Showing papers by "Shizuo Akira published in 2010"
TL;DR: Recent advances that have been made by research into the role of TLR biology in host defense and disease are described.
Abstract: The discovery of Toll-like receptors (TLRs) as components that recognize conserved structures in pathogens has greatly advanced understanding of how the body senses pathogen invasion, triggers innate immune responses and primes antigen-specific adaptive immunity. Although TLRs are critical for host defense, it has become apparent that loss of negative regulation of TLR signaling, as well as recognition of self molecules by TLRs, are strongly associated with the pathogenesis of inflammatory and autoimmune diseases. Furthermore, it is now clear that the interaction between TLRs and recently identified cytosolic innate immune sensors is crucial for mounting effective immune responses. Here we describe the recent advances that have been made by research into the role of TLR biology in host defense and disease.
7,494 citations
TL;DR: The role of PRRs, their signaling pathways, and how they control inflammatory responses are discussed.
6,987 citations
TL;DR: Results show that Jmjd3-mediated H3K27 demethylation is crucial for regulating M2 macrophage development leading to anti-helminth host responses.
Abstract: Polarization of macrophages to M1 or M2 cells is important for mounting responses against bacterial and helminth infections, respectively. Jumonji domain containing-3 (Jmjd3), a histone 3 Lys27 (H3K27) demethylase, has been implicated in the activation of macrophages. Here we show that Jmjd3 is essential for M2 macrophage polarization in response to helminth infection and chitin, though Jmjd3 is dispensable for M1 responses. Furthermore, Jmjd3 (also known as Kdm6b) is essential for proper bone marrow macrophage differentiation, and this function depends on demethylase activity of Jmjd3. Jmjd3 deficiency affected trimethylation of H3K27 in only a limited number of genes. Among them, we identified Irf4 as encoding a key transcription factor that controls M2 macrophage polarization. Collectively, these results show that Jmjd3-mediated H3K27 demethylation is crucial for regulating M2 macrophage development leading to anti-helminth host responses.
994 citations
TL;DR: It is shown that Toll-like receptor 4 (TLR4), a pivotal receptor for activation of innate immunity and cytokine release, is required for HMGB1-dependent activation of macrophage TNF release.
Abstract: During infection, vertebrates develop “sickness syndrome,” characterized by fever, anorexia, behavioral withdrawal, acute-phase protein responses, and inflammation. These pathophysiological responses are mediated by cytokines, including TNF and IL-1, released during the innate immune response to invasion. Even in the absence of infection, qualitatively similar physiological syndromes occur following sterile injury, ischemia reperfusion, crush injury, and autoimmune-mediated tissue damage. Recent advances implicate high-mobility group box 1 (HMGB1), a nuclear protein with inflammatory cytokine activities, in stimulating cytokine release. HMGB1 is passively released during cell injury and necrosis, or actively secreted during immune cell activation, positioning it at the intersection of sterile and infection-associated inflammation. To date, eight candidate receptors have been implicated in mediating the biological responses to HMGB1, but the mechanism of HMGB1-dependent cytokine release is unknown. Here we show that Toll-like receptor 4 (TLR4), a pivotal receptor for activation of innate immunity and cytokine release, is required for HMGB1-dependent activation of macrophage TNF release. Surface plasmon resonance studies indicate that HMGB1 binds specifically to TLR4, and that this binding requires a cysteine in position 106. A wholly synthetic 20-mer peptide containing cysteine 106 from within the cytokine-stimulating B box mediates TLR4-dependent activation of macrophage TNF release. Inhibition of TLR4 binding with neutralizing anti-HMGB1 mAb or by mutating cysteine 106 prevents HMGB1 activation of cytokine release. These results have implications for rationale, design, and development of experimental therapeutics for use in sterile and infectious inflammation.
727 citations
TL;DR: This study suggests that Dectin-2 is important in host defense against C. albicans by inducing Th17 cell differentiation and generates Clec4n(-/-) mice that had virtually no fungal alpha-mannan-induced cytokine production.
652 citations
TL;DR: The present data suggest that LGP2 facilitates viral RNA recognition by RIG-I and MDA5 through its ATPase domain.
Abstract: RNA virus infection is recognized by retinoic acid-inducible gene (RIG)-I-like receptors (RLRs), RIG-I, and melanoma differentiation-associated gene 5 (MDA5) in the cytoplasm RLRs are comprised of N-terminal caspase-recruitment domains (CARDs) and a DExD/H-box helicase domain The third member of the RLR family, LGP2, lacks any CARDs and was originally identified as a negative regulator of RLR signaling In the present study, we generated mice lacking LGP2 and found that LGP2 was required for RIG-I- and MDA5-mediated antiviral responses In particular, LGP2 was essential for type I IFN production in response to picornaviridae infection Overexpression of the CARDs from RIG-I and MDA5 in Lgp2(-/-) fibroblasts activated the IFN-beta promoter, suggesting that LGP2 acts upstream of RIG-I and MDA5 We further examined the role of the LGP2 helicase domain by generating mice harboring a point mutation of Lys-30 to Ala (Lgp2 (K30A/K30A)) that abrogated the LGP2 ATPase activity Lgp2 (K30A/K30A) dendritic cells showed impaired IFN-beta productions in response to various RNA viruses to extents similar to those of Lgp2(-/-) cells Lgp2(-/-) and Lgp2 (K30A/K30A) mice were highly susceptible to encephalomyocarditis virus infection Nevertheless, LGP2 and its ATPase activity were dispensable for the responses to synthetic RNA ligands for MDA5 and RIG-I Taken together, the present data suggest that LGP2 facilitates viral RNA recognition by RIG-I and MDA5 through its ATPase domain
600 citations
TL;DR: High-resolution mass spectrometry-based proteomics is used, combined with label-free quantitation algorithms, to determine the proteome of mouse splenic conventional and plasmacytoid DC subsets to a depth of 5,780 and 6,664 proteins, and found mutually exclusive expression of pattern recognition pathways not previously known to be different among conventional DC subset.
548 citations
TL;DR: The results identify the CARD9–Bcl-10 module as an essential component of the RIG-I-dependent proinflammatory response and establish Rig-I as a sensor able to activate the inflammasome in response to certain RNA viruses.
Abstract: Interleukin 1 beta (IL-1 beta) is a potent proinflammatory factor during viral infection. Its production is tightly controlled by transcription of Il1b dependent on the transcription factor NF-kappaB and subsequent processing of pro-IL-1 beta by an inflammasome. However, the sensors and mechanisms that facilitate RNA virus-induced production of IL-1 beta are not well defined. Here we report a dual role for the RNA helicase RIG-I in RNA virus-induced proinflammatory responses. Whereas RIG-I-mediated activation of NF-kappaB required the signaling adaptor MAVS and a complex of the adaptors CARD9 and Bcl-10, RIG-I also bound to the adaptor ASC to trigger caspase-1-dependent inflammasome activation by a mechanism independent of MAVS, CARD9 and the Nod-like receptor protein NLRP3. Our results identify the CARD9-Bcl-10 module as an essential component of the RIG-I-dependent proinflammatory response and establish RIG-I as a sensor able to activate the inflammasome in response to certain RNA viruses.
465 citations
TL;DR: Generation of PI3P in the normallyPI3P-deficient ER membrane makes the organelle a platform for autophagosome formation.
Abstract: Autophagy is a catabolic process that allows cells to digest their cytoplasmic constituents via autophagosome formation and lysosomal degradation. Recently, an autophagy-specific phosphatidylinositol 3-kinase (PI3-kinase) complex, consisting of hVps34, hVps15, Beclin-1, and Atg14L, has been identified in mammalian cells. Atg14L is specific to this autophagy complex and localizes to the endoplasmic reticulum (ER). Knockdown of Atg14L leads to the disappearance of the DFCP1-positive omegasome, which is a membranous structure closely associated with both the autophagosome and the ER. A point mutation in Atg14L resulting in defective ER localization was also defective in the induction of autophagy. The addition of the ER-targeting motif of DFCP1 to this mutant fully complemented the autophagic defect in Atg14L knockout embryonic stem cells. Thus, Atg14L recruits a subset of class III PI3-kinase to the ER, where otherwise phosphatidylinositol 3-phosphate (PI3P) is essentially absent. The Atg14L-dependent appearance of PI3P in the ER makes this organelle the platform for autophagosome formation.
413 citations
01 Jan 2010
TL;DR: The role of TLR biology in host defense and disease has been discussed in this article, where it has been shown that TLR signaling is associated with the pathogenesis of inflammatory and autoimmune diseases and that the interaction between TLRs and recently identified cytosolic innate immune sensors is crucial for mounting effective immune responses.
Abstract: The discovery of Toll-like receptors (TLRs) as components that recognize conserved structures in pathogens has greatly advanced understanding of how the body senses pathogen invasion, triggers innate immune responses and primes antigen-specific adaptive immunity. Although TLRs are critical for host defense, it has become apparent that loss of negative regulation of TLR signaling, as well as recognition of self molecules by TLRs, are strongly associated with the pathogenesis of inflammatory and autoimmune diseases. Furthermore, it is now clear that the interaction between TLRs and recently identified cytosolic innate immune sensors is crucial for mounting effective immune responses. Here we describe the recent advances that have been made by research into the role of TLR biology in host defense and disease.
402 citations
TL;DR: Results indicate that TRIM56 is an interferon-inducible E3 ubiquitin ligase that modulates STING to confer double-stranded DNA-mediated innate immune responses.
TL;DR: Hepatocyte-specific deletion of TAK1 in mice resulted in spontaneous hepatocyte death, inflammation, fibrosis, and carcinogenesis that was partially mediated by TNFR signaling, indicating that Tak1 is an essential component for cellular homeostasis in the liver.
Abstract: TGF-β–activated kinase 1 (TAK1) is a MAP3K family member that activates NF-κB and JNK via Toll-like receptors and the receptors for IL-1, TNF-α, and TGF-β. Because the TAK1 downstream molecules NF-κB and JNK have opposite effects on cell death and carcinogenesis, the role of TAK1 in the liver is unpredictable. To address this issue, we generated hepatocyte-specific Tak1-deficient (Tak1ΔHEP) mice. The Tak1ΔHEP mice displayed spontaneous hepatocyte death, compensatory proliferation, inflammatory cell infiltration, and perisinusoidal fibrosis at age 1 month. Older Tak1ΔHEP mice developed multiple cancer nodules characterized by increased expression of fetal liver genes including α-fetoprotein. Cultures of primary hepatocytes deficient in Tak1 exhibited spontaneous cell death that was further increased in response to TNF-α. TNF-α increased caspase-3 activity but activated neither NF-κB nor JNK in Tak1-deficient hepatocytes. Genetic abrogation of TNF receptor type I (TNFRI) in Tak1ΔHEP mice reduced liver damage, inflammation, and fibrosis compared with unmodified Tak1ΔHEP mice. In conclusion, hepatocyte-specific deletion of TAK1 in mice resulted in spontaneous hepatocyte death, inflammation, fibrosis, and carcinogenesis that was partially mediated by TNFR signaling, indicating that TAK1 is an essential component for cellular homeostasis in the liver.
TL;DR: Evidence is provided for the transcriptional mechanisms underlying TH17 development and points to a molecular basis for a novel therapeutic strategy against autoimmune disease.
Abstract: Interleukin (IL)-17-producing helper T (T(H)17) cells are a distinct T-cell subset characterized by its pathological role in autoimmune diseases. IL-6 and transforming growth factor-beta (TGF-beta) induce T(H)17 development, in which the orphan nuclear receptors, RORgammat and RORalpha, have an indispensable role. However, in the absence of IL-6 and TGF-beta, the ectopic expression of RORgammat or RORalpha leads to only a modest IL-17 production. Here we identify a nuclear IkappaB family member, IkappaBzeta (encoded by the Nfkbiz gene), as a transcription factor required for T(H)17 development in mice. The ectopic expression of IkappaBzeta in naive CD4(+) T cells together with RORgammat or RORalpha potently induces T(H)17 development, even in the absence of IL-6 and TGF-beta. Notably, Nfkbiz(-/-) mice have a defect in T(H)17 development and a resistance to experimental autoimmune encephalomyelitis (EAE). The T-cell-intrinsic function of IkappaBzeta was clearly demonstrated by the resistance to EAE of the Rag2(-/-) mice into which Nfkbiz(-/-) CD4(+) T cells were transferred. In cooperation with RORgammat and RORalpha, IkappaBzeta enhances Il17a expression by binding directly to the regulatory region of the Il17a gene. This study provides evidence for the transcriptional mechanisms underlying T(H)17 development and points to a molecular basis for a novel therapeutic strategy against autoimmune disease.
TL;DR: The data suggest that TLR4 knockout, but not TLR3 or TLR9 knockout, may play a neuroprotective role in ischemic brain injury induced by MCAO in mice.
TL;DR: These studies reveal that autophagy-related proteins are involved in the innate immune response and may contribute to the development of inflammatory disorders.
Abstract: Pattern recognition receptors detect microbial components and induce innate immune responses, the first line of host defense against infectious agents. However, aberrant activation of immune responses often causes massive inflammation, leading to the development of autoimmune diseases. Therefore, both activation and inactivation of innate immune responses must be strictly controlled. Recent studies have shown that the cellular machinery associated with protein degradation, such as autophagy, is important for the regulation of innate immunity. These studies reveal that autophagy-related proteins are involved in the innate immune response and may contribute to the development of inflammatory disorders.
TL;DR: Conditional ablation of TAK1 in liver parenchymal cells causes hepatocyte dysplasia and early-onset hepatocarcinogenesis, coinciding with biliary ductopenia and cholestasis and serves as a gatekeeper for a protumorigenic, NF-kappaB-independent function of NEMO in parenChymal liver cells.
TL;DR: The most recent discoveries about PRRs and their ligands are reviewed, their roles in intracellular and in vivo regulation of immune responses, and the systems biology of innate immunity are reviewed.
Abstract: Since the identification of Toll-like receptors, our knowledge about pattern-recognition receptors (PRRs) has increased rapidly. Classes of PRRs that have been recently discovered include RIG-I–like receptors, Nod-like receptors, and C-type lectin receptors. Recent studies have started to clarify the molecular basis of PRR-ligand interactions, yet the numbers of PRRs and their ligands continue to increase. New technologies have elucidated the network regulation of immune responses at the cellular and in vivo levels. We review the most recent discoveries about PRRs and their ligands, their roles in intracellular and in vivo regulation of immune responses, and the systems biology of innate immunity.
TL;DR: Assessing the effect of the TLR9 and/or TLR7 deletion on the production of various autoantibodies and the development of lupus nephritis in C57BL/6 mice congenic for the Nba2 (NZB autoimmunity 2) locus indicatesTLR7 has a pivotal role in a wide variety of autoimmune responses against DNA- and RNA-containing nuclear antigens, retroviral gp70 and glomerular matrix antig
TL;DR: HZ can influence adaptive immune responses to malaria infection and may have therapeutic value in vaccine adjuvant development, according to its method of synthesis and particle size.
TL;DR: It is concluded that TRIM23-mediated ubiquitin conjugation to NEMO is essential for TLR3- and RIG-I/MDA5-mediated antiviral innate and inflammatory responses.
Abstract: The rapid induction of type I IFN is a central event of the innate defense against viral infections and is tightly regulated by a number of cellular molecules. Viral components induce strong type I IFN responses through the activation of toll-like receptors (TLRs) and intracellular cytoplasmic receptors such as an RNA helicase RIG-I and/or MDA5. According to recent studies, the NF-κB essential modulator (NEMO, also called IKKγ) is crucial for this virus-induced antiviral response. However, the precise roles of signal activation by NEMO adaptor have not been elucidated. Here, we show that virus-induced IRF3 and NF-κB activation depends on the K(lys)-27-linked polyubiquitination to NEMO by the novel ubiquitin E3 ligase triparite motif protein 23 (TRIM23). Virus-induced IRF3 and NF-κB activation, as well as K27-linked NEMO polyubiquitination, were abrogated in TRIM23 knockdown cells, whereas TRIM23 knockdown had no effect on TNFα-mediated NF-κB activation. Furthermore, in NEMO-deficient mouse embryo fibroblast cells, IFN-stimulated response element-driven reporter activity was restored by ectopic expression of WT NEMO, as expected, but only partial recovery by NEMO K165/309/325/326/344R multipoints mutant on which TRIM23-mediated ubiquitin conjugation was substantially reduced. Thus, we conclude that TRIM23-mediated ubiquitin conjugation to NEMO is essential for TLR3- and RIG-I/MDA5-mediated antiviral innate and inflammatory responses.
TL;DR: It is shown that PKR is required for production of IFN-alpha/beta proteins in response to a subset of RNA viruses including encephalomyocarditis, Theiler's murineEncephalomyelitis, and Semliki Forest virus, but not influenza or Sendai virus.
TL;DR: Functional evidence is provided for what is believed to be a novel gene regulating hepatic lipogenesis and VLDL production in mice that influences plasma lipids and risk for myocardial infarction in humans.
Abstract: Recent genome-wide association studies have identified a genetic locus at human chromosome 8q24 as having minor alleles associated with lower levels of plasma triglyceride (TG) and LDL cholesterol (LDL-C), higher levels of HDL-C, as well as decreased risk for myocardial infarction. This locus contains only one annotated gene, tribbles homolog 1 (TRIB1), which has not previously been implicated in lipoprotein metabolism. Here we demonstrate a role for Trib1 as a regulator of lipoprotein metabolism in mice. Hepatic-specific overexpression of Trib1 reduced levels of plasma TG and cholesterol by reducing VLDL production; conversely, Trib1-knockout mice showed elevated levels of plasma TG and cholesterol due to increased VLDL production. Hepatic Trib1 expression was inversely associated with the expression of key lipogenic genes and measures of lipogenesis. Thus, we provide functional evidence for what we believe to be a novel gene regulating hepatic lipogenesis and VLDL production in mice that influences plasma lipids and risk for myocardial infarction in humans.
TL;DR: These observations demonstrate that systemic administration of TLR ligands can suppress both allergic and autoimmune responses, providing a plausible explanation for the hygiene hypothesis and opening new therapeutic perspectives for the prevention of these pathologies.
Abstract: Background
Infections may be associated with exacerbation of allergic and autoimmune diseases. Paradoxically, epidemiological and experimental data have shown that some microorganisms can also prevent these pathologies. This observation is at the origin of the hygiene hypothesis according to which the decline of infections in western countries is at the origin of the increased incidence of both Th1-mediated autoimmune diseases and Th2-mediated allergic diseases over the last decades. We have tested whether Toll-like receptor (TLR) stimulation can recapitulate the protective effect of infectious agents on allergy and autoimmunity.
TL;DR: The results identify the NLRP3 inflammasome as a sensor of Vibrio infections through the action of bacterial cytotoxins and differential activation of innate signaling pathways acting upstream of NF-κB.
Abstract: Vibrio vulnificus and Vibrio cholerae are Gram-negative pathogens that cause serious infectious disease in humans. The beta form of pro-IL-1 is thought to be involved in inflammatory responses and disease development during infection with these pathogens, but the mechanism of beta form of pro-IL-1 production remains poorly defined. In this study, we demonstrate that infection of mouse macrophages with two pathogenic Vibrio triggers the activation of caspase-1 via the NLRP3 inflammasome. Activation of the NLRP3 inflammasome was mediated by hemolysins and multifunctional repeat-in-toxins produced by the pathogenic bacteria. NLRP3 activation in response to V. vulnificus infection required NF-kappaB activation, which was mediated via TLR signaling. V. cholerae-induced NLRP3 activation also required NF-kappaB activation but was independent of TLR stimulation. Studies with purified V. cholerae hemolysin revealed that toxin-stimulated NLRP3 activation was induced by TLR and nucleotide-binding oligomerization domain 1/2 ligand-mediated NF-kappaB activation. Our results identify the NLRP3 inflammasome as a sensor of Vibrio infections through the action of bacterial cytotoxins and differential activation of innate signaling pathways acting upstream of NF-kappaB.
TL;DR: It is shown that plasmacytoid dendritic cells (pDCs) and type I interferon (IFN)–mediated signaling delineate the immunogenicity of live attenuated virus, inactivated whole-virus (WV), and split-Virus vaccines.
Abstract: A variety of different vaccine types are available for H1N1 influenza A virus infections; however, their immunological mechanisms of action remain unclear. Here, we show that plasmacytoid dendritic cells (pDCs) and type I interferon (IFN)-mediated signaling delineate the immunogenicity of live attenuated virus, inactivated whole-virus (WV), and split-virus vaccines. Although Toll-like receptor 7 acted as the adjuvant receptor for the immunogenicity of both live virus and WV vaccines, the requirement for type I IFN production by pDCs for the immunogenicity of the vaccines was restricted to WV. A split vaccine commonly used in humans failed to immunize naive mice, but a pDC-activating adjuvant could restore immunogenicity. In blood from human adults, however, split vaccine alone could recall memory T cell responses, underscoring the importance of this adjuvant pathway for primary, but not secondary, vaccination.
TL;DR: It is demonstrated that the viral polymerase plays an important role for regulating host anti-viral response through the binding to IPS-1 and inhibition of IFNβ production.
TL;DR: In vivo in vivo HSPC responses to bacterial infection are complex and not absolutely dependent upon key inflammatory signaling pathways, as shown in this study.
Abstract: Bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) can be activated by type I IFNs, TLR agonists, viruses, and bacteria to increase hematopoiesis. In this study, we report that endotoxin treatment in vivo induces TLR4, MyD88, and Toll/IL-1 resistance domain-containing adaptor-inducing IFN-β (TRIF)-dependent expansion of BM HSPCs. Bacterial infection by Staphylococcus aureus or cecal ligation and puncture also induces HSPC expansion, but MyD88, TRIF, type I IFN, cytokine, PG, or oxidative stress pathways are not required for their expansion. S. aureus-induced HSPC expansion in MyD88−/−TRIF−/− mice is also normal, but is associated with BM remodeling as granulocyte stores are released peripherally. Importantly, reduction in BM cellularity alone can reproduce HSPC expansion. These data show in vivo HSPC responses to bacterial infection are complex and not absolutely dependent upon key inflammatory signaling pathways.
TL;DR: This study identifies sufficient IFN-alpha production by PDC as an important determinant of vaccine efficacy and investigates differences in innate immune activation and adjuvant activity between the imidazoquinoline R848 and the ssRNA TLR7 agonist polyUs21.
TL;DR: The present finding of an unexpected role for MyD88 in preventing diabetes may provide a potential novel target/strategy for treating metabolic syndrome.
Abstract: Background: Multiple lines of evidence suggest innate immune response pathways to be involved in the development of obesity-associated diabetes although the molecular mechanism underling the disease is unknown. Recent observations suggest that saturated fatty acids can act as a ligand for toll-like receptor (TLR) 4, which is thought to mediate obesityassociated insulin resistance. Myeloid differentiation factor 88 (MyD88) is an adapter protein for TLR/IL-1 receptor signaling, which is involved in the activation of inflammatory pathways. To evaluate molecular mechanisms linking obesity-associated diabetes down-stream of TLR4, we investigated physiological role of MyD88 in high-fat diet (HFD)-induced obesity. Methodology/Principal Findings: In the present study, we found MyD88-deficient mice fed a HFD had increased circulating levels of insulin, leptin and cholesterol, as well as liver dysfunction (increased induction of ALT levels, increased activation of JNK andcleavageof PARP),which werelinkedto the onset ofseverediabetes. Onthe other hand,TNF-awouldnotbe involved in HFD-induced diabetes in MyD88-deficient mice, because TNF-a level was attenuated in MyD88-deficient mice fed with HFD. Conclusions/Significance: The present finding of an unexpected role for MyD88 in preventing diabetes may provide a potential novel target/strategy for treating metabolic syndrome.
TL;DR: hLF induces moderate activation of TLR4‐mediated innate immunity through its carbohydrate chains; however, hLF suppresses endotoxemia by interfering with lipopolysaccharide‐dependentTLR4 activation, probably through its polypeptide moiety.
Abstract: Lactoferrin (LF) has been implicated in innate immunity. Here we reveal the signal transduction pathway responsible for human LF (hLF)-triggered nuclear factor-kappaB (NF-kappaB) activation. Endotoxin-depleted hLF induces NF-kappaB activation at physiologically relevant concentrations in the human monocytic leukemia cell line, THP-1, and in mouse embryonic fibroblasts (MEFs). In MEFs, in which both tumor necrosis factor receptor-associated factor 2 (TRAF2) and TRAF5 are deficient, hLF causes NF-kappaB activation at a level comparable to that seen in wild-type MEFs, whereas TRAF6-deficient MEFs show significantly impaired NF-kappaB activation in response to hLF. TRAF6 is known to be indispensable in leading to NF-kappaB activation in myeloid differentiating factor 88 (MyD88)-dependent signaling pathways, while the role of TRAF6 in the MyD88-independent signaling pathway has not been clarified extensively. When we examined the hLF-dependent NF-kappaB activation in MyD88-deficient MEFs, delayed, but remarkable, NF-kappaB activation occurred as a result of the treatment of cells with hLF, indicating that both MyD88-dependent and MyD88-independent pathways are involved. Indeed, hLF fails to activate NF-kappaB in MEFs lacking Toll-like receptor 4 (TLR4), a unique TLR group member that triggers both MyD88-depependent and MyD88-independent signalings. Importantly, the carbohydrate chains from hLF are shown to be responsible for TLR4 activation. Furthermore, we show that lipopolysaccharide-induced cytokine and chemokine production is attenuated by intact hLF but not by the carbohydrate chains from hLF. Thus, we present a novel model concerning the biological function of hLF: hLF induces moderate activation of TLR4-mediated innate immunity through its carbohydrate chains; however, hLF suppresses endotoxemia by interfering with lipopolysaccharide-dependent TLR4 activation, probably through its polypeptide moiety.