Modulatory effects of sCD14 and LBP on LPS-host cell interactions

HIV patients treated with low-dose prednisolone exhibit lower immune activation than untreated patients

Background

HIV-associated general immune activation is a strong predictor for HIV disease progression, suggesting that chronic immune activation may drive HIV pathogenesis. Consequently, immunomodulating agents may decelerate HIV disease progression.

Methods

In an observational study, we determined immune activation in HIV patients receiving low-dose (5 mg/day) prednisolone with or without highly-active antiretroviral therapy (HAART) compared to patients without prednisolone treatment. Lymphocyte activation was determined by flow cytometry detecting expression of CD38 on CD8(+) T cells. The monocyte activation markers sCD14 and LPS binding protein (LBP) as well as inflammation markers soluble urokinase plasminogen activated receptor (suPAR) and sCD40L were determined from plasma by ELISA.

Results

CD38-expression on CD8+ T lymphocytes was significantly lower in prednisolone-treated patients compared to untreated patients (median 55.40% [percentile range 48.76-67.70] versus 73.34% [65.21-78.92], p = 0.0011, Mann-Whitney test). Similarly, we detected lower levels of sCD14 (3.6 μg/ml [2.78-5.12] vs. 6.11 μg/ml [4.58-7.70]; p = 0.0048), LBP (2.18 ng/ml [1.59-2.87] vs. 3.45 ng/ml [1.84-5.03]; p = 0.0386), suPAR antigen (2.17 μg/ml [1.65-2.81] vs. 2.56 μg/ml [2.24-4.26]; p = 0.0351) and a trend towards lower levels of sCD40L (2.70 pg/ml [1.90-4.00] vs. 3.60 pg/ml [2.95-5.30]; p = 0.0782). Viral load in both groups was similar (0.8 × 10⁵ ng/ml [0.2-42.4 × 10⁵] vs. 1.1 × 10⁵ [0.5-12.2 × 10⁵]; p = 0.3806). No effects attributable to prednisolone were observed when patients receiving HAART in combination with prednisolone were compared to patients who received HAART alone.

Conclusions

Patients treated with low-dose prednisolone display significantly lower general immune activation than untreated patients. Further longitudinal studies are required to assess whether treatment with low-dose prednisolone translates into differences in HIV disease progression.

Microbial translocation across the GI tract

The lumen of the gastrointestinal (GI) tract is home to an enormous quantity of different bacterial species, our microbiota, that thrive in an often symbiotic relationship with the host. Given that the healthy host must regulate contact between the microbiota and its immune system to avoid overwhelming systemic immune activation, humans have evolved several mechanisms to attenuate systemic microbial translocation (MT) and its consequences. However, several diseases are associated with the failure of one or more of these mechanisms, with consequent immune activation and deleterious effects on health. Here, we discuss the mechanisms underlying MT, diseases associated with MT, and therapeutic interventions that aim to decrease it.

Increased intestinal permeability correlates with sigmoid mucosa alpha-synuclein staining and endotoxin exposure markers in early Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder of aging. The pathological hallmark of PD is neuronal inclusions termed Lewy bodies whose main component is alpha-synuclein protein. The finding of these Lewy bodies in the intestinal enteric nerves led to the hypothesis that the intestine might be an early site of PD disease in response to an environmental toxin or pathogen. One potential mechanism for environmental toxin(s) and proinflammatory luminal products to gain access to mucosal neuronal tissue and promote oxidative stress is compromised intestinal barrier integrity. However, the role of intestinal permeability in PD has never been tested. We hypothesized that PD subjects might exhibit increased intestinal permeability to proinflammatory bacterial products in the intestine. To test our hypothesis we evaluated intestinal permeability in subjects newly diagnosed with PD and compared their values to healthy subjects. In addition, we obtained intestinal biopsies from both groups and used immunohistochemistry to assess bacterial translocation, nitrotyrosine (oxidative stress), and alpha-synuclein. We also evaluated serum markers of endotoxin exposure including LPS binding protein (LBP). Our data show that our PD subjects exhibit significantly greater intestinal permeability (gut leakiness) than controls. In addition, this intestinal hyperpermeability significantly correlated with increased intestinal mucosa staining for E. coli bacteria, nitrotyrosine, and alpha-synuclein as well as serum LBP levels in PD subjects. These data represent not only the first demonstration of abnormal intestinal permeability in PD subjects but also the first correlation of increased intestinal permeability in PD with intestinal alpha–synuclein (the hallmark of PD), as well as staining for gram negative bacteria and tissue oxidative stress. Our study may thus shed new light on PD pathogenesis as well as provide a new method for earlier diagnosis of PD and suggests potential therapeutic targets in PD subjects.

Trial Registration

Clinicaltrials.govNCT01155492

Postnatal development of hepatic innate immune response

The liver is an immunocompetent organ that plays a key role in the immune response to infections, and the development of hepatic immune function during early postnatal stages has not been thoroughly characterized. This study analyzed the constitutive expression of complement factors, namely C3 and C9, and pattern recognition receptors, namely CD14, toll-like receptor (TLR)-4, and lipopolysaccharide binding protein (LBP), in the liver of postnatal day (P)1, P21, and P70 rats, and compared the kinetics of induction of cytokines and chemokines in the liver of P 1 and P 21 animals. Our studies found that while the mRNA expression of C3, C9, CD14, and TLR-4 was lower in P1 animals, the mRNA level of LBP was higher in P1 animals as compared to older animals, and that the kinetics of induction of cytokines and chemokines was significantly delayed in P1 as compared to P21 liver following LPS stimulation. Our data suggest that hepatic innate immunity is deficient in the neonates and undergo significant development during early postnatal life.

Consequences of alteration in leucine zipper sequence of melittin in its neutralization of lipopolysaccharide-induced proinflammatory response in macrophage cells and interaction with lipopolysaccharide

The bee venom antimicrobial peptide, melittin, besides showing versatile activity against microorganisms also neutralizes lipopolysaccharide (LPS)-induced proinflammatory responses in macrophage cells. However, how the amino acid sequence of melittin contributes in its anti-inflammatory properties is mostly unknown. To determine the importance of the leucine zipper sequence of melittin in its neutralization of LPS-induced inflammatory responses in macrophages and interaction with LPS, anti-inflammatory properties of melittin and its three analogues and their interactions with LPS were studied in detail. Two of these analogues, namely melittin Mut-1 (MM-1) and melittin Mut-2 (MM-2), possess leucine to alanine substitutions in the single and double heptadic leucine residue(s) of melittin, respectively, whereas the third analogue is a scrambled peptide (Mel-SCR) that contains the amino acid composition of melittin with minor rearrangement in its leucine zipper sequence. Although MM-1 partly inhibited the production of proinflammatory cytokines in RAW 264.7 and rat primary macrophage cells in the presence of LPS, MM-2 and Mel-SCR were negligibly active. A progressive decrease in interaction of melittin with LPS, aggregation in LPS, and dissociation of LPS aggregates with alteration in the leucine zipper sequence of melittin was observed. Furthermore, with alteration in the leucine zipper sequence of melittin, these analogues failed to exhibit cellular responses associated with neutralization of LPS-induced inflammatory responses in macrophage cells by melittin. The data indicated a probable important role of the leucine zipper sequence of melittin in neutralizing LPS-induced proinflammatory responses in macrophage cells as well as in its interaction with LPS.

Endotoxin{middle dot}albumin complexes transfer endotoxin monomers to MD-2 resulting in activation of TLR4

Response to Gram-negative bacteria (GNB) is partially mediated by the recognition of GNB-derived endotoxin by host cells. Potent host response to endotoxin depends on the sequential interaction of endotoxin with lipopolysaccharide binding protein (LBP), CD14, MD-2 and TLR4. While CD14 facilitates the efficient transfer of endotoxin monomers to MD-2 and MD-2·TLR4, activation of MD-2·TLR4 can occur in the absence of CD14 through an unknown mechanism. Here, we show that incubation of purified endotoxin (E) aggregates (E(agg), M ( r ) ≥ 20 million) in PBS with ≥ 0.1% albumin in the absence of divalent cations Ca(2+) and Mg(2+), yields E·albumin complexes (M ( r ) ∼70,000). E·albumin transfers E monomers to sMD-2 or sMD-2·TLR4 ectodomain (TLR4(ecd)) with a 'K (d)' of ∼4 nM and induces MD-2·TLR4-dependent, CD14-independent cell activation with a potency only 10-fold less than that of monomeric E·CD14 complexes. Our findings demonstrate, for the first time, a mechanistic basis for delivery of endotoxin monomers to MD-2 and for activation of TLR4 that is independent of CD14.

Increased microbial translocation in ≤ 180 days old perinatally human immunodeficiency virus-positive infants as compared with human immunodeficiency virus-exposed uninfected infants of similar age

BACKGROUND

The effect of early versus deferred antiretroviral treatment (ART) on plasma concentration of lipopolysaccharide (LPS) and host LPS-binding molecules in human immunodeficiency virus (HIV)-infected infants up to 1 year of age was investigated.

METHODS

We evaluated 54 perinatally HIV-infected and 22 HIV-exposed uninfected infants (controls) at the first and second semester of life. All HIV-infected infants had a baseline CD4 of ≥ 25%, participated in the Comprehensive International Program of Research on AIDS Children with HIV Early Antiretroviral Therapy trial in South Africa, and were randomized in the following groups: group 1 (n = 20), ART deferred until CD4 < 25% or severe HIV disease; and group 2 (n = 34), ART initiation within 6 to 12 weeks of age. LPS, endotoxin-core antibodies, soluble CD14 (sCD14), and LPS-binding protein (LBP) were measured in cryopreserved plasma. T-cell activation was measured in fresh whole blood.

RESULTS

At the first semester, LPS concentration was higher in HIV-infected infants than in controls; sCD14, LBP, and T-cell activation were higher in group 1 than in group 2 and controls. Although LPS was not correlated with study variables, viral load was positively associated with sCD14, LBP, or endotoxin-core antibodies. At the second semester, LPS was not detectable and elevated host LPS-control molecules values were sustained in all groups and in conjunction with ART in all HIV-infected infants.

CONCLUSIONS

Although plasma concentration of LPS was higher in perinatally HIV-infected infants 0 to 6 months of age than in controls independent of ART initiation strategy, concentration of LPS-control molecules was higher in infants with deferred ART, suggesting the presence of increased microbial translocation in HIV-infected infants with sustained early viral replication.

Molecular characterization of stool microbiota in HIV-infected subjects by panbacterial and order-level 16S ribosomal DNA (rDNA) quantification and correlations with immune activation

BACKGROUND

The relationship between gut microbial community composition at the higher-taxonomic order level and local and systemic immunologic abnormalities in HIV disease may provide insight into how bacterial translocation impacts HIV disease.

METHODS

Antiretroviral-naive patients with HIV underwent upper endoscopy before and 9 months after starting antiretroviral treatment. Duodenal tissue was paraffin-embedded for immunohistochemical analysis and digested for fluorescence activated cell sorting for T-cell subsets and immune activation (CD38+/HLA-DR+) enumeration. Stool samples were provided from patients and control subjects for comparison. Metagenomic microbial DNA was extracted from feces for optimized 16S ribosomal RNA gene (rDNA) real-time quantitative polymerase chain reaction assays designed to quantify panbacterial loads and the relative abundances of proinflammatory Enterobacteriales order and the dominant Bacteroidales and Clostridiales orders.

RESULTS

Samples from 10 HIV subjects before initiating and from six subjects receiving antiretroviral treatment were available for analysis. There was a trend for a greater proportion of Enterobacteriales in HIV-positive subjects compared with control subjects (P = 0.099). There were significant negative correlations between total bacterial load and duodenal CD4 and CD8 T-cell activation levels (r = -0.74, P = 0.004 and r = -0.67, P = 0.013, respectively). The proportions of Enterobacteriales and Bacteroidales were significantly correlated with duodenal CD4 T-cell depletion and peripheral CD8 T-cell activation, respectively.

CONCLUSIONS

These data represent the first report of quantitative molecular and cellular correlations between total/universal and order-level gut bacterial populations and gastrointestinal-associated lymphoid tissue levels of immune activation in HIV-infected subjects. The correlations between lower overall 16S rDNA levels and tissue immune activation suggest that the gut microbiome may contribute to immune activation and influence HIV progression.

Endotoxemia is associated with altered innate and adaptive immune responses in untreated HIV-1 infected individuals

Background

Microbial translocation may contribute to the immunopathogenesis in HIV infection. We investigated if microbial translocation and inflammation were associated with innate and adaptive immune responses in adults with HIV.

Methodology/Principal Findings

This was an observational cohort study. Sera from HIV-infected and HIV-uninfected individuals were analyzed for microbial translocation (soluble CD14, lipopolysaccharides [LPS], endotoxin core antibody, and anti-α-galactosyl antibodies) and inflammatory markers (high sensitivity C-reactive protein, IL-6, IL-1 receptor antagonist, soluble tumor necrosis factor receptor II, and IL-10) with enzyme-linked immunosorbent assays. Peripheral blood mononuclear cells (PBMC) from HIV-infected persons and healthy controls (primed with single-stranded HIV-1-derived RNA) were stimulated with LPS, and cytokine production was measured. Finally, HIV-infected patients were immunized with Prevnar 7vPnC±CpG 7909 followed by Pneumo Novum PPV-23. Effects of microbial translocation and inflammation on immunization were analyzed in a predictive regression model. We included 96 HIV-infected individuals, 76 on highly active antiretroviral therapy (HAART), 20 HAART-naive, and 50 healthy controls. Microbial translocation and inflammatory markers were higher among HIV-infected persons than controls. Cytokine levels following LPS stimulation were increased in PBMCs from HAART-naive compared to HAART-treated HIV-infected persons. Further, RNA-priming of PBMCs from controls acted synergistically with LPS to augment cytokine responses. Finally, high serum LPS levels predicted poor vaccine responses among HAART-naive, but not among HAART-treated HIV-infected individuals.

Conclusions/Significance

LPS acts synergistically with HIV RNA to stimulate innate immune responses in vitro and increasing serum LPS levels seem to predict poor antibody responses after vaccination among HAART-naive HIV-infected persons. Thus, our results suggest that microbial translocation may be associated with innate and adaptive immune dysfunction in untreated HIV infection.

Effect of solar particle event radiation on gastrointestinal tract bacterial translocation and immune activation

Space flight conditions within the protection of Earth's gravitational field have been shown to alter immune responses, which could lead to potentially detrimental pathology. An additional risk of extended space travel outside the Earth's gravitational field is the effect of solar particle event (SPE) radiation exposure on the immune system. Organisms that could lead to infection include endogenous, latent viruses, colonizing pathogenics, and commensals, as well as exogenous microbes present in the spacecraft or other astronauts. In this report, the effect of SPE-like radiation on containment of commensal bacteria and the innate immune response induced by its breakdown was investigated at the radiation energies, doses and dose rates expected during an extravehicular excursion outside the Earth's gravitational field. A transient increase in serum lipopolysaccharide was observed 1 day after irradiation and was accompanied by an increase in acute-phase reactants and circulating proinflammatory cytokines, indicating immune activation. Baseline levels were reestablished by 5 days postirradiation. These findings suggest that astronauts exposed to SPE radiation could have impaired containment of colonizing bacteria and associated immune activation.

Endotoxin and CD14 in the progression of biliary atresia

Background

Biliary atresia (BA) is a typical cholestatic neonatal disease, characterized by obliteration of intra- and/or extra-hepatic bile ducts. However, the mechanisms contributing to the pathogenesis of BA remain uncertain. Because of decreased bile flow, infectious complications and damaging endotoxemia occur frequently in patients with BA. The aim of this study was to investigate endotoxin levels in patients with BA and the relation of these levels with the expression of the endotoxin receptor, CD14.

Methods

The plasma levels of endotoxin and soluble CD14 were measured with a pyrochrome Limulus amebocyte lysate assay and enzyme-linked immunosorbent assay in patients with early-stage BA when they received the Kasai procedure (KP), in patients who were jaundice-free post-KP and followed-up at the outpatient department, in patients with late-stage BA when they received liver transplantation, and in patients with choledochal cysts. The correlation of CD14 expression with endotoxin levels in rats following common bile duct ligation was investigated.

Results

The results demonstrated a significantly higher hepatic CD14 mRNA and soluble CD14 plasma levels in patients with early-stage BA relative to those with late-stage BA. However, plasma endotoxin levels were significantly higher in both the early and late stages of BA relative to controls. In rat model, the results demonstrated that both endotoxin and CD14 levels were significantly increased in liver tissues of rats following bile duct ligation.

Conclusions

The significant increase in plasma endotoxin and soluble CD14 levels during BA implies a possible involvement of endotoxin stimulated CD14 production by hepatocytes in the early stage of BA for removal of endotoxin; whereas, endotoxin signaling likely induced liver injury and impaired soluble CD14 synthesis in the late stages of BA.

Biomarkers of immune dysfunction in HIV

PURPOSE OF REVIEW

HIV infection is characterized by chronic immune system activation and inflammatory cytokine production. This review will highlight recent developments using plasma and cellular biomarkers of immune system activation and dysfunction to predict mortality and opportunistic disease in HIV-infected individuals.

RECENT FINDINGS

HIV infection results in features characteristic of early aging of the immune system or 'immune senescence', driven by chronic antigen exposure and immune system activation. Microbial translocation of gut bacterial components is associated with chronic immune activation and possibly systemic inflammation. Antiretroviral therapy may not fully normalize this condition. Baseline elevations of certain biomarkers of inflammation or coagulopathy, notably interleukin-6 (IL-6), C-reactive protein (CRP), and D-dimer, have been associated with mortality or opportunistic disease, after adjustment for appropriate variables, in several large randomized clinical trials. It is not known if elevated IL-6 or CRP causes this morbidity and mortality or if they are simply surrogate markers of a global inflammatory state.

SUMMARY

Several inflammatory biomarkers appear to add to our ability to predict mortality or opportunistic disease in HIV-infected individuals. Before biomarkers will be useful, it will be necessary to identify interventions that moderate biomarker levels, and then determine if this moderation attenuates disease outcomes.

Systemic endotoxin levels in chronic indolent periodontal infections

BACKGROUND AND OBJECTIVE

Periodontal disease has been linked with an increased risk of various systemic diseases. A plausible biologic explanation for this link includes the opportunity for oral pathogens to translocate to the circulation as a result of breakdown in integrity of the oral epithelium. This study refined a methodology used to detect endotoxin activity in the serum of subjects with indolent periodontal infections.

MATERIAL AND METHODS

The QCL Kinetic Chromogenic Assay (Cambrex) is a kinetic measure of endotoxin activity. Sera from 211 pregnant women with periodontitis enrolled in the Obstetrics and Periodontal Therapy Trial were used to develop the assay further and to evaluate the detection of endotoxin activity that might accompany a low-level bacteremia in chronic periodontitis.

RESULTS

We optimized the system to increase the sensitivity and reproducibility of the assay. The refined system was able to detect endotoxin activity in serum at > 0.0125 EU/mL. At baseline (13-16 wk of gestation), 35.5% of the women were positive for endotoxin activity (1.62 +/- 2.21; range: 0.38-15 EU/mL).

CONCLUSION

This report describes a sensitive measure of endotoxin activity in serum. The procedure allowed us to document levels of this microbial virulence factor in serum of individuals with indolent infections such as periodontal disease.

Role of CD14 in a mouse model of acute lung inflammation induced by different lipopolysaccharide chemotypes

BACKGROUND

Recognition of lipopolysaccharide (LPS) is required for effective defense against invading gram-negative bacteria. Recently, in vitro studies revealed that CD14 is required for activation of the myeloid differentiation factor (MyD)88-dependent Toll-like receptor (TLR)4 signaling pathway by smooth (S)-LPS, but not by rough (R)-LPS. The present study investigated the role of CD14 in induction of lung inflammation in mice by these different LPS chemotypes.

METHODOLOGY/RESULTS

Neutrophil accumulation and tumor necrosis factor (TNF) release in bronchoalveolar lavage fluid were determined 6 hours after intranasal treatment of wild type (WT) and CD14 knock-out (KO) mice with different doses S-LPS or R-LPS. The contribution of CD14 to lung inflammation induced by S-LPS or R-LPS depended on the LPS dose. At low doses, S-LPS and R-LPS induced neutrophil influx in a CD14-dependent manner. Low dose S-LPS-induced cytokine release also depended on CD14. Strikingly, neutrophil influx and TNF release induced by high dose S-LPS or R-LPS was diminished in the presence of CD14. Intranasal administration of sCD14 to CD14 KO mice treated with S-LPS partially reversed the inflammatory response to the response observed in WT mice.

CONCLUSIONS

In conclusion, CD14 modulates effects of both S-LPS and R-LPS within the lung in a similar way. Except for R-LPS-induced TNF release, S-LPS and R-LPS at low dose induced acute lung inflammation in a CD14-dependent manner, while the inflammatory response triggered by high dose S-LPS or R-LPS was diminished by CD14.

Role of CD14 in lung inflammation and infection

This article is one of ten reviews selected from the Yearbook of Intensive Care and Emergency Medicine 2010 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/yearbook. Further information about the Yearbook of Intensive Care and Emergency Medicine is available from http://www.springer.com/series/2855.

Increased bactericidal/permeability increasing protein in patients with cirrhosis

BACKGROUND

High levels of endotoxin in patients with cirrhosis are thought to be responsible for the activation of tumour necrosis factor-alpha (TNF)-alpha-mediated pro-inflammatory pathways involved in haemodynamic alterations. Bactericidal/permeability increasing protein (BPI) is a protein found in neutrophils with endotoxin-binding and neutralization capacity. It is not known whether defective BPI production or release is present in cirrhosis.

AIMS

We investigated the levels of BPI in cirrhotic patients and its relation to other endotoxin-binding proteins and inflammatory markers.

METHODS

Plasmatic levels of BPI, lipopolysaccharide-binding protein, soluble CD14, TNF-alpha and BPI mRNA expression in neutrophils were determined in 130 patients and 30 healthy controls. The capacity of patients' plasma to inhibit lipopolysaccharide (LPS)-mediated TNF-alpha production by monocytes from healthy donors was assessed in vitro.

RESULTS

Patients with cirrhosis exhibited an increase in BPI mRNA and plasma level of BPI when compared with healthy controls (P<0.05). Child C group displayed the highest frequency of patients with a high concentration of BPI. A positive correlation was found between TNF-alpha and plasma levels of BPI (P<0.01). High levels of BPI in plasma were able to significantly reduce in vitro TNF-alpha release by monocytes after a challenge with LPS (8.54 +/- 1.04 vs. 10.44 +/- 0.85 pg/ml, P=0.028).

CONCLUSION

BPI is increased in cirrhotic patients, especially in those with more severe liver disease. The amount of BPI in the plasma correlated with the TNF-alpha level and was able to reduce LPS-mediated TNF production by monocytes. BPI possibly plays a regulatory role by antagonizing the pro-inflammatory mechanisms mediated by TNF-alpha.

Increased tissue factor expression on circulating monocytes in chronic HIV infection: relationship to in vivo coagulation and immune activation

HIV infection is associated with an increased risk of thrombosis; and as antiretroviral therapy has increased the lifespan of HIV-infected patients, their risk for cardiovascular events is expected to increase. A large clinical study found recently that all-cause mortality for HIV(+) patients was related to plasma levels of interleukin-6 and to D-dimer products of fibrinolysis. We provide evidence that this elevated risk for coagulation may be related to increased proportions of monocytes expressing cell surface tissue factor (TF, thromboplastin) in persons with HIV infection. Monocyte TF expression could be induced in vitro by lipopolysaccharide and flagellin, but not by interleukin-6. Monocyte expression of TF was correlated with HIV levels in plasma, with indices of immune activation, and with plasma levels of soluble CD14, a marker of in vivo lipopolysaccharide exposure. TF levels also correlated with plasma levels of D-dimers, reflective of in vivo clot formation and fibrinolysis. Thus, drivers of immune activation in HIV disease, such as HIV replication, and potentially, microbial translocation, may activate clotting cascades and contribute to thrombus formation and cardiovascular morbidities in HIV infection.

Endotoxin receptor CD14 gene variants and histological features in chronic HCV infection

AIM: To analyze the correlation between CD14 rs2569190/C-159T single nucleotide polymorphism (SNP) and disease progression in chronic hepatitis C.

METHODS: Liver biopsy specimens from a total of 137 and 349 patients with chronic hepatitis C were separately evaluated with respect to necroinflammatory activity (grading) and architectural changes (staging). In one group, further histological lesions characteristic for hepatitis C, hepatitis C virus subtypes, and biochemical parameters of liver disease were also investigated. Samples of genomic DNA were genotyped for the respective SNP by 5’-nuclease assays using fluorescent dye-labeled allele-specific probes.

RESULTS: Genotype distribution did not deviate from the Hardy-Weinberg equilibrium. In the first group, patients homozygous for the variant allele T were found to be younger than C allele carriers (39.6 ± 12.5 vs 45.7 ± 11.5, P = 0.008). Among the histological lesions studied, portal lymphoid aggregates were more frequently observed among TT homozygotes than among C carriers (21/37 vs 32/100, P = 0.008). The presence of portal lymphoid aggregates was closely correlated with hepatic inflammation (P = 0.003) and with bile duct damage (P < 0.001). The degree of fibrosis, in contrast, was not found to be related to the CD14 gene C-159T polymorphism.

CONCLUSION: The data suggest a possible relationship between CD14 C-159T polymorphism and the formation of portal lymphoid aggregates, but not liver fibrosis progression in chronic hepatitis C.

Endotoxin-directed innate immunity in tracheal aspirates of mechanically ventilated human neonates

Mechanical ventilation of preterm infants is associated with pulmonary inflammation. Intubated infants often develop bacterial tracheal colonization, but little is known about endotoxin in tracheal aspirates (TAs) or the mobilization of innate immunity toward endotoxin, a potent stimulus that contributes to inflammatory disease. We characterized mobilization of endotoxin-directed innate immunity in TAs from an observational cohort of mechanically ventilated neonates. TA supernatants (n = 42; GA = 23-40 wk, postnatal age = 1-71 d) were assayed for endotoxin (Limulus amoebocyte lysate assay) and endotoxin-modulating proteins: bactericidal/ permeability-increasing protein (BPI), LPS-binding protein (LBP), and soluble cell differentiation antigen 14 (sCD14). TA cellular BPI was measured by ELISA, Western blot, flow cytometry, and bactericidal assay. TA mRNAs encoding endotoxin-modulating proteins were measured by quantitative real-time PCR (qRT-PCR). Endotoxin in TA supernatants was proportional to both postnatal age and polymorphonuclear leukocytes (PMN). Neonatal TAs were rich in PMN containing BPI and expressed mRNAs encoding Toll-like receptor (TLR) 4, CD14, and myeloid differentiation protein 2 (MD-2). Extracellular BPI was consistently detectable and correlated with TA PMN and GA. Both extracellular- and cellular-BPI increased during the first postnatal week. TA extracellular BPI, LBP, and sCD14 were positively correlated. TAs from intubated neonates demonstrate endotoxin accumulation and mobilization of endotoxin-directed innate immunity, potentially contributing to pulmonary inflammation.

Evidence for translocation of microbial products in patients with idiopathic CD4 lymphocytopenia

Translocation of microbial products has been described in chronic human immunodeficiency virus (HIV) infection and correlates with activation of the immune system. We investigated the potential translocation of microbial products in idiopathic CD4 lymphocytopenia (ICL), a rare disorder characterized by low CD4 T cell counts in the absence of HIV infection. Plasma lipopolysaccharide (LPS) levels and T cell activation were measured in a cross-sectional cohort study of patients with ICL and HIV infection and healthy control subjects. Increases in CD4 T cell proliferation but not CD8 T cell proliferation were observed in patients with ICL. LPS levels were significantly elevated both in patients with ICL and in patients with HIV infection, and they were strongly correlated with the proportion of proliferating CD4 T cells in the cohort of patients with ICL (r = 0.88; P= .003). The proportions of T helper (Th) 17 and Th1 CD4 cells in peripheral blood were similar between patients with ICL, patients with HIV infection, and control subjects. These findings suggest a potential association of translocation of microbial products with perturbed CD4 T cell homeostasis in individuals with CD4 lymphopenic states other than HIV infection.

Functional impact of endotoxin receptor CD14 polymorphisms on transcriptional activity

The polymorphism rs2569190 within the CD14 endotoxin (lipopolysaccharide, LPS) receptor gene is associated with various disease conditions that are assumed to rely on endotoxin sensitivity. In vitro experiments suggest that the T allele sensitizes the host for exogenous or endogenous LPS via an enhanced CD14 expression. To prove the impact of this single nucleotide polymorphism in its natural genomic context in vivo, two parameters of gene transcription were analyzed in peripheral blood mononuclear cells (PBMC) from single healthy individuals: (a) recruitment of RNA polymerase II by haplotype-specific chromatin immunoprecipitation and (b) the relative amount of transcripts by allele-specific transcript quantification (ASTQ). RNA polymerase II was found to be twice as much bound to the most prevalent haplotype, C-T-C-G, the only one carrying a T at the position rs2569190 of interest. ASTQ employing two independent read-out assays revealed, however, similar transcript numbers originating from C-T-C-G and non-C-T-C-G haplotypes. Total CD14 mRNA levels from freshly isolated PBMC, moreover, were neither related to donors' geno- nor haplogenotypes. Our data argue for a functional impact of the rs2569190 polymorphism in terms of a stronger transcription initiation on T allele gene variants even if preferential allele-specific binding does not result in an increase in transcript numbers. Endotoxin sensitivity associated with this genetic variation appears not to rely solely on a cis-acting regulatory impact of rs2569190 on CD14 gene transcription in PBMC.

Impaired Toll-like receptor 2 signalling in monocytes from 5-year-old allergic children

The relative composition of the two major monocytic subsets CD14(+)CD16(-) and CD14(+)CD16(+) is altered in some allergic diseases. These two subsets display different patterns of Toll-like receptor levels, which could have implications for activation of innate immunity leading to reduced immunoglobulin E-specific adaptive immune responses. This study aimed to investigate if allergic status at the age of 5 years is linked to differences in monocytic subset composition and their Toll-like receptor levels, and further, to determine if Toll-like receptor regulation and cytokine production upon microbial stimuli is influenced by the allergic phenotype. Peripheral blood mononuclear cells from 5-year-old allergic and non-allergic children were stimulated in vitro with lipopolysaccharide and peptidoglycan. Cells were analysed with flow cytometry for expression of CD14, Toll-like receptors 2 and 4 and p38-mitogen-activated protein kinase (MAPK). The release of cytokines and chemokines [tumour necrosis factor, interleukin (IL)-1 beta, IL-6, IL-8, IL-10, IL-12p70] into culture supernatants was measured with cytometric bead array. For unstimulated cells there were no differences in frequency of the monocytic subsets or their Toll-like receptor levels between allergic and non-allergic children. However, monocytes from allergic children had a significantly lower up-regulation of Toll-like receptor 2 upon peptidoglycan stimulation. Further, monocytes from allergic children had a higher spontaneous production of IL-6, but there were no differences between the two groups regarding p38-MAPK activity or cytokine and chemokine production upon stimulation. The allergic subjects in this study have a monocytic population that seems to display a hyporesponsive state as implicated by impaired regulation of Toll-like receptor 2 upon peptidoglycan stimulation.

Mechanical injury and cytokines cause loss of cartilage integrity and upregulate proteins associated with catabolism, immunity, inflammation, and repair

The objectives of this study were to perform a quantitative comparison of proteins released from cartilage explants in response to treatment with IL-1beta, TNF-alpha, or mechanical compression injury in vitro and to interpret this release in the context of anabolic-catabolic shifts known to occur in cartilage in response to these insults in vitro and their implications in vivo. Bovine calf cartilage explants from 6-12 animals were subjected to injurious compression, TNF-alpha (100 ng/ml), IL-1beta (10 ng/ml), or no treatment and cultured for 5 days in equal volumes of medium. The pooled medium from each of these four conditions was labeled with one of four iTRAQ labels and subjected to nano-2D-LC/MS/MS on a quadrupole time-of-flight instrument. Data were analysed by ProQuant for peptide identification and quantitation. k-means clustering and biological pathways analysis were used to identify proteins that may correlate with known cartilage phenotypic responses to such treatments. IL-1beta and TNF-alpha treatment caused a decrease in the synthesis of collagen subunits (p < 0.05) as well as increased release of aggrecan G2 and G3 domains to the medium (p < 0.05). MMP-1, MMP-3, MMP-9, and MMP-13 were significantly increased by all treatments compared with untreated samples (p < 0.10). Increased release of proteins involved in innate immunity and immune cell recruitment were noted following IL-1beta and TNF-alpha treatment, whereas increased release of intracellular proteins was seen most dramatically with mechanical compression injury. Proteins involved in insulin-like growth factor and TGF-beta superfamily pathway modulation showed changes in pro-anabolic pathways that may represent early repair signals. At the systems level, two principal components were sufficient to describe 97% of the covariance in the data. A strong correlation was noted between the proteins released in response to IL-1beta and TNF-alpha; in contrast, mechanical injury resulted in both similarities and unique differences in the groups of proteins released compared with cytokine treatment.

Delayed loss of control of plasma lipopolysaccharide levels after therapy interruption in chronically HIV-1-infected patients

OBJECTIVE

Increased circulating levels of lipopolysaccharide (LPS) have been demonstrated in HIV-1-infected progressors. We investigated the effect of antiretroviral therapy (ART) interruptions on plasma LPS levels.

DESIGN AND METHODS

Overall, 77 individuals participated in this study (51 HIV-positive and 26 healthy). Ten out of 51 HIV-positive participants were viremic ART-naive patients and 41 out of 51 were chronically suppressed patients on ART (three or more drugs, CD4 cell count more than 400 cells/microl, HIV-1 RNA less than 500 copies/ml for more than 8 months, less than 50 copies/ml at recruitment) undergoing therapy interruption. The limulus amebocyte assay was used to measure plasma LPS levels; enzyme-linked immunosorbent assay to measure plasma levels of endotoxin-core antibodies (EndoCAb), soluble (s)CD14, LPS-binding protein and IFN-alpha; immunoblotting to measure plasma gelsolin levels; and same day whole blood flow cytometry to measure levels of T-cell-activation markers (CD8/CD38, CD8/HLA-DR and CD3/CD95).

RESULTS

Increases in viremia and T-cell-activation markers were observed during therapy interruptions. During short-term therapy interruptions of less than 12 weeks, no change in LPS levels was found, whereas negative associations between viral load and LPS levels (Spearman's Rho = -0.612, P = 0.0152), viral load and EndoCAb change (DeltaEndoCAb, correlation = -0.502, P = 0.0204), and between DeltaLPS and DeltaEndoCAb (correlation = -0.851, P = 0.0073) were observed. In contrast, increased LPS (P = 0.0171) and sCD14 (P < 0.0001) levels were observed during long-term therapy interruption of more than 12 weeks compared with levels during ART, together with no association between LPS and viral load or EndoCAb. No association between immune activation and LPS was evident at any time point.

CONCLUSION

Increased plasma LPS levels were observed only after more than 12 weeks of ART interruption, despite presence of LPS-controlling host mechanisms.

Role of human CD36 in bacterial recognition, phagocytosis, and pathogen-induced JNK-mediated signaling

Scavenger receptor CD36 mediates Staphylococcus aureus phagocytosis and initiates TLR2/6 signaling. We analyzed the role of CD36 in the uptake and TLR-independent signaling of various bacterium, including Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, S. aureus, and Enterococcus faecalis. Expression of human CD36 in HeLa cells increased the uptake of both gram-positive and gram-negative bacteria compared with the control mock-transfected cells. Bacterial adhesion was associated with pathogen phagocytosis. Upon CD36 transfection, HEK293 cells, which demonstrate no TLR2/4 expression, acquired LPS responsiveness as assessed by IL-8 production. The cells demonstrated a marked 5- to 15-fold increase in cytokine release upon exposure to gram-negative bacteria, while the increase was much smaller (1.5- to 3-fold) with gram-positive bacteria and lipoteichoic acid. CD36 down-regulation utilizing CD36 small interfering RNA reduced cytokine release by 40-50% in human fibroblasts induced by both gram-negative and gram-positive bacteria as well as LPS. Of all MAPK signaling cascade inhibitors tested, only the inhibitor of JNK, a stress-activated protein kinase, potently blocked E. coli/LPS-stimulated cytokine production. NF-kappaB inhibitors were ineffective, indicating direct TLR-independent signaling. JNK activation was confirmed by Western blot analyses of phosphorylated JKN1/2 products. Synthetic amphipathic peptides with an alpha-helical motif were shown to be efficient inhibitors of E. coli- and LPS-induced IL-8 secretion as well as JNK1/2 activation/phosphorylation in CD36-overexpressing cells. These results indicate that CD36 functions as a phagocytic receptor for a variety of bacteria and mediates signaling induced by gram-negative bacteria and LPS via a JNK-mediated signaling pathway in a TLR2/4-independent manner.

Endotoxin receptor CD14 in PiZ alpha-1-antitrypsin deficiency individuals

BACKGROUND

CD14, a receptor for lipopolysaccharides (LPS), is found in both a membrane-bound form (mCD14) and a soluble form (sCD14). It is suggested that sCD14 is mainly released from blood monocytes by serine protease-mediated shedding. Because alpha1-antitrypsin (AAT), an inhibitor of serine proteases, has been shown to regulate CD14 expression in human monocytes in vitro, we sought to investigate plasma levels of sCD14 and monocyte expression of mCD14 in subjects at age 30 years with normal MM and deficient PiZZ and PiSZ genotypes of AAT.

METHODS

Plasma levels of AAT and sCD14 were measured in 75 PiZZ and 34 PiSZ individuals with normal lung function identified from the Swedish neonatal AAT deficiency screening, and in 95 age matched PiMM controls. The mCD14 expression in monocytes from 9 PiZZ, 6 PiSZ and 11 PiMM subjects was analysed by FACS and Quantitative Real Time Reverse Transcription PCA.

RESULTS

As expected, plasma AAT concentrations were PiMM>PiSZ>PiZZ (p < 0.001). Plasma sCD14 levels were higher in PiZZ than in PiMM subjects (p < 0.01). The expression level of mCD14 was higher (1.89-fold) in monocytes isolated from PiZZ subjects compared to PiMM controls (p = 0.00189).

CONCLUSION

This study is the first to show higher levels of plasma sCD14 and monocyte mCD14 expression in young, clinically healthy PiZZ AAT subjects.

Soluble hemojuvelin is released by proprotein convertase-mediated cleavage at a conserved polybasic RNRR site

As the principal iron-regulatory hormone, hepcidin plays an important role in systemic iron homeostasis. The regulation of hepcidin expression by iron loading appears to be unexpectedly complex and has attracted much interest. The GPI-linked membrane protein hemojuvelin (GPI-hemojuvelin) is an essential upstream regulator of hepcidin expression. A soluble form of hemojuvelin (s-hemojuvelin) exists in blood and acts as antagonist of GPI-hemojuvelin to downregulate hepcidin expression. The release of s-hemojuvelin is negatively regulated by both transferrin-bound iron (holo-Tf) and non-transferrin-bound iron (FAC), indicating s-hemojuvelin could be one of the mediators of hepcidin regulation by iron. In this report, we investigate the proteinase involved in the release of s-hemojuvelin and show that s-hemojuvelin is released by a proprotein convertase through the cleavage at a conserved polybasic RNRR site.

Sensitivity of mice to lipopolysaccharide is increased by a high saturated fat and cholesterol diet

Background

It was hypothesized that a pro-atherogenic, high saturated fat and cholesterol diet (HCD) would increase the inflammatory response to E. coli endotoxin (LPS) and increase its concentration in plasma after administration to mice.

Methods

C57Bl/6 mice were fed a HCD or a control diet (CD) for 4 weeks, and then treated with saline, 0.5, 1 or 2 mg LPS/kg, ip. Liver injury (alanine:2-oxoglutarate aminotransferase and aspartate aminotransferase, collagen staining), circulating cytokines (tumor necrosis factor-α, interleukin-6 and interferon-γ), factors that can bind LPS (serum amyloid A, apolipoprotein A1, LPS binding protein, and CD14), and plasma levels of LPS were measured. The hepatic response was assessed by measuring vascular cell adhesion molecule (VCAM)-1, inducible nitric oxide synthase (iNOS) and signal transducer and activator of transcription-1 proteins, and VCAM-1 and iNOS mRNAs. Hepatic mRNA encoding the LPS receptor, Toll like receptor 4, was also determined.

Results

Two mg LPS/kg killed 100% of mice fed HCD within 5 d, while no mice fed CD died. All mice treated with 0 to 1 mg LPS/kg survived 24 h. HCD increased plasma alanine:2-oxoglutarate aminotransferase and aspartate aminotransferase, and the enzymes were increased more by LPS in HCD than CD mice. Induction of plasma tumor necrosis factor-α, interleukin-6, and interferon-γ by LPS was greater with HCD than CD. Hepatic VCAM-1 and iNOS protein and mRNA were induced by LPS more in mice fed HCD than CD. Tyrosine phosphorylation of signal transducer and activator of transcription-1 caused by LPS was prolonged in HCD compared with CD mice. Despite the hepatic effects of HCD, diet had no effect on the LPS plasma concentration-time profile. HCD alone did not affect circulating levels of plasma apolipoprotein A1 or LPS binding protein. However, plasma concentrations of serum amyloid A and CD14, and hepatic toll-like receptor-4 mRNA were increased in mice fed HCD.

Conclusion

HCD increased the sensitivity of mice to LPS without affecting its plasma level. Although increased serum amyloid A and CD14 in the circulation may inhibit LPS actions, their overexpression, along with hepatic toll-like receptor-4 or other factors, may contribute to the heightened sensitivity to LPS.

Role of CD14 promoter polymorphisms in Helicobacter pylori infection--related gastric carcinoma

PURPOSE

Genetic variation in CD14 may affect CD14 expression and susceptibility to Helicobacter pylori infection-related cancers. This study examined functional single nucleotide polymorphisms (SNP) in the CD14 promoter and their associations with risk of developing gastric carcinoma in relation to H. pylori infection.

EXPERIMENTAL DESIGN

Thirty individual DNAs were sequenced to identify variants, and the function of the variants was examined by reporter gene assays. Genotypes and haplotypes were analyzed in 470 patients and 470 controls, and odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by logistic regression. Serologic H. pylori antibody and soluble CD14 (sCD14) levels were measured by ELISA.

RESULTS

Two SNPs (-651C>T and -260C>T) were identified, of which the -260CT and -260TT genotypes were associated with elevated risk of gastric carcinoma (OR, 1.77; 95% CI, 1.09-2.85 and OR, 1.95; 95% CI, 1.20-3.16, respectively). Haplotype analysis suggested a synergistic effect of the two SNPs (OR for the T(-651)-T(-260) haplotype, 3.39 versus OR for the C(-651)-T(-260) haplotype, 1.45; P = 0.02), which is consistent with reporter gene assays. A multiplicative joint effect between H. pylori infection and -260C>T polymorphism was observed (OR for the presence of both -260TT genotype and H. pylori infection, 4.03; 95% CI, 1.80-9.04). Patients had significantly higher sCD14 than controls (1,866 +/- 2,535 ng/mL versus 1,343 +/- 2,119 ng/mL; P < 0.001), and this difference was associated with the CD14 -260 polymorphism and H. pylori infection.

CONCLUSIONS

Functional polymorphism in CD14 is associated with greater risk of H. pylori-related gastric carcinoma, which might be mediated by elevated sCD14.

Metabolic endotoxemia initiates obesity and insulin resistance

Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPS-containing microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in high-fat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not whole-body, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases.

IL-22 induces lipopolysaccharide-binding protein in hepatocytes: a potential systemic role of IL-22 in Crohn's disease

Crohn's disease (CD) is a common, chronic, inflammatory bowel disease characterized by intestinal infiltration of activated immune cells and distortion of the intestinal architecture. In this study, we demonstrate that IL-22, a cytokine that is mainly produced by activated Th1 and Th17 cells, was present in high quantities in the blood of CD patients in contrast to IFN-gamma and IL-17. In a mouse colitis model, IL-22 mRNA expression was elevated predominantly in the inflamed intestine but also in the mesenteric lymph nodes. IL-22BP, the soluble receptor for IL-22, demonstrated an affinity to IL-22 that was at least 4-fold higher than its membrane-bound receptor, and its strong constitutive expression in the intestine and lymph nodes was decreased in the inflamed intestine. To investigate the possible role of systemic IL-22 in CD, we then administered IL-22 to healthy mice and found an up-regulation of LPS-binding protein (LBP) blood levels reaching concentrations known to neutralize LPS. This systemic up-regulation was associated with increased hepatic but not renal or pulmonary LBP mRNA levels. IL-22 also enhanced the secretion of LBP in human primary hepatocytes and HepG2 hepatoma cells in vitro. This increase was mainly transcriptionally regulated and synergistic with that of other LBP inducers. Finally, elevated LBP levels were detected in CD patients and the mouse colitis model. These data suggest that systemic IL-22 may contribute to the prevention of systemic inflammation provoked by LPS present in the blood of CD patients through its induction of hepatic LBP.

A gene family of putative immune recognition molecules in the hydroid Hydractinia

Animal taxa display a wide array of immune-type receptors that differ in their specificities, diversity, and mode of evolution. These molecules ensure effective recognition of potential pathogens for subsequent neutralization and clearance. We have characterized a family of putative immune recognition molecules in the colonial hydroid Hydractinia symbiolongicarpus. A complementary DNA fragment with high similarity to the sea urchin L: -rhamnose-binding lectin was isolated and used to screen 9.5 genome equivalents of a H. symbiolongicarpus bacterial artificial chromosome library. One of the resulting 19 positive clones was sequenced and revealed the presence of a 5,111-bp gene organized in 13 exons and 12 introns. The gene was predicted to encode a 726-amino acid secreted modular protein composed of a signal peptide, an anonymous serine-rich domain, eight thrombospondin type 1 repeats, and a L: -rhamnose-binding lectin domain. The molecule was thus termed Rhamnospondin (Rsp). Southern hybridization and sequence analyses indicated the presence of a second Rsp gene. The cDNA from both Rsp genes was sequenced in 18 individuals, revealing high levels of genetic polymorphism. Nucleotide substitutions were distributed throughout the molecule and showed a significantly higher number of synonymous substitutions per synonymous sites than its nonsynonymous counterparts. Whole-mount in situ hybridization and semi-quantitative reverse transcription polymerase chain reaction of microorganism-challenged colonies indicated that Rsp molecules were specifically and constitutively expressed in the hypostome of gastrozooids' mouth. Thus, the combination of (1) comparative analysis on domain composition and function, (2) polymorphism, and (3) expression patterns, suggest that Rsp genes encode a family of putative immune recognition receptors, which may act by binding microorganisms invading the colony through the polyp's mouth.

Contribution of Toll-like receptors to the innate immune response to Gram-negative and Gram-positive bacteria

Innate recognition of bacteria is a key step in the activation of inflammation and coagulation, and it is dependent on pathogen-associated molecular pattern (PAMP) ligation to Toll-like receptors (TLRs) and CD14. The dominant receptors activated when cells encounter a whole bacterium, which express several PAMPs, are poorly defined. Herein, we have stimulated various human cells with prototypic Gram-negative and Gram-positive bacteria. Receptor-dependent responses to whole bacteria were assessed using both TLR-transfected cells and specific monoclonal antibodies against TLRs, MD-2, and CD14. Enterobacteria-activated leukocytes and endothelial cells in a TLR4/MD-2-dependent manner, most likely via lipopolysaccharide (LPS). TLR2 activation was observed with a high bacterial inoculum, and in epithelial cells expressing TLR2 but not TLR4. Pseudomonas aeruginosa stimulated cells by both TLR2 and TLR4/MD-2. Gram-positive bacteria activated cells only at high concentrations, in a partially TLR2-dependent but TLR4/MD-2-independent manner. Either TLR or CD14 neutralization blocked activation to all bacterial strains tested with the exception of some Gram-positive strains in whole blood in which partial inhibition was noted. This study identifies dominant TLRs involved in responses to whole bacteria. It also validates the concept that host cell activation by bacterial pathogens can be therapeutically reduced by anti-TLR4, -TLR2, and -CD14 mAbs.

Presence of functional TLR2 and TLR4 on human adipocytes

In addition to the well-known role of adipose tissue in energy metabolism, it has recently been demonstrated that this tissue can secrete a large array of molecules, including inflammatory cytokines. Furthermore, recent studies suggest that adipose cells can behave as immune cells. Therefore, the aim of this study was to determine the presence of the two most prominent 'pattern recognition receptors' for bacterial and fungal cell wall components, TLR2 and TLR4 on human adipose cells, as well as to assess their functionality. We demonstrated that TLR2 and TLR4 were expressed at relatively high levels (compared to a monocyte cell line) on the surface of human adipose cells. Stimulation of human adipocytes with lipopolysaccharide (LPS), or with lipoteichoic acid (LTA), two specific ligands of TLR4 and TLR2, respectively, induced a strong increase in TNFalpha production. The specificity of the response was demonstrated by the use of anti-TLR4 and anti-TLR2 blocking antibodies, which were able to decrease LPS- or LTA-induced TNFalpha secretion. Thus, it is clear that these receptors are functional in human adipocytes. This study adds weight to the argument that human fat tissue plays a potential role in innate immunity.