Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0036690 (sepsis)
 59,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The family of Toll-like receptors (TLRs) is involved in the defense of an organism to microbial attack. TLR4-induced signaling is involved in infectious diseases, chronic inflammatory diseases and sepsis; therefore, we aimed at modulating TLR4-signaling via ligand-binding soluble receptors. Because recognition of microbial structures shows some species-specific traits, we specifically selected the mouse model for later in vivo studies. We first prepared the N-terminally Flag-tagged mouse (m) recombinant (r) soluble (s) fusion proteins mrsTLR4-IgGFc (T4Fc) and mrsMD-2 in Drosophila melanogaster Schneider 2 (S2) cells. The function of these molecules was tested by inhibition of synthesis of pro-inflammatory cytokines after stimulation of mouse macrophage RAW 264.7 cells with purified lipopolysaccharide (LPS). T4Fc alone had no inhibitory activity; however, a T4Fc/MD-2 complex blocked LPS activity. By analogy with 'cytokine traps', we then prepared a designer molecule (LPS-Trap) by fusing MD-2 to the C-terminus of soluble TLR4 via a flexible linker. LPS-Trap significantly inhibited TNF production by LPS-stimulated RAW 264.7 cells. Thus, the T4Fc/MD-2 complex as well as the LPS-Trap blocked LPS activity in vitro and might thus represent a new therapeutic option in sepsis by neutralization of TLR4-activating ligands.
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PMID:A designed TLR4/MD-2 complex to capture LPS. 1617 55

Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.
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PMID:Lipopolysaccharide signaling in endothelial cells. 1635 66

In addition to its well-known role in mineral and skeletal homeostasis, 1,25-dihydroxyvitamin D3 [1,25-(OH)2, D3] regulates the differentiation, growth and function of a broad range of immune system cells, including monocytes, dendritic cells, T and B lymphocytes. Vascular endothelial cells play a major role in the innate immune activation during infections, sepsis and transplant rejection; however, currently there are no data on the effect of 1,25-(OH)2 D3 on microbial antigen-induced endothelial cell activation. Here we show that 1,25-(OH)2 D3 pretreatment of human microvessel endothelial cells (HMEC) inhibited the enteric gram-negative bacterial lipopolysaccharide (LPS) activation of transcription factor NF-kappaB and interleukin (IL)-6, IL-8 and regulated upon activation normal T cell exposed and secreted (RANTES) release. The effect of 1,25-(OH)2 D3 was not due to increased cell death or inhibition of endothelial cell proliferation. 1,25-(OH)2 D3 pretreatment of HMEC did not block MyD88-independent LPS-induced interferon (IFN)-beta promoter activation. 1,25-(OH)2 D3 pretreatment of HMEC did not modulate Toll-like receptor 4 (TLR4) or MD-2 expression. These data suggest that 1,25-(OH)2 D3 may play a role in LPS-induced immune activation of endothelial cells during gram-negative bacterial infections, and a suggest a potential role for 1,25-(OH)2 D3 and its analogues as an adjuvant in the treatment of gram-negative sepsis.
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PMID:1,25-Dihydroxyvitamin D inhibits lipopolysaccharide-induced immune activation in human endothelial cells. 1636 34

Translocation of bacteria across the intestinal barrier is important in the pathogenesis of systemic sepsis, although the mechanisms by which bacterial translocation occurs remain largely unknown. We hypothesized that bacterial translocation across the intact barrier occurs after internalization of the bacteria by enterocytes in a process resembling phagocytosis and that TLR4 is required for this process. We now show that FcgammaRIIa-transfected enterocytes can internalize IgG-opsonized erythrocytes into actin-rich cups, confirming that these enterocytes have the molecular machinery required for phagocytosis. We further show that enterocytes can internalize Escherichia coli into phagosomes, that the bacteria remain viable intracellularly, and that TLR4 is required for this process to occur. TLR4 signaling was found to be necessary and sufficient for phagocytosis by epithelial cells, because IEC-6 intestinal epithelial cells were able to internalize LPS-coated, but not uncoated, latex particles and because MD2/TLR4-transfected human endothelial kidney (HEK)-293 cells acquired the capacity to internalize E. coli, whereas nontransfected HEK-293 cells and HEK-293 cells transfected with dominant-negative TLR4 bearing a P712H mutation did not. LPS did not induce membrane ruffling or macropinocytosis in enterocytes, excluding their role in bacterial internalization. Strikingly, the internalization of Gram-negative bacteria into enterocytes in vivo and the translocation of bacteria across the intestinal epithelium to mesenteric lymph nodes were significantly greater in wild-type mice as compared with mice having mutations in TLR4. These data suggest a novel mechanism by which bacterial translocation occurs and suggest a critical role for TLR4 in the phagocytosis of bacteria by enterocytes in this process.
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PMID:Enterocyte TLR4 mediates phagocytosis and translocation of bacteria across the intestinal barrier. 1649 66

Toll-like receptors (TLRs) belong to the family of pattern recognition receptors, as they recognize molecules sharing a broad structural pattern rather than a single defined structure. Bacterial LPS is recognized by MD-2, which is associated with the extracellular domain of TLR4. Understanding the molecular recognition pattern of MD-2 could lead to efficient inhibitors of the excessive LPS signaling needed for early treatment of sepsis. The effect of the acyl chain variability of lipid A on its biological activity indicates that in addition to electrostatic interactions, the recognition must also involve hydrophobic interactions. We show that the fluorescent hydrophobic probe bis-ANS binds to MD-2 with a dissociation constant in the 10 nanomolar range, both to glycosylated and to nonglycosylated MD-2, and requires its native conformation. The binding site of bis-ANS overlaps with the binding site of LPS and is in the proximity of the single tryptophan residue. Furthermore, photoincorporation of bis-ANS by UV light inhibits the ability of MD-2 to confer the LPS responsiveness to the TLR4-transfected HEK293 cell line. Our results show that the structural pattern recognized by MD-2 is defined by the hydrophobic patch and a pair of separated negative charges.
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PMID:Structural similarity between the hydrophobic fluorescent probe and lipid A as a ligand of MD-2. 1694 Jan 55

Neisseria meningitidis causes acute severe diseases, including sepsis and meningitis, and more benign manifestations such as chronic meningococcemia or colonization of the upper respiratory tract. The inflammatory response, which contributes to the pathogenesis of meningococcal disease, is initiated by pattern recognition receptors, among which Toll-like receptors (TLR)s have been ascribed a particularly important role. We have previously demonstrated that N. meningitidis induce proinflammatory cytokine expression through TLR2 and TLR4. Here we characterize the molecular basis for differential activation of the inflammatory response by two N. meningitidis strains. This difference was due to differential ability to activate signal transduction through TLR4, as HEK293 cells expressing TLR4 produced significantly different levels of interleukin-8 in response to these strains. At the level of signal transduction, the two strains differed substantially in their ability to activate the pathway to nuclear factor kappaB in HEK293-TLR4/MD2 cells at late, but not early, time points. TLR4 activates two signal transduction pathways: one dependent on the adaptor molecule MyD88 and one independent of MyD88, and these pathways induce distinct patterns of gene expression in response to TLR4 ligands. By using macrophages from TLR2-/- mice, we observed that the two strains differed in their ability to activate the TLR4-induced MyD88-independent pathway, but not the MyD88-dependent pathway. This idea was further supported by experiments where either of the two pathways was inhibited and IL-8 secretion was measured. These data therefore provide molecular insight into activation of the inflammatory response by N. meningitidis, which is one of the key events in the pathogenesis of meningococcal disease.
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PMID:Two neisseria meningitidis strains with different ability to stimulate toll-like receptor 4 through the MyD88-independent pathway. 1708 21

Toll-like receptors (TLRs) are mammalian innate immune recognition receptors that are activated by pathogen associated molecular patterns (PAMPs). TLR4 is the signaling molecule of the lipopolysaccharide (LPS) receptor complex. TLR4 associates with its adapter molecule, MD-2, which is absolutely required for LPS-induced activation of TLR4. MD-2 exists as a cell surface protein in association with TLR4 and as secreted forms consisting of MD-2 monomers and multimers. To facilitate the studies of MD-2 distribution, abundance, and function, we produced monoclonal antibodies (MAbs) to baculovirally expressed soluble MD-2 (sMD-2). Eleven MAbs were characterized by enzyme-linked immunosorbent assay (ELISA) with soluble TLR4/MD-2 complex (sTLR4/MD-2) and sMD-2, Western blotting against sMD-2 monomer and multimers, and inhibition of direct LPS binding to sMD-2. Four MAbs preferentially recognized mainly MD-2 oligomers, not monomers, as judged by Western blotting and ELISA. Anti-MD-2 MAbs useful for indirect immunofluorescent staining of cells expressing TLR4 and MD-2 were identified. One MAb that recognized all forms of MD-2 was used in an ELISA to measure sMD-2 in normal human sera as well as sera from intensive care patients with and without sepsis. Serum levels of sMD-2 were undetectable or very low in normal and in nonsepsis patients but significantly (p < 0.05) increased in sepsis patients. These MAbs should therefore be very useful new tools for studies of MD-2 expression and function in health and disease.
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PMID:Characterization of monoclonal antibodies to human soluble MD-2 protein. 1720 97

Sepsis and endotoxaemia are important causes of morbidity and mortality in humans. Research on sepsis focuses on rodent models most of which are poorly responsive to lipopolysaccharide (LPS), and thus do not mimic very well the high sensitivity of humans. Therefore, there is a need to develop more clinically relevant models. Horses suffer from a similar endotoxaemic syndrome to humans with high morbidity and mortality. LPS analogues that act as antagonists at Toll-like receptor 4 (TLR4) are being developed as novel treatments for endotoxaemia. Due to differences in recognition of ligands by TLR4 from different mammalian species, individual LPS molecules may act as agonists in some species and antagonists in others. The synthetic lipid A analogue E5531 is an antagonist at TLR4 in humans and mice, but its effects at TLR4 from other species are unknown. In the studies reported here, Escherichia coli LPS is a full agonist on equine bone marrow macrophage-like cells and its effects are antagonised by E5531. Similarly, E. coli LPS is an agonist and E5531 an antagonist on monocytes isolated from peripheral blood of healthy horses and human embryonic kidney (HEK) cells, transiently transfected to express horse TLR4 and its associated cell surface proteins MD2 and CD14. In contrast, both E. coli LPS and E5531 behave as agonists in horse whole blood by inducing production of equivalent amounts of the inflammatory mediator prostaglandin. This finding suggests that modification of E5531 may occur in whole blood, for example, deacylation, which alters its activity. This comparative study has revealed a novel pharmacological action of E5531 and emphasises the importance of extending studies of this nature beyond the normal rodent models.
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PMID:The cellular Toll-like receptor 4 antagonist E5531 can act as an agonist in horse whole blood. 1732 Jan 93

To identify new components that regulate the inflammatory cascade during sepsis, we characterized the functions of myeloid-related protein-8 (Mrp8, S100A8) and myeloid-related protein-14 (Mrp14, S100A9), two abundant cytoplasmic proteins of phagocytes. We now demonstrate that mice lacking Mrp8-Mrp14 complexes are protected from endotoxin-induced lethal shock and Escherichia coli-induced abdominal sepsis. Both proteins are released during activation of phagocytes, and Mrp8-Mrp14 complexes amplify the endotoxin-triggered inflammatory responses of phagocytes. Mrp8 is the active component that induces intracellular translocation of myeloid differentiation primary response protein 88 and activation of interleukin-1 receptor-associated kinase-1 and nuclear factor-kappaB, resulting in elevated expression of tumor necrosis factor-alpha (TNF-alpha). Using phagocytes expressing a nonfunctional Toll-like receptor 4 (TLR4), HEK293 cells transfected with TLR4, CD14 and MD2, and by surface plasmon resonance studies in vitro, we demonstrate that Mrp8 specifically interacts with the TLR4-MD2 complex, thus representing an endogenous ligand of TLR4. Therefore Mrp8-Mrp14 complexes are new inflammatory components that amplify phagocyte activation during sepsis upstream of TNFalpha-dependent effects.
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PMID:Mrp8 and Mrp14 are endogenous activators of Toll-like receptor 4, promoting lethal, endotoxin-induced shock. 1776 65

Overactivation of the immune system upon acute bacterial infection leads to septic shock. Specific bacterial products potently stimulate immune cells via toll-like receptors (TLRs). Gram-negative bacteria induce a predominantly TLR4-driven signal through LPS release. To neutralize LPS signaling in experimental models of sepsis, we generated mAbs toward the TLR4/myeloid differentiation protein-2 (MD-2) complex. The binding properties of an array of selected rat mAbs differed in respect to their specificity for TLR4/MD-2 complex. The specificity of one such mAb, 5E3, to murine TLR4 was confirmed by its recognition of an epitope within the second quarter of the ectodomain. 5E3 inhibited LPS-dependent cell activation in vitro and prevented proinflammatory cytokine production in vivo following LPS challenge in a dose-dependent manner. Furthermore, 5E3 protected mice from lethal shock-like syndrome when applied using both preventative and therapeutic protocols. Most notably, in the colon ascendens stent peritonitis model of polymicrobial abdominal sepsis, administration of a single dose of 5E3 (50 mug) protected mice against mortality. These results demonstrate that neutralizing TLR4/MD-2 is highly efficacious in protecting against bacterial infection-induced toxemia and offers TLR4/MD-2 mAb treatment as a potential therapy for numerous clinical indications.
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PMID:TLR4/MD-2 monoclonal antibody therapy affords protection in experimental models of septic shock. 1794 85


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