Cutting edge: repurification of lipopolysaccharide eliminates signaling through both human and murine toll-like receptor 2

Construction of Escherichia coli Mutant with Decreased Endotoxic Activity by Modifying Lipid A Structure

Escherichia coli BL21 (DE3) and its derivatives are widely used for the production of recombinant proteins, but these purified proteins are always contaminated with lipopolysaccharide (LPS). LPS is recognized by the toll-like receptor 4 and myeloid differentiation factor 2 complex of mammalian immune cells and leads to release of pro-inflammatory cytokines. It is a vital step to remove LPS from the proteins before use for therapeutic purpose. In this study, we constructed BL21 (DE3) ∆msbB28 ∆pagP38 mutant, which produces a penta-acylated LPS with reduced endotoxicity. The plasmids harboring pagL and/or lpxE were then introduced into this mutant to further modify the LPS. The new strain (S004) carrying plasmid pQK004 (pagL and lpxE) produced mono-phosphoryated tetra-acylated lipid A, which induces markedly less production of tumor necrosis factor-α in the RAW264.7 and IL-12 in the THP1, but still retains ability to produce recombinant proteins. This study provides a strategy to decrease endotoxic activity of recombinant proteins purified from E. coli BL21 backgrounds and a feasible approach to modify lipid A structure for alternative purposes such as mono-phosphoryl lipid A (MPL) as vaccine adjuvants.

Gene expression profiling of porcine mammary epithelial cells after challenge with Escherichia coli and Staphylococcus aureus in vitro

Postpartum Dysgalactia Syndrome (PDS) represents a considerable health problem of postpartum sows, primarily indicated by mastitis and lactation failure. The poorly understood etiology of this multifactorial disease necessitates the use of the porcine mammary epithelial cell (PMEC) model to identify how and to what extent molecular pathogen defense mechanisms prevent bacterial infections at the first cellular barrier of the gland. PMEC were isolated from three lactating sows and challenged with heat-inactivated potential mastitis-causing pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for 3 h and 24 h, in vitro. We focused on differential gene expression patterns of PMEC after pathogen challenge in comparison with the untreated control by performing microarray analysis. Our results show that a core innate immune response of PMEC is partly shared by E. coli and S. aureus. But E. coli infection induces much faster and stronger inflammatory response than S. aureus infection. An immediate and strong up-regulation of genes encoding cytokines (IL1A and IL8), chemokines (CCL2, CXCL1, CXCL2, CXCL3, and CXCL6) and cell adhesion molecules (VCAM1, ICAM1, and ITGB3) was explicitly obvious post-challenge with E. coli inducing a rapid recruitment and activation of cells of host defense mediated by IL1B and TNF signaling. In contrast, S. aureus infection rather induces the expression of genes encoding monooxygenases (CYP1A1, CYP3A4, and CYP1B1) initiating processes of detoxification and pathogen elimination. The results indicate that the course of PDS depends on the host recognition of different structural and pathogenic profiles first, which critically determines the extent and effectiveness of cellular immune defense after infection.

Galectin-3 is a sensor-regulator of toll-like receptor pathways in synovial fibroblasts

Galectin-3 is a β-galactoside-binding lectin that plays an important role in the modulation of immune responses. It has been shown to aggravate joint inflammation and destruction in experimental arthritis. We investigated the role of galectin-3 in TLR-induced cell activation in human synovial fibroblasts (SF) in order to better understand the mechanism(s) of the proinflammatory function of galectin-3 in arthritis. Galectin-3 expression in SF obtained from rheumatoid arthritis and osteoarthritis patients was inhibited by siRNA mediated gene-knockdown. Galectin-3 was also inhibited with modified citrus pectin (MCP), a polysaccharide galectin-3 ligand. Galectin-3 knockdown inhibited TLR-2, -3 and -4-induced IL-6 secretion, but not TLR-2, -3 and -4-mediated matrix metalloproteinase-3 or CC chemokine ligand-5 secretion. When the SF were stimulated with phorbol 12-myristate 13-acetate, a protein kinase C activator that bypasses the membranal receptors, galectin-3 knockdown no longer influenced IL-6 secretion. MCP reduced IL-6 levels in a dose-dependent manner. Our results indicate that galectin-3 is a positive sensor-regulator of TLR-induced IL-6 secretion in human synovial fibroblasts, thus adding new insights into the mechanisms by which galectin-3 augments synovial inflammation. These findings corroborate the potential role of glycan inhibitors of galectin-3 as a therapeutic approach for the treatment of inflammatory arthritis.

Production of inflammatory mediators and extracellular traps by carp macrophages and neutrophils in response to lipopolysaccharide and/or interferon-γ2

Neutrophilic granulocytes and macrophages are crucial for the innate immune response against infections. They migrate into the focus of inflammation, where they efficiently bind, engulf and kill bacteria by proteolytic enzymes, antimicrobial peptides, reactive oxygen (ROS) and nitrogen (RNS) species. Moreover, activated neutrophils and macrophages can form extracellular traps (ETs). Fish neutrophils and macrophages are morphologically, histochemically, and functionally similar to their mammalian counterparts, but their significance for regulation of inflammatory responses and pathogen killing needs further elucidation. We compared the activity of head kidney monocytes/macrophages and neutrophilic granulocytes of common carp and established that upon lipopolysaccharide stimulation, not only neutrophils, but also carp monocytes/macrophages release extracellular DNA and are capable to form macrophage extracellular traps (METs). To clarify whether many specific LPS functions reported for piscine phagocytes might be due to impurities in the commonly used LPS preparations we studied expression of inflammatory mediators, release of DNA, ROS and RNS in cells stimulated with LPS or its highly purified form (pLPS). Also IFN-γ2 stimulation and its synergism with LPS/pLPS in stimulating expression of pro-inflammatory mediators was studied. Results substantiate that a classical stimulation of TLR4 by LPS may indeed be absent in carp as most of the classically reported LPS effects are abolished or diminished when pLPS is used. Interestingly, we also observed a potent IL-10 expression in neutrophilic granulocytes upon LPS stimulation, which, apart from their pro-inflammatory function, clearly indicates a role in restrictive control of the inflammatory reaction.

Novel integrated and portable endotoxin detection system based on an electrochemical biosensor

This paper describes the design, implementation and validation of a sensitive and integral technology solution for endotoxin detection.

Different effects of Porphyromonas gingivalis lipopolysaccharide and TLR2 agonist Pam3CSK4 on the adhesion molecules expression in endothelial cells

Recent researches suggest an association between periodontitis and cardiovascular disease. Periodontopathic bacteria and/or their component might play a role in the development of atherosclerotic lesions. In the present study, we investigated in vitro the effect of Porphyromonas gingivalis lipopolysaccharide (LPS) on the expression of adhesion molecules in human umbilical vein endothelial cells (HUVECs) as well as its effect on Escherichia coli LPS-induced response. The effect of P. gingivalis LPS was compared with that of toll-like receptor 2 agonist synthetic triacylated lipoprotein Pam3-Cys-Ser-(Lys)4 (Pam3CSK4). Gene and protein expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin were measured using RT-PCR and flow cytometry, respectively. P. gingivalis LPS stimulated the expression levels of all adhesion molecules in a dose-dependent manner. However, the response of HUVECs to P. gingivalis LPS was markedly lower than that to E. coli LPS. Moreover, P. gingivalis LPS attenuated E. coli LPS-induced responses when HUVECs were simultaneously stimulated with both kinds of LPS. Treatment with Pam3CSK4 resulted in a minor increase of adhesion molecule expression and did not diminish E. coli LPS-induced responses. Our data suggest that P. gingivalis LPS induces in vitro the expression of adhesion molecules in endothelial cells, which might promote atherogenesis. Qualitatively different responses of HUVECs to P. gingivalis LPS and Pam3CSK4 suggest that besides TLR2 other signaling pathways might be involved in the effects of P. gingivalis LPS.

Alteration in immune responses toward N-deacetylation of hyaluronic acid

Hyaluronic acid (HA) is an ubiquitous nonsulfated glycosaminoglycan of the extracellular matrix in all mammalian connective tissues. Along with the age growth, HA will lose its N-acetyl groups in vivo; however, the significance of this physiological process remains largely unknown. Herein, three highly N-deacetylated HAs (dHAs), dHA-5 kDa (Mw: 5 kDa, DD: 100%), dHA-16 kDa (Mw: 16 kDa, DD: 94%) and dHA-110 kDa (Mw: 110 kDa, DD: 72%), were generated after hydrazinolysis. Their capability in the activation of antigen-presenting cells (APCs) was compared with that of their respective HAs. Our results demonstrated that both HAs and dHAs could activate the nuclear factor-kappa B (NF-κB) transcription factor in APCs and induced cytokine production through the Toll-like receptor (TLR)/MyD88 pathway. Notably, the capacity of dHAs in cytokine induction was much lower than that of HAs. In addition, the TLR-2 pathway was much involved following the appearance of zwitterionic motifs in dHAs. Thus, our findings highlight that N-deacetylation renders HA divergences in immune response, which might be implicated in age-induced functional change in endogenous glycosaminoglycans due to the structural modification in vivo.

EPA and DHA exposure alters the inflammatory response but not the surface expression of Toll-like receptor 4 in macrophages

Dietary intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and their respective enrichment in cell membranes have been negatively associated with atherosclerotic lesion development. This effect may be mediated, in part, by dampened inflammatory response of macrophages triggered by toll-like receptor 4 (TLR4) activation. This study investigated the influence of membrane fatty acid profile on TLR4-mediated inflammation in RAW 264.7 macrophages. Cells pretreated with myristic acid (MA), EPA, DHA or vehicle control for 24 h were stimulated with ultra-pure LPS, a specific TLR4 agonist, for 6 or 24 h, corresponding to early and late stages of TNFα and IL-6 protein induction. Treatment significantly increased cell membrane MA, EPA, and DHA by 4.5-, 20.6-, and 8.9-fold, respectively. MA significantly increased IL-6 secretion 6 h post-exposure to the fatty acid, but did not change TNFα secretion in response to any other treatment condition. EPA and DHA significantly reduced TNFα secretion by 36 and 41 %, respectively, in cells stimulated for 24 h but not 6 h. In contrast, EPA and DHA significantly reduced IL-6 secretion at both 6 h (67 and 72%, respectively) and 24 h (69 and 72%, respectively). MA or DHA treatment had no significant effect compared to vehicle on factors influencing cellular LPS recognition, including LPS-cell association, and cell surface expression of TLR4, TLR4-MD2 complex, and CD14. These data suggest that membrane fatty acid profiles influence the TLR4-mediated inflammatory response in macrophages, via mechanisms that occur downstream of TLR4 receptor activation.

TLR-2 and TLR-4 expression in monocytes of newborns with late-onset sepsis

OBJECTIVE

To analyze toll-like receptor (TLR)-2 and TLR-4 expression in monocytes of newborns with late-onset sepsis.

METHODS

This prospective study included 27 full-term newborns aged 8 to 29 days, with clinical and laboratory diagnosis of late-onset sepsis. Ten newborns (37%) had positive cultures. Cytokines were measured by cytometric bead array in peripheral blood, while TLR-2, TLR-4 expression, and median fluorescence intensity (MFI) were determined by immunophenotyping peripheral whole blood monocytes, and were analyzed with a BD FACSDiva flow cytometer (Becton, Dickinson and Company, USA). A comparison was performed with healthy adults.

RESULTS

Microorganisms were identified in 37% of these septic newborns, and all of them had high levels of pro-inflammatory cytokines (IL-8, IL-6, IL-1β) and anti-inflammatory cytokine (IL-10) corroborating the inflammatory/septic process. In monocytes, the frequency of TLR-4 expression was higher in infected newborns (p = 0.01).

CONCLUSION

This study investigated the innate immune response in septic newborns. Septic newborns that relied almost exclusively on the innate immune system showed little in vivo response at monocyte activation, suggesting impaired immune response and increased susceptibility to infection.

Location-specific expression of chemokines, TNF-α and S100 proteins in a teat explant model

The distal compartments of the udder are the first to interact with invading pathogens. The regulatory and effector functions of two major teat regions [Fürstenberg's rosette (FR); teat cistern (TC)] are largely unknown. The objective of this study was to establish an in vitro model with explants of the FR and the TC to analyse their response towards Escherichia coli LPS and Staphylococcus aureus lipoteichoic acid (LTA). Quantitative stereological analysis confirmed differences in the cellular composition of FR and TC explants. Chemokine (CXCL8, CCL5, CCL20) and TNF-α mRNA were expressed at low levels in both locations. Explant stimulation with LPS increased the mRNA abundance of all tested chemokines and TNF-α. Stimulation with LTA only induced CCL20 and CXCL8. LPS- and LTA-stimulated explant supernatants contained CXCL8 and CXCL3. Supernatants significantly attracted neutrophils in vitro. Compared with TC, the FR showed high constitutive mRNA expression of S100 proteins (A8, A9, A12). In the TC, both LPS and LTA significantly induced S100A8, whereas S100A9 and S100A12 expression was only induced by LPS. The novel model system underpins the role of the teat for recognising pathogens and shaping a pathogen- and location-specific immune response.

Recognition of LPS by TLR4: potential for anti-inflammatory therapies

LPS molecules of marine bacteria show structures distinct from terrestrial bacteria, due to the different environment that marine bacteria live in. Because of these different structures, lipid A molecules from marine bacteria are most often poor stimulators of the Toll-like receptor 4 (TLR4) pathway. Due to their low stimulatory potential, these lipid A molecules are suggested to be applicable as antagonists of TLR4 signaling in sepsis patients, where this immune response is amplified and unregulated. Antagonizing lipid A molecules might be used for future therapies against sepsis, therapies that currently do not exist. In this review, we will discuss these differences in lipid A structures and their recognition by the immune system. The modifications present in marine lipid A structures are described, and their potential as LPS antagonists will be discussed. Finally, since clinical trials built on antagonizing lipid A molecules have proven unsuccessful, we propose to also focus on different aspects of the TLR4 signaling pathway when searching for new potential drugs. Furthermore, we put forward the notion that bacteria probably already produce inhibitors of TLR4 signaling, making these bacterial products interesting molecules to investigate for future sepsis therapies.

Hygienic grooming is induced by contact chemicals in Drosophila melanogaster

In social insects, grooming is considered as a behavioral defense against pathogen and parasite infections since it contributes to remove microbes from their cuticle. However, stimuli which trigger this behavior are not well characterized yet. We examined if activating contact chemoreceptive sensilla could trigger grooming activities in Drosophila melanogaster. We monitored the grooming responses of decapitated flies to compounds known to activate the immune system, e.g., dead Escherichia coli (Ec) and lipopolysaccharides (LPS), and to tastants such as quinine, sucrose, and salt. LPS, quinine, and Ec were quite effective in triggering grooming movements when touching the distal border of the wings and the legs, while sucrose had no effect. Contact chemoreceptors are necessary and sufficient to elicit such responses, as grooming could not be elicited by LPS in poxn mutants deprived of external taste sensilla, and as grooming was elicited by light when a channel rhodopsin receptor was expressed in bitter-sensitive cells expressing Gr33a. Contact chemoreceptors distributed along the distal border of the wings respond to these tastants by an increased spiking activity, in response to quinine, Ec, LPS, sucrose, and KCl. These results demonstrate for the first time that bacterial compounds trigger grooming activities in D. melanogaster, and indicate that contact chemoreceptors located on the wings participate in the detection of such chemicals.

Porphyromonas gingivalis lipopolysaccharide weakly activates M1 and M2 polarized mouse macrophages but induces inflammatory cytokines

Porphyromonas gingivalis is associated with chronic periodontitis, an inflammatory disease of the tooth's supporting tissues. Macrophages are important in chronic inflammatory conditions, infiltrating tissue and becoming polarized to an M1 or M2 phenotype. As responses to stimuli differ between these phenotypes, we investigated the effect of P. gingivalis lipopolysaccharide (LPS) on M1 and M2 macrophages. M1 and M2 polarized macrophages were produced from murine bone marrow macrophages (BMMϕ) primed with gamma interferon (IFN-γ) or interleukin-4 (IL-4), respectively, and incubated with a low or high dose of P. gingivalis LPS or control TLR2 and TLR4 ligands. In M1-Mϕ, the high dose of P. gingivalis LPS (10 μg/ml) significantly increased the expression of CD40, CD86, inducible nitric oxide synthase, and nitric oxide secretion. The low dose of P. gingivalis LPS (10 ng/ml) did not induce costimulatory or antibacterial molecules but did increase the secretion of IL-1α, IL-6, IL-12p40, IL-12p70, and tumor necrosis factor alpha (TNF-α). P. gingivalis LPS marginally increased the expression of CD206 and YM-1, but it did enhance arginase expression by M2-Mϕ. Furthermore, the secretion of the chemokines KC, RANTES, eotaxin, and MCP-1 from M1, M2, and nonpolarized Mϕ was enhanced by P. gingivalis LPS. TLR2/4 knockout macrophages combined with the TLR activation assays indicated that TLR2 is the main activating receptor for P. gingivalis LPS and whole cells. In conclusion, although P. gingivalis LPS weakly activated M1-Mϕ or M2-Mϕ compared to control TLR ligands, it induced the secretion of inflammatory cytokines, particularly TNF-α from M1-Mϕ and IL-10 from M2-Mϕ, as well as chemotactic chemokines from polarized macrophages.

Toll-like receptor 4 activation in Barrett's esophagus results in a strong increase in COX-2 expression

BACKGROUND

Barrett's esophagus (BE) is known to progress to esophageal adenocarcinoma in a setting of chronic inflammation. Toll-like receptor (TLR) 4 has been linked to inflammation-associated carcinogenesis. We aimed to determine the expression and functional activity of TLR4 in the esophagus and whether TLR4 activation in BE could promote carcinogenesis by inducing COX-2 expression.

METHODS

TLR4 expression in esophageal adenocarcinoma, BE, duodenum, reflux esophagitis and normal squamous esophagus biopsies was assessed using real-time PCR and validated by in situ hybridization and immunohistochemistry. Ex vivo cultures of BE, duodenum and normal squamous esophagus biopsies and a BE cell line (BAR-T) were stimulated with the TLR4 agonist lipopolysaccharide (LPS). To evaluate the effect of TLR4 activation, NF-κB activation, IL8 secretion and expression and COX-2 expression were determined.

RESULTS

TLR4 expression was significantly increased in esophageal adenocarcinoma, BE, duodenum and reflux esophagitis compared to normal squamous esophagus. LPS stimulation resulted in NF-κB activation and a dose-dependent increase of IL8 secretion and mRNA expression. The induction of IL8 was more evident in BE compared to normal squamous esophagus. Upon LPS stimulation, COX-2 expression increased significantly in ex vivo cultured BE biopsies, which was observed in both epithelium and lamina propria cells. However, no effect was found in duodenum and normal squamous esophagus biopsies.

CONCLUSION

TLR4 activation in BE results in a strong increase in COX-2 and may contribute to malignant transformation.

Different effects of P. gingivalis LPS and E. coli LPS on the expression of interleukin-6 in human gingival fibroblasts

OBJECTIVE

Gingival fibroblasts (GFs) produce pro-inflammatory cytokines in response to stimulation with lipopolysaccharide (LPS) of Porphyromonas gingivalis, which is thought to be mediated by activation of toll-like receptors (TLR)2 and TLR4. The present study investigated the expression of interleukin (IL)-6, TLR2, and TLR4 in GFs of seven different donors upon stimulation with P. gingivalis LPS. The effects of P. gingivalis LPS were compared with those of TLR4 agonist Escherichia coli LPS and TLR2 agonist Pam3CSK4.

MATERIALS AND METHODS

GFs were stimulated with P. gingivalis LPS, E. coli LPS or Pam3CSK4 and the expression of IL-6, TLR2 and TLR4 was measured by qPCR. The surface expression of TLR2 and TLR4 was measured by flow cytometry.

RESULTS

In GFs from three donors, P. gingivalis LPS and Pam3CSK4 induced a markedly lower increase in IL-6 expression than E. coli LPS. This was accompanied by significant down-regulation of the TLR2 and TLR4 expression. In GFs from another four donors, an increase in IL-6 expression upon stimulation with P. gingivalis LPS and Pam3CSK4 was similar or even higher than that induced by E. coli LPS. In GFs of these donors, all stimuli induced an up-regulation of both mRNA and protein expression of TLR2 and did not influence that of TLR4.

CONCLUSIONS

This study suggests that P. gingivalis LPS and E. coli LPS differently regulate cytokine production in human gingival fibroblasts. Regulation of the expression level of TLR2 and TLR4 by periodontal pathogens might be an important factor controlling the inflammatory response in GFs.

Sialic acid rescues repurified lipopolysaccharide-induced acute renal failure via inhibiting TLR4/PKC/gp91-mediated endoplasmic reticulum stress, apoptosis, autophagy, and pyroptosis signaling

Lipopolysaccharides (LPS) through Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4) activation induce systemic inflammation where oxidative damage plays a key role in multiple organ failure. Because of the neutralization of LPS toxicity by sialic acid (SA), we determined its effect and mechanisms on repurified LPS (rLPS)-evoked acute renal failure. We assessed the effect of intravenous SA (10 mg/kg body weight) on rLPS-induced renal injury in female Wistar rats by evaluating blood and kidney reactive oxygen species (ROS) responses, renal and systemic hemodynamics, renal function, histopathology, and molecular mechanisms. SA can interact with rLPS through a high binding affinity. rLPS dose- and time-dependently reduced arterial blood pressure, renal microcirculation and blood flow, and increased vascular resistance in the rats. rLPS enhanced monocyte/macrophage (ED-1) infiltration and ROS production and impaired kidneys by triggering p-IRE1α/p-JNK/CHOP/GRP78/ATF4-mediated endoplasmic reticulum (ER) stress, Bax/PARP-mediated apoptosis, Beclin-1/Atg5-Atg12/LC3-II-mediated autophagy, and caspase 1/IL-1β-mediated pyroptosis in the kidneys. SA treatment at 30 min, but not 60 min after rLPS stimulation, gp91 siRNA and protein kinase C-α (PKC) inhibitor efficiently rescued rLPS-induced acute renal failure via inhibition of TLR4/PKC/NADPH oxidase gp91-mediated ER stress, apoptosis, autophagy and pyroptosis in renal proximal tubular cells, and rat kidneys. In response to rLPS or IFNγ, the enhanced Atg5, FADD, LC3-II, and PARP expression can be inhibited by Atg5 siRNA. Albumin (10 mg/kg body weight) did not rescue rLPS-induced injury. In conclusion, early treatment (within 30 min) of SA attenuates rLPS-induced renal failure via the reduction in LPS toxicity and subsequently inhibiting rLPS-activated TLR4/PKC/gp91/ER stress/apoptosis/autophagy/pyroptosis signaling.

A Murine Model of Lipopolysaccharide-Induced Peri-Implant Mucositis and Peri-Implantitis

Dental implants are a widely used treatment option for tooth replacement. However, they are susceptible to inflammatory diseases such as peri-implant mucositis and peri-implantitis, which are highly prevalent and may lead to implant loss. Unfortunately, the understanding of the pathogenesis of peri-implant mucositis and peri-implantitis is fragmented and incomplete. Therefore, the availability of a reproducible animal model to study these inflammatory diseases would facilitate the dissection of their pathogenic mechanisms. The objective of this study is to propose a murine model of experimental peri-implant mucositis and peri-implantitis. Screw-shaped titanium implants were placed in the upper healed edentulous alveolar ridges of C57BL/6J mice 8 weeks after tooth extraction. Following 4 weeks of osseointegration, Porphyromonas gingivalis -lipolysaccharide (LPS) injections were delivered to the peri-implant soft tissues for 6 weeks. No-injections and vehicle injections were utilized as controls. Peri-implant mucositis and peri-implantitis were assessed clinically, radiographically (microcomputerized tomograph [CT]), and histologically following LPS-treatment. LPS-injections resulted in a significant increase in soft tissue edema around the head of the implants as compared to the control groups. Micro-CT analysis revealed significantly greater bone loss in the LPS-treated implants. Histological analysis of the specimens demonstrated that the LPS-group had increased soft tissue vascularity, which harbored a dense mixed inflammatory cell infiltrate, and the bone exhibited noticeable osteoclast activity. The induction of peri-implant mucositis and peri-implantitis in mice via localized delivery of bacterial LPS has been demonstrated. We anticipate that this model will contribute to the development of more effective preventive and therapeutic approaches for these 2 conditions.

Innate immunity networks during infection with Borrelia burgdorferi

The recognition of Borrelia species represents a complex process in which multiple components of the immune system are involved. In this review, we summarize the interplay between the host innate system and Borrelia spp., from the recognition by pattern recognition receptors (PRRs) to the induction of a complex network of proinflammatory mediators. Several PRR families are crucial for recognition of Borrelia spp., including Toll-like receptors (TLRs) and Nucleotide Oligomerization Domain (NOD)-like receptors (NLRs). TLR-2 is crucial for the recognition of outer surface protein (Osp)A from Borrelia spp. and together with TLR8 mediates phagocytosis of the microorganism and production of type I interferons. Intracellular receptors such as TLR7, TLR8 and TLR9 on the one hand and the NLR receptor NOD2 on the other hand, represent the second major recognition system of Borrelia. PRR-dependent signals induce the release of pro-inflammatory cytokines such as interleukin-1 and T-helper-derived cytokines, which are thought to mediate the inflammation during Lyme disease. Understanding the regulation of host defense mechanisms against Borrelia has the potential to lead to the discovery of novel immunotherapeutic targets to improve the therapy against Lyme disease.

The immunobiology of toll-like receptor 4 agonists: from endotoxin tolerance to immunoadjuvants

Lipopolysaccharide (LPS, endotoxin) is a structural component of the gram-negative outer membrane. The lipid A moiety of LPS binds to the LPS receptor complex expressed by leukocytes, endothelial cells, and parenchymal cells and is the primary component of gram-negative bacteria that is recognized by the immune system. Activation of the LPS receptor complex by native lipid A induces robust cytokine production, leukocyte activation, and inflammation, which is beneficial for clearing bacterial infections at the local level but can cause severe systemic inflammation and shock at higher challenge doses. Interestingly, prior exposure to LPS renders the host resistant to shock caused by subsequent LPS challenge, a phenomenon known as endotoxin tolerance. Treatment with lipid A has also been shown to augment the host response to infection and to serve as a potent vaccine adjuvant. However, the adverse effects associated with the pronounced inflammatory response limit the use of native lipid A as a clinical immunomodulator. More recently, analogs of lipid A have been developed that possess attenuated proinflammatory activity but retain attractive immunomodulatory properties. The lipid A analog monophosphoryl lipid A exhibits approximately 1/1,000th of the toxicity of native lipid A but retains potent immunoadjuvant activity. As such, monophosphoryl lipid A is currently used as an adjuvant in several human vaccine preparations. Because of the potency of lipid A analogs as immunoadjuvants, numerous laboratories are actively working to identify and develop new lipid A mimetics and to optimize their efficacy and safety. Based on those characteristics, lipid A analogs represent an attractive family of immunomodulators.

I-BET151 selectively regulates IL-6 production

Orchestration of the inflammatory response is crucial for clearing pathogens. Although the production of multiple inflammatory cytokines has been thought to be regulated by common mechanisms, recent evidence indicates that the expression of some cytokines is differentially regulated by epigenetic regulatory mechanisms. In this study, we found that IL-6 production is selectively inhibited by the BET bromodomain protein (BRD) inhibitor I-BET151 in RAW264.7 cells stimulated with lipopolysaccharide (LPS), whereas I-BET151 did not alter the production of several other cytokines (TNFα, IL-1β and IL-10) at the concentration of IBET151 used. I-BET151 prevented the binding of CBP to the promoter of IL-6, but I-BET151 did not affect acetylation, phosphorylation, nuclear translocation, or DNA binding of p65-NF-κB. In vivo, I-BET151 treatment in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis decreased the early clinical symptoms, which are thought to be dependent on cytokine production. Altogether, these data suggest that targeting epigenetic-related proteins, such as BET proteins, may provide a strategy to reduce inflammation and the severity of inflammatory diseases, such as multiple sclerosis.

Spectrum and mechanisms of inflammasome activation by chitosan

Chitosan, the deacetylated derivative of chitin, can be found in the cell wall of some fungi and is used in translational applications. We have shown that highly purified preparations of chitosan, but not chitin, activate the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in primed mouse bone marrow-derived macrophages (BMMΦ), inducing a robust IL-1β response. In this article, we further define specific cell types that are activated and delineate mechanisms of activation. BMMΦ differentiated to promote a classically activated (M1) phenotype released more IL-1β in response to chitosan than intermediate or alternatively activated macrophages (M2). Chitosan, but not chitin, induced a robust IL-1β response in mouse dendritic cells, peritoneal macrophages, and human PBMCs. Three mechanisms for NLRP3 inflammasome activation may contribute: K(+) efflux, reactive oxygen species, and lysosomal destabilization. The contributions of these mechanisms were tested using a K(+) efflux inhibitor, high extracellular potassium, a mitochondrial reactive oxygen species inhibitor, lysosomal acidification inhibitors, and a cathepsin B inhibitor. These studies revealed that each of these pathways participated in optimal NLRP3 inflammasome activation by chitosan. Finally, neither chitosan nor chitin stimulated significant release from unprimed BMMΦ of any of 22 cytokines and chemokines assayed. This study has the following conclusions: 1) chitosan, but not chitin, stimulates IL-1β release from multiple murine and human cell types; 2) multiple nonredundant mechanisms appear to participate in inflammasome activation by chitosan; and 3) chitin and chitosan are relatively weak stimulators of inflammatory mediators from unprimed BMMΦ. These data have implications for understanding the nature of the immune response to microbes and biomaterials that contain chitin and chitosan.

The TLR signaling adaptor TRAM interacts with TRAF6 to mediate activation of the inflammatory response by TLR4

TLRs act as sentinels in professional immune cells to detect and initiate the innate immune response to pathogen challenge. TLR4 is a widely expressed TLR, responsible for initiating potent immune responses to LPS. TRAM acts to bridge TLR4 with TRIF, orchestrating the inflammatory response to pathogen challenge. We have identified a putative TRAF6-binding motif in TRAM that could mediate a novel signaling function for TRAM in TLR4 signaling. TRAM and TRAF6 association was confirmed by immunoprecipitation of endogenous, ectopically expressed and recombinant proteins, which was ablated upon mutation of a key Glu residue in TRAM (TRAM E183A). TRAF6 and TRAM were observed colocalizing using confocal microscopy following ectopic expression in cells and the ability of TRAM and TRAM E183A to activate luciferase-linked reporter assays was determined in HEK293 and TRAF6-deficient cells. Importantly, TRAM-deficient macrophages reconstituted with TRAM E183A display significantly reduced inflammatory TNF-α, IL-6, and RANTES protein production compared with WT TRAM. These results demonstrate a novel role for TRAM in TLR4-mediated signaling in regulating inflammatory responses via its interaction with TRAF6, distinct from its role as a bridging adaptor between TLR4 and TRIF.

Soluble IFN receptor potentiates in vivo type I IFN signaling and exacerbates TLR4-mediated septic shock

Circulating levels of a soluble type I IFNR are elevated in diseases, such as chronic inflammation, infections, and cancer, but whether it functions as an antagonist, agonist, or transporter is unknown. In this study, we elucidate the in vivo importance of the soluble type I IFNAR, soluble (s)IFNAR2a, which is generated by alternative splicing of the Ifnar2 gene. A transgenic mouse model was established to mimic the 10-15-fold elevated expression of sIFNAR2a observed in some human diseases. We generated transgenic mouse lines, designated SolOX, in which the transgene mRNA and protein-expression patterns mirrored the expression patterns of the endogenous gene. SolOX were demonstrated to be more susceptible to LPS-mediated septic shock, a disease model in which type I IFN plays a crucial role. This effect was independent of "classical" proinflammatory cytokines, such as TNF-α and IL-6, whose levels were unchanged. Because the increased levels of sIFNAR2a did not affect the kinetics of the increased interferonemia, this soluble receptor does not potentiate its ligand signaling by improving IFN pharmacokinetics. Mechanistically, increased levels of sIFNAR2a are likely to facilitate IFN signaling, as demonstrated in spleen cells overexpressing sIFNAR2a, which displayed quicker, higher, and more sustained activation of STAT1 and STAT3. Thus, the soluble IFNR is an important agonist of endogenous IFN actions in pathophysiological processes and also is likely to modulate the therapeutic efficacy of clinically administered IFNs.

Understanding the mechanisms controlling Leishmania amazonensis infection in vitro: the role of LTB4 derived from human neutrophils

Neutrophils are rapidly recruited to the site of Leishmania infection and play an active role in capturing and killing parasites. They are the main source of leukotriene B₄ (LTB₄), a potent proinflammatory lipid mediator. However, the role of LTB₄ in neutrophil infection by Leishmania amazonensis is not clear. In this study, we show that L. amazonensis or its lipophosphoglycan can induce neutrophil activation, degranulation, and LTB₄ production. Using pharmacological inhibitors of leukotriene synthesis, our findings reveal an LTB₄-driven autocrine/paracrine regulatory effect. In particular, neutrophil-derived LTB₄ controls L. amazonensis killing, degranulation, and reactive oxygen species production. In addition, L. amazonensis infection induces an early increase in Toll-like receptor 2 expression, which facilitates parasite internalization. Nuclear factor kappa B (NFkB) pathway activation represents a required upstream event for L. amazonensis–induced LTB₄ synthesis. These leishmanicidal mechanisms mediated by neutrophil-derived LTB₄ act through activation of its receptor, B leukotriene receptor 1 (BLT1).

Trained immunity or tolerance: opposing functional programs induced in human monocytes after engagement of various pattern recognition receptors

Upon priming with Candida albicans or with the fungal cell wall component β-glucan, monocytes respond with an increased cytokine production upon restimulation, a phenomenon termed "trained immunity." In contrast, the prestimulation of monocytes with lipopolysaccharide has long been known to induce tolerance. Because the vast majority of commensal microorganisms belong to bacterial or viral phyla, we sought to systematically investigate the functional reprogramming of monocytes induced by the stimulation of pattern recognition receptors (PRRs) with various bacterial or viral ligands. Monocytes were functionally programmed for either enhanced (training) or decreased (tolerance) cytokine production, depending on the type and concentration of ligand they encountered. The functional reprogramming of monocytes was also associated with cell shape, granulocity, and cell surface marker modifications. The training effect required p38- and Jun N-terminal protein kinase (JNK)-mediated mitogen-activated protein kinase (MAPK) signaling, with specific signaling patterns directing the functional fate of the cell. The long-term effects on the function of monocytes were mediated by epigenetic events, with both histone methylation and acetylation inhibitors blocking the training effects. In conclusion, our experiments identify the ability of monocytes to acquire adaptive characteristics after prior activation with a wide variety of ligands. Trained immunity and tolerance are two distinct and opposing functional programs induced by the specific microbial ligands engaging the monocytes.

Astrocytes modulate the polarization of CD4+ T cells to Th1 cells

T-cell characteristics are dynamic and influenced by multiple factors. To test whether cells and the environment in the central nervous system (CNS) can influence T-cells, we tested if culturing mouse CD4⁺ T-cells on mouse primary astrocytes, compared with standard feeder cells, modified T-cell polarization to Th1 and Treg subtypes. Astrocytes supported the production of Th1 cells and Tregs, which was diminished by inflammatory activation of astrocytes, and glutamate accumulation that may result from impaired glutamate uptake by astrocytes strongly promoted Th1 production. These results demonstrate that astrocytes and the environment in the CNS have the capacity to regulate T-cell characteristics.

Regulated assembly of vacuolar ATPase is increased during cluster disruption-induced maturation of dendritic cells through a phosphatidylinositol 3-kinase/mTOR-dependent pathway

The vacuolar (H(+))-ATPases (V-ATPases) are ATP-driven proton pumps composed of a peripheral V1 domain and a membrane-embedded V0 domain. Regulated assembly of V1 and V0 represents an important regulatory mechanism for controlling V-ATPase activity in vivo. Previous work has shown that V-ATPase assembly increases during maturation of bone marrow-derived dendritic cells induced by activation of Toll-like receptors. This increased assembly is essential for antigen processing, which is dependent upon an acidic lysosomal pH. Cluster disruption of dendritic cells induces a semi-mature phenotype associated with immune tolerance. Thus, semi-mature dendritic cells are able to process and present self-peptides to suppress autoimmune responses. We have investigated V-ATPase assembly in bone marrow-derived, murine dendritic cells and observed an increase in assembly following cluster disruption. This increased assembly is not dependent upon new protein synthesis and is associated with an increase in concanamycin A-sensitive proton transport in FITC-loaded lysosomes. Inhibition of phosphatidylinositol 3-kinase with wortmannin or mTORC1 with rapamycin effectively inhibits the increased assembly observed upon cluster disruption. These results suggest that the phosphatidylinositol 3-kinase/mTOR pathway is involved in controlling V-ATPase assembly during dendritic cell maturation.

Targeting dexamethasone to macrophages in a porcine endotoxemic model

OBJECTIVES

Macrophages are important cells in immunity and the main producers of pro-inflammatory cytokines. The main objective was to evaluate if specific delivery of glucocorticoid to the macrophage receptor CD163 is superior to systemic glucocorticoid therapy in dampening the cytokine response to lipopolysaccharide infusion in pigs.

DESIGN

Two randomized, placebo-controlled trials.

SETTING

University hospital laboratory.

SUBJECTS

Female farm-bred pigs (26-31 kg).

DESIGN

A humanized antibody that binds to pig and human CD163 was produced, characterized, and conjugated with dexamethasone. In the first study (total n = 12), pigs were randomly assigned to four groups: 1) saline; 2) dexamethasone (1.0 mg/kg); 3) dexamethasone (0.02 mg/kg); and 4) anti-CD163-conjugated dexamethasone (0.02 mg/kg). In the second study (total n = 36), two additional groups were included in addition to the four original groups: 5) anti-CD163-conjugated dexamethasone (0.005 mg/kg); 6) unconjugated anti-CD163. Treatments were given 20 hours prior to infusion of lipopolysaccharide (1 µg × kg × h) for 5 hours. Blood samples were analyzed for cytokines, cortisol, and adrenocorticotropic hormone.

RESULTS

In the saline group, lipopolysaccharide increased cytokine and plasma cortisol levels. In both studies, dexamethasone (1 mg/kg) and anti-CD163 dexamethasone (0.02 mg/kg) uniformly attenuated tumor necrosis factor-α peak levels (both p < 0.05) compared with low-dose dexamethasone (0.02 mg/kg). However, dexamethasone 1 mg/kg significantly suppressed plasma cortisol and adrenocorticotropic hormone levels compared with anti-CD163 dexamethasone (0.02 mg/kg; p < 0.05). No significant hemodynamic difference existed between groups. The anti-CD163 dexamethasone drug conjugate exhibited a fast plasma clearance, with a half-life of approximately 5-8 minutes.

CONCLUSION

Targeted delivery of dexamethasone to macrophages using a humanized CD163 antibody as carrier exhibits anti-inflammatory effects comparable with 50 times higher concentrations of free dexamethasone and does not inhibit endogenous cortisol production. This antibody-drug complex showing similar affinity and specificity for human CD163 is, therefore, a promising drug candidate in this novel type of anti-inflammatory therapy.

Dietary strawberries increase the proliferative response of CD3/CD28-activated CD8⁺ T cells and the production of TNF-α in lipopolysaccharide-stimulated monocytes from obese human subjects

Obesity increases the risk of developing bacterial and viral infections compared with normal weight. In a 7-week double-blind, randomised, cross-over trial, twenty obese volunteers (BMI between 30 and 40 kg/m²) were fed freeze-dried strawberry powder or strawberry-flavoured placebo preparations to determine the effects of dietary strawberries on immune function. Blood was collected at six time points during the study and peripheral blood mononuclear cells (PBMC) were isolated at each time point and activated with CD3 plus CD28 antibodies (T-lymphocyte activation) or lipopolysaccharide (LPS, monocyte activation). Interferon-γ, TNF-α, IL-4 and IL-10 were measured in supernatants from the activated T cells. Supernatants from the activated monocytes were analysed for the production of TNF-α, IL-1β, IL-6 and IL-8. PBMC were pre-stained with PKH (Paul Karl Horan) dye and activated with CD3 plus CD28 antibodies to determine the proliferative responses of CD4⁺ and CD8⁺ T-lymphocytes by flow cytometry. To detect global changes in gene expression, microarray analysis was performed on LPS- and vehicle-treated PBMC from two subjects before and after the strawberry intervention. No difference was observed for the production of T-cell cytokines between the intervention groups. The production of TNF-α was increased in the supernatants from LPS-activated PBMC in the group consuming strawberries compared with the placebo. A modest increase in the proliferation of the CD8⁺ T-lymphocyte population was observed at 24 h post-activation. These data suggest that dietary strawberries may increase the immunological response of T-lymphocytes and monocytes in obese people who are at greater risk for developing infections.

Survey of innate immune responses to Burkholderia pseudomallei in human blood identifies a central role for lipopolysaccharide

B. pseudomallei is a gram-negative bacterium that causes the tropical infection melioidosis. In northeast Thailand, mortality from melioidosis approaches 40%. As exemplified by the lipopolysaccharide-Toll-like receptor 4 interaction, innate immune responses to invading bacteria are precipitated by activation of host pathogen recognition receptors by pathogen associated molecular patterns. Human melioidosis is characterized by up-regulation of pathogen recognition receptors and pro-inflammatory cytokine release. In contrast to many gram-negative pathogens, however, the lipopolysaccharide of B. pseudomallei is considered only weakly inflammatory. We conducted a study in 300 healthy Thai subjects to investigate the ex vivo human blood response to various bacterial pathogen associated molecular patterns, including lipopolysaccharide from several bacteria, and to two heat-killed B. pseudomallei isolates. We measured cytokine levels after stimulation of fresh whole blood with a panel of stimuli. We found that age, sex, and white blood cell count modulate the innate immune response to B. pseudomallei. We further observed that, in comparison to other stimuli, the innate immune response to B. pseudomallei is most highly correlated with the response to lipopolysaccharide. The magnitude of cytokine responses induced by B. pseudomallei lipopolysaccharide was significantly greater than those induced by lipopolysaccharide from Escherichia coli and comparable to many responses induced by lipopolysaccharide from Salmonella minnesota despite lower amounts of lipid A in the B. pseudomallei lipopolysaccharide preparation. In human monocytes stimulated with B. pseudomallei, addition of polymyxin B or a TLR4/MD-2 neutralizing antibody inhibited the majority of TNF-α production. Challenging existing views, our data indicate that the innate immune response to B. pseudomallei in human blood is largely driven by lipopolysaccharide, and that the response to B. pseudomallei lipopolysaccharide in blood is greater than the response to other lipopolysaccharide expressing isolates. Our findings suggest that B. pseudomallei lipopolysaccharide may play a central role in stimulating the host response in melioidosis.

Nitric oxide production by endotoxin preparations in TLR4-deficient mice

Sepsis and septic shock result from an exacerbated systemic inflammatory reaction to infection. Their incidence is rising, and they have recently become the main cause of death in intensive care units. Septic shock is defined as sepsis accompanied by life-threatening refractory hypotension, for which excessive nitric oxide (NO), produced by inducible NO synthase iNOS, is thought responsible. LPS, a vital outer membrane component of Gram-negative bacteria, mimics most of the septic effects and is widely used as a model for septic shock. TLR4 is the signal-transducing receptor for LPS, evidenced by the resistance of TLR4-deficient C3H/HeJ and C57BL/10ScNJ mice. As expected, we found that TLR4 deficiency precludes LPS-induced cytokine production, independent of the purity of the LPS preparation. However, various conventional LPS preparations induced NO in TLR4-deficient mice to the same level as in control animals, while ultrapure LPS did not, indicating the presence of NO-producing contaminant(s). Nevertheless, despite identical iNOS induction pattern and systemic NO levels, the contaminant does not cause hypotension, hypothermia, or any other sign of morbidity. Using mice deficient for TLR2, TRL3, TLR4, TRL2x4, TLR9, MyD88 or TRIF, we found that the contaminant signals via TLR2 and MyD88. In conclusion, conventional LPS preparations generally used in endotoxic shock research contain TLR2 agonists that induce iNOS and high levels of systemic NO as such, and synergize with LPS towards the production of pro-inflammatory cytokines, morbidity and mortality. Surprisingly, the excessive iNOS-derived systemic NO production induced by impure LPS in TLR4⁻/⁻ is not accompanied by hypotension or morbidity.

Properties and prospects of adjuvants in influenza vaccination - messy precipitates or blessed opportunities?

Influenza is a major challenge to healthcare systems world-wide. While prophylactic vaccination is largely efficient, long-lasting immunity has not been achieved in immunized populations, at least in part due to the challenges arising from the antigen variation between strains of influenza A virus as a consequence of genetic drift and shift. From progress in our understanding of the immune system, the mode-of-action of vaccines can be divided into the stimulation of the adaptive system through inclusion of appropriate vaccine antigens and of the innate immune system by the addition of adjuvant to the vaccine formulation. A shared property of many vaccine adjuvants is found in their nature of water-insoluble precipitates, for instance the particulate material made from aluminum salts. Previously, it was thought that embedding of vaccine antigens in these materials provided a "depot" of antigens enabling a long exposure of the immune system to the antigen. However, more recent work points to a role of particulate adjuvants in stimulating cellular parts of the innate immune system. Here, we briefly outline the infectious medicine and immune biology of influenza virus infection and procedures to provide sufficient and stably available amounts of vaccine antigen. This is followed by presentation of the many roles of adjuvants, which involve humoral factors of innate immunity, notably complement. In a perspective of the ultrastructural properties of these humoral factors, it becomes possible to rationalize why these insoluble precipitates or emulsions are such a provocation of the immune system. We propose that the biophysics of particulate material may hold opportunities that could aid the development of more efficient influenza vaccines.

Pulmonary surfactant protein A-induced changes in the molecular conformation of bacterial deep-rough LPS lead to reduced activity on human macrophages

The lung is constantly exposed to immune stimulation by LPS from inhaled microorganisms. A primary mechanism to maintain immune homeostasis is based on anti-inflammatory regulation by surfactant protein A (SP-A), a secreted component of lung innate immunity. The architecture of LPS aggregates is strongly associated with biological activity. We therefore investigated whether SP-A affects the physico-chemical properties of LPS. Determination of the three-dimensional aggregate structure of LPS by small-angle X-ray scattering demonstrated that SP-A induced the formation of multi-lamellar aggregate structures. Determination of the acyl-chain-fluidity of LPS aggregates by Fourier transform infrared (FTIR) spectroscopy showed that the phase transition temperature of LPS was reduced in the presence of SP-A. The phosphate groups at the diglucosamine backbone of LPS represent important functional groups for the bioactivity of LPS. FTIR analysis revealed changes in the vibrational bands νas PO-(2), indicating an interaction of SP-A with the 1-phosphate, but not with the 4'-phosphate. The physico-chemical changes induced by SP-A were associated with up to 90% reduction in LPS-induced TNF-α-production by human macrophages. In conclusion, our data demonstrate that the SP-A/LPS interaction induces conformational changes in LPS aggregates leading to biologically less active structures, thereby providing a new molecular mechanism of immune modulation by SP-A.

Influence of lipid A acylation pattern on membrane permeability and innate immune stimulation

Lipid A, the hydrophobic anchor of lipopolysaccharide (LPS), is an essential component in the outer membrane of Gram-negative bacteria. It can stimulate the innate immune system via Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD2), leading to the release of inflammatory cytokines. In this study, six Escherichia coli strains which can produce lipid A with different acylation patterns were constructed; the influence of lipid A acylation pattern on the membrane permeability and innate immune stimulation has been systematically investigated. The lipid A species were isolated and identified by matrix assisted laser ionization desorption-time of flight/tandem mass spectrometry. N-Phenyl naphthylamine uptake assay and antibiotic susceptibility test showed that membrane permeability of these strains were different. The lower the number of acyl chains in lipid A, the stronger the membrane permeability. LPS purified from these strains were used to stimulate human or mouse macrophage cells, and different levels of cytokines were induced. Compared with wild type hexa-acylated LPS, penta-acylated, tetra-acylated and tri-acylated LPS induced lower levels of cytokines. These results suggest that the lipid A acylation pattern influences both the bacterial membrane permeability and innate immune stimulation. The results would be useful for redesigning the bacterial membrane structure and for developing lipid A vaccine adjuvant.

RAGE and TLRs: relatives, friends or neighbours?

The innate immune system forms the first line of protection against infectious and non-infectious tissue injury. Cells of the innate immune system detect pathogen-associated molecular patterns or endogenous molecules released as a result of tissue injury or inflammation through various innate immune receptors, collectively termed pattern-recognition receptors. Members of the Toll-like receptor (TLR) family of pattern-recognition receptors have well established roles in the host immune response to infection, while the receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor predominantly involved in the recognition of endogenous molecules released in the context of infection, physiological stress or chronic inflammation. RAGE and TLRs share common ligands and signaling pathways, and accumulating evidence points towards their co-operative interaction in the host immune response. At present however, little is known about the mechanisms that result in TLR versus RAGE signalling or RAGE-TLR cross-talk in response to their shared ligands. Here we review what is known in relation to the physicochemical basis of ligand interactions between TLRs and RAGE, focusing on three shared ligands of these receptors: HMGB1, S100A8/A9 and LPS. Our aim is to discuss what is known about differential ligand interactions with RAGE and TLRs and to highlight important areas for further investigation so that we may better understand the role of these receptors and their relationship in host defense.