Search PubMed⌕ Search

Biomedical subjects

Shizuo Akira

Publications and source records attributed to Shizuo Akira.

At least 163 records · Page 9Linked to original sources
PubMed2005

Requirement for TLR9 in the immunomodulatory activity of Propionibacterium acnes.

Propionibacterium acnes (formerly Corynebacterium parvum) is part of the human flora and, as such, is associated with several human pathologies. It possesses strong immunomodulatory activities, which makes this bacterium interesting for prophylactic and therapeutic vaccination. The bacterial component(s) and the host receptor(s) involved in the induction of these activities are poorly understood. We show in this study that TLR9 is crucial in generating the characteristic effects of killed P. acnes priming in the spleen, such as extramedullary hemopoiesis and organ enlargement, and granuloma formation in the liver. Furthermore, the ability to overproduce TNF-alpha and IFN-gamma in response to LPS, lipid A, synthetic lipopeptide Pam(3)CysK(4), or whole killed bacteria was present in P. acnes-primed wild-type, but not TLR9(-/-), mice. Finally, P. acnes priming failed to induce enhanced resistance to murine typhoid fever in TLR9(-/-) mice. Thus, TLR9 plays an essential role in the induction of immunomodulatory effects by P. acnes. Because IFN-gamma is a key mediator of these effects, and enhanced IFN-gamma mRNA expression was absent in spleen and liver of P. acnes-primed TLR9(-/-) mice, we conclude that TLR9 is required for the induction of IFN-gamma by P. acnes.

Animals↗
PubMed2005

A role for fungal {beta}-glucans and their receptor Dectin-1 in the induction of autoimmune arthritis in genetically susceptible mice.

A combination of genetic and environmental factors can cause autoimmune disease in animals. SKG mice, which are genetically prone to develop autoimmune arthritis, fail to develop the disease under a microbially clean condition, despite active thymic production of arthritogenic autoimmune T cells and their persistence in the periphery. However, in the clean environment, a single intraperitoneal injection of zymosan, a crude fungal beta-glucan, or purified beta-glucans such as curdlan and laminarin can trigger severe chronic arthritis in SKG mice, but only transient arthritis in normal mice. Blockade of Dectin-1, a major beta-glucan receptor, can prevent SKG arthritis triggered by beta-glucans, which strongly activate dendritic cells in vitro in a Dectin-1-dependent but Toll-like receptor-independent manner. Furthermore, antibiotic treatment against fungi can prevent SKG arthritis in an arthritis-prone microbial environment. Multiple injections of polyinosinic-polycytidylic acid double-stranded RNA also elicit mild arthritis in SKG mice. Thus, specific microbes, including fungi and viruses, may evoke autoimmune arthritis such as rheumatoid arthritis by stimulating innate immunity in individuals who harbor potentially arthritogenic autoimmune T cells as a result of genetic anomalies or variations.

Animals↗
PubMed2005

Induction of CXCL5 during inflammation in the rodent lung involves activation of alveolar epithelium.

The lung is continuously exposed to bacteria and their products, and has developed a complex defense mechanism, including neutrophil recruitment. In mice, keratinocyte cell-derived chemokine and macrophage inflammatory protein-2 are the major chemokines for neutrophil recruitment into the lung. We have previously described a role for C-X-C chemokine (CXCL5) in neutrophil trafficking during lipopolysaccharide (LPS)-induced lung inflammation in mice. The aims of the present study were to identify the cellular origin of CXCL5 and to determine the signaling cascades that regulate its expression in the lung during LPS-induced inflammation and in isolated LPS-stimulated CXCL5-expressing cells. Our immunohistochemical analysis indicates that alveolar epithelial type II (AEII) cells are the primary source of CXCL5 in the rodent lung. These in vivo observations were confirmed with primary AEII cells. In addition, our data indicate that the Toll-like receptor 4 (TLR4) signaling cascade involving TLR4, myeloid differentiation factor 88, and Toll-IL-1R domain-containing adapter protein is required to induce CXCL5 expression in the lung. Furthermore, p38 and c-Jun N-terminal kinases are involved in lung CXCL5 expression. Similarly, TLR4, and p38 and c-Jun N-terminal kinases, are associated with LPS-induced CXCL5 expression in AEII cells. These novel observations demonstrate that activation of AEII cells via TLR4-dependent signaling is important for the production of CXCL5 in the lung exposed to LPS.

Animals↗
PubMed2005

The nuclear IkappaB protein IkappaBNS selectively inhibits lipopolysaccharide-induced IL-6 production in macrophages of the colonic lamina propria.

Macrophages play an important role in the pathogenesis of chronic colitis. However, it remains unknown how macrophages residing in the colonic lamina propria are regulated. We characterized colonic lamina proprial CD11b-positive cells (CLPMphi). CLPMphi of wild-type mice, but not IL-10-deficient mice, displayed hyporesponsiveness to TLR stimulation in terms of cytokine production and costimulatory molecule expression. We compared CLPMphi gene expression profiles of wild-type mice with IL-10-deficient mice, and identified genes that are selectively expressed in wild-type CLPMphi. These genes included nuclear IkappaB proteins such as Bcl-3 and IkappaBNS. Because Bcl-3 has been shown to specifically inhibit LPS-induced TNF-alpha production, we analyzed the role of IkappaBNS in macrophages. Lentiviral introduction of IkappaBNS resulted in impaired LPS-induced IL-6 production, but not TNF-alpha production in the murine macrophage cell line RAW264.7. IkappaBNS expression led to constitutive and intense DNA binding of NF-kappaB p50/p50 homodimers. IkappaBNS was recruited to the IL-6 promoter, but not to the TNF-alpha promoter, together with p50. Furthermore, small interference RNA-mediated reduction in IkappaBNS expression in RAW264.7 cells resulted in increased LPS-induced production of IL-6, but not TNF-alpha. Thus, IkappaBNS selectively suppresses LPS-induced IL-6 production in macrophages. This study established that nuclear IkappaB proteins differentially regulate LPS-induced inflammatory cytokine production in macrophages.

Animals↗
PubMed2005

Interleukin-1 receptor-associated kinase-1 plays an essential role for Toll-like receptor (TLR)7- and TLR9-mediated interferon-{alpha} induction.

Toll-like receptors (TLRs) recognize microbial pathogens and trigger innate immune responses. Among TLR family members, TLR7, TLR8, and TLR9 induce interferon (IFN)-alpha in plasmacytoid dendritic cells (pDCs). This induction requires the formation of a complex consisting of the adaptor MyD88, tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and IFN regulatory factor (IRF) 7. Here we show an essential role of IL-1 receptor-associated kinase (IRAK)-1 in TLR7- and TLR9-mediated IRF7 signaling pathway. IRAK-1 directly bound and phosphorylated IRF7 in vitro. The kinase activity of IRAK-1 was necessary for transcriptional activation of IRF7. TLR7- and TLR9-mediated IFN-alpha production was abolished in Irak-1-deficient mice, whereas inflammatory cytokine production was not impaired. Despite normal activation of NF-kappaB and mitogen-activated protein kinases, IRF7 was not activated by a TLR9 ligand in Irak-1-deficient pDCs. These results indicated that IRAK-1 is a specific regulator for TLR7- and TLR9-mediated IFN-alpha induction in pDCs.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Regulation of lipopolysaccharide-inducible genes by MyD88 and Toll/IL-1 domain containing adaptor inducing IFN-beta.

Macrophages recognize lipopolysaccharide (LPS) by Toll-like receptor 4 and activate inflammatory responses by inducing expression of various genes. TLR4 activates intracellular signaling pathways via TIR domain containing adaptor molecules, MyD88, and Toll/IL-1 domain containing adaptor inducing IFN-beta (TRIF). Although macrophages lacking MyD88 or TRIF showed impaired cytokine production, activation of intracellular signaling molecules still occurred in response to LPS in these cells. In the present study, we implemented cDNA microarrays to investigate the contribution of MyD88 and TRIF in gene expression induced by LPS stimulation. Whereas wild-type macrophages induced 148 genes in response to LPS, macrophages lacking both MyD88 and TRIF did not upregulate any genes in response to LPS. Surprisingly, 80 LPS-inducible genes were redundantly regulated by either MyD88 or TRIF. In contrast, proinflammatory cytokines and chemokines were critically regulated by MyD88 or TRIF alone. Genes critically regulated by MyD88 alone tend to be induced quickly after LPS stimulation and regulated by mRNA stability as well as transcription. Genes known to be induced by type I interferons were simply dependent on TRIF for their expression. Taken together, MyD88 and TRIF play both redundant and distinct roles in LPS-induced gene expression.

Adaptor Proteins, Signal Transducing↗
PubMed2005

PI3K integrates the action of insulin and leptin on hypothalamic neurons.

Central control of energy balance depends on the ability of proopiomelanocortin (POMC) or agouti-related protein (Agrp) hypothalamic neurons to sense and respond to changes in peripheral energy stores. Leptin and insulin have been implicated as circulating indicators of adiposity, but it is not clear how changes in their levels are perceived or integrated by individual neuronal subtypes. We developed mice in which a fluorescent reporter for PI3K activity is targeted to either Agrp or POMC neurons and used 2-photon microscopy to measure dynamic regulation of PI3K by insulin and leptin in brain slices. We show that leptin and insulin act in parallel to stimulate PI3K in POMC neurons but in opposite ways on Agrp neurons. These results suggest a new view of hypothalamic circuitry, in which the effects of leptin and insulin are integrated by anorexigenic but not by orexigenic neurons.

Agouti-Related Protein↗
PubMed2005

Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7.

Short interfering RNA (siRNA) is used in RNA interference technology to avoid non-target-related induction of type I interferon (IFN) typical for long double-stranded RNA. Here we show that in plasmacytoid dendritic cells (PDC), an immune cell subset specialized in the detection of viral nucleic acids and production of type I IFN, some siRNA sequences, independent of their GU content, are potent stimuli of IFN-alpha production. Localization of the immunostimulatory motif on the sense strand of a potent IFN-alpha-inducing siRNA allowed dissection of immunostimulation and target silencing. Injection into mice of immunostimulatory siRNA, when complexed with cationic liposomes, induced systemic immune responses in the same range as the TLR9 ligand CpG, including IFN-alpha in serum and activation of T cells and dendritic cells in spleen. Immunostimulation by siRNA was absent in TLR7-deficient mice. Thus sequence-specific TLR7-dependent immune recognition in PDC needs to be considered as an additional biological activity of siRNA, which then should be termed immunostimulatory RNA (isRNA).

Animals↗
PubMed2005

CpG RNA: identification of novel single-stranded RNA that stimulates human CD14+CD11c+ monocytes.

Synthetic immunostimulatory nucleic acids such as CpG DNA are being harnessed therapeutically as vaccine adjuvants, anticancer or antiallergic agents. Efforts to identify nucleic acid-based agents capable of more specifically modulating the immune system are being developed. The current study identifies a novel class of single-stranded oligoribonucleotides (ORN) containing unmethylated CpG motifs and a poly(G) run at the 3' end (CpG ORN) that directly stimulate human CD14+CD11c+ monocytes but not dendritic cells or B cells. CpG ORN activate NF-kappaB and p38 MAPK, resulting in IL-6 and IL-12 production and costimulatory molecule up-regulation but not IFNalpha. Methylation of cytosine at the 5' portion in core CpG motif abrogates such activation. TLR3, 7, 8, or 9 alone did not confer response to CpG ORN, in contrast to previously reported respective nucleic acid ligands. These data suggest that CpG ORN represent a novel class of synthetic immunostimulatory nucleic acids with distinct target cells, receptors, and functions from that of previously known immunomodulatory nucleic acids.

3' Untranslated Regions↗
PubMed2005

A novel caspase-1/toll-like receptor 4-independent pathway of cell death induced by cytosolic Shigella in infected macrophages.

Shigella-induced macrophage cell death is an important step in the induction of acute inflammatory responses that ultimately lead to bacillary dysentery. Cell death was previously reported to be dependent upon the activation of caspase-1 via interaction with IpaB secreted by intracellular Shigella, but in this study, we show that Shigella infection of macrophages can also induce cell death independent of caspase-1 or IpaB activity. Time-lapse imaging and electron microscopic analyses indicated that caspase-1-dependent and -independent cell death is morphologically indistinguishable and that both resemble necrosis. Analyses of Shigella mutants or Escherichia coli using co-infection with Listeria suggested that a component common to Gram-negative bacteria is involved in inducing caspase-1-independent cell death. Further studies revealed that translocation of bacterial lipid A into the cytosol of macrophages potentially mediates cell death. Notably, cell death induced by cytosolic bacteria was TLR4-independent. These results identify a novel cell death pathway induced by intracellular Gram-negative bacteria that may play a role in microbial-host interactions and inflammatory responses.

Animals↗
PubMed2005

A20 is a negative regulator of IFN regulatory factor 3 signaling.

IFN regulatory factor 3 (IRF-3) is a critical transcription factor that regulates an establishment of innate immune status following detection of viral pathogens. Recent studies have revealed that two IkappaB kinase (IKK)-like kinases, NF-kappaB-activating kinase/Traf family member-associated NF-kappaB activator-binding kinase 1 and IKK-i/IKKepsilon, are responsible for activation of IRF-3, but the regulatory mechanism of the IRF-3 signaling pathway has not been fully understood. In this study, we report that IRF-3 activation is suppressed by A20, which was initially identified as an inhibitor of apoptosis and inducibly expressed by dsRNA. A20 physically interacts with NF-kappaB-activating kinase/Traf family member-associated NF-kappaB activator-binding kinase 1 and IKK-i/IKKepsilon, and inhibits dimerization of IRF-3 following engagement of TLR3 by dsRNA or Newcastle disease virus infection, leading to suppression of the IFN stimulation response element- and IFN-beta promoter-dependent transcription. Importantly, knocking down of A20 expression by RNA interference results in enhanced IRF-3-dependent transcription triggered by the stimulation of TLR3 or virus infection. Our study thus demonstrates that A20 is a candidate negative regulator of the signaling cascade to IRF-3 activation in the innate antiviral response.

Cell Line↗
PubMed2005

The Salmonella pathogenicity island (SPI)-2 and SPI-1 type III secretion systems allow Salmonella serovar typhimurium to trigger colitis via MyD88-dependent and MyD88-independent mechanisms.

Salmonella typhimurium can colonize the gut, invade intestinal tissues, and cause enterocolitis. In vitro studies suggest different mechanisms leading to mucosal inflammation, including 1) direct modulation of proinflammatory signaling by bacterial type III effector proteins and 2) disruption or penetration of the intestinal epithelium so that penetrating bacteria or bacterial products can trigger innate immunity (i.e., TLR signaling). We studied these mechanisms in vivo using streptomycin-pretreated wild-type and knockout mice including MyD88(-/-) animals lacking an adaptor molecule required for signaling via most TLRs. The Salmonella SPI-1 and the SPI-2 type III secretion systems (TTSS) contributed to inflammation. Mutants that retain only a functional SPI-1 (M556; sseD::aphT) or a SPI-2 TTSS (SB161; DeltainvG) caused attenuated colitis, which reflected distinct aspects of the colitis caused by wild-type S. typhimurium: M556 caused diffuse cecal inflammation that did not require MyD88 signaling. In contrast, SB161 induced focal mucosal inflammation requiring MyD88. M556 but not SB161 was found in intestinal epithelial cells. In the lamina propria, M556 and SB161 appeared to reside in different leukocyte cell populations as indicated by differential CD11c staining. Only the SPI-2-dependent inflammatory pathway required aroA-dependent intracellular growth. Thus, S. typhimurium can use two independent mechanisms to elicit colitis in vivo: SPI-1-dependent and MyD88-independent signaling to epithelial cells and SPI-2-dependent intracellular proliferation in the lamina propria triggering MyD88-dependent innate immune responses.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed2005

Toll-like receptor engagement converts T-cell autoreactivity into overt autoimmune disease.

Autoimmune diabetes mellitus in humans is characterized by immunological destruction of pancreatic beta islet cells. We investigated the circumstances under which CD8(+) T cells specific for pancreatic beta-islet antigens induce disease in mice expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) as a transgene under the control of the rat insulin promoter. In contrast to infection with LCMV, immunization with LCMV-GP derived peptide did not induce autoimmune diabetes despite large numbers of autoreactive cytotoxic T cells. Only subsequent treatment with Toll-like receptor ligands elicited overt autoimmune disease. This difference was critically regulated by the peripheral target organ itself, which upregulated class I major histocompatibility complex (MHC) in response to systemic Toll-like receptor-triggered interferon-alpha production. These data identify the 'inflammatory status' of the target organ as a separate and limiting factor determining the development of autoimmune disease.

Animals↗
PubMed2005

Toll-like receptor 9 mediates innate immune activation by the malaria pigment hemozoin.

Malaria parasites within red blood cells digest host hemoglobin into a hydrophobic heme polymer, known as hemozoin (HZ), which is subsequently released into the blood stream and then captured by and concentrated in the reticulo-endothelial system. Accumulating evidence suggests that HZ is immunologically active, but the molecular mechanism(s) through which HZ modulates the innate immune system has not been elucidated. This work demonstrates that HZ purified from Plasmodium falciparum is a novel non-DNA ligand for Toll-like receptor (TLR)9. HZ activated innate immune responses in vivo and in vitro, resulting in the production of cytokines, chemokines, and up-regulation of costimulatory molecules. Such responses were severely impaired in TLR9-/- and myeloid differentiation factor 88 (MyD88)-/-, but not in TLR2, TLR4, TLR7, or Toll/interleukin 1 receptor domain-containing adaptor-inducing interferon beta-/- mice. Synthetic HZ, which is free of the other contaminants, also activated innate immune responses in vivo in a TLR9-dependent manner. Chloroquine (CQ), an antimalarial drug, abrogated HZ-induced cytokine production. These data suggest that TLR9-mediated, MyD88-dependent, and CQ-sensitive innate immune activation by HZ may play an important role in malaria parasite-host interactions.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Toll-like receptor 6-independent signaling by diacylated lipopeptides.

Bacterial lipopeptides are strong immune modulators that activate early host responses after infection as well as initiating adjuvant effects on the adaptive immune system. These lipopeptides induce signaling in cells of the immune system through Toll-like receptor 2 (TLR2)-TLR1 or TLR2-TLR6 heteromers. So far it has been thought that triacylated lipopeptides, such as the synthetic N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteine (Pam3)-CSK4, signal through TLR2-TLR1 heteromers, whereas diacylated lipopeptides, like the macrophage-activating lipopeptide from Mycoplasma fermentans (MALP2) or S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteine (Pam2)-CGNNDESNISFKEK, induce signaling through TLR2-TLR6 heteromers. Using new synthetic lipopeptide derivatives we addressed the contribution of the lipid and, in particular, the peptide moieties with respect to TLR2 heteromer usage. In contrast to the current model of receptor usage, not only triacylated lipopeptides, but also diacylated lipopeptides like Pam2CSK4 and the elongated MALP2 analog Pam2CGNNDESNISFKEK-SK4 (MALP2-SK4) induced B lymphocyte proliferation and TNF-alpha secretion in macrophages in a TLR6-independent manner as determined with cells from TLR6-deficient mice. Our results indicate that both the lipid and the N-terminal peptides of lipoproteins contribute to the specificity of recognition by TLR2 heteromers and are responsible for the ligand-receptor interaction on host cells.

Amino Acid Sequence↗
PubMed2005

CpG-activated Thy1.2+ dendritic cells protect against lethal Listeria monocytogenes infection.

Synthetic oligodeoxynucleotides containing CpG motifs (CpG ODN) activate the innate immune system by interacting with Toll-like receptor 9. The resultant immune response increases host resistance to infection by a variety of pathogenic microorganisms, including Listeria monocytogenes. There is a considerable interest in harnessing the immunoprotective properties of CpG ODN, yet little is known of the cell phenotype(s) responsible for mediating this protection. This work demonstrates that treatment of mice with CpG ODN increases the number of Thy1.2+, CD11c+ dendritic cells (Thy1.2+ DC) in the spleen, which are both necessary and sufficient for transferring resistance to infection from CpG-treated donors to naive recipients. These CpG-activated Thy1.2+ DC are distinct from conventional (CD11c(hi), Thy1.2-) or plasmacytoid DC (mPDCA+), and secrete IFN-gamma that contributes to protection. These findings suggest that a novel Thy1.2+ DC subset plays a critical role in mediating the immunoprotective activity of CpG DNA.

Adoptive Transfer↗
PubMed2005

TRAF4 acts as a silencer in TLR-mediated signaling through the association with TRAF6 and TRIF.

Toll-like receptors (TLR) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase play an essential role in intracellular eradication of engulfed pathogens. Here, we demonstrate the physical and functional association between components of the cytosolic NADPH oxidase and TLR-mediated signaling molecules. Cytosolic components of NADPH oxidase suppressed TLR-mediated NF-kappaB activation as well as IFN-beta promoter activation. We demonstrate that TNF-associated factor (TRAF) 4 associates with p47(phox), a component of cytosolic NADPH oxidase, and physically interacts and functionally counteracts with TRAF6 and Toll-IL-1 receptor (TIR) domain-containing adaptor-inducing IFN-beta (TRIF) molecules that critically regulate TLR-mediated signaling. TRAF4 mRNA expression was elicited in RPMI 8226 cells following LPS or CpG DNA treatment. These results suggest that TRAF4 participates in the molecular mechanism underlying silencing of TLR-mediated signaling through the interaction with molecules harboring phagosome/endosome membrane.

Adaptor Proteins, Vesicular Transport↗