Cytokine induction by Gram-positive bacteria

Unveiling the Multifaceted Capabilities of Endophytic Aspergillus flavus Isolated from Annona squamosa Fruit Peels against Staphylococcus Isolates and HCoV 229E-In Vitro and In Silico Investigations

Recently, there has been a surge towards searching for primitive treatment strategies to discover novel therapeutic approaches against multi-drug-resistant pathogens. Endophytes are considered unexplored yet perpetual sources of several secondary metabolites with therapeutic significance. This study aims to isolate and identify the endophytic fungi from Annona squamosa L. fruit peels using morphological, microscopical, and transcribed spacer (ITS-rDNA) sequence analysis; extract the fungus's secondary metabolites by ethyl acetate; investigate the chemical profile using UPLC/MS; and evaluate the potential antibacterial, antibiofilm, and antiviral activities. An endophytic fungus was isolated and identified as Aspergillus flavus L. from the fruit peels. The UPLC/MS revealed seven compounds with various chemical classes. The antimicrobial activity of the fungal ethyl acetate extract (FEA) was investigated against different Gram-positive and Gram-negative standard strains, in addition to resistant clinical isolates using the agar diffusion method. The CPE-inhibition assay was used to identify the potential antiviral activity of the crude fungal extract against low pathogenic human coronavirus (HCoV 229E). Selective Gram-positive antibacterial and antibiofilm activities were evident, demonstrating pronounced efficacy against both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). However, the extract exhibited very weak activity against Gram-negative bacterial strains. The ethyl acetate extract of Aspergillus flavus L exhibited an interesting antiviral activity with a half maximal inhibitory concentration (IC50) value of 27.2 µg/mL against HCoV 229E. Furthermore, in silico virtual molecular docking-coupled dynamics simulation highlighted the promising affinity of the identified metabolite, orienting towards three MRSA biotargets and HCoV 229E main protease as compared to reported reference inhibitors/substrates. Finally, ADME analysis was conducted to evaluate the potential oral bioavailability of the identified metabolites.

Evaluating IL-6 and IL-10 as rapid diagnostic tools for Gram-negative bacteria and as disease severity predictors in pediatric sepsis patients in the intensive care unit

Background

To explore the diagnostic performance of interleukin (IL)-6 and IL-10 in discriminating Gram bacteria types and predicting disease severity in intensive care unit (ICU)-hospitalized pediatric sepsis patients.

Method

We retrospectively collected Th1/Th2 cytokine profiles of 146 microbiologically documented sepsis patients. Patients were categorized into Gram-positive (G+) or Gram-negative (G-) sepsis groups, and cytokine levels were compared. Subgroup analysis was designed to eliminate the influence of other inflammatory responses on cytokine levels.

Results

After propensity score matching, 78 patients were matched and categorized according to Gram bacteria types. Compared with G+ sepsis, IL-6 and IL-10 were significantly elevated in G- sepsis (p < 0.05). Spearman test proved the linear correlation between IL-6 and IL-10 (r = 0.654, p < 0.001), and their combination indicators (ratio and differences) were effective in identifying G- sepsis. In the subgroup analysis, such cytokine elevation was significant regardless of primary infection site. However, for patients with progressively deteriorating organ function [new or progressive multiple organ dysfunction syndrome (NPMODS)], differences in IL-6 and IL-10 levels were less significant between G+ and G- sepsis. In the receiver operating characteristic (ROC) curves of the G- sepsis group, the area under the curve (AUC) value for IL-6 and IL-10 was 0.679 (95% CI 0.561-0.798) and 0.637 (95% CI 0.512-0.762), respectively. The optimal cutoff value for diagnosing G- sepsis was 76.77 pg/ml and 18.90 pg/ml, respectively. While for the NPMODS group, the AUC for IL-6 and IL-10 was 0.834 (95% CI 0.766-0.902) and 0.781 (95% CI 0.701-0.860), respectively.

Conclusion

IL-6 and IL-10 are comparably effective in discriminating G+/G- sepsis in pediatric intensive care unit (PICU) patients. The deteriorated organ function observed in ICU patients reveals that complex inflammatory responses might have contributed to the cytokine pattern observed in severe sepsis patients, therefore confounding the discriminating efficacy of Th1/Th2 cytokines in predicting Gram bacteria types.

Myeloid liver kinase B1 contributes to lung inflammation induced by lipoteichoic acid but not by viable Streptococcus pneumoniae

Background

Liver kinase B1 (Lkb1, gene name Stk11) functions as a tumor suppressor in cancer. Myeloid cell Lkb1 potentiates lung inflammation induced by the Gram-negative bacterial cell wall component lipopolysaccharide and in host defense during Gram-negative pneumonia. Here, we sought to investigate the role of myeloid Lkb1 in lung inflammation elicited by the Gram-positive bacterial cell wall component lipoteichoic acid (LTA) and during pneumonia caused by the Gram-positive respiratory pathogen Streptococcus pneumoniae (Spneu).

Methods

Alveolar and bone marrow derived macrophages (AMs, BMDMs) harvested from myeloid-specific Lkb1 deficient (Stk11-ΔM) and littermate control mice were stimulated with LTA or Spneu in vitro. Stk11-ΔM and control mice were challenged via the airways with LTA or infected with Spneu in vivo.

Results

Lkb1 deficient AMs and BMDMs produced less tumor necrosis factor (TNF)α upon activation by LTA or Spneu. During LTA-induced lung inflammation, Stk11-ΔM mice had reduced numbers of AMs in the lungs, as well as diminished cytokine release and neutrophil recruitment into the airways. During pneumonia induced by either encapsulated or non-encapsulated Spneu, Stk11-ΔM and control mice had comparable bacterial loads and inflammatory responses in the lung, with the exception of lower TNFα levels in Stk11-ΔM mice after infection with the non-encapsulated strain.

Conclusion

Myeloid Lkb1 contributes to LTA-induced lung inflammation, but is not important for host defense during pneumococcal pneumonia.

Wall teichoic acid-dependent phagocytosis of intact cell walls of Lactiplantibacillus plantarum elicits IL-12 secretion from macrophages

Selected lactic acid bacteria can stimulate macrophages and dendritic cells to secrete IL-12, which plays a key role in activating innate and cellular immunity. In this study, we investigated the roles of cell wall teichoic acids (WTAs) displayed on whole intact cell walls (ICWs) of Lactiplantibacillus plantarum in activation of mouse macrophages. ICWs were prepared from whole bacterial cells of several lactobacilli without physical disruption, and thus retaining the overall shapes of the bacteria. WTA-displaying ICWs of several L. plantarum strains, but not WTA-lacking ICWs of strains of other lactobacilli, elicited IL-12 secretion from mouse bone marrow-derived macrophages (BMMs) and mouse macrophage-like J774.1 cells. The ability of the ICWs of L. plantarum to induce IL-12 secretion was abolished by selective chemical elimination of WTAs from ICWs, but was preserved by selective removal of cell wall glycopolymers other than WTAs. BMMs prepared from TLR2- or TLR4-deficient mouse could secret IL-12 upon stimulation with ICWs of L. plantarum and a MyD88 dimerization inhibitor did not affect ICW-mediated IL-12 secretion. WTA-displaying ICWs, but not WTA-lacking ICWs, were ingested in the cells within 30 min. Treatment with inhibitors of actin polymerization abolished IL-12 secretion in response to ICW stimulation and diminished ingestion of ICWs. When overall shapes of ICWs of L. plantarum were physically disrupted, the disrupted ICWs (DCWs) failed to induce IL-12 secretion. However, DCWs and soluble WTAs inhibited ICW-mediated IL-12 secretion from macrophages. Taken together, these results show that WTA-displaying ICWs of L. plantarum can elicit IL-12 production from macrophages via actin-dependent phagocytosis but TLR2 signaling axis independent pathway. WTAs displayed on ICWs are key molecules in the elicitation of IL-12 secretion, and the sizes and shapes of the ICWs have an impact on actin remodeling and subsequent IL-12 production.

Lipoteichoic acid, a cell wall component of Gram-positive bacteria, induces sleep and fever and suppresses feeding

Fragments of the bacterial cell wall are bioactive microbial molecules that have profound effects on the function of the brain. Some of the cell wall constituents are common to both Gram-positive and Gram-negative bacteria, e.g., peptidoglycans, while other cell wall components are specific to either Gram-positive or Gram-negative microbes. Lipopolysaccharide (LPS), also called endotoxin, is found exclusively in Gram-negative bacteria, while lipoteichoic acid (LTA) is specific to Gram-positive bacteria. The effects of peptidoglycans, their fragments, and LPS are well characterized, they induce sleep, fever and anorexia. In the present study, we investigated the sleep, body temperature and food intake modulating effects of LTA. We found that intraperitoneal injection of 100 and 250 μg LTA from B. subtilis and S. aureus increases non-rapid-eye movement sleep (NREMS) in mice. The effects were dose-dependent, and the changes were accompanied by decreased motor activity and feeding as well as febrile responses. Intraperitoneal injection of 10 μg LTA induced monophasic increases in body temperature, while 100 and 250 μg LTA from B. subtilis induced initial hypothermia followed by fever. Treatment with 250 μg LTA from S. aureus elicited monophasic hypothermia. Administration of 300 μg/kg LTA from S. aureus directly into the portal vein elicited similar sleep responses in rats but did not affect body temperature. The sleep-modulating effects of LTA were similar to that of LPS in mice, although LTA appears to be less potent. These findings suggest that the role of LTA in signaling by Gram-positive bacteria in the host body is analogous to the role of LPS/endotoxin in signaling by Gram-negative microbes. LTA may play a role in the development of sickness response in clinically manifest Gram-positive bacterial infections and may contribute to sleep signaling by the commensal intestinal microbiota.

Antibacterial and Anti-Inflammatory Activity of an Antimicrobial Peptide Synthesized with D Amino Acids

The peptide SET-M33 is a molecule synthesized in tetra-branched form which is being developed as a new antibiotic against Gram-negative bacteria. Its isomeric form with D amino acids instead of the L version (SET-M33D) is also able to kill Gram-positive bacteria because of its higher resistance to bacterial proteases (Falciani et al., PLoS ONE, 2012, 7, e46259). Here we report the strong in vitro activity of SET-M33D (MIC range 0.7-6.0 µM) against multiresistant pathogens of clinical interest, including Gram-positives Staphylococcus aureus, Staphylococcus saprophyticus, and Enterococcus faecalis, and various Gram-negative enterobacteriaceae. SET-M33D antibacterial activity is also confirmed in vivo against a MRSA strain of S. aureus with doses perfectly compatible with clinical use (5 and 2.5 mg/Kg). Moreover, SET-M33D strongly neutralized lipopolysaccharide (LPS) and lipoteichoic acid (LTA), thus exerting a strong anti-inflammatory effect, reducing expression of cytokines, enzymes, and transcription factors (TNF-α, IL6, COX-2, KC, MIP-1, IP10, iNOS, NF-κB) involved in the onset and evolution of the inflammatory process. These results, along with in vitro and in vivo toxicity data and the low frequency of resistance selection reported here, make SET-M33D a strong candidate for the development of a new broad spectrum antibiotic.

Bacterial Endotoxins and Their Role in Periparturient Diseases of Dairy Cows: Mucosal Vaccine Perspectives

During the periparturient period there is a significant increase in the incidence of multiple metabolic and infectious diseases in dairy cows. Dairy cows are fed high-grain diets immediately after calving to support production of large amounts of milk. Mounting evidence indicates these types of diets are associated with the release of high amounts of endotoxins in the rumen fluid. If infected, the udder and uterus additionally become important sources of endotoxins during the postpartum period. There is increasing evidence that endotoxins translocate from rumen, uterus, or udder into the systemic circulation and trigger chronic low-grade inflammatory conditions associated with multiple diseases including fatty liver, mastitis, retained placenta, metritis, laminitis, displaced abomasum, milk fever, and downer cow syndrome. Interestingly, endotoxin-related diseases are triggered by a bacterial component and not by a specific bacterium. This makes prevention of these type of diseases different from classical infectious diseases. Prevention of translocation of endotoxins into the host systemic circulation needs to take priority and this could be achieved with a new approach: mucosal vaccination. In this review article, we discuss all the aforementioned issues in detail and also report some of our trials with regards to mucosal vaccination of periparturient dairy cows.

Etiologic role of root canal infection in apical periodontitis and its relationship with clinical symptomatology

Evidence shows the polymicrobial etiology of endodontic infections, in which bacteria and their products are the main agents for the development, progression, and dissemination of apical periodontitis. Microbial factors in necrotic root canals (e.g., endotoxin) may spread into apical tissue, evoking and supporting a chronic inflammatory load. Thus, apical periodontitis is the result of the complex interplay between microbial factors and host defense against invasion of periradicular tissues. This review of the literature aims to discuss the complex network between endodontic infectious content and host immune response in apical periodontitis. A better understanding of the relationship of microbial factors with clinical symptomatology is important to establish appropriate therapeutic procedures for a more predictable outcome of endodontic treatment.

SOCS Proteins as Regulators of Inflammatory Responses Induced by Bacterial Infections: A Review

Severe bacterial infections can lead to both acute and chronic inflammatory conditions. Innate immunity is the first defense mechanism employed against invading bacterial pathogens through the recognition of conserved molecular patterns on bacteria by pattern recognition receptors (PRRs), especially the toll-like receptors (TLRs). TLRs recognize distinct pathogen-associated molecular patterns (PAMPs) that play a critical role in innate immune responses by inducing the expression of several inflammatory genes. Thus, activation of immune cells is regulated by cytokines that use the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway and microbial recognition by TLRs. This system is tightly controlled by various endogenous molecules to allow for an appropriately regulated and safe host immune response to infections. Suppressor of cytokine signaling (SOCS) family of proteins is one of the central regulators of microbial pathogen-induced signaling of cytokines, principally through the inhibition of the activation of JAK/STAT signaling cascades. This review provides recent knowledge regarding the role of SOCS proteins during bacterial infections, with an emphasis on the mechanisms involved in their induction and regulation of antibacterial immune responses. Furthermore, the implication of SOCS proteins in diverse processes of bacteria to escape host defenses and in the outcome of bacterial infections are discussed, as well as the possibilities offered by these proteins for future targeted antimicrobial therapies.

Lipopolysaccharide (LPS)-mediated priming of toll-like receptor 4 enhances oxidant-induced prostaglandin E2 biosynthesis in primary murine macrophages

Agonists and pseudo-agonists for toll-like receptor 4 (TLR4) are common in our environment. Thus, human exposure to these agents may result in "priming or sensitization" of TLR4. A body of evidence suggests that LPS-mediated sensitization of TLR4 can increase the magnitude of responses to exogenous agents in multiple tissues. We have previously shown that reactive oxygen and nitrogen species (RONS) stimulate TLR4. There is no evidence that LPS-primed TLR4 can influence the magnitude of responses to oxidants from either endogenous or exogenous sources. In the present study, we directly tested the hypothesis that LPS-primed TLR4 will sensitize primary murine peritoneal macrophages (pM) to oxidant-mediated prostaglandin E2 (PGE₂) production. We used potassium peroxychromate (PPC) and potassium peroxynitrite (PPN) as direct in vitro sources of exogenous RONS. Our results showed that a direct treatment with PPC or PPN alone as sources of exogenous oxidants had a limited effect on PGE₂ biosynthesis. In contrast, pM sensitized by prior incubation with LPS-EK, a TLR4-specific agonist, followed by oxidant stimulation exhibited increased transcriptional and translational expression of cyclooxygenase-2 (COX-2) with enhanced PGE₂ biosynthesis/production only in pM derived from TLR4-WT mice but not in TLR4-KO mice. Thus, we have shown a critical role for LPS-primed TLR4 in oxidant-induced inflammatory phenotypes that have the potential to initiate, propagate and maintain many human diseases.

Type I Interferon Induced by Streptococcus suis Serotype 2 is Strain-Dependent and May Be Beneficial for Host Survival

Streptococcus suis serotype 2 is an important porcine bacterial pathogen and emerging zoonotic agent mainly responsible for sudden death, septic shock, and meningitis, with exacerbated inflammation being a hallmark of the infection. However, serotype 2 strains are genotypically and phenotypically heterogeneous, being composed of a multitude of sequence types (STs) whose virulence greatly varies: the virulent ST1 (Eurasia), highly virulent ST7 (responsible for the human outbreaks in China), and intermediate virulent ST25 (North America) are the most important worldwide. Even though type I interferons (IFNs) are traditionally associated with important antiviral functions, recent studies have demonstrated that they may also play an important role during infections with extracellular bacteria. Upregulation of IFN-β levels was previously observed in mice following infection with this pathogen. Consequently, the implication of IFN-β in the S. suis serotype 2 pathogenesis, which has always been considered a strict extracellular bacterium, was evaluated using strains of varying virulence. This study demonstrates that intermediate virulent strains are significantly more susceptible to phagocytosis than virulent strains. Hence, subsequent localization of these strains within the phagosome results in recognition of bacterial nucleic acids by Toll-like receptors 7 and 9, leading to activation of the interferon regulatory factors 1, 3, and 7 and production of IFN-β. Type I IFN, whose implication depends on the virulence level of the S. suis strain, is involved in host defense by participating in the modulation of systemic inflammation, which is responsible for the clearance of blood bacterial burden. As such, when induced by intermediate, and to a lesser extent, virulent S. suis strains, type I IFN plays a beneficial role in host survival. The highly virulent ST7 strain, however, hastily induces a septic shock that cannot be controlled by type I IFN, leading to rapid death of the host. A better understanding of the underlying mechanisms involved in the control of inflammation and subsequent bacterial burden could help to develop control measures for this important porcine and zoonotic agent.

The road less traveled - defining molecular commensalism with Streptococcus sanguinis

The commensal oral microbial flora has evolved with the human host to support colonization of the various intraoral sites without triggering a significant immune response. In exchange, the commensal microbes provide critical protection against invading pathogens. The intrinsic ability of the oral flora to create a symbiotic microbial community with the host can be disturbed, selecting for the overgrowth of a dysbiotic community that can result in dental diseases, such as caries and periodontitis. Although the mechanisms of molecular pathogenesis in oral diseases are well characterized, much less is known about the molecular mechanisms used by the commensal flora to maintain oral health. Here we focus on the commensal species Streptococcus sanguinis, which is found in abundance in the early oral biofilm and is strongly correlated with oral health. Streptococcus sanguinis exhibits a variety of features that make it ideally suited as a model organism to explore the molecular basis for commensalism. As such, this review will describe our current mechanistic understanding of S. sanguinis commensalism and speculate upon its molecular traits that may be exploitable to maintain or restore oral health under conditions that would otherwise lead to disease.

Lipoteichoic acids from Staphylococcus aureus stimulate proliferation of human non-small-cell lung cancer cells in vitro

Pulmonary infections are frequent complications in lung cancer and may worsen its outcome and survival. Inflammatory mediators are suspected to promote tumor growth in non-small-cell lung cancer (NSCLC). Hence, bacterial pathogens may affect lung cancer growth by activation of inflammatory signalling. Against this background, we investigated the effect of purified lipoteichoic acids (LTA) of Staphylococcus aureus (S. aureus) on cellular proliferation and liberation of interleukin (IL)-8 in the NSCLC cell lines A549 and H226. A549 as well as H226 cells constitutively expressed TLR-2 mRNA. Even in low concentrations, LTA induced a prominent increase in cellular proliferation of A549 cells as quantified by automatic cell counting. In parallel, metabolic activity of A549 cells was enhanced. The increase in proliferation was accompanied by an increase in IL-8 mRNA expression and a dose- and time-dependent release of IL-8. Cellular proliferation as well as the release of IL-8 was dependent on specific ligation of TLR-2. Interestingly, targeting IL-8 by neutralizing antibodies completely abolished the LTA-induced proliferation of A549 cells. The pro-proliferative effect of LTA could also be reproduced in the squamous NSCLC cell line H226. In summary, LTA of S. aureus induced proliferation of NSCLC cell lines of adeno- and squamous cell carcinoma origin. Ligation of TLR-2 followed by auto- or paracrine signalling by endogenously synthesized IL-8 is centrally involved in LTA-induced tumor cell proliferation. Therefore, pulmonary infections may exert a direct pro-proliferative effect on lung cancer growth.

Structure and Mechanism of Staphylococcus aureus TarS, the Wall Teichoic Acid β-glycosyltransferase Involved in Methicillin Resistance

In recent years, there has been a growing interest in teichoic acids as targets for antibiotic drug design against major clinical pathogens such as Staphylococcus aureus, reflecting the disquieting increase in antibiotic resistance and the historical success of bacterial cell wall components as drug targets. It is now becoming clear that β-O-GlcNAcylation of S. aureus wall teichoic acids plays a major role in both pathogenicity and antibiotic resistance. Here we present the first structure of S. aureus TarS, the enzyme responsible for polyribitol phosphate β-O-GlcNAcylation. Using a divide and conquer strategy, we obtained crystal structures of various TarS constructs, mapping high resolution overlapping N-terminal and C-terminal structures onto a lower resolution full-length structure that resulted in a high resolution view of the entire enzyme. Using the N-terminal structure that encapsulates the catalytic domain, we furthermore captured several snapshots of TarS, including the native structure, the UDP-GlcNAc donor complex, and the UDP product complex. These structures along with structure-guided mutants allowed us to elucidate various catalytic features and identify key active site residues and catalytic loop rearrangements that provide a valuable platform for anti-MRSA drug design. We furthermore observed for the first time the presence of a trimerization domain composed of stacked carbohydrate binding modules, commonly observed in starch active enzymes, but adapted here for a poly sugar-phosphate glycosyltransferase.

Historically, β-lactam class antibiotics such as methicillin have been very successful in the treatment of bacterial infections, effectively destroying bacteria by rupturing their cell walls while posing little harm to the human organism. In recent years, however, the alarming emergence of Methicillin Resistant S. aureus or MRSA has resulted in a world-wide health crisis, calling on new strategies to combat pathogenesis and antibiotic resistance. As such, understanding the pathways and players that orchestrate resistance is important for overcoming these mechanisms and restoring our powerful β-lactam antibiotic arsenal. In this article we describe the crystal structure of TarS, an enzyme responsible for the glycosylation of wall teichoic acid polymers of the S. aureus cell wall, a process that has been shown to be specifically responsible for methicillin resistance in MRSA. TarS is therefore a promising drug target whose inhibition in combinational therapies would result in MRSA re-sensitization to β-lactam antibiotics. Here we present the first structure of TarS together with several snap-shots of its substrate/product complexes, and elucidate important catalytic features that are valuable for rational drug design efforts to combat resistance in MRSA.

Anti-inflammatory effects of Lactobacillus brevis K65 on RAW 264.7 cells and in mice with dextran sulphate sodium-induced ulcerative colitis

Lactic acid bacteria (LAB) with anti-inflammatory effects may be beneficial to the prevention or treatment for inflammation-related diseases, such as inflammatory bowel diseases. In an in vitro assay, heat-killed Lactobacillus brevis K65 (K65) reduced lipopolysaccharide-induced production of nitric oxide, tumour necrosis factor (TNF)-α and prostaglandin E2 in RAW 264.7 cells. In RAW 264.7 cells stably expressing an ind=ucible nitric oxide synthase (iNOS) reporter, viable K65 showed greater inhibition of iNOS production than its heat-killed form. In order to further examine the in vivo anti-inflammatory effect of K65, viable K65 was orally administered to BALB/c mice before and during the period of dextran sulphate sodium (DSS)-induced ulcerative colitis (UC). K65 improved UC symptoms, including reduced the levels of the pro-inflammatory cytokines, TNF-α, interleukin (IL)-6 and IL-1β, and lowered the activity of myeloperoxidase. Furthermore, K65 inhibited TNF-α, cyclo-oxygenase 2, forkhead box P3, and Toll-like receptor 4 mRNA expression in the colonic tissue of DSS-induced UC mice. Taken together, K65, a LAB with in vitro anti-inflammatory activity showed preventive effects on mice with DSS-induced UC by lowering the expression of inflammatory molecules.

Invited review: Role of bacterial endotoxins in the etiopathogenesis of periparturient diseases of transition dairy cows

The dairy industry continues to suffer severe economic losses due to the increased disease incidence cows experience during the transition period. It has long been the classical view that the major contributing factor to the development of these periparturient diseases is the considerable increase in nutritional demands for milk production. This classical view, however, fails to account for the substantial correlation between both metabolic and infectious diseases and the detrimental effects that can occur with the provision of high-energy diets to support these nutritional demands. Currently, increasing evidence implicates bacterial endotoxins in the etiopathology of most periparturient diseases. Bacterial endotoxins are components of the outer cell wall of gram-negative and gram-positive bacteria that are highly immunostimulatory and can trigger proinflammatory immune responses. The ability of endotoxins to translocate from the mucosal tissues, including the gastrointestinal tract, mammary gland, and uterus, into the systemic circulation has been observed. Once they have entered the circulation, endotoxins potentially contribute to disease either directly, through eliciting an inflammatory response, or indirectly through other factors such as the overreaction of the natural protective mechanisms of the host. Although the evidence implicating a role of endotoxins in the pathogenesis of transition diseases continues to grow, our current knowledge of the host response to mucosal endotoxin exposure and pathogenic mechanisms remain largely unknown. Developing our understanding of the connection between endotoxemia and dairy cattle disease holds significant potential for the future development of preventative measures that could benefit the productivity of the dairy industry as well as animal welfare.

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.

Structure and mechanism of Staphylococcus aureus TarM, the wall teichoic acid α-glycosyltransferase

Unique to Gram-positive bacteria, wall teichoic acids are anionic glycopolymers cross-stitched to a thick layer of peptidoglycan. The polyol phosphate subunits of these glycopolymers are decorated with GlcNAc sugars that are involved in phage binding, genetic exchange, host antibody response, resistance, and virulence. The search for the enzymes responsible for GlcNAcylation in Staphylococcus aureus has recently identified TarM and TarS with respective α- and β-(1-4) glycosyltransferase activities. The stereochemistry of the GlcNAc attachment is important in balancing biological processes, such that the interplay of TarM and TarS is likely important for bacterial pathogenicity and survival. Here we present the crystal structure of TarM in an unusual ternary-like complex consisting of a polymeric acceptor substrate analog, UDP from a hydrolyzed donor, and an α-glyceryl-GlcNAc product formed in situ. These structures support an internal nucleophilic substitution-like mechanism, lend new mechanistic insight into the glycosylation of glycopolymers, and reveal a trimerization domain with a likely role in acceptor substrate scaffolding.

Envelope Structures of Gram-Positive Bacteria

Gram-positive organisms, including the pathogens Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecalis, have dynamic cell envelopes that mediate interactions with the environment and serve as the first line of defense against toxic molecules. Major components of the cell envelope include peptidoglycan (PG), which is a well-established target for antibiotics, teichoic acids (TAs), capsular polysaccharides (CPS), surface proteins, and phospholipids. These components can undergo modification to promote pathogenesis, decrease susceptibility to antibiotics and host immune defenses, and enhance survival in hostile environments. This chapter will cover the structure, biosynthesis, and important functions of major cell envelope components in gram-positive bacteria. Possible targets for new antimicrobials will be noted.

TLR-mediated inflammatory responses to Streptococcus pneumoniae are highly dependent on surface expression of bacterial lipoproteins

Streptococcus pneumoniae infections induce inflammatory responses that contribute toward both disease pathogenesis and immunity, but the host–pathogen interactions that mediate these effects are poorly defined. We used the surface lipoprotein-deficient ∆lgt pneumococcal mutant strain to test the hypothesis that lipoproteins are key determinants of TLR-mediated immune responses to S. pneumoniae. We show using reporter assays that TLR2 signaling is dependent on pneumococcal lipoproteins, and that macrophage NF-κB activation and TNF-α release were reduced in response to the ∆lgt strain. Differences in TNF-α responses between Δlgt and wild-type bacteria were abrogated for macrophages from TLR2- but not TLR4-deficient mice. Transcriptional profiling of human macrophages revealed attenuated TLR2-associated responses to ∆lgt S. pneumoniae, comprising many NF-κB–regulated proinflammatory cytokine and chemokine genes. Importantly, non-TLR2–associated responses were preserved. Experiments using leukocytes from IL-1R–associated kinase-4–deficient patients and a mouse pneumonia model confirmed that proinflammatory responses were lipoprotein dependent. Our data suggest that leukocyte responses to bacterial lipoproteins are required for TLR2- and IL-1R–associated kinase-4–mediated inflammatory responses to S. pneumoniae.

Listeria monocytogenes MDR transporters are involved in LTA synthesis and triggering of innate immunity during infection

Multi-drug resistance (MDR) transporters are known eponymously for their ability to confer resistance to various antimicrobial drugs. However, it is likely that this is not their primary function and that MDR transporters evolved originally to play additional roles in bacterial physiology. In Listeria monocytogenes a set of MDR transporters was identified to mediate activation of innate immune responses during mammalian cell infection. This phenotype was shown to be dependent on c-di-AMP secretion, but the physiological processes underlying this phenomenon were not completely resolved. Here we describe a genetic approach taken to screen for L. monocytogenes genes or physiological pathways involved in MDR transporter-dependent triggering of the type I interferon response. We found that disruption of L. monocytogenes lipoteichoic acid (LTA) synthesis results in enhanced triggering of type I interferon responses in infected macrophage cells yet does not impact bacterial intracellular growth. This innate immune response required the MDR transporters and could be recapitulated by exposing macrophage cells to culture supernatants derived from LTA mutant bacteria. Notably, we found that the MDR transporters themselves are required for full production of LTA, an observation that links MDR transporters to LTA synthesis for the first time. In light of our findings, we propose that the MDR transporters play a role in regulating LTA synthesis, possibly via c-di-AMP efflux, a physiological function in cell wall maintenance that triggers the host innate immune system.

Identification of IFN-γ-producing innate B cells

Although B cells play important roles in the humoral immune response and the regulation of adaptive immunity, B cell subpopulations with unique phenotypes, particularly those with non-classical immune functions, should be further investigated. By challenging mice with Listeria monocytogenes, Escherichia coli, vesicular stomatitis virus and Toll-like receptor ligands, we identified an inducible CD11a(hi)FcγRIII(hi) B cell subpopulation that is significantly expanded and produces high levels of IFN-γ during the early stage of the immune response. This subpopulation of B cells can promote macrophage activation via generating IFN-γ, thereby facilitating the innate immune response against intracellular bacterial infection. As this new subpopulation is of B cell origin and exhibits the phenotypic characteristics of B cells, we designated these cells as IFN-γ-producing innate B cells. Dendritic cells were essential for the inducible generation of these innate B cells from the follicular B cells via CD40L-CD40 ligation. Increased Bruton's tyrosine kinase activation was found to be responsible for the increased activation of non-canonical NF-κB pathway in these innate B cells after CD40 ligation, with the consequent induction of additional IFN-γ production. The identification of this new population of innate B cells may contribute to a better understanding of B cell functions in anti-infection immune responses and immune regulation.

Lipoteichoic acid from Staphylococcus aureus directly affects cardiomyocyte contractility and calcium transients

Lipoteichoic acid (LTA) is the key pathogenic factor of gram-positive bacteria and contributes significantly to organ dysfunction in sepsis, a frequent complication in critical care patients. We hypothesized that LTA directly affects cardiomyocyte function, thus contributing to cardiac failure in sepsis. This study was designed to evaluate the effects of LTA on contractile properties and calcium-transients of isolated adult rat cardiomyocytes. When myocytes were exposed to LTA for 1h prior to analysis, the amplitudes of calcium-transients as well as sarcomere shortening increased to 130% and 142% at 1 Hz stimulation frequency. Relengthening of sarcomeres as well as decay of calcium-transients was accelerated after LTA incubation. Exposure to LTA for 24 h resulted in significant depression of calcium-transients as well as of sarcomere shortening compared to controls. One of the major findings of our experiments is that LTA most likely affects calcium-handling of the cardiomyocytes. The effect is exacerbated by reduced extracellular calcium, which resembles the clinical situation in septic patients. Functionally, an early stimulating effect of LTA with increased contractility of the cardiomyocytes may be an in vitro reflection of early hyperdynamic phases in clinical sepsis. Septic disorders have been shown to induce late hypodynamic states of the contractile myocardium, which is also supported at the single-cell level in vitro by results of our 24h-exposure to LTA.

Staphylococcus aureus lipoteichoic acid inhibits platelet activation and thrombus formation via the Paf receptor

Impaired healing is common in wounds infected with the major human pathogen Staphylococcus aureus, although the underlying mechanisms are poorly understood. Here, we show that S. aureus lipoteichoic acid (LTA) inhibits platelet aggregation caused by physiological agonists and S. aureus and reduced platelet thrombus formation in vitro. The presence of D-alanine on LTA is necessary for the full inhibitory effect. Inhibition of aggregation was blocked using a monoclonal anti-platelet activating factor receptor (PafR) antibody and Ginkgolide B, a well-defined PafR antagonist, demonstrating that the LTA inhibitory signal occurs via PafR. Using a cyclic AMP (cAMP) assay and a Western blot for phosphorylated VASP, we determined that cAMP levels increase upon platelet incubation with LTA, an effect which inhibits platelet activation. This was blocked when platelets were preincubated with Ginkgolide B. Furthermore, LTA reduced hemostasis in a mouse tail-bleed assay.

Effects of helium and air inhalation on the innate and early adaptive immune system in healthy volunteers ex vivo

BACKGROUND

Helium inhalation protects myocardium, brain and endothelium against ischemia/reperfusion injury in animals and humans, when applied according to specific "conditioning" protocols. Before widespread use of this "conditioning" agent in clinical practice, negative side effects have to be ruled out. We investigated the effect of prolonged helium inhalation on the responsiveness of the human immune response in whole blood ex vivo.

METHODS

Male healthy volunteers inhaled 30 minutes heliox (79%He/21%O(2)) or air in a cross over design, with two weeks between measurements. Blood was withdrawn at T0 (baseline), T1 (25 min inhalation) and T2-T5 (1, 2, 6, 24 h after inhalation) and incubated with lipopolysaccharide (LPS), lipoteichoic acid (LTA), T-cell stimuli anti-CD3/ anti-CD28 (TCS) or RPMI (as control) for 2, 4 and 24 hours or not incubated (0 h). An additional group of six volunteers inhaled 60 minutes of heliox or air, followed by blood incubation with LPS and RPMI. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interferon-γ (IFN-γ) and interleukin-2 (IL-2) was analyzed by cytometric bead array. Statistical analysis was performed by the Wilcoxon test for matched samples.

RESULTS

Incubation with LPS, LTA or TCS significantly increased TNF-α, IL-1β, IL-6, IL-8, IFN-γ and IL-2 in comparison to incubation with RPMI alone. Thirty min of helium inhalation did not influence the amounts of TNF-α, IL-1β, IL-6, IL-8, IFN-γ and IL-2 in comparison to air. Sixty min of helium inhalation did not affect cytokine production after LPS stimulation.

CONCLUSIONS

We conclude that 79% helium inhalation does not affect the responsiveness of the human immune system in healthy volunteers.

TRIAL REGISTRATION

Dutch Trial Register: http://www.trialregister.nl/ NTR2152.

Immunomodulatory properties of subcellular fractions of a G+ bacterium, Bacillus firmus

Mucosal immunization with non-living antigens usually requires the use of an adjuvant. The adjuvant activity of Bacillus firmus in the mucosal immunization of mice was described by our laboratory previously. In the present study, subcellular localization of B. firmus activities was followed. After mechanical disintegration, subcellular components of bacterium were fractionated by differential centrifugation and salting out. Bacterial cell walls, cytoplasmic membrane fraction, soluble cytoplasmic proteins, and ribosomal fractions were isolated. Their effect on the mouse immune system was studied. Lymphocyte proliferation and immunoglobulin formation in vitro were stimulated by bacterial cell wall (BCW), cytoplasmic membrane (CMF), and ribosomal fractions. BCW and CMF increased antibody formation after intratracheal immunization of mice with influenza A and B viruses, and increased protection against subsequent infection with influenza virus. The BCW fraction even induced intersubtypic cross-protection: Mice immunized with A/California/7/04 (H3N2) + BCW were resistant to the infection by the highly pathogenic A/PR/8/34 (H1N1) virus.

Effect of lipoteichoic acid on IL-2 and IL-5 release from T lymphocytes in asthma and COPD

Susceptibility to infections with gram-positive bacteria, which are an important trigger of exacerbations, is increased in COPD and asthma. Unraveling the underlying mechanisms may help developing therapeutic strategies to reduce exacerbation rates. The aim of this study was to evaluate the effects of lipoteichoic acid (LTA), a danger signal from gram-positive bacteria, on T cell cytokines related to bacterial infection defense in COPD and asthma. T cell populations within peripheral blood mononuclear cells (PBMCs) were ex-vivo activated towards T(H)2/T(C)2 subtypes and subsequently stimulated with LTA. IL-2 and IL-5 concentrations in cell culture supernatants were measured by ELISA comparative between non-smokers (NS), current smokers without airflow limitation (S), smokers with moderate to severe COPD and mild to moderate asthmatics (A) (each n=10). IL-2 and IL-5 baseline levels were without differences between the cohorts. After T cell activation, IL-2 and IL-5 releases were increased in all cohorts, however, for IL-2 this increase was significantly higher in S and by trend in COPD compared to the other groups. LTA time-dependently suppressed IL-2 release in NS, S and COPD but not in A. LTA reduced IL-5 release in COPD and A but not in NS and S. Summarized, LTA reduces T(H)2/T(C)2 cytokines indicating immunosuppressive effects, which are dysregulated in COPD and asthma. This implies a misguided response to gram-positive bacterial infections, which might help to explain the increased susceptibility to bacterial infections in COPD and asthma.

Systematic review of membrane components of gram-positive bacteria responsible as pyrogens for inducing human monocyte/macrophage cytokine release

Fifty years after the elucidation of lipopolysaccharides (LPS, endotoxin) as the principal structure of Gram-negative bacteria activating the human immune system, its Gram-positive counterpart is still under debate. Pyrogen tests based on the human monocyte activation have been validated for LPS detection as an alternative to the rabbit test and, increasingly, the limulus amebocyte lysate test. For full replacement, international validations with non-endotoxin pyrogens are in preparation. Following evidence-based medicine approaches, a systematic review of existing evidence as to the structural nature of the Gram-positive pyrogen was undertaken. For the three major constituents suggested, i.e., peptidoglycan, lipoteichoic acids (LTA), and bacterial lipoproteins (LP), the questions to be answered and a search strategy for relevant literature was developed, starting in MedLine. The evaluation was based on the Koch–Dale criteria for a mediator of an effect. A total of 380 articles for peptidoglycan, 391 for LP, and 285 for LTA were retrieved of which 12, 8, and 24, respectively, fulfilled inclusion criteria. The compiled data suggest that for peptidoglycan two Koch–Dale criteria are fulfilled, four for LTA, and two for bacterial LP. In conclusion, based on the best currently available evidence, LTA is the only substance that fulfills all criteria. LTA has been isolated from a large number of bacteria, results in cytokine release patterns inducible also with synthetic LTA. Reduction in bacterial cytokine induction with an inhibitor for LTA was shown. However, this systematic review cannot exclude the possibility that other stimulatory compounds complement or substitute for LTA in being the counterpart to LPS in some Gram-positive bacteria.

Differences in lipopolysaccharide- and lipoteichoic acid-induced cytokine/chemokine expression

Purpose

To investigate differences in cytokine/chemokine release in response to lipoteichoic acid (LTA) or lipopolysaccharide (LPS) and contributing cellular mechanisms, in order to improve understanding of the pathogenesis of sepsis.

Methods

Levels of cytokines/chemokines were measured in plasma and peritoneal lavage fluid of 10-week-old male mice (C57/B16) following intraperitoneal injection of LTA or LPS (250 µg), and in supernatants of murine J774.2 cells, immortalised blood monocytes, or isolated human monocytes treated with LTA or LPS (0–10 µg/ml). The role of cytokine/chemokine messenger RNA (mRNA) stability versus nuclear factor-kappaB (NF-κB) and activator protein-1 (AP-1) in mediating cytokine/chemokine release in J774 cells was also assessed.

Results

In mice, plasma levels of keratinocyte-derived chemokine (KC), macrophage inflammatory protein (MIP)-2, interleukin (IL)-10, interferon (IFN)-γ and tumour necrosis factor-alpha (TNF-α) and peritoneal lavage fluid levels of KC, MIP-2 and TNF-α increased significantly 1 h after LPS. Only KC and MIP-2 levels increased 1 h after LTA. LPS-treated (10 μg/ml) J774 cells released MIP-2, IL-10, IFN-γ and TNF-α but not KC (24 h), whereas cells treated with 10 μg/ml LTA released only MIP-2. LPS-stimulated human monocytes released IL-10 and IL-8 (24 h); by contrast, LTA-treated cells released only IL-8. LPS and LTA activated NF-κB and AP-1 in J774 cells. The protein synthesis inhibitor cycloheximide abolished LPS-induced IL-10 mRNA expression and increased LTA- and LPS-induced mRNA for MIP-2 in J774 cells.

Conclusion

LTA and LPS, at clinically relevant concentrations, induced differential cytokine/chemokine release in vitro and in vivo, via effects distal to activation of NF-κB/AP-1 that might include chromatin remodelling or mRNA stability.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-011-2444-5) contains supplementary material, which is available to authorized users.

Lipoteichoic acid in Streptomyces hygroscopicus: structural model and immunomodulatory activities

Gram positive bacteria produce cell envelope macroamphiphile glycopolymers, i.e. lipoteichoic acids or lipoglycans, whose functions and biosynthesis are not yet fully understood. We report for the first time a detailed structure of lipoteichoic acid isolated from a Streptomyces species, i.e. Streptomyces hygroscopicus subsp. hygroscopicus NRRL 2387T. Chemical, MS and NMR analyses revealed a polyglycerolphosphate backbone substituted with α-glucosaminyl and α-N-acetyl-glucosaminyl residues but devoid of any amino-acid substituent. This structure is very close, if not identical, to that of the wall teichoic acid of this organism. These data not only contribute to the growing recognition that lipoteichoic acid is a cell envelope component of Gram positive Actinobacteria but also strongly support the recently proposed hypothesis of an overlap between the pathways of lipoteichoic acid and wall teichoic acid synthesis in these bacteria. S. hygroscopicus lipoteichoic acid induced signalling by human innate immune receptor TLR2, confirming its role as a microbe-associated molecular pattern. Its activity was partially dependant on TLR1, TLR6 and CD14. Moreover, it stimulated TNF-α and IL-6 production by a human macrophage cell line to an extent similar to that of Staphylococcus aureus lipoteichoic acid. These results provide new clues on lipoteichoic acid structure/function relationships, most particularly on the role of the polyglycerolphosphate backbone substituents.

Type I interferon production induced by Streptococcus pyogenes-derived nucleic acids is required for host protection

Streptococcus pyogenes is a Gram-positive human pathogen that is recognized by yet unknown pattern recognition receptors (PRRs). Engagement of these receptor molecules during infection with S. pyogenes, a largely extracellular bacterium with limited capacity for intracellular survival, causes innate immune cells to produce inflammatory mediators such as TNF, but also type I interferon (IFN). Here we show that signaling elicited by type I IFNs is required for successful defense of mice against lethal subcutaneous cellulitis caused by S. pyogenes. Type I IFN signaling was accompanied with reduced neutrophil recruitment to the site of infection. Mechanistic analysis revealed that macrophages and conventional dendritic cells (cDCs) employ different signaling pathways leading to IFN-beta production. Macrophages required IRF3, STING, TBK1 and partially MyD88, whereas in cDCs the IFN-beta production was fully dependent on IRF5 and MyD88. Furthermore, IFN-beta production by macrophages was dependent on the endosomal delivery of streptococcal DNA, while in cDCs streptococcal RNA was identified as the IFN-beta inducer. Despite a role of MyD88 in both cell types, the known IFN-inducing TLRs were individually not required for generation of the IFN-beta response. These results demonstrate that the innate immune system employs several strategies to efficiently recognize S. pyogenes, a pathogenic bacterium that succeeded in avoiding recognition by the standard arsenal of TLRs.

Streptococcus pyogenes is an important human pathogen that causes a broad range of diseases. The bacterium colonizes the throat and the skin where it can evoke usually mild illness such as strep throat or scarlet fever. Systemic infections with S. pyogenes are less frequent but can develop into life-threatening diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. The immune system launches a usually successful response that is initiated by a so far not understood recognition of this pathogen by the cells of the innate immune system. These cells produce upon infection a variety of cytokines that orchestrate a full blown protective response. Among these cytokines, type I interferons play a critical role as demonstrated by our study. We further show that IFN-beta, the key type I interferon, is produced only after macrophages and dendritic cells have taken up the pathogen and liberated the bacterial nucleic acids for recognition in the intracellular vesicles. Importantly, macrophages and dendritic cells recognize different nucleic acids and employ different signaling pathways to respond. Our data suggest that the innate immune system employs several strategies to efficiently recognize S. pyogenes, a pathogenic bacterium that succeeded in avoiding recognition by the standard recognition mechanisms.

Vigorous, but differential mononuclear cell response of cirrhotic patients to bacterial ligands

AIM: To study the role of gram-positive and gram-negative bacteria in the pathogenesis of liver injury, specifically the activation of inflammatory mediators.

METHODS: Peripheral blood mononuclear cells of 20 out-patients were studied, 10 of them with cirrhosis. Peripheral blood mononuclear cells were isolated and exposed to lipopolysaccharide or lipoteichoic acid. CD14, Toll-like receptor 2 and 4 expression was determined by flow cytometry, and tumor necrosis factor (TNF) α, interleukin (IL)-1β, IL-6, IL-12 and IL-10 secretion in supernatants was determined by ELISA.

RESULTS: Higher CD14, Toll-like receptor 2 and 4 expression was observed in peripheral blood mononuclear cells from cirrhotic patients, (P < 0.01, P < 0.006, P < 0.111) respectively. Lipopolysaccharide and lipoteichoic acid induced a further increase in CD14 expression (P < 0.111 lipopolysaccharide, P < 0.013 lipoteichoic acid), and a decrease in Toll-like receptor 2 (P < 0.008 lipopolysaccharide, P < 0.008 lipoteichoic acid) and Toll-like receptor 4 (P < 0.008 lipopolysaccharide, P < 0.028 lipoteichoic acid) expression. With the exception of TNFα, absolute cytokine secretion of peripheral blood mononuclear cells was lower in cirrhotic patients under non-exposure conditions (P < 0.070 IL-6, P < 0.009 IL-1β, P < 0.022 IL-12). Once exposed to lipopolysaccharide or lipoteichoic acid, absolute cytokine secretion of peripheral blood mononuclear cells was similar in cirrhotic and non-cirrhotic patients, determining a more vigorous response in the former (P < 0.005 TNFα, IL-1β, IL-6, IL-2 and IL-10 lipopolysaccharide; P < 0.037 TNFα; P < 0.006 IL-1β; P < 0.005 IL-6; P < 0.007 IL-12; P < 0.014 IL-10 lipoteichoic acid). Response of peripheral blood mononuclear cells was more intense after lipopolysaccharide than after lipoteichoic acid exposure.

CONCLUSION: Peripheral blood mononuclear cells of cirrhotic patients are able to respond to a sudden bacterial ligand exposure, particularly lipopolysaccharide, suggesting that immune regulation mechanisms are still present.

IFN-α-producing PDCA-1+ Siglec-H- B cells mediate innate immune defense by activating NK cells

B cells have multiple functions in adaptive immunity, including antibody production, antigen presentation and regulation of T-cell responses. Recent evidences indicate that B cells have more subsets than previously thought and may have non-classical functions, such as involvement in innate immunity and immune regulation; however, how B cells respond to microbial infection and elicit innate defense remain unclear. In this study, we identified a new subset of PDCA-1(+) Siglec-H(-) CD19(+) B cells in mice during the early period of bacterial infection with Listeria monocytogenes. PDCA-1(+) Siglec-H(-) CD19(+) B cells secreted large amounts of IFN-α and thus facilitated IFN-γ production and cytotoxicity function of natural killer (NK) cells via IFN-α. B-cell-deficient Btk(-/-) mice were incapable of producing PDCA-1(+) CD19(+) B cells, and were more sensitive to L. monocytogenes infection. Adoptive transfer of PDCA-1(+) CD19(+) B cells to Btk(-/-) mice normalized their resistance to L. monocytogenes infection. Furthermore, we found that macrophages were essential for the inducible generation of PDCA-1(+) Siglec-H(-) CD19(+) B cells via CD40-CD40L ligation. Therefore, we have identified a new subset of PDCA-1(+) Siglec-H(-) CD19(+) B cells, which enhances innate immune responses against bacterial infection by activating NK cells via secretion of IFN-α.

Lactobacilli reduce cell cytotoxicity caused by Streptococcus pyogenes by producing lactic acid that degrades the toxic component lipoteichoic acid

Lactobacilli are known to prevent colonization by many pathogens; nevertheless, the mechanisms of their protective effect are largely unknown. In this work, we investigated the role of lactobacilli during infection of epithelial cells with group A streptococci (GAS). GAS cause a variety of illnesses ranging from noninvasive disease to more severe invasive infections, such as necrotizing fasciitis and toxic shock-like syndrome. Invasion of deeper tissues is facilitated by GAS-induced apoptosis and cell death. We found that lactobacilli inhibit GAS-induced host cell cytotoxicity and shedding of the complement regulator CD46. Further, survival assays demonstrated that lactic acid secreted by lactobacilli is highly bactericidal toward GAS. In addition, lactic acid treatment of GAS, but not heat killing, prior to infection abolishes the cytotoxic effects against human cells. Since lipoteichoic acid (LTA) of GAS is heat resistant and cytotoxic, we explored the effects of lactic acid on LTA. By applying such an approach, we demonstrate that lactic acid reduces epithelial cell damage caused by GAS by degrading both secreted and cell-bound LTA. Taken together, our experiments reveal a mechanism by which lactobacilli prevent pathogen-induced host cell damage.

Growth temperature-dependent expression of structural variants of Listeria monocytogenes lipoteichoic acid

Investigating the expression of lipoteichoic acid (LTA) from Listeria monocytogenes, we found two distinct structural variants of LTA (LTA1 and LTA2) using NMR and MS technology. While both LTA consisted of a poly-glycerophosphate backbone (differing in length) bound via a disaccharide to a diacyl-glycerol moiety, one LTA type (LTA2) possessed a second diacyl-glycerol moiety linked to the disaccharide via a phosphodiester. As examined in vitro, LTA2 in contrast to LTA1 failed to activate the L-ficolin dependent pathway of complement. Most interestingly, growth temperature had a strong influence on the expression levels of LTA1 and LTA2 in the cell wall: while the amount of LTA1 was comparable, the expression of LTA2 was low when Listeria had grown at room temperature (ratio of LTA1 to LTA2 was 1:0.06), but increased when Listeria had been cultivated at 37°C (ratio of LTA1 to LTA2 was 1:0.68). The observed shift in LTA expression, probably accompanying the switch from the saprophytic to the virulent entity, indicates an important adaptation to the different structural requirements inside the host cells.

Establishment of an in vitro Peyer's patch cell culture system correlative to in vivo study using intestine and screening of lactic acid bacteria enhancing intestinal immunity

Some lactic acid bacteria (LAB) are known as representative of probiotics. To screen LAB effective to enhance intestinal immunity, in the present study, we developed an accurate and convenient in vitro evaluation system using Peyer's patch cells (PP-cells) isolated from the mice intestine. We observed that the amount of immunoglobulin A (IgA) produced by PP-cells co-cultured with LAB was well correlative to that in PP-cells, intestine and feces isolated from live mice after oral administration of LAB [correlation coefficient (r)=0.888, 0.883, and 0.920, respectively]. In addition, using this in vitro system, we suggest that the IgA level of PP-cells co-culturing with plant-derived LAB might be more enhanced than with animal-derived LAB.

Regulation of lipopolysaccharide-induced inflammatory response by heat shock protein 27 in THP-1 cells

HSP27 is a member of the small HSP family which has been linked to different signaling pathways regulating critical cellular functions. But the role of HSP27 in LPS-induced inflammatory signaling pathways is still unclear. In the present study, both overexpression and RNA interference experiments indicated that HSP27 increased LPS-induced expression of iNOS and COX-2 and release of NO/PGE2 through enhancing NF-kappaB but not MAPK activation. The effects of HSP27 on LPS-induced iNOS/COX-2 expression and relative signaling cascade were closely related with the phosphorylation of HSP27. Further studies have shown that HSP27-regulated LPS-induced activation of NF-kappaB by interacting with TRAF6 and increasing the association of TRAF6-IKKgamma. This could be a probable mechanism by which HSP27 modulates LPS-induce inflammatory signaling pathways. Thus, HSP27 may play a potential role in regulating inflammatory responses in immunologic system.

Lipoteichoic acid from Staphylococcus aureus exacerbates respiratory disease in porcine respiratory coronavirus-infected pigs

The objective of this study was to assess if lipoteichoic acid (LTA), produced by Staphylococcus aureus, exacerbates respiratory disease in porcine respiratory coronavirus (PRCV)-infected pigs, as has previously been shown with lipopolysaccharide. Piglets were inoculated with PRCV and 24 h later with S. aureus LTA. Clinical signs, lung virus titres, inflammatory cells and cytokines in bronchoalveolar lavage fluid (BALF) were compared with those of animals in PRCV- and LTA-inoculated control groups.

All PRCV–LTA-inoculated pigs except one developed severe respiratory disease, whereas clinical signs in the control groups were minimal or absent. Virus titres and grossly visible pulmonary lesions were similar in the PRCV–LTA- and PRCV-inoculated groups and were not detected in the LTA group. Neutrophil percentages in BALF were higher in the PRCV–LTA than in the PRCV group. There was no significant difference in interferon (IFN)-γ, interleukin (IL)-1, IL-6, IL-12/IL-23 and tumour necrosis factor (TNF)-α concentrations in BALF between the PRCV–LTA and PRCV groups, but levels of IL-6, IL-12/IL-23 and IFN-γ were higher in the PRCV–LTA-inoculated than in the LTA-inoculated controls.

The findings suggest that the experimentally-induced respiratory disease was not mediated by cytokine over-production, but rather reflected the concerted action of particular cytokine interactions and/or as yet unidentified mediators. This is the first in vivo study to report the synergistic interaction between a virus and LTA in enhancing the severity of respiratory disease in the pig. Given that Gram-positive bacteria, capable of producing LTA, are commonly found in pig accommodation, the role of this compound in the development of the porcine respiratory disease complex requires further investigation.

Antibody responses in patients with invasive Staphylococcus aureus infections

Correlation between antibody response and clinical outcome in Staphylococcus aureus bacteremia has yielded conflicting results. Immunization schedules have failed in clinical trials. Is the humoral response toward S. aureus of protective nature? A prospective study was performed in patients with invasive S. aureus (ISA) infections during the period 2003-2005. The antibody levels were determined at the beginning and at the end of treatment and one month later (n = 96, n = 71, and n = 51, respectively). As controls, 115 healthy individuals were used. A quantitative enzyme-linked immunosorbent assay (ELISA) against eight purified antigens was performed. Bacterial isolates were grouped as to the production of alpha-toxin, agr type, and pulsed-field gel electrophoresis (PFGE) type. Large variations were seen in the antibody levels. The levels in the second sample were the highest. A correlation between agr group, PFGE group, alpha-toxin production, and initial antibody levels was observed. Patients with fatal outcome displayed lower initial antibody levels to all antigens and significantly so in regard to teichoic acid, lipase, enterotoxin A, and scalded skin syndrome toxin. In episodes with complicated bacteremia, initial significantly low levels to teichoic acid and lipase were registered. Low initial antibody levels against several antigens were associated with increased mortality and complicated bacteremia in invasive S. aureus infections. Bacterial properties, strain, and toxin production affected the antibody response.

GanedenBC30 cell wall and metabolites: anti-inflammatory and immune modulating effects in vitro

BACKGROUND

This study was performed to evaluate anti-inflammatory and immune modulating properties of the probiotic, spore-forming bacterial strain: Bacillus coagulans: GBI-30, (PTA-6086, GanedenBC30TM). In addition, cell wall and metabolite fractions were assayed separately to address whether biological effects were due to cell wall components only, or whether secreted compounds from live bacteria had additional biological properties. The spores were heat-activated, and bacterial cultures were grown. The culture supernatant was harvested as a source of metabolites (MTB), and the bacteria were used to isolate cell wall fragments (CW). Both of these fractions were compared in a series of in vitro assays.

RESULTS

Both MTB and CW inhibited spontaneous and oxidative stress-induced ROS formation in human PMN cells and increased the phagocytic activity of PMN cells in response to bacteria-like carboxylated fluorospheres. Both fractions supported random PMN and f-MLP-directed PMN cell migration, indicating a support of immune surveillance and antibacterial defense mechanisms. In contrast, low doses of both fractions inhibited PMN cell migration towards the inflammatory mediators IL-8 and LTB4. The anti-inflammatory activity was strongest for CW, where the PMN migration towards IL-8 was inhibited down to dilutions of 1010.Both MTB and CW induced the expression of the CD69 activation marker on human CD3- CD56+ NK cells, and enhanced the expression of CD107a when exposed to K562 tumor cells in vitro.The fractions directly modulated cytokine production, inducing production of the Th2 cytokines IL-4, IL-6, and IL-10, and inhibiting production of IL-2.Both fractions further modulated mitogen-induced cytokine production in the following manner: Both fractions enhanced the PHA-induced production of IL-6 and reduced the PHA-induced production of TNF-alpha. Both fractions enhanced the PWM-induced production of TNF-alpha and IFN-gamma. In addition, MTB also enhanced both the PHA- and the PWM-induced expression of IL-10.

CONCLUSION

The data suggest that consumption of GanedenBC30TM may introduce both cell wall components and metabolites that modulate inflammatory processes in the gut. Both the cell wall and the supernatant possess strong immune modulating properties in vitro. The anti-inflammatory effects, combined with direct induction of IL-10, are of interest with respect to possible treatment of inflammatory bowel diseases as well as in support of a healthy immune system.

Moscatilin repressed lipopolysaccharide-induced HIF-1alpha accumulation and NF-kappaB activation in murine RAW264.7 cells

In the present study, we investigated the signaling pathways involved in the inhibition of cyclooxygenase 2 (COX-2) and iNOS by moscatilin under LPS challenge in murine macrophage-derived cell line RAW264.7. The results showed that moscatilin (10-100 microM) had a significant inhibition in a concentration-dependent manner on proinflammatory enzymes (COX-2 and iNOS) expression and macrophage activation under LPS (100 ng/mL) treatment. Hypoxia-inducible factor 1 (HIF-1)alpha was reported to initiate inflammation under cytokine stimulation or hypoxic conditions. In addition, the increase in transcriptional activity and translation process of HIF-1alpha under LPS stimulation resulted in HIF-1alpha accumulation. Moscatilin, a purified compound from Chinese herbs, had a dominant repression on HIF-1alpha expression via down regulating HIF-1alpha mRNA without inhibition of cell viability, translation machinery, or proteasome-mediated degradation of HIF-1alpha. Moreover, the results showed that moscatilin suppressed nuclear translocation of nuclear factor (NF)-kappaB subunits, p65 and p50, and NF-kappaB activity by inhibiting phosphorylation of inhibitor of kappaBalpha. Taken together, we demonstrated that moscatilin inhibited both COX-2 and iNOS expressions after LPS treatment in RAW264.7. Furthermore, the inhibition of moscatilin seemed to be dependent on the repression of HIF-1alpha accumulation and NF-kappaB activation.

Lipoteichoic acid enhances IL-6 production in human synovial fibroblasts via TLR2 receptor, PKCdelta and c-Src dependent pathways

Patients with rheumatoid arthritis (RA) are at increased risk of developing infections and appear to be particularly susceptible to septic arthritis. Lipoteichoic acid (LTA), a cell wall component of Gram-positive bacteria is an amphiphilic, negatively charged glycolipid. However, the effects of LTA on human synovial fibroblasts are largely unknown. We investigated the signaling pathway involved in IL-6 production stimulated by LTA in rheumatoid arthritis synovial fibroblasts (RASF). LTA caused concentration- and time-dependent increases in IL-6 production. LTA-mediated IL-6 production was attenuated by Toll-like receptor 2 (TLR2) monoclonal antibody or siRNA. Pretreatment with PKCdelta inhibitor (rottlerin), c-Src inhibitor (PP2), AP-1 inhibitor (tanshinone IIA) and NF-kappaB inhibitor (PDTC and TPCK) also inhibited the potentiating action of LTA. However, focal adhesion kinase (FAK) mutant and siRNA did not affect LTA-mediated IL-6 production. Stimulation of cells with LTA increased the PKCdelta and c-Src phosphorylation and kinase activity. LTA increased the accumulation of p-c-Jun and p-p65 in the nucleus, as well as AP-1 and NF-kappaB luciferase activity. LTA-mediated increase of AP-1 and NF-kappaB luciferase activity was inhibited by rottlerin and PP2 or TLR2 and PKCdelta siRNA or c-Src mutant. Our results suggest that LTA-increased IL-6 production in human synovial fibroblasts via the TLR2 receptor, PKCdelta, c-Src, AP-1 and NF-kappaB signaling pathways.