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PubMed2002

Toll-like receptors 2 and 4 are up-regulated during intestinal inflammation.

BACKGROUND & AIMS: Bacterial wall products play an important role in the activation of immune and nonimmune cells of the intestinal mucosa. Toll-like receptors (TLRs) TLR2 and TLR4 have been identified as signaling receptors activated by bacterial wall components. METHODS: Expression of TLRs in human intestinal mucosa obtained by endoscopy and surgery was analyzed by immunohistochemistry. Intestinal macrophages were isolated by immunomagnetic beads armed with a CD33 antibody. Reverse-transcription polymerase chain reaction was performed for TLR1-5. Results were confirmed by Northern blot and flow cytometry. Interleukin-1beta messenger RNA (mRNA) was quantified by a polymerase chain reaction-enzyme-linked immunosorbent assay-kit. RESULTS: Immunohistochemistry revealed a significant increase in the TLR2 and TLR4 antigen expression on submucosal cells in inflamed intestinal mucosa compared with non-inflamed mucosa. TLR expression was localized in intestinal macrophages by double-labeling techniques. No TLR-polymerase chain reaction product could be obtained with mRNA from CD33-positive macrophages from normal mucosa. We observed an induction of mRNA for TLR2, TLR4, and TLR5 in inflammation-associated macrophages. TLR1 and TLR3 were only detectable in blood monocytes. Monocytes reacted to lipopolysaccharide stimulation with a 3-fold and in vitro differentiated macrophages with a 16-fold increase of cellular interleukin-1beta mRNA. Macrophages from normal mucosa did not respond to lipopolysaccharide showing the functional relevance of TLR expression. CONCLUSIONS: This study shows the inflammation-dependent induction of TLR2 and TLR4 expression in intestinal macrophages. The absence of TLRs abolishes the reactivity of mucosal macrophages to bacterial wall products. Presence of TLRs may thereby contribute to the inflammatory process.

Blood Cells↗
PubMed2003

Toll-like receptor 4 mediates inflammatory signaling by bacterial lipopolysaccharide in human hepatic stellate cells.

Bacterial lipopolysaccharide (LPS) stimulates Kupffer cells and participates in the pathogenesis of alcohol-induced liver injury. However, it is unknown whether LPS directly affects hepatic stellate cells (HSCs), the main fibrogenic cell type in the injured liver. This study characterizes LPS-induced signal transduction and proinflammatory gene expression in activated human HSCs. Culture-activated HSCs and HSCs isolated from patients with hepatitis C virus-induced cirrhosis express LPS-associated signaling molecules, including CD14, toll-like receptor (TLR) 4, and MD2. Stimulation of culture-activated HSCs with LPS results in a rapid and marked activation of NF-kappaB, as assessed by in vitro kinase assays for IkappaB kinase (IKK), IkappaBalpha steady-state levels, p65 nuclear translocation, NF-kappaB-dependent luciferase reporter gene assays, and electrophoretic mobility shift assays. Lipid A induces NF-kappaB activation in a similar manner. Both LPS- and lipid A-induced NF-kappaB activation is blocked by preincubation with either anti-TLR4 blocking antibody (HTA125) or Polymyxin B. Lipid A induces NF-kappaB activation in HSCs from TLR4-sufficient (C3H/OuJ) mice but not from TLR4-deficient (C3H/HeJ) mice. LPS also activates c-Jun N-terminal kinase (JNK), as assessed by in vitro kinase assays. LPS up-regulates IL-8 and MCP-1 gene expression and secretion. LPS-induced IL-8 secretion is completely inhibited by the IkappaB super repressor (Ad5IkappaB) and partially inhibited by a specific JNK inhibitor, SP600125. LPS also up-regulates cell surface expression of ICAM-1 and VCAM-1. In conclusion, human activated HSCs utilize components of TLR4 signal transduction cascade to stimulate NF-kappaB and JNK and up-regulate chemokines and adhesion molecules. Thus, HSCs are a potential mediator of LPS-induced liver injury.

Animals↗
PubMed2004

Toll-like receptor 2 and Toll-like receptor 4 expression in human adrenals.

Toll-like receptors (TLRs) are key elements in the innate immune response, functioning as pattern-recognition receptors for the detection and response to endotoxins and other microbial ligands. Inflammatory cytokines play an important role in the activation of the hypothalamic-pituitary-adrenal HPA axis during inflammation and sepsis. The newly recognized major role of TLR2 and TLR4 and the adrenal stress response during critical illnesses such as inflammation and sepsis demand comprehensive analysis of their interactions. Therefore, we analyzed TLR2 and TLR4 expression in human adrenal glands. Western blot analysis demonstrated the expression of TLR2 and TLR4 in the human adrenocortical cell line NCI-H295. Immunohistochemical analysis of normal human adrenal glands revealed TLR2 and TLR4 expression in the adrenal cortex, but not in the adrenal medulla. Considering the crucial role of the HPA axis and the innate immune response during acute sepsis or septic shock, elucidating the functional interaction of these systems should be of great clinical relevance.

Adrenal Cortex↗
PubMed2003

Activation of innate immunity in the CNS triggers neurodegeneration through a Toll-like receptor 4-dependent pathway.

Innate immunity is an evolutionarily ancient system that provides organisms with immediately available defense mechanisms through recognition of pathogen-associated molecular patterns. We show that in the CNS, specific activation of innate immunity through a Toll-like receptor 4 (TLR4)-dependent pathway leads to neurodegeneration. We identify microglia as the major lipopolysaccharide (LPS)-responsive cell in the CNS. TLR4 activation leads to extensive neuronal death in vitro that depends on the presence of microglia. LPS leads to dramatic neuronal loss in cultures prepared from wild-type mice but does not induce neuronal injury in CNS cultures derived from tlr4 mutant mice. In an in vivo model of neurodegeneration, stimulating the innate immune response with LPS converts a subthreshold hypoxic-ischemic insult from no discernable neuronal injury to severe axonal and neuronal loss. In contrast, animals bearing a loss-of-function mutation in the tlr4 gene are resistant to neuronal injury in the same model. The present study demonstrates a mechanistic link among innate immunity, TLRs, and neurodegeneration.

Animals↗
PubMed2001

Secreted MD-2 is a large polymeric protein that efficiently confers lipopolysaccharide sensitivity to Toll-like receptor 4.

Toll-like receptor 4 (TLR4), the principal signaling receptor for lipopolysaccharide (LPS) in mammals, requires the binding of MD-2 to its extracellular domain for maximal responsiveness. MD-2 contains a leader sequence but lacks a transmembrane domain, and we asked whether it is secreted into the medium as an active protein. As a source of secreted MD-2 (sMD-2), we used culture supernatants from cells stably transduced with epitope-tagged human MD-2. We show that sMD-2 exists as a heterogeneous collection of large disulfide-linked oligomers formed from stable dimeric subunits and that concentrations of sMD-2 as low as 50 pM enhance the responsiveness of TLR4 reporter cells to LPS. An MD-2-like activity is also released by monocyte-derived dendritic cells from normal donors. When coexpressed, TLR4 indiscriminately associates in the endoplasmic reticulum/cis Golgi with different-sized oligomers of MD-2, and excess MD-2 is secreted into the medium. We conclude that normal and transfected cells secrete a soluble form of MD-2 that binds with high affinity to TLR4 and that could play a role in regulating responses to LPS and other pathogen-derived substances in vivo.

Antigens, Surface↗
PubMed2000

A novel synthetic acyclic lipid A-like agonist activates cells via the lipopolysaccharide/toll-like receptor 4 signaling pathway.

ER-112022 is a novel acyclic synthetic lipid A analog that contains six symmetrically organized fatty acids on a noncarbohydrate backbone. Chinese hamster ovary (CHO)-K1 fibroblasts and U373 human astrocytoma cells do not respond to lipopolysaccharide (LPS) in the absence of CD14. In contrast, exposure to ER-112022 effectively induced activation of CHO and U373 cells under serum-free conditions. Expression of CD14 was not necessary for cells to respond to ER-112022, although the presence of soluble CD14 enhanced the sensitivity of the response. Several lines of evidence suggested that ER-112022 stimulates cells via the LPS signal transduction pathway. First, the diglucosamine-based LPS antagonists E5564 and E5531 blocked ER-112022-induced stimulation of CHO-K1, U373, and RAW264.7 cells. Second, ER-112022 was unable to activate C3H/HeJ mouse peritoneal macrophages, containing a mutation in Toll-like receptor (TLR) 4, as well as HEK293 cells, an epithelial cell line that does not express TLR4. Third, ER-112022 activated NF-kappaB in HEK293 cells transfected with TLR4/MD-2. Finally, tumor necrosis factor release from primary human monocytes exposed to ER-112022 was blocked by TLR4 antibodies but not by TLR2 antibodies. Our results suggest that ER-112022 and the family of lipid A-like LPS antagonists can functionally associate with TLR4 in the absence of CD14. Synthetic molecules like ER-112022 may prove to be valuable tools to characterize elements in the LPS receptor complex, as well as to activate or inhibit the TLR4 signaling pathway for therapeutic purposes.

Animals↗
PubMed2003

Receptors involved in the oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine-mediated synthesis of interleukin-8. A role for Toll-like receptor 4 and a glycosylphosphatidylinositol-anchored protein.

We demonstrated previously that oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) and, specifically, the component lipid 1-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphorylcholine increase interleukin-8 (IL-8) synthesis in aortic endothelial cells. The goal of the current studies was to characterize the receptor complex mediating the increased transcription of IL-8. We demonstrate that scavenger receptor class A, types I and II, lectin-like ox-LDL receptor-1, macrophage receptor with collagenous structure, and CD36 are not responsible for the increase in IL-8. Using dominant-negative constructs and antisense oligonucleotides, we demonstrate a role for Toll-like receptor 4 (TLR4) as the ox-PAPC receptor mediating IL-8 transcription. We demonstrate that a glycosylphosphatidylinositol (GPI)-anchored protein is also necessary because phosphatidylinositol-specific phospholipase C pretreatment inhibited the effect of ox-PAPC. CD14, a GPI-anchored protein that associates with TLR4 in mediating lipopolysaccharide action, did not appear to mediate ox-PAPC action because ox-PAPC-induced IL-8 transcription was not blocked by anti-CD14 neutralizing antibodies nor was it augmented by the addition of soluble CD14 or overexpression of membrane CD14. Instead, anti-TLR4 antibodies immunoprecipitated a 37-kDa protein that also bound ox-PAPC. A protein of this same size was found in aerolysin overlays used to detect GPI-anchored proteins. Therefore, these studies suggest that ox-PAPC may initially bind to a 37-kDa GPI-anchored protein, which interacts with TLR4 to induce IL-8 transcription.

Animals↗
PubMed2003

Bruton's tyrosine kinase is a Toll/interleukin-1 receptor domain-binding protein that participates in nuclear factor kappaB activation by Toll-like receptor 4.

In this study we have identified members of the Toll-like receptor (TLR) family (namely, TLRs 4, 6, 8, and 9) as proteins to which the intracellular protein tyrosine kinase, Bruton's tyrosine kinase (Btk), binds. Detailed analysis of the interaction between Btk and TLR8 demonstrates that the presence of both Box 2 and 3 motifs in the Toll/interleukin-1 receptor domain was required for the interaction. Furthermore, co-immunoprecipitation experiments revealed that Btk can also interact with key proteins involved in TLR4 signal transduction, namely, MyD88, Mal (MyD88 adapter-like protein), and interleukin-1 receptor-associated kinase-1, but not TRAF-6. The ability of Btk to interact with TLR4 and Mal suggests a role for Btk in lipopolysaccharide (LPS) signal transduction. Stimulation of the human monocytic cell line THP-1 with LPS resulted in an increase in the level of tyrosine phosphorylation of Btk (indicative of activation). The autokinase activity of Btk was also stimulated after LPS stimulation. In addition, a dominant negative form of Btk inhibited TLR4-mediated activation of a nuclear factor kappaB (NFkappaB)-dependent reporter gene in HEK293 cells as well as LPS-induced activation of NFkappaB in the astrocytoma cell line U373 and the monocytic cell line RAW264.7. Further investigation revealed that the Btk-specific inhibitor, LFM-A13, inhibited the activation of NFkappaB by LPS in THP-1 cells. Our findings implicate Btk as a Toll/interleukin-1 receptor domain-binding protein that is important for NFkappaB activation by TLR4.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed2003

Interferon regulatory factor-3-mediated activation of the interferon-sensitive response element by Toll-like receptor (TLR) 4 but not TLR3 requires the p65 subunit of NF-kappa.

Interferon regulatory factor (IRF) 3 is a transcription factor that binds the interferon-sensitive response element (ISRE) and is activated by Toll-like receptor 3 (TLR3) and TLR4. We have found that a dominant negative form of I kappa B kinase 2 and a mutant form of I kappa B, which acts as a super-repressor of NF-kappa B, blocked activation of the ISRE by the TLR4 ligand lipopolysaccharide but not the TLR3 ligand poly(I-C). TLR4 failed to activate the ISRE in mouse embryonic fibroblasts bearing a targeted deletion of p65, whereas the response to TLR3 in these cells was normal. The p65 subunit of NF-kappa B was detected in the lipopolysaccharide-activated but not poly(I-C)-activated ISRE-binding complex. Finally, p65 promoted transactivation of gene expression by IRF-3. These results therefore indicate that IRF-3-mediated activation of the ISRE by TLR4 but not TLR3 requires the p65 subunit of NF-kappa B.

Animals↗
PubMed2004

BCL10 mediates lipopolysaccharide/toll-like receptor-4 signaling through interaction with Pellino2.

Toll-like receptor (TLR) pathways signal through microbial components stimulation to induce innate immune responses. Herein, we demonstrate that BCL10, a critical molecule that signals between the T cell receptor and IkappaB kinase complexes, is involved in the innate immune system and is required for appropriate TLR4 pathway and nuclear factor-kappaB (NF-kappaB) activation. In response to lipopolysaccharide (LPS) stimulation, BCL10 was recruited to TLR4 signaling complexes and associated with Pellino2, an essential component down-stream of BCL10 in the TLR4 pathway. In a BCL10-deficient macrophage cell line, LPS-induced NF-kappaB activation was consistently defective, whereas activator protein-1 and Elk-1 signaling was intact. In addition, we found that BCL10 was targeted by SOCS3 for negative regulation in LPS signaling. The recruitment of BCL10 to TLR4 signaling complexes was attenuated by induced expression of SOCS3 in a feedback loop. Furthermore, ectopic SOCS3 expression blocked the interaction between BCL10 and Pellino2 together with BCL10-generated NF-kappaB activation and inducible nitric-oxide synthase expression. Together, these data define an important role of BCL10 in the innate immune system.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Structural model of MD-2 and functional role of its basic amino acid clusters involved in cellular lipopolysaccharide recognition.

The receptor complex resulting from association of MD-2 and the ectodomain of Toll-like receptor 4 (TLR4) mediates lipopolysaccharide (LPS) signal transduction across the cell membrane. We prepared a tertiary structure model of MD-2, based on the known structures of homologous lipid-binding proteins. Analysis of circular dichroic spectra of purified bacterially expressed MD-2 indicates high content of beta-type secondary structure, in agreement with the structural model. Bacterially expressed MD-2 was able to confer LPS responsiveness to cells expressing TLR4 despite lacking glycosylation. We identified several clusters of basic residues on the surface of MD-2. Mutation of each of two clusters encompassing the residues Lys(89)-Arg(90)-Lys(91) and Lys(125)-Lys(125) significantly decreased the signal transduction of the respective MD-2 mutants either upon co-expression with TLR4 or upon addition as soluble protein into the supernatant of cells overexpressing TLR4. These basic clusters lie at the edge of the beta-sheet sandwich, which in cholesterol-binding protein connected to Niemann-Pick disease C2 (NPC2), dust mite allergen Der p2, and ganglioside GM2-activator protein form a hydrophobic pocket. In contrast, mutation of another basic cluster composed of Arg(69)-Lys(72), which according to the model lies further apart from the hydrophobic pocket only weakly decreased MD-2 activity. Furthermore, addition of the peptide, comprising the surface loop between Cys(95) and Cys(105), predicted by model, particularly in oxidized form, decreased LPS-induced production of tumor necrosis factor alpha and interleukin-8 upon application to monocytic cells and fibroblasts, respectively, supporting its involvement in LPS signaling. Our structural model of MD-2 is corroborated by biochemical analysis and contributes to the unraveling of molecular interactions in LPS recognition.

Amino Acid Motifs↗
PubMed2005

Lipopolysaccharide improves cardiomyocyte survival and function after serum deprivation.

Toll-like receptor-4 (TLR4) and its signaling molecule interleukin-1 receptor-associated kinase (IRAK-1) play an important role in host defense and tissue inflammation. Intriguingly, systemic administration of lipopolysaccharide (LPS), the agonist for TLR4, confers a cardio-protective effect against ischemic injury. However, the mechanisms leading to the cardiac protection remain largely unknown. The present study was designed to investigate the role of TLR4 activation by LPS in protecting cardiomyocytes (CM) against apoptosis in an in vitro model of ischemia and to explore the downstream mechanisms leading to the protective effect. Incubation with LPS led to activation of IRAK-1 and protected CMs against serum deprivation (SD)-induced apoptosis as demonstrated by DNA laddering, histone-DNA fragment enzyme-linked immunosorbent assay, and activation of caspase-3. Phosphatidylinositol 3-kinase/Akt, extracellular signal-regulated kinase 1/2, and IkappaB kinase beta appear to contribute to the anti-apoptotic effect of LPS since the specific inhibitors, wortmannin, PD98059, and dominant negative IKKbeta transgene expression reversed the LPS effect. To assess whether LPS improves CM function, we examined intracellular Ca(2+) transients and cell shortening in single adult rat CMs. SD for 6 h dramatically inhibited Ca(2+) transients and CM contractility. LPS at 500 ng/ml significantly improved the [Ca(2+)](i) transients and enhanced contractility in control CMs as well as in CMs subjected to SD. Importantly, transient ischemia led to rapid activation of IRAK-1 in cultured CMs and in adult rat myocardium. Adenovirus-mediated transgene expression of IRAK-1 but not its kinase-deficient mutant IRAK-1(K239S) protected CMs against SD-induced apoptosis. Taken together, these data suggest an important role of TLR4 signaling via IRAK-1 in protecting against SD-induced apoptosis.

Adenoviridae↗
PubMed2005

Association study of a functional Toll-like receptor 4 polymorphism with susceptibility to gastric mucosa-associated lymphoid tissue lymphoma.

Toll-like receptor 4, as part of innate immune response, is the main receptor for lipopolysaccharide on marginal zone B cells. The rare allele of TLR4 Asp299Gly attenuates receptor signaling and diminishes the inflammatory response. We genotyped 87 patients with gastric mucosa-associated lymphoid tissue (MALT) lymphoma, 594 Helicobacter pylori positive controls and 358 healthy blood donors to investigate an association of TLR4 Asp299Gly in the development of gastric MALT lymphoma. Heterozygote genotype was significantly less frequent in patients with gastric MALT lymphoma compared to H. pylori-infected controls (4.6% vs. 11.6%, Fischer's exact P=0.019, odds ratio=0.37, 95% confidence interval 0.13-1.03). Because 10% of caucasians are carriers of the rare allele G TLR4 Asp299Gly appears to be only one factor in the genetic susceptibility to gastric lymphoma. Further studies in larger samples are needed to confirm our findings and fully elucidate the role of TLR4 and its genetic variants in the pathophysiology of H. pylori infection and gastric lymphoma.

Adolescent↗
PubMed2005

Intra-uterine growth restriction downregulates the hepatic toll like receptor-4 expression and function.

Maternal starvation is a significant cause of intrauterine growth restriction (IUGR) in the world and increases the risk of infection in the neonate. We examined the effect of maternal starvation on Toll like receptor (TLR)4 expression in hepatic, splenic and intestinal tissues obtained from the adult IUGR offspring of prenatal calorie restricted rats. The hepatic TLR4 protein concentration was undetectable in the IUGR rats that had restricted milk intake during the suckling period (SM/SP; n = 4. p < 0.05) as compared to the normal growth controls (CM/CP; n = 4), and access to ad lib milk intake during the sucking period partially corrected the hepatic TLR4 expression (SM/CP; n = 4). IUGR had no effect on the splenic (n = 4) or intestinal (n = 4) TLR4 mRNA levels. In the liver, IUGR led to a 20% increase in baseline tumor necrosis factor (TNF)-alpha mRNA expression (p < 0.03) and a 70% increase in interleukin-1beta (IL-1beta) mRNA expression (p < 0.008) as compared to the control rats (CM/CP; n = 7). LPS-induced hepatic TNF-alpha release was significantly higher in SM/SP as compared to CM/CP. We propose that IUGR dysregulates TLR4 expression and function in the offspring, which may help explain the increased risk of Gram-negative sepsis and inflammatory diseases in this population.

Aging↗
PubMed2003

Monocytes heterozygous for the Asp299Gly and Thr399Ile mutations in the Toll-like receptor 4 gene show no deficit in lipopolysaccharide signalling.

Toll-like receptor 4 (TLR4)-mediated recognition of lipopolysaccharide (LPS) is required for efficient recognition of Gram-negative bacterial infections. Two commonly occurring mutations in the human TLR4 gene (Asp299Gly and Thr399Ile) have recently been shown to be associated with blunted physiological responses to inhaled LPS, and with increased risk of Gram-negative bacteraemia in sepsis patients and reduced risk of atherosclerosis in an Italian population. Here we show that monocytes from individuals heterozygous for both mutations in the TLR4 gene exhibit no deficit in recognition of LPS of Escherichia coli, Neisseria meningitidis, Bacteroides fragilis, Yersinia pestis, Chlamydia trachomatis, Porphyromonas gingivalis, or Pseudomonas aeruginosa. We propose that the relatively high frequency of these mutations in the Caucasian population may reflect modified responses of carriers to alternative TLR4 agonists.

Aspartic Acid↗
PubMed2001

A functional polymorphism of toll-like receptor 4 is not associated with likelihood or severity of meningococcal disease.

Human Toll-like receptor 4 (TLR4) transduces proinflammatory cytokine release by human cells in response to lipopolysaccharide (LPS). This study tested the hypothesis that, if TLR4 is rate limiting for a successful response to bacterial LPS in humans, a human gene polymorphism that results in the amino acid substitution Asp299Gly and causes reduced expression and function of TLR4 should influence susceptibility to or severity of natural gram-negative infection. The allele frequency of the Asp299Gly polymorphism was 5.9% among 879 blood donors, 6.5% among 1047 patients with microbiologically proven meningococcal disease, and 4.1% among 86 patients who died of meningococcal disease. No significant differences were observed, including those analyzed after stratification of the infected population by age and by meningococcal serogroup. Therefore, this functional TLR4 polymorphism does not influence susceptibility to or severity of meningococcal disease.

Adolescent↗
PubMed2001

Lipopolysaccharide-binding protein increases toll-like receptor 4-dependent activation by nontypeable Haemophilus influenzae.

Nontypeable Haemophilus influenzae (NTHi) is a common cause of respiratory tract infections. This study investigated the ability of NTHi to bind lipopolysaccharide-binding protein (LBP) derived from respiratory epithelial cells and the subsequent stimulation of transfected cells expressing membrane-bound CD14 and toll-like receptor 2 (TLR2) or TLR4. In the absence of LBP, NTHi at high concentrations (100 bacteria/epithelial cell) were required to induce signals through TLR2 and TLR4. Flow cytometry showed that NTHi in the stationary phase bound more LBP than did log-phase bacteria. Of interest, as few as 1 LBP-bearing bacterium/cell induced strong signaling through TLR4. In contrast, LBP bound to NTHi did not promote any increased signaling mediated by TLR2, compared with NTHi without LBP. These data suggest that, upon NTHi infection, low numbers of bacteria binding LBP may activate TLR4-bearing cells, such as alveolar macrophages, and consequently induce an inflammatory response.

Acute-Phase Proteins↗
PubMed2004

Toll-like receptor 4 is critical to innate host defense in a murine model of bordetellosis.

Bordetellae are important respiratory pathogens that cause pertussis (whooping cough) in humans and analogous diseases in domestic and wild animals. Immunity to Bordetella is poorly understood, in particular the early innate immune responses that contribute to inflammation, pathology, and the subsequent generation of adaptive immunity. Using B. bronchiseptica, which naturally infects mice, we show that Toll-like receptor-4 (TLR4) is required for cytokine responses to this pathogen's lipopolysaccharide (LPS) and that TLR4 deficiency results in impaired cytokine responses in vitro and in vivo. TLR4-deficient mice rapidly succumb following inoculation with as few as 1000 organisms, indicating that TLR4 is critical to innate host defense against bordetellosis.

Animals↗