TLR2 synergizes with both TLR4 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Streptococcus pneumoniae

Bacterial surface lipoproteins mediate epithelial microinvasion by Streptococcus pneumoniae

Streptococcus pneumoniae, a common colonizer of the upper respiratory tract, invades nasopharyngeal epithelial cells without causing disease in healthy participants of controlled human infection studies. We hypothesized that surface expression of pneumococcal lipoproteins, recognized by the innate immune receptor TLR2, mediates epithelial microinvasion. Mutation of lgt in serotype 4 (TIGR4) and serotype 6B (BHN418) pneumococcal strains abolishes the ability of the mutants to activate TLR2 signaling. Loss of lgt also led to the concomitant decrease in interferon signaling triggered by the bacterium. However, only BHN418 lgt::cm but not TIGR4 lgt::cm was significantly attenuated in epithelial adherence and microinvasion compared to their respective wild-type strains. To test the hypothesis that differential lipoprotein repertoires in TIGR4 and BHN418 lead to the intraspecies variation in epithelial microinvasion, we employed a motif-based genome analysis and identified an additional 525 a.a. lipoprotein (pneumococcal accessory lipoprotein A; palA) encoded by BHN418 that is absent in TIGR4. The gene encoding palA sits within a putative genetic island present in ~10% of global pneumococcal isolates. While palA was enriched in the carriage and otitis media pneumococcal strains, neither mutation nor overexpression of the gene encoding this lipoprotein significantly changed microinvasion patterns. In conclusion, mutation of lgt attenuates epithelial inflammatory responses during pneumococcal-epithelial interactions, with intraspecies variation in the effect on microinvasion. Differential lipoprotein repertoires encoded by the different strains do not explain these differences in microinvasion. Rather, we postulate that post-translational modifications of lipoproteins may account for the differences in microinvasion.IMPORTANCEStreptococcus pneumoniae (pneumococcus) is an important mucosal pathogen, estimated to cause over 500,000 deaths annually. Nasopharyngeal colonization is considered a necessary prerequisite for disease, yet many people are transiently and asymptomatically colonized by pneumococci without becoming unwell. It is therefore important to better understand how the colonization process is controlled at the epithelial surface. Controlled human infection studies revealed the presence of pneumococci within the epithelium of healthy volunteers (microinvasion). In this study, we focused on the regulation of epithelial microinvasion by pneumococcal lipoproteins. We found that pneumococcal lipoproteins induce epithelial inflammation but that differing lipoprotein repertoires do not significantly impact the magnitude of microinvasion. Targeting mucosal innate immunity and epithelial microinvasion alongside the induction of an adaptive immune response may be effective in preventing pneumococcal colonization and disease.

Nucleic acid sensing Toll-like receptors 3 and 9 play complementary roles in the development of bacteremia after nasal colonization associated with influenza co-infection

Streptococcus pneumoniae can cause mortality in infant, elderly, and immunocompromised individuals owing to invasion of bacteria to the lungs, the brain, and the blood. In building strategies against invasive infections, it is important to achieve greater understanding of how the pneumococci are able to survive in the host. Toll-like receptors (TLRs), critically important components in the innate immune system, have roles in various stages of the development of infectious diseases. Endosomal TLRs recognize nucleic acids of the pathogen, but the impact on the pneumococcal diseases of immune responses from signaling them remains unclear. To investigate their role in nasal colonization and invasive disease with/without influenza co-infection, we established a mouse model of invasive pneumococcal diseases directly developing from nasal colonization. TLR9 KO mice had bacteremia more frequently than wildtype in the pneumococcal mono-infection model, while the occurrence of bacteremia was higher among TLR3 KO mice after infection with influenza in advance of pneumococcal inoculation. All TLR KO strains showed poorer survival than wildtype after the mice had bacteremia. The specific and protective role of TLR3 and TLR9 was shown in developing bacteremia with/without influenza co-infection respectively, and all nucleic sensing TLRs would contribute equally to protecting sepsis after bacteremia.

Asthma-associated bacterial infections: Are they protective or deleterious?

Eosinophilic, noneosinophilic, or mixed granulocytic inflammations are the hallmarks of asthma heterogeneity. Depending on the priming of lung immune and structural cells, subjects with asthma might generate immune responses that are TH2-prone or TH17-prone immune response. Bacterial infections caused by Haemophilus, Moraxella, or Streptococcus spp. induce the secretion of IL-17, which in turn recruit neutrophils into the airways. Clinical studies and experimental models of asthma indicated that neutrophil infiltration induces a specific phenotype of asthma, characterized by an impaired response to corticosteroid treatment. The understanding of pathways that regulate the TH17-neutrophils axis is critical to delineate and develop host-directed therapies that might control asthma and its exacerbation episodes that course with infectious comorbidities. In this review, we outline clinical and experimental studies on the role of airway epithelial cells, S100A9, and high mobility group box 1, which act in concert with the IL-17-neutrophil axis activated by bacterial infections, and are related with asthma that is difficult to treat. Furthermore, we report critically our view in the light of these findings in an attempt to stimulate further investigations and development of immunotherapies for the control of severe asthma.

Toll-like receptors in cardiac hypertrophy

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that can identify pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). TLRs play an important role in the innate immune response, leading to acute and chronic inflammation. Cardiac hypertrophy, an important cardiac remodeling phenotype during cardiovascular disease, contributes to the development of heart failure. In previous decades, many studies have reported that TLR-mediated inflammation was involved in the induction of myocardium hypertrophic remodeling, suggesting that targeting TLR signaling might be an effective strategy against pathological cardiac hypertrophy. Thus, it is necessary to study the mechanisms underlying TLR functions in cardiac hypertrophy. In this review, we summarized key findings of TLR signaling in cardiac hypertrophy.

Mitochondrial ROS production by neutrophils is required for host antimicrobial function against Streptococcus pneumoniae and is controlled by A2B adenosine receptor signaling

Polymorphonuclear cells (PMNs) control Streptococcus pneumoniae (pneumococcus) infection through various antimicrobial activities. We previously found that reactive oxygen species (ROS) were required for optimal antibacterial function, however, the NADPH oxidase is known to be dispensable for the ability of PMNs to kill pneumococci. In this study, we explored the role of ROS produced by the mitochondria in PMN antimicrobial defense against pneumococci. We found that the mitochondria are an important source of overall intracellular ROS produced by murine PMNs in response to infection. We investigated the host and bacterial factors involved and found that mitochondrial ROS (MitROS) are produced independent of bacterial capsule or pneumolysin but presence of live bacteria that are in direct contact with PMNs enhanced the response. We further found that MyD88-/- PMNs produced less MitROS in response to pneumococcal infection suggesting that released bacterial products acting as TLR ligands are sufficient for inducing MitROS production in PMNs. To test the role of MitROS in PMN function, we used an opsonophagocytic killing assay and found that MitROS were required for the ability of PMNs to kill pneumococci. We then investigated the role of MitROS in host resistance and found that MitROS are produced by PMNs in response to pneumococcal infection. Importantly, treatment of mice with a MitROS scavenger prior to systemic challenge resulted in reduced survival of infected hosts. In exploring host pathways that control MitROS, we focused on extracellular adenosine, which is known to control PMN anti-pneumococcal activity, and found that signaling through the A2B adenosine receptor inhibits MitROS production by PMNs. A2BR-/- mice produced more MitROS and were significantly more resistant to infection. Finally, we verified the clinical relevance of our findings using human PMNs. In summary, we identified a novel pathway that controls MitROS production by PMNs, shaping host resistance against S. pneumoniae.

Pneumolysin boosts the neuroinflammatory response to Streptococcus pneumoniae through enhanced endocytosis

In pneumococcal meningitis, bacterial growth in the cerebrospinal fluid results in lysis, the release of toxic factors, and subsequent neuroinflammation. Exposure of primary murine glia to Streptococcus pneumoniae lysates leads to strong proinflammatory cytokine and chemokine production, blocked by inhibition of the intracellular innate receptor Nod1. Lysates enhance dynamin-dependent endocytosis, and dynamin inhibition reduces neuroinflammation, blocking ligand internalization. Here we identify the cholesterol-dependent cytolysin pneumolysin as a pro-endocytotic factor in lysates, its elimination reduces their proinflammatory effect. Only pore-competent pneumolysin enhances endocytosis in a dynamin-, phosphatidylinositol-3-kinase- and potassium-dependent manner. Endocytic enhancement is limited to toxin-exposed parts of the membrane, the effect is rapid and pneumolysin permanently alters membrane dynamics. In a murine model of pneumococcal meningitis, mice treated with chlorpromazine, a neuroleptic with a complementary endocytosis inhibitory effect show reduced neuroinflammation. Thus, the dynamin-dependent endocytosis emerges as a factor in pneumococcal neuroinflammation, and its enhancement by a cytolysin represents a proinflammatory control mechanism.

Blockade of TLR2 and TLR4 Attenuates Inflammatory Response and Parasite Load in Cutaneous Leishmaniasis

Human cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is characterized by a pronounced inflammatory response associated with ulcer development. Monocytes/macrophages, the main cells harboring parasites, are largely responsible for parasite control. Toll-like receptor (TLR) signaling leads to the transcription of inflammatory mediators, such as IL-1β and TNF during innate immune response. TLR antagonists have been used in the treatment of inflammatory disease. The neutralization of these receptors may attenuate an exacerbated inflammatory response. We evaluated the ability of TLR2 and TLR4 antagonists to modulate host immune response in L. braziliensis-infected monocytes and cells from CL patient skin lesions. Following TLR2 and TLR4 neutralization, decreased numbers of infected cells and internalized parasites were detected in CL patient monocytes. In addition, reductions in oxidative burst, IL-1β, TNF and CXCL9 production were observed. TNF production by cells from CL lesions also decreased after TLR2 and TLR4 neutralization. The attenuation of host inflammatory response after neutralizing these receptors suggests the potential of TLR antagonists as immunomodulators in association with antimonial therapy in human cutaneous leishmaniasis.

Nucleic Acid-Sensing Toll-Like Receptors Play a Dominant Role in Innate Immune Recognition of Pneumococci

Streptococcus pneumoniae (or pneumococcus) is a highly prevalent human pathogen. Toll-like receptors (TLRs) function as immune sensors that can trigger host defenses against this bacterium. Defects in TLR-activated signaling pathways, including deficiency in the adaptor protein myeloid differentiation factor 88 (MyD88), are associated with markedly increased susceptibility to infection. However, the individual MyD88-dependent TLRs predominantly involved in antipneumococcal defenses have not been identified yet. Here we find that triple knockout mice simultaneously lacking TLR7, TLR9, and TLR13, which sense the presence of bacterial DNA (TLR9) and RNA (TLR7 and TLR13) in the phagolysosomes of phagocytic cells, display a phenotype that largely resembles that of MyD88-deficient mice and rapidly succumb to pneumococcal pneumonitis due to defective neutrophil influx into the lung. Accordingly, TLR7/9/13 triple knockout resident alveolar macrophages were largely unable to respond to pneumococci with the production of neutrophil-attracting chemokines and cytokines. Mice with single deficiencies of TLR7, TLR9, or TLR13 showed unaltered ability to control lung infection but were moderately more susceptible to encephalitis, in association with a decreased ability of microglia to mount cytokine responses in vitro Our data point to a dominant, tissue-specific role of nucleic acid-sensing pathways in innate immune recognition of S. pneumoniae and also show that endosomal TLRs are largely capable of compensating for the absence of each other, which seems crucial to prevent pneumococci from escaping immune recognition. These results may be useful to develop novel strategies to treat infections by antibiotic-resistant pneumococci based on stimulation of the innate immune system.IMPORTANCE The pneumococcus is a bacterium that frequently causes infections in the lungs, ears, sinus cavities, and meninges. During these infections, body defenses are triggered by tissue-resident cells that use specialized receptors, such as Toll-like receptors (TLRs), to sense the presence of bacteria. We show here that pneumococci are predominantly detected by TLRs that are located inside intracellular vacuoles, including endosomes, where these receptors can sense the presence of nucleic acids released from ingested bacteria. Mice that simultaneously lacked three of these receptors (specifically, TLR7, TLR9, and TLR13) were extremely susceptible to lung infection and rapidly died after inhalation of pneumococci. Moreover, tissue-resident macrophages from these mice were impaired in their ability to respond to the presence of pneumococci by producing inflammatory mediators capable of recruiting polymorphonuclear leucocytes to infection sites. This information may be useful to develop drugs to treat pneumococcal infections, particularly those caused by antibiotic-resistant strains.

Interleukin-1 signaling induced by Streptococcus suis serotype 2 is strain-dependent and contributes to bacterial clearance and inflammation during systemic disease in a mouse model of infection

Streptococcus suis serotype 2 is an important porcine pathogen and zoonotic agent causing sudden death, septic shock and meningitis, with exacerbated inflammation being a hallmark of the infection. A rapid, effective and balanced innate immune response against S. suis is critical to control bacterial growth without causing excessive inflammation. Even though interleukin (IL)-1 is one of the most potent and earliest pro-inflammatory mediators produced, its role in the S. suis pathogenesis has not been studied. We demonstrated that a classical virulent European sequence type (ST) 1 strain and the highly virulent ST7 strain induce important levels of IL-1 in systemic organs. Moreover, bone marrow-derived dendritic cells and macrophages contribute to its production, with the ST7 strain inducing higher levels. To better understand the underlying mechanisms involved, different cellular pathways were studied. Independently of the strain, IL-1β production required MyD88 and involved recognition via TLR2 and possibly TLR7 and TLR9. This suggests that the recognized bacterial components are similar and conserved between strains. However, very high levels of the pore-forming toxin suilysin, produced only by the ST7 strain, are required for efficient maturation of pro-IL-1β via activation of different inflammasomes resulting from pore formation and ion efflux. Using IL-1R^−/− mice, we demonstrated that IL-1 signaling plays a beneficial role during S. suis systemic infection by modulating the inflammation required to control and clear bacterial burden, thus promoting host survival. Beyond a certain threshold, however, S. suis-induced inflammation cannot be counterbalanced by this signaling, making it difficult to discriminate its role.

Enhancement of natural killer activity and IFN-γ production in an IL-12-dependent manner by a Brassica rapa L

Certain food components possess immunomodulatory effects. The aim of this study was to elucidate the mechanism of the immunostimulatory activity of Brassica rapa L. We demonstrated an enhancement of natural killer (NK) activity and interferon (IFN)-γ production in mice that were orally administered an insoluble fraction of B. rapa L. The insoluble fraction of B. rapa L. significantly induced IFN-γ production in mouse spleen cells in an interleukin (IL)-12-dependent manner, and NK1.1+ cells were the main cells responsible for producing IFN-γ. Additionally, the results suggested that the active compounds in the insoluble fraction were recognized by Toll-like receptor (TLR) 2, TLR4, and C-type lectin receptors on dendritic cells, and they activated signaling cascades such as MAPK, NF-κB, and Syk. These findings suggest that B. rapa L. is a potentially promising immuno-improving material, and it might be useful for preventing immunological disorders such as infections and cancers by activating innate immunity.

Pathogen-associated molecular patterns alter molecular clock gene expression in mouse splenocytes

Circadian rhythms are endogenous 24-h oscillations that influence a multitude of physiological processes. The pathogen-associated molecular pattern (PAMP), lipopolysaccharide, has been shown to modify the circadian molecular clock. The aim of this study was to determine if other PAMPs alter clock gene expression. Therefore, mRNA levels of clock genes (Per2, Bmal1, Rev-erbα, and Dbp) were measured after an ex vivo challenge with several PAMPs and to further test the relevance of PAMP alteration of the molecular clock, an in vivo poly(I:C) challenge was performed. This study revealed that several other PAMPs are also capable of altering clock gene expression.

Oridonin attenuates the release of pro-inflammatory cytokines in lipopolysaccharide-induced RAW264.7 cells and acute lung injury

Acute lung injury (ALI) is a life-threatening inflammatory disease owing to the lack of specific and effective therapies. Oridonin (Ori) is an active diterpenoid isolated from Rabdosiarubescens (R.rubescens) that has been shown to possess a broadspectrum pharmacological properties including anti-inflammatory, antitumour, antioxidative and neuroregulatory effects. However, its potential protective mechanism in ALI is not well characterized. In this study, we demonstrated that Ori reduces the mortality of mice with ALI induced by a high dose of lipopolysaccharide (LPS), which suggests that Ori has a protective effect on LPS induced ALI. Next, our results confirmed that Ori improves LPS-induced localized pulmonary pathology and decreased the concentration of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) in the serum. Nuclear factor-kappa B (NF-κB) is capable of regulating the transcription of pro-inflammatory factors. Interestingly, our results showed that Ori inhibits the expression of TLR4/MyD88 and phosphorylation of NF-κB p65 in lung tissues. To confirm this, we further validated the possible regulatory anti-inflammatory mechanisms of Ori in vitro. LPS-induced RAW264.7 cells, which are widely used as an inflammation model to evaluate the potential protective effect of drugs in vitro, were chosen for this study. Similar results were observed, that is, pre-treatment with Ori, markedly inhibited the nuclear translocation and phosphorylation of NF-κB p65 induced by LPS and subsequently decreased the release of pro-inflammatory cytokines that were increased by LPS. Overall, these results demonstrated that Ori exerts a therapeutic effect on ALI by inhibiting the release of pro-inflammatory cytokines, such as IL-1β, IL-6, and TNF-α, through the TLR4/MyD88/NF-κB axis.

Anatomical site-specific contributions of pneumococcal virulence determinants

Streptococcus pneumoniae is an opportunistic pathogen globally associated with significant morbidity and mortality. It is capable of causing a wide range of diseases including sinusitis, conjunctivitis, otitis media, pneumonia, bacteraemia, sepsis, and meningitis. While its capsular polysaccharide is indispensible for invasive disease, and opsonising antibodies against the capsule are the basis for the current vaccines, a long history of biomedical research indicates that other components of this Gram-positive bacterium are also critical for virulence. Herein we review the contribution of pneumococcal virulence determinants to survival and persistence in the context of distinct anatomical sites. We discuss how these determinants allow the pneumococcus to evade mucociliary clearance during colonisation, establish lower respiratory tract infection, resist complement deposition and opsonophagocytosis in the bloodstream, and invade secondary tissues such as the central nervous system leading to meningitis. We do so in a manner that highlights both the critical role of the capsular polysaccharide and the accompanying and necessary protein determinants. Understanding the complex interplay between host and pathogen is necessary to find new ways to prevent pneumococcal infection. This review is an attempt to do so with consideration for the latest research findings.

The role of Toll-like receptor 9 in gynecologic cancer

Toll-like receptor 9 (TLR9) plays a major role in the fight against DNA viruses infections. Despite its antitumor properties, inappropriate activation of TLR9 during chronic inflammation may cause the activation of transcription factors inducing pro-cancerous activities. Thus, the relationship between TLR9 and cancer remains highly confrontational especially in gynecological cancers and cervical cancer induced by viruses. In this review, we focus on the beneficial and detrimental role of TLR9 in gynecological carcinogenesis. TLR9 contributes to tumor regression by inducing cytotoxic T cell response (CTL), reducing the numbers of myeloid-derived suppressor cells (MDSCs), the tumor-associated macrophages (TAMs) and the regulatory T cells (T regs). It can however, also promote tumor progression and invasiveness of cervical tissue. Therefore, the dichotomous role of TLR9 needs to be carefully investigated in the setting of neoplastic disease.

Inflammasome/IL-1β Responses to Streptococcal Pathogens

Inflammation mediated by the inflammasome and the cytokine IL-1β are some of the earliest and most important alarms to infection. These pathways are responsive to the virulence factors that pathogens use to subvert immune processes, and thus are typically activated only by microbes with potential to cause severe disease. Among the most serious human infections are those caused by the pathogenic streptococci, in part because these species numerous strategies for immune evasion. Since the virulence factor armament of each pathogen is unique, the role of IL-1β and the pathways leading to its activation varies for each infection. This review summarizes the role of IL-1β during infections caused by streptococcal pathogens, with emphasis on emergent mechanisms and concepts countering paradigms determined for other organisms.

Angptl4 is upregulated under inflammatory conditions in the bone marrow of mice, expands myeloid progenitors, and accelerates reconstitution of platelets after myelosuppressive therapy

BACKGROUND

Upon inflammation, myeloid cell generation in the bone marrow (BM) is broadly enhanced by the action of induced cytokines which are produced locally and at multiple sites throughout the body.

METHODS

Using microarray studies, we found that Angptl4 is upregulated in the BM during systemic inflammation.

RESULTS

Recombinant murine Angptl4 (rmAngptl4) stimulated the proliferation of myeloid colony-forming units (CFUs) in vitro. Upon repeated in vivo injections, rmAngptl4 increased BM progenitor cell frequency and this was paralleled by a relative increase in phenotypically defined granulocyte-macrophage progenitors (GMPs). Furthermore, in vivo treatment with rmAngptl4 resulted in elevated platelet counts in steady-state mice while allowing a significant acceleration of reconstitution of platelets after myelosuppressive therapy. The administration of rmAngptl4 increased the number of CD61(+)CD41(low)-expressing megakaryocytes (MK) in the BM of steady-state and in the spleen of transplanted mice. Furthermore, rmAngptl4 improved the in vitro differentiation of immature MKs from hematopoietic stem and progenitor cells. Mechanistically, using a signal transducer and activator of transcription 3 (STAT3) reporter knockin model, we show that rmAngptl4 induces de novo STAT3 expression in immature MK which could be important for the effective expansion of MKs after myelosuppressive therapy.

CONCLUSION

Whereas the definitive role of Angptl4 in mediating the effects of lipopolysaccharide (LPS) on the BM has to be demonstrated by further studies involving multiple cytokine knockouts, our data suggest that Angptl4 plays a critical role during hematopoietic, especially megakaryopoietic, reconstitution following stem cell transplantation.

Toll-Like Receptor 9-Mediated Inflammation Triggers Alveolar Bone Loss in Experimental Murine Periodontitis

Chronic periodontitis is a local inflammatory disease induced by a dysbiotic microbiota and leading to destruction of the tooth-supporting structures. Microbial nucleic acids are abundantly present in the periodontium, derived through release after phagocytic uptake of microbes and/or from biofilm-associated extracellular DNA. Binding of microbial DNA to its cognate receptors, such as Toll-like receptor 9 (TLR9), can trigger inflammation. In this study, we utilized TLR9 knockout (TLR9(-/-)) mice and wild-type (WT) controls in a murine model of Porphyromonas gingivalis-induced periodontitis and report the first in vivo evidence that TLR9 signaling mediates the induction of periodontal bone loss. P. gingivalis-infected WT mice exhibited significantly increased bone loss compared to that in sham-infected WT mice or P. gingivalis-infected TLR9(-/-) mice, which were resistant to bone loss. Consistent with this, the expression levels of interleukin 6 (IL-6), tumor necrosis factor (TNF), and receptor-activator of nuclear factor kappa B ligand (RANKL) were significantly elevated in the gingival tissues of the infected WT mice but not in infected TLR9(-/-) mice compared to their levels in controls. Ex vivo studies using splenocytes and bone marrow-derived macrophages revealed significantly diminished cytokine production in TLR9(-/-) cells relative to the cytokine production in WT cells in response to P. gingivalis, thereby implicating TLR9 in inflammatory responses to this organism. Intriguingly, compared to the cytokine production in WT cells, TLR9(-/-) cells exhibited significantly decreased proinflammatory cytokine production upon challenge with lipopolysaccharide (LPS) (TLR4 agonist) or Pam3Cys (TLR2 agonist), suggesting possible cross talk between TLR9, TLR4, and TLR2. Collectively, our results provide the first proof-of-concept evidence implicating TLR9-triggered inflammation in periodontal disease pathogenesis, thereby identifying a new potential therapeutic target to control periodontal inflammation.

Mechanisms of interferon-γ production by neutrophils and its function during Streptococcus pneumoniae pneumonia

Bacterial pneumonia is a common public health problem associated with significant mortality, morbidity, and cost. Neutrophils are usually the earliest leukocytes to respond to bacteria in the lungs. Neutrophils rapidly sequester in the pulmonary microvasculature and migrate into the lung parenchyma and alveolar spaces, where they perform numerous effector functions for host defense. Previous studies showed that migrated neutrophils produce IFN-γ early during pneumonia induced by Streptococcus pneumoniae and that early production of IFN-γ regulates bacterial clearance. IFN-γ production by neutrophils requires Rac2, Hck/Lyn/Fgr Src family tyrosine kinases, and NADPH oxidase. Our current studies examined the mechanisms that regulate IFN-γ production by lung neutrophils during acute S. pneumoniae pneumonia in mice and its function. We demonstrate that IFN-γ production by neutrophils is a tightly regulated process that does not require IL-12. The adaptor molecule MyD88 is critical for IFN-γ production by neutrophils. The guanine nucleotide exchange factor CalDAG-GEFI modulates IFN-γ production. The CD11/CD18 complex, CD44, Toll-like receptors 2 and 4, TRIF, and Nrf2 are not required for IFN-γ production by neutrophils. The recently described neutrophil-dendritic cell hybrid cell, identified by its expression of Ly6G and CD11c, is present at low numbers in pneumonic lungs and is not a source of IFN-γ. IFN-γ produced by neutrophils early during acute S. pneumoniae pneumonia induces transcription of target genes in the lungs, which are critical for host defense. These studies underline the complexity of the neutrophil responses during pneumonia in the acute inflammatory response and in subsequent resolution or initiation of immune responses.

TLR9: an important molecule in the fight against hepatitis B virus

Hepatitis B virus (HBV) is the most prevalent infectious agent that can induce severe liver disease. Patients infected with long-term HBV, including chronic, asymptomatic and occult forms, cannot clear HBV from infected hepatocytes completely. It is not clear why some people can clear the infection while others cannot. Furthermore, the main mechanisms responsible for progression of the infections are not fully understood. It has been hypothesised that differences in genetic and immunological parameters between patients and subjects who successfully clear HBV infections are responsible for inducing the long-term forms of the infection. Previous investigations showed that Toll-like receptors (TLRs) play important roles in immune responses, especially innate immunity, against viral infections, including hepatitis B. TLR9 detects intracellular viral dsDNA, which results in the activation of an immune response against HBV. However, defects in this system may result in an attenuated response ultimately leading to long-term HBV infections. Targeting the defects in TLR9 or reactivating the downstream pathways that are normally switched on by TLR9 in response to HBV infection is a new approach to the treatment of long-term HBV infection. However, the pathways and defects seen in patients with long-term HBV need to be thoroughly explored before therapeutics can be applied in the clinical setting. Furthermore, the apparently multigenic nature of long-term HBV infection suggests that treatment of patients may need to be personalised.

The role of macrophages in the innate immune response to Streptococcus pneumoniae and Staphylococcus aureus: mechanisms and contrasts

Macrophages are critical mediators of innate immune responses against bacteria. The Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus express a range of virulence factors, which challenge macrophages' immune competence. We review how macrophages respond to this challenge. Macrophages employ a range of strategies to phagocytose and kill each pathogen. When the macrophages capacity to clear bacteria is overwhelmed macrophages play important roles in orchestrating the inflammatory response through pattern recognition receptor-mediated responses. Macrophages also ensure the inflammatory response is tightly constrained, to avoid tissue damage, and play an important role in downregulating the inflammatory response once initial bacterial replication is controlled.

Macrophages sense and kill bacteria through carbon monoxide-dependent inflammasome activation

Microbial clearance by eukaryotes relies on complex and coordinated processes that remain poorly understood. The gasotransmitter carbon monoxide (CO) is generated by the stress-responsive enzyme heme oxygenase-1 (HO-1, encoded by Hmox1), which is highly induced in macrophages in response to bacterial infection. HO-1 deficiency results in inadequate pathogen clearance, exaggerated tissue damage, and increased mortality. Here, we determined that macrophage-generated CO promotes ATP production and release by bacteria, which then activates the Nacht, LRR, and PYD domains-containing protein 3 (NALP3) inflammasome, intensifying bacterial killing. Bacterial killing defects in HO-1-deficient murine macrophages were restored by administration of CO. Moreover, increased CO levels enhanced the bacterial clearance capacity of human macrophages and WT murine macrophages. CO-dependent bacterial clearance required the NALP3 inflammasome, as CO did not increase bacterial killing in macrophages isolated from NALP3-deficient or caspase-1-deficient mice. IL-1β cleavage and secretion were impaired in HO-1-deficient macrophages, and CO-dependent processing of IL-1β required the presence of bacteria-derived ATP. We found that bacteria remained viable to generate and release ATP in response to CO. The ATP then bound to macrophage nucleotide P2 receptors, resulting in activation of the NALP3/IL-1β inflammasome to amplify bacterial phagocytosis by macrophages. Taken together, our results indicate that macrophage-derived CO permits efficient and coordinated regulation of the host innate response to invading microbes.

Recognition of Streptococcus pneumoniae and muramyl dipeptide by NOD2 results in potent induction of MMP-9, which can be controlled by lipopolysaccharide stimulation

Matrix metallopeptidase 9 (MMP-9) is a protease involved in the degradation of extracellular matrix collagen. Evidence suggests that MMP-9 is involved in pathogenesis during Streptococcus pneumoniae infection. However, not much is known about the induction of MMP-9 and the regulatory processes involved. We show here that the Gram-positive bacteria used in this study induced large amounts of MMP-9, in contrast to the Gram-negative bacteria that were used. An important pathogen-associated molecular pattern (PAMP) for Gram-positive bacteria is muramyl dipeptide (MDP). MDP is a very potent inducer of MMP-9 and showed a dose-dependent MMP-9 induction. Experiments using peripheral blood mononuclear cells (PBMCs) from Crohn's disease patients with nonfunctional NOD2 showed that MMP-9 induction by Streptococcus pneumoniae and MDP is NOD2 dependent. Increasing amounts of lipopolysaccharide (LPS), an important PAMP for Gram-negative bacteria, resulted in decreasing amounts of MMP-9. Moreover, the induction of MMP-9 by MDP could be counteracted by simultaneously adding LPS. The inhibition of MMP-9 expression by LPS was found to be regulated posttranscriptionally, independently of tissue inhibitor of metalloproteinase 1 (TIMP-1), an endogenous inhibitor of MMP-9. Collectively, these data show that Streptococcus pneumoniae is able to induce large amounts of MMP-9. These high MMP-9 levels are potentially involved in Streptococcus pneumoniae pathogenesis.

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.

Noncovalent association of protein and capsular polysaccharide on bacteria-sized latex beads as a model for polysaccharide-specific humoral immunity to intact gram-positive extracellular bacteria

Intact Streptococcus pneumoniae expressing type 14 capsular polysaccharide (PPS14) and type III S. agalactiae containing a PPS14 core capsule identical to PPS14 exhibit noncovalent associations of PPS14 and bacterial protein, in contrast to soluble covalent conjugates of these respective Ags. Both bacteria and conjugates induce murine PPS14-specific IgG responses dependent on CD4⁺ T cells. Further, secondary immunization with conjugate and S. agalactiae, although not S. pneumoniae, results in a boosted response. However, in contrast to conjugate, PPS14-specific IgG responses to bacteria lack affinity maturation use the 44.1-idiotype and are dependent on marginal zone B cells. To better understand the mechanism underlying this dichotomy, we developed a minimal model of intact bacteria in which PPS14 and pneumococcal surface protein A (PspA) were stably attached to 1 μm (bacteria-sized) latex beads, but not directly linked to each other, in contrast to PPS14-PspA conjugate. Beads coated simultaneously with PPS14+[PspA], similar to conjugate, induced in mice boosted PPS14-specific IgG secondary responses, dependent on T cells and ICOS-dependent costimulation, and in which priming could be achieved with PspA alone. In contrast to conjugate, but similar to intact bacteria, the primary PPS14-specific IgG response to beads coated simultaneously with PPS14+[PspA] peaked rapidly, with the secondary response highly enriched for the 44.1-idiotype and lacking affinity maturation. These results demonstrate that noncovalent association in a particle, of polysaccharide and protein, recapitulates essential immunologic characteristics of intact bacteria that are distinct from soluble covalent conjugates of these respective Ags.

Differential use of TLR2 and TLR9 in the regulation of immune responses during the infection with Trypanosoma cruzi

Pathogens express ligands for several TLRs that may play a role in the induction or control of the inflammatory response during infection. Concerning Trypanosoma cruzi, the agent of Chagas disease, we have previously characterized glycosylphosphatidylinositol (GPI) anchored mucin-like glycoproteins (tGPI-mucin) and unmethylated CpG DNA sequences as TLR2 and TLR9 agonists, respectively. Here we sought to determine how these TLRs may modulate the inflammatory response in the following cell populations: F4/80⁺CD11b⁺ (macrophages), F4/80^lowCD11b⁺ (monocytes) and MHCII⁺CD11c^high (dendritic cells). For this purpose, TLR2^−/− and TLR9^−/− mice were infected with Y strain of T. cruzi and different immunological parameters were evaluated. According to our previous data, a crucial role of TLR9 was evidenced in the establishment of Th1 response, whereas TLR2 appeared to act as immunoregulator in the early stage of infection. More precisely, we demonstrated here that TLR2 was mainly used by F4/80⁺CD11b⁺ cells for the production of TNF-α. In the absence of TLR2, an increased production of IL-12/IL-23p40 and IFN-γ was noted suggesting that TLR2 negatively controls the Th1 response. In contrast, TLR9 was committed to IL-12/IL-23p40 production by MHCII⁺CD11c^high cells that constitute the main source of IL-12/IL-23p40 during infection. Importantly, a down-regulation of TLR9 response was observed in F4/80⁺CD11b⁺ and F4/80^lowCD11b⁺ populations that correlated with the decreased TLR9 expression level in these cells. Interestingly, these cells recovered their capacity to respond to TLR9 agonist when MHCII⁺CD11c^high cells were impeded from producing IL-12/IL-23p40, thereby indicating possible cross-talk between these populations. The differential use of TLR2 and TLR9 by the immune cells during the acute phase of the infection explains why TLR9- but not TLR2-deficient mice are susceptible to T. cruzi infection.

Limited anti-inflammatory role for interleukin-1 receptor like 1 (ST2) in the host response to murine postinfluenza pneumococcal pneumonia

Interleukin-1 receptor like 1 (ST2) is a negative regulator of Toll-like receptor (TLR) signaling. TLRs are important for host defense during respiratory tract infections by both influenza and Streptococcus (S.) pneumoniae. Enhanced susceptibility to pneumococcal pneumonia is an important complication following influenza virus infection. We here sought to determine the role of ST2 in primary influenza A infection and secondary pneumococcal pneumonia. ST2 knockout (st2^−/−) and wild-type (WT) mice were intranasally infected with influenza A virus; in some experiments mice were infected 2 weeks later with S. pneumoniae. Both mouse strains cleared the virus similarly during the first 14 days of influenza infection and had recovered their weights equally at day 14. Overall st2^−/− mice tended to have a stronger pulmonary inflammatory response upon infection with influenza; especially 14 days after infection modest but statistically significant elevations were seen in lung IL-6, IL-1β, KC, IL-10, and IL-33 concentrations and myeloperoxidase levels, indicative of enhanced neutrophil activity. Interestingly, bacterial lung loads were higher in st2^−/− mice during the later stages of secondary pneumococcal pneumonia, which was associated with relatively increased lung IFN-γ levels. ST2 deficiency did not impact on gross lung pathology in either influenza or secondary S. pneumoniae pneumonia. These data show that ST2 plays a limited anti-inflammatory role during both primary influenza and postinfluenza pneumococcal pneumonia.

Combining a peptide vaccine with oral ingestion of Lentinula edodes mycelia extract enhances anti-tumor activity in B16 melanoma-bearing mice

New anticancer vaccines must overcome regulatory T cell (Treg)-mediated immunosuppression. We previously reported that oral ingestion of Lentinula edodes mycelia (L.E.M.) extract restores melanoma-reactive T cells in melanoma-bearing mice via a mitigation of Treg-mediated immunosuppression. In this study, we investigated the effect of oral ingestion of the extract on peptide vaccine-induced anti-tumor activity. The day after subcutaneous inoculation in the footpad with B16 melanoma, mice were freely fed the extract and were vaccinated with a tyrosinase-related protein 2(180-188) peptide. The peptide vaccine was repeated thrice weekly. Melanoma growth was significantly suppressed in mice treated with both the peptide vaccine and L.E.M. extract compared with mice treated with vaccine or extract alone, and the effect was CD8(+) T cell-dependent. The combination therapy increased H-2K(b)-restricted and B16 melanoma-reactive T cells in the draining lymph nodes and spleen. Flow cytometric and immunohistological analyses revealed that the combination therapy significantly decreased the percentage of Tregs in the draining lymph nodes and spleen of melanoma-bearing mice compared to treatment with vaccine or extract alone. Kinetic analyses of peptide-specific T cells and Tregs revealed that induction of peptide-specific T cells by the peptide vaccine alone was transient, but when combined with L.E.M. extract, it efficiently prolonged the duration of peptide-specific T cell induction without increasing the percentage of Tregs. These results indicate that combination therapy enhances peptide vaccine-induced anti-tumor activity due to attenuation of the increase in the percentage of Tregs in tumor-bearing hosts.

Immune receptors involved in Streptococcus suis recognition by dendritic cells

Streptococcus suis is an important swine pathogen and an emerging zoonotic agent of septicemia and meningitis. Knowledge on host immune responses towards S. suis, and strategies used by this pathogen for subversion of these responses is scarce. The objective of this study was to identify the immune receptors involved in S. suis recognition by dendritic cells (DCs). Production of cytokines and expression of co-stimulatory molecules by DCs were shown to strongly rely on MyD88-dependent signaling pathways, suggesting that DCs recognize S. suis and become activated mostly through Toll-like receptor (TLR) signaling. Supporting this fact, TLR2^−/− DCs were severely impaired in the release of several cytokines and the surface expression of CD86 and MHC-II. The release of IL-12p70 and CXC10, and the expression of CD40 were found to depend on signaling by both TLR2 and TLR9. The release of IL-23 and CXCL1 were partially dependent on NOD2. Finally, despite the fact that MyD88 signaling was crucial for DC activation and maturation, MyD88-dependent pathways were not implicated in S. suis internalization by DCs. This first study on receptors involved in DC activation by S. suis suggests a major involvement of MyD88 signaling pathways, mainly (but not exclusively) through TLR2. A multimodal recognition involving a combination of different receptors seems essential for DC effective response to S. suis.

The role of TLR2 in the host response to pneumococcal pneumonia in absence of the spleen

Background

Asplenic individuals are susceptible for overwhelming infection with Streptococcus pneumoniae, carrying a high mortality. Although Toll-like receptor (TLR)-2 is considered the major receptor for Gram-positive bacteria in innate immunity, it does not play a major role in host defense against pneumococcal pneumonia. We wanted to investigate if in absence of an intact spleen as a first line of defense, the role of TLR2 during pneumococcal pneumonia becomes more significant, thereby explaining its insignificant role during infections in immune competent hosts.

Methods

We intranasally infected splenectomized wildtype (WT), TLR2 knock-out (KO) and TLR2/4 double KO mice with either serotype 2 or 3 S. pneumoniae.

Results

There were no differences between asplenic WT and TLR2KO mice of bacterial loads in lung homogenates and blood, cytokine and chemokine levels in the lungs, and lung pathology scores. TLR2/4 double KO mice were not impaired in bacterial control as well, which indicates that besides the interaction between S. pneumoniae and TLR2, the interaction between pneumolysin and TLR4 does not stimulate antibacterial defense in the asplenic host either.

Conclusions

These results argue against a significant role of TLR2 in host defense during S. pneumoniae pneumonia in the asplenic state. Therefore, other components can provide sufficient backup mechanisms for TLR2 deficiency in the defense against intrapulmonary infections with S. pneumoniae of the otherwise immune competent host.

Interleukin 1 receptor-associated kinase m impairs host defense during pneumococcal pneumonia

BACKGROUND

 Streptococcus pneumoniae is the most common causative organism in community-acquired pneumonia. Pneumococci that try to invade the lower airways are recognized by innate immune cells through pattern recognition receptors, including Toll-like receptors 2, 4, and 9. Interleukin 1 (IL-1) receptor-associated kinase (IRAK)-M is a proximal inhibitor of Toll-like receptor signaling.

METHODS

To determine the role of IRAK-M in host defense during pneumococcal pneumonia, IRAK-M- deficient and wild-type mice were intranasally infected with S. pneumoniae.

RESULTS

IRAK-M-deficient mice demonstrated a reduced lethality after infection with S. pneumoniae via the airways. Whereas bacterial burdens were similar in IRAK-M-deficient and wild-type mice early (3 hours) after infection, from 24 hours onward the number of pneumococci recovered from lungs and distant body sites were 10-100-fold lower in the former mouse strain. The diminished bacterial growth and dissemination in IRAK-M-deficient mice were preceded by an increased early influx of neutrophils into lung tissue and elevated pulmonary levels of IL-1β and CXCL1. IRAK-M deficiency did not influence bacterial growth after intravenous administration of S. pneumoniae.

CONCLUSIONS

These data suggest that IRAK-M impairs host defense during pneumococcal pneumonia at the primary site of infection at least in part by inhibiting the early immune response.

Targeting pattern recognition receptors in cancer immunotherapy

Pattern recognition receptors (PRRs) are known for many years for their role in the recognition of microbial products and the subsequent activation of the immune system. The 2011 Nobel Prize for medicine indeed rewarded J. Hoffmann/B. Beutler and R. Steinman for their revolutionary findings concerning the activation of the immune system, thus stressing the significance of understanding the mechanisms of activation of the innate immunity. Such immunostimulatory activities are of major interest in the context of cancer to induce long-term antitumoral responses. Ligands for the toll-like receptors (TLRs), a well-known family of PRR, have been shown to have antitumoral activities in several cancers. Those ligands are now undergoing extensive clinical investigations both as immunostimulant molecules and as adjuvant along with vaccines. However, when considering the use of these ligands in tumor therapy, one shall consider the potential effect on the tumor cells themselves as well as on the entire organism. Recent data indeed demonstrate that TLR activation in tumor cells could trigger both pro- or antitumoral effect depending on the context. This review discusses this balance between the intrinsic activation of PRR in tumor cells and the extrinsic microenvironment activation in term of overall effect of PRR ligands on tumor development. We review recent advances in the field and underline appealing prospects for clinical development of PRR agonists in the light of our current knowledge on their expression and activation.

Expression of Toll-like receptors 2, 4 and 9 in patients with Guillain-Barré syndrome

OBJECTIVE

A myriad of transcription factors and inflammatory cytokines have been described to participate in the pathogenesis of Guillain-Barré syndrome (GBS). However, the innate immunity components--Toll-like receptors (TLRs)--have never been explored in this disease. We therefore investigated the expression of TLR2, 4 and 9 in the peripheral circulation of GBS patients as well as healthy controls.

METHODS

Twenty-one GBS patients and 21 healthy donors participated in this study. Peripheral blood mononuclear cells were used for mRNA and protein analysis of TLR-related molecules. Also, peripheral blood mononuclear cells from different subjects were incubated with different TLR agonists and the subsequent IFN-γ secretion was determined.

RESULTS

Expression of TLR2, 4 and 9 as well as their related signaling molecules were higher in GBS patients compared to healthy controls. Disability scores of GBS patients had a strong positive correlation with the high levels of expression of TLR2, 4 and 9.

CONCLUSIONS

The TLR signaling pathway may be involved in the pathogenesis of GBS.

Distinct Toll-like receptor signals regulate cerebral parasite load and interferon α/β and tumor necrosis factor α-dependent T-cell infiltration in the brains of Trypanosoma brucei-infected mice

BACKGROUND

The penetration of T cells and trypanosomes into the brain parenchyma is a major pathogenetic event in African trypanosomiasis.

METHODS

The role of innate immune responses in the penetration of T cells and Trypanosoma brucei brucei into the brain was studied in knockout mice by using double immunofluorescent staining and real-time polymerase chain reaction.

RESULTS

We demonstrate that Toll-like receptor (TLR)-MyD88-mediated signaling is required for T-cell and parasite penetration into the brain and microglial activation, besides controlling parasitemia and antigen-specific T-cell activation. Among different TLR-deficient mice studied, TLR9 mediated parasitemia control and T-cell penetration into the brain. TLR-MyD88 signals increased levels of interferon (IFN) β and tumor necrosis factor (TNF) α transcripts in the brains of infected mice and both TNF-α and IFN-α/β, receptors promoted T-cell and trypanosoma infiltration into the brain parenchyma. Both resident and infiltrating inflammatory cells in the brain controlled parasite densities in a TLR2- and TLR9-MyD88-mediated manner. However, neither IFN-α/β nor TNF-α contributed to parasite control in the brain.

CONCLUSIONS

Our data indicate that innate immune TLR signals stimulate the expression of TNF-α and IFN-α/β that initiate brain invasion of T cells and trypanosomes, and control T. brucei brucei load in the brain by molecules distinct from these.

Pathogenesis and pathophysiology of pneumococcal meningitis

Pneumococcal meningitis continues to be associated with high rates of mortality and long-term neurological sequelae. The most common route of infection starts by nasopharyngeal colonization by Streptococcus pneumoniae, which must avoid mucosal entrapment and evade the host immune system after local activation. During invasive disease, pneumococcal epithelial adhesion is followed by bloodstream invasion and activation of the complement and coagulation systems. The release of inflammatory mediators facilitates pneumococcal crossing of the blood-brain barrier into the brain, where the bacteria multiply freely and trigger activation of circulating antigen-presenting cells and resident microglial cells. The resulting massive inflammation leads to further neutrophil recruitment and inflammation, resulting in the well-known features of bacterial meningitis, including cerebrospinal fluid pleocytosis, cochlear damage, cerebral edema, hydrocephalus, and cerebrovascular complications. Experimental animal models continue to further our understanding of the pathophysiology of pneumococcal meningitis and provide the platform for the development of new adjuvant treatments and antimicrobial therapy. This review discusses the most recent views on the pathophysiology of pneumococcal meningitis, as well as potential targets for (adjunctive) therapy.

Toll-like receptors in health and disease in the brain: mechanisms and therapeutic potential

The discovery of mammalian TLRs (Toll-like receptors), first identified in 1997 based on their homology with Drosophila Toll, greatly altered our understanding of how the innate immune system recognizes and responds to diverse microbial pathogens. TLRs are evolutionarily conserved type I transmembrane proteins expressed in both immune and non-immune cells, and are typified by N-terminal leucine-rich repeats and a highly conserved C-terminal domain termed the TIR [Toll/interleukin (IL)-1 receptor] domain. Upon stimulation with their cognate ligands, TLR signalling elicits the production of cytokines, enzymes and other inflammatory mediators that can have an impact on several aspects of CNS (central nervous system) homoeostasis and pathology. For example, TLR signalling plays a crucial role in initiating host defence responses during CNS microbial infection. Furthermore, TLRs are targets for many adjuvants which help shape pathogen-specific adaptive immune responses in addition to triggering innate immunity. Our knowledge of TLR expression and function in the CNS has greatly expanded over the last decade, with new data revealing that TLRs also have an impact on non-infectious CNS diseases/injury. In particular, TLRs recognize a number of endogenous molecules liberated from damaged tissues and, as such, influence inflammatory responses during tissue injury and autoimmunity. In addition, recent studies have implicated TLR involvement during neurogenesis, and learning and memory in the absence of any underlying infectious aetiology. Owing to their presence and immune-regulatory role within the brain, TLRs represent an attractive therapeutic target for numerous CNS disorders and infectious diseases. However, it is clear that TLRs can exert either beneficial or detrimental effects in the CNS, which probably depend on the context of tissue homoeostasis or pathology. Therefore any potential therapeutic manipulation of TLRs will require an understanding of the signals governing specific CNS disorders to achieve tailored therapy.

Clostridium butyricum activates TLR2-mediated MyD88-independent signaling pathway in HT-29 cells

Oral administration of Clostridium butyricum as probiotic is increasingly gaining importance in the treatment of diarrhea and the improvement of animal performance. However, the mechanisms of host cell receptor recognition of C. butyricum and the downstream immune signaling pathways leading to these benefits remain unclear. The objective of this study was to analyze the mechanisms involved in C. butyricum induction of the toll-like receptor (TLR) signaling. Knockdown of myeloid differentiation primary response protein 88 (MyD88) expression using small interfering RNA in this manner did not affect C. butyricum-induced elevated levels of nuclear factor κB (NF-κB), interleukin-8 (IL-8), IL-6, and tumor necrosis factor alpha (TNF-α), suggesting a MyD88-independent route to TLR signaling transduction. However, a significant reduction in the levels of NF-κB, IL-8, IL-6, and TNF-α was evident in the absence of TLR2 expression, implying the need for TLR2 in C. butyricum recognition. Hence, C. butyricum activates TLR2-mediated MyD88-independent signaling pathway in human epithelial cells, which adds to our understanding of the molecular mechanisms of this probiotic action on gut epithelium.

Alcohol abuse and Streptococcus pneumoniae infections: consideration of virulence factors and impaired immune responses

Alcohol is the most frequently abused substance in the world. Both acute and chronic alcohol consumption have diverse and well-documented effects on the human immune system, leading to increased susceptibility to infections like bacterial pneumonia. Streptococcus pneumoniae is the most common bacterial etiology of community-acquired pneumonia worldwide. The frequency and severity of pneumococcal infections in individuals with a history of alcohol abuse is much higher than the general population. Despite this obvious epidemiological relevance, very few experimental studies have focused on the interaction of pneumococci with the immune system of a host acutely or chronically exposed to alcohol. Understanding these host-pathogen interactions is imperative for designing effective prophylactic and therapeutic interventions for such populations. Recent advances in pneumococcal research have greatly improved our understanding of pneumococcal pathogenesis and virulence mechanisms. Additionally, a large body of data is available on the effect of alcohol on the physiology of the lungs and the innate and adaptive immune system of the host. The purpose of this review is to integrate the available knowledge in these diverse areas of for a better understanding of the how the compromised immune system derived from alcohol exposure responds to pneumococcal infections.

Inactivation of TLR9 by a suppressive oligodeoxynucleotides can ameliorate the clinical signs of EAN

Susceptible-strain animals immunized with P2 peptide could generate the disease of experimental autoimmune neuritis (EAN) with inflammation and demyelination of peripheral nerve. A myriad of transcription factors and inflammatory cytokines have been found to participate in this process; however, the roles of toll-like receptors (TLRs) are poorly understood in EAN. The aim of this study is to explore the role of TLR9 in the pathogenesis of EAN. The EAN was induced in Lewis rat by immunization with P2(53-78) and complete Freund's adjuvant. CpG oligodeoxynucleotides (ODN) (cODN), a suppressive ODN (sODN) and a control non-specific ODN (nODN) were respectively administered to explore the role of TLR9 in EAN both in vivo and vitro. Following immunization up to the peak phase of EAN, EAN rats inoculated with sODN had remarkably better clinical score of EAN and expressed a significantly inhibited TLR9 signaling pathway. Our study suggests that TLR9 may be involved in the pathogenesis of EAN.

Importance of Toll-like receptor 9 in host defense against M1T1 group A Streptococcus infections

Timely recognition and elimination of invasive group A Streptococcus (GAS) by innate immunity is crucial to control infection. The intracellular pattern recognition receptor Toll-like receptor 9 (TLR9) promotes macrophage hypoxia-inducible factor-1α levels, oxidative burst and nitric oxide production in response to GAS. TLR9 contributes to GAS clearance in vivo in both localized cutaneous and systemic infection models.

TLR1/2 activation during heterologous prime-boost vaccination (DNA-MVA) enhances CD8+ T Cell responses providing protection against Leishmania (Viannia)

BACKGROUND

Leishmania (Viannia) parasites present particular challenges, as human and murine immune responses to infection are distinct from other Leishmania species, indicating a unique interaction with the host. Further, vaccination studies utilizing small animal models indicate that modalities and antigens that prevent infection by other Leishmania species are generally not protective.

METHODOLOGY

Using a newly developed mouse model of chronic L. (Viannia) panamensis infection and the heterologous DNA prime - modified vaccinia virus Ankara (MVA) boost vaccination modality, we examined whether the conserved vaccine candidate antigen tryparedoxin peroxidase (TRYP) could provide protection against infection/disease.

RESULTS

Heterologous prime - boost (DNA/MVA) vaccination utilizing TRYP antigen can provide protection against disease caused by L. (V.) panamensis. However, protection is dependent on modulating the innate immune response using the TLR1/2 agonist Pam3CSK4 during DNA priming. Prime-boost vaccination using DNA alone fails to protect. Prior to infection protectively vaccinated mice exhibit augmented CD4 and CD8 IFNγ and memory responses as well as decreased IL-10 and IL-13 responses. IL-13 and IL-10 have been shown to be independently critical for disease in this model. CD8 T cells have an essential role in mediating host defense, as CD8 depletion reversed protection in the vaccinated mice; vaccinated mice depleted of CD4 T cells remained protected. Hence, vaccine-induced protection is dependent upon TLR1/2 activation instructing the generation of antigen specific CD8 cells and restricting IL-13 and IL-10 responses.

CONCLUSIONS

Given the general effectiveness of prime-boost vaccination, the recalcitrance of Leishmania (Viannia) to vaccine approaches effective against other species of Leishmania is again evident. However, prime-boost vaccination modality can with modulation induce protective responses, indicating that the delivery system is critical. Moreover, these results suggest that CD8 T cells should be targeted for the development of a vaccine against infection caused by Leishmania (Viannia) parasites. Further, TLR1/2 modulation may be useful in vaccines where CD8 T cell responses are critical.

Role of phosphoinositide 3-kinase-Akt signaling pathway in the age-related cytokine dysregulation in splenic macrophages stimulated via TLR-2 or TLR-4 receptors

Age-associated defects in both B-lymphocytes and macrophages in elderly result in a reduction in the efficacy of vaccines to many Gram positive bacteria like Streptococcus pneumoniae. Splenic macrophages from aged mice have been shown to have a defect in production of pro-inflammatory cytokines (IL-6, IL-12, IL-1β, TNF-α) but exhibit increased production of IL-10 upon TLR-4 ligation. Here we showed that aged macrophages demonstrate similar cytokine dysregulation phenotype upon stimulation with TLR-2 ligands, or killed S. pneumoniae. We hypothesized that an age-associated increase in activity of phosphatidyl inositol 3-kinase (PI3K)-Akt signaling pathway may be playing a causal role in the age-associated cytokine dysregulation. We found that gene expression of both the regulatory (p85β) and the catalytic (p110δ) subunits of Class IA PI3K is higher in aged than in young splenic macrophages. The age-associated increase in the activity of PI3K was also demonstrated by an upregulation of P-Akt and its downstream target, glycogen synthase kinase-3 (GSK-3). Inhibition of PI3K enhanced induction of pro-inflammatory cytokines, by TLR-2/TLR-1, TLR-2/TLR-6 and TLR-4 ligands as well as heat killed S. pneumoniae (HKSP). Therefore, targeting PI3-Kinase could rescue cytokine dysregulation in aged macrophages and enhance the relevant pro-inflammatory cytokines needed to support B-cell activation and differentiation.

Synergistic interactions of TLR2/6 and TLR9 induce a high level of resistance to lung infection in mice

Infectious pneumonias exact an unacceptable mortality burden worldwide. Efforts to protect populations from pneumonia have focused historically on antibiotic development and vaccine-enhanced adaptive immunity. However, we have reported recently that the lungs' innate defenses can be induced therapeutically by inhalation of a bacterial lysate that protects mice against otherwise lethal pneumonia. In this study, we tested in mice the hypothesis that TLRs are required for this antimicrobial phenomenon and found that resistance could not be induced in the absence of the TLR signaling adaptor protein MyD88. We then attempted to recapitulate the protection afforded by the bacterial lysate by stimulating the lung epithelium with aerosolized synthetic TLR ligands. Although most single or combination treatments yielded no protection, simultaneous treatment with ligands for TLR2/6 and TLR9 conferred robust, synergistic protection against virulent gram-positive and gram-negative pathogens. Protection was associated with rapid pathogen killing in the lungs, and pathogen killing could be induced from lung epithelial cells in isolation. Taken together, these data demonstrate the requirement for TLRs in inducible resistance against pneumonia, reveal a remarkable, unanticipated synergistic interaction of TLR2/6 and TLR9, reinforce the emerging evidence supporting the antimicrobial capacity of the lung epithelium, and may provide the basis for a novel clinical therapeutic that can protect patients against pneumonia during periods of peak vulnerability.

Type I interferons protect from Toll-like receptor 9-associated liver injury and regulate IL-1 receptor antagonist in mice

BACKGROUND & AIMS

Liver inflammation and injury are mediated by the innate immune response, which is regulated by Toll-like receptors (TLR). Activation of TLR9 induces type I interferons (IFNs) via the interferon regulatory factor (IRF)-7. We investigated the roles of type I IFNs in TLR9-associated liver injury.

METHODS

Wild-type (WT), IRF7-deficient, and IFN-α/β receptor 1 (IFNAR1)-deficient mice were stimulated with TLR9 or TLR2 ligands. Findings from mice were verified in cultured hepatocytes and liver mononuclear cells (LMNCs) as well as in vivo experiments using recombinant type I IFN and interleukin-1 receptor antagonist (IL-1ra).

RESULTS

Type I IFNs were up-regulated during TLR9-associated liver injury in WT mice. IRF7- and IFNAR1-deficient mice, which have disruptions in type I IFN production or signaling, respectively, had increased liver damage and inflammation, decreased recruitment of dendritic cells, and increased production of tumor necrosis factor α by LMNCs. These findings indicate that type I IFNs have anti-inflammatory activities in liver. IL-1ra, which is produced by LMNCs and hepatocytes, is an IFN-regulated antagonist of the proinflammatory cytokine IL-1β; IRF7- and IFNAR1-deficient mice had decreased levels of IL-1ra compared with WT mice. IL-1ra protected cultured hepatocytes from IL-1β-mediated sensitization to cytotoxicity from tumor necrosis factor α. In vivo exposure to type I IFN, which induced IL-1ra, or administration of IL-1ra reduced TLR9-associated liver injury; the protective effect of type I IFNs therefore appears to be mediated by IFN-dependent induction of IL-1ra.

CONCLUSIONS

Type I IFNs have anti-inflammatory effects mediated by endogenous IL-1ra, which regulates the extent of TLR9-induced liver damage. Type I IFN signaling is therefore required for protection from immune-mediated liver injury.

Morphine inhibits murine dendritic cell IL-23 production by modulating Toll-like receptor 2 and Nod2 signaling

IL-23, produced by dendritic cells (DCs) and macrophages, plays a critical role in innate immunity against bacterial infection. Our previous studies show that morphine disrupts the IL-23/IL-17 mediated pulmonary mucosal host defense and increases susceptibility to Streptococcus pneumoniae lung infection. To determine the mechanism by which morphine modulates IL-23 production, mouse bone marrow-derived dendritic cells (BMDCs) and macrophages (BMDMs) were treated with morphine, and infected with S. pneumoniae or stimulated with Toll-like receptor (TLR) and Nod2 ligands. We found that a significant increase in IL-23 protein production was observed in S. pneumoniae, TLR2 ligand lipoteichoic acid (LTA), and TLR4 ligand pneumolysin (PLY) stimulated BMDCs and BMDMs. Interestingly, although Nod2 ligand muramyldipeptide (MDP) alone had no effect on IL-23 production, it potentiated LTA induced IL-23 production to the same level as that observed following S. pneumoniae infection, suggesting that S. pneumoniae induced IL-23 production in DCs involves activation of both TLR2 and Nod2 signaling mechanisms. Furthermore, pretreatment of DCs with MyD88 (myeloid differentiation primary response gene 88) and IL-1 receptor-associated kinase (IRAK) 1/4 inhibitors, or TLR2 antibody diminished the S. pneumoniae induced IL-23 and abolished the inhibitory effects of morphine, indicating that S. pneumoniae induced IL-23 production depends on activation of the TLR2-MyD88-IRAK1/4 signaling pathway. Moreover, morphine decreased S. pneumoniae induced phosphorylation of interferon regulatory factor 3 (IRF3) and activating transcription factor 2 in DCs. Taken together, our study shows that morphine impairs S. pneumoniae induced IL-23 production through MyD88-IRAK1/4-dependent TLR2 and Nod2 signaling in DCs.

Targeting the TLR9-MyD88 pathway in the regulation of adaptive immune responses

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are innate immune receptors critical in the innate immune defense against invading pathogens. Recent advances also reveal a crucial role for TLRs in shaping adaptive immune responses, conferring a potential therapeutic value to their modulation in the treatment of diseases.

AREAS COVERED IN THIS REVIEW

The aim of this review is to discuss TLR9, the TLR9-MyD88 signaling pathway and its role in regulation of adaptive immune responses, as well as potential therapeutic implications by targeting this pathway.

WHAT THE READER WILL GAIN

This review shows that the TLR9-MyD88 signaling pathway plays a critical role in promoting adaptive immune responses and that modulation of this pathway may have enormous therapeutic potential in enhancing vaccine potency, controlling autoimmunity, as well as improving the outcome of viral-vector-mediated gene therapy.

TAKE HOME MESSAGE

Although TLR9 agonists have been used as adjuvants for enhancing vaccine potency, further exploitation of the TLR9-MyD88 pathway and its dynamic interaction with the immune system in vivo is needed to provide more effective therapeutic inventions in the design of vaccines for infectious diseases, allergies and cancer, in the control of autoimmunity, as well as in the improvement of viral-vector-mediated gene therapy.

Pneumococci: immunology of the innate host response

Despite the development of vaccines and antibiotics, Streptococcus pneumoniae (the pneumococcus) continues to be a major cause of human morbidity and mortality throughout the world. In recent years our understanding of how the host innate immune system recognizes and responds to pneumococcal infection has advanced significantly. Herein, we highlight some of the key features of the innate response to the pneumococcus.

New understandings on the pathophysiology of bacterial meningitis

PURPOSE OF REVIEW

Currently, dexamethasone is the only adjuvant of proven benefit in bacterial meningitis. Dexamethasone halves the risk of poor outcome, but only in selected patient groups. New therapies based upon an understanding of the pathophysiology are needed. This article summarizes our knowledge on the pathophysiology of bacterial meningitis with special emphasis on pneumococcal meningitis, the experimentally best characterized subtype.

RECENT FINDINGS

Experimental studies made clear that the harmful inflammatory reaction is initiated by the interaction of bacterial products with host pattern recognition receptors (PRRs) such as Toll-like receptors. PRR signalling leads to MyD88-dependent production of proinflammatory cytokines of the interleukin-1 family. Secretion of interleukin-1 family cytokines forms a positive feedback loop that boosts MyD88-dependent production of proinflammatory mediators. As a consequence, great numbers of neutrophils are recruited to the subarachnoid space. Activated neutrophils release many potentially cytotoxic agents including oxidants and matrix metalloproteinases that can cause collateral damage to brain tissue. Additionally to the inflammatory response, direct bacterial cytotoxicity has been identified as a contributor to tissue damage.

SUMMARY

Promising pathophysiologically targeted approaches for adjunctive therapy of acute bacterial meningitis include limiting the release of toxic bacterial products (e.g. nonbacteriolytic antibiotics) and interfering in the generation of host-derived cytotoxins.