Toll-like receptor-2 mediates Treponema glycolipid and lipoteichoic acid-induced NF-kappaB translocation.

Recently Toll-like receptors (TLRs) have been found to be involved in cellular activation by microbial products, including lipopolysaccharide, lipoproteins, and peptidoglycan. Although for these ligands the specific transmembrane signal transducers TLR-4, TLR-2, or TLR-2 and -6 have now been identified, the molecular basis of recognition of lipoteichoic acids (LTAs) and related glycolipids has not been completely understood. In order to determine the role of TLRs in immune cell activation by these stimuli, experiments involving TLR-2-negative cell lines, TLR-expression plasmids, macrophages from TLR-4-deficient C3H/HeJ-mice, and inhibitory TLR-4/MD-2 antibodies were performed. Glycolipids from Treponema maltophilum and Treponema brennaborense, as well as highly purified LTAs from Staphylococcus aureus and Bacillus subtilis exhibited TLR-2 dependence in nuclear factor kappaB activation and cytokine induction; however, T. brennaborense additionally appeared to signal via TLR-4. Fractionation of the T. brennaborense glycolipids by hydrophobic interaction chromatography and subsequent cell stimulation experiments revealed two peaks of activity, one exhibiting TLR-2-, and a second TLR-4-dependence. Furthermore, we show involvement of the signaling molecules MyD88 and NIK in cell stimulation by LTAs and glycolipids by dominant negative overexpression experiments. In summary, the results presented here indicate that TLR-2 is the main receptor for Treponema glycolipid and LTA-mediated inflammatory response.

LPS-binding protein protects mice from septic shock caused by LPS or gram-negative bacteria.

LPS-binding protein (LBP) recognizes bacterial LPS and transfers it to CD14, thereby enhancing host cell stimulation, eventually resulting in pathogenic states such as septic shock. Recently, LBP also was shown to detoxify LPS by transferring LPS into HDL particles in vitro. Thus, the predominant in vivo function of LBP has remained unclear. To investigate the biological activity of acute phase concentrations of recombinant murine LBP, high concentrations of LBP were investigated in vitro and in vivo. Although addition of low concentrations of LBP to a murine macrophage cell line enhanced LPS-induced TNF-alpha synthesis, acute phase concentrations of LBP blocked this effect in comparison to low-dose LBP. When injected into mice intraperitoneally, LBP inhibited LPS-mediated cytokine release and prevented hepatic failure resulting in a significantly decreased mortality rate in LPS-challenged and D-galactosamine-sensitized mice, as well as in a murine model of bacteremia. These results complement a recent study revealing LBP-deficient mice to be dramatically more susceptible to an intraperitoneal Salmonella infection as compared with normal mice. We conclude that acute phase LBP has a protective effect against LPS and bacterial infection and may represent a physiologic defense mechanism against infection. Despite the limitations of any murine sepsis model, the results shown may imply that LBP could have beneficial effects during gram-negative peritonitis in humans.

The transcriptional activation pattern of lipopolysaccharide binding protein (LBP) involving transcription factors AP-1 and C/EBP beta.

Lipopolysaccharide (LPS) Binding Protein (LBP) is an acute phase protein with the ability to recognize bacterial LPS and transport it to the CD14 molecule or into HDL particles. It is synthesized in hepatocytes and secreted into the blood stream. LBP levels significantly rise during the acute phase response and levels of LBP may be important for an appropriate host reaction to bacterial challenge and for developing the sepsis syndrome. In order to elucidate the mechanisms of LBP regulation we investigated its transcription pattern and performed promoter studies under experimental conditions mimicking an acute phase scenario. In human hepatoma cell lines stimulation with IL-1 beta, IL-6, TNF-alpha and dexamethasone leads to strong transcriptional activation of the LBP gene in a dose- and time-dependent manner. IL-6 alone induces LBP significantly, whereas IL-1 beta mainly increases the IL-6 effect when applied in combination. Our results furthermore show that AP-1 and C/EBP beta are transcription factors involved in the activation of the LBP gene, as revealed by Luciferase reporter gene analysis and electromobility shift assays. Elucidating the mechanism of transcriptional activation of LBP potentially may help in understanding host-pathogen response patterns and mechanisms involved in the acute phase reaction and in the pathophysiology of sepsis.