Cellular reprogramming by gram-positive bacterial components: a review

Innate and germline immune memory: specificity and heritability of the ancient immune mechanisms for adaptation and survival

The immune memory is one of the defensive strategies developed by both unicellular and multicellular organisms for ensuring their integrity and functionality. While the immune memory of the vertebrate adaptive immune system (based on somatic recombination) is antigen-specific, encompassing the generation of memory T and B cells that only recognize/react to a specific antigen epitope, the capacity of vertebrate innate cells to remember past events is a mostly non-specific mechanism of adaptation. This "innate memory" can be considered as germline-encoded because its effector tools (such as innate receptors) do not need somatic recombination for being active. Also, in several organisms the memory-related information is integrated in the genome of germline cells and can be transmitted to the progeny for several generations, but it can also be erased depending on the environmental conditions. Overall, depending on the organism, its environment and its living habits, innate immune memory appears to be a mechanism for achieving better protection and survival against repeated exposure to microbes/stressful agents present in the same environment or occurring in the same anatomical district, able to adapt to changes in the environmental cues. The anatomical and functional complexity of the organism and its lifespan drive the generation of different immune memory mechanisms, for optimal adaptation to changes in the living/environmental conditions. The concept of innate immunity being non-specific needs to be revisited, as a wealth of evidence suggests a significant degree of specificity both in the primary immune reaction and in the ensuing memory-like responses. This is clearly evident in invertebrate metazoans, in which distinct scenarios can be observed, with both non-specific (immune enhancement) or specific (immune priming) memory-like responses. In the case of mammals, there is evidence that some degree of specificity can be attained in different situations, for instance as organ-specific protection rather than microorganism-specific reaction. Thus, depending on the challenges and conditions, innate memory can be non-specific or specific, can be integrated in the germline and transmitted to the progeny or be short-lived, thereby representing an exceptionally plastic mechanism of defensive adaptation for ensuring individual and species survival.

Studies of the Impact of the Bifidobacterium Species on Inducible Nitric Oxide Synthase Expression and Nitric Oxide Production in Murine Macrophages of the BMDM Cell Line

Bifidobacterium species are one of the most important probiotic microorganisms which are present in both, infants and adults. Nowadays, growing data describing their healthy properties arise, indicating they could act at the cellular and molecular level. However, still little is known about the specific mechanisms promoting their beneficial effects. Nitric oxide (NO), produced by inducible nitric oxide synthase (iNOS), is involved in the protective mechanisms in the gastrointestinal tract, where it can be provided by epithelial cells, macrophages, or bacteria. The present study explored whether induction of iNOS-dependent NO synthesis in macrophages stems from the cellular action of Bifidobacterium species. The ability of ten Bifidobacterium strains belonging to 3 different species (Bifidobacterium longum, Bifidobacterium adolescentis, and Bifidobacterium animalis) to activate MAP kinases, NF-κB factor, and iNOS expression in a murine bone-marrow-derived macrophages cell line was determined by Western blotting. Changes in NO production were determined by the Griess reaction. It was performed that the Bifidobacterium strains were able to induce NF-қB-dependent iNOS expression and NO production; however, the efficacy depends on the strain. The highest stimulatory activity was observed for Bifidobacterium animalis subsp. animals CCDM 366, whereas the lowest was noted for strains Bifidobacterium adolescentis CCDM 371 and Bifidobacterium longum subsp. longum CCDM 372. Both TLR2 and TLR4 receptors are involved in Bifidobacterium-induced macrophage activation and NO production. We showed that the impact of Bifidobacterium on the regulation of iNOS expression is determined by MAPK kinase activity. Using pharmaceutical inhibitors of ERK 1/2 and JNK, we confirmed that Bifidobacterium strains can activate these kinases to control iNOS mRNA expression. Concluding, the induction of iNOS and NO production may be involved in the protective mechanism of action observed for Bifidobacterium in the intestine, and the efficacy is strain-dependent.

Variability of the innate immune response is globally constrained by transcriptional bursting

Transcription of almost all mammalian genes occurs in stochastic bursts, however the fundamental control mechanisms that allow appropriate single-cell responses remain unresolved. Here we utilise single cell genomics data and stochastic models of transcription to perform global analysis of the toll-like receptor (TLR)-induced gene expression variability. Based on analysis of more than 2000 TLR-response genes across multiple experimental conditions we demonstrate that the single-cell, gene-by-gene expression variability can be empirically described by a linear function of the population mean. We show that response heterogeneity of individual genes can be characterised by the slope of the mean-variance line, which captures how cells respond to stimulus and provides insight into evolutionary differences between species. We further demonstrate that linear relationships theoretically determine the underlying transcriptional bursting kinetics, revealing different regulatory modes of TLR response heterogeneity. Stochastic modelling of temporal scRNA-seq count distributions demonstrates that increased response variability is associated with larger and more frequent transcriptional bursts, which emerge via increased complexity of transcriptional regulatory networks between genes and different species. Overall, we provide a methodology relying on inference of empirical mean-variance relationships from single cell data and new insights into control of innate immune response variability.

Staphylococcus aureus induces tolerance in human monocytes accompanied with expression changes of cell surface markers

Exposure of human monocytes to lipopolysaccharide (LPS) or other pathogen-associated molecular pattern (PAMPs) induces a temporary insensitivity to subsequent LPS challenges, a cellular state called endotoxin tolerance (ET), associated with the pathogenesis of sepsis. In this study, we aimed to characterize the cellular state of human monocytes from healthy donors stimulated with Staphylococcus aureus in comparison to TLR2-specific ligands. We analyzed S. aureus induced gene expression changes after 2 and 24 hours by amplicon sequencing (RNA-AmpliSeq) and compared the pro-inflammatory response after 2 hours with the response in re-stimulation experiments. In parallel, glycoprotein expression changes in human monocytes after 24 hours of S. aureus stimulation were analyzed by proteomics and compared to stimulation experiments with TLR2 ligands Malp-2 and Pam3Cys and TLR4 ligand LPS. Finally, we analyzed peripheral blood monocytes of patients with S. aureus bloodstream infection for their ex vivo inflammatory responses towards S. aureus stimulation and their glycoprotein expression profiles. Our results demonstrate that monocytes from healthy donors stimulated with S. aureus and TLR ligands of Gram-positive bacteria entered the tolerant cell state after activation similar to LPS treatment. In particular reduced gene expression of pro-inflammatory cytokines (TNF, IL1β) and chemokines (CCL20, CCL3, CCL4, CXCL2, CXCL3 and CXCL8) could be demonstrated. Glycoprotein expression changes in monocytes tolerized by the different TLR agonists were highly similar while S. aureus-stimulated monocytes shared some of the PAMP-induced changes but also exhibited a distinct expression profile. 11 glycoproteins (CD44, CD274, DSC2, ICAM1, LAMP3, LILRB1, PTGS2, SLC1A3, CR1, FGL2, and HP) were similarly up- or downregulated in all four comparisons in the tolerant cell state. Monocytes from patients with S. aureus bacteremia revealed preserved pro-inflammatory responsiveness to S. aureus stimulation ex vivo, expressed increased CD44 mRNA but no other glycoprotein of the tolerance signature was differentially expressed.

Induction of Innate Memory in Human Monocytes Exposed to Mixtures of Bacterial Agents and Nanoparticles

We assessed whether concomitant exposure of human monocytes to bacterial agents and different engineered nanoparticles can affect the induction of protective innate memory, an immune mechanism that affords better resistance to diverse threatening challenges. Monocytes were exposed in vitro to nanoparticles of different chemical nature, shape and size either alone or admixed with LPS, and cell activation was assessed in terms of production of inflammatory (TNFα, IL-6) and anti-inflammatory cytokines (IL-10, IL-1Ra). After return to baseline conditions, cells were re-challenged with LPS and their secondary "memory" response measured. Results show that nanoparticles alone are essentially unable to generate memory, while LPS induced a tolerance memory response (less inflammatory cytokines, equal or increased anti-inflammatory cytokines). LPS-induced tolerance was not significantly affected by the presence of nanoparticles during the memory generation phase, although with substantial donor-to-donor variability. This suggests that, despite the overall lack of significant effects on LPS-induced innate memory, nanoparticles may have donor-specific effects. Thus, future nanosafety assessment and nanotherapeutic strategies will need a personalized approach in order to ensure both the safety and efficacy of nano medical compounds for individual patients.

Post-transcriptional regulatory feedback encodes JAK-STAT signal memory of interferon stimulation

Immune cells fine tune their responses to infection and inflammatory cues. Here, using live-cell confocal microscopy and mathematical modelling, we investigate interferon-induced JAK-STAT signalling in innate immune macrophages. We demonstrate that transient exposure to IFN-γ stimulation induces a long-term desensitisation of STAT1 signalling and gene expression responses, revealing a dose- and time-dependent regulatory feedback that controls JAK-STAT responses upon re-exposure to stimulus. We show that IFN-α/β1 elicit different level of desensitisation from IFN-γ, where cells refractory to IFN-α/β1 are sensitive to IFN-γ, but not vice versa. We experimentally demonstrate that the underlying feedback mechanism involves regulation of STAT1 phosphorylation but is independent of new mRNA synthesis and cognate receptor expression. A new feedback model of the protein tyrosine phosphatase activity recapitulates experimental data and demonstrates JAK-STAT network’s ability to decode relative changes of dose, timing, and type of temporal interferon stimulation. These findings reveal that STAT desensitisation renders cells with signalling memory of type I and II interferon stimulation, which in the future may improve administration of interferon therapy.

Induction of Trained Immunity Protects Neonatal Mice Against Microbial Sepsis by Boosting Both the Inflammatory Response and Antimicrobial Activity

Background

Neonates are susceptible to a wide range of microbial infection and at a high risk to develop severe sepsis and septic shock. Emerged evidence has shown that induction of trained immunity triggers a much stronger inflammatory response in adult monocytes/macrophages, thereby conferring protection against microbial infection.

Methods

This study was carried out to examine whether trained immunity is inducible and exerts its protection against microbial sepsis in neonates.

Results

Induction of trained immunity by Bacillus Calmette-Guerin (BCG) plus bacterial lipoprotein (BLP) protected neonatal mice against cecal slurry peritonitis-induced polymicrobial sepsis, and this protection is associated with elevated circulating inflammatory cytokines, increased neutrophil recruitment, and accelerated bacterial clearance. In vitro stimulation of neonatal murine macrophages with BCG+BLP augmented both inflammatory response and antimicrobial activity. Notably, BCG+BLP stimulation resulted in epigenetic remodeling characterized by histone modifications with enhanced H3K4me3, H3K27Ac, and suppressed H3K9me3 at the promoters of the targeted inflammatory and antimicrobial genes. Critically, BCG+BLP stimulation led to a shift in cellular metabolism with increased glycolysis, which is the prerequisite for subsequent BCG+BLP-triggered epigenetic reprogramming and augmented inflammatory response and antimicrobial capacity.

Conclusion

These results illustrate that BCG+BLP induces trained immunity in neonates, thereby protecting against microbial infection by boosting both inflammatory and antimicrobial responses.

Functional Transcriptomic Studies of Immune Responses and Endotoxin Tolerance in Early Human Sepsis

BACKGROUND

Limited studies have functionally evaluated the heterogeneity in early ex vivo immune responses during sepsis. Our aim was to characterize early sepsis ex vivo functional immune response heterogeneity by studying whole blood endotoxin responses and derive a transcriptional metric of ex vivo endotoxin response.

METHODS

Blood collected within 24 h of hospital presentation from 40 septic patients was divided into two fractions and incubated with media (unstimulated) or endotoxin. Supernatants and cells were isolated, and responses measured using: supernatant cytokines, lung endothelial permeability after supernatant exposure, and RNA expression. A transcriptomic signature was derived in unstimulated cells to predict the ex vivo endotoxin response. The signature was tested in a separate cohort of 191 septic patients to evaluate for association with clinical outcome. Plasma biomarkers were quantified to measure in vivo host inflammation.

RESULTS

Ex vivo response to endotoxin varied and was unrelated to immunosuppression, white blood cell count, or the causative pathogen. Thirty-five percent of patients demonstrated a minimal response to endotoxin, suggesting early immunosuppression. High ex vivo cytokine production by stimulated blood cells correlated with increased in vitro pulmonary endothelial cell permeability and was associated with attenuated in vivo host inflammation. A four-gene signature of endotoxin response detectable without the need for a functional assay was identified. When tested in a separate cohort of septic patients, its expression was inversely associated with hospital mortality.

CONCLUSIONS

An attenuated ex vivo endotoxin response in early sepsis is associated with greater host in vivo inflammation and a worse clinical outcome.

Investigation of innate immune function in adult and geriatric horses

In order to better understand the influence of age on innate immune function in horses, blood was collected from twelve adult horses (aged 10-16 years; mean: 13 years) and ten geriatric horses (aged 18-26 years; mean: 21.7 years) for analysis of plasma myeloperoxidase, complete blood counts, and cytokine and receptor expression in response to in vitro stimulation with heat-inactivated Rhodococcus equi, heat-inactivated Escherichia coli, and PMA/ionomycin. Gene expression was measured using RT-PCR for IFNγ, IL-1β, IL-6, IL-8, IL-10, IL-12α, IL-13, IL-17α, TLR2, TLR4, and TNFα. Endocrine function and body weight were measured to assess any potential impacts of ACTH, insulin, or body weight on immune function; none of the horses had pituitary pars intermedia dysfunction. The geriatric horse group had lower concentrations of plasma myeloperoxidase (P = 0.0459) and lower absolute monocyte counts (P = 0.0477); however, the difference in monocyte counts was no longer significant after outliers were removed. Additionally, only two significant differences in cytokine/receptor expression in whole blood were observed. Compared with adult horses, the geriatric horses had increased TNFα expression after in vitro stimulation with heat-inactivated R. equi (P = 0.0224) and had decreased IL-17α expression after PMA/ionomycin stimulation when one outlier was excluded (P = 0.0334). These changes may represent a compensatory mechanism by which geriatric horses could ensure adequate immune responses despite potentially dysfunctional neutrophil activity and/or decreased monocyte counts. Aging may influence equine innate immune function, and additional research is warranted to confirm and further explore these findings.

An Early Neutrophil Recruitment into the Infectious Site Is Critical for Bacterial Lipoprotein Tolerance-Afforded Protection against Microbial Sepsis

Bacterial lipoprotein (BLP)-induced tolerance represents an essential regulatory mechanism during bacterial infection and has been shown to protect against microbial sepsis. This protection is generally attributed to BLP-tolerized monocytes/macrophages characterized by hyporesponsiveness in producing inflammatory cytokines and, simultaneously, an augmented antimicrobial activity. However, the contribution of polymorphonuclear neutrophils (PMNs), another major player in innate immunity against bacterial infection, to BLP tolerance-afforded protection against microbial sepsis has not been identified. In this study, we report that induction of BLP tolerance protected mice against cecal ligation and puncture-induced polymicrobial sepsis, with significantly improved survival. Importantly, BLP tolerization via i.p. injection triggered an early PMN recruitment even before bacterial infection and promoted further PMN influx into the infectious site (i.e., the peritoneal cavity upon cecal ligation and puncture-associated septic challenge). Notably, this early PMN influx was mediated by BLP tolerization-induced PMN chemoattractant CXCL2-formed concentration gradient between the circulation and peritoneal cavity. Critically, blockage of PMN influx with the CXCR2 antagonist SB225002 abolished BLP tolerance-afforded protection and rendered BLP-tolerized mice more vulnerable to microbial infection with impaired bacterial clearance and increased overall mortality. Thus, our results highlight that an early recruitment of PMNs in the infectious site, as an important cellular mechanism, contributes to BLP tolerance-afforded protection against microbial sepsis.

Anti-Inflammatory Mechanisms of Koreanaside A, a Lignan Isolated from the Flower of Forsythia koreana, against LPS-Induced Macrophage Activation and DSS-Induced Colitis Mice: The Crucial Role of AP-1, NF-κB, and JAK/STAT Signaling

The current treatment options for inflammatory bowel disease (IBD) are unsatisfactory. Therefore, novel and safer therapies are needed. We previously reported that koreanaside A (KA) showed high radical scavenging activity and suppressed vascular cell adhesion molecule 1 (VCAM-1) expression in vascular smooth muscle cells. However, the molecular mechanisms involved in its anti-inflammatory effect have not been reported. KA inhibited pro-inflammatory mediators such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), nitric oxide (NO), and prostaglandin E₂ (PGE₂). KA inhibited the production and mRNA expression of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) induced by LPS. KA downregulated the myeloid differentiation primary response 88 (MyD88)-dependent inflammatory gene expressions in the MyD88-overexpressed cells. KA suppressed the LPS-induced transcriptional and DNA-binding activities of activator protein-1 (AP-1) and nuclear factor-kappa B (NF-κB). KA was found to inhibit the phosphorylation of Janus kinase 1/2 (JAK1/2) and signal transducers and activators of transcription 1/3 (STAT1/3). In DSS-induced colitis mice, KA relieved the symptoms of colitis by suppressing inflammatory cell infiltration, restoring tight junction (TJ)- and epithelial–mesenchymal transition (EMT)-related protein expression, and inactivating AP-1, NF-κB, and STAT1/3. Therefore, KA reduced inflammatory responses by downregulating AP-1, NF-κB, and JAK/STAT signaling in LPS-induced macrophages and DSS-induced colitis mice.

Oral administration of lipoteichoic acid from Lactobacillus rhamnosus GG overcomes UVB-induced immunosuppression and impairs skin tumor growth in mice

There is increasing evidence of the relevant connection and regulation between the gut and skin immune axis. In fact, oral administration of lipoteichoic acid (LTA) from Lactobacillus rhamnosus GG (LGG) prevents the development of UV-induced skin tumors in chronically exposed mice. Here we aim to evaluate whether this LTA is able to revert UV-induced immunosuppression as a mechanism involved in its anti-tumor effect and whether it has an immunotherapeutic effect against cutaneous squamous cell carcinoma. Using a mouse model of contact hypersensitivity, we demonstrate that LTA overcomes UV-induced skin immunosuppression. This effect was in part achieved by modulating the phenotype of lymph node resident dendritic cells (DC) and the homing of skin migratory DC. Importantly, oral LTA reduced significantly the growth of established skin tumors once UV radiation was discontinued, demonstrating that it has a therapeutic, besides the already demonstrated preventive antitumor effect. The data presented here strongly indicates that oral administration of LTA represents a promising immunotherapeutic approach for different conditions in which the skin immune system is compromised.

Staphylococcal LTA antagonizes the B cell-mitogenic potential of LPS

Lipoteichoic acid (LTA) of Gram-positive bacteria is regarded as the counterpart biomolecule of lipopolysaccharide (LPS) of Gram-negative bacteria because of their structural and immunological similarities. Although LPS induces a strong polyclonal expansion of B cells, little is known about the effect of LTA on B cell proliferation. In the present study, we prepared LTAs from Gram-positive bacteria and examined their effect on splenic B cell proliferation. Unlike LPS, LTA did not induce B cell proliferation. Instead, Staphylococcus aureus LTA (Sa.LTA) appeared to inhibit LPS-induced B cell proliferation in vitro, ex vivo, and in vivo models. Such effect was observed neither in splenocytes from Toll-like receptor 2 (TLR2)-deficient mice nor in the purified splenic B cells. Furthermore, decreased ERK phosphorylation appeared to be responsible for this phenomenon. Collectively, our results support that Sa.LTA inhibited LPS-induced B cell proliferation through the decrease of ERK phosphorylation via TLR2 signaling pathway.

Direct effects of fermented cow's milk product with Lactobacillus paracasei CBA L74 on human enterocytes

Cow's milk fermented with Lactobacillus paracasei CBA L74 (FM-CBAL74) exerts a preventive effect against infectious diseases in children. We evaluated if this effect is at least in part related to a direct modulation of non-immune and immune defence mechanisms in human enterocytes. Human enterocytes (Caco-2) were stimulated for 48 h with FM-CBAL74 at different concentrations. Cell growth was assessed by colorimetric assay; cell differentiation (assessed by lactase expression), tight junction proteins (zonula occludens1 and occludin), mucin 2, and toll-like receptor (TRL) pathways were analysed by real-time PCR; innate immunity peptide synthesis, beta-defensin-2 (HBD-2) and cathelicidin (LL-37) were evaluated by ELISA. Mucus layer thickness was analysed by histochemistry. FMCBA L74 stimulated cell growth and differentiation, tight junction proteins and mucin 2 expression, and mucus layer thickness in a dose-dependent fashion. A significant stimulation of HBD-2 and LL-37 synthesis, associated with a modulation of TLR pathway, was also observed. FM-CBAL74 regulates non-immune and immune defence mechanisms through a direct interaction with the enterocytes. These effects could be involved in the preventive action against infectious diseases demonstrated by this fermented product in children.

KATP channel block inhibits the Toll-like receptor 2-mediated stimulation of NF-κB by suppressing the activation of Akt, mTOR, JNK and p38-MAPK

Changes in the K_ATP channel activity have been shown to regulate inflammation and immune responses. Using human keratinocytes, we investigated the effect of K_ATP channel inhibition on inflammatory mediator production in relation to the Toll like receptor-2-mediated-Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK, which regulate the transcription genes involved in immune and inflammatory responses. 5-Hydroxydecanoate (a selective K_ATP channel blocker), glibenclamide (a cell surface and mitochondrial K_ATP channel inhibitor), the Akt inhibitor, rapamycin, Bay 11-7085 and N-acetylcysteine reduced the lipoteichoic acid- or peptidoglycan-induced production of cytokines and chemokines, and production of reactive oxygen species and increased the levels and activities of Kir 6.2, NF-κB, phosphorylated-Akt and mTOR, and the activation of JNK and p38-MAPK in keratinocytes. Inhibitors of c-JNK (SP600125) and p38-MAPK (SB203580) attenuated the lipoteichoic acid- or peptidoglycan-induced production of inflammatory mediators, the activation of the JNK and p38-MAPK, and the production of reactive oxygen species in keratinocytes. The results show that K_ATP channel blockers may reduce the bacterial component-stimulated production of inflammatory mediators in keratinocytes by suppressing the Toll-like receptor-2-mediated activation of the Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK. The suppressive effect of K_ATP channel blockers appears to be achieved by the inhibition of reactive oxygen species production.

Immunostimulatory Activity of Opuntia ficus-indica var. Saboten Cladodes Fermented by Lactobacillus plantarum and Bacillus subtilis in RAW 264.7 Macrophages

To increase the functionality of Opuntia ficus-indica var. saboten cladodes, it was fermented by Lactobacillus plantarum and Bacillus subtilis. Eighty percent methanol extracts were investigated for their effects on nitric oxide (NO) production, cytokine secretion, nuclear factor-κB (NF-κB) activity, and mitogen-activated protein kinase (MAPK) phosphorylation in RAW 264.7 cells. Methanol extracts of L. plantarum culture medium (LPCME) and B. subtilis culture medium (BSCME) did not affect lipopolysaccharide (LPS)-induced NO production but, at 500 μg/mL, increased interferon (IFN)-γ-induced NO production by 55.2 and 66.5 μM, respectively, in RAW 264.7 cells. In RAW 264.7 cells not treated with LPS and IFN-γ, LPCME did not affect NO production, but BSCME increased NO production significantly in a dose-dependent manner. In addition, BSCME induced the expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in RAW 264.7 cells in a dose-dependent manner. BSCME at 500 μg/mL increased TNF-α and IL-1β mRNA levels by 83.8% and 82.2%, respectively. BSCME increased NF-κB-dependent luciferase activity in a dose-dependent manner; 500 μg/mL BSCME increased activity 9.1-fold compared with the control. BSCME induced the phosphorylation of p38, c-JUN NH₂-terminal protein kinase (JNK), and extracellular signal-regulated kinase (ERK) in a dose-dependent manner, but did not affect total ERK levels. In conclusion, BSCME exerted immunostimulatory effects, which were mediated by MAPK phosphorylation and NF-κB activation, resulting in increased TNF-α and IL-1β gene expression in RAW 264.7 macrophages. Therefore, BSCM shows promise for use as an immunostimulatory therapeutic.

NF-κB activation is critical for bacterial lipoprotein tolerance-enhanced bactericidal activity in macrophages during microbial infection

Tolerance to bacterial components represents an essential regulatory mechanism during bacterial infection. Bacterial lipoprotein (BLP)-induced tolerance confers protection against microbial sepsis by attenuating inflammatory responses and augmenting antimicrobial activity in innate phagocytes. It has been well-documented that BLP tolerance-attenuated proinflammatory cytokine production is associated with suppressed TLR2 signalling pathway; however, the underlying mechanism(s) involved in BLP tolerance-enhanced antimicrobial activity is unclear. Here we report that BLP-tolerised macrophages exhibited accelerated phagosome maturation and enhanced bactericidal activity upon bacterial infection, with upregulated expression of membrane-trafficking regulators and lysosomal enzymes. Notably, bacterial challenge resulted in a strong activation of NF-κB pathway in BLP-tolerised macrophages. Importantly, activation of NF-κB pathway is critical for BLP tolerance-enhanced antimicrobial activity, as deactivation of NF-κB in BLP-tolerised macrophages impaired phagosome maturation and intracellular killing of the ingested bacteria. Finally, activation of NF-κB pathway in BLP-tolerised macrophages was dependent on NOD1 and NOD2 signalling, as knocking-down NOD1 and NOD2 substantially inhibited bacteria-induced activation of NF-κB and overexpression of Rab10 and Acp5, two membrane-trafficking regulators and lysosomal enzymes contributed to BLP tolerance-enhanced bactericidal activity. These results indicate that activation of NF-κB pathway is essential for BLP tolerance-augmented antimicrobial activity in innate phagocytes and depends primarily on both NOD1 and NOD2.

Extremes of Interferon-Stimulated Gene Expression Associate with Worse Outcomes in the Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome (ARDS) severity may be influenced by heterogeneity of neutrophil activation. Interferon-stimulated genes (ISG) are a broad gene family induced by Type I interferons, often as a response to viral infections, which evokes extensive immunomodulation. We tested the hypothesis that over- or under-expression of immunomodulatory ISG by neutrophils is associated with worse clinical outcomes in patients with ARDS. Genome-wide transcriptional profiles of circulating neutrophils isolated from patients with sepsis-induced ARDS (n = 31) and healthy controls (n = 19) were used to characterize ISG expression. Hierarchical clustering of expression identified 3 distinct subject groups with Low, Mid and High ISG expression. ISG accounting for the greatest variability in expression were identified (MX1, IFIT1, and ISG15) and used to analyze a prospective cohort at the Colorado ARDS Network site. One hundred twenty ARDS patients from four urban hospitals were enrolled within 72 hours of initiation of mechanical ventilation. Circulating neutrophils were isolated from patients and expression of ISG determined by PCR. Samples were stratified by standard deviation from the mean into High (n = 21), Mid, (n = 82) or Low (n = 17) ISG expression. Clinical outcomes were compared between patients with High or Low ISG expression to those with Mid-range expression. At enrollment, there were no differences in age, gender, co-existing medical conditions, or type of physiologic injury between cohorts. After adjusting for age, race, gender and BMI, patients with either High or Low ISG expression had significantly worse clinical outcomes than those in the Mid for number of 28-day ventilator- and ICU-free days (P = 0.0006 and 0.0004), as well as 90-day mortality and 90-day home with unassisted breathing (P = 0.02 and 0.004). These findings suggest extremes of ISG expression by circulating neutrophils from ARDS patients recovered early in the syndrome are associated with poorer clinical outcomes.

Receptor for the F4 fimbriae of enterotoxigenic Escherichia coli (ETEC)

Infection with F4(+) enterotoxigenic Escherichia coli (ETEC) responsible for diarrhea in neonatal and post-weaned piglets leads to great economic losses in the swine industry. These pathogenic bacteria express either of three fimbrial variants F4ab, F4ac, and F4ad, which have long been known for their importance in host infection and initiating protective immune responses. The initial step in infection for the bacterium is to adhere to host enterocytes through fimbriae-mediated recognition of receptors on the host cell surface. A number of receptors for ETEC F4 have now been described and characterized, but their functions are still poorly understood. The current review summarizes the latest research addressing the characteristics of F4 fimbriae receptors and the interactions of F4 fimbriae and their receptors on host cells. These include observations that as follows: (1) FaeG mediates the binding activities of F4 and is an essential component of the F4 fimbriae, (2) the F4 fimbrial receptor gene is located in a region of chromosome 13, (3) the biochemical properties of F4 fimbrial receptors that form the binding site of the bacterium are now recognized, and (4) specific receptors confer susceptibility/resistance to ETEC F4 infection in pigs. Characterizing the host-pathogen interaction will be crucial to understand the pathogenicity of the bacteria, provide insights into receptor activation of the innate immune system, and develop therapeutic strategies to prevent this illness.

HMGB1 Binds to Lipoteichoic Acid and Enhances TNF-α and IL-6 Production through HMGB1-Mediated Transfer of Lipoteichoic Acid to CD14 and TLR2

Lipoteichoic acid (LTA) is a component of the cell wall of Gram-positive bacteria and induces a toll-like receptor 2 (TLR2)-mediated inflammatory response upon initial binding to lipopolysaccharide-binding protein (LBP) and subsequent transfer to CD14. In this study, we identified a novel role for the nuclear protein high-mobility group box 1 (HMGB1) in LTA-mediated inflammation. Results of ELISA, surface plasmon resonance and native PAGE electrophoretic mobility shift analyses indicated that HMGB1 binds to LTA in a concentration-dependent manner and that this binding is inhibited by LBP. Native PAGE, fluorescence-based transfer and confocal imaging analyses indicated that HMGB1 catalytically disaggregates LTA and transfers LTA to CD14. NF-κB p65 nuclear transmigration, degradation of IκBα and reporter assay results demonstrated that NF-κB activity in HEK293-hTLR2/6 cells is significantly upregulated by a mixture of LTA and soluble CD14 in the presence of HMGB1. Furthermore, the production of TNF-α and IL-6 in J774A.1 and RAW264.7 cells increased significantly following treatment with a mixture of LTA and HMGB1 compared with treatment with LTA or HMGB1 alone. Thus, we propose that HMGB1 plays an important role in LTA-mediated inflammation by binding to and transferring LTA to CD14, which is subsequently transferred to TLR2 to induce an inflammatory response.

An Endotoxin Tolerance Signature Predicts Sepsis and Organ Dysfunction at Initial Clinical Presentation

Background

Sepsis involves aberrant immune responses to infection, but the exact nature of this immune dysfunction remains poorly defined. Bacterial endotoxins like lipopolysaccharide (LPS) are potent inducers of inflammation, which has been associated with the pathophysiology of sepsis, but repeated exposure can also induce a suppressive effect known as endotoxin tolerance or cellular reprogramming. It has been proposed that endotoxin tolerance might be associated with the immunosuppressive state that was primarily observed during late-stage sepsis. However, this relationship remains poorly characterised. Here we clarify the underlying mechanisms and timing of immune dysfunction in sepsis.

Methods

We defined a gene expression signature characteristic of endotoxin tolerance. Gene-set test approaches were used to correlate this signature with early sepsis, both newly and retrospectively analysing microarrays from 593 patients in 11 cohorts. Then we recruited a unique cohort of possible sepsis patients at first clinical presentation in an independent blinded controlled observational study to determine whether this signature was associated with the development of confirmed sepsis and organ dysfunction.

Findings

All sepsis patients presented an expression profile strongly associated with the endotoxin tolerance signature (p < 0.01; AUC 96.1%). Importantly, this signature further differentiated between suspected sepsis patients who did, or did not, go on to develop confirmed sepsis, and predicted the development of organ dysfunction.

Interpretation

Our data support an updated model of sepsis pathogenesis in which endotoxin tolerance-mediated immune dysfunction (cellular reprogramming) is present throughout the clinical course of disease and related to disease severity. Thus endotoxin tolerance might offer new insights guiding the development of new therapies and diagnostics for early sepsis.

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Addresses sepsis that affects up to 18 million persons annually with up to 5 million deaths worldwide.

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Describes an endotoxin tolerance gene expression signature associated with consecutive treatments with endotoxin and reflecting cellular reprogramming.

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Using a meta-analysis of the literature demonstrates the statistically significant association (p < 0.01; AUC 96.1%) of this endotoxin tolerance signature with early (day 1–3 after ICU admission) sepsis in 593 patients in 11 adult or child cohorts.

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Demonstrates, at first clinical presentation, the ability of this signature to predict the eventual diagnosis of sepsis and organ failure in an independent blinded controlled observational study of a unique cohort of possible sepsis patients.

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This study provides new insights that have the potential to guide the development of new therapies and diagnostics for early sepsis.

Gene expression profiling of bovine mammary gland epithelial cells stimulated with lipoteichoic acid plus peptidoglycan from Staphylococcus aureus

A Gram-positive bacterium, Staphylococcus aureus is known to be one of the major pathogenic bacteria responsible for causing bovine mastitis. Among the various cell wall components of S. aureus, lipoteichoic acid (LTA) and peptidoglycan (PGN) are closely associated with inflammatory responses. However, the role of LTA and PGN derived from S. aureus in bovine mastitis has not been clearly elucidated. In this study, we characterized the gene expression profile of a bovine mammary gland epithelial cell line, MAC-T cells, in the presence of LTA and PGN from S. aureus. LTA plus PGN, but not LTA or PGN alone, activated MAC-T cells. The analysis of transcriptional profiles using an Affymetrix genechip microarray showed that stimulation with LTA plus PGN produced a total of 2019 (fold change >1.2) differentially expressed genes (DEGs), with 801 up-regulated genes and 1218 down-regulated genes. Of the up-regulated genes, 14 inflammatory mediator-related DEGs, 22 intra-cellular signaling molecule-related DEGs, and 15 transcription factor-related DEGs were observed, whereas among the down-regulated DEGs 17 inflammation-related DEGs were found. The microarray results were confirmed using real-time RT-PCR of 18 genes with substantial changes in expression (9 each from the up-regulated and down-regulated DEGs). These results provide a comprehensive analysis of gene-expression profiles elicited by S. aureus LTA and PGN in MAC-T cells, contributing to an understanding of the pathogenesis for S. aureus-induced bovine mastitis.

Exposure-dependent control of malaria-induced inflammation in children

In malaria-naïve individuals, Plasmodium falciparum infection results in high levels of parasite-infected red blood cells (iRBCs) that trigger systemic inflammation and fever. Conversely, individuals in endemic areas who are repeatedly infected are often asymptomatic and have low levels of iRBCs, even young children. We hypothesized that febrile malaria alters the immune system such that P. falciparum re-exposure results in reduced production of pro-inflammatory cytokines/chemokines and enhanced anti-parasite effector responses compared to responses induced before malaria. To test this hypothesis we used a systems biology approach to analyze PBMCs sampled from healthy children before the six-month malaria season and the same children seven days after treatment of their first febrile malaria episode of the ensuing season. PBMCs were stimulated with iRBC in vitro and various immune parameters were measured. Before the malaria season, children's immune cells responded to iRBCs by producing pro-inflammatory mediators such as IL-1β, IL-6 and IL-8. Following malaria there was a marked shift in the response to iRBCs with the same children's immune cells producing lower levels of pro-inflammatory cytokines and higher levels of anti-inflammatory cytokines (IL-10, TGF-β). In addition, molecules involved in phagocytosis and activation of adaptive immunity were upregulated after malaria as compared to before. This shift was accompanied by an increase in P. falciparum-specific CD4⁺Foxp3⁻ T cells that co-produce IL-10, IFN-γ and TNF; however, after the subsequent six-month dry season, a period of markedly reduced malaria transmission, P. falciparum–inducible IL-10 production remained partially upregulated only in children with persistent asymptomatic infections. These findings suggest that in the face of P. falciparum re-exposure, children acquire exposure-dependent P. falciparum–specific immunoregulatory responses that dampen pathogenic inflammation while enhancing anti-parasite effector mechanisms. These data provide mechanistic insight into the observation that P. falciparum–infected children in endemic areas are often afebrile and tend to control parasite replication.

Malaria remains a major cause of disease and death worldwide. When mosquitoes infect people with malaria parasites for the first time, the parasite rapidly multiplies in the blood and the body responds by producing molecules that cause inflammation and fever, and sometimes the infection progresses to life-threatening disease. However, in regions where people are repeatedly infected with malaria parasites, most infections do not cause fever and parasites often do not multiply uncontrollably. For example, in Mali where this study was conducted, children are infected with malaria parasites ≥100 times/year but only get malaria fever ∼2 times/year and often manage to control parasite numbers in the blood. To understand these observations we collected immune cells from the blood of healthy children before the malaria season and 7 days after malaria fever. We simulated malaria infection at these time points by exposing the immune cells to malaria parasites in a test-tube. We found that re-exposing immune cells to parasites after malaria fever results in reduced expression of molecules that cause fever and enhanced expression of molecules involved in parasite killing. These findings help explain how the immune system prevents fever and controls malaria parasite growth in children who are repeatedly infected with malaria parasites.

A novel synthetic lipopeptide is allergy-protective by the induction of LPS-tolerance

BACKGROUND

Exposure to the environment of traditional farms can protect children from some allergic disease. Due to this exposure, TLR2 expression in these children is increased. TLR2 ligands derived from gram-positive bacteria are found in the dust of these farms.

OBJECTIVES

We proved whether a synthetic lipopeptide binding to the TLR1/2 heterodimer is able to protect from allergic disease in two different murine models of allergy. We also investigated the immunological mechanisms underlying the protective properties of the lipopeptide.

METHODS

We synthesized a lipopeptide derived from a germination lipoprotein of Bacillus cereus (LPGerD). We evaluated the immunomodulatory activity of LPGerD in a murine model of systemic sensitization (OVA/Alum) and in a model in which mice were sensitized with OVA pulsed bone-marrow-derived dendritic cells (BMDCs) via the airways. Furthermore, the induction of LPS tolerance was studied.

RESULTS

Treatment of mice with LPGerD in a mouse model of asthma led to protection against sensitization and airway inflammation. Similarly, bone-marrow-derived dendritic cells (BMDCs) pre-treated with LPGerD were not able to prime mice for allergic immune response. We observed that pre-treatment with LPGerD led to the induction of a LPS-tolerant state in BMDCs. These cells secreted markedly lower amounts of pro-inflammatory cytokines upon LPS stimulation. Furthermore, we observed an up-regulation of IRAK-M mRNA in BMDCs pre-treated with LPGerD.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results suggest that induction of a LPS-tolerant state in antigen-presenting cells (APCs) may contribute to the protective effect of a farming environment. TLR2 agonists similar to those appearing in cowshed dust extracts, such as our synthetic LPGerD, lead to the ignorance of the LPS stimulus, which is important for the activation of APCs to mount a Th2 immune response. This substance might be a promising candidate for allergy-preventive treatments as LPGerD had only low pro-inflammatory characteristics.

Exploring the immunomodulatory potential of microbial-associated molecular patterns derived from the enteric bacterial microbiota

The human intestinal lumen represents one of the most densely populated microbial niches in the biological world and, as a result, the intestinal innate immune system exists in a constant state of stimulation. A key component in the innate defence system is the intestinal epithelial layer, which acts not only as a physical barrier, but also as an immune sensor. The expression of pattern recognition receptors, such as Toll-like receptors, in epithelial cells allows innate recognition of a wide range of highly conserved bacterial moieties, termed microbial-associated molecular patterns (MAMPs), from both pathogenic and non-pathogenic bacteria. To date, studies of epithelial immunity have largely concentrated on inflammatory pathogenic antigens; however, this review discusses the major types of MAMPs likely to be produced by the enteric bacterial microbiota and, using data from in vitro studies, animal model systems and clinical observations, speculates on their immunomodulatory potential.

Role of macrophage receptor with collagenous structure in innate immune tolerance

Macrophages play a key role in host defense against microbes, in part, through phagocytosis. Macrophage receptor with collagenous structure (MARCO) is a scavenger receptor on the cell surface of macrophages that mediates opsonin-independent phagocytosis. The goal of our study is to investigate the role of MARCO in LPS or lipotechoic acid-induced macrophage tolerance. Although it has been established that expression of MARCO and phagocytosis is increased in tolerant macrophages, the transcriptional regulation and biological role of MARCO in tolerant macrophages have not been investigated. In this study, we confirm that tolerized mouse bone marrow-derived macrophages (BMDM) selectively increase expression of MARCO (both transcript and cell surface receptor) and increase phagocytosis. We found that H3K4me3 dynamic modification of a promoter site of MARCO was increased in tolerized BMDM. Blocking methylation by treatment with 5-aza-2'-deoxycytidine resulted in reduced H3K4me3 binding in the promoter of MARCO, decreased expression of MARCO, and impaired phagocytosis in tolerized BMDM. However, 5-aza-2'-deoxycytidine had no effect on the inflammatory component of innate immune tolerance. In aggregate, we found that histone methylation was critical to MARCO expression and phagocytosis in tolerized macrophages, but did not affect the inflammatory component of innate immune tolerance.

MicroRNA-146a is upregulated by and negatively regulates TLR2 signaling

TLR signaling is a crucial component of the innate immune response to infection. MicroRNAs (miRNAs) have been shown to be upregulated during TLR signaling. Specifically, microRNA-146a (miR-146a) plays a key role in endotoxin tolerance by downregulating interleukin-1 receptor-associated kinase 1 (IRAK-1). The aim of this study was to assess the role of miR-146a in the TLR2 signaling and development of bacterial lipoprotein (BLP) self-tolerance and cross-tolerance to bacteria. Expression of miR-146a increased in a dose- and time-dependent manner in BLP-stimulated human THP-1 promonocytic cells. In BLP-tolerised cells miR-146a was even further upregulated in response to BLP re-stimulation (p<0.001). Re-stimulation of BLP-tolerised cells with heat-killed gram-negative Salmonella typhimurium (S. typhimurium), but not gram-positive Staphylococcus aureus (S. aureus), led to significant overexpression of miR-146a (p<0.05). Transfection of naive cells with a miR-146a mimic substantially suppressed TNF-α production (p<0.05). Furthermore, overexpression of miR-146a resulted in strong reduction in IRAK-1 and phosphorylated IκBα expression in naive and S. typhimurium-stimulated THP-1 cells. Collectively, miR-146a is upregulated in response to BLP and bacterial stimulation in both naive and BLP-tolerised cells. Overexpression of miR-146a induces a state analogous to tolerance in BLP-stimulated cells and therefore may represent a future target for exogenous modulation of tolerance during microbial infection and sepsis.

Nonpathogenic Lactobacillus rhamnosus activates the inflammasome and antiviral responses in human macrophages

In this study, we have utilized global gene expression profiling to compare the responses of human primary macrophages to two closely related, well-characterized Lactobacillus rhamnosus strains GG and LC705, since our understanding of the responses elicited by nonpathogenic bacteria in human innate immune system is limited. Macrophages are phagocytic cells of the innate immune system that perform sentinel functions to initiate appropriate responses to surrounding stimuli. Macrophages that reside on gut mucosa encounter ingested and intestinal bacteria. Bacteria of Lactobacillus genus are nonpathogenic and used in food and as supplements with health-promoting probiotic potential. Our results demonstrate that live GG and LC705 induced quantitatively different gene expression profiles in macrophages. A gene ontology analysis revealed functional similarities and differences in responses to GG and LC705 that were reflected in host defense responses. Both GG and LC705 induced interleukin-1β production in macrophages that required caspase-1 activity. LC705, but not GG, induced type I interferon -dependent gene activation that correlated with its ability to prevent influenza A virus replication and production of viral proteins in macrophages. Our results indicate that nonpathogenic bacteria are able to activate the inflammasome. In addition, our results suggest that L. rhamnosus may prime the antiviral potential of human macrophages.

Lipoteichoic acid from Lactobacillus rhamnosus GG as an oral photoprotective agent against UV-induced carcinogenesis

Probiotics are live micro-organisms that when administered in adequate amounts confer a health benefit on the host. Cell surface molecules of these micro-organisms are being studied in relation to their ability to interact with the host. The cell wall of lactobacilli possesses lipoteichoic acids (LTA) which are molecules with immunomodulatory properties. UV radiation (UVR) has been proposed as the main cause of skin cancer because of its mutagenic and immunosuppressive effects. Photoprotection with some nutrition interventions including probiotics has recently been shown. The aim of the present study was to investigate whether the oral administration of purified LTA from Lactobacillus rhamnosus GG can modulate the immune-suppressive effect of UVR and skin tumour development in female Crl:SKH-1-hrBR mice. For this purpose, two irradiation models were studied: (1) a chronic irradiation scheme consisting of daily irradiations during twenty consecutive days and (2) a long-term irradiation schedule, irradiating the animals three times per week, during 34 weeks for tumour development. The results showed that T-cells in the inguinal lymph node of LTA-treated mice produced higher levels of (1) interferon-γ and (2) a number of total, helper and cytotoxic T-cells compared with non-treated mice. Moreover, a significant delay in tumour appearance was found in LTA-treated mice. An increased IgA+ cell number was found in the small intestine together with a higher number of activated dendritic cells in the mesenteric lymph nodes. The latter results might be indicative of a direct effect of LTA in the gut, affecting the cutaneous immune system and restoring homeostasis through the gut–skin axis.

Lipoteichoic acid from Lactobacillus plantarum induces nitric oxide production in the presence of interferon-γ in murine macrophages

Lipoteichoic acid (LTA) is a major immuno-stimulating component of Gram-positive bacteria. LTA from the beneficial bacterium Lactobacillus plantarum induces weak nitric oxide (NO) production in murine macrophages. Currently, it is not clear if LTA from L. plantarum is able to stimulate the innate immune response, even in the presence of inflammation. In the present study, we prepared highly pure and structurally intact LTA from L. plantarum and investigated its ability to induce NO in the presence of interferon (IFN)-γ in the RAW 264.7 murine macrophage cell line and bone marrow-derived macrophages (BMMs) from mice. L. plantarum LTA alone was unable to induce NO production, even at 30μg/ml. However, LTA in the presence of IFN-γ significantly induced NO production in RAW 264.7 cells. The observed NO production was inhibited by a NO synthase (NOS) inhibitor l-NAME and an inducible NOS (iNOS) inhibitor l-NIL, suggesting that iNOS is specifically required for this action. Western blot analysis and reverse transcription and polymerase chain reaction further confirmed that L. plantarum LTA increased protein and mRNA levels of iNOS, respectively. However, such induction was substantially inhibited in BMMs from Toll-like receptor 2 (TLR2)-deficient mice and the macrophages treated with an inhibitor blocking platelet-activating factor receptor. In addition, L. plantarum LTA plus IFN-γ induced IFN-β expression and STAT1 phosphorylation, which are key pathways for inducing iNOS expression. Electrophoretic mobility shift assay demonstrated that L. plantarum LTA in the presence of IFN-γ remarkably increased the DNA-binding activity of NF-κB transcription factor, which is known to be involved in the iNOS gene expression. Collectively, these results suggest that LTA from L. plantarum alone has no inflammatory potential but does induce NO production under conditions of inflammation, such as the presence of IFN-γ.

Bacteria-specific neutrophil dysfunction associated with interferon-stimulated gene expression in the acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a poorly understood condition with greater than 30% mortality. Massive recruitment of neutrophils to the lung occurs in the initial stages of the ARDS. Significant variability in the severity and duration of ARDS-associated pulmonary inflammation could be linked to heterogeneity in the inflammatory capacity of neutrophils. Interferon-stimulated genes (ISGs) are a broad gene family induced by Type I interferons. While ISGs are central to anti-viral immunity, the potential exists for these genes to evoke extensive modification in cellular response in other clinical settings. In this prospective study, we sought to determine if ISG expression in circulating neutrophils from ARDS patients is associated with changes in neutrophil function. Circulating neutrophil RNA was isolated, and hierarchical clustering ranked patients' expression of three ISGs. Neutrophil response to pathogenic bacteria was compared between normal and high ISG-expressing neutrophils. High neutrophil ISG expression was found in 25 of 95 (26%) of ARDS patients and was associated with reduced migration toward interleukin-8, and altered responses to Staphylococcus aureus, but not Pseudomonas aeruginosa, which included decreased p38 MAP kinase phosphorylation, superoxide anion release, interleukin-8 release, and a shift from necrotic to apoptotic cell death. These alterations in response were reflected in a decreased capacity to kill S. aureus, but not P. aeruginosa. Therefore, the ISG expression signature is associated with an altered circulating neutrophil response phenotype in ARDS that may predispose a large subgroup of patients to increased risk of specific bacterial infections.

Bacterial lipoprotein-induced tolerance is reversed by overexpression of IRAK-1

Tolerance to bacterial cell wall components including bacterial lipoprotein (BLP) represents an essential regulatory mechanism during bacterial infection. Reduced Toll-like receptor 2 (TLR2) and IL-1 receptor-associated kinase 1 (IRAK-1) expression is a characteristic of the downregulated TLR signaling pathway observed in BLP-tolerised cells. In this study, we attempted to clarify whether TLR2 and/or IRAK-1 are the key molecules responsible for BLP-induced tolerance. Transfection of HEK293 cells and THP-1 cells with the plasmid encoding TLR2 affected neither BLP tolerisation-induced NF-κB deactivation nor BLP tolerisation-attenuated pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) production, indicating that BLP tolerance develops despite overexpression of TLR2 in these cells. In contrast, overexpression of IRAK-1 reversed BLP-induced tolerance, as transfection of IRAK-1 expressing vector resulted in a dose-dependent NF-κB activation and TNF-α release in BLP-tolerised cells. Furthermore, BLP-tolerised cells exhibited markedly repressed NF-κB p65 phosphorylation and impaired binding of p65 to several pro-inflammatory cytokine gene promoters including TNF-α and interleukin-6 (IL-6). Overexpression of IRAK-1 restored the nuclear transactivation of p65 at both TNF-α and IL-6 promoters. These results indicate a crucial role for IRAK-1 in BLP-induced tolerance, and suggest IRAK-1 as a potential target for manipulation of the TLR-mediated inflammatory response during microbial sepsis.

Endotoxin tolerance attenuates airway allergic inflammation in model mice by suppression of the T-cell stimulatory effect of dendritic cells

Prior exposure of dendritic cells (DCs) and monocytes/macrophages to LPS causes unresponsiveness to subsequent LPS stimulation, a phenomenon called endotoxin tolerance (ET). ET impairs antigen presentation of these cells to T cells by down-regulating expression of MHC class II and co-stimulatory molecules such as CD86 and CD40. Some epidemiological studies have shown that endotoxin acts as a protective factor for allergic diseases. Accordingly, LPS has beneficial effects on the onset of airway allergic inflammation in model animals by T(h)1 skewing or induction of regulatory T cells. However, results derived from asthma model animals are controversial, probably due to the difficulty of handling LPS. We previously generated a monoclonal agonistic antibody against Toll-like receptor (TLR) 4, named UT12, which mimics the biological activities of LPS, exhibiting more potent and sustained ET than does LPS. In this study, we took advantage of UT12 to generate prolonged ET to explore the possibility that ET is involved in the inhibitory effects of the TLR4 signals on asthma model mice. Induction of ET by UT12 inhibited the capacity of DCs to expand ovalbumin (OVA)-specific T(h)2 and T(h)17 cells, without inducing T(h)1 cell or regulatory T-cell populations or producing inhibitory cytokines. Accordingly, administration of UT12 before the OVA sensitization significantly suppressed airway allergic inflammation by OVA inhalation. Taken together, these results demonstrate that ET induced by activating TLR4 signals attenuates airway allergic inflammation through direct suppression of the T-cell stimulatory effect of DCs in asthma model mice.

The flavonoids luteolin and quercetagetin inhibit lipoteichoic acid actions on H9c2 cardiomyocytes

Dental focal infections are infections in the mouth that cause subsequent infection and symptoms in other parts of the body. Dental conditions such as periodontitis have been associated with coronary heart disease. In this study, we investigated the effect of flavonoids on activation of mitogen-activated protein kinase (MAPK) family members, protein kinase B (AKT), and IL-1 beta expression by rat heart embryonic (H9c2) cells upon stimulation with LTA. Pretreatment with four flavonoids, including quercetin, genistein, quercetagetin, and luteolin diminished LTA-induced ERK1/2, JNK, p38, and AKT phosphorylation and IL-1 beta gene expression. Our findings indicate that flavonoids interfere with LTA signal transduction.

ST2 negatively regulates TLR2 signaling, but is not required for bacterial lipoprotein-induced tolerance

Activation of TLR signaling is critical for host innate immunity against bacterial infection. Previous studies reported that the ST2 receptor, a member of the Toll/IL-1 receptor superfamily, functions as a negative regulator of TLR4 signaling and maintains LPS tolerance. However, it is undetermined whether ST2 negatively regulates TLR2 signaling and furthermore, whether a TLR2 agonist, bacterial lipoprotein (BLP)-induced tolerance is dependent on ST2. In this study, we show that BLP stimulation-induced production of proinflammatory cytokines and immunocomplex formation of TLR2-MyD88 and MyD88-IL-1R-associated kinase (IRAK) were significantly enhanced in ST2-deficient macrophages compared with those in wild-type controls. Furthermore, overexpression of ST2 dose-dependently attenuated BLP-induced NF-kappaB activation, suggesting a negative regulatory role of ST2 in TLR2 signaling. A moderate but significantly attenuated production of TNF-alpha and IL-6 on a second BLP stimulation was observed in BLP-pretreated, ST2-deficient macrophages, which is associated with substantially reduced IRAK-1 protein expression and downregulated TLR2-MyD88 and MyD88-IRAK immunocomplex formation. ST2-deficient mice, when pretreated with a nonlethal dose of BLP, benefitted from an improved survival against a subsequent lethal BLP challenge, indicating BLP tolerance develops in the absence of the ST2 receptor. Taken together, our results demonstrate that ST2 acts as a negative regulator of TLR2 signaling, but is not required for BLP-induced tolerance.

Transcriptional control of the TNF gene

The cytokine TNF is a critical mediator of immune and inflammatory responses. The TNF gene is an immediate early gene, rapidly transcribed in a variety of cell types following exposure to a broad range of pathogens and signals of inflammation and stress. Regulation of TNF gene expression at the transcriptional level is cell type- and stimulus-specific, involving the recruitment of distinct sets of transcription factors to a compact and modular promoter region. In this review, we describe our current understanding of the mechanisms through which TNF transcription is specifically activated by a variety of extracellular stimuli in multiple cell types, including T cells, B cells, macrophages, mast cells, dendritic cells, and fibroblasts. We discuss the role of nuclear factor of activated T cells and other transcription factors and coactivators in enhanceosome formation, as well as the contradictory evidence for a role for nuclear factor kappaB as a classical activator of the TNF gene. We describe the impact of evolutionarily conserved cis-regulatory DNA motifs in the TNF locus upon TNF gene transcription, in contrast to the neutral effect of single nucleotide polymorphisms. We also assess the regulatory role of chromatin organization, epigenetic modifications, and long-range chromosomal interactions at the TNF locus.

Endotoxin tolerance: new mechanisms, molecules and clinical significance

Prior exposure of innate immune cells like monocytes/macrophages to minute amounts of endotoxin cause them to become refractory to subsequent endotoxin challenge, a phenomenon called "endotoxin tolerance". Clinically, this state is associated with monocytes/macrophages in sepsis patients where they contribute to "immunosuppression" and mortality. The molecular mechanisms underlying endotoxin tolerance remain elusive. The recent appreciation of inflammation as a self-regulating process, the relative contribution of MyD88 versus TRIF signaling pathways in inducing activation or tolerance, plasticity of NF-kappaB function and the role of chromatin modification and microRNAs in LPS-induced gene reprogramming urges a re-evaluation of endotoxin tolerance. This review integrates these new findings into an up-to-date account of endotoxin tolerance, its molecular basis and clinical implications in different pathologies.

Intra-amniotic LPS modulation of TLR signaling in lung and blood monocytes of fetal sheep

Epidemiological studies suggest that intra-uterine exposure to inflammation may prime postnatal immune responses. In fetal sheep, intra-amniotic injection of lipopolysaccharide (LPS) induced chorioamnionitis, lung inflammation and maturation, matured lung monocytes to macrophages and initiated systemic tolerance of fetal monocytes to subsequent challenge with LPS. We hypothesized that LPS-mediated chorioamnionitis altered the response of lung and blood monocytes to Toll-like receptor (TLR) ligands such as PamCysK4 (TLR2), flagellin (TLR5), and human CpG-DNA (TLR9). Time-mated ewes were given intra-amniotic injections of LPS or saline. Blood and lung monocytes were assessed after 2 days, 7 days and 2 days and 7 days repetitive LPS injections before delivery at 124 days gestational age (term 150 days). Responsiveness of blood and lung monocytes to TLR-ligands in vitro was assessed by interleukin (IL)-6, tumor necrosis factor-alpha (TNF-alpha) and hydrogen peroxide. Monocytes from preterm controls had minimal responses. Lipopolysaccharide-mediated chorioamnionitis increased IL-6, TNF- alpha and hydrogen peroxide to all TLR agonists in blood and lung monocytes. Repetitive exposure to antenatal LPS reduced IL-6, TNF- alpha and hydrogen peroxide to TLR-ligands suggesting tolerance. Tolerance to TLR-ligands reduced IL-1 receptor associated kinase-4 expression. Thus, repeated fetal exposure to LPS induced tolerance to other TLR-ligands. These modulations of fetal innate immunity have implications for host defense and injury responses in preterm infants.

Glycyrrhiza inflata-derived chalcones, Licochalcone A, Licochalcone B and Licochalcone D, inhibit phosphorylation of NF-kappaB p65 in LPS signaling pathway

Licorice root has been used as a traditional medicine for the treatment of gastric ulcer, bronchial asthma and inflammation. Licochalcone A is a major component of Xinjiang licorice, Glycyrrhiza inflata. Previously we showed that Licochalcone A significantly inhibited LPS-induced NF-kappaB transcriptional activation by abrogating the phosphorylation of NF-kappaB p65 at serine 276. Glycyrrhiza inflata contains not only Licochalcone A but also Licochalcone B, Licochalcone C, Licochalcone D, Echinatin and Isoliquiritigenin, harboring the common structure of chalcones. No chalcones had any effect on LPS-induced IkappaB degradation, nuclear translocation and DNA binding activity of NF-kappaB p65; however, we observed that Licochalcone B and Licochalcone D significantly inhibited LPS-induced phosphorylation at serine 276 and transcriptional activation of NF-kappaB, the same as Licochalcone A. Interestingly, we also found that Licochalcone A, Licochalcone B and Licochalcone D effectively inhibited LPS-induced activation of PKA, which is required for the phosphorylation of NF-kappaB p65 at serine 276. Consequently, Licochalcone B and Licochalcone D significantly reduced the LPS-induced production of NO, TNFalpha and MCP-1. On the other hand, Licochalcone C, Echinatin and Isoliquitigenin failed to inhibit LPS-induced NF-kappaB activation. These findings suggest that the anti-inflammatory effect of Glycyrrhiza inflata is ascribable to the potent inhibition of NF-kappaB by Licochalcone A, Licochalcone B and Licochalcone D.

Effects of gram-positive microorganisms and their products on in vivo survival of hemopoietic clonogenic cells

The effects of gram-positive bacterial strains (Lactobacillus acidophilus and Lactobacillus rhamnosus) and their subcellular components on the survival of hemopoietic clonogenic cells were evaluated by the formation of endogenous splenic colonies. The effects of these preparations on NO production were studied by the spin-trap paramagnetic resonance spectroscopy. Bacterial preparations from gram-positive bacteria stimulated survival of hemopoietic clonogenic cells, but did not induce NO production in contrast to E. coli LPS.

Differential immunostimulatory effects of Gram-positive bacteria due to their lipoteichoic acids

Lipoteichoic acid (LTA) is a major immunostimulating component in the cell wall of Gram-positive bacteria as lipopolysaccharide of Gram-negative bacteria. However, LTA is expressed on not only pathogenic but also nonpathogenic Gram-positive bacteria. In order to examine whether the immunostimulating potentials of Gram-positive bacteria are correlated with their LTAs, we prepared highly pure LTAs from Staphylococcus aureus (pathogenic), Bacillus subtilis (non-pathogenic), or Lactobacillus plantarum (beneficial). When a murine macrophage cell-line, RAW 264.7, was stimulated with heat-killed bacteria, both S. aureus and B. subtilis induced nitric oxide (NO) production in a dose-dependent manner while L. plantarum showed a minimal induction. Interestingly, purified LTAs from S. aureus and B. subtilis, but not from L. plantarum, were able to induce the production of NO. The differential inflammatory potentials of LTAs coincided with their abilities to activate Toll-like receptor 2 (TLR2), which is known to recognize Gram-positive bacteria and LTA, and transcription factors NF-kappaB and AP-1. Similar results were obtained with the expression of cytokines related to inflammation by RAW 264.7 and human peripheral blood mononuclear cells as well. The ability of LTA to induce TNF-alpha and NO production was abolished when the LTAs were treated with 0.2 N NaOH. Collectively, we suggest that the immunostimulating potentials of Gram-positive bacteria differ due to their LTAs with differential potencies in the stimulation of TLR2.