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Adjuvants are important vaccine components, composed of a variety of chemical and biological materials that enhance the vaccine antigen-specific immune responses by stimulating the innate immune cells in both direct and indirect manners to produce a variety cytokines, chemokines, and growth factors. It has been developed by empirical methods for decades and considered difficult to choose a single screening method for an ideal vaccine adjuvant, due to their diverse biochemical characteristics, complex mechanisms of, and species specificity for their adjuvanticity. We therefore established a robust adjuvant screening strategy by combining multiparametric analysis of adjuvanticity in vivo and immunological profiles in vitro (such as cytokines, chemokines, and growth factor secretion) of various library compounds derived from hot-water extracts of herbal medicines, together with their diverse distribution of nano-sized physical particle properties with a machine learning algorithm. By combining multiparametric analysis with a machine learning algorithm such as rCCA, sparse-PLS, and DIABLO, we identified that human G-CSF and mouse RANTES, produced upon adjuvant stimulation in vitro, are the most robust biological parameters that can predict the adjuvanticity of various library compounds. Notably, we revealed a certain nano-sized particle population that functioned as an independent negative parameter to adjuvanticity. Finally, we proved that the two-step strategy pairing the negative and positive parameters significantly improved the efficacy of screening and a screening strategy applying principal component analysis using the identified parameters. These novel parameters we identified for adjuvant screening by machine learning with multiple biological and physical parameters may provide new insights into the future development of effective and safe adjuvants for human use.

The commensal microbiota within the gastrointestinal tract is essential in maintaining homeostasis. Indeed, dysregulation in the repertoire of microbiota can result in the development of intestinal immune-inflammatory diseases. Further, this immune regulation by gut microbiota is important systemically, impacting health and disease of organ systems beyond the local environment of the gut. What has not been explored is how distant organs might in turn shape the microbiota via microbe-targeted molecules. Here, we provide evidence that surfactant protein D (SP-D) synthesized in the gallbladder and delivered into intestinal lumen binds selectively to species of gut commensal bacteria. SP-D-deficient mice manifest intestinal dysbiosis and show a susceptibility to dextran sulfate sodium-induced colitis. Further, fecal transfer from SP-D-deficient mice to wild-type, germ-free mice conveyed colitis susceptibility. Interestingly, colitis caused a notable increase in Sftpd gene expression in the gallbladder, but not in the lung, via the activity of glucocorticoids produced in the liver. These findings describe a unique mechanism of interorgan regulation of intestinal immune homeostasis by SP-D with potential clinical implications such as cholecystectomy.

Cellular components released into the external milieu as a result of cell death and sensed by the body are generally termed damage-associated molecular patterns (DAMPs). Although DAMPs are conventionally thought to be protective to the host by evoking inflammatory responses important for immunity and wound repair, there is the prevailing notion that dysregulated release of DAMPs can also underlie or exacerbate disease development. However, the critical issue for how resultant DAMP-mediated responses are regulated has heretofore not been fully addressed. In the present study, we identify prostaglandin E2 (PGE2) as a DAMP that negatively regulates immune responses. We show that the production of PGE2 is augmented under cell death-inducing conditions via the transcriptional induction of the cyclooxygenase 2 (COX2) gene and that cell-released PGE2 suppresses the expression of genes associated with inflammation, thereby limiting the cell's immunostimulatory activities. Consistent with this, inhibition of the PGE2 synthesis pathway potentiates the inflammation induced by dying cells. We also provide in vivo evidence for a protective role of PGE2 released upon acetaminophen-induced liver injury as well as a pathogenic role for PGE2 during tumor cell growth. Our study places this classically known lipid mediator in an unprecedented context-that is, an inhibitory DAMP vis-à-vis activating DAMPs, which may have translational implications for designing more effective therapeutic regimens for inflammation-associated diseases.

Recent years have seen a number of regulatory approvals for immune oncology or immunotherapies based on their ability to enhance antitumor immune responses. Nevertheless, the majority of patients remain refractory to these treatments; hence, new therapies that augment current immunotherapies are required. Innate immune receptors that recognize nucleic acids are potent activators of subsequent T‐cell responses and, as a result, can evoke potent antitumor immune responses. Herein, we present a novel compound N‐{3‐[(1,4′‐bipiperidin)‐1′‐yl]propyl}‐6‐[4‐(4‐methylpiperazin‐1‐yl)phenyl]picolinamide (SINCRO; STING‐mediated interferon‐inducing and cytotoxic reagent, original) as an anticancer drug that activates the cytosolic DNA‐sensing STING (stimulator of interferon genes) signaling pathway leading to the induction of type I interferon (IFN) genes. Indeed, IFN‐β gene induction by SINCRO is abolished in STING‐deficient cells. In addition to its IFN‐inducing activity, SINCRO shows STING‐independent cytotoxic activity against cancer cells. SINCRO does not evoke DNA double‐strand break or caspase‐3 cleavage. Thus, SINCRO induces cell death in a method different from conventional apoptosis‐inducing pathways. Finally, we provide evidence that giving SINCRO significantly attenuates in vivo tumor growth by both type I IFN‐dependent and independent mechanisms. Thus, SINCRO is an attractive anticancer compound with dual function in that it evokes type I IFN response to promote antitumor immunity as well as inducing tumor cell death. SINCRO may provide a new platform for the development of drugs for effective cancer therapy.

The regulation of intestinal homeostasis by the immune system involves the dynamic interplay between gut commensal microbiota and resident immune cells. It is well known that a large and diverse lymphocyte antigen receptor repertoire enables the immune system to recognize and respond to a wide range of invading pathogens. There is also an emerging appreciation for a critical role the T-cell receptor (TCR) repertoire serves in the maintenance of peripheral tolerance by regulatory T cells (Tregs). Nevertheless, how the diversity of the TCR repertoire in Tregs affects intestinal homeostasis remains unknown. To address this question, we studied mice whose T cells express a restricted TCR repertoire. We observed the development of spontaneous colitis, accompanied by the induction of T-helper type 17 cells in the colon that is driven by gut commensal microbiota. We provide further evidence that a restricted TCR repertoire causes a loss of tolerogenicity to microbiota, accompanied by a paucity of peripherally derived, Helios(-) Tregs and hyperactivation of migratory dendritic cells. These results thus reveal a new facet of the TCR repertoire in which Tregs require a diverse TCR repitoire for intestinal homeostasis, suggesting an additional driving force in the evolutional significance of the TCR repertoire.

Interferons (IFNs) are a broad class of cytokines elicited on challenge to the host defense and are essential for mobilizing immune responses to pathogens. Divided into three classes, type I, type II, and type III, all IFNs share in common the ability to evoke antiviral activities initiated by the interaction with their cognate receptors. The nine-member IFN regulatory factor (IRF) family, first discovered in the context of transcriptional regulation of type I IFN genes following viral infection, are pivotal for the regulation of the IFN responses. In this review, we briefly describe cardinal features of the three types of IFNs and then focus on the role of the IRF family members in the regulation of each IFN system.

High-mobility group box 1 (HMGB1) is a DNA-binding protein abundantly expressed in the nucleus that has gained much attention for its regulation of immunity and inflammation. Despite this, whether and how HMGB1 contributes to protective and/or pathological responses in vivo is unclear. In this study, we constructed Hmgb1-floxed (Hmgb1(f)(/f)) mice to achieve the conditional inactivation of the gene in a cell- and tissue-specific manner by crossing these mice with an appropriate Cre recombinase transgenic strain. Interestingly, although mice with HMGB1 ablation in myeloid cells apparently develop normally, they are more sensitive to endotoxin shock compared with control mice, which is accompanied by massive macrophage cell death. Furthermore, these mice also show an increased sensitivity to Listeria monocytogenes infection. We also provide evidence that the loss of HMGB1 in macrophages results in the suppression of autophagy, which is commonly induced by lipopolysaccharide stimulation or L. monocytogenes infection. Thus, intracellular HMGB1 contributes to the protection of mice from endotoxemia and bacterial infection by mediating autophagy in macrophages. These newly generated HMGB1 conditional knockout mice will serve a useful tool with which to study further the in vivo role of this protein in various pathological conditions.

A major function of innate immune receptors is to recognize pathogen-associated molecular patterns and then evoke immune responses appropriate to the nature of the invading pathogen(s). Because innate immune cells express various types of these receptors, distinct combinations of signaling pathways are activated in response to a given pathogen. Although the conventional wisdom is that these signaling pathways cooperate with one another to ensure an effective host response, a more nuanced view recognizes antagonism between the individual pathways, where the attenuation of a signaling pathway(s) by others may shape the immune response. In this study, we show that, on Listeria monocytogenes infection, Toll-like receptor-triggered MyD88 signaling pathways suppress type I IFN gene induction, which is detrimental to macrophage bactericidal activity. These pathways target and suppress the IFN regulatory factor 3 (IRF3) transcription factor that is activated by the stimulator of IFN genes-TANK-binding kinase-1 kinase pathway. We also provide evidence for the involvement of the MAPK phosphatase family members, which renders IRF3 hypophosphorylated on Toll-like receptor signaling by enhancing the formation of an MAPK phosphatase-IRF3-TANK-binding kinase-1 ternary complex. This study, therefore, reveals a hitherto unrecognized and important contribution of a beneficial innate signaling interference against bacterial infections.

The regulation of the Il12b gene, encoding the shared p40 subcomponent for IL-12 and IL-23, is critical for innate immune responses and subsequent T cell polarization. This gene is robustly induced upon Toll-like receptor (TLR) stimulation, wherein an enhancer located 10kb upstream of the transcription start site is required for promoter activity; however, the underlying mechanisms that regulate this enhancer in cooperation with the promoter has remained elusive. We show here that the Il12b enhancer contains functional ISREs for recognition by interferon regulatory factors (IRFs), and provide evidence that TLR-activated IRF5 mediates cooperativity of the enhancer with the promoter which also contains ISREs. By contrast, IRF3 activated by cytosolic RIG-I-like receptor (RLR) signaling binds to these ISREs and causes gene suppression. Consistently, IRF5 binding is accompanied with chromatin remodeling of both regulatory regions and the formation of a productive transcriptional complex containing other transcription factors, whereas these events are inhibited by IRF3 binding. We show that the ISREs embedded in the enhancer are indeed critical for its activation by IRF5. We also adduce evidence that the 5' sequences of the enhancer and promoter ISREs, all of which deviate from consensus ISREs, critically affect the function of IRF3. The dual commitment of these IRFs in the regulation of the Il12b enhancer and promoter is unique and may have implications for understanding the evolution of this gene.

Members of the interferon-regulatory factor (IRF) proteins family were originally identified as transcriptional regulators of the Type I interferon system. Thanks to consistent advances made in our understanding of the immunobiology of innate receptors, it is now clear that several IRFs are critical for the elicitation of innate pattern recognition receptors, and—as a consequence—for adaptive immunity. In addition, IRFs have attracted great attentions as they modulate cellular responses that are involved in tumorigenesis. The regulation of oncogenesis by IRFs has important implications for understanding the host susceptibility to several Types of cancers, their progression, as well as the potential for therapeutic interventions.

Blunting immunopathology without abolishing host defense is the foundation for safe and effective modulation of infectious and autoimmune diseases. Sphingosine 1-phosphate receptor 1 (S1PR1) agonists are effective in treating infectious and multiple autoimmune pathologies; however, mechanisms underlying their clinical efficacy are yet to be fully elucidated. Here, we uncover an unexpected mechanism of convergence between S1PR1 and interferon alpha receptor 1 (IFNAR1) signaling pathways. Activation of S1PR1 signaling by pharmacological tools or endogenous ligand sphingosine-1 phosphate (S1P) inhibits type 1 IFN responses that exacerbate numerous pathogenic conditions. Mechanistically, S1PR1 selectively suppresses the type I IFN autoamplification loop in plasmacytoid dendritic cells (pDCs), a specialized DC subset, for robust type I IFN release. S1PR1 agonist suppression is pertussis toxin-resistant, but inhibited by an S1PR1 C-terminal–derived transactivating transcriptional activator (Tat)-fusion peptide that blocks receptor internalization. S1PR1 agonist treatment accelerates turnover of IFNAR1, suppresses signal transducer and activator of transcription 1 (STAT1) phosphorylation, and down-modulates total STAT1 levels, thereby inactivating the autoamplification loop. Inhibition of S1P-S1PR1 signaling in vivo using the selective antagonist Ex26 significantly elevates IFN-α production in response to CpG-A. Thus, multiple lines of evidence demonstrate that S1PR1 signaling sets the sensitivity of pDC amplification of IFN responses, thereby blunting pathogenic immune responses. These data illustrate a lipid G-protein coupled receptor (GPCR)-IFNAR1 regulatory loop that balances effective and detrimental immune responses and elevated endogenous S1PR1 signaling. This mechanism will likely be advantageous in individuals subject to a range of inflammatory conditions.

Although the mechanisms by which innate pathogen-recognition receptors enhance adaptive immune responses are increasingly well understood, whether signaling events from distinct classes of receptors affect each other in modulating adaptive immunity remains unclear. We found here that the activation of cytosolic RIG-I-like receptors (RLRs) resulted in the selective suppression of transcription of the gene encoding the p40 subunit of interleukin 12 (Il12b) that was effectively induced by the activation of Toll-like receptors (TLRs). The RLR-activated transcription factor IRF3 bound dominantly, relative to IRF5, to the Il12b promoter, where it interfered with the TLR-induced assembly of a productive transcription-factor complex. The activation of RLRs in mice attenuated TLR-induced responses of the T helper type 1 cell (T(H)1 cell) and interleukin 17-producing helper T cell (T(H)17 cell) subset types and, consequently, viral infection of mice caused death at sublethal doses of bacterial infection. The innate immune receptor cross-interference we describe may have implications for infection-associated clinical episodes.

The activation of the innate immune responses by DNA exposed within the cytosol has gained much attention and, in this context, several cytosolic DNA sensors have been identified. However, previous studies revealed the operation of redundant and complex mechanisms and it still remains to be clarified how the DNA-mediated evocation of diverse innate immune responses can be achieved. Here we show that two RIG-I-like receptors (RLRs), RIG-I and MDA5, known as cytosolic RNA receptors, nonredundantly function as cytosolic DNA receptors that lead to the selective activation of type I IFN genes. We demonstrate that overexpression of otherwise IFN-inducible RIG-I or MDA5 in IFN signal-deficient cells results in a marked enhancement of type I IFN gene induction upon cytosolic DNA stimulation, while in their absence the induction is impaired. Interestingly, the DNA-mediated induction of other cytokine genes was barely affected by the absence of RLRs. Indeed, unlike the RNA-RLR pathway that activates the transcription factors IRF3 and NF-κB, the DNA-RLR pathway is primarily responsible for the IRF3 activation critical for type I IFN gene transcription, illustrating a deliberate divergence of the DNA signaling pathways. Expectedly, the RLR pathway also contributes to intricate innate immune responses against infection by a DNA virus. Our study may provide insights into the complexity of host defense mechanisms that thwart immune evasion by DNA-containing pathogens.

Central to innate immunity is the sensing of pathogen-associated molecular patterns by cytosolic and membrane-associated receptors. In particular, DNA is a potent activator of immune responses during infection or tissue damage, and evidence indicates that, in addition to the membrane-associated Toll-like receptor 9, an unidentified cytosolic DNA sensor(s) can activate type I interferon (IFN) and other immune responses. Here we report on a candidate DNA sensor, previously named DLM-1 (also called Z-DNA binding protein 1 (ZBP1)), for which biological function had remained unknown; we now propose the alternative name DAI (DNA-dependent activator of IFN-regulatory factors). The artificial expression of otherwise IFN-inducible DAI (DLM-1/ZBP1) in mouse fibroblasts selectively enhances the DNA-mediated induction of type I IFN and other genes involved in innate immunity. On the other hand, RNA interference of messenger RNA for DAI (DLM-1/ZBP1) in cells inhibits this gene induction programme upon stimulation by DNA from various sources. Moreover, DAI (DLM-1/ZBP1) binds to double-stranded DNA and, by doing so, enhances its association with the IRF3 transcription factor and the TBK1 serine/threonine kinase. These observations underscore an integral role of DAI (DLM-1/ZBP1) in the DNA-mediated activation of innate immune responses, and may offer new insight into the signalling mechanisms underlying DNA-associated antimicrobial immunity and autoimmune disorders.

Signaling by Toll-like receptors (TLRs) is central to evoking innate immunity, wherein each TLR is activated by distinct pathogen-derived agonists. It has been shown previously that TLR signaling occurs in synergy when certain TLR agonist combinations simultaneously activate immune cells. This synergism may constitute a mechanism critical to ensuring the effective activation of the immune system by multiple TLR activating molecules associated with a given pathogen; however, its underlying mechanism(s) remain unclarified. Here, we provide evidence that TLRs utilizing the MyD88 adaptor selectively cooperate with those utilizing the TRIF adaptor for synergistic induction of a set of target genes, and that this synergism is abrogated in cells lacking either MyD88 or TRIF. Moreover, we also provide evidence that this TLR synergy is mediated, at least in part, by activation of the transcription factor interferon regulatory factor 5 (IRF5). Thus, our findings offer a mechanistic insight into TLR synergy, revealing the hitherto unknown cross talk between the MyD88 and TRIF pathways for a robust TLR-mediated activation of the immune system.

The contact wire breaking accident caused by the arc between the contact wire and the pantograph happens rarely in the DC electric railway system. The contact wire breaking phenomenon is discussed and investigated based on the experimental data performed 30 years ago. The material of the contact strip and the contact wire has changed, however, and the breaking characteristics of the contact wire caused by the arc should be different. In this paper, the contact wire breaking characteristics are carefully investigated using the recent materials. It is cleared that the breaking index of 750As is approximately appropriate in the limited condition and the other breaking condition is summarized based on the experimental data more than 400 times.

The recognition of microbial components by Toll-like receptors (TLRs) initiates signal transduction pathways, which trigger the expression of a series of target genes. It has been reported that TLR signaling is enhanced by cytokines such as IFN-γ, but the mechanisms underlying this enhancement remain unclear. The MyD88 adaptor, which is essential for signaling by many TLRs, recruits members of the IFN regulatory factor (IRF) family of transcription factors, such as IRF5 and IRF7, to evoke the activation of TLR target genes. In this study we demonstrate that IRF1, which is induced by IFN-γ, also interacts with and is activated by MyD88 upon TLR activation. We provide evidence that MyD88-associated IRF1 migrates into the nucleus more efficiently than non-MyD88-associated IRF1 and that this IRF1 selectively participates in the TLR-dependent gene induction program. The critical role of MyD88-dependent “IRF1 licensing” is underscored by the observation that the induction of a specific gene subset downstream of the TLR–MyD88 pathway, such as IFN-β, inducible NO synthase, and IL-12p35, are impaired inIrf1-deficient cells. Thus, our present study places IRF1 as an additional member participating in MyD88 signaling and provides a mechanistic insight into the enhancement of the TLR-dependent gene induction program by IFN-γ.

Robust type-I interferon (IFN-alpha/beta) induction in plasmacytoid dendritic cells, through the activation of Toll-like receptor 9 (TLR9), constitutes a critical aspect of immunity. It is absolutely dependent on the transcription factor IRF-7, which interacts with and is activated by the adaptor MyD88. How plasmacytoid dendritic cells, but not other cell types (such as conventional dendritic cells), are able to activate the MyD88-IRF-7-dependent IFN induction pathway remains unknown. Here we show that the spatiotemporal regulation of MyD88-IRF-7 signalling is critical for a high-level IFN induction in response to TLR9 activation. The IFN-inducing TLR9 ligand, A/D-type CpG oligodeoxynucleotide (CpG-A), is retained for long periods in the endosomal vesicles of plasmacytoid dendritic cells, together with the MyD88-IRF-7 complex. However, in conventional dendritic cells, CpG-A is rapidly transferred to lysosomal vesicles. We further show that conventional dendritic cells can also mount a robust IFN induction if CpG-A is manipulated for endosomal retention using a cationic lipid. This strategy also allows us to demonstrate endosomal activation of the IFN pathway by the otherwise inactive TLR9 ligand B/K-type oligodeoxynucleotide (CpG-B). Thus, our study offers insights into the regulation of TLR9 signalling in space, potentially suggesting a new avenue for therapeutic intervention.

The activation of Toll-like receptors (TLRs) is central to innate and adaptive immunity. All TLRs use the adaptor MyD88 for signalling, but the mechanisms underlying the MyD88-mediated gene induction programme are as yet not fully understood. Here, we demonstrate that the transcription factor IRF-5 is generally involved downstream of the TLR-MyD88 signalling pathway for gene induction of proinflammatory cytokines, such as interleukin-6 (IL-6), IL-12 and tumour-necrosis factor-alpha. In haematopoietic cells from mice deficient in the Irf5 gene (Irf5-/- mice), the induction of these cytokines by various TLR ligands is severely impaired, whereas interferon-alpha induction is normal. We also provide evidence that IRF-5 interacts with and is activated by MyD88 and TRAF6, and that TLR activation results in the nuclear translocation of IRF-5 to activate cytokine gene transcription. Consistently, Irf5-/- mice show resistance to lethal shock induced by either unmethylated DNA or lipopolysaccharide, which correlates with a marked decrease in the serum levels of proinflammatory cytokines. Thus, our study identifies IRF-5 as a new, principal downstream regulator of the TLR-MyD88 signalling pathway and a potential target of therapeutic intervention to control harmful immune responses.

Toll-like receptor (TLR) activation is central to immunity, wherein the activation of the TLR9 subfamily members TLR9 and TLR7 results in the robust induction of type I IFNs (IFN-α/β) by means of the MyD88 adaptor protein. However, it remains unknown how the TLR signal “input” can be processed through MyD88 to “output” the induction of the IFN genes. Here, we demonstrate that the transcription factor IRF-7 interacts with MyD88 to form a complex in the cytoplasm. We provide evidence that this complex also involves IRAK4 and TRAF6 and provides the foundation for the TLR9-dependent activation of the IFN genes. The complex defined in this study represents an example of how the coupling of the signaling adaptor and effector kinase molecules together with the transcription factor regulate the processing of an extracellular signal to evoke its versatile downstream transcriptional events in a cell. Thus, we propose that this molecular complex may function as a cytoplasmic transductional-transcriptional processor.

Type I interferons (IFN-α/β) affect many aspects of immune responses. Many pathogen-associated molecules, including bacterial lipopolysaccharide (LPS) and virus-associated double-stranded RNA, induce IFN gene expression through activation of distinct Toll-like receptors (TLRs). Although much has been studied about the activation of the transcription factor IRF-3 and induction of IFN - β gene by the LPS-mediated TLR4 signaling, definitive evidence is missing about the actual role of IRF-3 in LPS responses in vitro and in vivo. Using IRF-3 deficient mice, we show here that IRF-3 is indeed essential for the LPS-mediated IFN - β gene induction. Loss of IRF-3 also affects the expression of profile of other cytokine/chemokine genes. We also provide evidence that the LPS/TLR4 signaling activates IRF-7 to induce IFN - β , if IRF-7 is induced by IFNs prior to LPS simulation. Finally, the IRF-3 -deficient mice show resistance to LPS-induced endotoxin shock. These results place IRF-3 as a molecule central to LPS/TLR4 signaling.

Thermal loading in diesel engine pistons has increased dramatically in recent years due to applications of technologies to meet low emission and high power requirements. Control of piston temperatures, therefore, has become one of the determining factors in a successful engine design. Using CFD tools to calculate the coefficient of heat transfer for the cooling gallery, which is influential in piston cooling, a new approach for piston temperature prediction has been developed. Compared with conventional temperature estimation based on past experience, this approach improves prediction results and enables an optimum cooling condition to be successfully obtained at the design stage.

Cam/tappet wear is one of the most difficult reliability and durability problems to predict during the development of a prototype engine valve-train system. In the present study, the cam/tappet surface temperature was measured and calculated to determine the effect of surface temperature on the lubricating conditions at a cam/tappet contact. The measurement method, sometimes called the dynamic thermocouple technique, was based on the Seebeck effect: by using different materials for the cam and tappet, the cam/tappet contact point becomes the hot junction of a ‘thermocouple’. The cam/tappet contact surface temperature can therefore be measured continuously. The measured temperature results show good agreement with predictions. Temperature spikes, however, were not found in the test using new oil, but were shown by the theoretical model. Such results indicate that the cam/tappet interface operates in effective lubricating conditions, even when the oil temperature is relatively high. Further research with degraded oil supplied at high temperature is needed for a thorough understanding of abnormal cam wear.

The interferon-regulatory factor (IRF) family, originally identified as transcriptional regulators of the type I interferon system, consists of nine members in mammals. A large number of studies have revealed the versatile and critical functions performed by this transcription factor family in immunity and other biological processes. Most notably, the advances in the study of signal transducing innate immune receptors have placed many IRF members as central mediators in the regulation of innate immune responses. In parallel, mechanistic studies have made it clearer that many IRFs exert their function either in cooperation or competition with other factors. In this article, we discuss current advances on the multipurpose and critical functions of IRFs in the regulation of innate immunity, particularly as they instruct adaptive immunity.

The activation of innate immune responses by nucleic acids is crucial to protective and pathological immunities and is mediated by the transmembrane Toll-like receptors (TLRs) and cytosolic receptors. However, it remains unknown whether a mechanism exists that integrates these nucleic-acid-sensing systems. Here we show that high-mobility group box (HMGB) proteins 1, 2 and 3 function as universal sentinels for nucleic acids. HMGBs bind to all immunogenic nucleic acids examined with a correlation between affinity and immunogenic potential. Hmgb1(-/-) and Hmgb2(-/-) mouse cells are defective in type-I interferon and inflammatory cytokine induction by DNA or RNA targeted to activate the cytosolic nucleic-acid-sensing receptors; cells in which the expression of all three HMGBs is suppressed show a more profound defect, accompanied by impaired activation of the transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor (NF)-kappaB. The absence of HMGBs also severely impairs the activation of TLR3, TLR7 and TLR9 by their cognate nucleic acids. Our results therefore indicate a hierarchy in the nucleic-acid-mediated activation of immune responses, wherein the selective activation of nucleic-acid-sensing receptors is contingent on the more promiscuous sensing of nucleic acids by HMGBs. These findings may have implications for understanding the evolution of the innate immune system and for the treatment of immunological disorders.

Interferons-alpha/beta, which are produced upon viral infection, are key soluble factors for the establishment of an antiviral state, but are also produced at low levels in the absence of infection. Herein, we demonstrate that a weak signal by these constitutively produced IFN-alpha/beta show a preventive role in cellular transformation. Ifnar1-deficient (Ifnar1(-/-)) MEF, which are devoid of IFN-alpha/beta signal, undergo a spontaneous transformation during long-term cell culture. Similar to Irf1(-/-) MEF, primary Ifnar1(-/-) MEF become tumorigenic in nude mice by the expression of activated c-Ha-Ras oncoprotein. However, Ifnar1(-/-) MEF do not show any abnormal growth properties. A similar observation is made in Ifnb(-/-) MEF that fail to produce constitutive IFN-alpha/beta, whereas such a transforming property is not found in MEF that lack any of the IFN receptor downstream molecules including Stat1, IRF9 and IRF1. Furthermore, Ifnar1(-/-) mice develop chemically-induced skin papilloma more severely than wild-type mice. In addition, the expression levels of IFNAR1 mRNA are significantly decreased in human gastric cancer tissues. These results suggest a cell-intrinsic role of the weak signal by constitutively produced IFN-alpha/beta to prevent cells from transformation, which may be mediated by a hitherto-unknown pathway(s) downstream of the IFN-alpha/beta receptor.

A conundrum of innate antiviral immunity is how nucleic acid-sensing Toll-like receptors (TLRs) and RIG-I/MDA5 receptors cooperate during virus infection. The conventional wisdom has been that the activation of these receptor pathways evokes type I IFN (IFN) responses. Here, we provide evidence for a critical role of a Toll-like receptor 3 (TLR3)-dependent type II IFN signaling pathway in antiviral innate immune response against Coxsackievirus group B serotype 3 (CVB3), a member of the positive-stranded RNA virus family picornaviridae and most prevalent virus associated with chronic dilated cardiomyopathy. TLR3-deficient mice show a vulnerability to CVB3, accompanied by acute myocarditis, whereas transgenic expression of TLR3 endows even type I IFN signal-deficient mice resistance to CVB3 and other types of viruses, provided that type II IFN signaling remains intact. Taken together, our results indicate a critical cooperation of the RIG-I/MDA5-type I IFN and the TLR3-type II IFN signaling axes for efficient innate antiviral immune responses.

DNA, whether it is microbe-derived or host-derived, evokes immune responses when exposed to the cytosol of a cell. We previously reported that DNA-dependent activator of IFN regulatory factors (DAI), also referred to as DLM-1/ZBP1, functions as a DNA sensor that activates the innate immune system. In the present study, we examined the regulation of the complex DNA-sensing system by DAI and other molecules. We first show that DAI directly interacts with DNA in vitro and that it requires three DNA-binding domains for full activation in vivo . We also show that the artificially induced dimerization of DAI results in the DNA-independent activation of type I IFN genes, thereby providing a better understanding for the molecular basis of DAI activation. Furthermore, we provide evidence for the presence of additional DNA sensors, either positively or negatively regulating cytosolic DNA-mediated innate immune responses. These results in toto provide insights into the mechanism of DAI activation and reveal the complex regulatory mechanisms underlying DNA-mediated protective and pathologic immune responses.

The recognition of microbial components by Toll-like receptors (TLRs) is an event central to the activation of innate and adaptive immune systems. TLR activation triggers the induction of downstream target genes, wherein the TLR-interacting adaptor molecule MyD88 recruits various signaling molecules and transcription factors. Two members of the IFN regulatory factor (IRF) family of transcription factors, IRF-5 and IRF-7, interact with MyD88 and induce proinflammatory cytokines and type I IFNs, respectively. Here, we show that IRF-4 also interacts with MyD88 and acts as a negative regulator of TLR signaling. IRF-4 mRNA is induced by TLR activation, and IRF-4 competes with IRF-5, but not with IRF-7, for MyD88 interaction. The TLR-dependent induction of proinflammatory cytokines is markedly enhanced in peritoneal macrophages from mice deficient in the Irf4 gene, whereas the induction is inhibited by the ectopic expression of IRF-4 in a macrophage cell line. The critical function of IRF-4 in TLR signaling in vivo is underscored by the observation that Irf4 -deficient mice show hypersensitivity to DNA-induced shock, with elevated serum proinflammatory cytokine levels. This study may provide an insight into the complex regulatory mechanisms of MyD88 signaling by IRFs.

The type-I interferon (IFN-alpha/beta) response is critical to immunity against viruses and can be triggered in many cell types by cytosolic detection of viral infection, or in differentiated plasmacytoid dendritic cells by the Toll-like receptor 9 (TLR9) subfamily, which generates signals via the adaptor MyD88 to elicit robust IFN induction. Using mice deficient in the Irf7 gene (Irf7-/- mice), we show that the transcription factor IRF-7 is essential for the induction of IFN-alpha/beta genes via the virus-activated, MyD88-independent pathway and the TLR-activated, MyD88-dependent pathway. Viral induction of MyD88-independent IFN-alpha/beta genes is severely impaired in Irf7-/- fibroblasts. Consistently, Irf7-/- mice are more vulnerable than Myd88-/- mice to viral infection, and this correlates with a marked decrease in serum IFN levels, indicating the importance of the IRF-7-dependent induction of systemic IFN responses for innate antiviral immunity. Furthermore, robust induction of IFN production by activation of the TLR9 subfamily in plasmacytoid dendritic cells is entirely dependent on IRF-7, and this MyD88-IRF-7 pathway governs the induction of CD8+ T-cell responses. Thus, all elements of IFN responses, whether the systemic production of IFN in innate immunity or the local action of IFN from plasmacytoid dendritic cells in adaptive immunity, are under the control of IRF-7.

Swift elimination of undesirable cells is an important feature in tumour suppression and immunity. The tumour suppressor p53 and interferon-alpha and -beta (IFN-alpha/beta) are essential for the induction of apoptosis in cancerous cells and in antiviral immune responses, respectively, but little is known about their interrelationship. Here we show that transcription of the p53 gene is induced by IFN-alpha/beta, accompanied by an increase in p53 protein level. IFN-alpha/beta signalling itself does not activate p53; rather, it contributes to boosting p53 responses to stress signals. We show examples in which p53 gene induction by IFN-alpha/beta contributes to tumour suppression. Furthermore, we show that p53 is activated in virally infected cells to evoke an apoptotic response and that p53 is critical for antiviral defence of the host. Our study reveals a hitherto unrecognized link between p53 and IFN-alpha/beta in tumour suppression and antiviral immunity, which may have therapeutic implications.

In addition to the serotype-specific primers described previously (1 to 7), a new serotype 8-specific primer has been designed, allowing detection of all astrovirus serotypes. A total of 1,382 diarrheal stool samples in 5 regions in Japan were examined by reverse transcription-polymerase chain reaction (RT-PCR). The incidence of astrovirus infection in all 5 regions was 5.9% (82 of 1,382 samples) and infection occurred mainly from November to April. Serotypes 1, 3, and 4 were detected in 66, 14, and 2 of the 82 positive samples, respectively. None of the other serotypes was detected. The highest detection rate was from 0 to 1 year old, 39.0%, and the next highest was from 1 to 2 years old, 34.1%. The primers provide a useful approach for study of the epidemiology of astroviruses.