Peptidoglycan of Staphylococcus aureus upregulates monocyte expression of CD14, Toll-like receptor 2 (TLR2), and TLR4 in human blood: possible implications for priming of lipopolysaccharide signaling

Transferrin Is Up-Regulated by Microbes and Acts as a Negative Regulator of Immunity to Induce Intestinal Immunotolerance

Cross-talks (e.g., host-driven iron withdrawal and microbial iron uptake between host gastrointestinal tract and commensal microbes) regulate immunotolerance and intestinal homeostasis. However, underlying mechanisms that regulate the cross-talks remain poorly understood. Here, we show that bacterial products up-regulate iron-transporter transferrin and transferrin acts as an immunosuppressor by interacting with cluster of differentiation 14 (CD14) to inhibit pattern recognition receptor (PRR) signaling and induce host immunotolerance. Decreased intestinal transferrin is found in germ-free mice and human patients with ulcerative colitis, which are characterized by impaired intestinal immunotolerance. Intestinal transferrin and host immunotolerance are returned to normal when germ-free mice get normal microbial commensalism, suggesting an association between microbial commensalism, transferrin, and host immunotolerance. Mouse colitis models show that transferrin shortage impairs host's tolerogenic responses, while its supplementation promotes immunotolerance. Designed peptide blocking transferrin-CD14 interaction inhibits immunosuppressive effects of transferrin. In monkeys with idiopathic chronic diarrhea, transferrin shows comparable or even better therapeutic effects than hydrocortisone. Our findings reveal that by up-regulating host transferrin to silence PRR signaling, commensal bacteria counteract immune activation induced by themselves to shape host immunity and contribute for intestinal tolerance.

Gene co-expression in response to Staphylococcus aureus infection reveals networks of genes with specific functions during bovine subclinical mastitis

Staphylococcus aureus is one of the most prevalent contagious bacterial pathogen of bovine mastitis. The subclinical mastitis it causes has long-term economic implications and it is difficult to control. To further understanding of the genetic basis of mammary gland defense against S. aureus infection, the transcriptomes of milk somatic cells from 15 cows with persistent natural S. aureus infection (S. aureus-positive, SAP) and 10 healthy control cows (HC) were studied by deep RNA-sequencing technology. Comparing the transcriptomes of SAP to HC group revealed 4,077 differentially expressed genes (DEG; 1,616 up- and 2,461 downregulated). Functional annotation indicated enrichment of DEG in 94 Gene Ontology (GO) and 47 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Terms related to the immune response and disease processes were mostly enriched for by upregulated DEG, whereas biological process terms related to cell adhesion, cell movement and localization, and tissue development were mostly enriched for by downregulated DEG. Weighted gene co-expression network analysis grouped DEG into 7 modules, the most important module (colored turquoise by software and here referred to as Turquoise module) was positively significantly correlated with S. aureus subclinical mastitis. The 1,546 genes in the Turquoise module were significantly enriched in 48 GO terms and 72 KEGG pathways, with 80% of them being disease- and immune-related terms [e.g., immune system process (GO:0002376), cytokine-cytokine receptor interaction (bta04060) and S. aureus infection (bta05150)]. Some DEG such as IFNG, IL18, IL1B, NFKB1, CXCL8, and IL12B were enriched in immune and disease pathways suggesting their possible involvement in the regulation of the host response to S. aureus infection. Four modules (Yellow, Brown, Blue, and Red) were negatively correlated (significantly) with S. aureus subclinical mastitis, and were enriched in functional annotations involved in the regulation of cell migration, cell communication, metabolic process, and blood circulatory system development, respectively. Application of sparse partial least squares discriminant analysis to genes of the Turquoise module identified 5 genes (NR2F6, PDLIM5, RAB11FIP5, ACOT4, and TMEM53) capable of explaining the majority of the differences in the expression patterns between SAP and HC cows. In conclusion, this study has furthered understanding of the genetic changes in the mammary gland and the molecular mechanisms underlying S. aureus mastitis, as well as revealed a list of candidate discriminant genes with potential regulatory roles in response to S. aureus infection.

ROS Production by a Single Neutrophil Cell and Neutrophil Population upon Bacterial Stimulation

The reactive oxygen species (ROS) production by a single neutrophil after stimulation with S. aureus and E. coli was estimated by an electrochemical amperometric method with a high time resolution. This showed significant variability in the response of a single neutrophil to bacterial stimulation, from a "silent cell" to a pronounced response manifested by a series of chronoamperometric spikes. The amount of ROS produced by a single neutrophil under the influence of S. aureus was 5.5-fold greater than that produced under the influence of E. coli. The response of a neutrophil granulocyte population to bacterial stimulation was analyzed using luminol-dependent biochemiluminescence (BCL). The stimulation of neutrophils with S. aureus, as compared to stimulation with E. coli, caused a total response in terms of ROS production that was seven-fold greater in terms of the integral value of the light sum and 13-fold greater in terms of the maximum peak value. The method of ROS detection at the level of a single cell indicated the functional heterogeneity of the neutrophil population, but the specificity of the cellular response to different pathogens was the same at the cellular and population levels.

IL-32 is induced by activation of toll-like receptors in multiple myeloma cells

Multiple myeloma (MM) is a hematological cancer characterized by accumulation of malignant plasma cells in the bone marrow. The patients are immune suppressed and suffer from recurrent and chronic infections. Interleukin-32 is a non-conventional, pro-inflammatory cytokine expressed in a subgroup of MM patients with a poor prognosis. IL-32 has also been shown to promote proliferation and survival of the cancer cells. Here we show that activation of toll-like receptors (TLRs) promotes expression of IL-32 in MM cells through NFκB activation. In patient-derived primary MM cells, IL-32 expression is positively associated with expression of TLRs. Furthermore, we found that several TLR genes are upregulated from diagnosis to relapse in individual patients, predominantly TLRs sensing bacterial components. Interestingly, upregulation of these TLRs coincides with an increase in IL-32. Taken together, these results support a role for IL-32 in microbial sensing in MM cells and suggest that infections can induce expression of this pro-tumorigenic cytokine in MM patients.

Ex vivo and in vitro Monocyte Responses Do Not Reflect in vivo Immune Responses and Tolerance

Cytokine production by ex vivo (EV)-stimulated leukocytes is commonly used to gauge immune function and frequently proposed to guide immunomodulatory therapy. However, whether EV cytokine production capacity accurately reflects the in vivo (IV) immune status is largely unknown. We investigated relationships between EV monocyte cytokine responses and IV cytokine responses in a large cohort of healthy volunteers using a highly standardized IV model of short-lived LPS-induced systemic inflammation, which captures hallmarks of both hyperinflammation and immunological tolerance. Therefore, 110 healthy volunteers were intravenously challenged with 1 ng/kg LPS twice: on day 0 to determine the extent of the IV (hyper)inflammatory response and on day 7 to determine the degree of IV endotoxin tolerance. Baseline EV monocyte cytokine production capacity was assessed prior to LPS administration. Short-term and long-term EV tolerance was assessed in monocytes isolated 4 h and 7 days after LPS administration, respectively. No robust correlations were observed between baseline EV cytokine production capacity and IV cytokine responses following LPS administration. However, highly robust inverse correlations were observed between IV cytokine responses and EV cytokine responses of monocytes isolated 4 h after IV LPS administration. No correlations between IV and EV tolerance were found. In conclusion, attenuated EV cytokine production capacity reflects ongoing IV inflammation rather than immune suppression. Results of EV assays should be interpreted with caution at the risk of improper use of immuno-stimulatory drugs.

Investigation of novel putative immunogenic targets against Staphylococcus aureus using a reverse vaccinology strategy

BACKGROUND

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) strains is a significant public health concern. Considering the high morbidity and mortality of invasive S. aureus infections and multi-drug resistant strains, there is an urgent need for non-antibiotic immune-based approaches to cure these infections. Despite all efforts, vaccine candidates targeting S. aureus failed in human clinical trials, and no approved vaccine is available against this pathogen. Therefore, this study aimed to introduce suitable candidates for immunization against S. aureus using a comprehensive reverse vaccinology approach.

METHODS

In this study, we retrieved putative immunogenic targets from three different levels (literature review, automated reverse vaccinology, and manual reverse vaccinology) and evaluated them using several immunoinformatics analyses including antigenicity, allergenicity, PSI-BLAST to human proteome, physiochemical properties, B-cell, and T-cell epitopes. In the next step, the quartile method scoring was used to the shortlisted proteins. Finally, the molecular docking and immune simulation of immunogenic targets were performed.

RESULTS

This study presents 12 vaccine candidates, including three enzymatic proteins (WP_000222271.1, WP_001170274, and WP_000827736.1), three cell wall-associated proteins (WP_001125631.1, WP_000731642, and WP_000751265.1), two hemolysins (WP_000594517.1, and WP_000916697.1), one secretion involved protein (WP_000725226.1), one heme‑iron binding protein (WP_001041573.1), one superantigen like protein (WP_000668994.1) and one hypothetical proteins (WP_000737711.1).

CONCLUSION

Through quartile scoring method, immune simulation and molecular docking, four promising targets including lytic transglycosylase IsaA, HlgA, secretory antigen precursor SsaA, and heme uptake protein IsdB were selected as the shortlisted proteins. It seems that a polarized immunization (Th1/Th17) response is needed for protection against this bacterium. An optimized formulation based on these putative immunogenic proteins and a wisely adjuvant selection may drive the immune system toward a full protection.

Bacterial species-specific modulatory effects on phenotype and function of camel blood leukocytes

Background

Recent studies have reported pathogen-species-specific modulating effects on the innate immune system. Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae are important pathogenic bacteria responsible for different infectious diseases in several animal species. In the present study, a whole blood culture with S. aureus, E. coli, or S. agalactiae and flow cytometry were used to investigate, whether stimulation with different bacterial species induces different immunomodulation patterns in camel leukocytes. The expression of different cell surface myeloid markers and cell adhesion molecules on monocytes and neutrophils was investigated. In addition, the capacity of monocytes and neutrophils to produce reactive oxygen species (ROS) was analyzed.

Results

Stimulation with either of the bacterial species resulted in the expansion of the camel CD14^highMHCII^high monocyte subset with a reduced fraction of CD14^highMHCII^low monocytes. For the CD14^lowMHCII^high monocytes, however, only stimulation with S. aureus or S. agalactiae increased their fractions in blood. Although all bacterial species elicited the upregulation of cell surface MHC class II molecules on granulocytes, the increase was, however, highest on cells stimulated with S. aureus. The expression levels of the two adhesion molecules, CD11a and CD18, on neutrophils and monocytes were differently affected by bacterial stimulation. Functionally, E. coli failed to stimulate ROS production in monocytes, while induced a strong ROS production response in granulocytes. S. agalactiae elicited a week ROS production in granulocytes when compared to the other two pathogens.

Conclusions

The different responsiveness of monocytes and granulocytes toward different bacterial species indicates different host-pathogen interaction mechanisms for the two cell populations. In addition, the phenotypic and functional differences between cells stimulated with E. coli, S. aureus, or S. agalactiae suggests pathogen-species-specific modulating effects of the bacterial pathogens on the camel innate myeloid cells.

Staphylococcus aureus membrane vesicles contain immunostimulatory DNA, RNA and peptidoglycan that activate innate immune receptors and induce autophagy

Gram-positive bacteria ubiquitously produce membrane vesicles (MVs), and although they contribute to biological functions, our knowledge regarding their composition and immunogenicity remains limited. Here we examine the morphology, contents and immunostimulatory functions of MVs produced by three Staphylococcus aureus strains; a methicillin resistant clinical isolate, a methicillin sensitive clinical isolate and a laboratory-adapted strain. We observed differences in the number and morphology of MVs produced by each strain and showed that they contain microbe-associated molecular patterns (MAMPs) including protein, nucleic acids and peptidoglycan. Analysis of MV-derived RNA indicated the presence of small RNA (sRNA). Furthermore, we detected variability in the amount and composition of protein, nucleic acid and peptidoglycan cargo carried by MVs from each S. aureus strain. S. aureus MVs activated Toll-like receptor (TLR) 2, 7, 8, 9 and nucleotide-binding oligomerization domain containing protein 2 (NOD2) signalling and promoted cytokine and chemokine release by epithelial cells, thus identifying that MV-associated MAMPs including DNA, RNA and peptidoglycan are detected by pattern recognition receptors (PRRs). Moreover, S. aureus MVs induced the formation of and colocalized with autophagosomes in epithelial cells, while inhibition of lysosomal acidification using bafilomycin A1 resulted in accumulation of autophagosomal puncta that colocalized with MVs, revealing the ability of the host to degrade MVs via autophagy. This study reveals the ability of DNA, RNA and peptidoglycan associated with MVs to activate PRRs in host epithelial cells, and their intracellular degradation via autophagy. These findings advance our understanding of the immunostimulatory roles of Gram-positive bacterial MVs in mediating pathogenesis, and their intracellular fate within the host.

Neonatal BCG Vaccination Influences Cytokine Responses to Toll-like Receptor Ligands and Heterologous Antigens

Background

BCG vaccination is associated with a reduction in all-cause infant mortality in high-mortality settings. The underlying mechanisms remain uncertain, but long-term modulation of the innate immune response (trained immunity) may be involved.

Methods

Whole-blood specimens, collected 7 days after randomization from 212 neonates enrolled in a randomized trial of neonatal BCG vaccination, were stimulated with killed pathogens and Toll-like receptor (TLR) ligands to interrogate cytokine responses.

Results

BCG-vaccinated infants had increased production of interleukin 6 (IL-6) in unstimulated samples and decreased production of interleukin 1 receptor antagonist, IL-6, and IL-10 and the chemokines macrophage inflammatory protein 1α (MIP-1α), MIP-1β, and monocyte chemoattractant protein 1 (MCP-1) following stimulation with peptidoglycan (TLR2) and R848 (TLR7/8). BCG-vaccinated infants also had decreased MCP-1 responses following stimulation with heterologous pathogens. Sex and maternal BCG vaccination status interacted with neonatal BCG vaccination.

Conclusions

Neonatal BCG vaccination influences cytokine responses to TLR ligands and heterologous pathogens. This effect is characterized by decreased antiinflammatory cytokine and chemokine responses in the context of higher levels of IL-6 in unstimulated samples. This supports the hypothesis that BCG vaccination modulates the innate immune system. Further research is warranted to determine whether there is an association between these findings and the beneficial nonspecific (heterologous) effects of BCG vaccine on all-cause mortality.

Lactococcus lactis and Lactobacillus salivarius differently modulate early immunological response of Wistar rats co-administered with Listeria monocytogenes

In the light of the increasing resistance of bacterial pathogens to antibiotics, one of the main global strategies in applied science is development of alternative treatments, which would be safe both for the host and from the environmental perspective. Accordingly, the aim of this study was to test whether two lactic acid bacteria (LAB) strains, Lactococcus lactis BGBU1-4 and Lactobacillus salivarius BGHO1, could be applied as safe supplements for Listeria infection. Two major research objectives were set: to compare the effects of BGBU1-4 and BGHO1 on early immune response in gut tissue of Wistar rats co-administered with Listeria monocytogenes ATCC19111 and next, to test how this applies to their usage as therapeutics in acute ATCC19111 infection. Intestinal villi (IV), Peyer's patches (PP) and mesenteric lymph nodes (MLN) were used for the analysis. The results showed that BGHO1 increased the mRNA expression of innate immune markers CD14, interleukin (IL)-1β and tumour necrosis factor (TNF)-α in PP and IV, and, in parallel, caused a decrease of listeriolysin O (LLO) mRNA expression in same tissues. In MLN of BGHO1 treated rats, LLO expression was increased, along with an increase of the expression of OX-62 mRNA and CD69, pointing to the activation of adaptive immunity. On the other hand, in BGBU1-4 treated rats, there was no reduction of LLO mRNA expression and no induction of innate immunity markers in intestinal tissue. Additionally, CD14 and IL-1β, as well as LLO, but not OX-62 mRNA and CD69 expression, were elevated in MLN of BGBU1-4 treated rats. However, when applied therapeutically, both, BGBU1-4 and BGHO1, lowered Listeria count in spleens of infected rats. Our results not only reveal the potential of LAB to ameliorate Listeria infections, but suggest different immunological effects of two different LAB strains, both of which could be effective in Listeria elimination.

Immunohistochemical characterization of Toll-like receptor 2 in gut epithelial cells and macrophages of goldfish Carassius auratus fed with a high-cholesterol diet

Toll-like receptors (TLRs) are a group of pattern recognition molecules that play a crucial role in innate immunity. The structural conservation of the archaic TLR system suggests that the regulation of the immune response might be similar in fish and mammals. Several TLRs (TLR-1, -2, and -4) are expressed by activated macrophages, "foam cells" in human atherosclerotic lesions. To date, 20 different TLRs were identified in more than a dozen different fish species. In this study we found that feeding goldfish, Carrassius auratus, a high-cholesterol diet (HCD) resulted macrophage foam cell formation in the intestinal tissues. The expression of TLR2 has been found in foam cells and in the cytoplasm of enterocytes, however the staining was more intense at the apical surface of polarized intestinal epithelial cells and in the lamina propria. In the intestinal epithelial cells and in the lamina propria cells of the control fish the TLR2 was expressed at low levels. The intestinal epithelium is directly involved in the mucosal immune response through its expression of proinflammatory genes, release of inflammatory cytokines, and recruitment of inflammatory cells.

Cloning and expression study of a Toll-like receptor 2 (tlr2) gene from turbot, Scophthalmus maximus

Toll-like receptor 2 (TLR2) in mammals is a member of the ancient Toll-like family of receptors that predominantly recognizes conserved components of Gram-positive bacteria. In the present study, a tlr2 gene and its 5'-flanking sequence were cloned from turbot, Scophthalmus maximus, its responsive expressions to various immunostimulants were subsequently studied in vivo. The turbot (sm)tlr2 gene spans over 9.0 kb with a structure of 12 exon-11 intron and encodes 816 amino acids. The deduced protein shows the highest sequence identity (76.1%) to Japanese flounder Tlr2 and possesses a signal peptide sequence, a leucine-rich repeat (LRR) domain composed of 19 LRR motifs, a transmembrane region and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis grouped it with other neoteleostei Tlr2as. A number of transcription factor binding sites known to be important for the basal transcriptional activity of TLR3 and response of TLR2 to lipopolysaccharide (LPS) signalling in mammals were predicted in the 5'-flanking sequence of smtlr2. Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of smtlr2 mRNA in all twelve examined tissues with higher levels in the lymphomyeloid-rich tissues and liver. Further, smtlr2 expression was up-regulated following stimulation with LPS, peptidoglycan (PGN) or polyinosinic: polycytidylic acid [poly(I:C)] in the gills, head kidney, spleen and muscle. Finally, for all three immunostimulants, a two-wave induced smtlr2 expression was observed in the head kidney and spleen in a 7-day time course and the strongest inducibility in the head kidney. These findings suggest a possible role of Smtlr2 in the immune responses to the infections of a broad range of pathogens that include Gram-positive and Gram-negative bacteria and RNA virus.

Modeling and Hemofiltration Treatment of Acute Inflammation

The body responds to endotoxins by triggering the acute inflammatory response system to eliminate the threat posed by gram-negative bacteria (endotoxin) and restore health. However, an uncontrolled inflammatory response can lead to tissue damage, organ failure, and ultimately death; this is clinically known as sepsis. Mathematical models of acute inflammatory disease have the potential to guide treatment decisions in critically ill patients. In this work, an 8-state (8-D) differential equation model of the acute inflammatory response system to endotoxin challenge was developed. Endotoxin challenges at 3 and 12 mg/kg were administered to rats, and dynamic cytokine data for interleukin (IL)-6, tumor necrosis factor (TNF), and IL-10 were obtained and used to calibrate the model. Evaluation of competing model structures was performed by analyzing model predictions at 3, 6, and 12 mg/kg endotoxin challenges with respect to experimental data from rats. Subsequently, a model predictive control (MPC) algorithm was synthesized to control a hemoadsorption (HA) device, a blood purification treatment for acute inflammation. A particle filter (PF) algorithm was implemented to estimate the full state vector of the endotoxemic rat based on time series cytokine measurements. Treatment simulations show that: (i) the apparent primary mechanism of HA efficacy is white blood cell (WBC) capture, with cytokine capture a secondary benefit; and (ii) differential filtering of cytokines and WBC does not provide substantial improvement in treatment outcomes vs. existing HA devices.

Toll-like receptor 2 of tongue sole Cynoglossus semilaevis: Signaling pathway and involvement in bacterial infection

Toll-like receptor (TLR) 2 is a member of the TLR family that plays a pivotal role in innate immunity. In mammals, TLR2 is known to recognize specific microbial structures and trigger MyD88-dependent signaling to induce various cytokine responses. In this study, we examined the expression and function of the tongue sole Cynoglossus semilaevis TLR2, CsTLR2. CsTLR2 is composed of 898 amino acid residues and shares 25.6%-27.3% overall sequence identities with known teleost TLR2. CsTLR2 is a transmembrane protein with a toll/interleukin-1 receptor domain and eight leucine-rich repeats. Expression of CsTLR2 occurred in multiple tissues and was upregulated during bacterial infection. Stimulation of the CsTLR2 pathway led to enhanced expression of MyD88-dependent signaling molecules. Recombinant CsTLR2 (rCsTLR2) corresponding to the extracellular region was able to bind to a wide range of bacteria. Under both in vitro and in vivo conditions, rCsTLR2 significantly reduced bacterial infection. These observations add new insights into the signaling and function of teleost TLR2.

Variation of Circulating Inflammatory Mediators in Staphylococcus aureus and Escherichia coli Bloodstream Infection

Background

The aim of this study was to examine the behavior of circulating inflammatory mediators and to exclude gram-positive from gram-negative bloodstream infections. Results may be helpful in selection of optimal specific antibiotic therapies.

Material/Methods

Mice (25–27 g) were randomized to 3 groups infected with Staphylococcus aureus (S. aureus) ATCC 25923, Escherichia coli (E. coli) ATCC 25922, or phosphate-buffered saline (PBS). The white blood cell count (WBC) and the concentrations of serum C-reactive protein (CRP), procalcitonin (PCT), interleukin (IL)-1α, IL-1β, IL-6, IL-10, monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1α (MIP-1α) were detected in blood samples at different time intervals after intravenous tail injection.

Results

The results showed that compared to the control mice, infected animals exhibited significantly higher levels of all mediators after bacterial infection. Moreover, compared to the mice that received S. aureus, animals with E. coli infection showed significantly greater increases in serum IL-1α, IL-1β, IL-6, MCP-1, and MIP-1α levels.

Conclusions

These results suggest that the use of the analyzed serum markers at an early stage of bloodstream infection may give useful information for the clinician to distinguish gram-negative from gram-positive infections.

Oral antibiotics increase blood neutrophil maturation and reduce bacteremia and necrotizing enterocolitis in the immediate postnatal period of preterm pigs

Immature immunity may predispose preterm neonates to infections and necrotizing enterocolitis (NEC). Intravenous antibiotics are frequently given to prevent and treat sepsis, while oral antibiotics are seldom used. We hypothesized that oral antibiotics promote maturation of systemic immunity and delay gut bacterial colonization and thereby protect preterm neonates against both NEC and bacteremia in the immediate postnatal period. Preterm pigs were given formula and administered saline (CON) or broad-spectrum antibiotics orally (ORA) or systemically (SYS) for 5 d after birth. Temporal changes in blood parameters and bacterial composition in the intestine, blood and immune organs were analyzed. Newborn preterm pigs had few blood neutrophils and a high frequency of progenitor cells. Neutrophils gradually matured after preterm birth with increasing CD14 and decreasing CD172a expressions. Preterm neutrophil and monocyte TLR2 expression and TLR2-mediated blood cytokine responses were low relative to adults. ORA pigs showed enhanced blood neutrophil maturation with reduced cell size and CD172a expression. Only ORA pigs, but not SYS pigs, were protected from a high density of gut Gram-positive bacteria, high gut permeability, Gram-positive bacteremia and NEC. Neonatal oral antibiotics may benefit mucosal and systemic immunity via delayed gut colonization and enhanced blood neutrophil maturation just after preterm birth.

Structural and functional features of a developmentally regulated lipopolysaccharide-binding protein

Mammalian lipopolysaccharide (LPS) binding proteins (LBPs) occur mainly in extracellular fluids and promote LPS delivery to specific host cell receptors. The function of LBPs has been studied principally in the context of host defense; the possible role of LBPs in nonpathogenic host-microbe interactions has not been well characterized. Using the Euprymna scolopes-Vibrio fischeri model, we analyzed the structure and function of an LBP family protein, E. scolopes LBP1 (EsLBP1), and provide evidence for its role in triggering a symbiont-induced host developmental program. Previous studies showed that, during initial host colonization, the LPS of V. fischeri synergizes with peptidoglycan (PGN) monomer to induce morphogenesis of epithelial tissues of the host animal. Computationally modeled EsLBP1 shares some but not all structural features of mammalian LBPs that are thought important for LPS binding. Similar to human LBP, recombinant EsLBP1 expressed in insect cells bound V. fischeri LPS and Neisseria meningitidis lipooligosaccharide (LOS) with nanomolar or greater affinity but bound Francisella tularensis LPS only weakly and did not bind PGN monomer. Unlike human LBP, EsLBP1 did not bind N. meningitidis LOS:CD14 complexes. The eslbp1 transcript was upregulated ~22-fold by V. fischeri at 24 h postinoculation. Surprisingly, this upregulation was not induced by exposure to LPS but, rather, to the PGN monomer alone. Hybridization chain reaction-fluorescent in situ hybridization (HCR-FISH) and immunocytochemistry (ICC) localized eslbp1 transcript and protein in crypt epithelia, where V. fischeri induces morphogenesis. The data presented here provide a window into the evolution of LBPs and the scope of their roles in animal symbioses.

Mammalian lipopolysaccharide (LPS)-binding protein (LBP) is implicated in conveying LPS to host cells and potentiating its signaling activity. In certain disease states, such as obesity, the overproduction of this protein has been a reliable biomarker of chronic inflammation. Here, we describe a symbiosis-induced invertebrate LBP whose tertiary structure and LPS-binding characteristics are similar to those of mammalian LBPs; however, the primary structure of this distantly related squid protein (EsLBP1) differs in key residues previously believed to be essential for LPS binding, suggesting that an alternative strategy exists. Surprisingly, symbiotic expression of eslbp1 is induced by peptidoglycan derivatives, not LPS, a pattern converse to that of RegIIIγ, an important mammalian immunity protein that binds peptidoglycan but whose gene expression is induced by LPS. Finally, EsLBP1 occurs along the apical surfaces of all the host’s epithelia, suggesting that it was recruited from a general defensive role to one that mediates specific interactions with its symbiont.

Soluble β-(1,3)-glucans enhance LPS-induced response in the monocyte activation test, but inhibit LPS-mediated febrile response in rabbits: Implications for pyrogenicity tests

In the present study, we aimed to determine the influence of β-(1,3)-d-glucans on the LPS-induced pro-inflammatory cytokine response in the Monocyte Activation Test (MAT) for pyrogens, and on the LPS-induced febrile response in the Rabbit Pyrogen Test (RPT), thus evaluating the resulting effect in the outcome of each test. It was found that β-(1,3)-d-glucans elicited the production of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α, also known as endogenous pyrogens, but not enough to classify them as pyrogenic according to MAT. The same β-(1,3)-d-glucans samples were non-pyrogenic by RPT. However, β-(1,3)-d-glucans significantly enhanced the LPS-induced pro-inflammatory cytokines response in MAT, insomuch that samples containing non-pyrogenic concentrations of LPS become pyrogenic. On the other hand, β-(1,3)-d-glucans had no effect on sub-pyrogenic LPS doses in the RPT, but surprisingly, inhibited the LPS-induced febrile response of pyrogenic LPS concentrations. Thus, while β-(1,3)-d-glucans could mask the LPS pyrogenic activity in the RPT, they exerted an overstimulation of pro-inflammatory cytokines in the MAT. Hence, MAT provides higher safety since it evidences an unwanted biological response, which is not completely controlled and is overlooked by the RPT.

CD14 expression is increased on monocytes in patients with anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitis and correlates with the expression of ANCA autoantigens

Monocyte subsets with differing functional properties have been defined by their expression of CD14 and CD16. We investigated these subsets in anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) and determined their surface expression of ANCA autoantigens. Flow cytometry was performed on blood from 14 patients with active AAV, 46 patients with AAV in remission and 21 controls. The proportion of classical (CD14(high) CD16(neg/low)), intermediate (CD14(high) CD16(high)) and non-classical (CD14(low) CD16(high)) monocytes and surface expression levels of CD14 and CD16 were determined, as well as surface expression of proteinase 3 (PR3) and myeloperoxidase (MPO) on monocyte subsets. There was no change in the proportion of monocytes in each subset in patients with AAV compared with healthy controls. The expression of CD14 on monocytes from patients with active AAV was increased, compared with patients in remission and healthy controls (P < 0.01). Patients with PR3-ANCA disease in remission also had increased monocyte expression of CD14 compared with controls (P < 0.01); however, levels in patients with MPO-ANCA disease in remission were lower than active MPO-ANCA patients, and not significantly different from controls. There was a correlation between CD14 and both PR3 and MPO expression on classical monocytes in AAV patients (r = 0.79, P < 0.0001 and r = 0.42, P < 0.005, respectively). In conclusion, there was an increase in monocyte CD14 expression in active AAV and PR3-ANCA disease in remission. The correlation of CD14 expression with ANCA autoantigen expression in AAV may reflect cell activation, and warrants further investigation into the potential for increased CD14 expression to trigger disease induction or relapse.

Design of bio-molecular interfaces using liquid crystals demonstrating endotoxin interactions with bacterial cell wall components

Liquid crystals offer a promising approach to study and quantify the interactions between different bacterial cell membrane components with endotoxin at an aqueous interface.

Recognition of TLR2 N-glycans: critical role in ArtinM immunomodulatory activity

TLR2 plays a critical role in the protection against Paracoccidioides brasiliensis conferred by ArtinM administration. ArtinM, a D-mannose-binding lectin from Artocarpus heterophyllus, induces IL-12 production in macrophages and dendritic cells, which accounts for the T helper1 immunity that results from ArtinM administration. We examined the direct interaction of ArtinM with TLR2using HEK293A cells transfected with TLR2, alone or in combination with TLR1 or TLR6, together with accessory proteins. Stimulation with ArtinM induced NF-κB activation and interleukin (IL)-8 production in cells transfected with TLR2, TLR2/1, or TLR2/6. Murine macrophages that were stimulated with ArtinM had augmented TLR2 mRNA expression. Furthermore, pre-incubation of unstimulated macrophages with an anti-TLR2 antibody reduced the cell labeling with ArtinM. In addition, a microplate assay revealed that ArtinM bound to TLR2 molecules that had been captured by specific antibodies from a macrophages lysate. Notably,ArtinM binding to TLR2 was selectively inhibited when the lectin was pre-incubated with mannotriose. The biological relevance of the direct interaction of ArtinM with TLR2 glycans was assessed using macrophages from TLR2-KOmice, which produced significantly lower levels of IL-12 and IL-10 in response to ArtinM than macrophages from wild-type mice. Pre-treatment of murine macrophages with pharmacological inhibitors of signaling molecules demonstrated the involvement of p38 MAPK and JNK in the IL-12 production induced by ArtinM and the involvement ofPI3K in IL-10 production. Thus, ArtinM interacts directly with TLR2 or TLR2 heterodimers in a carbohydrate recognition-dependent manner and functions as a TLR2 agonist with immunomodulatory properties.

Positive crosstalk of MAMP signaling pathways in rice cells

Plants have evolved efficient defense mechanisms known as priming and synergy, both of which can mobilize defense responses more extensively against successive pathogen invasion or simultaneous stimulation by different signal molecules. However, the mechanisms underlying these phenomena were largely unknown. In the present study, we used cultured rice cells and combination of purified MAMP molecules as a model system to study the mechanisms of these phenomena. We found that the pretreatment of rice cells with a low concentration of bacterial lipopolysaccharide (LPS) apparently primed the defense responses induced by successive N-acetylchitooctaose (GN8) treatment. On the other hand, simultaneous treatment with GN8 and LPS also resulted in the similar enhancement of defense responses observed for the LPS-induced priming, indicating that the synergistic effects of these MAMPs are basically responsible for such enhancement of defense responses, though the effect could be interpreted as "priming" under some experimental conditions. These results also indicate that such a positive crosstalk of signaling cascade downstream of MAMP receptors seems to occur very rapidly, probably at early step(s) of signaling pathway. Comprehensive analysis of phytohormones revealed a specific enhancement of the synthesis of jasmonic acid (JA), both in the LPS pretreatment and also simultaneous treatment, indicating a role of JA in the enhancement of downstream responses.

Increased expression of Toll-like receptors by monocytes and natural killer cells in ANCA-associated vasculitis

Introduction

Toll-like receptors (TLRs) are a family of receptors that sense pathogen associated patterns such as bacterial cell wall proteins. Bacterial infections are associated with anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). Here, we assessed the expression of TLRs 2, 4, and 9 by peripheral blood leukocytes from patients with AAV, and investigated TLR mediated responses ex vivo.

Methods

Expression of TLRs was determined in 38 AAV patients (32 remission, 6 active disease), and 20 healthy controls (HC). Membrane expression of TLRs 2, 4, and 9, and intracellular expression of TLR9 by B lymphocytes, T lymphocytes, NK cells, monocytes and granulocytes was assessed using 9-color flowcytometry. Whole blood from 13 patients and 7 HC was stimulated ex vivo with TLR 2, 4 and 9 ligands and production of cytokines was analyzed.

Results

In patients, we observed increased proportions of TLR expressing NK cells. Furthermore, patient monocytes expressed higher levels of TLR2 compared to HC, and in a subset of patients an increased proportion of TLR4⁺ monocytes was observed. Monocytes from nasal carriers of Staphylococcus aureus expressed increased levels of intracellular TLR9. Membrane expression of TLRs by B lymphocytes, T lymphocytes, and granulocytes was comparable between AAV patients and HC. Patients with active disease did not show differential TLR expression compared to patients in remission. Ex vivo responses to TLR ligands did not differ significantly between patients and HC.

Conclusions

In AAV, monocytes and NK cells display increased TLR expression. Increased TLR expression by these leukocytes, probably resulting from increased activation, could play a role in disease (re)activation.

Toll-like receptor 2 mediates the activation of human monocytes and endothelial cells by antiphospholipid antibodies

The presence of antiphospholipid antibodies (aPLAs) is associated with arterial or venous thrombosis and/or recurrent fetal loss. The proposed pathogenic mechanisms for aPLA effects include the inflammatory activation of monocytes and endothelial cells. Toll-like receptors (TLRs) are candidate signaling intermediates. The aim of this study was to investigate the relative contribution of TLR2 and TLR4 in cell activation by aPLAs. Of 32 patient-derived aPLAs, 19 induced an inflammatory activation of human monocytes and umbilical vein endothelial cells (HUVECs). In HUVECs, inflammatory responses to these aPLAs were increased by TNF pretreatment, which increases the expression of TLR2 but not TLR4. Anti-TLR2 but not anti-TLR4 antibodies reduced the aPLA-induced activation of monocytes and HUVECs. aPLAs activated TLR2-expressing human embryonic kidney 293 (HEK293) cells but not TLR4-expressing cells. Binding studies demonstrated an interaction between aPLAs and TLR2 but not TLR4. A role for CD14, a coreceptor for TLR2 and TLR4, can be inferred by observations that anti-CD14 antibodies reduced responses to aPLAs in monocytes, and that responses in HEK293 cells expressing TLR2 and CD14 were greater than in HEK293 cells expressing TLR2 alone. Our results demonstrate a role for TLR2 and CD14 in human endothelial cell and monocyte activation by aPLAs.

Effects of the TLR2 agonists MALP-2 and Pam3Cys in isolated mouse lungs

Background

Gram-positive and Gram-negative bacteria are main causes of pneumonia or acute lung injury. They are recognized by the innate immune system via toll-like receptor-2 (TLR2) or TLR4, respectively. Among all organs, the lungs have the highest expression of TLR2 receptors, but little is known about the pulmonary consequences of their activation. Here we studied the effects of the TLR2/6 agonist MALP-2, the TLR2/1 agonist Pam₃Cys and the TLR4 agonist lipopolysaccharide (LPS) on pro-inflammatory responses in isolated lungs.

Methodology/Principal Findings

Isolated perfused mouse lungs were perfused for 60 min or 180 min with MALP-2 (25 ng/mL), Pam₃Cys (160 ng/mL) or LPS (1 µg/mL). We studied mediator release by enzyme linked immunosorbent assay (ELISA), the activation of mitogen activated protein kinase (MAPK) and AKT/protein kinase B by immunoblotting, and gene induction by quantitative polymerase chain reaction. All agonists activated the MAPK ERK1/2 and p38, but neither JNK or AKT kinase. The TLR ligands upregulated the inflammation related genes Tnf, Il1β, Il6, Il10, Il12, Ifng, Cxcl2 (MIP-2α) and Ptgs2. MALP-2 was more potent than Pam₃Cys in inducing Slpi, Cxcl10 (IP10) and Parg. Remarkable was the strong induction of Tnc by MALP2, which was not seen with Pam₃Cys or LPS. The growth factor related genes Areg and Hbegf were not affected. In addition, all three TLR agonists stimulated the release of IL-6, TNF, CXCL2 and CXCL10 protein from the lungs.

Conclusions/Significance

TLR2 and TLR4 activation leads to similar reactions in the lungs regarding MAPK activation, gene induction and mediator release. Several genes studied here have not yet been appreciated as targets of TLR2-activation in the lungs before, i.e., Slpi, tenascin C, Parg and Traf1. In addition, the MALP-2 dependent induction of Tnc may indicate the existence of TLR2/6-specific pathways.

Pneumococcal vaccines for allergic airways diseases

BACKGROUND

Asthma is a common global health problem. Environmental exposures such as bacteria may protect against asthma development.

OBJECTIVE

This review aims to examine the possible protective role of pneumococcal infection and vaccination in asthma.

METHODS

A review of known experimental biology and human epidemiology relating to asthma and pneumococcal infection was performed.

RESULTS

Pneumococcal infection can modulate components of allergic airways disease such as airways hyperresponsiveness and airway eosinophilia. Exposure to killed pneumococcus can reproduce these effects and the mechanism may involve control by T regulatory cells.

CONCLUSIONS

Pneumococcal immunoregulatory therapy is a potentially important approach to asthma management that requires further evaluation in well-designed research studies.

Translocation of bacterial NOD2 agonist and its link with inflammation

INTRODUCTION

The gut is often considered as the motor of critical illness through bacterial translocation, which amplifies the inflammatory response and alters the immune status. However, systemic bacterial translocation was rarely proven and endotoxin measurement only reflects translocation of Gram-negative-derived products. The process could be more frequently identified if peptidoglycan, derived from both Gram-negative and Gram-positive bacteria, was measured.

METHODS

We developed a new tool to detect circulating peptidoglycan-like structure using a NOD2-transfected cell line. We also measured plasma and cell-associated endotoxin and different plasma markers of inflammation. We studied 21 patients undergoing abdominal aortic surgery (AAS), and 21 patients undergoing carotid artery surgery (CAS) were included as negative controls. Patients were sampled during surgery until two days post-surgery.

RESULTS

In 90.5% of the AAS patients, a NOD2 agonist peak was detected in plasma before aortic clamping, but after gut manipulation by the surgeon, and persisted after blood reperfusion. As expected, no peak was detected in plasma from CAS patients (P = 0.003). Leukocyte-bound endotoxin appeared after blood reperfusion in 71% of the AAS patients, and circulating endotoxin was detected for 57% of them. The levels of interleukin (IL)-6, IL-10 and of inflammatory markers (C-reactive protein, procalcitonin) were maximal at postoperative day 1 or 2 in AAS patients. The levels of circulating NOD2 agonist positively correlated with those of cortisol and IL-10.

CONCLUSIONS

The measurement of circulating NOD2 agonist gives a higher informative tool than that of circulating endotoxin for early and sensitive detection of the translocation of bacterial products. The data suggest that circulating NOD2 agonist contributes to further enhance the stress response following surgery.

Purification, cloning, and functional characterization of a novel immunomodulatory protein from Antrodia camphorata (bitter mushroom) that exhibits TLR2-dependent NF-κB activation and M1 polarization within murine macrophages

A new immunomodulatory protein, designated ACA, was purified from the mycelium extract of Antrodia camphorata , a well-known folk medicine bitter mushroom in Taiwan, and N-terminally sequenced. By taking advantage of its N-terminal amino acid sequence, the full-length ACA gene was cloned using rapid amplification of cDNA ends (RACE) approach. This gene encodes a 136 amino acid protein that is homologous to the phytotoxic proteins from fungi. On the basis of the data of N-terminal sequencing and N-glycosidase F treatment, the native ACA was confirmed to be a glycoprotein. The similarity in activation of TLR4-deficient macrophages by both the native ACA and recombinant ACA (rACA) suggested that the glycosyl group(s) of the native ACA was insignificant in macrophage activation. Moreover, the failure of rACA to induce TLR2-deficient macrophages and to activate the RAW 264.7 macrophages transfected with the dominate-negative MyD88 (dnMyD88) indicated that the ACA-mediated macrophage activation was TLR2/MyD88 dependent. Microarray assay of the ACA-activated NFκB-related gene expression showed that rACA demonstrated a LPS-mimetic proinflammatory response toward RAW 264.7 macrophages. Furthermore, rACA enhanced phagocytosis activity and CD86 (B7-2) expression as well as induced TNF-α and IL-1β production within murine peritoneal macrophages. A time-dependent induction of mRNA expression of cytokines TNF-α, IL-1β, IL-6, and IL-12 as well as chemokines CCL3, CCL4, CCL5, and CCL10, but not IL-10, CCL17, CCL22, and CCL24, was observed after the ACA treatment of the macrophages. These results proposed that ACA exhibited M1 polarization and differentiation in macrophages. Thus, ACA is an important immunomodulatory protein of A. camphorata.

Enhanced monocyte response and decreased central memory T cells in children with invasive Staphylococcus aureus infections

Staphylococcus aureus has emerged as a significant pathogen causing severe invasive disease in otherwise healthy people. Despite considerable advances in understanding the epidemiology, resistance mechanisms, and virulence factors produced by the bacteria, there is limited knowledge of the in vivo host immune response to acute, invasive S. aureus infections. Herein, we report that peripheral blood mononuclear cells from patients with severe S. aureus infections demonstrate a distinctive and robust gene expression profile which is validated in a distinct group of patients and on a different microarray platform. Application of a systems-wide modular analysis framework reveals significant over-expression of innate immunity genes and under-expression of genes related to adaptive immunity. Simultaneous flow cytometry analyses demonstrated marked alterations in immune cell numbers, with decreased central memory CD4 and CD8 T cells and increased numbers of monocytes. CD14+ monocyte numbers significantly correlated with the gene expression levels of genes related to the innate immune response. These results demonstrate the value of applying a systems biology approach that reveals the significant alterations in the components of circulating blood lymphocytes and monocytes in invasive S. aureus infections.

Differential expression of toll-like receptor genes: sepsis compared with sterile inflammation 1 day before sepsis diagnosis

Toll-like receptors (TLRs) are critical components of innate immunity. This study was designed to evaluate differential expression of genes for TLR and associated signal transduction molecules in critically ill patients developing sepsis compared with those with sterile inflammation. Uninfected critically ill patients with systemic inflammatory response syndrome were prospectively followed daily for development of sepsis. They were divided into two groups and compared in a case-control manner: (a) preseptic patients (n = 45) who subsequently developed sepsis, and (b) uninfected systemic inflammatory response syndrome patients (n = 45) who remained uninfected. Whole blood RNA was collected (PAXGene tube) at study entry and 1, 2, and 3 days before clinical sepsis diagnosis (or time-matched uninfected control) and analyzed via Affymetrix Hg_U133 Plus 2.0 microarrays. Genes were considered differentially expressed if they met univariate significance controlled for multiple comparisons at P < 0.005. Differentially expressed probes were uploaded into the Database for Annotation, Visualization and Integrated Discovery. The TLR pathway (Kyoto Encyclopedia of Genes and Genomes-KEGG) significance was determined via Expression Analysis Systematic Explorer (EASE) scoring. A total of 2,974 Affymetrix probes representing 2,190 unique genes were differentially expressed 1 day before sepsis diagnosis. Thirty-six probes representing 25 genes were annotated to the TLR pathway (KEGG) via the Database for Annotation, Visualization and Integrated Discovery with an EASE score at P < 0.0004. Notable TLR genes demonstrating increased expression include TLR-4 (median, 1.43-fold change), TLR-5 (2.08-fold change), and MAPK14 (1.90-fold change). An additional 11 unique genes were manually annotated into the TLR pathway based on known relevance such as TLR-8 (1.54-fold change). The total 36 genes contained 28 showing increased expression and 8 showing decreased expression. Differential gene expression was noted for TLR receptors (eight genes), TLR intracellular signal transduction cascade molecules (27 genes), and TLR-related effector molecules (one gene). The TLR and downstream signaling genes are differentially expressed in critically ill patients developing sepsis compared with those with sterile inflammation. These expression differences occur before phenotypic-based diagnosis of clinical sepsis.

Host-microbe symbiosis: the squid-Vibrio association--a naturally occurring, experimental model of animal/bacterial partnerships

Many, if not most, animals have specific symbiotic relationships with bacterial partners. Recent studies suggest that vertebrates create alliances with highly complex consortia of hundreds to thousands of prokaryotic phylotypes. In contrast, invertebrates often have binary associations, i.e., relationships with a population of a single bacterial species. In this chapter, the association between the Hawaiian sepiolid squid Euprymna scolopes and the marine luminous bacterium Vibrio fisheri is highlighted. This symbiosis offers a relatively simple, yet naturally occurring, association that can be experimentally manipulated. Studies of this system are providing insight into the precise mechanisms by which a beneficial animal-bacterial symbiosis can be established and maintained.

Induction of TLR2 expression by inflammatory stimuli is required for endothelial cell responses to lipopeptides

Human endothelial cells (EC) express Toll-like receptor 4 (TLR4), a receptor for lipopolysaccharides (LPS), but little or no TLR2, a lipopeptide receptor. The aim of this study was to investigate to what extent inflammatory stimuli modify the expression by EC of TLR4 and TLR2, of the TLR2 co-receptors TLR1 and TLR6 and of the TLR2-accessory proteins CD14 and CD36. Stimulation of umbilical vein derived EC with TNF-alpha, LPS or IL-1beta for 24h induced a strong increase in TLR2 mRNA but not in TLR1, TLR4 and TLR6 mRNA. Inflammatory activation had little effect on CD14 mRNA, but decreased the expression of CD36 mRNA. TLR2 antigen was readily detected by flow cytometry on activated EC, but not on resting EC. A significant proportion of TLR2 was found to be located intracellularly. By using specific signalling pathway inhibitors we established that the induction of TLR2 by inflammatory stimuli was dependent on NF-kappaB, p38-MAP kinase and c-Jun kinase. IRAK-1 phosphorylation after treatment with 10mug/ml of lipoteichoic acid (LTA), a TLR2 agonist, was only observed in TNF-alpha-stimulated EC and not in resting EC. Furthermore, LTA potentiated the increase of the inflammatory markers E-Selectin or IL-8 in EC pre-treated with TNF-alpha, LPS or IL-1beta, but not in resting EC. These results imply that the up-regulated TLR2 is functionally active. Interestingly, LTA had no effect on TLR2 expression, nor maintained TLR2 expression, in activated EC. This suggests that lipopeptide responses of EC are dependent on the continued presence of inflammatory cytokines, provided by other cell types, or LPS. In conclusion, inflammatory stimuli induce a high TLR2 expression in EC, which in turn enables the cells to strongly respond to lipopeptides. The up-regulation of TLR2 may be of relevance for the vascular effects of Gram-positive bacteria.

Increased surface toll-like receptor 2 expression in superantigen shock

OBJECTIVE

Examination of the interaction between gram-positive bacterial superantigens and toll-like receptor 2 (TLR2) in health and critical illness.

DESIGN

Laboratory ex vivo model and prospective clinical, cohort study.

SETTING

Two research laboratories in university hospitals and two intensive care units.

SUBJECTS/PATIENTS

Laboratory study was performed in transfected HeLa cells and primary human monocytes from healthy volunteers. Clinical study used cells from 20 healthy controls and 45 critically ill patients with circulatory shock.

INTERVENTIONS

HeLa cells and purified monocytes were exposed to purified superantigens or isogenic bacterial supernatants and readout obtained by cytokine enzyme-linked immunosorbent assay, flow cytometry, and quantitative real-time polymerase chain reaction. Peripheral blood mononuclear cells from patients with circulatory shock were compared with controls using flow cytometry and measurement of cytokines after ligand exposure.

MEASUREMENTS AND MAIN RESULTS

Superantigens were unable to signal through ligation by TLR2. However, TLR2 was up-regulated on the surface of primary human monocytes, without detectable TLR2 messenger RNA neosynthesis, by a range of superantigens and superantigen-containing Streptococcus pyogenes supernatants, although not by isogenic superantigen-negative strains. Superantigen mutant constructs with disrupted major histocompatibility complex class II-binding sites did not support TLR2 up-regulation. TLR2 up-regulation was associated with an increase in the proinflammatory response to TLR2 ligands only at high ligand concentrations. TLR2 was up-regulated in a small subset of patients with severe S. pyogenes sepsis but not in patients with any other category of septic or circulatory shock; responses to TLR2 ligands were reduced in all categories of critically ill patient, however.

CONCLUSIONS

Superantigens up-regulate monocyte surface TLR2 expression through major histocompatibility complex class II signaling. Enhanced surface TLR2 expression may be a specific feature of patients with S. pyogenes-induced shock. Importantly, intensity of TLR2 signaling is not necessarily coupled to TLR2 expression when ligand concentrations are low or after onset of critical illness.

Activation of cytokine synthesis by systemic infusions of lipopolysaccharide and peptidoglycan in a porcine model in vivo and in vitro

BACKGROUND

The incidence of gram-positive and mixed bacterial infections in surgical patients has increased, and there has been an alarming rise in the number of drug-resistant bacteria. Peptidoglycan (PepG) is a cell wall component of gram-positive bacteria that stimulates inflammatory responses both ex vivo and in vivo. The systemic effects of PepG on inflammation have not been studied in a large animal model.

METHODS

Anesthetized pigs were subjected to 8-h continuous intravenous infusions of lipopolysaccharide (LPS) (4 mcg/kg/h), PepG (40 mcg/kg/h), LPS plus PepG, or saline. The concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-8, and IL-10 were measured in the plasma prior to infusion (time 0) and thereafter every second hour until the end of the experiments. Heparinized whole blood samples drawn at time 0 and after a 6-h infusion of LPS or PepG were incubated ex vivo with PepG (10 mcg/mL), LPS (10 ng/mL), or a combination of PepG and LPS to study the immunologic consequences of systemic inflammation. Concentrations of TNF-alpha, IL-8, and IL-1beta were measured in the supernatant liquids.

RESULTS

In vivo, there was transient upregulation of TNF-alpha after infusion of LPS, PepG, or the combination. Interleukin-6 and IL-8 were upregulated by LPS but not by PepG. In vitro studies of whole blood obtained at time 0 revealed a synergistic effect of LPS and PepG on the release of TNF-alpha. Incubation of whole blood obtained after 6 h of infusion of LPS or PepG revealed tolerance and cross-tolerance between the two bacterial components in the induction of TNF-alpha, IL-8, and IL-1beta.

CONCLUSIONS

Peptidoglycan is a potent inducer of TNF-alpha in this large animal model. Peptidoglycan and LPS synergized to increase the formation of the proinflammatory cytokine TNF-alpha. The study demonstrates for the first time the development of tolerance and cross-tolerance between LPS and PepG in a large animal model. These phenomena could be of importance for the signs and symptoms of sepsis.

Both TLR2 and TLR4 are required for the effective immune response in Staphylococcus aureus-induced experimental murine brain abscess

Toll-like receptors (TLRs) play central roles in the innate reaction to bacterial products and transmit specific immune responses against these pathogens. TLRs are expressed on numerous cell types, including innate immune cells, and on astrocytes, neurons, and microglial cells of the central nervous system (CNS). Lipoproteins and lipopolysaccharides are specifically recognized by TLR2 and TLR4, respectively. We examined the in vivo role of TLR2 and TLR4 in Staphylococcus aureus-induced brain abscess. Phenotypically, 87% of TLR2(-/-) mice and 43% of TLR4(-/-) mice died whereas all wild-type (WT) mice recovered. Clearance of bacteria from the CNS was significantly delayed in TLR2(-/-) mice compared with TLR4(-/-) and WT animals. Recruitment of granulocytes and macrophages to the CNS, as well as microglial activation and expansion, was up-regulated in TLR2(-/-) mice. Although inflammation persisted especially in the CNS of TLR2(-/-) mice, but also of TLR4(-/-) mice, WT mice terminated the infection more effectively. Collectively, these data show that the immune response to experimental S. aureus-induced brain abscess depends crucially on the recognition of S. aureus by TLR2 but that TLR4 is also required for an optimal intracerebral immune response in this disorder.

Peptidoglycan-mediated IL-8 expression in human alveolar type II epithelial cells requires lipid raft formation and MAPK activation

Staphylococcus aureus, a major sepsis-causing Gram-positive bacterium, invades pulmonary epithelial cells and causes lung diseases. In the lung, alveolar type II epithelial cells play an important role in innate immunity by secreting chemokines and antimicrobial peptides upon bacterial infection whereas type I cells mainly function in gas-exchange. In this study, we investigated the ability of S. aureus peptidoglycan (PGN) to induce expression of a chemokine, IL-8, in a human alveolar type II epithelial cell line, A549. PGN induces IL-8 mRNA and protein expression in a dose- and time-dependent manner. Supplementation of soluble CD14 further enhanced the PGN-induced IL-8 expression. Interestingly, PGN-induced IL-8 expression was inhibited by nystatin, a specific inhibitor for lipid rafts, but not by chlorpromazine, a specific inhibitor for clathrin-coated pits. Furthermore, PGN-induced IL-8 expression was attenuated by inhibitors for MAP kinases such as ERK, p38 kinase, and JNK/SAPK, whereas no inhibitory effect was observed by inhibitors for reactive oxygen species or protein kinase C. Electrophoretic mobility shift assay demonstrates that PGN increased the DNA binding of the transcription factors, AP-1 and NF-kappaB while minimally, NF-IL6, all of which are involved in the transcription of IL-8. Taken together, these results suggest that PGN induces IL-8 expression in a CD14-enhanced manner in human alveolar type II epithelial cells, through the formation of lipid rafts and the activation of MAP kinases, which ultimately leads to activation of AP-1, NF-kappaB, and NF-IL6.

Kinetics of Toll-like receptor-4 splice variants expression in lipopolysaccharide-stimulated antigen presenting cells of healthy donors and patients with cystic fibrosis

Toll-like receptors (TLR) are key components of innate immune system. As TLR activation could induce potentially harmful inflammatory response, activation of TLR signaling pathways has to be under tight control. Besides other control mechanisms, an inhibitory function of murine TLR4 splice variants was recently demonstrated. In this study we investigated expression of four TLR4 splice variants in human antigen presenting cells (APC). Furthermore, we studied modification in TLR4 splice variants expression in APC in cystic fibrosis (CF) patients chronically infected by Gram-negative bacteria. We developed a novel reliable real-time PCR detection system that allowed monitoring of individual TLR4 splice variants expression. In APC from healthy donors we detected a characteristic transient increase of two out of four splice variants after lipopolysaccharide (LPS) stimulation. Similarly to murine TLR4, one of these variants, NM 003266, might translate to a potentially inhibitory protein. In contrast to controls, CF monocytes had significantly changed LPS-induced expression of TLR4 gene and its variants including reduced ability to up-regulate the expression of the potentially inhibitory variant upon stimulation. In accordance with this observation, monocytes from CF patients produced significantly more tumor necrosis factor after LPS stimulation than healthy controls. Our results thus describe the kinetics of TLR4 splicing variants expression after LPS stimulation and indicate a possible alteration of its regulation in CF patients.

TLR-TLR cross talk in human PBMC resulting in synergistic and antagonistic regulation of type-1 and 2 interferons, IL-12 and TNF-alpha

Currently, single TLR agonists are being utilized for vaccination and tumor immunotherapy. Here we investigated the effects of tandem combinations of TLR agonists on the production of cytokines with major focus on IFN-alpha, -beta, -gamma, TNF-alpha, and IL-12. Using a primary human PBMC culture system, we found that tandem combinations of TLR2-9 agonists can be inert, additive, synergistic or antagonistic. The most interesting combination was TLR2 or TLR4 agonists in combination with TLR7/8 or TLR8 agonists. TLR4-TLR7/8 combinations synergistically up-regulated IFN-gamma and IL-12, enhanced IFN-alpha and also moderately induced TNF-alpha. TLR2-TLR7/8 like TLR4-TLR7/8 synergistically up-regulated IFN-gamma but not IL-12. TLR9 agonist CpG2216 produced high IFN-alpha but failed to up regulate IFN-gamma singly or in tandem. Furthermore, TLR9-induced type-1 IFN was down regulated in combination with TLR7, or TLR8 agonists. TLR3 induced significant IFN-alpha/-beta responses when used in a complex with membrane permeability enhancer DOTAP, and additively enhanced response with agonists to TLR2, 5, 7/8, and 8. To our knowledge, this study is the first to compare cytokine responses of all the possible tandem combinations of TLR agonists in human PBMC. We identified certain combinations of TLR agonists that may or may not have advantages over single agonists, for generating an "optimal cytokine combination" preferred in combating diseases.

ALTERATIONS IN INFLAMMATORY CAPACITY AND TLR EXPRESSION ON MONOCYTES AND NEUTROPHILS AFTER CARDIOPULMONARY BYPASS

Cardiopulmonary bypass (CPB) is associated with immune paresis, which predisposes to the development of postoperative sepsis. The aims of this study were to characterize the ex vivo cytokine responses to bacterial cell wall components in whole blood from patients undergoing CPB and to determine whether altered leukocyte expression of Toll-like receptors (TLRs) is involved in immune paresis after CPB. We recruited 6 patients undergoing routine cardiac surgery with CPB. Preoperatively, at the end of CPB and 20 h later, blood was obtained, anticoagulated, and leukocyte surface expression of CD14, TLR2, and TLR4 was quantified by flow cytometry. In addition, blood was incubated at 37 degrees C in the presence of peptidoglycan (PepG) and/or lipopolysaccharide (LPS), and plasma cytokines were measured by enzyme immunoassay. At the end of CPB, ex vivo production of tumor necrosis factor alpha, interleukin (IL) 1beta, IL-8, and IL-10 in response to PepG or LPS was virtually abolished (P < 0.05). The following day, there was recovery of all cytokine responses to PepG. Tumor necrosis factor alpha and IL-1beta responses to LPS partially recovered, whereas IL-8 and IL-10 responses recovered. At the end of CPB, there was more than 50% reduction in neutrophil TLR2 and TLR4 expression (P < 0.05), with recovery to baseline the following day. There was a 29% reduction in monocyte TLR4 expression at the end of CPB (P < 0.05) and more than 120% increase in monocyte TLR2 and 4 expression the following day (P < 0.05). In conclusion, reduced ex vivo production of cytokines cannot be fully accounted for by downregulation of TLR expression, although receptor upregulation may contribute to the later recovery of responsiveness.

Structural characterisation and expression analysis of toll-like receptor 2 gene from catfish

Toll-like receptors (TLRs) are important components of innate immunity. They were found to recognise specific structures on pathogens termed pathogen-associated molecular patterns (PAMPs) and utilise conserved signaling pathways to activate pro-inflammatory cytokines and type-1 interferons. In spite of much understanding gained from the mammalian systems, many fish TLRs are unknown. Recent studies in Japanese flounder as well as in zebrafish suggested that the ligand binding and activation of inflammatory responses in fish may be different from and more complex than those found in mammals. In channel catfish, the major aquaculture species in the United States, only partial sequences of TLR3 and TLR5 were reported. As a part of efforts to characterise the innate immune components in channel catfish, here we cloned and sequenced both the cDNA and the gene for TLR2, a receptor believed mostly responsible for recognition of lipopeptides on the surface of most Gram-positive bacteria. However, expression analysis after infection with a Gram-negative bacterium, Edwardsiella ictaluri indicated that TLR2 was modestly down-regulated in the head kidney tissue of blue catfish, and with a similar pattern in the head kidney of channel catfish though the down-regulation in channel catfish was not statistically significant. In the spleen, an insignificant down-regulation was initially observed early after infection, with an increase of TLR expression later after infection. These results suggest the involvement of TLR2 in the responses after the bacterial infection. As LPS is believed to be the major PAMP for Gram-negative bacteria, additional research is warranted to determine the functions and mechanisms of TLR2 in infections of Gram-negative bacteria.

Analysis of Components of the CD14/TLR System on Leukocytes of Patients with Atopic Dermatitis

BACKGROUND

Atopic dermatitis (AD) is frequently associated with skin infections that may be a consequence of an impaired function of the innate immune response. Conversely, the frequent bacterial colonization may also influence the systemic immune reactions, including the Toll-like receptor (TLR) system, through the translocation of bacterial components into the circulation. Therefore, we characterized phenotypic and functional properties of the TLR system in patients with extrinsic and intrinsic AD.

METHODS

The absolute number of surface CD14, TLR2, TLR4 and CD180 and the CD14-mediated uptake of bodipy-labeled endotoxin and bacteria by whole blood leukocytes was studied by flow cytometry. We measured the serum soluble CD14 concentration by an inhibitory flow cytometric method.

RESULTS

We observed a significant overexpression of TLR2 and TLR4 on monocytes, TLR2 and CD14 on granulocytes and CD180 on lymphocytes of intrinsic AD patients compared to healthy controls. The serum soluble CD14 was not different in the intrinsic AD patients, while it was diminished in the extrinsic AD group compared to the controls. The endotoxin and bacterium uptake showed no differences.

CONCLUSIONS

The observed upregulation of CD14, TLR2, TLR4 and CD180 on peripheral leukocytes seems to be rather a consequence than the cause of the repeated bacterial infections in AD.

Staphylococcal colonization and infection: homeostasis versus disbalance of human (innate) immunity and bacterial virulence

PURPOSE OF REVIEW

This review identifies trends in the study of interactions between Staphylococcus aureus and humans. When nasal colonization is in the neutral state, infection clearly represents a state of host-pathogen disbalance. The features leading from apparent homeostatic colonization to pathogenesis are identified at an increasing rate.

RECENT FINDINGS

Persistent carriage of S. aureus predisposes to infection but limits bacteraemia-associated mortality. Intermittent carriage is usually imposed and of lesser clinical relevance. The nature and function of several staphylococcal virulence factors have been elucidated and near complete gene catalogues have been established. There does not seem to be a difference in virulence, however, between methicillin-susceptible and resistant S. aureus. Biological selection takes place in the nose and innate immune features relevant to colonization have been discovered. Acquired immunity remains underexposed, but the host factors involved in the host-pathogen interaction have been identified.

SUMMARY

Virulence assessment of S. aureus has been facilitated by novel technology: genome-wide inventories of virulence potential can be made and new pathogenic mechanisms have been presumptively identified. These involve invasion procedures but also (innate) immune evasion strategies. These cross-fertilizing developments shed light on the feasibility of novel prophylactic or therapeutic strategies for combating staphylococcal carriage and disease.

Peptidoglycan--an endotoxin in its own right?

Studies aimed at dissecting the complex pathophysiology of sepsis with multiple organ failure have traditionally focused on lipopolysaccharide of gram-negative bacteria, which is widely regarded as the classical endotoxin. However, gram-positive sepsis now accounts for up to 50% of all cases, calling for a shift of focus. Peptidoglycan (PepG) is the major cell wall component of gram-positive bacteria and has been increasingly recognized as an important proinflammatory molecule. During gram-positive infections, PepG reaches the circulation by bacterial breakdown or translocation from the intestine. Administration of PepG induces all the classical features of infectious illness and endotoxemia and may cause systemic inflammation with organ failure in animal models. Its potency, however, is crucially dependent on various features of its complex structure. PepG interacts with the innate immune system through receptors mainly expressed on monocytes/macrophages but may induce inflammatory changes in other cell types as well. Among the most extensively studied receptor systems are the nucleotide-binding oligomerization domains, the toll-like receptors, and the PepG recognition proteins. Based on the current available literature, we would like to propose that PepG must be regarded as an endotoxin in its own right and to encourage further work in the field of PepG signaling.