Identification of Lps2 as a key transducer of MyD88-independent TIR signalling

Identification of Mouse Cytomegalovirus Resistance Loci by ENU Mutagenesis

Host resistance to infection depends on the efficiency with which innate immune responses keep the infectious agent in check. Innate immunity encompasses components with sensing, signaling and effector properties. These elements with non-redundant functions are encoded by a set of host genes, the resistome. Here, we review our findings concerning the resistome. We have screened randomly mutagenized mice for susceptibility to a natural opportunistic pathogen, the mouse cytomegalovirus. We found that some genes with initially no obvious functions in innate immunity may be critical for host survival to infections, falling into a newly defined category of genes of the resistome.

The TRIF-dependent signaling pathway is not required for acute cerebral ischemia/reperfusion injury in mice

TIR domain-containing adaptor protein (TRIF) is an adaptor protein in Toll-like receptor (TLR) signaling pathways. Activation of TRIF leads to the activation of interferon regulatory factor 3 (IRF3) and nuclear factor kappa B (NF-kappaB). While studies have shown that TLRs are implicated in cerebral ischemia/reperfusion (I/R) injury and in neuroprotection against ischemia afforded by preconditioning, little is known about TRIF's role in the pathological process following cerebral I/R. The present study investigated the role that TRIF may play in acute cerebral I/R injury. In a mouse model of cerebral I/R induced by transient middle cerebral artery occlusion, we examined the activation of NF-kappaB and IRF3 signaling in ischemic cerebral tissue using ELISA and Western blots. Neurological function and cerebral infarct size were also evaluated 24h after cerebral I/R. NF-kappaB activity and phosphorylation of the inhibitor of kappa B (IkappaBalpha) increased in ischemic brains, but IRF3, inhibitor of kappaB kinase complex-epsilon (IKKepsilon), and TANK-binding kinase1 (TBK1) were not activated after cerebral I/R in wild-type (WT) mice. Interestingly, TRIF deficit did not inhibit NF-kappaB activity or p-IkappaBalpha induced by cerebral I/R. Moreover, although cerebral I/R induced neurological and functional impairments and brain infarction in WT mice, the deficits were not improved and brain infarct size was not reduced in TRIF knockout mice compared to WT mice. Our results demonstrate that the TRIF-dependent signaling pathway is not required for the activation of NF-kappaB signaling and brain injury after acute cerebral I/R.

Selective activation of the p38 MAPK pathway by synthetic monophosphoryl lipid A

TLR4 stimulation by lipopolysaccharide can cause both MAL/MyD88- and TRAM/TRIF (Toll IL-1 receptor domain-containing adaptor-inducing IFNbeta)-dependent signaling events. Monophosphoryl lipid A (MPLA), a low toxicity derivative of endotoxic lipopolysaccharide, enhances antibody responses, T cell expansion, and recall responses against antigens without causing excessive inflammatory side effects. Previously, we proposed that TRIF-biased activation of TLR4 by MPLA is responsible for its reduced toxicity while retaining potent adjuvant effects. However, some TRIF-associated genes, such as MCP-1, are only weakly expressed, and some MyD88-associated inflammatory and anti-inflammatory cytokines, such as tumor necrosis factor alpha and interleukin-10, are strongly activated after MPLA stimulation despite weak NF-kappaB but strong IRF3 activation. We now report that synthetic derivatives of MPLA retained TRIF bias as compared with synthetic diphosphoryl lipid A, indicating a change in a single phosphoryl group is sufficient for TRIF-biased TLR4 stimulation. We extend our previous observations by showing that sMLA induces strong p38 MAPK but weak JNK activation, resulting in high IP-10 (interferon-inducible protein 10), tumor necrosis factor alpha, and interleukin-10 but low MCP-1 transcript levels. Results of this study identify a novel biochemical mechanism for regulation of sMLA-induced gene expression.

Inhibitors of MyD88-dependent proinflammatory cytokine production identified utilizing a novel RNA interference screening approach

BACKGROUND

The events required to initiate host defenses against invading pathogens involve complex signaling cascades comprised of numerous adaptor molecules, kinases, and transcriptional elements, ultimately leading to the production of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha). How these signaling cascades are regulated, and the proteins and regulatory elements participating are still poorly understood.

RESULTS

We report here the development a completely random short-hairpin RNA (shRNA) library coupled with a novel forward genetic screening strategy to identify inhibitors of Toll-like receptor (TLR) dependent proinflammatory responses. We developed a murine macrophage reporter cell line stably transfected with a construct expressing diphtheria toxin-A (DT-A) under the control of the TNF-alpha-promoter. Stimulation of the reporter cell line with the TLR ligand lipopolysaccharide (LPS) resulted in DT-A induced cell death, which could be prevented by the addition of an shRNA targeting the TLR adaptor molecule MyD88. Utilizing this cell line, we screened a completely random lentiviral short hairpin RNA (shRNA) library for sequences that inhibited TLR-mediated TNF-alpha production. Recovery of shRNA sequences from surviving cells led to the identification of unique shRNA sequences that significantly inhibited TLR4-dependent TNF-alpha gene expression. Furthermore, these shRNA sequences specifically blocked TLR2 but not TLR3-dependent TNF-alpha production.

CONCLUSIONS

Thus, we describe the generation of novel tools to facilitate large-scale forward genetic screens in mammalian cells and the identification of potent shRNA inhibitors of TLR2 and TLR4- dependent proinflammatory responses.

Severe retinal degeneration caused by a novel rhodopsin mutation

PURPOSE

To identify a new mouse mutation developing early-onset dominant retinal degeneration, to determine the causative gene mutation, and to investigate the underlying mechanism.

METHODS

Retinal phenotype was examined by indirect ophthalmoscopy, histology, transmission electron microscopy, immunohistochemistry, Western blot analysis, and electroretinography. Causative gene mutation was determined by genomewide linkage analysis and DNA sequencing. Structural modeling was used to predict the impact of the mutation on protein structure.

RESULTS

An ENU-mutagenized mouse line (R3), displaying attenuated retinal vessels and pigmented patches, was identified by fundus examination. Homozygous R3/R3 mice lost photoreceptors rapidly, leaving only a single row of photoreceptor nuclei at postnatal day 18. The a- and b-waves of ERG were flat in R3/R3 mice, whereas heterozygous R3/+ mice showed reduced amplitude of a- and b-waves. The R3/+ mice had a slower rate of photoreceptor cell loss than compound heterozygous R3/- mice with a null mutant allele. The R3 mutation was mapped and verified to be a rhodopsin point mutation, a c.553T>C for a p.C185R substitution. The side chain of Arg(185) impacted on the extracellular loop of the protein. Mutant rhodopsin-C185R protein accumulated in the photoreceptor inner segments, cellular bodies, or both.

CONCLUSIONS

Rhodopsin C185R mutation leads to severe retinal degeneration in R3 mutant mice. A dosage-dependent accumulation of misfolded mutant proteins likely triggers or stimulates the death of rod photoreceptors. The presence of a wild-type rhodopsin allele can delay the loss of photoreceptor cells in R3/+ mice.

Innate immune response during Yersinia infection: critical modulation of cell death mechanisms through phagocyte activation

Yersinia pestis, the etiological agent of plague, is one of the most deadly pathogens on our planet. This organism shares important attributes with its ancestral progenitor, Yersinia pseudotuberculosis, including a 70-kb virulence plasmid, lymphotropism during growth in the mammalian host, and killing of host macrophages. Infections with both organisms are biphasic, where bacterial replication occurs initially with little inflammation, followed by phagocyte influx, inflammatory cytokine production, and tissue necrosis. During infection, plasmid-encoded attributes facilitate bacterial-induced macrophage death, which results from two distinct processes and corresponds to the inflammatory crescendo observed in vivo: Naïve cells die by apoptosis (noninflammatory), and later in infection, activated macrophages die by pyroptosis (inflammatory). The significance of this redirected cell death for the host is underscored by the importance of phagocyte activation for immunity to Yersinia and the protective role of pyroptosis during host responses to anthrax lethal toxin and infections with Francisella, Legionella, Pseudomonas, and Salmonella. The similarities of Y. pestis and Y. pseudotuberculosis, including conserved, plasmid-encoded functions inducing at least two distinct mechanisms of cell death, indicate that comparative studies are revealing about their critical pathogenic mechanism(s) and host innate immune responses during infection. Validation of this idea and evidence of similar interactions with the host immune system are provided by Y. pseudotuberculosis-priming, cross-protective immunity against Y. pestis. Despite these insights, additional studies indicate much remains to be understood concerning effective host responses against Yersinia, including chromosomally encoded attributes that also contribute to bacterial evasion and modulation of innate and adaptive immune responses.

Caspase-8 deficiency in epidermal keratinocytes triggers an inflammatory skin disease

Expression of enzymatically inactive caspase-8, or deletion of caspase-8 from basal epidermal keratinocytes, triggers chronic skin inflammation in mice. Unlike similar inflammation resulting from arrest of nuclear factor kappaB activation in the epidermal cells, the effect induced by caspase-8 deficiency did not depend on TNF, IL-1, dermal macrophage function, or expression of the toll-like receptor adapter proteins MyD88 or TRIF. Both interferon regulatory factor (IRF) 3 and TANK-binding kinase were constitutively phosphorylated in the caspase-8-deficient epidermis, and knockdown of IRF3 in the epidermis-derived cells from these mice abolished the expression of up-regulated genes. Temporal and spatial analyses of the alterations in gene expression that result from caspase-8 deficiency reveal that the changes are initiated before birth, around the time that cornification develops, and occur mainly in the suprabasal layer. Finally, we found that caspase-8-deficient keratinocytes display an enhanced response to gene activation by transfected DNA. Our findings suggest that an enhanced response to endogenous activators of IRF3 in the epidermis, presumably generated in association with keratinocyte differentiation, contributes to the skin inflammatory process triggered by caspase-8 deficiency.

A host type I interferon response is induced by cytosolic sensing of the bacterial second messenger cyclic-di-GMP

The innate immune system responds to unique molecular signatures that are widely conserved among microbes but that are not normally present in host cells. Compounds that stimulate innate immune pathways may be valuable in the design of novel adjuvants, vaccines, and other immunotherapeutics. The cyclic dinucleotide cyclic-di-guanosine monophosphate (c-di-GMP) is a recently appreciated second messenger that plays critical regulatory roles in many species of bacteria but is not produced by eukaryotic cells. In vivo and in vitro studies have previously suggested that c-di-GMP is a potent immunostimulatory compound recognized by mouse and human cells. We provide evidence that c-di-GMP is sensed in the cytosol of mammalian cells via a novel immunosurveillance pathway. The potency of cytosolic signaling induced by c-di-GMP is comparable to that induced by cytosolic delivery of DNA, and both nucleic acids induce a similar transcriptional profile, including triggering of type I interferons and coregulated genes via induction of TBK1, IRF3, nuclear factor kappaB, and MAP kinases. However, the cytosolic pathway that senses c-di-GMP appears to be distinct from all known nucleic acid-sensing pathways. Our results suggest a novel mechanism by which host cells can induce an inflammatory response to a widely produced bacterial ligand.

In vivo lipopolysaccharide exposure of human blood leukocytes induces cross-tolerance to multiple TLR ligands

In vitro and in vivo experiments in mice have shown that exposure of cells to the TLR4 ligand LPS induces tolerance toward a second exposure to LPS and induces cross-tolerance to certain other TLR ligands. Recently, we found that LPS tolerance in experimental human endotoxemia and Gram-negative sepsis is associated with elevated levels of IL-1R-associated kinase M, an intracellular negative regulator of MyD88-dependent TLR signaling. In the present study, we investigated whether in vivo exposure of humans to LPS induces tolerance in circulating leukocytes to other TLR agonists that rely either on MyD88- dependent or on MyD88-independent signaling. Analysis of TNF, IL-1beta, IL-6, and IL-10 levels in whole blood demonstrated that leukocytes were hyporesponsive to ex vivo LPS restimulation 3-8 h after i.v. LPS injection (4 ng/kg). Reduced cytokine release during the same interval was also observed in whole blood further stimulated with MyD88-dependent ligands for TLR2, TLR5, and TLR7 or with whole bacteria. Strikingly, blood leukocytes were also tolerant to a ligand for TLR3, which signals solely through a MyD88-independent (Toll IL-1R domain-containing adaptor-inducing IFN-beta (TRIF)-dependent) pathway. The hyporesponsiveness of leukocytes to TLR3 ligation was associated with reduced rather than increased levels of the recently identified TRIF inhibitor SARM. Taken together, these data indicate that systemic LPS challenge of human volunteers induces cross-tolerance to multiple TLR ligands that signal in a MyD88-dependent or MyD88-independent manner and suggest that LPS exposure of human blood leukocytes may hamper the inflammatory response to various microbial components.

Pathogen recognition and inflammatory signaling in innate immune defenses

The innate immune system constitutes the first line of defense against invading microbial pathogens and relies on a large family of pattern recognition receptors (PRRs), which detect distinct evolutionarily conserved structures on pathogens, termed pathogen-associated molecular patterns (PAMPs). Among the PRRs, the Toll-like receptors have been studied most extensively. Upon PAMP engagement, PRRs trigger intracellular signaling cascades ultimately culminating in the expression of a variety of proinflammatory molecules, which together orchestrate the early host response to infection, and also is a prerequisite for the subsequent activation and shaping of adaptive immunity. In order to avoid immunopathology, this system is tightly regulated by a number of endogenous molecules that limit the magnitude and duration of the inflammatory response. Moreover, pathogenic microbes have developed sophisticated molecular strategies to subvert host defenses by interfering with molecules involved in inflammatory signaling. This review presents current knowledge on pathogen recognition through different families of PRRs and the increasingly complex signaling pathways responsible for activation of an inflammatory and antimicrobial response. Moreover, medical implications are discussed, including the role of PRRs in primary immunodeficiencies and in the pathogenesis of infectious and autoimmune diseases, as well as the possibilities for translation into clinical and therapeutic applications.

The toll-Like receptor adaptor TRIF contributes to otitis media pathogenesis and recovery

Background

Toll-like receptor (TLR) signalling is crucial for innate immune responses to infection. The involvement of TLRs in otitis media (OM), the most prevalent childhood disease in developed countries, has been implicated by studies in middle ear cell lines, by association studies of TLR-related gene polymorphisms, and by altered OM in mice bearing mutations in TLR genes. Activated TLRs signal via two alternative intracellular signaling molecules with differing effects; MyD88 (Myeloid differentiation primary response gene 88) inducing primarily interleukin expression and TRIF (Tir-domain-containing adaptor inducing interferon β) mediating type I interferon (IFN) expression. We tested the hypothesis that TRIF and type I IFN signaling play a role in OM, using a murine model of OM induced by non-typeable Haemophilus influenzae (NTHi). The ME inflammatory response to NTHi was examined in wild-type (WT) and TRIF-/- mice by qPCR, gene microarray, histopathology and bacterial culture.

Results

Expression of TRIF mRNA was only modesty enhanced during OM, but both type I IFN signalling genes and type I IFN-inducible genes were significantly up-regulated in WT mice. TRIF-deficient mice showed reduced but more persistent mucosal hyperplasia and less leukocyte infiltration into the ME in response to NTHi infection than did WT animals. Viable bacteria could be cultured from MEs of TRIF-/- mice for much longer in the course of disease than was the case for middle ears of WT mice.

Conclusion

Our results demonstrate that activation of TRIF/type I IFN responses is important in both the pathogenesis and resolution of NTHi-induced OM.

Modulation of adaptive immunity with Toll-like receptors

The discovery of Toll-like receptors (TLRs), and their role in sensing infections represents one of the most seminal advances in immunology in recent years. It is now clear that TLRs play a fundamental role in innate recognition of microbes, and stimulate and tune the quality of the adaptive immune response. However, major knowledge gaps remain in our understanding of how TLRs regulate the development and persistence of T- and B-cell memory. Here, we review our current understanding of how TLR-signaling shapes the adaptive immune response, and highlight unanswered questions, the solution of which will be imperative in the rational exploitation of TLRs in vaccine design and immune therapy.

Requirement of TLR4 and CD14 in dendritic cell activation by Hemagglutinin B from Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that is one of the causative agents of chronic adult periodontal disease. Among the potential virulence factors of P. gingivalis are the hemagglutinins. Recombinant Hemagglutinin B (rHagB) from P. gingivalis has been shown to activate the immune system by inducing specific antibodies that protect against experimental periodontal bone loss following P. gingivalis infection. Since different microbial products can stimulate dendritic cells (DC) through Toll-like receptors (TLRs), subsequently leading to T cell activation and antibody production, we wanted to investigate the immunostimulatory effect of rHagB on DC and the role of TLR signaling in this process. Using an endotoxin free rHagB preparation, our results show that stimulation of murine bone marrow-derived DC with rHagB leads to upregulation of the costimulatory molecules CD86 and CD40, activation of p38 and ERK MAP kinases, transcription factors NF-kappaB, CREB and IRF-3 and the production of IL-6, TNF-alpha, IL-12p40 and to a lesser extent IL-10 and IFN-beta. This activation process was absolutely dependent on TLR4 and CD14. While upregulation of CD86 was independent of the adaptor molecule MyD88, CD40 upregulation and optimal cytokine (IL-6, TNF-alpha, IL-12p40, IL-10 and IFN-beta) production required both MyD88 and TRIF molecules. These results are of importance since they are the first to provide insights into the interaction of rHagB with DC and TLRs. The information from this study will aid in the design of effective vaccines strategies against chronic adult periodontal disease.

TLR4-mediated induction of TLR2 signaling is critical in the pathogenesis and resolution of otitis media

Otitis media is the most prevalent childhood disease in developed countries. The involvement of Toll-like receptors (TLRs) in otitis media pathophysiology has been implicated by studies in cell lines and association studies of TLR gene polymorphisms. However, precise functions of TLRs in the etiology of otitis media in vivo have not been examined. We investigated the inflammatory response to nontypeable Haemophilus influenzae using a model of otitis media in wild-type, TLR2(- /-) and TLR4(-/ -) mice by gene microarray, qPCR, immunohistochemistry, Western blot analysis and histopathology. Toll-like receptor-2(- /-) and TLR4(- /-) mice exhibited a more profound, persistent inflammation with impaired bacterial clearance compared to controls. While wild-type mice induced tumor necrosis factor-a (TNF) after non-typeable H. influenzae challenge, TLR2(-/-) and TLR4(-/-) mice lack TNF induction in the early phase of otitis media. Moreover, lack of TLR2 resulted in a late increase in IL-10 expression and prolonged failure to clear bacteria. Toll-like receptor-4(-/- ) mice showed impaired early bacterial clearance and loss of TLR2 induction in early otitis media. Our results demonstrate that both TLR2 and TLR4 signalling are critical to the regulation of infection in non-typeable H. influenzae-induced otitis media. Toll-like receptor-4 signalling appears to induce TLR2 expression, and TLR2 activation is critical for bacterial clearance and timely resolution of otitis media.

iNOS-producing inflammatory dendritic cells constitute the major infected cell type during the chronic Leishmania major infection phase of C57BL/6 resistant mice

Leishmania major parasites reside and multiply in late endosomal compartments of host phagocytic cells. Immune control of Leishmania growth absolutely requires expression of inducible Nitric Oxide Synthase (iNOS/NOS2) and subsequent production of NO. Here, we show that CD11b⁺ CD11c⁺ Ly-6C⁺ MHC-II⁺ cells are the main iNOS-producing cells in the footpad lesion and in the draining lymph node of Leishmania major-infected C57BL/6 mice. These cells are phenotypically similar to iNOS-producing inflammatory DC (iNOS-DC) observed in the mouse models of Listeria monocytogenes and Brucella melitensis infection. The use of DsRed-expressing parasites demonstrated that these iNOS-producing cells are the major infected population in the lesions and the draining lymph nodes. Analysis of various genetically deficient mouse strains revealed the requirement of CCR2 expression for the recruitment of iNOS-DC in the draining lymph nodes, whereas their activation is strongly dependent on CD40, IL-12, IFN-γ and MyD88 molecules with a partial contribution of TNF-α and TLR9. In contrast, STAT-6 deficiency enhanced iNOS-DC recruitment and activation in susceptible BALB/c mice, demonstrating a key role for IL-4 and IL-13 as negative regulators. Taken together, our results suggest that iNOS-DC represent a major class of Th1-regulated effector cell population and constitute the most frequent infected cell type during chronic Leishmania major infection phase of C57BL/6 resistant mice.

Leishmania spp. are protozoan parasites infecting a variety of mammals, including humans and mice. Much information has been gleaned from murine models of Leishmania major infection. The control of L. major infection by resistant C57BL/6 mice requires the secretion of type 1 (Th1) cytokines (i.e. IFN-γ) by T cells as well as the expression of inducible nitric oxide synthase (iNOS) by phagocytic cells. Conversely, susceptible BALB/c mice are unable to control infection and develop a type 2 (Th2) immune response characterized by the secretion of IL-4 and IL-13 cytokines. In this study, we showed that the main iNOS-producing cells in the lesion and the draining lymph node are phenotypically similar to iNOS-producing “inflammatory” dendritic cells (DC), which are already described in the mouse models of Listeria monocytogenes and Brucella melitensis infection. Our data also highlighted a strong association between the recruitment and activation of these inflammatory DC and the resistance to L. major infection. In addition, we showed that iNOS production by these inflammatory DC is positively regulated by Th1 response and negatively by Th2 response. Taken together, our results provide new insights into how innate and adaptive immune responses fight L. major infection. A better understanding of the mechanisms regulating inflammatory DC recruitment and activation could lead to new therapeutic strategies against Leishmania infection.

[Effect of antisense oligonucleotide against Smac/DIABLO on inhibition of hydrogen peroxide induced myocardial apoptosis of neonatal rats]

OBJECTIVE

To investigate the effects of antisense phosphorothioate oligonucleotides against Smac/DIABLO (asODN) on hydrogen peroxide (H2O2) induced myocardial apoptosis in neonatal rats.

METHODS

Primary myocardial cells from neonatal rats were cultured in vitro, and randomly divided into A (normal control, without transfection), B (with treatment of single liposome), C (with transfection of scrODN), D (with transfection of asODN), E (with H2O2, stimulation), F (with H2O2 stimulation after scrODN transfection), and G (with H2O2 stimulation after asODN transfection) groups. The expression of asODN mRNA and protein were determined with RT-PCR and Western blotting, respectively. The changes in cellular nuclear morphology were observed with 33258 fluorescent staining, and the percentage of nuclear apoptosis was calculated. DNA fragmentation was observed by agarose gel electrophoresis. Activation of caspase-3 and caspase-9 were evaluated by caspase colorimetric analysis kit.

RESULTS

The expression of Smac/DIABLO mRNA and protein was obviously inhibited by asODN, which was about 80% percent lower than the protein level in A,B and C groups, but there was no difference noted among A,B and C groups( P > 0.05). Not only the nuclear apoptotic percentage, but also the activity of caspase-3 and caspase-9 in A, C and D groups were in very low levels. But these indices in G group 24 hours after H2O2 stimulation were obviously lower than that in E and F groups [the nuclear apoptotic percentage were (19 +/- 5) %, (52 +/- 3) %, (55 +/- 5) %, respectively, P < 0.01)]. The DNA ladders in G group were also decreased markedly.

CONCLUSION

Myocardial apoptosis induced by H2O2 can be inhibited by asODN in rat.

Campylobacter jejuni-induced activation of dendritic cells involves cooperative signaling through Toll-like receptor 4 (TLR4)-MyD88 and TLR4-TRIF axes

Campylobacter jejuni is an important cause of human enteritis and has been linked to the development of autoimmune diseases. Recently we showed that infection of murine dendritic cells (DCs) with C. jejuni resulted in DC activation and induction of Campylobacter-specific Th1-effector responses. Toll-like receptor (TLR) signaling through myeloid differentiation factor 88 (MyD88) and/or Toll-interleukin 1 (IL-1) receptor domain-containing adaptor-inducing beta interferon (IFN-beta) (TRIF) is critical in inducing immunity against pathogens. In this study, we investigated the role of TLR2, TLR4, MyD88, and TRIF signaling in C. jejuni-induced inflammatory activation of DCs. DC upregulation of major histocompatibility complex class II and costimulatory molecules after C. jejuni challenge was profoundly impaired by TLR2, TLR4, MyD88, and TRIF deficiencies. Similarly, C. jejuni-induced secretion of IL-12, IL-6, and tumor necrosis factor alpha was significantly inhibited in TLR2(-/-), TLR4(-/-), MyD88(-/-), and TRIF(-/-) DCs compared to that in wild-type DCs; however, the magnitude of inhibition was greater in MyD88(-/-), TRIF(-/-), and TLR4(-/-) DCs than in TLR2(-/-) DCs. Furthermore, C. jejuni induced interferon regulatory factor 3 phosphorylation and IFN-beta secretion by DCs in a TLR4-TRIF-dependent fashion, further demonstrating activation of this pathway by C. jejuni. Importantly, TLR2, TLR4, MyD88, and TRIF deficiencies all markedly impaired the Th1-priming ability of C. jejuni-infected DCs. Thus, our results show that cooperative signaling through the TLR4-MyD88 and TLR4-TRIF axes represents a novel mechanism mediating C. jejuni-induced inflammatory responses of DCs. To our knowledge, such a mechanism has not been demonstrated previously for an intact bacterium.

Radioresistant cells expressing TLR5 control the respiratory epithelium's innate immune responses to flagellin

Bacterial products (such as endotoxins and flagellin) trigger innate immune responses through TLRs. Flagellin-induced signalling involves TLR5 and MyD88 and, according to some reports, TLR4. Whereas epithelial and dendritic cells are stimulated by flagellin in vitro, the cell contribution to the in vivo response is still unclear. Here, we studied the respective roles of radioresistant and radiosensitive cells in flagellin-induced airway inflammation in mice. We found that i.n. delivery of flagellin elicits a transient change in respiratory function and an acute, pro-inflammatory response in the lungs, characterized by TLR5- and MyD88-dependent chemokine secretion and neutrophil recruitment. In contrast, TLR4, CD14 and TRIF were not essential for flagellin-mediated responses, indicating that TLR4 does not cooperate with TLR5 in the lungs. Respiratory function, chemokine secretion and airway infiltration by neutrophils were dependent on radioresistant, TLR5-expressing cells. Furthermore, lung haematopoietic cells also responded to flagellin by activating TNF-alpha production. We suggest that the radioresistant lung epithelial cells are essential for initiating early, TLR5-dependent signalling in response to flagellin and thus triggering the lung's innate immune responses.

Glycogen synthase kinase-3 promotes the synergistic action of interferon-gamma on lipopolysaccharide-induced IL-6 production in RAW264.7 cells

Macrophages are the major effector cells of the innate immune system. Their function requires the integration of signals from pathogens, such as those induced by lipopolysaccharide (LPS), and from the host, such as those induced by interferon-gamma (IFN-gamma). The priming by IFN-gamma of Toll-like receptor-induced macrophage activation has long been recognized, but the mechanisms underlying this priming action remain unclear. We report in this study that the priming of macrophage-derived RAW264.7 cells by IFN-gamma is highly dependent on glycogen synthase kinase-3 (GSK3). Cooperative interactions of GSK3 and signal transducer and activator of transcription-3 (STAT3) were revealed by the findings that GSK3 inhibitors, or knockdown of the GSK3 beta isoform, strongly reduced the activation of STAT3, but not STAT1, induced by IFN-gamma without affecting upstream signaling events, and GSK3 was associated with STAT3. Direct inhibition of STAT3 activation abolished the synergistic action of IL-6 production by IFN-gamma administered with LPS. Similarly, inhibition of GSK3 abolished the synergistic stimulation of IFN-gamma on IL-6 production, and GSK3 was recruited to the IFN-gamma receptor by co-treatment with IFN-gamma and LPS. These results demonstrate the dependency of macrophage priming by IFN-gamma on STAT3 and GSK3, providing novel targets for intervention.

Differential role for c-Rel and C/EBPbeta/delta in TLR-mediated induction of proinflammatory cytokines

TLR stimulation triggers a signaling pathway via MyD88 and IL-1R-associated kinase 4 that is essential for proinflammatory cytokine induction. Although NF-kappaB has been shown to be one of the key transcriptional regulators of these cytokines, evidence suggests that other factors may also be important. In this study, we showed that MyD88-deficient macrophages have defective c-Rel activation, which has been linked to IL-12p40 induction, but not IL-6 or TNF-alpha. We also investigated other transcription factors and showed that C/EBPbeta and C/EBPdelta expression was limited in MyD88- or IL-1R-associated kinase 4-deficient macrophages treated with LPS. Importantly, the absence of both C/EBPbeta and C/EBPdelta resulted in the impaired induction of proinflammatory cytokines stimulated by several TLR ligands. Our results identify c-Rel and C/EBPbeta/delta as important transcription factors in a MyD88-dependent pathway that regulate the induction of proinflammatory cytokines.

The adaptor molecule MyD88 directly promotes CD8 T cell responses to vaccinia virus

Vaccinia virus (VACV) elicits a robust CD8 T cell response that plays an important role in host resistance. To date, there is little information on the molecules that are essential to generate large pools of VACV-specific effector CD8 T cells. In this study, we show that the adaptor molecule MyD88 is critical for the magnitude of primary CD8 T cell responses to both dominant and subdominant VACV epitopes. MyD88(-/-) mice exhibit profound reduction in CD8 T cell expansion and antiviral cytokine production. Surprisingly, the defect was not due to impaired APC function, as MyD88(-/-) dendritic cells matured normally and were able to promote strong CD8 T cell priming following VACV infection. Rather, adoptive transfer experiments demonstrated that intrinsic MyD88-dependent pathways in CD8 T cells were critical. MyD88-deficient CD8 T cells failed to accumulate in wild-type hosts and poor expansion of MyD88-deficient VACV-specific CD8 T cells resulted after virus infection. In contrast, no defect was evident in the absence of TRIF, TLR2, TLR4, TLR9, and IL-1R. Together, our results highlight an important role for MyD88 in initial antiviral CD8 T cell responses and suggest that targeting this pathway may be useful in promoting and sustaining anti-VACV immunity.

Protein kinase D1 is essential for MyD88-dependent TLR signaling pathway

Protein kinase D1 (PKD1) has been shown to be involved in certain MAPK activation and cytokine expression by several TLR ligands. However, the precise physiological role of PKD1 in individual signaling from TLRs has not been fully addressed. In this study, we provide evidence that PKD1 is being activated by TLR ligands, except the TLR3 ligand. PKD1 activation by TLR ligands is dependent on MyD88, IL-1R-associated kinase 4 and 1, but independent of TNF-alpha receptor-associated factor 6. PKD1-knockdown macrophages and bone marrow-derived dendritic cells revealed that PKD1 is indispensable for the MyD88-dependent ubiquitination of TNF-alpha receptor-associated factor 6; activation of TGF-beta-activated kinase 1, MAPKs, and transcription factors; and expression of proinflammatory genes induced by TLR ligands, but is not involved in expression of type I IFNs induced by TLR ligands and TRIF-dependent genes induced by TLR3 and TLR4 ligands. These results demonstrate that PKD1 is essential for MyD88-dependent proinflammatory immune responses.

ERIS, an endoplasmic reticulum IFN stimulator, activates innate immune signaling through dimerization

We report here the identification and characterization of a protein, ERIS, an endoplasmic reticulum (ER) IFN stimulator, which is a strong type I IFN stimulator and plays a pivotal role in response to both non-self-cytosolic RNA and dsDNA. ERIS (also known as STING or MITA) resided exclusively on ER membrane. The ER retention/retrieval sequence RIR was found to be critical to retain the protein on ER membrane and to maintain its integrity. ERIS was dimerized on innate immune challenges. Coumermycin-induced ERIS dimerization led to strong and fast IFN induction, suggesting that dimerization of ERIS was critical for self-activation and subsequent downstream signaling.

Somatostatin limits intestinal ischemia-reperfusion injury in macaques via suppression of TLR4-NF-kappaB cytokine pathway

OBJECTIVE

Intestinal ischemia-reperfusion (IIR)-induced gut injury remains a challenge for critically ill patients despite the oxidative stress theory that has been elaborated. This study aimed to test whether Toll-like receptor 4 (TLR4) is involved in gut injury during IIR and whether somatostatin (SST) affects TLR4-nuclear factor-kappaB (NF-kappaB) cytokine pathway in the intestinal mucosa of macaques.

DESIGN

Fifteen macaques were randomized into control, IIR, and SST + IIR groups. Pieces of isolated ileal epithelium from each animal were incubated with lipopolysaccharide (LPS), interferon-gamma, or SST. Expression of TLR4 and NF-kappaBp65 was evaluated by immunohistochemical staining, Western blot analysis and reverse transcription polymerase chain reaction. Cytokine levels were measured by ELISA. Radioimmunoassay was used to determine of SST levels.

MEASUREMENTS AND MAIN RESULTS

Significant overexpression (IIR vs control) of ileal TLR4 (0.17 +/- 0.03 vs 0.05 +/- 0.02), NF-kappaBp65 (0.55 +/- 0.11 vs 0.15 +/- 0.05), and TNF-alpha (213.2 +/- 29.2 vs 56.0 +/- 10.04) after IIR was greatly decreased (p < 0.05) by prophylactic use of SST (TLR4: 0.06 +/- 0.02; NF-kappaBp65: 0.26 +/- 0.09; TNF-alpha: 97.1 +/- 32.3) in vivo. TLR4 expression in the ileal epithelium treated with LPS and SST (1,330 +/- 93) was significantly lower than that in the ileal epithelium treated with LPS alone (2,088 +/- 126) in vitro. SST levels in plasma (3.67 +/- 0.41 ng/ml) and ileal mucosa (1,402.3 +/- 160 ng/mg protein) of the IIR group were significantly lower than those (6.09 +/- 1.29 ng/ml, 2,234. 8 +/- 301.8 ng/mg protein) in the control group (p < 0.05).

CONCLUSIONS

Endogenous SST is a crucial inhibitor of massive inflammatory injury in the intestinal mucosa via direct suppression of the TLR4-NF-kappaB cytokine pathway induced by LPS in ileal epithelium. IIR attacks caused shortages of endogenous SST in the plasma and intestinal mucosa of macaques in this study. Therefore, preventive supplements of SST may limit intestinal injury of macaques by IIR.

Lipopolysaccharide potentiates effector T cell accumulation into nonlymphoid tissues through TRIF

LPS is a natural adjuvant that potentiates Ag-specific T cell survival and Th1 differentiation by stimulating MyD88 and Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) signaling pathways. In this study, we reveal the TRIF pathway is critical for amplifying murine effector T cell accumulation into nonlymphoid tissues following immunization with Ag plus LPS. Although LPS increased the accumulation of splenic T cells in TRIF-deficient mice, markedly fewer T cells were recovered from liver and lung in comparison to wild type. Most of the T cells primed in TRIF-deficient mice failed to up-regulate CXCR3 and had an overall reduced capacity to produce IFN-gamma, demonstrating effector T cell differentiation was linked to their migration. To investigate the role of TRIF-dependent cytokines, neutralization studies were performed in wild type mice. Although TNF neutralization reduced T cell numbers, its coneutralization with IL-10 unexpectedly restored the T cells, suggesting the balance between pro- and anti-inflammatory cytokines influences T cell survival rather than their magnitude. To investigate a role for costimulatory molecules, we tested whether the T cell defect in TRIF-deficient mice could be corrected with enforced costimulation. Boosting with a CD40 agonist in addition to LPS restored the effector CD8 T cell response in livers of TRIF-deficient mice while only partially restoring CD4 T cells, suggesting that LPS primes CD8 and CD4 T cell immunity through different mechanisms. Overall, our data support targeting TRIF for vaccines aimed to direct immune responses to nonlymphoid tissues.

Reduced c-myc expression levels limit follicular mature B cell cycling in response to TLR signals

The splenic B cell compartment is comprised of two major, functionally distinct, mature B cell subsets, i.e., follicular mature (FM) and marginal zone (MZ) B cells. Whereas MZ B cells exhibit a robust proliferative response following stimulation with the TLR4 ligand LPS, FM B cells display markedly delayed and reduced levels of proliferation to the identical stimulus. The current study was designed to identify a potential mechanism(s) accounting for this differential responsiveness. In contrast to the delay in cell cycle entry, FM and MZ B cells exhibited nearly identical LPS-driven alterations in the expression level of cell surface activation markers. Furthermore, both the NF-kappaB and mTOR signaling cascades were similarly activated by LPS stimulation in FM vs MZ B cells, while inducible activation of ERK and AKT were nearly absent in both subsets. MZ B cells, however, exhibited higher basal levels of phospho-AKT and pS6, consistent with a preactivated status. Importantly, both basal and LPS activation-induced c-myc expression was markedly reduced in FM vs MZ B cells and enforced c-myc expression fully restored the defective proliferative response in FM B cells. These data support a model wherein TLR responses in FM B cells are tightly regulated by limiting c-myc levels, thereby providing an important checkpoint to control nonspecific FM B cell activation in the absence of cognate Ag.

TIR-containing adaptors in Toll-like receptor signalling

While the Toll-like receptors (TLRs) are responsible for the recognition and response to pathogen ligands, increasing evidence suggests that the family of five cytosolic Toll/IL-1 receptor (TIR) adaptor proteins also play a crucial role in the specificity of the response. Genetic studies in mice, and increasingly in human polymorphic populations, have given us a greater understanding the role these adaptors play in orchestrating and coordinating the multifaceted immune response to multiple exogenous threats. Importantly, with growing evidence of the critical role TLRs play in responses to host danger signals and autoimmune disease, a more comprehensive understanding and appreciation of the role these adaptors play in disease progression may provide future targets for therapeutic intervention in human disease. Importantly, growing evidence supports the concept of pathway specific and inflammatory control by a better understanding of how these adaptors interact with other signalling mediators, where they localise within the cell and the inflammatory programs they initiate as a way of manipulating immune responses. This review deals with our current understanding of these TIR-containing adaptor proteins and how mutagenesis of specific residues and domains has increased our knowledge of their function in TLR immune responses.

TRIF, and TRIF-interacting TLRs differentially modulate several adenovirus vector-induced immune responses

The use of Adenovirus (Ad)-based vectors has proven to be a useful platform for the development of gene therapy and vaccine protocols. The immunological mechanisms underlying these properties need to be identified and understood to foster safer, more efficacious use of this important gene transfer platform. Our recent studies have confirmed an important role for MyD88 dependent toll-like receptor (TLR) pathways as mediators of these responses. In this study, we confirm that TLR3, TLR4 and TRIF (TIR-domain-containing adapter-inducing interferon-beta) can also have augmentative or inhibitory roles during Ad-induced immune responses. Importantly, our studies revealed that TLR4 acts to suppress several aspects of the Ad-induced innate immune response, a finding not previously reported for this TLR in any model system. In addition, using MyD88 and TRIF double knockout mice, we demonstrate that the MyD88 and TRIF adaptor proteins can play either additive or redundant roles in mediating certain aspects of Ad vector-induced innate and adaptive immune responses. Furthering this complexity, our model system strongly suggests that non-TLR based systems must not only exist, but also have a significant role to play during Ad vector-mediated induction of adaptive immune responses.

Predicting novel features of toll-like receptor 3 signaling in macrophages

The Toll-like receptor (TLR) 3 plays a critical role in mammalian innate immune response against viral attacks by recognizing double-stranded RNA (dsRNA) or its synthetic analog polyinosinic-polycytidylic acid (poly (I∶C)). This leads to the activation of MAP kinases and NF-κB which results in the induction of type I interferons and proinflammatory cytokines to combat the viral infection. To understand the complex interplay of the various intracellular signaling molecules in the regulation of NF-κB and MAP kinases, we developed a computational TLR3 model based upon perturbation-response approach. We curated literature and databases to determine the TLR3 signaling topology specifically for murine macrophages. For initial model creation, we used wildtype temporal activation profiles of MAP kinases and NF-κB and, for model testing, used TRAF6 KO and TRADD KO data. From dynamic simulations we predict i) the existence of missing intermediary steps between extracellular poly (I∶C) stimulation and intracellular TLR3 binding, and ii) the presence of a novel pathway which is essential for JNK and p38, but not NF-κB, activation. Our work shows activation dynamics of signaling molecules can be used in conjunction with perturbation-response models to decipher novel signaling features of complicated immune pathways.

A toll-like receptor 4 variant is associated with fatal outcome in children with invasive meningococcal disease

AIMS

Toll-like receptor 4 (TLR4) is the major endotoxin signalling receptor of the innate immune system and is required for efficient recognition of bacterial infections. Here, we analysed a possible association between the TLR4 variant Asp299Gly and disease outcome in children with invasive meningococcal disease.

METHODS

In total, 197 children with invasive meningococcal disease were analysed for the TLR4 Asp299Gly variant. Genotyping results were correlated with mortality, the frequency of ventilation support, application of inotropic substances, skin grafting, and limb loss.

RESULTS

The overall Asp299Gly allele frequency was 9.4%. Detection of a heterozygous Asp299Gly TLR4 mutation was significantly associated with fatal outcome (non-survivor group: 31.6% vs. survivor group: 12.1%; p = 0.021) and was even more pronounced in patients with disease onset less than 24 months of age (non-survivor group: 42.8% vs. survivor group: 10.2%; p = 0.006). In this age group, ventilation support was also more frequent in patients with the Asp299Gly genotype (37.5% vs. 6.2%).

CONCLUSION

Our data suggest that the heterozygous TLR4 Asp299Gly genotype is associated with an increased mortality in children with invasive meningococcal disease.

Mice with mutations of Dock7 have generalized hypopigmentation and white-spotting but show normal neurological function

The classical recessive coat color mutation misty (m) arose spontaneously on the DBA/J background and causes generalized hypopigmentation and localized white-spotting in mice, with a lack of pigment on the belly, tail tip, and paws. Here we describe moonlight (mnlt), a second hypopigmentation and white-spotting mutation identified on the C57BL/6J background, which yields a phenotypic copy of m/m coat color traits. We demonstrate that the 2 mutations are allelic. m/m and mnlt/mnlt phenotypes both result from mutations that truncate the dedicator of cytokinesis 7 protein (DOCK7), a widely expressed Rho family guanine nucleotide exchange factor. Although Dock7 is transcribed at high levels in the developing brain and has been implicated in both axon development and myelination by in vitro studies, we find no requirement for DOCK7 in neurobehavioral function in vivo. However, DOCK7 has non-redundant role(s) related to the distribution and function of dermal and follicular melanocytes.

Poly (I:C) induced immune response in lymphoid tissues involves three sequential waves of type I IFN expression

An IFN-alpha heteroduplex-tracking assay (IFN-HTA) was developed to quantify the frequency of expression of the 16 genes coding for related interferon-alpha (IFN-alpha) subtypes in mice. In mLN of mice treated with Poly (I:C), we observed the induction of three sequential waves of type I IFN production, instead of two as is commonly described: early IFNs after 1 h (IFN-beta), late IFNs after 3 h (mostly IFN-alpha1, -alpha2, -alpha 4 and -alpha 5) and "secondary late IFNs" after 6 h (IFN-alpha 6T and -alpha 8/6). The late IFN wave was associated with the upregulation of the interferon regulatory factor (IRF)-7 mRNA and proteins, whereas the secondary late IFN wave was associated with a slight upregulation of IRF-8 mRNA. Type I IFNs produced in the thymus were associated with a distinct IRF mRNA expression pattern. This IFN-HTA strategy can serve as a useful tool to qualify and quantify the expression of various IFN-alpha subtypes under distinct immune responses and thus provides a first step in evaluating their function.

TLR2 and TLR4 signaling shapes specific antibody responses to Salmonella typhi antigens

TLR directly induce innate immune responses by sensing a variety of microbial components and are critical for the fine-tuning of subsequent adaptive immune responses. However, their impact and mechanism of action on antibody responses against bacterial antigens are not yet fully understood. Salmonella enterica serovar Typhi (S. typhi) porins have been characterized as inducers of long-lasting specific antibody responses in mice. In this report, we show that immunization of TLR4-deficient (TLR4(-/-)), myeloid differentiating gene 88-deficient and Toll/IL-R domain-containing adaptor-inducing IFN-beta-deficient mice with S. typhi porins led to significantly reduced B-cell responses. TLR2(-/-) mice, as well, showed reduced IgG titers with a more pronounced impairment in the production of IgG3 anti-porins antibodies. Adoptive transfer of TLR2(-/-)- or TLR4(-/-)-B cells into B-cell-deficient mice revealed a direct effect of TLR4 on B cells for the primary IgM response, whereas stimulation of B cells via TLR2 was important for IgG production. Furthermore, S. typhi porins were found to efficiently elicit maturation of CD11c(+) conventional DC. Taken together, S. typhi porins represent not only a suitable B-cell antigen for vaccination, but exhibit potent TLR-dependent stimulatory functions on B cells and DC, which help to further enhance and shape the antibody response.

TANK-binding kinase-1 plays an important role during in vitro and in vivo type I IFN responses to DNA virus infections

TANK-binding kinase-1 (TBK1) and the inducible IkappaB kinase (IKK-i) have recently been shown to activate type I IFN responses elicited by intracellular detection of RNA or DNA from infecting viruses. Detection of viral RNA is mediated by retinoic acid inducible gene-I or melanoma differentiation-associated gene-5 pathways in which TBK1 and IKK-i have been demonstrated to play redundant roles in IFN activation. In this study, we have examined whether such redundancy occurs in the type I IFN response to DNA viral challenges by examining induction of IFNs and IFN-mediated signaling and gene programs in TBK1(-/-) macrophages. In contrast to the normal IFN responses in TBK1(-/-) macrophages infected with an RNA virus, IFN responses were severely abrogated during DNA virus infections in TBK1(-/-) macrophages. Because both TBK1 and IKK-i are expressed in macrophages, our studies suggest that TBK1 and IKK-i differ functionally in DNA virus-mediated IFN responses; however, they are redundant in RNA virus-mediated IFN responses. Confirmatively, reconstitution of TBK1(-/-)IKK-i(-/-) fibroblasts revealed that TBK1 rescued IFN responses to transfected B-DNA to a much stronger degree than IKK-i. Finally, we demonstrate the requirement for the TBK1-IFN regulatory factor-3 pathway in host defense against a DNA virus infection in vivo.

Brucella TIR Domain-containing Protein Mimics Properties of the Toll-like Receptor Adaptor Protein TIRAP

Toll-like receptors (TLRs) play essential roles in the activation of innate immune responses against microbial infections. TLRs and downstream adaptor molecules contain a conserved cytoplasmic TIR domain. TIRAP is a TIR domain-containing adaptor protein that recruits the signaling adaptor MyD88 to a subset of TLRs. Many pathogenic microorganisms subvert TLR signaling pathways to suppress host immune responses to benefit their survival and persistence. Brucella encodes a TIR domain-containing protein (TcpB) that inhibits TLR2- and TLR4-mediated NF-kappaB activation. Sequence analysis indicated a moderate level of similarity between TcpB and the TLR adaptor molecule TIRAP. We found that TcpB could efficiently block TIRAP-induced NF-kappaB activation. Subsequent studies revealed that by analogy to TIRAP, TcpB interacts with phosphoinositides through its N-terminal domain and colocalizes with the plasma membrane and components of the cytoskeleton. Our findings suggest that TcpB targets the TIRAP-mediated pathway to subvert TLR signaling. In vivo mouse studies indicated that TcpB-deficient Brucella is defective in systemic spread at the early stages of infection.

Trif is not required for immune complex glomerulonephritis: dying cells activate mesangial cells via Tlr2/Myd88 rather than Tlr3/Trif

Viral RNA or bacterial products can activate glomerular mesangial cells via a subset of Toll-like receptors (Tlr). Because Tlr2-deficient mice were recently found to have attenuated nephrotoxic serum nephritis (NSN), we hypothesized that endogenous Tlr agonists can activate glomerular mesangial cells. Primary mesangial cells from C57BL/6 mice expressed Tlr1-6 and Tlr11 mRNA at considerable levels and produced Il-6 when being exposed to the respective Tlr ligands. Exposure to necrotic cells activated cultured primary mesangial cells to produce Il-6 in a Tlr2/Myd88-dependent manner. Apoptotic cells activated cultured mesangial cells only when being enriched to high numbers. Apoptotic cell-induced Il-6 release was Myd88 dependent, and only purified apoptotic cell RNA induced Trif signaling in mesangial cells. Does Trif signaling contribute to disease activity in glomerulonephritis? To answer this question, we induced autologous NSN by injection of NS raised in rabbits in Trif-mutant and wild-type mice. Lack of Trif did not alter the functional and histomorphological abnormalities of NSN, including the evolution of anti-rabbit IgG and anti-rabbit-specific nephritogenic T cells. We therefore conclude that apoptotic cell RNA is a poor activator of Trif signaling in mesangial cells and that necrotic cells' releases rather activate mesangial cells via the Tlr2/Myd88 signaling pathway.

Myeloid differentiation primary response gene 88 is required for the resolution of otitis media

BACKGROUND

Signaling defects in the Toll-like receptor (TLR) pathway, such as interleukin-1 receptor-associated kinase 4 deficiency, highlight the prominence of TLR signaling in the defense against bacterial disease. Because myeloid differentiation primary response gene 88 (MyD88) can transduce signals from almost all TLRs, we studied its role in otitis media (OM), the most common upper respiratory tract bacterial infectious disease in young children.

METHODS

The middle ears (MEs) of wild-type (WT) and MyD88(-/-) mice were inoculated with nontypeable Haemophilus influenzae (NTHi). ME infection and inflammation were monitored for 21 days after surgery. Bone marrow-derived macrophages from WT and MyD88(-/-) mice were infected with NTHi in vitro to assess their interaction with bacteria.

RESULTS

In WT mice, MyD88 expression was detected in the ME stroma at baseline. MyD88(-/-) mice displayed prolonged ME mucosal thickening and delayed recruitment of neutrophils and macrophages. Although WT mice cleared NTHi within 5 days, viable NTHi were isolated for up to 21 days in MyD88(-/-) mice. The interaction between macrophages and NTHi was significantly altered in MyD88(-/-) mice.

CONCLUSIONS

In this mouse model, MyD88-mediated signaling was important for clearance of infection and resolution of inflammation in acute OM due to NTHi. The role played by innate signaling in children susceptible to chronic or recurrent OM deserves further study.

TLR4 ligands induce IFN-alpha production by mouse conventional dendritic cells and human monocytes after IFN-beta priming

Exacerbation of disease in systemic lupus erythematosus (SLE) is associated with bacterial infection. In conventional dendritic cells (cDCs), the TLR4 ligand bacterial LPS induces IFN-beta gene expression but does not induce IFN-alpha. We hypothesized that when cDCs are primed by cytokines, as may frequently be the case in SLE, LPS would then induce the production of IFN-alpha, a cytokine believed to be important in lupus pathogenesis. In this study we show that mouse cDCs and human monocytes produce abundant IFN-alpha following TLR4 engagement whether the cells have been pretreated either with IFN-beta or with a supernatant from DCs activated by RNA-containing immune complexes from lupus patients. This TLR4-induced IFN-alpha induction is mediated by both an initial TRIF-dependent pathway and a subsequent MyD88-dependent pathway, in contrast to TLR3-induced IFN-alpha production, which is entirely TRIF-dependent. There is also a distinct requirement for IFN regulatory factors (IRFs), with LPS-induced IFN-alpha induction being entirely IRF7- and partially IRF5-dependent, in contrast to LPS-induced IFN-beta gene induction which is known to be IRF3-dependent but largely IRF7-independent. This data demonstrates a novel pathway for IFN-alpha production by cDCs and provides one possible explanation for how bacterial infection might precipitate disease flares in SLE.

Toll-like receptor 3 signaling on macrophages is required for survival following coxsackievirus B4 infection

Toll-like receptor 3 (TLR3) has been proposed to play a central role in the early recognition of viruses by sensing double stranded RNA, a common intermediate of viral replication. However, several reports have demonstrated that TLR3 signaling is either dispensable or even harmful following infection with certain viruses. Here, we asked whether TLR3 plays a role in the response to coxsackievirus B4 (CB4), a prevalent human pathogen that has been associated with pancreatitis, myocarditis and diabetes. We demonstrate that TLR3 signaling on macrophages is critical to establish protective immunity to CB4. TLR3 deficient mice produced reduced pro-inflammatory mediators and are unable to control viral replication at the early stages of infection resulting in severe cardiac damage. Intriguingly, the absence of TLR3 did not affect the activation of several key innate and adaptive cellular effectors. This suggests that in the absence of TLR3 signaling on macrophages, viral replication outpaces the developing adaptive immune response. We further demonstrate that the MyD88-dependent signaling pathways are not only unable to compensate for the loss of TLR3, they are also dispensable in the response to this RNA virus. Our results demonstrate that TLR3 is not simply part of a redundant system of viral recognition, but rather TLR3 plays an essential role in recognizing the molecular signatures associated with specific viruses including CB4.

Lipid A receptor TLR4-mediated signaling pathways

Lipid A is a strong activator of monocytes to release immune stimulators such as proinflammatory cytokines. Overproduction of inflammatory cytokines such as TNF and IL-6 is known to cause septic shock that frequently leads to multiple organ failure and finally to death. In recent years, Lipid A has also been recognized by a Toll-like receptor, TLR4. Activation of TLR4by LPS or Lipid A triggers signal transduction via the cytoplasmic domain called the Toll/IL-1 Receptor (TIR) domain. Intracellular TIR domain-containing adaptor molecules are involved in the TLR4-mediated signaling pathways. Moreover, a subset of LPS-inducible genes is regulated in two steps by the inducible nuclear protein. Additionally, the TLR4-mediated activation of signaling cascadesis elaborately down-regulated by a number of negative regulators. In this chapter, we discuss the mechanisms of the activation or de-activation program mediated by the Lipid A receptor TLR4.

Systems biology of innate immunity

Systems biology is the comprehensive and quantitative analysis of the interactions between all of the components of biological systems over time. Systems biology involves an iterative cycle, in which emerging biological problems drive the development of new technologies and computational tools. These technologies and tools then open new frontiers that revolutionize biology. Innate immunity is well suited for systems analysis, because the relevant cells can be isolated in various functional states and their interactions can be reconstituted in a biologically meaningful manner. Application of the tools of systems biology to the innate immune system will enable comprehensive analysis of the complex interactions that maintain the difficult balance between host defense and inflammatory disease. In this review, we discuss innate immunity in the context of the systems biology concepts, emergence, robustness, and modularity, and we describe emerging technologies we are applying in our systems-level analyses. These technologies include genomics, proteomics, computational analysis, forward genetics screens, and analyses that link human genetic polymorphisms to disease resistance.

The adaptor protein MyD88 is essential for E coli-induced preterm delivery in mice

OBJECTIVE

We used a mouse model of infection-induced preterm delivery to examine the roles of 2 adaptor proteins with central functions in Toll-like receptor signaling: MyD88 (myeloid differentiation primary-response gene 88) and TRIF (Toll/IL-1 receptor (TIR)-domain-containing adaptor protein-inducing IFN-beta).

STUDY DESIGN

Mice deficient (KO) for MyD88, TRIF, both (DKO) or neither (WT) were inoculated into the uterus with killed Escherichia coli. Delivery outcomes, fetal status, serum progesterone, and nuclear translocation of the transcription factor nuclear factor kappa B (NFkappaB) were determined.

RESULTS

Preterm birth (delivery in less than 48 hours) occurred in WT and TRIF-KO animals in a dose-dependent fashion, reaching 100% with 5-10 x 10(9) bacteria, while MyD88-KO and DKO animals were completely protected from delivery. Intrauterine fetal survival, maintenance of circulating progesterone levels, and nuclear translocation of NFkappaB were also dependent upon MyD88 but not TRIF. In contrast, induction of uterine interleukin (IL)-1beta and tumor necrosis factor alpha (TNF-alpha) depends upon actions of both MyD88 and TRIF.

CONCLUSION

E coli-induced preterm delivery in the mouse is completely dependent upon MyD88 but not TRIF.

Microbe sensing, positive feedback loops, and the pathogenesis of inflammatory diseases

The molecular apparatus that protects us against infection can also injure us by causing autoimmune or autoinflammatory disease. It now seems that at times, defects within the sensing arm of innate immunity contribute to diseases of this type. The initiation of an immune response is often microbe dependent and, in many cases, Toll-like receptor (TLR) dependent. Positive feedback loops triggering immune activation may occur when TLR signaling pathways stimulate host cells in an unchecked manner. Or, immune activation may persist because of failure to eradicate an inciting infection. Or on occasion, endogenous DNA may trigger specific immune responses that beget further responses in a TLR-dependent autoamplification loop. Specific biochemical defects that cause loop-related autoimmunity have been revealed by random germline mutagenesis and by gene targeting. We have also developed some insight into critical points at which feedback loops can be interrupted.

TRAF6 and MEKK1 play a pivotal role in the RIG-I-like helicase antiviral pathway

Type I interferons (IFN-alpha/beta) are essential for immune defense against viruses and induced through the actions of the cytoplasmic helicases, RIG-I and MDA5, and their downstream adaptor molecule IPS-1. TRAF6 and the downstream kinase TAK1 have been shown to be essential for the production of proinflammatory cytokines through the TLR/MyD88/TRIF pathway. Although binding of TRAF6 with IPS-1 has been demonstrated, the role of the TRAF6 pathway in IFN-alpha/beta production has not been fully understood. Here, we demonstrate that TRAF6 is critical for IFN-alpha/beta induction in response to viral infection and intracellular double-stranded RNA, poly(I:C). Activation of NF-kappaB, JNK, and p38, but not IRF3, was impaired in TRAF6-deficient mouse embryo fibroblasts in response to vesicular stomatitis virus and poly(I:C). However, TAK1 was not required for IFN-beta induction in this process, since normal IFN-alpha/beta production was observed in TAK1-deficient mouse embryo fibroblasts. Instead, another MAP3K, MEKK1, was important for the activation of the IFN-beta promoter in response to poly(I:C). Forced expression of MEKK1 in combination with IRF3 was sufficient for the induction of IFN-beta, whereas suppression of MEKK1 expression by small interfering RNA inhibited the induction of IFN-beta by poly(I:C). These data suggest that IPS-1 requires TRAF6 and MEKK1 to activate NF-kappaB and mitogen-activated protein kinases that are critical for the optimal induction of type I interferons.

A novel IFN regulatory factor 3-dependent pathway activated by trypanosomes triggers IFN-beta in macrophages and fibroblasts

Innate immune recognition of intracellular pathogens involves both extracellular and cytosolic surveillance mechanisms. The intracellular protozoan parasite Trypanosoma cruzi triggers a robust type I IFN response in both immune and nonimmune cell types. In this study, we report that signaling through TBK1 and IFN regulatory factor 3 is required for T. cruzi-mediated expression of IFN-beta. The TLR adaptors MyD88 and TRIF, as well as TLR4 and TLR3, were found to be dispensable, demonstrating that T. cruzi induces IFN-beta expression in a TLR-independent manner. The potential role for cytosolic dsRNA sensing pathways acting through RIG-I and MDA5 was ruled out because T. cruzi was shown to trigger robust expression of IFN-beta in macrophages lacking the MAVS/IPS1/VISA/CARDif adaptor protein. The failure of T. cruzi to activate HEK293-IFN-beta-luciferase cells, which are highly sensitive to cytosolic triggers of IFN-beta expression including Listeria, Sendai virus, and transfected dsRNA and dsDNA, further indicates that the parasite does not engage currently recognized cytosolic surveillance pathways. Together, these findings identify the existence of a novel TLR-independent pathogen-sensing mechanism in immune and nonimmune cells that converges on TBK1 and IFN regulatory factor 3 for activation of IFN-beta gene expression.

Resident enteric microbiota and CD8+ T cells shape the abundance of marginal zone B cells

Since enteric microbial composition is a distinctive and stable individual trait, microbial heterogeneity may confer lifelong, non-genetic differences between individuals. Here we report that C57BL/6 mice bearing restricted flora microbiota, a distinct but diverse resident enteric microbial community, are numerically and functionally deficient in marginal zone (MZ) B cells. Surprisingly, MZ B-cell levels are minimally affected by germ-free conditions or null mutations of various TLR signaling molecules. In contrast, MZ B-cell depletion is exquisitely dependent on cytolytic CD8(+) T cells, and includes targeting of a cross-reactive microbial/endogenous MHC class 1B antigen. Thus, members of certain enteric microbial communities link with CD8(+) T cells as a previously unappreciated mechanism that shapes innate immunity dependent on innate-like B cells.

Pycnogenol, an extract from French maritime pine, suppresses Toll-like receptor 4-mediated expression of adipose differentiation-related protein in macrophages

Adipose differentiation-related protein (ADRP) is highly expressed in macrophages and human atherosclerotic lesions. We demonstrated that Toll-like receptor (TLR) 4-mediated signals, which are involved in atherosclerosis formation, enhanced the expression of ADRP in macrophages. Lipopolysaccharide (LPS) enhanced the ADRP expression in RAW264.7 cells or peritoneal macrophages from wild-type mice, but not in macrophages from TLR4-deficient mice. Actinomycin D almost completely abolished the LPS effect, whereas cycloheximide decreased the expression at 12 h, indicating that the LPS-induced ADRP expression was stimulated at the transcriptional level and was also mediated by new protein synthesis. LPS enhanced the ADRP promoter activity, in part, by stimulating activator protein (AP)-1 binding to the Ets/AP-1 element. In addition, preceding the increase of the ADRP mRNA, LPS induced the expression of interleukin (IL)-6, IL-1alpha, and interferon-beta mRNAs, all of which stimulated the ADRP expression. Antibodies against these cytokines or inhibitors of c-Jun NH(2)-terminal kinase and nuclear factor (NF)-kappaB suppressed the ADRP mRNA level. Thus TLR4 signals stimulate the ADRP expression both in direct and indirect manners. Pycnogenol (PYC), an extract of French maritime pine, suppressed the expression of ADRP and the above-mentioned cytokines. PYC suppressed the ADRP promoter activity and enhancer activity of AP-1 and NF-kappaB, whereas it did not affect the LPS-induced DNA binding of these factors. In conclusion, TLR4-mediated signals stimulate the ADRP expression in macrophages while PYC antagonizes this process. PYC, a widely used dietary supplement, might be useful for prevention of atherosclerosis.