Endotoxaemia modulates Toll-like receptors on leucocytes in humans

Muscle-Specific Deletion of Toll-like Receptor 4 Impairs Metabolic Adaptation to Wheel Running in Mice

PURPOSE

Toll-like receptor 4 (TLR4) is an inflammatory receptor expressed ubiquitously in immune cells as well as skeletal muscle and other metabolic tissues. Skeletal muscle develops favorable inflammation-mediated metabolic adaptations from exercise training. Multiple inflammatory myokines, downstream from TLR4, are proposed links to the metabolic benefits of exercise. In addition, activation of TLR4 alters skeletal muscle substrate preference. The role of skeletal muscle TLR4 (mTLR4) in exercise metabolism has not previously been investigated. Herein, we aimed to specifically test the significance of mTLR4 to exercise-induced metabolic adaptations.

METHODS

We developed a novel muscle-specific TLR4 knockout (mTLR4-/-) mouse model on C57BL/6J background. Male mTLR4-/- mice and wild-type (WT) littermates were compared under sedentary (SED) and voluntary wheel running (WR) conditions for 4 wk.

RESULTS

mTLR4 deletion revealed marked reductions in downstream interleukin-1 receptor-associated kinase-4 (IRAK4) phosphorylation. In addition, the disruption of mTLR4 signaling prominently blunted the metabolic adaptations in WR-mTLR4-/- mice as opposed to substantial improvements exhibited by the WT counterparts. Voluntary WR in WT mice, relative to SED, resulted in significant increases in skeletal muscle fatty acid oxidation, glucose oxidation, and associated mitochondrial enzyme activities, all of which were not significantly changed in mTLR4-/- mice.

CONCLUSIONS

This study introduces a novel mTLR4-/- mouse model and identifies mTLR4 as an immunomodulatory effector of exercise-induced metabolic adaptations in skeletal muscle.

Human lipopolysaccharide models provide mechanistic and therapeutic insights into systemic and pulmonary inflammation

Inflammation is a key feature in the pathogenesis of sepsis and acute respiratory distress syndrome (ARDS). Sepsis and ARDS continue to be associated with high mortality. A key contributory factor is the rudimentary understanding of the early events in pulmonary and systemic inflammation in humans, which are difficult to study in clinical practice, as they precede the patient's presentation to medical services. Lipopolysaccharide (LPS), a constituent of the outer membrane of Gram-negative bacteria, is a trigger of inflammation and the dysregulated host response in sepsis. Human LPS models deliver a small quantity of LPS to healthy volunteers, triggering an inflammatory response and providing a window to study early inflammation in humans. This allows biological/mechanistic insights to be made and new therapeutic strategies to be tested in a controlled, reproducible environment from a defined point in time. We review the use of human LPS models, focussing on the underlying mechanistic insights that have been gained by studying the response to intravenous and pulmonary LPS challenge. We discuss variables that may influence the response to LPS before considering factors that should be considered when designing future human LPS studies.

Altered Toll-Like Receptor Signalling in Children with Down Syndrome

Toll-like receptors (TLRs) are the key in initiating innate immune responses. TLR2 is crucial in recognising lipopeptides from gram-positive bacteria and is implicated in chronic inflammation. Children with Down syndrome (DS) are prone to infections from these pathogens and have an increased risk of autoimmunity. Sparstolonin B (SsnB) is a TLR antagonist which attenuates cytokine production and improves outcomes in sepsis. We hypothesised that TLR signalling may be abnormal in children with DS and contribute to their clinical phenotype. We evaluated TLR pathways in 3 ways: determining the expression of TLR2 on the surface of neutrophils and monocytes by flow cytometry, examining the gene expression of key regulatory proteins involved in TLR signal propagation, MyD88, IRAK4, and TRIF, by quantitative PCR, and lastly determining the cytokine production by ELISA following immunomodulation with proinflammatory stimuli (lipopolysaccharide (LPS), Pam3Csk4) and the anti-inflammatory agent SsnB. We report TLR2 expression being significantly increased on neutrophils, total monocytes, and intermediate and nonclassical monocytes in children with DS (n = 20, mean age 8.8 ± SD 5.3 years, female n = 11) compared to controls (n = 15, mean age 6.2 ± 4.2 years, female n = 5). At baseline, the expression of MyD88 was significantly lower, and TRIF significantly raised in children with DS. The TLR antagonist SsnB was effective in reducing TLR2 and CD11b expression and abrogating cytokine production in both cohorts. We conclude that TLR signalling and the TLR2 pathway are dysregulated in DS, and this disparate innate immunity may contribute to chronic inflammation in DS. SsnB attenuates proinflammatory mediators and may be of therapeutic benefit.

Review: From therapy to experimental model: a hundred years of endotoxin administration to human subjects

This article is a review of studies in which endotoxin has been administered to human subjects for experimental purposes. Data are presented in tabular form so the reader can better appreciate the objectives of individual studies. Although the original intention was to focus on the adverse events associated with these studies, unexpected serious adverse events rarely have been reported.

The discriminative capacity of soluble Toll-like receptor (sTLR)2 and sTLR4 in inflammatory diseases

Background

The extracellular domains of cytokine receptors are released during inflammation, but little is known about the shedding of Toll-like receptors (TLR) and whether they can be used as diagnostic biomarkers.

Methods

The release of sTLR2 and sTLR4 was studied in in-vitro stimulations, as well as in-vivo during experimental human endotoxemia (n = 11, 2 ng/kg LPS), and in plasma of 394 patients with infections (infectious mononucleosis, measles, respiratory tract infections, bacterial sepsis and candidemia) or non-infectious inflammation (Crohn’s disease, gout, rheumatoid arthritis, autoinflammatory syndromes and pancreatitis). Using C-statistics, the value of sTLR2 and sTLR4 levels for discrimination between infections and non-infectious inflammatory diseases, as well as between viral and bacterial infections was analyzed.

Results

In-vitro, peripheral blood mononuclear cells released sTLR2 and sTLR4 by exposure to microbial ligands. During experimental human endotoxemia, plasma concentrations peaked after 2 hours (sTLR4) and 4 hours (sTLR2). sTLR4 did not correlate with cytokines, but sTLR2 correlated positively with TNFα (r_s = 0.80, P < 0.05), IL-6 (r_s = 0.65, P < 0.05), and IL-1Ra (r_s = 0.57, P = 0.06), and negatively with IL-10 (r_s = -0.58, P = 0.06), respectively. sTLR4 had a similar area under the ROC curve [AUC] for differentiating infectious and non-infectious inflammation compared to CRP: 0.72 (95% CI 0.66-0.79) versus 0.74 (95% CI 0.69-0.80) [P = 0.80], while sTLR2 had a lower AUC: 0.60 (95% CI 0.54-0.66) [P = 0.0004]. CRP differentiated bacterial infections better from viral infections than sTLR2 and sTLR4: AUC 0.94 (95% CI 0.90-0.96) versus 0.58 (95% CI 0.51-0.64) and 0.75 (95% CI 0.70-0.80), respectively [P < 0.0001 for both].

Conclusions

sTLRs are released into the circulation, and suggest the possibility to use sTLRs as diagnostic tool in inflammatory conditions.

Toll-like receptor signaling in neonatal sepsis and inflammation: a matter of orchestration and conditioning

Altered neonatal Toll-like receptor (TLR) function is hypothesized to contribute to the heightened susceptibility to infection and perpetuated inflammation in term and preterm neonates, clinically evident in neonatal sepsis and increased rates of inflammatory disorders. Current data indicate that basal TLR expression in term neonates equals adult expression patterns, while expression in preterm infants seems to increase, depending on gestational age. Regarding TLR signaling, some studies suggest TLR incompetence in neonates associated with impaired pro-inflammatory responses, others describe neonatal TLR function well developed and allude to its hyper-inflammation tendency. We discuss the competing positions and considerable limitations of research approaches and conclude that neonatal innate immunity is not generally less able to respond to TLR stimulation. Moreover, we describe pre-conditioning factors other than immaturity having a comparable impact. In the long term, better understanding of the complex interplay of pre- and postnatal conditions and maturation-dependent neonatal TLR function may provide new therapeutic approaches.

Evaluation of Toll-like, chemokine, and integrin receptors on monocytes and neutrophils from peripheral blood of septic patients and their correlation with clinical outcomes

Recognition of pathogens is performed by specific receptors in cells of the innate immune system, which may undergo modulation during the continuum of clinical manifestations of sepsis. Monocytes and neutrophils play a key role in host defense by sensing and destroying microorganisms. This study aimed to evaluate the expression of CD14 receptors on monocytes; CD66b and CXCR2 receptors on neutrophils; and TLR2, TLR4, TLR5, TLR9, and CD11b receptors on both cell types of septic patients. Seventy-seven septic patients (SP) and 40 healthy volunteers (HV) were included in the study, and blood samples were collected on day zero (D0) and after 7 days of therapy (D7). Evaluation of the cellular receptors was carried out by flow cytometry. Expression of CD14 on monocytes and of CD11b and CXCR2 on neutrophils from SP was lower than that from HV. Conversely, expression of TLR5 on monocytes and neutrophils was higher in SP compared with HV. Expression of TLR2 on the surface of neutrophils and that of TLR5 on monocytes and neutrophils of SP was lower at D7 than at D0. In addition, SP who survived showed reduced expression of TLR2 and TLR4 on the surface of neutrophils at D7 compared to D0. Expression of CXCR2 for surviving patients was higher at follow-up compared to baseline. We conclude that expression of recognition and cell signaling receptors is differentially regulated between SP and HV depending on the receptor being evaluated.

Toll-like receptors in neonatal sepsis

Toll-like receptors are vital transmembrane receptors that initiate the innate immune response to many micro-organisms. The discovery of these receptors has improved our understanding of host-pathogen interactions, and these receptors play an important role in the pathogenesis of multiple neonatal conditions such as sepsis and brain injury. Toll-like receptors, especially TLRs 2 and 4, are associated with necrotizing enterocolitis, periventricular leukomalacia and sepsis.

CONCLUSION

Toll-like receptor modulation may potentially be used as immunomodulators in the management of neonatal sepsis.

Low dose LPS does not increase TLR4 expression on monocytes in a human in vivo model

BACKGROUND AND PURPOSE

Toll like receptor 4 (TLR4) is the major recognition receptor for lipopolysaccharides and plays a major role in the inflammatory response. CD11b is expressed on the surface of many leukocytes including monocytes. The CD11b/CD18 complex is involved in the inflammatory response by mediating migration and adhesion of leukocytes. The aim of this human in vivo study was to investigate the expression of TLR4 and CD11b on the surface of human monocytes after in vivo low-dose LPS stimulation.

METHODS

We performed a double-blind, randomized crossover study with 16 healthy males who received a bolus injection of bacterial lipopolysaccharide (LPS; 0.4ng/kg) or normal saline. Vital parameters, blood counts, serum cytokine levels, the expression of TLR4, and CD11b on CD14 positive cells were analyzed.

RESULTS

The experimentally induced inflammatory response was reflected by transient increases in body temperature, circulating leukocyte numbers, and plasma levels of pro- (TNF-α, IL-6) and anti-inflammatory cytokines (IL-10, IL-1ra). In contrast to a significant increase in CD11b expression, no changes in TLR4 expression on circulating monocytes were detectable.

CONCLUSION

Early changes in TLR4 expression on circulating monocytes are not necessarily part of the inflammatory response to low dose LPS in humans whereas the detected increase of CD11b expression might already be sufficient for optimized recognition and signalling.

Surface expression and genotypes of Toll-like receptors 2 and 4 in patients with juvenile idiopathic arthritis and systemic lupus erythematosus

BACKGROUND

Chronic arthritis is a common feature of juvenile idiopathic arthritis (JIA) and systemic lupus erythematosus (SLE). It was subsequently discovered that Toll-like receptors (TLRs) are able to upregulate cytokine production in response to endogenous ligands released after tissue damage, suggesting that TLRs can maintain an inflammatory response even in absence of pathogen. Thus, TLRs may contribute to increased inflammation in JIA and SLE patients. The aim of this study was to investigate the role of TLRs in JIA and SLE. We examined the in vivo expression and polymorphisms of TLR2 and TLR4 in peripheral monocytes of patients with JIA and SLE during active and inactive disease phases.

METHODS

This single center cohort study consisted of JIA and SLE affected children and control subjects. TLR2 and TLR4 protein expression on CD14+ monocytes was examined by flow cytometry. TLR2 and TLR4 genotypes were determined using the polymerase chain reaction-restriction fragment length polymorphism method (RFLP-PCR).

RESULTS

A significant reduction in the level of TLR4 expression (p ≤ 0.001) was observed on monocytes of patients with JIA and SLE compared with that of healthy control subjects. There was no correlation between the TLR2 or TLR4 genotypes and the observed differential TLR protein expression on monocytes.

CONCLUSIONS

To conclude, our observations suggest involvement of investigated TLRs in the pathogenesis of JIA and SLE. It still remains to be elucidated whether reduced TLR4 expression is cause of chronic arthritis or a result of some feedback loop.

Effects of prasugrel on platelet inhibition during systemic endotoxaemia: a randomized controlled trial

P2Y12 receptor antagonists have become a mainstay for the treatment of CVD (cardiovascular diseases). However, they have rarely been evaluated under pathophysiological conditions apart from arterial diseases. We hypothesized interactions between prasugrel and enhanced vWF (von Willebrand Factor) release in a model of systemic inflammation, and compared the pharmacodynamic effects of prasugrel against placebo on agonist-induced platelet aggregation and shear-induced platelet plug formation. A total of 20 healthy male volunteers were enrolled in a double-blind placebo-controlled two-way crossover trial. Each volunteer received either placebo or a 60 mg loading dose of prasugrel 2 h before endotoxin or placebo infusion. Platelet inhibition was measured with MEA (multiple electrode aggregometry), the PFA-100 system and the VASP (vasodilator-stimulated phosphoprotein) phosphorylation assay. Prasugrel blunted various platelet aggregation pathways, including those induced by ADP (−81%), AA (arachidonic acid) (−60%), ristocetin (−75%; P<0.001 for all) and, to a lesser degree, collagen or TRAP (thrombin-receptor-activating peptide). Prasugrel decreased shear-induced platelet plug formation, but vWF release during endotoxaemia partly antagonized the inhibitory effect of prasugrel as measured with the PFA-100 system. Endotoxaemia acutely decreased ristocetin and TRAP-induced platelet aggregation, and enhanced ristocetin-induced aggregation after 24 h. Strong in vivo blockade of P2Y12 inhibits a broad spectrum of platelet aggregation pathways. However, vWF release may reduce prasugrel's effects under high-shear conditions.

Recent advances in Toll-like receptors and anterior uveitis

Uveitis involves acute, recurrent or chronic inflammation of the uvea, and occurs when the normal state of ocular immune privilege has broken down. Accumulating evidence implicates the role of microbial triggers in the development of various forms of immune-mediated uveitis in addition to its causative role in infectious uveitis. Toll-like receptors (TLRs) are the most important pattern-recognition receptors of the innate immune system that recognize pathogen-associated molecular patterns of microbes. Activation of TLRs by pathogen-associated molecular patterns leads to the induction of an inflammatory cascade and activation of both innate and adaptive arms of the immune response. TLRs have been implicated in the pathogenesis of various inflammatory diseases, including uveitis. This review provides an update on recent progress in TLR research and uveitis, specifically summarizing new evidence for the role of TLRs in anterior uveitis. There have been important observations from studies involving human ocular tissue, clinical uveitis and from experimental animal models of uveitis, such as endotoxin-induced uveitis. The 'Toll rush' has certainly gained momentum, and future advances in this field have the potential for selectively targeting the TLR pathway and ultimately translating into better therapies for patients with sight-threatening uveitis.

Identification of candidate genes linking systemic inflammation to atherosclerosis; results of a human in vivo LPS infusion study

Background

It is widely accepted that atherosclerosis and inflammation are intimately linked. Monocytes play a key role in both of these processes and we hypothesized that activation of inflammatory pathways in monocytes would lead to, among others, proatherogenic changes in the monocyte transcriptome. Such differentially expressed genes in circulating monocytes would be strong candidates for further investigation in disease association studies.

Methods

Endotoxin, lipopolysaccharide (LPS), or saline control was infused in healthy volunteers. Monocyte RNA was isolated, processed and hybridized to Hver 2.1.1 spotted cDNA microarrays. Differential expression of key genes was confirmed by RT-PCR and results were compared to in vitro data obtained by our group to identify candidate genes.

Results

All subjects who received LPS experienced the anticipated clinical response indicating successful stimulation. One hour after LPS infusion, 11 genes were identified as being differentially expressed; 1 down regulated and 10 up regulated. Four hours after LPS infusion, 28 genes were identified as being differentially expressed; 3 being down regulated and 25 up regulated. No genes were significantly differentially expressed following saline infusion. Comparison with results obtained in in vitro experiments lead to the identification of 6 strong candidate genes (BATF, BID, C3aR1, IL1RN, SEC61B and SLC43A3)

Conclusion

In vivo endotoxin exposure of healthy individuals resulted in the identification of several candidate genes through which systemic inflammation links to atherosclerosis.

Enhanced expression of Toll-like receptor 2 in lesional tissues and peripheral blood monocytes of patients with oral lichen planus

Some members of the Toll-like receptor (TLR) family, which plays key roles in both innate and adaptive immune responses, are involved in the pathogenesis of autoimmune, chronic inflammatory and infectious diseases. However, the role of TLR in the pathogenesis of oral lichen planus (OLP) has not been investigated. The aim of this study was to understand the roles of TLR in OLP. The expression of TLR genes in OLP tissues was analyzed by cDNA microarray and reverse transcription polymerase chain reaction, and TLR protein expression in OLP tissues and peripheral blood monocytes was examined by immunohistochemical analysis and flow cytometry, respectively. Furthermore, TLR ligand-induced cytokine production from peripheral blood monocytes was measured by enzyme-linked immunosorbent assay. Among 10 TLR genes, the average expression ratio of the genes for TLR1, 2, 3, 5, 6 and 10 in OLP tissues compared to that in the normal buccal mucosae was more than 1.0. In contrast, the average ratio of the genes for TLR7, 8 and 9 was less than 1.0. TLR2 but not TLR4 was highly expressed in the cells of the spinous layer and infiltrating monocytes in OLP tissues, and the mean fluorescence intensity of TLR2 on peripheral blood monocytes was significantly higher in OLP patients than in healthy controls. Furthermore, the peripheral blood monocytes from OLP patients produced considerably higher amounts of interleukin (IL)-12 and lower amounts of IL-10 than those from healthy controls. In OLP, the T-helper cell (Th)1/Th2 balance appears to shift toward Th1 dominance, probably depending on the upregulation of TLR2 expression and these alterations in TLR2-mediated immunity may be involved in the pathogenesis and maintenance of OLP.

Human neonatal peripheral blood leukocytes demonstrate pathogen-specific coordinate expression of TLR2, TLR4/MD2, and MyD88 during bacterial infection in vivo

Toll-like receptors (TLRs) play important roles in infection. We have previously reported TLR2 is up-regulated in neonatal Gram-positive (G+) bacteremia, whereas TLR4 is up-regulated in neonatal Gram-negative (G-) bacteremia. For functional signaling, TLR4 requires myeloid differentiation (MD)-2, and both TLR2 and TLR4 signal need myeloid differentiation factor (MyD88). However, it is unknown whether newborns can enhance expression of MD-2 and MyD88 with bacterial infection in coordination with TLR expression. We characterized neonatal peripheral blood leukocyte expression of MD-2 and MyD88 in relation to TLR2/4 in newborns. TLR2 mRNA expression by PBMCs and TLR2 protein expression by monocytes and granulocytes were significantly increased in the G+ bacteremia group. TLR4 mRNA on PMBCs and protein expression on monocytes and granulocytes were significantly increased in the G- bacterial group. Remarkably, although, MyD88 mRNA was increased in all patients with documented bacterial infection and correlated with both TLR2 and TLR4, MD-2 mRNA was selectively increased in G- bacterial group, wherein it correlated with TLR4 but not with TLR2 mRNA. Our findings demonstrate that during bacterial infection in vivo, newborns selectively and coordinately amplify the TLR2-MyD88 pathway in G+ bacterial infection and the TLR4/MD2/MyD88 pathway in G- bacterial infection, suggesting key roles for innate immune pathway in neonatal responses to bacterial infection.

Spontaneous bacterial peritonitis: from pathophysiology to prevention

Patients with cirrhosis present an increased susceptibility to bacterial infections, which are the cause of hospital admission in about 10% of patients and are present in about 40% of those admitted for ongoing complications. Lastly, about a third of patients develop nosocomial infections. Spontaneous bacterial peritonitis (SBP) is the most frequent infection in advanced cirrhosis; it is mostly caused by Gram-negative bacteria of intestinal origin, but Gram-positive cocci can be involved in nosocomial-acquired SBP. Its occurrence is associated with complications, such as renal and circulatory failure, cardiac dysfunction, coagulopathy, encephalopathy, and relative adrenal insufficiency, ultimately leading to multi-organ failure and death within a few days or weeks in about 30% of cases. The main mechanism underlying the development of SBP, as well as other bacterial infections in cirrhosis, is represented by bacterial translocation from the intestinal lumen to mesenteric lymph nodes or other extraintestinal organs and sites. This process is facilitated by several factors, including changes in intestinal flora, portal hypertension, and, mainly, impairment in local/systemic immune defense mechanisms. Bacterial infections in advanced cirrhosis evoke an enhanced systemic inflammatory response, which explains the ominous fate of PBS. Indeed, an exaggerated production of cytokines ensues, which ultimately activates vasodilating systems and generates reactive oxygen species. Primary antibiotic prophylaxis of PBS is warranted in those conditions implying an increased incidence of bacterial infections, such as gastro-intestinal bleeding and low protein content in ascites associated with severe liver and/or renal dysfunction. Fluoroquinolones are commonly employed, but the frequent occurrence of resistant bacterial strains make third generation cephalosporins preferable in specific settings. The high PBS recurrence indicates secondary antibiotic prophylaxis.

TLR4: the receptor bridging Acanthamoeba challenge and intracellular inflammatory responses in human corneal cell lines

Acanthamoeba keratitis (AK) is a painful, vision-threatening infection caused by pathogenic strains of the protozoan, Acanthamoeba. Toll-like receptors (TLRs), which are important components of innate immunity, have an important role in the detection of foreign pathogens and the signaling cascades in host cells. However, no report on the interaction between Acanthamoeba and TLR has been found. In this study we analyzed the role of the TLR and its signaling pathway in human telomerase-immortalized corneal epithelial cells (HUCLs) and stromal fibroblasts (THSFs) challenged by Acanthamoeba. We show that the expressions of TLR4, myeloid differentiation protein 88 (MyD88), nuclear factor (NF)-kappaB, phospho-IkappaB, phospho-extracellular signal-regulated kinases 1/2 (p-Erk1/2) and the inflammatory cytokines interleukin (IL)-8, tumor necrosis factor (TNF)-alpha and interferon (IFN)-beta were significantly increased in Acanthamoeba-treated cells. Pretreatment with anti-TLR antibodies or the specific inhibitors pyrrolidine dithiocarbamate (PDTC) (for the NF-kappaB pathway) and U0126 (for the ERK pathway) was conducted. It was found that anti-TLR4 antibody attenuated the production of cytokines induced by Acanthamoeba infection. PDTC inhibited the production of IL-8 and TNF-alpha whereas U0126 inhibited the synthesis of IFN-beta. Thus, TLR4 is a receptor for Acanthamoeba and exerts an effect through TLR4-MyD88-NF-kappaB and TLR4-ERK1/2 pathways to induce the secretion of cytokines in human corneal cell lines challenged by Acanthamoeba.

High expression of Toll-like receptor 4 on CD14+ monocytes in acute infectious diseases

Toll-like receptor 4 (TLR4) recognizes lipopolysaccharide (LPS) and other exogenous and endogenous molecules, and is thought to contribute to defense mechanisms against infections. Our objective was to elucidate the clinical significance of TLR4 in acute infectious diseases by analyzing its sequential expression on CD14+ monocytes. Peripheral blood samples were obtained from 36 patients with acute infectious diseases on admission and after treatment within certain intervals. The TLR4 expression on CD14+ monocytes was analyzed using flow cytometry and was presented as a mean fluorescence intensity (MFI). TLR4 expression during the acute phase of infection was highly enhanced compared to that of normal subjects (MFI: 22.1 vs 8.5). TLR4 expression was promptly reduced to normal levels in parallel with the disease improvement. In patients who died despite treatment, the enhancement of TLR4 expression during the acute phase was less prominent compared to those who survived (MFI: 14.6 vs 23.5) and its sequential change was also subtle. These results indicate that monocytes respond to acute infections by the induction of TLR4 expression and that a poor response may be associated with a poor prognosis.

Bacteroides fragilis signals through Toll-like receptor (TLR) 2 and not through TLR4

Although it is desirable to identify the interactions between endotoxin/LPS and the innate immune mechanism, it is often not possible to isolate these interactions from other cell wall-related structures of protein or polysaccharide origin. There is no universally accepted method to extract different LPSs from different bacteria, and their natural state will be influenced by their interactions with the associated molecules in the bacterial outer membrane. It is now believed that Toll-like receptor (TLR) 4 is the main signal transducer of classical LPS (i.e. Escherichia coli LPS), while TLR2 is used by certain non-classical LPSs. There are contradictory reports as to whether Bacteroides fragilis LPS, a non-classical LPS, signals primarily through TLR2 or TLR4. This study was designed to address this problem. Different non-purified and purified B. fragilis LPSs extracted by different methods together with different heat-killed, whole-cell populations of B. fragilis were used to elucidate the TLR specificity. All of these B. fragilis preparations showed a significant signalling specificity for TLR2 but not for TLR4. This indicates that changing the extraction methods, with or without applying a repurification procedure, and varying the cell populations do not alter the TLR specificity of B. fragilis LPS.

Mortality in human sepsis is associated with downregulation of Toll-like receptor 2 and CD14 expression on blood monocytes

Pattern recognition receptors are a key component of the first line host defense against infection, recognizing specific microbial products. We hypothesize that monocyte hyporesponsiveness in human sepsis is associated with a downregulation of the pattern recognition receptors Toll-like receptor (TLR)-2 and TLR4.Protein expression of CD14, TLR2 and TLR4 on blood monocytes was examined using flow cytometry from 29 patients with sepsis and 14 healthy controls. In addition LPS stimulated TNF-alpha and IL-10 production was studied in a 24 hour whole blood assay.We found an increased expression of CD14, TLR2 and TLR4 in patients with sepsis compared to controls (p < 0.01). In patients with sepsis, death was associated with significant lower CD14 and TLR2 expression at admission (CD14: 25.7 +- 19.1 vs 39.1 +- 17.3 mean fluorescence intensity [MFI], p = 0.02; TLR2: 21.8 +- 9.4 vs. 30.9 +- 9.6, p = 0.01). At 72 hours the TLR2 expression on monocytes was associated with the IL-10 inducibility after LPS stimulation (r = 0.52, p = 0.02) and the CD14 expression with the IL-6, IL-10 and TNF inducibility.We conclude that septic patients are characterized by an increased expression of CD14, TLR2 and TLR4 on monocytes compared to controls. Death is associated with downregulation of TLR2 and CD14 expression on monocytes correlating with reduced cytokine inducibility. We suggest that CD14 and TLR2 are a key factor in monocyte hyporesponsibility during severe sepsis.

Toll-like receptors, transduction-effector pathways, and disease diversity: evidence of an immunobiological paradigm explaining all human illness?

Membrane-bound Toll-like receptors (TLRs) are frontline guardians in the mammalian innate immune system. They primarily function to recognize pathogen-associated molecular patterns (PAMPs) of invading microorganisms and on activation mount rapid, nonspecific innate responses and trigger sequential delayed specific adaptive cellular responses, which are mediated by complex signal transduction pathways involving adaptor molecules, costimulatory ligands and receptors, kinases, transcription factors, and modulated gene expression. Increasing evidence of multiple functionality and diversity suggests TLRs play critical roles in noninfective medical conditions such as cardiovascular, gastrointestinal, neurologic, musculoskeletal, obstetric, renal, liver, and dermatologic diseases, allergy, autoimmunity, and tissue regeneration. The significance of TLR heterogeneity underscores the possibility for establishing a universal immunobiological model to explain all human disease. Novel immunomodulatory therapies targeting specific or multiple TLRs may in the future offer new tools to combat or eradicate pathogenesis potentially transforming the landscape of current medical treatments.

The effect of systemic iNOS inhibition during human endotoxemia on the development of tolerance to different TLR-stimuli

The phenomenon of repeated exposure to endotoxin resulting in diminished release of pro-inflammatory cytokines is called endotoxin tolerance, in which there is a putative role for nitric oxide (NO). We investigated the effect of selective inducible NO-synthase (iNOS) inhibition during experimental human endotoxemia on the development of tolerance to various Toll-like receptor (TLR) agonists ex vivo. Volunteers received 2 ng/kg Escherichia coli endotoxin in the absence ( n = 7) or presence ( n = 7) of the selective iNOS inhibitor aminoguanidine (bolus 5 mM followed by a continuous infusion of 1.5 mmol/h). At 0, 2 and 4 h, blood samples were drawn for ex vivo stimulation with different TLR agonists. Experimental endotoxemia did not induce tolerance to TLR-2 and TLR-7 stimulation. In TLR-3, TLR-4 and TLR-5 stimulated whole blood, pro- and anti-inflammatory cytokine release was attenuated at 4 h, indicating that endotoxin-induced tolerance is not confined to subsequent TLR-4 stimulation alone. Aminoguanidine-treated subjects also developed tolerance to TLR-4 stimulation. In contrast, tolerance to TLR-3 stimulation did not occur for IL-10, and tolerance in TLR-5 stimulated blood did not develop for both pro- and anti-inflammatory cytokines. The role of NO in the development of tolerance is different for the various TLRs stimulated and pro- and anti-inflammatory cytokines measured.

Intra-arterial vitamin C prevents endothelial dysfunction caused by ischemia-reperfusion

OBJECTIVE

Ischemia-reperfusion (IR) injury causes tissue injury and endothelial dysfunction. There is evidence that oxidative stress plays an important role.

METHODS

We tested if IR-induced endothelial dysfunction could be prevented by administration of the antioxidant vitamin C. Twenty-six healthy male subjects and eight male patients with peripheral arterial disease (PAD) were enrolled in this randomised placebo-controlled study. Forearm blood flow (FBF) measurements in response to the vasodilators acetylcholine (ACh; endothelium-dependent agonist) or nitroglycerin (NTG; endothelium-independent) were performed before and after forearm ischemia for 20 min. FBF responses were reassessed during reperfusion with intra-arterial co-administration of 24 mg/min vitamin C or placebo. In six volunteers responses to the NO-synthase inhibitor N-monomethyl-L-arginine (L-NMMA) were also assessed before and after ischemia with and without vitamin C.

RESULTS

ACh-induced vasodilation was blunted in subjects receiving placebo after reperfusion (p<0.05 versus baseline). Administration of vitamin C completely prevented impaired responsiveness. NTG-induced vasodilation was not affected by reperfusion or vitamin C. This finding was consistent in patients with PAD and impaired endothelial function, where local vitamin C infusion restored FBF reactivity to ACh before and after IR injury (p<0.05 versus baseline). Again, NTG-induced vasodilation was not affected. Blunted L-NMMA responses seen during reperfusion could be completely reversed by vitamin C.

CONCLUSIONS

Our data indicate that IR-induced vascular injury can be prevented by administration of antioxidants.

S-ibuprofen effectively inhibits thromboxane B2 levels and platelet function in an experimental model of lipopolysaccharide-stimulated and non-stimulated whole blood

OBJECTIVE

The present study aimed at testing the effect of S- and R-ibuprofen on thromboxane B(2) (TXB(2)), collagen-epinephrine closure time (CEPI-CT) and collagen-adenosine 5'-diphosphate closure time (CADP-CT) in lipopolysaccharide (LPS)-stimulated and non-stimulated human whole blood.

MATERIALS AND METHODS

Whole blood was incubated with S- or R-ibuprofen with and without prior stimulation with LPS. To verify ibuprofen's potential effects on TXB(2), varying ratios of concentrations of S- and R-ibuprofen ranging from 0 to 100% were used. TXB(2) levels were measured by ELISA. The effects of S- and R-ibuprofen enantiomers on platelet aggregability were tested utilizing a PFA-100 apparatus.

RESULTS

In non-stimulated and LPS-stimulated whole blood, S-ibuprofen markedly decreased TXB(2) levels at concentrations ranging from 10 to 200 microg/ml. R-ibuprofen showed its inhibiting effect at concentrations >100 microg/ml. In inflammatory and non-inflammatory conditions, CEPI-CT was prolonged at concentrations of 12.5 and 75 microg/ml for S-ibuprofen and at a concentration of 150 microg/ml of combined R- and S-ibuprofen. S-ibuprofen was significantly more effective than R-ibuprofen (p < 0.05). The combined use of S- and R-ibuprofen did not additively or synergistically prolong CEPI-CTs. CADP-CTs remained unaffected by both enantiomers.

CONCLUSIONS

S-ibuprofen was more effective than the R-ibuprofen enantiomer in inhibiting TXB(2) plasma levels and aggregability of thrombocytes in non-inflammatory and inflammatory conditions.

Microbial Products Stimulate Human Toll-like Receptor 2 Expression through Histone Modification Surrounding a Proximal NF-κB-binding Site

Previous studies have yielded conflicting results regarding the ability of microbial products to activate TLR2 gene expression in human monocytes. In this study, we found that TLR2 mRNA was rapidly up-regulated in human monocytes treated with TLR2 and TLR4 agonists, and this corresponded to an increase in cell surface receptor levels. This induction was abrogated by actinomycin D as well as a pharmacologic inhibitor of NF-kappaB, suggesting that the TLR2 gene is transcriptionally activated via NF-kappaB. Microbial agonists were found to shift the transcription initiation site of the TLR2 gene, and sequence examination revealed a near-consensus NF-kappaB-binding element immediately upstream of this site. Electromobility shift assays confirmed that NF-kappaB bound to this putative site in vitro. However, luciferase reporter plasmids driven by the TLR2 promoter were not responsive to TLR2 agonists. Overexpression of the NF-kappaB p65 subunit was sufficient to induce expression of the endogenous TLR2 mRNA, and co-transfection of the CREB-binding protein and p300 co-activators further increased TLR2 mRNA levels. Chromatin immunoprecipitation analysis revealed that p65, CREB-binding protein, and p300 are recruited to the TLR2 promoter upon stimulation of human monocytes followed by histone hyperacetylation. Taken together, these results define a mechanism whereby histone modification and increased promoter access induce expression of human TLR2 following infection.

Time-course of Toll-like receptor 2 expression, as a predictor of recurrence in patients with bacterial infectious diseases

The clinical course of bacterial infectious diseases is often variable, especially in elderly patients. Thus, new biological markers have been sought to predict the disease outcome. Recent studies have revealed that Toll-like receptor (TLR) 2 and/or TLR4 on circulating monocytes are significantly up-regulated in bacterial infections. However, the lack of reliable quantification methods hampers extensive study on the modulation of these molecules in response to the patient's clinical condition. In this study, we developed a new quantitative flow cytometric analysis system for TLR2. We then carried out a longitudinal study on TLR2 expression levels on monocytes from patients suffering from bacterial infectious diseases during and after antibiotic treatment. The clinical outcome divided 37 patients into 'cure' (n = 24) and 'recurrence' (n = 13) groups. A significant difference between the two groups was recognized in the TLR2 levels just after antibiotic treatment (antibody-binding sites/cell, 4395 +/- 784 versus 5794 +/- 1484, P < 0.001). The risk of recurrence was associated significantly with TLR2 (P < 0.001), but not C-reactive protein (P = 0.351) levels assayed during the first remission. Furthermore, antibiotic effectiveness was associated inversely with TLR2 levels during antibiotic administration (P < 0.001). Taken together, TLR2 expression levels on monocytes provide critical information for planning treatment against bacterial infectious diseases.

Effects of low dose endotoxemia on endothelial progenitor cells in humans

BACKGROUND

Endothelial progenitor cells (EPCs) are a specific subtype of hematopoietic stem cells that migrate from the bone marrow to the peripheral circulation where they contribute to the repair of injured endothelium and to the formation of new blood vessels. Levels of circulating EPCs have been investigated in different inflammatory disease states. However, data on circulating EPC levels and systemic inflammation remain scarce and contradictory.

OBJECTIVE

We investigated a putative relationship of low grade experimental endotoxemia to changes in circulating EPC levels.

METHODS

Randomized, double-blind, placebo-controlled parallel group trial in 36 healthy male volunteers. Thirty-two volunteers received 2 ng/kg LPS intravenously, the remaining four an equal volume of physiologic saline solution as placebo.

RESULTS

Endothelial progenitor cells showed a significant decrease over the observation period among the 32 subjects challenged with LPS (P<0.0001) and reached their nadir at 6 h, with a median decrease of 62% (interquartile range: 48-81%) compared with baseline levels. Circulating EPCs returned to values comparable to baseline 24 h after LPS challenge.

CONCLUSION

Infusion of 2 ng/kg LPS led to a significant decrease in peripheral EPCs. These results suggest that the early phase of acute inflammation is associated with a decrease in peripheral EPCs.

The C-reactive protein (+)1444C/T alteration modulates the inflammation and coagulation response in human endotoxemia

BACKGROUND

C-reactive protein (CRP) plays a major role in the immune system and is an independent risk marker of cardiovascular disease. However, CRP's role in atherogenesis as innocent bystander, causative, or even protective agent, remains unresolved. The (+)1444C/T alteration in the CRP gene has been reported to determine basal CRP concentrations. We hypothesized that this alteration may also be associated with the degree of inflammatory response and coagulation activation in a well-standardized model of systemic inflammation.

METHODS

We administered 2 ng/kg endotoxin [Escherichia coli bacterial lipopolysaccharide (LPS)] intravenously to stimulate inflammation in 91 healthy young Caucasian male paid volunteers (age range, 19-40 years). Participants were confined to bed rest and fasted for 8.5 h after LPS infusion. We collected blood samples before LPS infusion and at 0, 2, 6, and 24 h after LPS infusion to measure inflammation markers [interleukin 6 (IL6), tumor necrosis factor-alpha (TNFalpha)], temperature, and coagulation markers (prothrombin fragment F(1+2), D-dimer). We analyzed the CRP 3' untranslated variant with a mutagenic separated PCR assay.

RESULTS

Basal concentrations of high-sensitivity CRP were approximately 40% lower in (+)1444CC alteration carriers than in T homozygous (TT) allele carriers (P = 0.04). In contrast, basal IL6 concentrations were 2-fold higher in wild-type C homozygous (CC) than in TT individuals (P = 0.01). In response to the LPS challenge, CC individuals had 4-fold higher peak TNFalpha concentrations (P <0.01), >2.5-fold higher peak IL6 concentrations (P <0.01), and increased temperature (P <0.01). Twenty-four hours after LPS challenge, prothrombin fragment F(1+2) concentrations were 75% higher and D-dimer concentrations 50% higher in CC than in TT individuals (P <0.05).

CONCLUSIONS

Genetic factors regulating CRP concentrations also modulate the individual response to endotoxin-stimulated inflammation.

Endotoxin enhances microvascular thrombosis in mouse cremaster venules via a TLR4-dependent, neutrophil-independent mechanism

Endotoxemia promotes adhesive interactions between platelets and microvascular endothelium in vivo. We sought to determine whether endotoxin (lipopolysaccharide, LPS) modified platelet thrombus formation in mouse cremaster venules and whether Toll-like receptor 4 (TLR4) and neutrophils were involved in the response. Intravital videomicroscopy was performed in the cremaster microcirculation of pentobarbital-anesthetized mice; venular platelet thrombi were induced with a light/dye endothelial injury model. C57BL/6 mice treated with Escherichia coli endotoxin had enhanced rates of venular platelet thrombus formation: the time to microvessel occlusion was reduced by approximately 50% (P < 0.005) compared with saline-treated animals. Enhanced microvascular thrombosis was evident as early as 2 h after LPS administration. LPS had no effect on thrombosis in either of two mouse strains with altered TLR4 signaling (C57BL/10ScNJ or C3H/HeJ), whereas it enhanced thrombosis in the control strains (C57BL/10J and C3H/HeN). LPS also enhanced platelet adhesion to endothelium in the absence of light/dye injury. Platelet adhesion, but not enhanced thrombosis, was inhibited by depletion of circulating neutrophils. LPS failed to enhance platelet aggregation ex vivo and did not influence platelet P-selectin expression, a marker of platelet activation. These findings support the notion that endotoxemia promotes platelet thrombus formation independent of neutrophils and without enhancement of platelet aggregation, via a TLR4-dependent mechanism.

Polymorphism in the tissue factor region is associated with basal but not endotoxin-induced tissue factor-mRNA levels in leukocytes

OBJECTIVE

Tissue factor (TF) plays a central role during disseminated intravascular coagulation (DIC) in sepsis. We hypothesized that a frequent D/I polymorphism, at nucleotide position -1208 in the promoter region, could influence TF-mRNA and downstream coagulation.

METHODS

Basal- and lipopolysaccharide (LPS)-induced TF-mRNA expression, microparticle-associated TF-procoagulant activity and coagulation were determined in healthy men (n = 74) before and after endotoxin (LPS) infusion (2 ng kg(-1)). Basal values of TF-mRNA ranged between 34 and > 37.5 cycles.

RESULTS

Baseline TF-mRNA levels significantly differed between genotypes: I/I carriers had almost 2-fold higher TF-mRNA levels compared to D/D carriers at baseline (P < 0.01). In accordance, higher levels of microparticle-associated TF-procoagulant activity could be seen in I/I carriers. However, the genotype did not affect basal or LPS-induced levels of prothrombin fragment F1+2, D-dimer or cytokines including tumor necrosis factor and interleukin-6.

CONCLUSION

The TF-1208 polymorphism is functional in that it regulates basal TF-mRNA in circulating monocytes and circulating microparticle-associated TF-procoagulant activity in vivo, but does not influence the relative increase in TF-mRNA or coagulation activation during low-grade endotoxemia.

Cellular and molecular mechanisms underlying LPS-associated myocyte impairment

Recently we reported that Toll-like receptor 4 (TLR4)-positive immune cells of unknown identity were responsible for the LPS-induced depression of cardiac myocyte shortening. The aim of this study is to identify the TLR4-positive cell type that is responsible for the LPS-induced cardiac dysfunction. Neither neutrophil depletion alone nor mast cell deficiency had any impact on the impairment of myocyte shortening during LPS treatment. In contrast, LPS-treated, macrophage-deficient mice demonstrated a partial reduction in shortening compared with saline-treated, macrophage-deficient mice. Because the removal of macrophages could only partially restore myocyte shortening, we also investigated the effects of removing both neutrophils and macrophages on myocyte shortening. Interestingly, endotoxemic, neutrophil-depleted, and macrophage-deficient mice had completely restored myocyte shortening. Because both macrophages and neutrophils can produce nitric oxide (NO) and TNF-α, we examined LPS-treated inducible NO synthase knockout (iNOSKO) mice and TNF receptor (TNFR)-deficient mice. Eliminating both TNFR1 and TNFR2 was required to restore myocyte shortening during LPS treatment, whereas iNOS deficiency had no effect. These data suggest that macrophages and to a lesser degree neutrophils cause cardiac impairment, presumably via TNF-α.

Expression of toll-like receptors in neonatal sepsis

Despite recent identification of specific pattern recognition receptors (PRR) for distinct microbial structures, data indicating their relevance in human infectious diseases are limited. We determined the expression levels of the Toll-like receptor (TLR)2 and TLR4 by flow cytometry on granulocytes and monocytes of healthy neonates compared with healthy adults. The basal expression of TLR2 was only slightly lower in neonatal phagocytes, whereas no differences could be detected for TLR4. Analyzing neonates with sepsis, we found an impressive up-regulation of TLR2 on blood phagocytes already at initial presentation of symptoms. Comparison with C-reactive protein, IL-8, and IL-6 suggested that TLR2 expression on monocytes is comparably valuable as an early sepsis marker. TLR2 was differentially regulated during neonatal sepsis, showing a constant up-regulation on monocytes but only a transient increase on granulocytes. Surprisingly, TLR4 showed no remarkable changes. Our results revealed a mild deficiency of TLR2 expression in newborns and demonstrated a differential expression of TLR2 but not TLR4 in the course of neonatal sepsis, which could reflect specific inflammatory responses to distinct pathogens. The definition of TLR expression patterns might open a new field of therapeutic targets for neonatal sepsis.

Expression of tumour necrosis factor receptor and Toll-like receptor 2 and 4 on peripheral blood leucocytes of human volunteers after endotoxin challenge: a comparison of flow cytometric light scatter and immunofluorescence gating

Toll-like receptors (TLRs) are involved in the recognition of bacterial products and thus participate in the induction of the inflammatory cascade. However, much less is known about the evolution of leucocyte TLR expression during human inflammatory stress. We hypothesized that a decrease in leucocyte TLRs could account for the so-called tolerance or hyporesponsiveness state to subsequent stimulation with bacteria-derived products. Because of the profound monocytopenia that ensues after in vivo lipopolysaccharide (LPS) challenge, we also compared monocyte TLR expression using two different techniques of flow cytometric gating. In a first set of experiments, 17 healthy volunteers underwent LPS challenge. Blood was drawn at different time-points and analysed by flow cytometry using light scatter gating and one-colour analysis to assess the expression of the tumour necrosis factor receptor (TNFR) and TLR2 and TLR4 on both monocytes and granulocytes. In a second set of experiments, the assessment of those receptors was made using a more specific gating method that utilized light scatter and CD14 immunofluorescence in a two-colour analysis. This was performed using whole blood drawn from five healthy volunteers and incubated ex vivo for different time periods with or without LPS and in 12 volunteers who underwent LPS challenge in vivo. The pattern of expression for monocyte TNFR was similar for both types of gating. Using only the light scatter gating, an initial drop of TLR 2 and 4 was observed on monocytes. By contrast, when using light scatter x immunofluorescence gating, an up-regulation of these two receptors following both in vivo and in vitro LPS exposure was observed. LPS up-regulates the expression of TLRs on monocytes and granulocytes. Depending upon the methodology utilized, contrasting results were obtained with respect to TLR2 and TLR4 expression. The flow cytometric gating technique used is of importance in determining cellular TLR2 and TLR4 expression, especially in blood samples exhibiting significant monocytopenia.

TLR signaling in the gut in health and disease

The human intestine has evolved in the presence of diverse enteric microflora. TLRs convert the recognition of pathogen-associated molecules in the gut into signals for anti-microbial peptide expression, barrier fortification, and proliferation of epithelial cells. Healing of injured intestinal epithelium and clearance of intramucosal bacteria require the presence of intact TLR signaling. Nucleotide oligomerization domain (Nod)1 and Nod2 are additional pattern recognition receptors that are required for defense against invasive enteric pathogens. Through spatial and functional localization of TLR and Nod molecules, the normal gut maintains a state of controlled inflammation. By contrast, patients with inflammatory bowel disease demonstrate inflammation in response to the normal flora. A subset of these patients carry polymorphisms in TLR and CARD15/NOD2 genes. A better understanding of the delicate regulation of TLR and Nod molecules in the gut may lead to improved treatment for enteric infections and idiopathic inflammatory bowel diseases.

Bacterial translocation (BT) in cirrhosis

Gut flora and bacterial translocation (BT) play an important role in the pathogenesis of the complications of cirrhosis. Research on the pathogenesis of BT and its clinical significance transcends established boundaries between microbiology, cell biology, intestinal pathophysiology, and immunology. This review delineates multiple mechanisms involved in the process of BT, with an emphasis on alterations in intestinal flora and mucosal barrier function, particularly immunological defense mechanisms. Current knowledge on the innate and adaptive immune response that allows a "friendly" communication between bacteria and host is summarized, and alterations occurring in cirrhosis that may facilitate BT are discussed. In addition, definition of a "pathological" BT is proposed together with an analysis of the anatomical site and route of BT. Finally, therapeutic approaches for the prevention of BT in experimental and human cirrhosis are reviewed. Future research in the field of BT in cirrhosis will allow the development of new therapeutic targets in the prevention of infections and other complications of cirrhosis.

The physiological regulation of toll-like receptor expression and function in humans

Eleven mammalian toll-like receptors (TLRs 1-11) have been identified to date and are known to play a crucial role in the regulation of immune responses; however, the factors that regulate TLR expression and function in vivo are poorly understood. Therefore, in the present study, we investigated the physiological regulation of TLR expression and function in humans. To examine the influence of diurnal rhythmicity on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers (n = 8) at time points coinciding with the peak and nadir in the endogenous circulating cortisol concentration. While no diurnal rhythmicity in the expression of TLRs 1, 2, 4 or 9 was observed, the upregulation of costimulatory (CD80 and CD86) and antigen-presenting (MHC class II) molecules on CD14(+) monocytes following activation with specific TLR ligands was greater (P < 0.05) in samples obtained in the evening compared with the morning. To examine the influence of physical stress on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers (n = 11) at rest and following 1.5 h of strenuous exercise in the heat (34 degrees C). Strenuous exercise resulted in a decrease (P < 0.005) in the expression of TLRs 1, 2 and 4 on CD14(+) monocytes. Furthermore, the upregulation of CD80, CD86, MHC class II and interleukin-6 by CD14(+) monocytes following activation with specific TLR ligands was decreased (P < 0.05) in samples obtained following exercise compared with at rest. These results demonstrate that TLR function is subject to modulation under physiological conditions in vivo and provide evidence for the role of immunomodulatory hormones in the regulation of TLR function.

Endotoxin down-modulates P-selectin glycoprotein ligand-1 (PSGL-1, CD162) on neutrophils in humans

P-selectin glycoprotein ligand-1 (PSGL-1, CD162), the counter-receptor for P-selectin and possibly E- and L-selectin, mediates rolling of leukocytes during inflammation and, thus, plays a pivotal role in hemostasis and inflammation. PSGL-1 is constitutively expressed on circulating leukocytes. Until recently, PSGL-1 has been considered not to be regulated upon cell activation. As modulation of PSGL-1 has only recently been reported for three proinflammatory substances, PSGL-1 regulation was examined during systemic inflammation in humans. Nine healthy human volunteers received a bolus of 2 ng/kg LPS i.v. Endotoxin infusion down-modulated PSGL-1 expression on neutrophils, with a maximum at 6-8 hr (-22%; P =0.001 vs. baseline and placebo), which correlated with peak neutrophilia. Similar PSGL-1 down-regulation was observed on monocytes. sPSGL-1 plasma levels increased trendwise after LPS infusion (+12% at 6 hr; P =0.10). In vitro LPS stimulation of whole blood significantly down-regulated PSGL-1 on neutrophils (-43%) and monocytes (-35%) as early as 2 hr ( P <0.05; n =5) in both EDTA and lepirudin anticoagulated samples. In summary, PSGL-1 is down-modulated on neutrophils and monocytes during endotoxemia in humans. PSGL-1 down-regulation could potentially facilitate the development of neutrophilia.

Simvastatin prevents vascular hyporeactivity during inflammation

BACKGROUND

There is growing evidence that statins exert anti-inflammatory and antioxidative vascular actions that are independent of lipid lowering. We tested whether hyporeactivity to the endothelium-dependent vasodilator acetylcholine (ACh) and the vasoconstrictor norepinephrine (NE) during acute experimental inflammation could be prevented by simvastatin.

METHODS AND RESULTS

In a randomized, placebo-controlled, parallel group study, forearm blood flow (FBF) responses to NE, ACh, and the endothelium-independent vasodilator nitroglycerin (NTG) were assessed at baseline, after 4 days of simvastatin 80 mg PO or placebo treatment, and during Escherichia coli endotoxin (lipopolysaccharide [LPS])-induced inflammation in 20 healthy volunteers. Additionally, markers of inflammation and neutrophil oxidative burst were assessed. Simvastatin and placebo had no effect on FBF or oxidative/inflammatory markers. LPS administration decreased the responses of FBF to NE by 43% (P<0.05) and decreased responses to ACh by 48% (P<0.05) but did not decrease FBF responses to NTG. Simvastatin completely preserved responses to NE and to ACh. The LPS-induced increases in neutrophil oxidative burst and plasma tumor necrosis factor-alpha concentrations were mitigated by simvastatin (P<0.05 versus placebo).

CONCLUSIONS

This study demonstrates potent vasoprotective properties of high-dose simvastatin during endotoxemia that may be useful for patients with acute systemic inflammation and associated vascular hyporeactivity.

Differential expression of Toll-like receptor (TLR)-2 and TLR-4 on monocytes in human sepsis

Toll-like receptors (TLRs) are a recently described family of immune receptors involved in the recognition of pathogen-associated molecular patterns (PAMPs). The central role of TLR-2 and TLR-4 in microbial responses suggests they may be implicated in the pathogenesis of human sepsis. We hypothesized that the incidence and outcome of sepsis would be influenced by the expression of TLR-2 and TLR-4 on monocytes. We have examined the expression of TLR-2 and TLR-4 mRNA and protein and their response to pro- and anti-inflammatory agents on monocytes from subjects in the intensive therapy unit (ITU) with and without Gram-negative, Gram-positive or polymicrobial sepsis. We compared these data to ITU and healthy control subjects. TLR-2 mRNA was significantly up-regulated on monocytes from subjects with both Gram-positive and Gram-negative sepsis. Similarly, we detected increased levels of TLR-2 protein on the surface of monocytes from sepsis subjects relative to ITU controls. TLR-4 mRNA was increased in Gram-positive subjects; however, there was no corresponding increase in TLR-4 protein. Although TLR-4 mRNA expression in healthy control monocytes could be modulated in vitro by culture with lipopolysaccharide or interleukin-10, this was not observed in monocytes obtained from sepsis and ITU control subjects, suggesting that septic and ITU control milieus may alter the immunoregulation of TLR-4 mRNA expression on monocytes. TLR-2 mRNA was not modulated in culture by any stimulus in any group. We suggest that expression and regulatory response of monocyte TLR-2, and to a lesser extent TLR-4 may be abnormal in human sepsis.

Triad3A, an E3 ubiquitin-protein ligase regulating Toll-like receptors

Activation of Toll-like receptors (TLRs) results in a proinflammatory response needed to combat infection. Thus, limiting TLR signaling is essential for preventing a protective response from causing injury to the host. Here we describe how a RING finger protein, Triad3A, acts as an E3 ubiquitin-protein ligase and enhances ubiquitination and proteolytic degradation of some TLRs. Triad3A overexpression promoted substantial degradation of TLR4 and TLR9 with a concomitant decrease in signaling, but did not affect TLR2 expression or signaling. Conversely, a reduction in endogenous Triad3A by small interfering RNA increased TLR expression and enhanced TLR activation. Thus, ubiquitination by Triad3A represents one pathway by which the intensity and duration of TLR signaling is controlled.

Toll-like receptors and the host defense against microbial pathogens: bringing specificity to the innate-immune system

Toll-like receptors (TLRs) have been identified as a major class of pattern-recognition receptors. Recognition of pathogen-associated molecular patterns (PAMPs) by TLRs, alone or in heterodimerization with other TLR or non-TLR receptors, induces signals responsible for the activation of genes important for an effective host defense, especially proinflammatory cytokines. Although a certain degree of redundancy exists between signals induced by the various TLRs, recent studies have identified intracellular pathways specific for individual TLRs. This leads to the release of cytokine profiles specific for particular PAMPs, and thus, TLRs confer a certain degree of specificity to the innate-immune response. In addition to the activation of the innate-immune response, TLR-mediated recognition represents a link between the innate- and acquired-immune systems, by inducing the maturation of dendritic cells and directing the T helper responses. Alternatively, recent data have also suggested TLR-mediated escape mechanisms used by certain pathogenic microorganisms, especially through TLR2 induction of anti-inflammatory cytokines. Finally, the crucial role of TLRs for the host defense against infections has been strengthened recently by the description of patients partially defective in the TLR-activation pathways.