The IRAK4 scaffold integrates TLR4-driven TRIF and MYD88 signaling pathways

Interleukin-1 receptor-associated kinases (IRAKs) -4, -2, and -1 are involved in transducing signals from Toll-like receptors (TLRs) via the adaptor myeloid differentiation primary-response protein 88 (MYD88). How MYD88/IRAK4/2/1 complexes are formed, their redundancies, and potential non-enzymatic roles are subjects of debate. Here, we examine the hierarchical requirements for IRAK proteins in the context of TLR4 activation and confirmed that the kinase activity of IRAK4 is essential for MYD88 signaling. Surprisingly, the IRAK4 scaffold is required for activation of the E3 ubiquitin ligase TNF receptor-associated factor 6 (TRAF6) by both MYD88 and TIR domain-containing adaptor protein inducing IFN-β (TRIF), a unique adaptation in the TLR4 response. IRAK4 scaffold is, therefore, essential in integrating MYD88 and TRIF in TLR4 signaling.

Lymphocyte crosstalk is required for monocyte-intrinsic trained immunity to Plasmodium falciparum

Plasmodium falciparum (P. falciparum) induces trained innate immune responses in vitro, where initial stimulation of adherent PBMCs with P. falciparum-infected RBCs (iRBCs) results in hyperresponsiveness to subsequent ligation of TLR2. This response correlates with the presence of T and B lymphocytes in adherent PBMCs, suggesting that innate immune training is partially due to adaptive immunity. We found that T cell-depleted PBMCs and purified monocytes alone did not elicit hyperproduction of IL-6 and TNF-α under training conditions. Analysis of P. falciparum-trained PBMCs showed that DCs did not develop under control conditions, and IL-6 and TNF-α were primarily produced by monocytes and DCs. Transwell experiments isolating purified monocytes from either PBMCs or purified CD4+ T cells, but allowing diffusion of secreted proteins, enabled monocytes trained with iRBCs to hyperproduce IL-6 and TNF-α after TLR restimulation. Purified monocytes stimulated with IFN-γ hyperproduced IL-6 and TNF-α, whereas blockade of IFN-γ in P. falciparum-trained PBMCs inhibited trained responses. Assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-Seq) on monocytes from patients with malaria showed persistently open chromatin at genes that appeared to be trained in vitro. Together, these findings indicate that the trained immune response of monocytes to P. falciparum is not completely cell intrinsic but depends on soluble signals from lymphocytes.

Recurrent Respiratory Syncytial Virus Infection in a CD14-Deficient Patient

BACKGROUND

Recurrent respiratory syncytial virus (RSV) infection requiring hospitalization is rare and the underlying mechanism is unknown. We aimed to determine the role of CD14-mediated immunity in the pathogenesis of recurrent RSV infection.

METHODS

We performed genotyping and longitudinal immunophenotyping of the first patient with a genetic CD14 deficiency who developed recurrent RSV infection. We analyzed gene expression profiles and interleukin (IL)-6 production by patient peripheral blood mononuclear cells in response to RSV pre- and post-fusion (F) protein. We generated CD14-deficient human nasal epithelial cells cultured at air-liquid interface (HNEC-ALI) of patient-derived cells and after CRISPR-based gene editing of control cells. We analyzed viral replication upon RSV infection.

RESULTS

Sanger sequencing revealed a homozygous single-nucleotide deletion in CD14, resulting in absence of the CD14 protein in the index patient. In vitro, viral replication was similar in wild-type and CD14-/- HNEC-ALI. Loss of immune cell CD14 led to impaired cytokine and chemokine responses to RSV pre- and post-F protein, characterized by absence of IL-6 production.

CONCLUSIONS

We report an association of recurrent RSV bronchiolitis with a loss of CD14 function in immune cells. Lack of CD14 function led to defective immune responses to RSV pre- and post-F protein without a change in viral replication.

Astrocyte- and Neuron-Derived CXCL1 Drives Neutrophil Transmigration and Blood-Brain Barrier Permeability in Viral Encephalitis

Herpes simplex virus (HSV)-1 encephalitis has significant morbidity partly because of an over-exuberant immune response characterized by leukocyte infiltration into the brain and increased blood-brain barrier (BBB) permeability. Determining the role of specific leukocyte subsets and the factors that mediate their recruitment into the brain is critical to developing targeted immune therapies. In a murine model, we find that the chemokines CXCL1 and CCL2 are induced in the brain following HSV-1 infection. Ccr2 (CCL2 receptor)-deficient mice have reduced monocyte recruitment, uncontrolled viral replication, and increased morbidity. Contrastingly, Cxcr2 (CXCL1 receptor)-deficient mice exhibit markedly reduced neutrophil recruitment, BBB permeability, and morbidity, without influencing viral load. CXCL1 is produced by astrocytes in response to HSV-1 and by astrocytes and neurons in response to IL-1α, and it is the critical ligand required for neutrophil transendothelial migration, which correlates with BBB breakdown. Thus, the CXCL1-CXCR2 axis represents an attractive therapeutic target to limit neutrophil-mediated morbidity in HSV-1 encephalitis.

Expression of SARS coronavirus 1 spike protein from a herpesviral vector induces innate immune signaling and neutralizing antibody responses

SARS coronavirus 1 (SARS-CoV-1) causes a respiratory infection that can lead to acute respiratory distress characterized by inflammation and high levels of cytokines in the lung tissue. In this study we constructed a herpes simplex virus 1 replication-defective mutant vector expressing SARS-CoV-1 spike protein as a potential vaccine vector and to probe the effects of spike protein on host cells. The spike protein expressed from this vector is functional in that it localizes to the surface of infected cells and induces fusion of ACE2-expressing cells. In immunized mice, the recombinant vector induced antibodies that bind to spike protein in an ELISA assay and that show neutralizing activity. The spike protein expressed from this vector can induce the expression of cytokines in an ACE2-independent, MyD88-dependent process. These results argue that the SARS-CoV-1 spike protein intrinsically activates signaling pathways that induce cytokines and contribute directly to the inflammatory process of SARS.

Alcohol-induced adipose tissue macrophage phenotypic switching is independent of myeloid Toll-like receptor 4 expression

Alcoholic liver disease results from a combination of immune and metabolic pathogenic events. In addition to liver injury, chronic alcohol consumption also causes adipose tissue inflammation. The specific immune mechanisms that drive this process are unknown. Here, we sought to determine the role of the innate immune receptor Toll-like receptor 4 (TLR4) in alcohol-induced adipose tissue inflammation. Using a model of chronic, multiple-binge alcohol exposure, we showed that alcohol-mediated accumulation of proinflammatory adipose tissue macrophages was absent in global TLR4 knockout mice. Proinflammatory macrophage accumulation did not depend on macrophage TLR4 expression; LysMCre-driven deletion of Tlr4 from myeloid cells did not affect circulating endotoxin or the accumulation of M1 macrophages in adipose tissue following alcohol exposure. Proinflammatory cytokine/chemokine production in the adipose stromal vascular fraction also occurred independently of TLR4. Finally, the levels of other adipose immune cells, such as dendritic cells, neutrophils, B cells, and T cells, were modulated by chronic, multiple-binge alcohol and the presence of TLR4. Together, these data indicate that TLR4 expression on cells, other than myeloid cells, is important for the alcohol-induced increase in proinflammatory adipose tissue macrophages.

Micro RNAs from DNA Viruses are Found Widely in Plasma in a Large Observational Human Population

Viral infections associate with disease risk and select families of viruses encode miRNAs that control an efficient viral cycle. The association of viral miRNA expression with disease in a large human population has not been previously explored. We sequenced plasma RNA from 40 participants of the Framingham Heart Study (FHS, Offspring Cohort, Visit 8) and identified 3 viral miRNAs from 3 different human Herpesviridae. These miRNAs were mostly related to viral latency and have not been previously detected in human plasma. Viral miRNA expression was then screened in the plasma of 2763 participants of the remaining cohort utilizing high-throughput RT-qPCR. All 3 viral miRNAs associated with combinations of inflammatory or prothrombotic circulating biomarkers (sTNFRII, IL-6, sICAM1, OPG, P-selectin) but did not associate with hypertension, coronary heart disease or cancer. Using a large observational population, we demonstrate that the presence of select viral miRNAs in the human circulation associate with inflammatory biomarkers and possibly immune response, but fail to associate with overt disease. This study greatly extends smaller singular observations of viral miRNAs in the human circulation and suggests that select viral miRNAs, such as those for latency, may not impact disease manifestation.

Cyclic GMP-AMP Synthase Is the Cytosolic Sensor of Plasmodium falciparum Genomic DNA and Activates Type I IFN in Malaria

Innate immune receptors have a key role in the sensing of malaria and initiating immune responses. As a consequence of infection, systemic inflammation emerges and is directly related to signs and symptoms during acute disease. We have previously reported that plasmodial DNA is the primary driver of systemic inflammation in malaria, both within the phagolysosome and in the cytosol of effector cells. In this article, we demonstrate that Plasmodium falciparum genomic DNA delivered to the cytosol of human monocytes binds and activates cyclic GMP-AMP synthase (cGAS). Activated cGAS synthesizes 2'3'-cGAMP, which we subsequently can detect using liquid chromatography-tandem mass spectrometry. 2'3'-cGAMP acts as a second messenger for STING activation and triggers TBK1/IRF3 activation, resulting in type I IFN production in human cells. This induction of type I IFN was independent of IFI16. Access of DNA to the cytosolic compartment is mediated by hemozoin, because incubation of purified malaria pigment with DNase abrogated IFN-β induction. Collectively, these observations implicate cGAS as an important cytosolic sensor of P. falciparum genomic DNA and reveal the role of the cGAS/STING pathway in the induction of type I IFN in response to malaria parasites.

Group B Streptococcus Degrades Cyclic-di-AMP to Modulate STING-Dependent Type I Interferon Production

Induction of type I interferon (IFN) in response to microbial pathogens depends on a conserved cGAS-STING signaling pathway. The presence of DNA in the cytoplasm activates cGAS, while STING is activated by cyclic dinucleotides (cdNs) produced by cGAS or from bacterial origins. Here, we show that Group B Streptococcus (GBS) induces IFN-β production almost exclusively through cGAS-STING-dependent recognition of bacterial DNA. However, we find that GBS expresses an ectonucleotidase, CdnP, which hydrolyzes extracellular bacterial cyclic-di-AMP. Inactivation of CdnP leads to c-di-AMP accumulation outside the bacteria and increased IFN-β production. Higher IFN-β levels in vivo increase GBS killing by the host. The IFN-β overproduction observed in the absence of CdnP is due to the cumulative effect of DNA sensing by cGAS and STING-dependent sensing of c-di-AMP. These findings describe the importance of a bacterial c-di-AMP ectonucleotidase and suggest a direct bacterial mechanism that dampens activation of the cGAS-STING axis.

miR-718 represses proinflammatory cytokine production through targeting phosphatase and tensin homolog (PTEN)

Bacterial sepsis involves a complex interaction between the host immune response and bacterial LPS. LPS binds Toll-like receptor (TLR) 4, which leads to the release of proinflammatory cytokines that are essential for a potent innate immune response against pathogens. The innate immune system is tightly regulated, as excessive inflammation can lead to organ failure and death. MicroRNAs have recently emerged as important regulators of the innate immune system. Here we determined the function of miR-718, which is conserved across mammals and overlaps with the 5' UTR of the interleukin 1 receptor-associated kinase (IRAK1) gene. As IRAK1 is a key component of innate immune signaling pathways that are downstream of most TLRs, we hypothesized that miR-718 helps regulate the innate immune response. Activation of TLR4, but not TLR3, induced the expression of miR-718 in macrophages. miR-718 expression was also induced in the spleens of mice upon LPS injection. miR-718 modulates PI3K/Akt signaling by directly down-regulating phosphatase and tensin homolog (PTEN), thereby promoting phosphorylation of Akt, which leads to a decrease in proinflammatory cytokine production. Phosphorylated Akt induces let-7e expression, which, in turn, down-regulates TLR4 and further diminishes TLR4-mediated proinflammatory signals. Decreased miR-718 expression is associated with bacterial burden during Neisseria gonorrhoeae infection and alters the infection dynamics of N. gonorrhoeae in vitro Furthermore, miR-718 regulates the induction of LPS tolerance in macrophages. We propose a role for miR-718 in controlling TLR4 signaling and inflammatory cytokine signaling through a negative feedback regulation loop involving down-regulation of TLR4, IRAK1, and NF-κB.

Endoplasmic Reticulum Stress-induced Hepatocellular Death Pathways Mediate Liver Injury and Fibrosis via Stimulator of Interferon Genes

Fibrosis, driven by inflammation, marks the transition from benign to progressive stages of chronic liver diseases. Although inflammation promotes fibrogenesis, it is not known whether other events, such as hepatocyte death, are required for the development of fibrosis. Interferon regulatory factor 3 (IRF3) regulates hepatocyte apoptosis and production of type I IFNs. In the liver, IRF3 is activated via Toll-like receptor 4 (TLR4) signaling or the endoplasmic reticulum (ER) adapter, stimulator of interferon genes (STING). We hypothesized that IRF3-mediated hepatocyte death is an independent determinant of chemically induced liver fibrogenesis. To test this, we performed acute or chronic CCl₄ administration to WT and IRF3-, Toll/Interleukin-1R (TIR) domain-containing adapter-inducing interferon-β (TRIF)-, TRIF-related adaptor molecule (TRAM)-, and STING-deficient mice. We report that acute CCl₄ administration to WT mice resulted in early ER stress, activation of IRF3, and type I IFNs, followed by hepatocyte apoptosis and liver injury, accompanied by liver fibrosis upon repeated administration of CCl₄ Deficiency of IRF3 or STING prevented hepatocyte death and fibrosis both in acute or chronic CCl₄ In contrast, mice deficient in type I IFN receptors or in TLR4 signaling adaptors, TRAM or TRIF, upstream of IRF3, were not protected from hepatocyte death and/or fibrosis, suggesting that the pro-apoptotic role of IRF3 is independent of TLR signaling in fibrosis. Hepatocyte death is required for liver fibrosis with causal involvement of STING and IRF3. Thus, our results identify that IRF3, by its association with STING in the presence of ER stress, couples hepatocyte apoptosis with liver fibrosis and indicate that innate immune signaling regulates outcomes of liver fibrosis via modulation of hepatocyte death in the liver.

Use of murine embryonic fibroblasts to define Toll-like receptor activation and specificity

Toll-like receptors (TLRs) are critically involved in the innate immune response to bacterial, viral and fungal pathogens. We have studied human peripheral blood mononuclear cells, murine embryonic fibroblasts (MEFs) and a panel of human cell lines, including HEK, HeLa, AGS, ECV304 and U373 cells, for expression of TLR-specific mRNAs and for TLR-ligand dependent cytokine secretion. Peripheral blood cells expressed multiple TLRs; however, many studies have shown that blood contains multiple, heterogeneous cell populations with distinct patterns of TLR expression. Cell lines had variable expression of TLRs, and in most cases lacked TLR2 and TLR8 expression and only weakly expressed mRNAs for TLR5, TLR7 and TLR9. In contrast, MEFs expressed high levels of mRNA for TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8 and TLR9. MEFs were highly responsive to TLR-ligand activation and secreted high levels of both IL-6 and MCP-1 in response to TLR ligands. MEFs from mice with targeted deletions of TLR2, TLR4 and MyD88 demonstrated profound defects in their IL-6 response to their specific ligands, consistent with studies of macrophages and tissues from adult knockout animals. MEF cultures are homogenous and amenable to biochemical analysis and should allow rigorous studies of the contribution of individual TLRs to the innate immune response.

Cell activation by Toll-like receptors: role of LBP and CD14

Members of the Toll-like receptor (TLR) family have been shown to be important in the activation of cells by a variety of microbial ligands. TLRs are thought to mediate the `recognition event' that follows an encounter between a mammalian cell and a microbial agent. In the case of the response to bacterial lipopolysaccharide (LPS), it is clear that the ability of these cell surface proteins to initiate the events necessary for activation of cells to produce cytokines is dependent upon `accessory proteins' such as the pattern recognition protein CD14 and the lipopolysaccharide binding protein (LBP). While the role of these proteins in the LPS-specific response is defined, their role in other TLR responses has not been defined, but it is important in understanding these events and, potentially, in designing new therapeutic strategies. Here we report on the role of these proteins in the response to yeast zymosan. The requirements for this response (which unlike the response to LPS is a response to a particulate antigen) and the role of other serum proteins are defined.

Type I Interferon Induction by Neisseria gonorrhoeae: Dual Requirement of Cyclic GMP-AMP Synthase and Toll-like Receptor 4

The innate immune system is the first line of defense against Neisseria gonorrhoeae (GC). Exposure of cells to GC lipooligosaccharides induces a strong immune response, leading to type I interferon (IFN) production via TLR4/MD-2. In addition to living freely in the extracellular space, GC can invade the cytoplasm to evade detection and elimination. Double-stranded DNA introduced into the cytosol binds and activates the enzyme cyclic-GMP-AMP synthase (cGAS), which produces 2'3'-cGAMP and triggers STING/TBK-1/IRF3 activation, resulting in type I IFN expression. Here, we reveal a cytosolic response to GC DNA that also contributes to type I IFN induction. We demonstrate that complete IFN-β induction by live GC depends on both cGAS and TLR4. Type I IFN is detrimental to the host, and dysregulation of iron homeostasis genes may explain lower bacteria survival in cGAS(-/-) and TLR4(-/-) cells. Collectively, these observations reveal cooperation between TLRs and cGAS in immunity to GC infection.

Cutting Edge: DNA in the Lung Microenvironment during Influenza Virus Infection Tempers Inflammation by Engaging the DNA Sensor AIM2

Innate sensing of nucleic acids lies at the heart of antiviral immunity. During viral infection, dying cells may also release nucleic acids into the tissue microenvironment. It is unknown what effect such host signals have on the quality or duration of the immune response to viruses. In this study, we uncovered an immune-regulatory pathway that tempers the intensity of the host response to influenza A virus (IAV) infection. We found that host-derived DNA accumulates in the lung microenvironment during IAV infection. Ablation of DNA in the lung resulted in increased mortality, increased cellular recruitment, and increased inflammation following IAV challenge. The released DNA, in turn, was sensed by the DNA receptor absent in melanoma 2. Aim2(-/-) mice showed similarly exaggerated immune responses to IAV. Taken together, our results identify a novel mechanism of cross-talk between pathogen- and damage-associated molecular pattern-sensing pathways, wherein sensing of host-derived DNA limits immune-mediated damage to infected tissues.

Positive Selection Drives Preferred Segment Combinations during Influenza Virus Reassortment

Influenza A virus (IAV) has a segmented genome that allows for the exchange of genome segments between different strains. This reassortment accelerates evolution by breaking linkage, helping IAV cross species barriers to potentially create highly virulent strains. Challenges associated with monitoring the process of reassortment in molecular detail have limited our understanding of its evolutionary implications. We applied a novel deep sequencing approach with quantitative analysis to assess the in vitro temporal evolution of genomic reassortment in IAV. The combination of H1N1 and H3N2 strains reproducibly generated a new H1N2 strain with the hemagglutinin and nucleoprotein segments originating from H1N1 and the remaining six segments from H3N2. By deep sequencing the entire viral genome, we monitored the evolution of reassortment, quantifying the relative abundance of all IAV genome segments from the two parent strains over time and measuring the selection coefficients of the reassorting segments. Additionally, we observed several mutations coemerging with reassortment that were not found during passaging of pure parental IAV strains. Our results demonstrate how reassortment of the segmented genome can accelerate viral evolution in IAV, potentially enabled by the emergence of a small number of individual mutations.

Metabolic danger signals, uric acid and ATP, mediate inflammatory cross-talk between hepatocytes and immune cells in alcoholic liver disease

Inflammation defines the progression of ALD from reversible to advanced stages. Translocation of bacterial LPS to the liver from the gut is necessary for alcohol-induced liver inflammation. However, it is not known whether endogenous, metabolic danger signals are required for inflammation in ALD. Uric acid and ATP, 2 major proinflammatory danger signals, were evaluated in the serum of human volunteers exposed to a single dose of ethanol or in supernatants of primary human hepatocytes exposed to ethanol. In vitro studies were used to evaluate the role of uric acid and ATP in inflammatory cross-talk between hepatocytes and immune cells. The significance of signaling downstream of uric acid and ATP in the liver was evaluated in NLRP3-deficient mice fed a Lieber-DeCarli ethanol diet. Exposure of healthy human volunteers to a single dose of ethanol resulted in increased serum levels of uric acid and ATP. In vitro, we identified hepatocytes as a significant source of these endogenous inflammatory signals. Uric acid and ATP mediated a paracrine inflammatory cross-talk between damaged hepatocytes and immune cells and significantly increased the expression of LPS-inducible cytokines, IL-1β and TNF-α, by immune cells. Deficiency of NLRP3, a ligand-sensing component of the inflammasome recognizing uric acid and ATP, prevented the development of alcohol-induced liver inflammation in mice and significantly ameliorated liver damage and steatosis. Endogenous metabolic danger signals, uric acid, and ATP are involved in inflammatory cross-talk between hepatocytes and immune cells and play a crucial role in alcohol-induced liver inflammation.

Both bone marrow-derived and non-bone marrow-derived cells contribute to AIM2 and NLRP3 inflammasome activation in a MyD88-dependent manner in dietary steatohepatitis

BACKGROUND & AIMS

Inflammation promotes the progression of non-alcoholic steatohepatitis (NASH). Toll-like receptor 4 (TLR4) and TLR9 activation through myeloid differentiation primary response gene 88 (MyD88) and production of mature interleukin-1β (IL-1β) via inflammasome activation contribute to steatohepatitis. Here, we investigated the inter-relationship between TLR signalling and inflammasome activation in dietary steatohepatitis.

METHODS

Wild type (WT), TLR4- and MyD88-deficient (KO) mice received methionine-choline-deficient (MCD) or -supplemented (MCS) diets for 5 weeks and a subset was challenged with TLR9 ligand CpG-DNA.

RESULTS

TLR4, TLR9, AIM2 (absent in melanoma 2) and NLRP3 (NLR family pyrin domain containing 3) inflammasome mRNA, and mature IL-1β protein levels were increased in MCD diet-induced steatohepatitis compared to MCS controls. TLR9 stimulation resulted in greater up-regulation of the DNA-sensing AIM2 expression and IL-1β production in livers of MCD compared to MCS diet-fed mice. High mobility group box 1 (HMGB1), a TLR9-activating danger molecule and phospho-HMGB1 protein levels were also increased in livers of MCD diet-fed mice. MyD88- but not TLR4-deficiency prevented up-regulation of AIM2, NLRP3 mRNA and IL-1β protein production in dietary steatohepatitis. Selective MyD88 deficiency either in bone marrow (BM)-derived or non-BM-derived cells attenuated hepatic up-regulation of inflammasome mRNA, caspase-1 activation and IL-1β protein production, but only BM-derived cell-specific MyD88-deficiency attenuated liver injury.

CONCLUSIONS

Our data demonstrate that both bone marrow-derived and non-BM-derived cells contribute to inflammasome activation in a MyD88-dependent manner in dietary steatohepatitis. We show that AIM2 inflammasome expression and activation are further augmented by TLR9 ligands in dietary steatohepatitis.

Interferon γ-inducible protein (IFI) 16 transcriptionally regulates type i interferons and other interferon-stimulated genes and controls the interferon response to both DNA and RNA viruses

The interferon γ-inducible protein 16 (IFI16) has recently been linked to the detection of nuclear and cytosolic DNA during infection with herpes simplex virus-1 and HIV. IFI16 binds dsDNA via HIN200 domains and activates stimulator of interferon genes (STING), leading to TANK (TRAF family member-associated NF-κB activator)-binding kinase-1 (TBK1)-dependent phosphorylation of interferon regulatory factor (IRF) 3 and transcription of type I interferons (IFNs) and related genes. To better understand the role of IFI16 in coordinating type I IFN gene regulation, we generated cell lines with stable knockdown of IFI16 and examined responses to DNA and RNA viruses as well as cyclic dinucleotides. As expected, stable knockdown of IFI16 led to a severely attenuated type I IFN response to DNA ligands and viruses. In contrast, expression of the NF-κB-regulated cytokines IL-6 and IL-1β was unaffected in IFI16 knockdown cells, suggesting that the role of IFI16 in sensing these triggers was unique to the type I IFN pathway. Surprisingly, we also found that knockdown of IFI16 led to a severe attenuation of IFN-α and the IFN-stimulated gene retinoic acid-inducible gene I (RIG-I) in response to cyclic GMP-AMP, a second messenger produced by cyclic GMP-AMP synthase (cGAS) as well as RNA ligands and viruses. Analysis of IFI16 knockdown cells revealed compromised occupancy of RNA polymerase II on the IFN-α promoter in these cells, suggesting that transcription of IFN-stimulated genes is dependent on IFI16. These results indicate a broader role for IFI16 in the regulation of the type I IFN response to RNA and DNA viruses in antiviral immunity.

Dicer's role as an antiviral: still an enigma

Dicer is a multifunctional protein that is essential across species for the generation of microRNAs, a function that is highly conserved across the plant and animal kingdoms. Intriguingly, Dicer exhibits antiviral functions in lower organisms including Drosophila melanogaster and Caenorhabditis elegans. Antiviral activity occurs via small interfering RNA production following cytoplasmic sensing of viral dsRNA. Notably, such antiviral activity has not yet been clearly demonstrated in higher organisms such as mammals. Here, we review the evidence for Dicer as an innate antiviral across species.

Chronic alcohol-induced microRNA-155 contributes to neuroinflammation in a TLR4-dependent manner in mice

Introduction

Alcohol-induced neuroinflammation is mediated by pro-inflammatory cytokines and chemokines including tumor necrosis factor-α (TNFα), monocyte chemotactic protein-1 (MCP1) and interleukin-1-beta (IL-1β). Toll-like receptor-4 (TLR4) pathway induced nuclear factor-κB (NF-κB) activation is involved in the pathogenesis of alcohol-induced neuroinflammation. Inflammation is a highly regulated process. Recent studies suggest that microRNAs (miRNAs) play crucial role in fine tuning gene expression and miR-155 is a major regulator of inflammation in immune cells after TLR stimulation.

Aim

To evaluate the role of miR-155 in the pathogenesis of alcohol-induced neuroinflammation.

Methods

Wild type (WT), miR-155- and TLR4-knockout (KO) mice received 5% ethanol-containing or isocaloric control diet for 5 weeks. Microglia markers were measured by q-RTPCR; inflammasome activation was measured by enzyme activity; TNFα, MCP1, IL-1β mRNA and protein were measured by q-RTPCR and ELISA; phospho-p65 protein and NF-κB were measured by Western-blotting and EMSA; miRNAs were measured by q-PCR in the cerebellum. MiR-155 was measured in immortalized and primary mouse microglia after lipopolysaccharide and ethanol stimulation.

Results

Chronic ethanol feeding up-regulated miR-155 and miR-132 expression in mouse cerebellum. Deficiency in miR-155 protected mice from alcohol-induced increase in inflammatory cytokines; TNFα, MCP1 protein and TNFα, MCP1, pro-IL-1β and pro-caspase-1 mRNA levels were reduced in miR-155 KO alcohol-fed mice. NF-κB was activated in WT but not in miR-155 KO alcohol-fed mice. However increases in cerebellar caspase-1 activity and IL-1β levels were similar in alcohol-fed miR-155-KO and WT mice. Alcohol-fed TLR4-KO mice were protected from the induction of miR-155. NF-κB activation measured by phosphorylation of p65 and neuroinflammation were reduced in alcohol-fed TLR4-KO compared to control mice. TLR4 stimulation with lipopolysaccharide in primary or immortalized mouse microglia resulted in increased miR-155.

Conclusion

Chronic alcohol induces miR-155 in the cerebellum in a TLR4-dependent manner. Alcohol-induced miR-155 regulates TNFα and MCP1 expression but not caspase-dependent IL-1β increase in neuroinflammation.

Alcohol-induced IL-1β in the brain is mediated by NLRP3/ASC inflammasome activation that amplifies neuroinflammation

Alcohol-induced neuroinflammation is mediated by proinflammatory cytokines, including IL-1β. IL-1β production requires caspase-1 activation by inflammasomes-multiprotein complexes that are assembled in response to danger signals. We hypothesized that alcohol-induced inflammasome activation contributes to increased IL-1β in the brain. WT and TLR4-, NLRP3-, and ASC-deficient (KO) mice received an ethanol-containing or isocaloric control diet for 5 weeks, and some received the rIL-1ra, anakinra, or saline treatment. Inflammasome activation, proinflammatory cytokines, endotoxin, and HMGB1 were measured in the cerebellum. Expression of inflammasome components (NLRP1, NLRP3, ASC) and proinflammatory cytokines (TNF-α, MCP-1) was increased in brains of alcohol-fed compared with control mice. Increased caspase-1 activity and IL-1β protein in ethanol-fed mice indicated inflammasome activation. TLR4 deficiency protected from TNF-α, MCP-1, and attenuated alcohol-induced IL-1β increases. The TLR4 ligand, LPS, was not increased in the cerebellum. However, we found up-regulation of acetylated and phosphorylated HMGB1 and increased expression of the HMGB1 receptors (TLR2, TLR4, TLR9, RAGE) in alcohol-fed mice. NLRP3- or ASC-deficient mice were protected from caspase-1 activation and alcohol-induced IL-1β increase in the brain. Furthermore, in vivo treatment with rIL-1ra prevented alcohol-induced inflammasome activation and IL-1β, TNF-α, and acetylated HMGB1 increases in the cerebellum. Conversely, intracranial IL-1β administration induced TNF-α and MCP-1 in the cerebellum. In conclusion, alcohol up-regulates and activates the NLRP3/ASC inflammasome, leading to caspase-1 activation and IL-1β increase in the cerebellum. IL-1β amplifies neuroinflammation, and disruption of IL-1/IL-1R signaling prevents alcohol-induced inflammasome activation and neuroinflammation. Increased levels of acetylated and phosphorylated HMGB1 may contribute to alcoholic neuroinflammation.

Tuning innate immune activation by surface texturing of polymer microparticles: the role of shape in inflammasome activation

Polymeric microparticles have been widely investigated as platforms for delivery of drugs, vaccines, and imaging contrast agents and are increasingly used in a variety of clinical applications. Microparticles activate the inflammasome complex and induce the processing and secretion of IL-1β, a key innate immune cytokine. Recent work suggests that although receptors are clearly important for particle phagocytosis, other physical characteristics, especially shape, play an important role in the way microparticles activate cells. We examined the role of particle surface texturing not only on uptake efficiency but also on the subsequent immune cell activation of the inflammasome. Using a method based on emulsion processing of amphiphilic block copolymers, we prepared microparticles with similar overall sizes and surface chemistries but having either smooth or highly microtextured surfaces. In vivo, textured (budding) particles induced more rapid neutrophil recruitment to the injection site. In vitro, budding particles were more readily phagocytosed than smooth particles and induced more lipid raft recruitment to the phagosome. Remarkably, budding particles also induced stronger IL-1β secretion than smooth particles through activation of the NLRP3 inflammasome. These findings demonstrate a pronounced role of particle surface topography in immune cell activation, suggesting that shape is a major determinant of inflammasome activation.

Sialylneolacto-N-tetraose c (LSTc)-bearing liposomal decoys capture influenza A virus

Influenza is a severe disease in humans and animals with few effective therapies available. All strains of influenza virus are prone to developing drug resistance due to the high mutation rate in the viral genome. A therapeutic agent that targets a highly conserved region of the virus could bypass resistance and also be effective against multiple strains of influenza. Influenza uses many individually weak ligand binding interactions for a high avidity multivalent attachment to sialic acid-bearing cells. Polymerized sialic acid analogs can form multivalent interactions with influenza but are not ideal therapeutics due to solubility and toxicity issues. We used liposomes as a novel means for delivery of the glycan sialylneolacto-N-tetraose c (LSTc). LSTc-bearing decoy liposomes form multivalent, polymer-like interactions with influenza virus. Decoy liposomes competitively bind influenza virus in hemagglutination inhibition assays and inhibit infection of target cells in a dose-dependent manner. Inhibition is specific for influenza virus, as inhibition of Sendai virus and respiratory syncytial virus is not observed. In contrast, monovalent LSTc does not bind influenza virus or inhibit infectivity. LSTc decoy liposomes prevent the spread of influenza virus during multiple rounds of replication in vitro and extend survival of mice challenged with a lethal dose of virus. LSTc decoy liposomes co-localize with fluorescently tagged influenza virus, whereas control liposomes do not. Considering the conservation of the hemagglutinin binding pocket and the ability of decoy liposomes to form high avidity interactions with influenza hemagglutinin, our decoy liposomes have potential as a new therapeutic agent against emerging influenza strains.

IL-1 receptor antagonist ameliorates inflammasome-dependent alcoholic steatohepatitis in mice

Alcoholic liver disease (ALD) is characterized by steatosis and upregulation of proinflammatory cytokines, including IL-1β. IL-1β, type I IL-1 receptor (IL-1R1), and IL-1 receptor antagonist (IL-1Ra) are all important regulators of the IL-1 signaling complex, which plays a role in inflammation. Furthermore, IL-1β maturation is dependent on caspase-1 (Casp-1). Using IL-1Ra-treated mice as well as 3 mouse models deficient in regulators of IL-1β activation (Casp-1 and ASC) or signaling (IL-1R1), we found that IL-1β signaling is required for the development of alcohol-induced liver steatosis, inflammation, and injury. Increased IL-1β was due to upregulation of Casp-1 activity and inflammasome activation. The pathogenic role of IL-1 signaling in ALD was attributable to the activation of the inflammasome in BM-derived Kupffer cells. Importantly, in vivo intervention with a recombinant IL-1Ra blocked IL-1 signaling and markedly attenuated alcohol-induced liver inflammation, steatosis, and damage. Furthermore, physiological doses of IL-1β induced steatosis, increased the inflammatory and prosteatotic chemokine MCP-1 in hepatocytes, and augmented TLR4-dependent upregulation of inflammatory signaling in macrophages. In conclusion, we demonstrated that Casp-1-dependent upregulation of IL-1β and signaling mediated by IL-1R1 are crucial in ALD pathogenesis. Our findings suggest a potential role of IL-1R1 inhibition in the treatment of ALD.

Trefoil factor 2 rapidly induces interleukin 33 to promote type 2 immunity during allergic asthma and hookworm infection

The repair protein trefoil factor 2 promotes Th2 responses to helminth infection and allergens in part by inducing IL-33.

The molecular mechanisms that drive mucosal T helper type 2 (T_H2) responses against parasitic helminths and allergens remain unclear. In this study, we demonstrate in mice that TFF2 (trefoil factor 2), an epithelial cell–derived repair molecule, is needed for the control of lung injury caused by the hookworm parasite Nippostrongylus brasiliensis and for type 2 immunity after infection. TFF2 is also necessary for the rapid production of IL-33, a T_H2-promoting cytokine, by lung epithelia, alveolar macrophages, and inflammatory dendritic cells in infected mice. TFF2 also increases the severity of allergic lung disease caused by house dust mite antigens or IL-13. Moreover, TFF2 messenger RNA expression is significantly increased in nasal mucosal brushings during asthma exacerbations in children. These experiments extend the biological functions of TFF2 from tissue repair to the initiation and maintenance of mucosal T_H2 responses.

CD14 deficiency impacts glucose homeostasis in mice through altered adrenal tone

The toll-like receptors comprise one of the most conserved components of the innate immune system, signaling the presence of molecules of microbial origin. It has been proposed that signaling through TLR4, which requires CD14 to recognize bacterial lipopolysaccharide (LPS), may generate low-grade inflammation and thereby affect insulin sensitivity and glucose metabolism. To examine the long-term influence of partial innate immune signaling disruption on glucose homeostasis, we analyzed knockout mice deficient in CD14 backcrossed into the diabetes-prone C57BL6 background at 6 or 12 months of age. CD14-ko mice, fed either normal or high-fat diets, displayed significant glucose intolerance compared to wild type controls. They also displayed elevated norepinephrine urinary excretion and increased adrenal medullary volume, as well as an enhanced norepinephrine secretory response to insulin-induced hypoglycemia. These results point out a previously unappreciated crosstalk between innate immune- and sympathoadrenal- systems, which exerts a major long-term effect on glucose homeostasis.

Innate immune responses to Helicobacter pylori infection: an overview

Innate immune receptors detect Helicobacter pylori infection and trigger downstream signaling events that result in the production of cytokines and interferon-β. This chapter gives an overview of the receptors and their roles in responding to H. pylori infection and details the downstream signaling events. The tools that have been developed to study the innate immune response to H. pylori are also discussed. Understanding the immune response to H. pylori is critical to develop better treatments for H. pylori-induced disease states including gastric malignancies and cancer.

Methods for in vivo and in vitro analysis of innate immune responses to Helicobacter pylori infection

It is estimated that half of the world's population is infected by Helicobacter pylori (H. pylori) (Polk and Peek, Nat Rev Cancer 10:403-414, 2010; Peek et al., Physiol Rev 90:831-858, 2010). Following infection, H. pylori induces a chronic innate immune response that is thought to contribute to gastric complications. Due to the widespread prevalence of H. pylori, it is important to study the innate immune responses that result from the infection. A variety of in vitro and in vivo techniques have been developed by our laboratory to study this immune response (Fox et al., Am J Pathol 171:1520-1528, 2007; Kurt-Jones et al., Infect Immun 75:471-480, 2007; Kurt-Jones et al., J Endotoxin Res 10:419-424, 2004). These methods are described here.

Antibodies to cell surface proteins redirect intracellular trafficking pathways

Antibody-mediated intracellular delivery of therapeutic agents has been considered for treatment of a variety of diseases. These approaches involve targeting cell-surface receptor proteins expressed by tumors or viral proteins expressed on infected cells. We examined the intracellular trafficking of a viral cell-surface-expressed protein, rabies G, with or without binding a specific antibody, ARG1. We found that antibody binding shifts the native intracellular trafficking pathway of rabies G in an Fc-independent manner. Kinetic studies indicate that the ARG1/rabies G complex progressively co-localized with clathrin, early endosomes, late endosomes, and lysosomes after addition to cells. This pathway was different from that taken by rabies G without addition of antibody, which localized with recycling endosomes. Findings were recapitulated using a cellular receptor with a well-defined endogenous recycling pathway. We conclude that antibody binding to cell-surface proteins induces redirection of intracellular trafficking of unbound or ligand bound receptors to a specific degradation pathway. These findings have broad implications for future developments of antibody-based therapeutics.

C21orf91 genotypes correlate with herpes simplex labialis (cold sore) frequency: description of a cold sore susceptibility gene

BACKGROUND

Herpes simplex virus type 1 (HSV-1) infects >70% of the United States population. We identified a 3-megabase region on human chromosome 21 containing 6 candidate genes associated with herpes simplex labialis (HSL, "cold sores").

METHODS

We conducted single nucleotide polymorphism (SNP) scans of the chromosome 21 region to define which of 6 possible candidate genes were associated with cold sore frequency. We obtained the annual HSL frequency for 355 HSV-1 seropositive individuals and determined the individual genotypes by SNPlex for linkage analysis and parental transmission disequilibrium testing (ParenTDT).

RESULTS

Two-point linkage analysis showed positive linkage between cold sore frequency and 2 SNPs within the C21orf91 region, 1 of which is nonsynonymous. ParenTDT analysis revealed a strong association between another C21orf91 SNP, predicted to lie in the 3' untranslated region, and frequent HSL (P = .0047). C21orf 91 is a predicted open reading frame of unknown function that encodes a cytosolic protein.

CONCLUSIONS

We evaluated candidate genes in the cold sore susceptibility region using fine mapping with 45 SNP markers. 2 complementary techniques identified C21orf91 as a gene of interest for susceptibility to HSL. We propose that C21orf91 be designated the Cold Sore Susceptibility Gene-1 (CSSG1).

Pattern recognition receptors and the innate immune response to viral infection

The innate immune response to viral pathogens is critical in order to mobilize protective immunity. Cells of the innate immune system detect viral infection largely through germline-encoded pattern recognition receptors (PRRs) present either on the cell surface or within distinct intracellular compartments. These include the Toll-like receptors (TLRs), the retinoic acid-inducble gene I-like receptors (RLRs), the nucleotide oligomerization domain-like receptors (NLRs, also called NACHT, LRR and PYD domain proteins) and cytosolic DNA sensors. While in certain cases viral proteins are the trigger of these receptors, the predominant viral activators are nucleic acids. The presence of viral sensing PRRs in multiple cellular compartments allows innate cells to recognize and quickly respond to a broad range of viruses, which replicate in different cellular compartments. Here, we review the role of PRRs and associated signaling pathways in detecting viral pathogens in order to evoke production of interferons and cytokines. By highlighting recent progress in these areas, we hope to convey a greater understanding of how viruses activate PRR signaling and how this interaction shapes the anti-viral immune response.

Abstract 963: Glioma treatment with temozolomide and Notch inhibition blocks tumor recovery through the induction of senescence and tumor clearance

Current glioma therapy relies on induction of cytotoxicity after removal of the bulk tumor through the combination of surgery, radiation and temozolomide (TMZ); however, these therapies do not result in a long-term cure. Our lab previously demonstrated that some glioma cells undergo a transient cell cycle arrest in response to chemotherapy. Treatment with TMZ decreases sphere formation; however, after a short recovery period, a small number of cells resume sphere formation and self-renewal, measured by secondary sphere formation. Blocking the Notch pathway in neurosphere cultures with gamma-secretase inhibitors (GSIs) after TMZ treatment targeted the cells capable of recovery. TMZ + GSI treated cells do not recover and are no longer capable of self-renewal. TMZ + GSI synergy is dependent on the sequence of the drug treatments. Recovery was inhibited when GSI was administered 24 hrs after TMZ treatment. TMZ + GSI treatment also decreases tumorigenicity. When glioma cell lines were treated in vitro and implanted in immunodeficient mice, TMZ + GSI treatment extended latency and greatly increased survival. In addition, in vivo TMZ + GSI treatment completely blocked tumor progression and resulted in the loss of a palpable tumor in 50% of mice, while none of the TMZ-only treated mice survived. TMZ + GSI treated cultures and xenografts display a senescent phenotype. We observed an increase in the number of cells expressing senescence-associated beta-galactosidase and a decrease in Ki67 positive cells. Gene expression was also analyzed after drug treatments to confirm the induction of senescence. p21 is upregulated in cells that have undergone either a transient cell cycle arrest or senescence. We found that upregulation of p21 occurred initially in both TMZ-only and TMZ + GSI treatments, but only remained upregulated in the TMZ + GSI samples. This demonstrates that the addition of GSIs shifts TMZ-treated cells from a transient arrested state to a permanent senescent state. New therapy combinations, such as TMZ + GSI, are arising in a promising new field of cytostatic therapy and therapy-induced senescence (TIS). A key feature of TIS is the secretory profile of senescent cells. It was previously demonstrated that senescent tumor cells secrete inflammatory cytokines and activate the innate immune system for tumor clearance. We found that TMZ + GSI treatment resulted in upregulation of secreted IL-6 and IL-8 cytokines. We are currently the effect of senescent glioma cells on the innate immune system and tumor clearance. Overall, this data demonstrates the importance of the Notch pathway in chemoprotection and maintenance of TMZ-treated gliomas. The addition of GSIs to current treatments is promising target-directed therapy to decrease the rate of brain tumor recurrence inducing senescence.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 963. doi:10.1158/1538-7445.AM2011-963

Type I interferons protect from Toll-like receptor 9-associated liver injury and regulate IL-1 receptor antagonist in mice

BACKGROUND & AIMS

Liver inflammation and injury are mediated by the innate immune response, which is regulated by Toll-like receptors (TLR). Activation of TLR9 induces type I interferons (IFNs) via the interferon regulatory factor (IRF)-7. We investigated the roles of type I IFNs in TLR9-associated liver injury.

METHODS

Wild-type (WT), IRF7-deficient, and IFN-α/β receptor 1 (IFNAR1)-deficient mice were stimulated with TLR9 or TLR2 ligands. Findings from mice were verified in cultured hepatocytes and liver mononuclear cells (LMNCs) as well as in vivo experiments using recombinant type I IFN and interleukin-1 receptor antagonist (IL-1ra).

RESULTS

Type I IFNs were up-regulated during TLR9-associated liver injury in WT mice. IRF7- and IFNAR1-deficient mice, which have disruptions in type I IFN production or signaling, respectively, had increased liver damage and inflammation, decreased recruitment of dendritic cells, and increased production of tumor necrosis factor α by LMNCs. These findings indicate that type I IFNs have anti-inflammatory activities in liver. IL-1ra, which is produced by LMNCs and hepatocytes, is an IFN-regulated antagonist of the proinflammatory cytokine IL-1β; IRF7- and IFNAR1-deficient mice had decreased levels of IL-1ra compared with WT mice. IL-1ra protected cultured hepatocytes from IL-1β-mediated sensitization to cytotoxicity from tumor necrosis factor α. In vivo exposure to type I IFN, which induced IL-1ra, or administration of IL-1ra reduced TLR9-associated liver injury; the protective effect of type I IFNs therefore appears to be mediated by IFN-dependent induction of IL-1ra.

CONCLUSIONS

Type I IFNs have anti-inflammatory effects mediated by endogenous IL-1ra, which regulates the extent of TLR9-induced liver damage. Type I IFN signaling is therefore required for protection from immune-mediated liver injury.

Mutations in bone marrow-derived stromal stem cells unmask latent malignancy

Neoplastic epithelia may remain dormant and clinically unapparent in human patients for decades. Multiple risk factors including mutations in tumor cells or the stromal cells may affect the switch from dormancy to malignancy. Gene mutations, including p53 mutations, within the stroma of tumors are associated with a worse clinical prognosis; however, it is not known if these stromal mutations can promote tumors in genetically at-risk tissue. To address this question, Apc(Min/+) and Apc(Min/+) Rag2(-/-) mice, which have a predilection to mammary carcinoma (as well as wild-type (wt) mice), received mesenchymal stem cells (MSC) with mutant p53 (p53MSC) transferred via tail vein injection. In the wt mouse, p53MSC circulated in the periphery and homed to the marrow cavity where they could be recovered up to a year later without apparent effect on the health of the mouse. No mammary tumors were found. However, in mice carrying the Apc(Min/+) mutation, p53MSC homed to mammary tissue and significantly increased the incidence of mammary carcinoma. Tumor necrosis factor (TNF)-alpha-dependent factors elaborated from mesenchymal cells converted quiescent epithelia into clinically apparent disease. The increased cancer phenotype was completely preventable with neutralization of TNF-alpha or by transfer of CD4(+) regulatory T cells from immune competent donors, demonstrating that immune competency to regulate inflammation was sufficient to maintain neoplastic dormancy even in the presence of oncogenic epithelial and stromal mutations. The significant synergy between host immunity and mesenchymal cells identified here may restructure treatments to restore an anticancer microenvironment.

Periprosthetic osteolysis: characterizing the innate immune response to titanium wear-particles

Osteolysis of bone following total hip replacement is a major clinical problem. Examination of the areas surrounding failed implants has indicated an increase in the bone-resorption-inducing cytokine, interleukin 1β (IL-1β). NALP3, a NOD-like receptor protein located in the cytosol of macrophages, signals the cleavage of pro-IL-1β into its mature, secreted form, IL-1β. Here we showed that titanium particles stimulate the NALP3 inflammasome. We demonstrated that titanium induces IL-1β secretion from macrophages. This response depended on the expression of components of the NALP3 inflammasome, including NALP3, ASC, and Caspase-1. We also showed that titanium particles trigger the recruitment of neutrophils and that this acute inflammatory response depends on the expression of the IL-1 receptor and IL-1α/β. Moreover, administration of the IL-1 receptor antagonist (IL-1Ra) diminished neutrophil recruitment in response to titanium particles. Together, these results suggest that titanium particle-induced acute inflammation is due to activation of the NALP3 inflammasome, which leads to increased IL-1β secretion and IL-1-associated signaling, including neutrophil recruitment. Efficacy of IL-1Ra treatment introduces the potential for antagonist-based therapies for implant osteolysis.

UNC93B1 mediates host resistance to infection with Toxoplasma gondii

UNC93B1 associates with Toll-Like Receptor (TLR) 3, TLR7 and TLR9, mediating their translocation from the endoplasmic reticulum to the endolysosome, hence allowing proper activation by nucleic acid ligands. We found that the triple deficient ‘3d’ mice, which lack functional UNC93B1, are hyper-susceptible to infection with Toxoplasma gondii. We established that while mounting a normal systemic pro-inflammatory response, i.e. producing abundant MCP-1, IL-6, TNFα and IFNγ, the 3d mice were unable to control parasite replication. Nevertheless, infection of reciprocal bone marrow chimeras between wild-type and 3d mice with T. gondii demonstrated a primary role of hemopoietic cell lineages in the enhanced susceptibility of UNC93B1 mutant mice. The protective role mediated by UNC93B1 to T. gondii infection was associated with impaired IL-12 responses and delayed IFNγ by spleen cells. Notably, in macrophages infected with T. gondii, UNC93B1 accumulates on the parasitophorous vacuole. Furthermore, upon in vitro infection the rate of tachyzoite replication was enhanced in non-activated macrophages carrying mutant UNC93B1 as compared to wild type gene. Strikingly, the role of UNC93B1 on intracellular parasite growth appears to be independent of TLR function. Altogether, our results reveal a critical role for UNC93B1 on induction of IL-12/IFNγ production as well as autonomous control of Toxoplasma replication by macrophages.

One third of the human population in the world is chronically infected with Toxoplasma gondii. While the majority of infected individuals are asymptomatic, toxoplasmosis is a major cause of congenital disease, abortion, and a life-threatening opportunistic disease in immunocompromised individuals. Early activation of the innate immune system and cytokine production by myeloid cells is required for establishment of protective immunity to T. gondii infection. In mice, a mutation in the UNC93B1 gene abolishes signaling via the intracellular innate immune receptors, namely Toll-like receptors (TLR) 3, 7 and 9, thus, named triple-deficiency (3d) mice. Our results demonstrate that the hyper-susceptibility of 3d mice to T. gondii infection is associated with impaired IL-12 production, delayed IFNγ production, and uncontrolled parasite replication in macrophages. Overall, our study reveals a critical role for UNC93B1 in the immunological control of T. gondii infection.

Discovery of a novel TLR2 signaling inhibitor with anti-viral activity

Blockade of Toll-like receptor (TLR)-mediated inflammatory responses represents a new approach in the development of anti-inflammation therapeutics. In the present study, we have screened for TLR2-mediated inflammation inhibitors from small molecule compound libraries using a sensitive cell line stably expressing TLR2, CD14, and an NF-kappaB-driven-luciferase reporter gene. Lymphocytic choriomeningitis virus (LCMV) was used as a virus model. This arenavirus activates a TLR2/CD14-dependent NF-kappaB signaling pathway. We have identified 10 potential anti-inflammatory compounds out of 101,306 compounds. We further evaluated 1 of these positive compounds, E567. We demonstrated that compound E567 efficiently inhibits both LCMV and Herpes simplex virus 1 (HSV-1) induced cytokine responses in both human and mouse cell cultures. We also demonstrated that E567 inhibits cytokine responses in the mouse. Remarkably, E567 is also capable of inhibiting LCMV replication in mice. This is a new model for developing drugs for use in treating viral illnesses.

Overexpression of interleukin-1beta induces gastric inflammation and cancer and mobilizes myeloid-derived suppressor cells in mice

Polymorphisms of interleukin-1beta (IL-1beta) are associated with an increased risk of solid malignancies. Here, we show that stomach-specific expression of human IL-1beta in transgenic mice leads to spontaneous gastric inflammation and cancer that correlate with early recruitment of myeloid-derived suppressor cells (MDSCs) to the stomach. IL-1beta activates MDSCs in vitro and in vivo through an IL-1RI/NF-kappaB pathway. IL-1beta transgenic mice deficient in T and B lymphocytes develop gastric dysplasia accompanied by a marked increase in MDSCs in the stomach. Antagonism of IL-1 receptor signaling inhibits the development of gastric preneoplasia and suppresses MDSC mobilization. These results demonstrate that pathologic elevation of a single proinflammatory cytokine may be sufficient to induce neoplasia and provide a direct link between IL-1beta, MDSCs, and carcinogenesis.

Overexpression of interleukin-1beta induces gastric inflammation and cancer and mobilizes myeloid-derived suppressor cells in mice

Polymorphisms of interleukin-1beta (IL-1beta) are associated with an increased risk of solid malignancies. Here, we show that stomach-specific expression of human IL-1beta in transgenic mice leads to spontaneous gastric inflammation and cancer that correlate with early recruitment of myeloid-derived suppressor cells (MDSCs) to the stomach. IL-1beta activates MDSCs in vitro and in vivo through an IL-1RI/NF-kappaB pathway. IL-1beta transgenic mice deficient in T and B lymphocytes develop gastric dysplasia accompanied by a marked increase in MDSCs in the stomach. Antagonism of IL-1 receptor signaling inhibits the development of gastric preneoplasia and suppresses MDSC mobilization. These results demonstrate that pathologic elevation of a single proinflammatory cytokine may be sufficient to induce neoplasia and provide a direct link between IL-1beta, MDSCs, and carcinogenesis.

Lymphocytic choriomeningitis virus (LCMV) infection of CNS glial cells results in TLR2-MyD88/Mal-dependent inflammatory responses

In response to invading pathogens, Toll-like receptors (TLR) play a critical role in the initiation of the innate immune response, which can be either beneficial or detrimental to the host. In the present study, we demonstrated that central nervous system (CNS) glial cells are activated by Lymphocytic Choriomeningitis Virus (LCMV) in a TLR2-MyD88/Mal-dependent manner. Specifically, in response to LCMV, both astrocytes and microglial cells isolated from wild-type (WT) mice produced chemokines, such as MCP-1, RANTES and TNF-alpha. Similar responses occurred in TLR3 KO and TLR4 KO glial cells. In striking contrast, both astrocytes and microglial cells isolated from mice deficient in TLR2, MyD88, and Mal did not produce any of these chemokines. In addition, LCMV infection of glial cells induced up-regulation of TLR2, MHC class-I and II, CD40, CD86 in a MyD88-dependent manner. These results define a functional role for TLR signaling in viral infection-induced activation of CNS glial cells as well as for the immunopathology in the CNS.

Type 1 IFN mediates cross-talk between innate and adaptive immunity that abrogates transplantation tolerance

TLR activation of innate immunity prevents the induction of transplantation tolerance and shortens skin allograft survival in mice treated with costimulation blockade. The mechanism by which TLR signaling mediates this effect has not been clear. We now report that administration of the TLR agonists LPS (TLR4) or polyinosinic:polycytidylic acid (TLR3) to mice treated with costimulation blockade prevents alloreactive CD8(+) T cell deletion, primes alloreactive CTLs, and shortens allograft survival. The TLR4- and MyD88-dependent pathways are required for LPS to shorten allograft survival, whereas polyinosinic:polycytidylic acid mediates its effects through a TLR3-independent pathway. These effects are all mediated by signaling through the type 1 IFN (IFN-alphabeta) receptor. Administration of IFN-beta recapitulates the detrimental effects of TLR agonists on transplantation tolerance. We conclude that the type 1 IFN generated as part of an innate immune response to TLR activation can in turn activate adaptive immune responses that abrogate transplantation tolerance. Blocking of type 1 IFN-dependent pathways in patients may improve allograft survival in the presence of exogenous TLR ligands.

Innate immunity to respiratory viruses

Pattern recognition receptors are critically involved in the development of innate and adaptive antiviral immunity. Innate immune activation by viruses may occur via cell surface, intracellular and cytosolic pattern recognition receptors. These receptors sense viral components and may activate unique downstream pathways to generate antiviral immunity. In this article, we summarize the pattern recognition receptors that recognize major human respiratory viral pathogens, including influenza virus, respiratory syncytial virus and adenovirus. We also provide an overview of the current knowledge of regulation of type I interferons and inflammatory cytokines in viral infection.

Autophagy and innate immunity to viruses

Evaluation of: Lee HK, Lund JM, Ramanathan B, Mizushima N, Iwasaki A: Autophagy-dependent viral recognition by plasmacytoid dendritic cells. Science 315, 1398–1401 (2007). Plasmacytoid dendritic cells play a key role in the innate immune response to viral infection. They produce high amounts of IFN-α in response to viral nucleic acids. Nucleic acid stimulation of IFN-α production occurs through the activation of Toll-like receptors localized in the endosome. Lee and colleagues have identified autophagy as an essential component for IFN-α production in response to certain viruses, including a ssRNA virus and a dsDNA virus. Their findings indicate that autophagy may deliver viral replication intermediates located in the cytosol to Toll-like receptors located in the endosome to trigger cytokine production.

Cutting Edge: Antibody-mediated TLR7-dependent recognition of viral RNA

TLR7 recognizes the genome of ssRNA viruses such as Coxsackievirus B. Because TLR7 is expressed in intracellular compartments, viral RNA must be internalized before its recognition by TLR7. In this study, we define plasmacytoid dendritic cells (pDC) as peripheral blood mononuclear immune cells that respond to Coxsackievirus. pDC activation by Coxsackievirus B requires the presence of specific antiviral Abs. We show that Fc receptors mediate the recognition of virus-Ab complexes and that TLR7 is required for human and murine pDC production of cytokines. These data define a pathway by which intracellular TLR7 senses viral RNA and indicate a role for TLRs in association with Abs in sustaining virus-specific responses.

Role of MyD88 in Route-Dependent Susceptibility to Vesicular Stomatitis Virus Infection

TLRs are important components of the innate immune response. The role of the TLR signaling pathway in host defense against a natural viral infection has been largely unexplored. We found that mice lacking MyD88, an essential adaptor protein in TLR signaling pathway, were extremely sensitive to intranasal infection with vesicular stomatitis virus, and this susceptibility was dose dependent. We demonstrated that this increased susceptibility correlates with the impaired production of IFN-alpha and defective induction and maintenance of neutralizing Ab. These studies outline the important role of the TLR signaling pathway in nasal mucosae-respiratory tracts-neuroepithelium environment in the protection against microbial pathogen infections. We believe that these results explain how the route of infection, probably by virtue of activating different cell populations, can lead to entirely different outcomes of infection based on the underlying genetics of the host.

Toll like receptors and viruses

Toll like receptors (TLRs) are 'pattern recognition proteins' that discriminate between self and non-self. They interact with products of infectious agents to activate cells of the innate immune system and also stimulate the adaptive immune system. Intracellular and extracellular TLRs recognise a wide range of viruses leading to the production of different cytokines. In this paper, we summarise the types of TLRs that recognise viruses, the cytokines produced, the specific cell types involved and the activation pathways that have been characterised. We also provide an overview of the viruses demonstrated to interact with TLRs. A greater understanding of relationships between viruses or viral products and TLRs should improve understanding of pathogenesis and lead to the development of new anti-viral therapies.

Trefoil family factor 2 is expressed in murine gastric and immune cells and controls both gastrointestinal inflammation and systemic immune responses

Trefoil family factor 2 (TFF2), also known as spasmolytic peptide, is a low-molecular-weight protein that is upregulated in gastric tissues infected with Helicobacter or having other inflammatory conditions, but a precise function is yet to be elucidated. The role of TFF2 in the development of gastritis, colitis, and inflammatory cytokine responses was examined both in vivo and in vitro using wild-type and TFF2 knockout mice. TFF2 knockout and wild-type mice were infected with Helicobacter felis (H. felis) to induce gastritis. Colitis was induced in TFF2 knockout and wild-type mice by administering dextran sodium sulfate (DSS) in drinking water. Histopathology, clinical disease (colitis), and antibody levels (H. felis) were examined. TFF2 expression in tissues was determined by reverse transcriptase PCR, and the inflammatory and proliferative responses of TFF2-expressing macrophages and spleen cells were examined by cytokine enzyme-linked immunosorbent assay, thymidine incorporation, and gene array studies. TFF2 knockout mice have increased susceptibility to H. felis-induced gastritis, with enhanced gastric inflammation. They were also more susceptible to DSS-induced colitis, with prolonged colonic hemorrhage and persistent weight loss. Remarkably, TFF2 expression was not limited to the gastrointestinal tract, as suggested in previous studies, but was also present in macrophages and lymphocytes. The inflammatory and proliferative responses of these immune cell types were dysregulated in TFF2 knockout mice. TFF2-/- cells were hyperresponsive to interleukin 1 beta stimulation but showed normal responses to lipopolysaccharide, suggesting a specific role for TFF2 in interleukin 1 receptor but not Toll-like receptor 4 signaling via their Toll-interleukin 1 resistance domains. TFF2-/- lymphocytes also produced higher levels of interleukin 2 than wild-type cells. Thus, TFF2 was expressed in the gastrointestinal cells and in immune cells and was a negative regulator of gastrointestinal inflammation and immune cell cytokine responses. Our studies suggest that TFF2 not only controls gastrointestinal repair but also regulates mononuclear cell inflammatory responses.

Role for TLR2 in NK cell-mediated control of murine cytomegalovirus in vivo

Natural killer (NK) cells are essential for the early control of murine cytomegalovirus (MCMV) infection. Here, we demonstrate that toll-like receptor 2 (TLR2) plays a role in the NK cell-mediated control of MCMV. TLR2 knockout (KO) mice had elevated levels of MCMV in the spleen and liver on day 4 postinfection compared to C57BL/6 mice. In vivo depletion of NK cells with anti-NK1.1 antibodies, however, eliminated the differences in viral titers between the two groups, suggesting that the effect of TLR2 on MCMV clearance on day 4 was NK cell mediated. The defect in early antiviral control was associated with a decreased NK cell population in the spleen and liver and reduced amounts of interleukin-18 and alpha/beta interferon secreted in the TLR2 KO mice. Our studies suggest that in addition to the reported involvement of TLR9 and TLR3, TLR2 is also involved in innate immune responses to MCMV infection.