MD-2 Mediates the Ability of Tetra-Acylated and Penta-Acylated Lipopolysaccharides to AntagonizeEscherichia coliLipopolysaccharide at the TLR4 Signaling Complex

Abstract

We have demonstrated previously that tetra-acylated LPS derived from the oral bacterium, Porphyromonas gingivalis, and penta-acylated msbB LPS derived from a mutant strain of Escherichia coli can antagonize the ability of canonical hexa-acylated E. coli LPS to signal through the TLR4 signaling complex in human endothelial cells. Activation of the TLR4 signaling complex requires the coordinated function of LPS binding protein (LBP), CD14, MD-2, and TLR4. To elucidate the specific molecular components that mediate antagonism, we developed a recombinant human TLR4 signaling complex that displayed efficient LPS-dependent antagonism of E. coli LPS in HEK293 cells. Notably, changes in the expression levels of TLR4 in HEK293 cells modulated the efficiency of antagonism by P. gingivalis LPS. Both soluble (s) CD14 and membrane (m) CD14 supported efficient P. gingivalis LPS-dependent and msbB LPS-dependent antagonism of E. coli LPS in the recombinant TLR4 system. When cells expressing TLR4, MD-2, and mCD14 were exposed to LPS in the absence of serum-derived LBP, efficient LPS-dependent antagonism of E. coli LPS was still observed indicating that LPS-dependent antagonism occurs downstream of LBP. Experiments using immunoprecipitates of sCD14 or sMD-2 that had been pre-exposed to agonist and antagonist indicated that LPS-dependent antagonism occurs partially at sCD14 and potently at sMD-2. This study provides novel evidence that expression levels of TLR4 can modulate the efficiency of LPS-dependent antagonism. However, MD-2 represents the principal molecular component that tetra-acylated P. gingivalis LPS and penta-acylated msbB LPS use to antagonize hexa-acylated E. coli LPS at the TLR4 signaling complex.

MD-2–Dependent Pulmonary Immune Responses to Inhaled Lipooligosaccharides

“…MD-2-null mice do not mobilize airway inflammatory responses to nasally instilled LOS aggregates but are responsive to purified monomeric LOS:MD-2 (unpublished observation), confirming that the loss of responsiveness of MD-2-null mice to endotoxin is due to the absence of MD-2. In vitro, differences in potency of hexaacylated versus underacylated endotoxin species in inducing TLR4-dependent cell activation reflect differences in the functional properties of endotoxin bound to MD-2 (17,19). Thus, the differences we observed in this study in the ability of LOS wt versus LOS msbB to induce airway inflammation most likely reflect differences in the functional properties of hexacylated versus pentacylated LOS bound to MD-2 in the airway.…”

“…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). On the basis of these observations, it has been suggested that the elaboration of underacylated endotoxins by Pseudomonas aeruginosa early in the evolution of pulmonary infection in cystic fibrosis (15,20,21) and by Yersinia pestis in pneumonic plague (22) contributes greatly to the virulence of these airway bacterial pathogens by blunting early host inflammatory responses needed for efficient mobilization of host defenses.…”

Neuroprotective activity of Ethanolic Extract of Tinospora cordifolia on LPS induced Neuroinflammation

“…This lipid A is responsible for the potent immunostimulatory property of LPS [3,4]. LPS projects its potency and act as an endotoxin by its greater affinity towards Toll-like receptor 4 (TLR 4) [5]. TLRs initiate key inflammatory responses and also shape adaptive immunity.…”

Impact of Dental Plaque Biofilms in Periodontal Disease: Management and Future Therapy

“…As an example, an in vitro study is showing that the TLR response can be manipulated by P. gingivalis toward two types of lipopolysaccharides: PgLPS1690 (type I) and PgLPS1435/1449 (type II). Type I is a TLR4 agonist, thus activating the immune system, while type II is a TLR4 antagonist inhibiting the immune response to P. gingivalis [57]. The expression of these two types of LPS is regulated by the concentration of iron from the hemin found in the GCF [58].…”