicinal sulfhydryl groups of proteins to form stable ring structures. Here we show the regulatory function of PAO in immune responses from macrophages. PAO significantly induced the secretion of interleukin (IL)-12p40 in lipopolysaccharide-stimulated macrophages. The mRNA expression and the gene promoter activity of IL-12p40 were enhanced by PAO. These results suggest that PAO may enhance IL-12p40 production at the transcriptional level. Furthermore, the effects of PAO on several signaling molecules regulating IL-12p40 expression were investigated. PAO attenuated the induced binding activity of cAMP response element (CRE), but not of NF-kappaB. Moreover, CRE promoter activity was dose-dependently inhibited by PAO and the increased secretion of IL-12p40 by PAO was reduced by forskolin, a cAMP activator. These results suggest that PAO enhances IL-12p40 production by inhibiting CRE activity.

Interferon regulatory factors in hematopoietic cell differentiation and immune regulation

Members of the interferon regulatory factor (IRF) family are transcription factors implicated in the regulation of a variety of biological processes. Originally identified as intracellular mediators of the induction and biological activities of interferons, their central role in host resistance to pathogens has recently been confirmed by the recognition of their involvement in the regulation of gene expression in responses triggered by Toll-like receptors and other pattern recognition receptors (PRRs). Their function in regulating the development as well as the activity of hematopoietic cells puts them at the interface between innate and adaptive immune responses. IRFs also regulate cell growth and apoptosis in several cell types, thereby affecting susceptibility to and the progression of cancer. In this review the role of some members of the family more deeply involved in the differentiation of hematopoietic cells and in immune regulation is addressed, with a specific focus on T cells and dendritic cells.

Transcriptional regulation of Foxp3 gene: multiple signal pathways on the road

Foxp3, forkhead/winged helix transcription factor 3, is a master transcription factor for the development and function of regulatory T cells. Foxp3 has been proved to be associated with immunoregulation, autoimmune diseases, infections, and tumor immune evasion/escape. Foxp3 regulates other critical gene transcriptions. However, the mechanism how the transcription of Foxp3 itself is regulated remains partly clear. In this article, we provided an overview of the current understanding of the transcriptional regulation of Foxp3 gene, including signaling pathways initiated by TCR, IL-2R/STAT pathway, TGF-beta/Smad pathway, PI3K/Akt/mTOR axis, Notch signal pathway, IFN/IRF and IFN/nitric oxide axis, and epigenetic mechanisms. Some therapeutic agents on Foxp3 regulation were also reviewed. Points for attention in further study of Foxp3 transcription regulation, such as the combinations/cross-talks, the bi-directional functions, and species specificity of these pathways, were discussed as well.

Cholera toxin inhibits IL-12 production and CD8alpha+ dendritic cell differentiation by cAMP-mediated inhibition of IRF8 function

Prior studies have demonstrated that cholera toxin (CT) and other cAMP-inducing factors inhibit interleukin (IL)-12 production from monocytes and dendritic cells (DCs). We show that CT inhibits Th1 responses in vivo in mice infected with Toxoplasma gondii. This correlated with low serum IL-12 levels and a selective reduction in the numbers of CD8α⁺ conventional DCs (cDCs) in lymphoid organs. CT inhibited the function of interferon (IFN) regulatory factor (IRF) 8, a transcription factor known to positively regulate IL-12p35 and p40 gene expression, and the differentiation of CD8α⁺ and plasmacytoid DCs (pDCs). Fluorescence recovery after photobleaching analysis showed that exposure to CT, forskolin, or dibutyryl (db) cAMP blocked LPS and IFN-γ–induced IRF8 binding to chromatin. Moreover, CT and dbcAMP inhibited the binding of IRF8 to the IFN-stimulated response element (ISRE)–like element in the mouse IL-12p40 promoter, likely by blocking the formation of ISRE-binding IRF1–IRF8 heterocomplexes. Furthermore, CT inhibited the differentiation of pDCs from fms-like tyrosine kinase 3 ligand–treated bone marrow cells in vitro. Therefore, because IRF8 is essential for IL-12 production and the differentiation of CD8α⁺ cDCs and pDCs, these data suggest that CT and other Gs-protein agonists can affect IL-12 production and DC differentiation via a common mechanism involving IRF8.

Cooperative NCoR/SMRT interactions establish a corepressor-based strategy for integration of inflammatory and anti-inflammatory signaling pathways

Innate immune responses to bacterial or viral infection require rapid transition of large cohorts of inflammatory response genes from poised/repressed to actively transcribed states, but the underlying repression/derepression mechanisms remain poorly understood. Here, we report that, while the nuclear receptor corepressor (NCoR) and silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressors establish repression checkpoints on broad sets of inflammatory response genes in macrophages and are required for nearly all of the transrepression activities of liver X receptors (LXRs), they can be selectively recruited via c-Jun or the Ets repressor Tel, respectively, establishing NCoR-specific, SMRT-specific, and NCoR/SMRT-dependent promoters. Unexpectedly, the binding of NCoR and SMRT to NCoR/SMRT-dependent promoters is frequently mutually dependent, establishing a requirement for both proteins for LXR transrepression and enabling inflammatory signaling pathways that selectively target NCoR or SMRT to also derepress/activate NCoR/SMRT-dependent genes. These findings reveal a combinatorial, corepressor-based strategy for integration of inflammatory and anti-inflammatory signals that play essential roles in immunity and homeostasis.

Down-regulation of dendritic cell signaling pathways by Leishmania amazonensis amastigotes

We have previously reported a link between a deficient Th1 response to Leishmania amazonensis (La) parasites and profound impairments in the cytokine/chemokine network at early stages of the infection. To define the molecular basis of these deficiencies, we focused on early and intracellular events in La-infected dendritic cells (DCs) in this study. La amastigote-infected DCs were less mature and less potent antigen-presenting cells (APC) than their promastigote-infected counterparts, as judged by the lower expression of CD40 and CD83, suppressed cytokine expression (IL-12p40 and IL-10), reduced effectiveness for priming CD4+ T cells from naïve or infected mice. Infection with La promastigotes, but not amastigotes, triggered transient expression of IL-12p40 by DC. Both forms of parasites markedly suppressed IL-12p40, IL-12p70, and IL-6 production and increased IL-10 production when DCs were treated with LPS, IFN-gamma/LPS or IFN-alpha/LPS as positive stimuli. Of note, pre-infection of DCs with live amastigotes resulted in multiple alterations in innate signaling pathways, including degradation of STAT2, decreased phosphorylation of STAT1, 2, 3 and ERK1/2, and markedly reduced expression of interferon regulatory factor-1 (IRF-1) and IRF-8, some of which were partially reversed by pretreatment of parasites with proteasome or protease inhibitors. The impaired IL-12 production in infected DCs was not attributed to increased IL-10 production. Together, our data suggest that La parasites, especially in their intracellular forms, have evolved unique strategies to actively down-regulate early innate signaling events, resulting in impaired DC function and Th1 activation.

The contribution of transcription factor IRF1 to the interferon-gamma-interleukin 12 signaling axis and TH1 versus TH-17 differentiation of CD4+ T cells

Interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) drive T helper type 1 (T(H)1) differentiation, but the mechanisms underlying the regulation of the complicated gene networks involved in this differentiation are not fully understood. Here we show that the IFN-gamma-induced transcription factor IRF1 was essential in T(H)1 differentiation by acting on Il12rb1, the gene encoding the IL-12 receptor beta1 subunit (IL-12Rbeta1). IRF1 directly interacted with and activated the Il12rb1 promoter in CD4+ T cells. Notably, the IRF1-dependent induction of IL-12Rbeta1 was essential for IFN-gamma-IL-12 signaling but was dispensable for IL-23-IL-17 signaling. Because both IL-12 and IL-23 bind to and transmit signals through IL-12Rbeta1, our data suggest that distinct thresholds of IL-12Rbeta1 expression are required for T(H)1 versus T(H)-17 differentiation.

Cloning, promoter analysis and expression in response to bacterial exposure of sea bass (Dicentrarchus labrax L.) interleukin-12 p40 and p35 subunits

Interleukin-12 (IL-12) is a heterodimeric cytokine pivotal in resistance to microbial and viral infections. In the search for immunoregulatory genes in sea bass the genes for the two IL-12 subunits p40 and p35 were cloned and sequenced. Molecular characterization of these two genes was performed at both the cDNA and genomic levels. Sea bass IL-12 p40 and p35 conserve most cysteines involved in the intra-chain disulfide bonds of human IL-12 subunits as well as the important structural residues for human IL-12 heterodimerization. The gene organization of sea bass IL-12 p40 is similar to the human orthologue, whilst the sea bass IL-12 p35 gene structure, as reported for pufferfish, differs from the human one in containing an additional exon and lacking a second copy of a duplicated exon present in the mammalian genes. The promoter analysis of both sea bass and pufferfish IL-12 genes showed the presence of the main cis-acting elements involved in the transcriptional regulation of human and mouse orthologues. The involvement of IL-12 in sea bass anti-bacterial immune responses was demonstrated by investigating the expression profiles of IL-1beta, IL-12 p40 and p35 in the head-kidney and spleen following intraperitoneal injection of UV-killed and live Photobacterium damselae ssp. piscicida (Phdp). Finally, the importance of nuclear factor (NF)-kappaB on UV-killed Phdp-induced IL-12 p40 and p35 gene transcription was shown by the use of pyrrolidine dithiocarbamate (PDTC).

Repression of interferon regulatory factor 1 by hepatitis C virus core protein results in inhibition of antiviral and immunomodulatory genes

Hepatitis C virus (HCV) proteins are known to interfere at several levels with both innate and adaptive responses of the host. A key target in these effects is the interferon (IFN) signaling pathway. While the effects of nonstructural proteins are well established, the role of structural proteins remains controversial. We investigated the effect of HCV structural proteins on the expression of interferon regulatory factor 1 (IRF-1), a secondary transcription factor of the IFN system responsible for inducing several key antiviral and immunomodulatory genes. We found substantial inhibition of IRF-1 expression in cells expressing the entire HCV replicon. Suppression of IRF-1 synthesis was mainly mediated by the core structural protein and occurred at the transcriptional level. The core protein in turn exerted a transcriptional repression of several interferon-stimulated genes, targets of IRF-1, including interleukin-15 (IL-15), IL-12, and low-molecular-mass polypeptide 2. These data recapitulate in a unifying mechanism, i.e., repression of IRF-1 expression, many previously described pathogenetic effects of HCV core protein and suggest that HCV core-induced IRF-1 repression may play a pivotal role in establishing persistent infection by dampening an effective immune response.

IL10 and IL12B polymorphisms each influence IL-12p70 secretion by dendritic cells in response to LPS

Dendritic cells (DC) are the main producers of the cytokine IL-12p70, through which they play a direct role in the development of IFN-gamma-secreting Th1 cells, costimulation of CTL differentiation and NK-cell activation. In contrast, IL-10, which is also produced by DC, negatively regulates IL-12 production. IL-12p70 production varies widely between individuals, and several polymorphisms in the gene encoding IL-12p40 (IL12B) have been identified that influence susceptibility and severity of infectious, autoimmune and neoplastic disease. Here we show that polymorphisms not only of IL12B, but also in the IL10 promoter, influence IL-12p70 secretion by monocyte-derived DC in response to LPS. Although IL12B promoter homozygotes were prone to making more IL-12p70, presence of the IL10 high genotype restricted IL-12p70 production in these individuals. These observations provide a further genetic control of IL-12p70 regulation and emphasize the complexity of production of this cytokine. They also suggest genotypes that might influence the outcome of DC immunotherapy.

Hydrogen peroxide increases interleukin-12 p40/p70 molecular ratio and induces Th2-predominant responses in mice

To investigate the influence of oxidative stress on the immune response, mice were injected with H(2)O(2), and peritoneal macrophages were isolated and stimulated in vitro with lipopolysaccharide (LPS). H(2)O(2) significantly augmented both interleukin (IL)-12p40 and IL-12p70 production and increased the p40/p70 molecular ratio. This was confirmed by mRNA analysis, which showed that H(2)O(2) increased LPS-induced mRNA expression of both IL-12p40 and IL-12p35 subunits with an increased p40/p35 ratio. Analysis of anti-ovalbumin (OVA) antibodies revealed that H(2)O(2) injection significantly increased the production of type 2 helper T cell (Th2)-associated antibody classes [immunoglobulin (Ig)E and IgG1] but not a Th1-associated antibody class (IgG2a). To confirm the Th2-predominant immune response, we analyzed the profile of cytokine production by spleen T cells of OVA-immunized and H(2)O(2)-injected mice. H(2)O(2) significantly increased the production of IL-4 but not that of interferon-gamma. Together, these results suggest that H(2)O(2)-induced overproduction of IL-12p40 promotes the Th2-predominant response through increased production of IL-12p40-homodimers, which could serve as an antagonist of the Th1-inducing cytokine IL-12p70.

Role of the IBD5 susceptibility locus in the inflammatory bowel diseases

The field of inflammatory bowel disease genetics plays a leading role in the genetics of complex traits. One of the first genetic loci for a complex trait to be identified by genome-wide linkage scans and confirmed by multiple studies was IBD1 for Crohn's disease. Shortly after this initial success, a second susceptibility locus, the IBD5 risk haplotype, was discovered and unequivocally replicated. In this review, we examine the genetics and potential functional implications of the IBD5 locus on disease susceptibility, prognosis, classification, and treatment. In addition, we discuss the challenges faced when the region identified by association contains multiple genes that are not easily separated by recombination-the primary tool of the human geneticist.

Expression and DNA binding activity of the recombinant interferon regulatory factor-1 (IRF-1) of mouse

Interferon regulatory factor-1 (IRF-1) is a positive transcription factor for genes involved in immune response, cell growth regulation and apoptosis in mammalian cells. Many agents like virus, interferon (IFN), double-stranded RNA (dsRNA), proinflammatory cytokines, prolactin etc. induce IRF-1 at transcriptional level. IRF-1 transcriptionally activates many IRF-1-regulated genes during normal physiological and pathological conditions. We have expressed recombinant mouse IRF-1 (329 amino acids) as a GST(glutathione-S-transferase)-IRF-1 fusion protein from a 1029 bp IRF-1 cDNA in pGEX-2TK expression vector in Escherichia coli XL-1 blue cells. Recombinant GST-IRF-1 was highly expressed as a approximately 66 kDa soluble protein by IPTG-induction, and was biologically active in terms of its DNA binding activity with a 24 bp specific oligonucleotide, i.e. 32P(GAAAGT)4 but not with a similar but nonspecific oligonucleotide i.e. 32P(GAAA)6. GST-alone expressed from the vector did not bind 32P(GAAAGT)4. We observed multiple (1-4) GST-IRF-1-(GAAAGT)4 protein-DNA complexes which were competed out by 25x- to 100x-fold molar excess of (GAAAGT)4 showing that the complexes 1-4 were specific for IRF-1. Such GAAANN (N = any nucleotide) hexanucleotides occur in the promoters of many virus- and interferon-inducible mammalian genes. Multimeric GAAAGT/C sequences are inducible by virus, IFN, dsRNA and IRF-1. Specificity of DNA binding by IRF-1 lies in the 5th and 6th nucleotides in the GAAAGT sequence. Multiple IRF-1-DNA complexes should stimulate transcription by IRF-1.

Interleukin-12: an update on its immunological activities, signaling and regulation of gene expression

Interleukin-12 (IL-12) is a heterodimeric cytokine composed of the p35 and p40 subunits. It is produced by antigen-presenting cells and plays a critical role in host defense against intracellular microbial infection and control of malignancy via its ability to stimulate both innate and adaptive immune effector cells. The potency of IL-12 renders itself to stringent regulation of the timing, locality and magnitude of its production during an immune response. Subversion of the delicate control and balance frequently leads to immunologic disorders. In this article, we provide an update, since our last review of the subject four years ago, on recent advances in: (1) uncovering of novel activities of IL-12 and related molecules in various immunological settings and models; and (2) dissection of the physiological pathways involved in the modulation of IL-12 production by pathogens and immune regulators. The increased understanding of IL-12 immunobiology and expression will likely benefit the development of therapeutic modalities to correct immune dysfunctions.

C5a negatively regulates toll-like receptor 4-induced immune responses

The complement system and the Toll-like receptors (TLRs) are two central arms of innate immunity that are critical to host defense as well as the development of adaptive immunity. Most pathogens activate both complement and TLRs, suggesting the potential for crosstalk between the two systems. We show here that the complement-derived C5a anaphylatoxin negatively regulates TLR4- and CD40-induced synthesis of IL-12 family cytokines (IL-12, IL-23, and IL-27) from inflammatory macrophages (M phi s) by extracellular signal-regulated kinase- and phosphoinositide 3 kinase-dependent pathways. This decreased cytokine response translates into a decreased T helper type 1 (Th1) response in vitro and in vivo. Accordingly, we found enhanced Th1 immunity in C5a receptor-deficient mice, something that conferred protection from Leishmania major infection. Our findings identify the negative impact of C5a on IL-12 family cytokines as an important mechanism for regulating Th1 polarization in response to innate and adaptive immune network activation.

Ubiquitin-dependent degradation of interferon regulatory factor-8 mediated by Cbl down-regulates interleukin-12 expression

Interferon regulatory factor (IRF)-8/interferon consensus sequence-binding protein is regulated by both transcription and degradation. IRF-8 induced in peritoneal macrophages by interferon-gamma and lipopolysaccharide was degraded rapidly, and degradation of IRF-8 was blocked by MG132, the proteasome inhibitor, but inhibitors of calpain and lysosomal enzymes had no effect. The ubiquitination of IRF-8 was shown by co-immunoprecipitation from RAW264.7 macrophages retrovirally transduced with IRF-8 and hemagglutinin-ubiquitin. The dominant negative ubiquitin mutants K48R and K29R inhibited IRF-8 degradation in 293T cells, confirming the relationship between ubiquitination of IRF-8 and its degradation. IRF-8 carboxyl-terminal truncation mutants were not ubiquitinated and were consequently stable, indicating that the carboxyl-terminal domain of IRF-8 controls ubiquitination. The ubiquitin-protein isopeptide ligase (E3) that ubiquitinated IRF-8 was likely to be Cbl, which formed a complex with IRF-8, demonstrable by both immunoprecipitation and gel filtration. Furthermore, IRF-8 stability was increased by dominant negative Cbl, and IRF-8 ubiquitination was significantly attenuated in Cbl-/- cells. Reflecting increased stability and expression, the IRF-8 carboxyl-terminal deletion mutant induced interleukin (IL)-12 p40 promoter activity much more strongly than IRF-8 did. Furthermore, IRF-8-induced IL-12 p40 synthesis in RAW264.7 cells was enhanced by dominant negative Cbl, and peritoneal macrophages from Cbl-/- mice showed increased IL-12 p40 protein production. Taken together, these results suggest that the proteasomal degradation of IRF-8 mediated by the ubiquitin E3 ligase Cbl down-regulates IL-12 expression.

NOD macrophages produce high levels of inflammatory cytokines upon encounter of apoptotic or necrotic cells

During the development of type 1 diabetes, pancreatic beta-cells are subject to an immune attack, leading to their apoptotic or necrotic cell death. Apoptotic beta-cells are also present during periods of tissue remodeling, such as in early life. Macrophages should clear apoptotic cells silently without production of pro-inflammatory cytokines. The aim of the present study was to investigate the cytokine pattern of NOD macrophages exposed to apoptotic or necrotic cells in vitro. In contrast to the limited response of macrophages from C57BL/6 or NOR mice, NOD macrophages reacted aberrantly to both necrotic and apoptotic cells, with secretion of inappropriately high amounts of IL1beta and TNFalpha. Further exploration of the macrophage behavior showed an excessive response of NOD macrophages when exposed to LPS (high iNOS and IL12p40 levels), accompanied by hyper-activation of NF-kappaB(p65). In contrast, NOD macrophages failed to up-regulate IL1beta and IL12p40 in response to IFNgamma. This failure correlated with low protein levels and a low phosphorylation state of STAT1alpha. We conclude that NOD macrophages have severely aberrant cytokine expression patterns that could contribute to the initiation or continuation of an immune attack towards the pancreatic beta-cells and thus onset and progression of type 1 diabetes.

Roles of interferon-regulatory factors in T-helper-cell differentiation

Members of the interferon-regulatory factor family of transcription factors have long been known to be intracellular mediators of the effects of interferons. In recent years, interferon-regulatory factors have also been shown to have an essential role in the differentiation of T helper cells, both by modulating the functions of antigen-presenting cells and by having direct effects on the T helper cells themselves. Depending on the interferon-regulatory factor involved, the differentiation of T helper cells to either T helper 1 cells or T helper 2 cells can be influenced. In this article, we provide an overview of this relatively new and still underappreciated role of interferon-regulatory factors.

Stress-induced versus preovulatory and pregnancy hormonal levels in modulating cytokine production following whole blood stimulation

Estradiol, progesterone, prolactin and cortisol concentrations are substantially increased during pregnancy. Also, cortisol and prolactin levels are elevated during stress. In the present study, we exposed peripheral blood to estradiol, progesterone, prolactin and cortisol alone or in combination for 24 h before stimulation with T-dependent (phytohemagglutinin, PHA) and independent activators (lipopolysaccharide, LPS) to study their immunomodulatory role in interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and IL-10 production in a whole blood model. This should be similar to in vivo exposure conditions such as long-term stress, preovulatory or pregnancy periods. The present study showed that the stress-induced and preovulatory levels of prolactin and estradiol, respectively, increased the production of IFN-gamma and IL-12 levels (and IL-10 in the case of estradiol) in PHA + LPS-stimulated whole blood, and inhibited a hydrocortisone (100 nmol/l) suppressive effect on IFN-gamma, IL-12 and IL-10 productions. In LPS-stimulated whole blood, however, prolactin enhanced only IL-10 production levels in a non-concentration-dependent manner. Higher prolactin levels as in pregnancy did not modulate any of the cytokines, but pregnancy estradiol concentrations only induced higher IL-10 levels in PHA + LPS-stimulated whole blood. All progesterone levels tested revealed no effect on any of the cytokines following whole blood stimulation. Our results indicate that (1) a long exposure time of prolactin and estradiol to whole blood modulates the production of cytokines in a concentration- and stimulus-dependent manner; (2) stress-induced levels of prolactin and preovulatory estradiol concentrations can regulate cortisol-induced cytokine suppression, and (3) even though the cytokine pattern is different, pregnancy estradiol and cortisol levels decreased the IFN-gamma/IL-10 ratio, thereby keeping the anti-inflammatory IL-10 levels favored during pregnancy, which could be useful in regulating inflammatory-mediated autoimmune diseases.

Role of IFN regulatory factor-1 and IL-12 in immunological resistance to pathogenesis of N-methyl-N-nitrosourea-induced T lymphoma

IFN regulatory factor-1 (IRF-1) is a critical effector molecule in IFN signaling and acts as a tumor suppressor and tumor susceptibility gene. IL-12 is a key factor in the induction of innate resistance and generation of Th1 cells and CTL. Our recent study has revealed an intimate relationship between IRF-1 and IL-12 in that IRF-1 regulates the production of IL-12 by selectively controlling transcriptional activation of IL-12 p35 gene. In this work, we find that IRF-1-deficient mice are highly susceptible to N-methyl-N-nitrosourea (MNU)-induced T lymphomas. This susceptibility is associated with strong defects in the expression of IL-12, lymphotoxin (LT)beta, and IFN-gamma. Consistently, IL-12 p35(-/-), IFN-gamma(-/-), and LTbeta(-/-) mice are also highly vulnerable to MNU-induced carcinogenesis. Administration of rIL-12 to IRF-1(-/-) mice restores normal expression of LTbeta and IFN-gamma, and significantly enhances the ability of IRF-1(-/-) mice to resist MNU-induced pathogenesis. This strongly suggests an IRF-1/IL-12/IFN-gamma regulatory axis in tumor surveillance. By DNA microarray analysis, we comprehensively identify differences and patterns in gene expression in splenocytes of wild-type (WT) vs IRF-1(-/-) mice challenged with MNU. This study contributes to efforts to elucidate the cellular/molecular mechanisms and the downstream players involved in IRF-1-mediated host defense against lymphoproliferative malignancies.