Shield as Signal: Lipopolysaccharides and the Evolution of Immunity to Gram-Negative Bacteria

Munford, Robert S.; Varley, Alan W.

doi:10.1371/journal.ppat.0020067

Cited by 122 publications

(125 citation statements)

References 70 publications

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“…For example, the TLR4/MD-2/CD14 receptor complex is a robust cellular sensor of Gram-negative bacteria through its ability to recognize the lipid A moiety of LPS (reviewed in Refs. 56,57). This recognition results in the recruitment of adapter molecules and subsequent intracellular signal transduction that evokes a potent pro-inflammatory response.…”

Section: Discussionmentioning

confidence: 99%

Analysis of Proteinase-activated Receptor 2 and TLR4 Signal Transduction

Rallabhandi

Nhu

Toshchakov

et al. 2008

Journal of Biological Chemistry

135

149

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Proteinase-activated receptor 2 (PAR 2 ), a seven-transmembrane G protein-coupled receptor, is activated at inflammatory sites by proteolytic cleavage of its extracellular N terminus by trypsin-like enzymes, exposing a tethered, receptor-activating ligand. Synthetic agonist peptides (AP) that share the tethered ligand sequence also activate PAR 2 , often measured by Ca 2؉ release. PAR 2 contributes to inflammation through activation of NF-B-regulated genes; however, the mechanism by which this occurs is unknown. Overexpression of human PAR 2 in HEK293T cells resulted in concentration-dependent, PAR 2 AP-inducible NF-B reporter activation that was protein synthesis-independent, yet blocked by inhibitors that uncouple G i proteins or sequester intracellular Ca 2؉ . Because previous studies described synergistic PAR 2 -and TLR4-mediated cytokine production, we hypothesized that PAR 2 and TLR4 might interact at the level of signaling. In the absence of TLR4, PAR 2 -induced NF-B activity was inhibited by dominant negative (DN)-TRIF or DN-TRAM constructs, but not by DN-MyD88, findings confirmed using cell-permeable, adapter-specific BB loop blocking peptides. Co-expression of TLR4/MD-2/CD14 with PAR 2 in HEK293T cells led to a synergistic increase in AP-induced NF-B signaling that was MyD88-dependent and required a functional TLR4, despite the fact that AP exhibited no TLR4 agonist activity. Co-immunoprecipitation of PAR 2 and TLR4 revealed a physical association that was AP-dependent. The response to AP or lipopolysaccharide was significantly diminished in TLR4 ؊/؊ and PAR 2 ؊/؊ macrophages, respectively, and SW620 colonic epithelial cells exhibited synergistic responses to co-stimulation with AP and lipopolysaccharide. Our data suggest a unique interaction between two distinct innate immune response receptors and support a novel paradigm of receptor cooperativity in inflammatory responses.

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Section: Discussionmentioning

confidence: 99%

Analysis of Proteinase-activated Receptor 2 and TLR4 Signal Transduction

Rallabhandi

Nhu

Toshchakov

et al. 2008

Journal of Biological Chemistry

135

149

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“…Approximately 100-fold higher amounts of pentaacylated LOS msbB , in comparison to hexaacylated LOS wt , were needed to induce comparable airway inflammatory responses. The potency of tetraacylated endotoxin species is likely to be even lower (18). If such differences are also manifest during infections of the airways and lungs, this would result in delayed mobilization of airway host defenses, giving invading bacteria more time to further multiply, adapt, and disseminate.…”

Section: Discussionmentioning

confidence: 99%

“…Among the most important structural determinants of endotoxin activity are the number, chain length, and location of fatty acyl chains within lipid A (13)(14)(15)(16)(17). In general, the most potent endotoxin species are hexaacylated, whereas either less or more highly acylated endotoxins are substantially less potent inducers of host proinflammatory responses (15,18). Differences in the potency of hexa-, tetra-, and pentaacylated endotoxins reflect differences in the ability of endotoxin-bound MD-2 to induce activation of TLR4 (17,19).…”

mentioning

confidence: 99%

MD-2–Dependent Pulmonary Immune Responses to Inhaled Lipooligosaccharides

Hađina¹,

Weiss²,

McCray³

et al. 2008

Am J Respir Cell Mol Biol

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Endotoxins represent one of the most potent classes of microbial immunoactive components that can cause pulmonary inflammation. The aim of this study was to compare the inflammatory potency of two types of Neisseria meningitidis endotoxins (lipooligosaccharides) in lungs: wild type (hexaacylated, LOS wt ) and mutant type (pentaacylated, LOS msbB ), and to determine the importance of MD-2 in endotoxin responses in lungs in vivo. Endotoxin-normoresponsive mice (BALB/c) were exposed to selected doses of penta-and hexaacylated lipooligosaccharides (LOS) by nasal aspiration. Cellular and cytokine/chemokine inflammatory responses in bronchoalveolar lavage were measured at 1-, 4-, 8-, 16-, 24-, and 48-hour time points. MD-2-null mice were exposed to one dose of hexaacylated LOS and inflammatory responses were measured after 4 and 24 hours. Inhalation of hexaacylated LOS resulted in strong inflammatory responses, while pentaacylated LOS was much less potent in inducing increases of neutrophils, TNF-a, macrophage inflammatory protein-1a, IL-6, granulocyte colony-stimulating factor, and IL-1b concentration in bronchoalveolar lavage. Similar kinetics of inflammatory responses in lungs were found in both types of endotoxin exposures. Inhalation of hexaacylated LOS in MD-2-null mice resulted in significantly lower numbers of neutrophils in bronchoalveolar lavage than in normoresponsive mice. Markedly lower inflammatory potency of pentaacylated LOS was observed compared with hexaacylated LOS. Hyporesponsiveness in MD-2-null mice after nasal aspiration of wild-type LOS indicate its essential role in airway responsiveness to endotoxin.

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“…For example, early studies conducted in our laboratory indicated that not only did P. gingivalis LPS fail to elicit strong host innate immune responses such as E-selectin induction, but it also antagonized the immunostimulatory activity of agonsitic LPS (Darveau et al, 1995). Subsequent investigations demonstrated that the antagonistic capacity displayed by P. gingivalis LPS isolates was due to competitive inhibition of agonistic LPS interaction at the host Toll-like receptor 4 (TLR4) complex (Hajishengallis et al, 2002;Coats et al, 2003;Coats et al, 2005;Coats et al, 2007), which forms a major host sensing mechanism to Gram-negative bacterial infections (Beutler, 2000;Munford et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Porphyromonas gingivalis Resistance to Polymyxin B Is Determined by the Lipid A 4′‐Phosphatase, PGN_0524

Coats

Jain

et al. 2009

Int J Oral Sci

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). Approximately 2,700 independent Tn4400'-derived mutants of P. gingivalis were examined for increased sensitivity to PMB killing at a relatively low dose (50 µg⋅mL -1 ). A single PMB-sensitive mutant was obtained in this phenotypic screen. We determined that the Tn4400' transposon was integrated into the gene encoding the lipid A 4'-phosphatase, PGN_0524, demonstrating that this insertion event was responsible for its increased susceptibility of this clone to PMB-dependent killing. The resulting mutant strain, designated 0524-Tn4400', was highly sensitive to PMB killing relative to wild-type P.gingivalis, and exhibited the same sensitivity as the previously characterized strain, 0524KO, which bears a genetically engineered deletion in the PGN_0524 locus. Positive ion mass spectrometric structural (MALDI-TOF MS) analyses revealed that lipid A isolates from 0524-Tn4400' and 0524KO strains displayed strikingly similar MALDI-TOF MS spectra that were substantially different from the wildtype P. gingivalis lipid A spectrum. Finally, intact 0524-Tn4400' and 0524KO mutant bacteria, as well as their corresponding LPS isolates, were significantly more potent in stimulating Toll-like receptor 4 (TLR4)-dependent E-selectin expression in human endothelial cells relative to intact wild-type P. gingivalis or its corresponding LPS isolate. Conclusion The combined molecular evidence provided in this report suggests that PGN_0524, a lipid A 4'-phosphatase, is the sole genetic element conferring the ability of the periodontopathogen, P. gingivalis, to evade the killing activity of cationic antimicrobial peptides, such as PMB. These data strongly implicate PGN_0524 as a critical virulence factor for the ability of P. gingivalis to evade front-line host innate defenses that are dependent upon cationic antimicrobial peptide activity and TLR4 sensing.

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Shield as Signal: Lipopolysaccharides and the Evolution of Immunity to Gram-Negative Bacteria

Cited by 122 publications

References 70 publications

Analysis of Proteinase-activated Receptor 2 and TLR4 Signal Transduction

Analysis of Proteinase-activated Receptor 2 and TLR4 Signal Transduction

MD-2–Dependent Pulmonary Immune Responses to Inhaled Lipooligosaccharides

Porphyromonas gingivalis Resistance to Polymyxin B Is Determined by the Lipid A 4′‐Phosphatase, PGN_0524

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