Cooperative interactions between TLR4 and TLR9 regulate interleukin 23 and 17 production in a murine model of gram negative bacterial pneumonia

Klebsiella pneumoniae emerging anti-immunology paradigms: from stealth to evasion

Klebsiella pneumoniae (KP) is a global threat to human health due to the isolation of multidrug-resistant strains. Despite advancements in understanding KP's population structure, antibiotic resistance mechanisms, and transmission patterns, a gap remains in how KP evades defenses, allowing the pathogen to flourish in tissues despite an activated immune system. KP infection biology has been shaped by the notion that the pathogen has evolved to shield from defenses more than actively suppress them. This review describes new paradigms of how KP exploits the coevolution with the innate immune system to hijack immune effectors and receptors to ablate signaling pathways and to counteract cell-intrinsic immunity, making apparent that KP can no longer be considered only as a stealth pathogen.

Interleukin-23 Involved in Fibrotic Autoimmune Diseases: New Discoveries

Interleukin (IL)-23 is a central pro-inflammatory cytokine with a broad range of effects on immune responses. IL-23 is pathologically linked to the induction of the production of the pro-inflammatory cytokines IL-17 and IL-22, which stimulate the differentiation and proliferation of T helper type 17 (Th17) cells. Recent discoveries suggest a potential pro-fibrotic role for IL-23 in the development of chronic inflammatory autoimmune diseases characterized by intense fibrosis. In this review, we summarized the biological features of IL-23 and gathered recent research on the role of IL-23 in fibrotic autoimmune conditions, which could provide a theoretical basis for clinical targeting and drug development.

Immunometabolic control by Klebsiella pneumoniae

Klebsiella pneumoniae is a common Gram-negative pathogen associated with community-acquired and healthcare-associated infections. Its ability to acquire genetic elements resulted in its rapid development of resistance to virtually all antimicrobial agents. Once infection is established, K. pneumoniae is able to evade the host immune response and perhaps more importantly, undergo metabolic rewiring to optimize its ability to maintain infection. K. pneumoniae lipopolysaccharide and capsular polysaccharide are central factors in the induction and evasion of immune clearance. Less well understood is the importance of immunometabolism, the intersection between cellular metabolism and immune function, in the host response to K. pneumoniae infection. Bacterial metabolism itself is perceived as a metabolic stress to the host, altering the microenvironment at the site of infection. In this review, we will discuss the metabolic responses induced by K. pneumoniae, particularly in response to stimulation with the metabolically active bacteria versus pathogen-associated molecular patterns alone, and their implications in shaping the nature of the immune response and the infection outcome. A better understanding of the immunometabolic response to K. pneumoniae may help identify new targets for therapeutic intervention in the treatment of multidrug-resistant bacterial infections.

Novel adjuvant nano-vaccine induced immune response against Acinetobacter baumannii

Developing adjuvant vaccines to combat rising multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infections is a promising and cost-effective approach. The aim of this analysis was to construct a pDNA-CPG C274-adjuvant nano-vaccine and investigate its immunogenicity and protection in BALB/c mice. The CPG ODN C274 adjuvant was chemically synthesized and cloned into pcDNA3.1( +), and the cloning was verified using PCR and BamHI/EcoRV restriction enzyme digestion. Then, utilizing a complex coacervation approach, pDNA-CPG C274 was encapsulated by chitosan (CS) nanoparticles (NPs). TEM and DLS are used to explore the properties of the pDNA/CSNP complex. TLR-9 pathway activation was investigated in human HEK-293 and RAW 264.7 mouse cells. The vaccine's immunogenicity and immune-protective effectiveness were investigated in BALB/c mice. The pDNA-CPG C274/CSNPs were small (mean size 79.21 ± 0.23 nm), positively charged (+ 38.87 mV), and appeared to be spherical. A continuous slow release pattern was achieved. TLR-9 activation was greatest in the mouse model with CpG ODN (C274) at concentrations of 5 and 10 μg/ml with 56% and 55%, respectively (**P < 0.01). However, in HEK-293 human cells, by increasing the concentration of CpG ODN (C274) from 1 to 50 μg/ml, the activation rate of TLR-9 also increased, so that the highest activation rate (81%) was obtained at the concentration of 50 μg/ml (***P < 0.001). pDNA-CPG C274/CSNPs immunized BALB/c mice produced increased amounts of total-IgG, as well as IFN-γ and IL-1B in serum samples, compared to non-encapsulated pDNA-CPG C274. Furthermore, liver and lung injuries, as well as bacterial loads in the liver, lung, and blood, were reduced, and BALB/c mice immunized with pDNA-CPG C274/CSNPs showed potent protection (50-75%) against acute fatal Intraperitoneal A. baumannii challenge. pDNA-CPG C274/CSNPs evoked total-IgG antibodies, Th1 cellular immunity, and the TLR-9 pathway, as well as protection against an acute fatal A. baumannii challenge. Our findings suggest that this nano-vaccine is a promising approach for avoiding A. baumannii infection when used as a powerful adjuvant.

Microbial-Derived Toll-like Receptor Agonism in Cancer Treatment and Progression

Simple Summary

Toll like receptors (TLRs) are a group of transmembrane receptors belonging to the class of pattern recognition receptors (PRR), which are involved in recognition of pathogen associated molecular patterns (PAMPs), inducing immune response. During the past decade, a number of preclinical and clinical breakthroughs in the field of TLR agonists has immerged in cancer research and some of these agents have performed exceptionally well in clinical trials. Based on evidence from scientific studies, we draw attention to several microbial based TLR agonists and discuss their relevance in various cancer and explore various microbial based TLR agonists for developing effective immunotherapeutic strategies against cancer.

Abstract

Toll-like receptors (TLRs) are typical transmembrane proteins, which are essential pattern recognition receptors in mediating the effects of innate immunity. TLRs recognize structurally conserved molecules derived from microbes and damage-associated molecular pattern molecules that play an important role in inflammation. Since the first discovery of the Toll receptor by the team of J. Hoffmann in 1996, in Drosophila melanogaster, numerous TLRs have been identified across a wide range of invertebrate and vertebrate species. TLR stimulation leads to NF-κB activation and the subsequent production of pro-inflammatory cytokines and chemokines, growth factors and anti-apoptotic proteins. The expression of TLRs has also been observed in many tumors, and their stimulation results in tumor progression or regression, depending on the TLR and tumor type. The anti-tumoral effects can result from the activation of anti-tumoral immune responses and/or the direct induction of tumor cell death. The pro-tumoral effects may be due to inducing tumor cell survival and proliferation or by acting on suppressive or inflammatory immune cells in the tumor microenvironment. The aim of this review is to draw attention to the effects of TLR stimulation in cancer, the activation of various TLRs by microbes in different types of tumors, and, finally, the role of TLRs in anti-cancer immunity and tumor rejection.

Bacterial Cyclic Dinucleotides and the cGAS-cGAMP-STING Pathway: A Role in Periodontitis?

Host cells can recognize cytosolic double-stranded DNAs and endogenous second messengers as cyclic dinucleotides-including c-di-GMP, c-di-AMP, and cGAMP-of invading microbes via the critical and essential innate immune signaling adaptor molecule known as STING. This recognition activates the innate immune system and leads to the production of Type I interferons and proinflammatory cytokines. In this review, we (1) focus on the possible role of bacterial cyclic dinucleotides and the STING/TBK1/IRF3 pathway in the pathogenesis of periodontal disease and the regulation of periodontal immune response, and (2) review and discuss activators and inhibitors of the STING pathway as immune response regulators and their potential utility in the treatment of periodontitis. PubMed/Medline, Scopus, and Web of Science were searched with the terms "STING", "TBK 1", "IRF3", and "cGAS"-alone, or together with "periodontitis". Current studies produced evidence for using STING-pathway-targeting molecules as part of anticancer therapy, and as vaccine adjuvants against microbial infections; however, the role of the STING/TBK1/IRF3 pathway in periodontal disease pathogenesis is still undiscovered. Understanding the stimulation of the innate immune response by cyclic dinucleotides opens a new approach to host modulation therapies in periodontology.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Comprehensive characterization of hepatocyte-derived extracellular vesicles identifies direct miRNA-based regulation of hepatic stellate cells and DAMP-based hepatic macrophage IL-1β and IL-17 upregulation in alcoholic hepatitis mice

Extracellular vesicles (EVs) have been growingly recognized as biomarkers and mediators of alcoholic liver disease (ALD) in human and mice. Here we characterized hepatocyte-derived EVs (HC-EVs) and their cargo for their biological functions in a novel murine model that closely resembles liver pathology observed in patients with alcoholic hepatitis (AH), the most severe spectrum of ALD. The numbers of circulating EVs and HC-EVs were significantly increased by 10-fold in AH mice compared with control mice. The miRNA (miR)-seq analysis detected 20 upregulated and 4 downregulated miRNAs (P < 0.001-0.05) in AH-HC-EVs. Treatment of murine primary hepatic stellate cells (HSCs) with AH-HC-EVs induced α-SMA (P < 0.05) and Col1a1 (P < 0.001). Smad7 and Nr1d2 genes, which were downregulated in HSCs from the AH mice, were predicted targets of 20 miRs upregulated in AH-HC-EVs. Among them were miR-27a and miR-181 which upon transfection in HSCs, indeed repressed Nr1d2, the quiescent HSC marker. AH-HC-EVs were also enriched with organelle proteins and mitochondrial DNA (10-fold, P < 0.05) and upregulated IL-1β and IL-17 production by hepatic macrophages (HMs) from AH mice in a TLR9-dependent manner. These results demonstrate HC-EV release is intensified in AH and suggest that AH-HC-EVs orchestrate liver fibrogenesis by directly targeting the quiescent HSC transcripts via a unique set of miRNAs and by amplifying HSC activation via DAMP-based induction of profibrogenic IL-1β and IL-17 by HMs. KEY MESSAGES: • Circulating EVs and HC-EVs were increased in AH mice compared with control mice • AH-HC-EVs were enriched in miRNAs, organelle proteins, and mitochondrial DNA • AH-HC-EVs increased cytokine production by AH-HMs in a TLR9-dependent manner.

Effect of Toll-like receptor 4 deficiency on clinical severity and expression of Th1/Th2/Th17-associated cytokines in a murine model of experimental autoimmune neuritis

INTRODUCTION

The aim was to observe the effect of Toll-like receptor 4 (TLR4) deficiency on clinical severity and expression of Th1/Th2/Th17-associated cytokines in experimental autoimmune neuritis (EAN).

MATERIAL AND METHODS

We selected C57BL/10 wild type (WT) mice and TLR4 knockout (KO) mice with the C57BL/10 background for induction of the EAN model by immunizing mice twice (days 0 and 8) via subcutaneous injection of 180 μg P0 peptide 180-199 emulsion in 25 μl of PBS and 0.5 mg Mycobacterium tuberculosis (Difco, USA) in 25 μl of Freund's incomplete adjuvant into the back of mice. The concentrations of serum cytokines (IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ and TNF) were determined using the Ms Th1/Th2/Th17 CBA kit.

RESULTS

We found that TLR4 deficiency could attenuate the clinical severity and delay the onset of EAN. Moreover, our data showed that the sera levels of IFN-γ, TNF, IL-6 and IL-17A were elevated in the WT mice with EAN when compared with the naive WT mice, but only the production of IL-17A was significantly lower in the TLR4 KO mice with EAN than in their WT counterparts.

CONCLUSIONS

Based on these findings, TLR4 may contribute to the pathogenesis of EAN by regulating Th17 cells and the production of Th17-associated factors. However, the exact mechanism remains unclear and more evidence is needed to elucidate its role in EAN.

Identification of RBP4 from bighead carp (Hypophthalmichthys nobilis) / silver carp (Hypophthalmichthys molitrix) and effects of CpG ODN on RBP4 expression under A. hydrophila challenge

Retinol-binding protein 4 (RBP4) is known as a highly conserved adipokine for immune activation. Aeromonas hydrophila (A. hydrophila) is the most common zoonotic pathogen in aquaculture, which causes serious economic losses to aquaculture, especially to bighead carp (Hypophthalmichthys nobilis, H. nobilis) and silver carp (Hypophthalmichthys molitrix, H. molitrix). Recent studies along with our previous findings have shown that synthetic oligodeoxynucleotides containing CpG motifs (CpG ODN) can play a good role in aquatic animals against infection. In order to clarify the relationship between CpG ODN and RBP4 under A. hydrophila infection, firstly, full-length RBP4 cDNAs from H. nobilis and H. molitrix were cloned. And characteristics of RBP4, including sequence and structure, tissue distribution and genetic evolution were analyzed. In addition, mRNA expression levels of RBP4, cytokine, toll-like receptors (TLRs), morbidity and survival rates of H. nobilis and H. molitrix were observed post CpG ODN immunization or following challenge. The results indicated that hn/hm_RBP4 (RBP4 genes obtained from H. nobilis and H. molitrix) had the highest homology with Megalobrama amblycephala. Distribution data showed that the expression level of hn_RBP4 mRNA was higher than that of hm_RBP4. After CpG ODN immunization followed by A.hydrophila challenge, significantly higher survival was observed in both carps, together with up-regulated RBP4 expression. Meanwhile, hn/hm_IL-1β level was relatively flat (and decreased), hn/hm_IFN-γ, hn/hm_TLR4 and hn/hm_TLR9 levels increased significantly, but hn/hm_STRA6 showed no significant change, compared with control. Moreover, CpG ODN immunization could induce stronger immune protective responses (higher IFN-γ/gentle IL-1β level and lower morbidity/higher survival rate) against A. hydrophila in H. nobilis, along with higher RBP4 level, when compared with that in H. molitrix. These results demonstrated that RBP4 was well involved in the immune protection of CpG ODN. Based on the results, we speculated that in the case of A. hydrophila infection, TLR9 signaling pathway was activated by CpG ODN. Subsequently, CpG ODN up-regulated RBP4, and RBP4 activated TLR4 signaling pathway. Then TLR4 and TLR9 synergistically improved the anti-infection responses. Our findings have good significance for improving resistance to pathogen infection in freshwater fish.

Preclinical Efficacy of a Trivalent Human FcγRI-Targeted Adjuvant-Free Subunit Mucosal Vaccine against Pulmonary Pneumococcal Infection

Lack of safe and effective mucosal adjuvants has severely hampered the development of mucosal subunit vaccines. In this regard, we have previously shown that immunogenicity of vaccine antigens can be improved by targeting the antigens to the antigen-presenting cells. Specifically, groups of mice immunized intranasally with a fusion protein (Bivalent-FP) containing a fragment of pneumococcal-surface-protein-A (PspA) as antigen and a single-chain bivalent antibody raised against the anti-human Fc-gamma-receptor-I (hFcγRI) elicited protective immunity to pulmonary Streptococcus pneumoniae infection. In order to further enhance the immunogenicity, an additional hFcγRI-binding moiety of the single chain antibody was incorporated. The modified vaccine (Trivalent-FP) induced significantly improved protection against lethal pulmonary S. pneumoniae challenge compared to Bivalent-FP. In addition, the modified vaccine exhibited over 85% protection with only two immunizations. Trivalent-FP also induced S. pneumoniae-specific systemic and mucosal antibodies. Moreover, Trivalent-FP also induced IL-17- and IL-22-producing CD4⁺ T cells. Furthermore, it was found that the hFcγRI facilitated uptake and presentation of Trivalent-FP. In addition, Trivalent-FP also induced IL-1α, MIP-1α, and TNF-α; modulated recruitment of dendritic cells and macrophages; and induced CD80/86 and MHC-II expression on antigen presenting cells.

Interleukin 23 and autoimmune diseases: current and possible future therapies

PURPOSE

IL-23 is a central proinflammatory cytokine with a wide range of influence over immune response. It is implicated in several autoimmune diseases due to the infinite inflammatory loops it can create through the positive feedbacks of both IL-17 and IL-22 arms. This made IL-23 a key target of autoimmune disorders therapy, which indeed was proven to inhibit inflammation and ameliorate diseases. Current autoimmune treatments targeting IL-23 are either by preventing IL-23 ligation to its receptor (IL-23R) via antibodies or inhibiting IL-23 signaling by signaling downstream mediators' inhibitors, with each approach having its own pros and cons.

METHODS

Literature review was done to further understand the biology of IL-23 and current therapies.

RESULTS

In this review, we discuss the biological features of IL-23 and its role in the pathogenesis of autoimmune diseases including psoriasis, rheumatoid arthritis and inflammatory bowel diseases. Advantages, limitations and side effects of each concept will be reviewed, suggesting several advanced IL-23-based bio-techniques to generate new and possible future therapies to overcome current treatments problems.

Toll-like receptor 4: A promising therapeutic target for pneumonia caused by Gram-negative bacteria

Gram‐negative bacteria (GNB) emerge as important pathogens causing pulmonary infection, which can develop into sepsis due to bacterial resistance to antibiotics. GNB pneumonia poses a huge social and economic burden all over the world. During GNB infection in the lung, Toll‐like receptor 4 (TLR4) can form a complex with MD2 and CD14 after recognizing lipopolysaccharide of GNB, initiate the MyD88‐ and TRIF‐dependent signalling pathways and stimulate host non‐specific immune response. In this review, we summarize recent progress in our understanding of the role of TLR4 in GNB pneumonia. The latest experimental results, especially in TLR4 knockout animals, suggest a promising potential of targeting TLR4 signalling pathway for the treatment of GNB pneumonia. Furthermore, we highlight the benefits of Traditional Chinese Medicine as novel candidates for the therapy of GNB pneumonia due to the modulation of TLR4 signalling pathway. Finally, we discuss the promise and challenge in the development of TLR4‐based drugs for GNB pneumonia.

Klebsiella pneumoniae infection biology: living to counteract host defences

Klebsiella species cause a wide range of diseases including pneumonia, urinary tract infections (UTIs), bloodstream infections and sepsis. These infections are particularly a problem among neonates, elderly and immunocompromised individuals. Klebsiella is also responsible for a significant number of community-acquired infections. A defining feature of these infections is their morbidity and mortality, and the Klebsiella strains associated with them are considered hypervirulent. The increasing isolation of multidrug-resistant strains has significantly narrowed, or in some settings completely removed, the therapeutic options for the treatment of Klebsiella infections. Not surprisingly, this pathogen has then been singled out as an 'urgent threat to human health' by several organisations. This review summarises the tremendous progress that has been made to uncover the sophisticated immune evasion strategies of K. pneumoniae. The co-evolution of Klebsiella in response to the challenge of an activated immune has made Klebsiella a formidable pathogen exploiting stealth strategies and actively suppressing innate immune defences to overcome host responses to survive in the tissues. A better understanding of Klebsiella immune evasion strategies in the context of the host-pathogen interactions is pivotal to develop new therapeutics, which can be based on antagonising the anti-immune strategies of this pathogen.

Induction of inducible nitric oxide synthase (iNOS) in Porphyromonas gingivalis LPS-treated mouse macrophage cell line (RAW264.7) requires Toll-like receptor 9

OBJECTIVE

The aim of this study is to investigate the involvement of TLR9 in the regulation of iNOS expression and nitric oxide (NO) production in Porphyromonas gingivalis LPS-treated mouse macrophages.

METHODS

Mouse macrophage cell line (RAW264.7) was transfected with siRNAs against TLR9 and then stimulated with P. gingivalis LPS. At indicated time points, the activated cells were lysed. Gene and protein expression of iNOS were determined by RT-PCR and immunoblotting, respectively. The level of nitric oxide (NO) production in the supernatant of the activated cells was determined by Griess reaction assay.

RESULTS AND CONCLUSION

Depletion of TLR9 in mouse macrophages demonstrated the markedly decreased iNOS gene and protein expression by P. gingivalis LPS compared to those of the wild-type or control siRNA transfected cells. In consistent with these results, the level of NO secretion was also significantly diminished in TLR9-depleted cells after challenged with P. gingivalis LPS. These results indicate that TLR9 involves in the regulation of the iNOS expression and the NO secretion in P. gingivalis LPS-treated macrophages.

Bacterial pathogenesis and interleukin-17: interconnecting mechanisms of immune regulation, host genetics, and microbial virulence that influence severity of infection

Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Natural killer cell-intrinsic type I IFN signaling controls Klebsiella pneumoniae growth during lung infection

Klebsiella pneumoniae is a significant cause of nosocomial pneumonia and an alarming pathogen owing to the recent isolation of multidrug resistant strains. Understanding of immune responses orchestrating K. pneumoniae clearance by the host is of utmost importance. Here we show that type I interferon (IFN) signaling protects against lung infection with K. pneumoniae by launching bacterial growth-controlling interactions between alveolar macrophages and natural killer (NK) cells. Type I IFNs are important but disparate and incompletely understood regulators of defense against bacterial infections. Type I IFN receptor 1 (Ifnar1)-deficient mice infected with K. pneumoniae failed to activate NK cell-derived IFN-γ production. IFN-γ was required for bactericidal action and the production of the NK cell response-amplifying IL-12 and CXCL10 by alveolar macrophages. Bacterial clearance and NK cell IFN-γ were rescued in Ifnar1-deficient hosts by Ifnar1-proficient NK cells. Consistently, type I IFN signaling in myeloid cells including alveolar macrophages, monocytes and neutrophils was dispensable for host defense and IFN-γ activation. The failure of Ifnar1-deficient hosts to initiate a defense-promoting crosstalk between alveolar macrophages and NK cell was circumvented by administration of exogenous IFN-γ which restored endogenous IFN-γ production and restricted bacterial growth. These data identify NK cell-intrinsic type I IFN signaling as essential driver of K. pneumoniae clearance, and reveal specific targets for future therapeutic exploitations.

IL-36γ is a crucial proximal component of protective type-1-mediated lung mucosal immunity in Gram-positive and -negative bacterial pneumonia

Interleukin-36γ (IL-36γ) is a member of novel IL-1-like proinflammatory cytokine family that are highly expressed in epithelial tissues and several myeloid-derived cell types. Little is known about the role of the IL-36 family in mucosal immunity, including lung anti-bacterial responses. We used murine models of IL-36γ deficiency to assess the contribution of IL-36γ in the lung during experimental pneumonia. Induction of IL-36γ was observed in the lung in response to Streptococcus pneumoniae (Sp) infection, and mature IL-36γ protein was secreted primarily in microparticles. IL-36γ-deficient mice challenged with Sp demonstrated increased mortality, decreased lung bacterial clearance and increased bacterial dissemination, in association with reduced local expression of type-1 cytokines, and impaired lung macrophage M1 polarization. IL-36γ directly stimulated type-1 cytokine induction from dendritic cells in vitro in a MyD88-dependent manner. Similar protective effects of IL-36γ were observed in a Gram-negative pneumonia model (Klebsiella pneumoniae). Intrapulmonary delivery of IL-36γ-containing microparticles reconstituted immunity in IL-36γ^-/- mice. Enhanced expression of IL-36γ was also observed in plasma and bronchoalveolar lavage fluid of patients with acute respiratory distress syndrome because of pneumonia. These studies indicate that IL-36γ assumes a vital proximal role in the lung innate mucosal immunity during bacterial pneumonia by driving protective type-1 responses and classical macrophage activation.

Induction of endogenous retroelements as a potential mechanism for mouse-specific drug-induced carcinogenicity

A number of chemical compounds have been shown to induce liver tumors in mice but not in other species. While several mechanisms for this species-specific tumorigenicity have been proposed, no definitive mechanism has been established. We examined the effects of the nongenotoxic rodent hepatic carcinogen, WY-14,643, in male mice from a high liver tumor susceptible strain (C3H/HeJ), and from a low tumor susceptible strain (C57BL/6). WY-14,643, a PPARα activator induced widespread increases in the expression of some endogenous retroelements, namely members of LTR and LINE elements in both strains. The expression of a number of known retroviral defense genes was also elevated. We also demonstrated that basal immune-mediated viral defense was elevated in C57BL/6 mice (the resistant strain) and that WY-14,643 further activated those immuno-defense processes. We propose that the previously reported >100X activity of retroelements in mice drives mouse-specific tumorigenicity. We also propose that C57BL/6's competent immune to retroviral activation allows it to remove cells before the activation of these elements can result in significant chromosomal insertions and mutation. Finally, we showed that WY-14,643 treatment induced gene signatures of DNA recombination in the sensitive C3H/HeJ strain.

Gram-negative bacteria facilitate tumor outgrowth and metastasis by promoting lipid synthesis in lung cancer patients

BACKGROUND

Lung cancer is the leading cause of cancer-related death worldwide. Patients with lung cancer are very frequently present with pulmonary infections, in particular with Gram-negative bacteria. Herein, we investigated the effect of the co-presence of Gram-negative bacteria on outgrowth and metastasis of lung cancer cells in clinical patients.

METHODS

Lung cancer cells were isolated from clinical surgical tissues. Heat-inactivated E. coli was used as Gram-negative bacteria. Tumor outgrowth and invasion in vitro was analyzed with MTT assay and Biocoat Matrigel Invasion Chamber. Tumor growth and metastasis in vivo was evaluated in BALB/c nude mice. Lipid synthesis was evidenced by expressions of FASN and ACC1, as well as BODIPY Fluorophores staining. Block lipid synthesis was performed with C75 as a FAS inhibitor and transfection with ACC1 siRNA. Knockdown of TLR4 and TLR9 signaling was achieved by transfection with specific shRNAs and administration of specific antagonists.

RESULTS

Gram-negative bacteria significantly promoted lung cancer development including growth and metastasis in dose dependent manner. Mechanistically, Gram-negative bacteria activate TLR4 and TLR9 signaling and enhance lipid synthesis in human lung cancer cells. Knockdown of TLR4 and/or TLR9 was able to block Gram-negative bacteria mediated lipid synthesis and lung cancer development. Interference with lipid synthesis efficiently abrogated Gram-negative-bacteria-induced lung cancer development. In lung cancer patients, higher expressions of innate immune receptors, TLR4 and TLR9, were observed in those with Gram-negative infections and associated with the aberrant lipid synthesis that was observed in vitro.

CONCLUSIONS

Pulmonary infections with Gram-negative bacteria lead to aberrant lipid synthesis through TLR4 and TLR9 signaling in lung cancer patients and result in rapid proliferation and metastasis of lung cancer cells. These findings reveal a new mechanism for pulmonary infection-trigged caner development and provide clues for exploring therapeutics for lung cancer patients.

Klebsiella pneumoniae: Going on the Offense with a Strong Defense

Klebsiella pneumoniae causes a wide range of infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Historically, K. pneumoniae has caused serious infection primarily in immunocompromised individuals, but the recent emergence and spread of hypervirulent strains have broadened the number of people susceptible to infections to include those who are healthy and immunosufficient. Furthermore, K. pneumoniae strains have become increasingly resistant to antibiotics, rendering infection by these strains very challenging to treat. The emergence of hypervirulent and antibiotic-resistant strains has driven a number of recent studies. Work has described the worldwide spread of one drug-resistant strain and a host defense axis, interleukin-17 (IL-17), that is important for controlling infection. Four factors, capsule, lipopolysaccharide, fimbriae, and siderophores, have been well studied and are important for virulence in at least one infection model. Several other factors have been less well characterized but are also important in at least one infection model. However, there is a significant amount of heterogeneity in K. pneumoniae strains, and not every factor plays the same critical role in all virulent Klebsiella strains. Recent studies have identified additional K. pneumoniae virulence factors and led to more insights about factors important for the growth of this pathogen at a variety of tissue sites. Many of these genes encode proteins that function in metabolism and the regulation of transcription. However, much work is left to be done in characterizing these newly discovered factors, understanding how infections differ between healthy and immunocompromised patients, and identifying attractive bacterial or host targets for treating these infections.

STAT6 Signaling Attenuates Interleukin-17-Producing γδ T Cells during Acute Klebsiella pneumoniae Infection

γδ T cells are prevalent at mucosal and epithelial surfaces and are a critical first line of defense against bacterial and fungal pathogens. γδ17 cells are a subset of γδ T cells which, in the presence of IL-23 and IL-1β, produce large quantities of interleukin-17A (IL-17A), a cytokine crucial to these cells' antibacterial and antifungal function. STAT6, an important transcription factor in Th2 differentiation and inhibition of Th1 differentiation, is expressed at high levels in the T cells of people with parasitic infections and asthma. Our group and others have shown that STAT6 attenuates IL-17A protein expression by CD4(+) T cells. By extension, we hypothesized that STAT6 activation also inhibits innate γδ17 cell cytokine secretion. We show here that γδ17 cells expressed the type I IL-4 receptor (IL-4R), and IL-4 increased STAT6 phosphorylation in γδ T cells. IL-4 inhibited γδ17 cell production of IL-17A. IL-4 also decreased γδ17 cell expression of IL-23R as well as Sgk1. To determine whether STAT6 signaling regulates γδ17 cell numbers in vivo, we used a model of Klebsiella pneumoniae in mice deficient in STAT6. We chose K. pneumoniae for our in vivo model, since K. pneumoniae increases IL-17A expression and γδ17 numbers. K. pneumoniae infection of STAT6 knockout mice resulted in a statistically significant increase in the number of γδ17 cells compared to that of wild-type mice. These studies are the first to demonstrate that γδ17 cells express the type I IL-4R and that STAT6 signaling negatively regulates γδ17 cells, a cell population that plays a front-line role in mucosal immunity.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Novel inflammatory pathways in periodontitis

New insights into the biological mechanisms involved in modulating periodontal inflammation and alveolar bone loss are paving the way for novel therapeutic strategies for periodontitis. The neutrophil adhesion cascade for transmigration in response to infection or inflammation is a key paradigm in immunity. Developmental endothelial locus-1 (Del-1) is one of several newly identified endogenous inhibitors of the leukocyte adhesion cascade. Del-1 competes with intercellular adhesion molecule-1 (ICAM-1) on endothelial cells for binding to the LFA-1 integrin on neutrophils, thereby regulating neutrophil recruitment and local inflammation. In animal periodontitis models, Del-1 deficiency resulted in severe inflammation and alveolar bone loss, but local treatment with recombinant Del-1 prevented neutrophil infiltration and bone loss. The expression of Del-1 is inhibited by the pro-inflammatory cytokine IL-17. Nucleic-acid-receptor-mediated inflammatory responses may be important in periodontal disease pathogenesis. Bacterial nucleic acids released during inflammation are detected by host microbial DNA sensors, e.g., Toll-like receptor-9 (TLR-9), leading to the activation of pro- and/or anti-inflammatory signaling pathways. DNA from periodontitis-associated bacteria induced pro-inflammatory cytokine production in human macrophage-like cells through the TLR-9 and NF-κB signaling pathways, but had less effect on human osteoblasts. Inhibition of TLR-9 signaling in human macrophages reduced cytokine production in response to P. gingivalis DNA. Differential expression of a polymorphic site in the TLR-9 gene promoter region and increased TLR-9 gene and protein expression were reported in chronic periodontitis. Further research to confirm that periodontal bacterial DNA contributes to destructive inflammation in vivo could provide alternative therapeutic targets to control periodontitis.

Arterial Catheterization and Infection: Toll-like Receptors in Defense against Microorganisms and Therapeutic Implications

Radial artery catheterization has become a preferred route over femoral artery catheterization, in order to monitor the blood pressure of hemodynamically unstable patients or for repeated sampling of arterial blood gases. While the incidence of catheter-related infection is lower in the radial artery than the femoral artery, infection remains a major issue that requires attention. In this review of the literature, we discuss infectious complications of radial artery catheterization, with a focus on various risk factors and establishing the most common causative agents. We also critically review the role of the innate immune system involving Toll-like receptors (TLRs) in host-defense, with the goal of establishing a common pathway used by the innate immune system via TLRs to combat the pathogens that most commonly cause infection in radial artery catheterization. If this pathway can be therapeutically manipulated to preemptively attack pathogenic agents, immunomodulation may be an option in reducing the incidence of infection in this procedure.

The role of platelet MyD88 in host response during gram-negative sepsis

BACKGROUND

Beside their role in hemostasis, platelets serve as sentinel cells in host defense during infection. In sepsis, platelets have been implicated in both beneficial (antibacterial) and detrimental responses (thrombosis and organ damage). Toll-like receptors and their common adaptor, myeloid differentiation factor 88 (MyD88), are essential for pathogen recognition and protective immunity. Platelets express functional Toll-like receptors and MyD88, which participate in platelet responsiveness to bacterial agonists.

OBJECTIVE

Considering the pivotal involvement of platelets and MyD88 in the host response to bacteria, we studied the role of platelet MyD88 in gram-negative sepsis using intravenous and airway infections with the common human sepsis pathogen Klebsiella pneumoniae.

METHODS

Platelet-specific Myd88(-/-) mice were generated by crossing mice with a conditional Myd88 flox allele with mice expressing Cre recombinase controlled by the platelet factor 4 promoter. In a reverse approach, full Myd88(-/-) mice were transfused with wild-type platelets.

RESULTS

In both settings, platelet MyD88 did not impact on bacterial growth or dissemination. In addition, platelet MyD88 did not influence hallmark sepsis responses such as thrombocytopenia, coagulation or endothelial activation, or distant organ injury. Platelet MyD88 played no role in lung pathology during pneumonia-derived sepsis.

CONCLUSION

Despite known literature, platelet MyD88-dependent TLR signaling does not contribute to the host response during gram-negative sepsis.

Toll-Like Receptor 9 Contributes to Defense against Acinetobacter baumannii Infection

Acinetobacter baumannii is a common nosocomial pathogen capable of causing severe diseases associated with significant morbidity and mortality in impaired hosts. Pattern recognition receptors, such as the Toll-like receptors (TLRs), play a key role in pathogen detection and function to alert the immune system to infection. Here, we examine the role for TLR9 signaling in response to A. baumannii infection. In a murine model of A. baumannii pneumonia, TLR9(-/-) mice exhibit significantly increased bacterial burdens in the lungs, increased extrapulmonary bacterial dissemination, and more severe lung pathology compared with those in wild-type mice. Following systemic A. baumannii infection, TLR9(-/-) mice have significantly increased bacterial burdens in the lungs, as well as decreased proinflammatory cytokine and chemokine production. These results demonstrate that TLR9-mediated pathogen detection is important for host defense against the opportunistic pathogen Acinetobacter baumannii.

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.

Directing traffic: IL-17 and IL-22 coordinate pulmonary immune defense

Respiratory infections and diseases are among the leading causes of death worldwide, and effective treatments probably require manipulating the inflammatory response to pathogenic microbes or allergens. Here, we review mechanisms controlling the production and functions of interleukin-17 (IL-17) and IL-22, cytokines that direct several aspects of lung immunity. Innate lymphocytes (γδ T cells, natural killer cells, innate lymphoid cells) are the major source of IL-17 and IL-22 during acute infections, while CD4(+) T-helper 17 (Th17) cells contribute to vaccine-induced immunity. The characterization of dendritic cell (DC) subsets has revealed their central roles in T-cell activation. CD11b(+) DCs stimulated with bacteria or fungi secrete IL-1β and IL-23, potent inducers of IL-17 and IL-22. On the other hand, recognition of viruses by plasmacytoid DCs inhibits IL-1β and IL-23 release, increasing susceptibility to bacterial superinfections. IL-17 and IL-22 primarily act on the lung epithelium, inducing antimicrobial proteins and neutrophil chemoattractants. Recent studies found that stimulation of macrophages and DCs with IL-17 also contributes to antibacterial immunity, while IL-22 promotes epithelial proliferation and repair following injury. Chronic diseases such as asthma and chronic obstructive pulmonary disease have been associated with IL-17 and IL-22 responses directed against innocuous antigens. Future studies will evaluate the therapeutic efficacy of targeting the IL-17/IL-22 pathway in pulmonary inflammation.

Allergic airway inflammation decreases lung bacterial burden following acute Klebsiella pneumoniae infection in a neutrophil- and CCL8-dependent manner

The Th17 cytokines interleukin-17A (IL-17A), IL-17F, and IL-22 are critical for the lung immune response to a variety of bacterial pathogens, including Klebsiella pneumoniae. Th2 cytokine expression in the airways is a characteristic feature of asthma and allergic airway inflammation. The Th2 cytokines IL-4 and IL-13 diminish ex vivo and in vivo IL-17A protein expression by Th17 cells. To determine the effect of IL-4 and IL-13 on IL-17-dependent lung immune responses to acute bacterial infection, we developed a combined model in which allergic airway inflammation and lung IL-4 and IL-13 expression were induced by ovalbumin sensitization and challenge prior to acute lung infection with K. pneumoniae. We hypothesized that preexisting allergic airway inflammation decreases lung IL-17A expression and airway neutrophil recruitment in response to acute K. pneumoniae infection and thereby increases the lung K. pneumoniae burden. As hypothesized, we found that allergic airway inflammation decreased the number of K. pneumoniae-induced airway neutrophils and lung IL-17A, IL-17F, and IL-22 expression. Despite the marked reduction in postinfection airway neutrophilia and lung expression of Th17 cytokines, allergic airway inflammation significantly decreased the lung K. pneumoniae burden and postinfection mortality. We showed that the decreased lung K. pneumoniae burden was independent of IL-4, IL-5, and IL-17A and partially dependent on IL-13 and STAT6. Additionally, we demonstrated that the decreased lung K. pneumoniae burden associated with allergic airway inflammation was both neutrophil and CCL8 dependent. These findings suggest a novel role for CCL8 in lung antibacterial immunity against K. pneumoniae and suggest new mechanisms of orchestrating lung antibacterial immunity.

Toll-like receptor 9 deficiency protects mice against Pseudomonas aeruginosa lung infection

Pseudomonas aeruginosa is an opportunistic pathogen involved in nosocomial infections. While a number of studies have demonstrated the roles of TLR2, TLR4 and TLR5 in host defense againt P. aeruginosa infection, the implication of TLR9 in this process has been overlooked. Here, we show that P. aeruginosa DNA stimulates the inflammatory response through TLR9 pathway in both a cell line and primary alveolar macrophages (AMs). This activation requires asparagine endopeptidase- and endosomal acidification. Interestingly, TLR9^-/- mice resisted to lethal lung infection by P. aeruginosa, compared to WT C57BL/6 mice. The resistance of TLR9^-/- mice to P. aeruginosa infection was associated with: (i) a higher ability of TLR9^-/- AMs to kill P. aeruginosa; (ii) a rapid increase in the pro-inflammatory cytokines such as TNFα, IL-1β and IL-6 production; and (iii) an increase in nitric oxide (NO) production and inductible NO synthase expression in AMs. In addition, inhibition of both IL-1β and NO production resulted in a significant decrease of P. aeruginosa clearance by AMs. Altogether these results indicate that TLR9 plays a detrimental role in pulmonary host defense toward P. aeruginosa by reducing the AMs clearance activity and production of IL-1β and NO necessary for bacteria killing.

TLR4 contributes to the host response to Klebsiella intraocular infection

PURPOSE/AIM

Klebsiella pneumoniae causes a blinding infection called endogenous endophthalmitis. The role of innate immune recognition of K. pneumoniae in the eye during infection is not known. We hypothesized that intraocular recognition of K. pneumoniae was mediated by Toll-like receptor (TLR)-4 and may be dependent on MagA-regulated hypermucoviscosity.

MATERIALS AND METHODS

Experimental endophthalmitis was induced in C57BL/6J or TLR4(-/-) mice by intravitreal injection of 100 CFU of wild type or ΔmagA K. pneumoniae. Infection and inflammation were quantified by determining viable K. pneumoniae per eye, retinal responses via electroretinography, myeloperoxidase activity of infiltrating neutrophils and the proinflammatory cytokine and chemokine response.

RESULTS

C57BL/6J and TLR4(-/-) mice could not control intraocular wild-type K. pneumoniae growth. TLR4(-/-) mice were less able than C57BL/6J to control the intraocular growth of ΔmagA K. pneumoniae. Retinal function testing suggested that infection with ΔmagA K. pneumoniae resulted in less retinal function loss. There was a TLR4-dependent delay in initial neutrophil recruitment, regardless of the infecting organism. The proinflammatory cytokine/chemokine data supported these results. These findings were not due to an inability of TLR4(-/-) neutrophils to recognize or kill K. pneumoniae.

CONCLUSIONS

These studies suggest that TLR4 is important in the early intraocular recognition and host response to K. pneumoniae. However, the role of MagA in TLR4-mediated intraocular recognition and subsequent inflammation is less clear.

Intranasal vaccination promotes detrimental Th17-mediated immunity against influenza infection

Influenza disease is a global health issue that causes significant morbidity and mortality through seasonal epidemics. Currently, inactivated influenza virus vaccines given intramuscularly or live attenuated influenza virus vaccines administered intranasally are the only approved options for vaccination against influenza virus in humans. We evaluated the efficacy of a synthetic toll-like receptor 4 agonist CRX-601 as an adjuvant for enhancing vaccine-induced protection against influenza infection. Intranasal administration of CRX-601 adjuvant combined with detergent split-influenza antigen (A/Uruguay/716/2007 (H3N2)) generated strong local and systemic immunity against co-administered influenza antigens while exhibiting high efficacy against two heterotypic influenza challenges. Intranasal vaccination with CRX-601 adjuvanted vaccines promoted antigen-specific IgG and IgA antibody responses and the generation of polyfunctional antigen-specific Th17 cells (CD4⁺IL-17A⁺TNFα⁺). Following challenge with influenza virus, vaccinated mice transiently exhibited increased weight loss and morbidity during early stages of disease but eventually controlled infection. This disease exacerbation following influenza infection in vaccinated mice was dependent on both the route of vaccination and the addition of the adjuvant. Neutralization of IL-17A confirmed a detrimental role for this cytokine during influenza infection. The expansion of vaccine-primed Th17 cells during influenza infection was also accompanied by an augmented lung neutrophilic response, which was partially responsible for mediating the increased morbidity. This discovery is of significance in the field of vaccinology, as it highlights the importance of both route of vaccination and adjuvant selection in vaccine development

Influenza virus remains a global health risk causing significant morbidity and mortality each year, with the elderly (>65 years) and the very young particularly prone to severe respiratory disease. Scientists are working to develop highly efficacious vaccines capable of eliciting broad cross-clade protection from influenza infection. Adjuvants as well as the route of immunization are known to modulate the type, quality and breadth of immune responses to vaccines. In this study, we demonstrated intranasal vaccination with influenza antigens, and a novel synthetic TLR4-based adjuvant system provided protection against a lethal heterologous viral challenge. Immunization stimulated mucosal influenza-specific IgA antibody responses together with systemic IgG antibodies. While intranasal immunization stimulated the production of protective antibodies, vaccination via this route also promoted the generation of influenza-specific Th17 CD4⁺ T cells. These vaccine-induced Th17 cells increased inflammation and morbidity without contributing to viral clearance following challenge. Antibody neutralization of IL-17A during influenza infection significantly reduced the enhanced lung neutrophilic response, which was partially responsible for mediating the increased morbidity. This discovery is of significance in the field of vaccinology, as it demonstrates the importance of both route of immunization and adjuvant selection in vaccine development.

Protective role of Mincle in bacterial pneumonia by regulation of neutrophil mediated phagocytosis and extracellular trap formation

BACKGROUND

Nosocomial infections with Klebsiella pneumoniae are a frequent cause of Gram-negative bacterial sepsis. To understand the functioning of host innate immune components in this disorder, we examined a previously uninvestigated role of the C-type lectin receptor Mincle in pneumonic sepsis caused by K. pneumoniae.

METHODS

Disease progression in wild-type and Mincle(-/-) mice undergoing pulmonary infection with K. pneumoniae was compared.

RESULTS

Whereas the wild-type mice infected with a sublethal dose of bacteria could resolve the infection with bacterial clearance and regulated host response, the Mincle(-/-) mice were highly susceptible with a progressive increase in bacterial burden, despite their ability to mount an inflammatory response that turned to an exaggerated hyperinflammation with the onset of severe pneumonia. This correlated with severe lung pathology with a massive accumulation of neutrophils in their lungs. Importantly, Mincle(-/-) neutrophils displayed a defective ability to phagocytize nonopsonic bacteria and an impaired ability to form extracellular traps (NETs), an important neutrophil function against invading pathogens, including K. pneumoniae.

CONCLUSION

Our results demonstrate protective role of Mincle in host defense against K. pneumoniae pneumonia by coordinating bacterial clearance mechanisms of neutrophils. A novel role for Mincle in the regulation of neutrophil NET formation may have implications in chronic disease conditions characterized by deregulated NET formation.

IL-23 protection against Plasmodium berghei infection in mice is partially dependent on IL-17 from macrophages

Although IL-12 is believed to contribute to protective immune responses, the role played by IL-23 (a member of the IL-12 family) in malaria is elusive. Here, we show that IL-23 is produced during infection with Plasmodium berghei NK65. Mice deficient in IL-23 (p19KO) had higher parasitemia and died earlier than wild-type (WT) controls. Interestingly, p19KO mice had lower numbers of IL-17-producing splenic cells than their WT counterparts. Furthermore, mice deficient in IL-17 (17KO) suffered higher parasitemia than the WT controls, indicating that IL-23-mediated protection is dependent on induction of IL-17 during infection. We found that macrophages were responsible for IL-17 production in response to IL-23. We observed a striking reduction in splenic macrophages in the p19KO and 17KO mice, both of which became highly susceptible to infection. Thus, IL-17 appears to be crucial for maintenance of splenic macrophages. Adoptive transfer of macrophages into macrophage-depleted mice confirmed that macrophage-derived IL-17 is required for macrophage accumulation and parasite eradication in the recipient mice. We also found that IL-17 induces CCL2/7, which recruit macrophages. Our findings reveal a novel protective mechanism whereby IL-23, IL-17, and macrophages reduce the severity of infection with blood-stage malaria parasites.

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.

Innate Immune Responses in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a common complication of mechanical ventilation, resulting in substantial morbidity, mortality, and health care cost. Early upper airway colonization by pathogenic bacteria and microaspiration are the primary pathogenic events leading to VAP. Patients at risk for VAP have defects in structural/mechanical defenses of the respiratory tract. In addition, critical illness, including sepsis, trauma, and postoperative states, is associated with profound defects in both innate and acquired antibacterial immunity, influencing antimicrobial effector functions of both leukocytes and structural/parenchymal cells. Factors present within the lung microenvironment, including alveolar stretch, cyclical atelectasis, changes in oxygen tension, and respiratory tract microbiota, substantially impact antibacterial host responses. Mechanisms accounting for dysregulated immune homeostasis are incompletely understood, but likely involve: (1) alterations in the balance of pro- and anti-inflammatory cytokines; (2) changes in pathogen recognition receptor and G-protein coupled receptor expression and downstream signaling cascades; and (3) dysregulated cell death responses. Antibiotics and preventive strategies are the mainstay of therapy in patients with VAP. However, novel approaches are needed to reverse immunological reprogramming that occurs during critical illness and/or mechanical ventilation, and to identify patients who are most likely to benefit from immunomodulatory therapy.

Burn injury triggered dysfunction in dendritic cell response to TLR9 activation and resulted in skewed T cell functions

Severe trauma such as burn injury is often associated with a systemic inflammatory syndrome characterized by a hyperactive innate immune response and suppressed adaptive immune function. Dendritic cells (DCs), which sense pathogens via their Toll-like receptors (TLRs), play a pivotal role in protecting the host against infections. The effect of burn injury on TLR-mediated DC function is a debated topic and the mechanism controlling the purported immunosuppressive response remains to be elucidated. Here we examined the effects of burn injury on splenic conventional DC (cDC) and plasmacytoid DC (pDC) responses to TLR9 activation. We demonstrate that, following burn trauma, splenic cDCs' cytokine production profile in response to TLR9 activation became anti-inflammatory dominant, with high production of IL-10 (>50% increase) and low production of IL-6, TNF-α and IL-12p70 (∼25-60% reduction). CD4+ T cells activated by these cDCs were defective in producing Th1 and Th17 cytokines. Furthermore, burn injury had a more accentuated effect on pDCs than on cDCs. Following TLR9 activation, pDCs displayed an immature phenotype with an impaired ability to secrete pro-inflammatory cytokines (IFN-α, IL-6 and TNF-α) and to activate T cell proliferation. Moreover, cDCs and pDCs from burn-injured mice had low transcript levels of TLR9 and several key molecules of the TLR signaling pathway. Although hyperactive innate immune response has been associated with severe injury, our data show to the contrary that DCs, as a key player in the innate immune system, had impaired TLR9 reactivity, an anti-inflammatory phenotype, and a dysfunctional T cell-priming ability. We conclude that burn injury induced impairments in DC immunobiology resulting in suppression of adaptive immune response. Targeted DC immunotherapies to promote their ability in triggering T cell immunity may represent a strategy to improve immune defenses against infection following burn injury.

TLR9-dependent IL-23/IL-17 is required for the generation of Stachybotrys chartarum-induced hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease that develops after repeated exposure to inhaled particulate Ag. Stachybotrys chartarum is a dimorphic fungus that has been implicated in a number of respiratory illnesses, including HP. In this study, we have developed a murine model of S. chartarum-induced HP that reproduces pathology observed in human HP, and we have hypothesized that TLR9-mediated IL-23 and IL-17 responses are required for the generation of granulomatous inflammation induced by inhaled S. chartarum. Mice that undergo i.p. sensitization and intratracheal challenge with 10(6) S. chartarum spores developed granulomatous inflammation with multinucleate giant cells, accompanied by increased accumulation of T cells. S. chartarum sensitization and challenge resulted in robust pulmonary expression of IL-17 and IL-23. S. chartarum-mediated granulomatous inflammation required intact IL-23 or IL-17 responses and required TLR9, because TLR9(-/-) mice displayed reduced IL-17 and IL-23 expression in whole lung associated with decreased accumulation of IL-17 expressing CD4(+) and γδ T cells. Compared with S. chartarum-sensitized dendritic cells (DC) isolated from WT mice, DCs isolated from TLR9(-/-) mice had a reduced ability to produce IL-23 in responses to S. chartarum. Moreover, shRNA knockdown of IL-23 in DCs abolished IL-17 production from splenocytes in response to Ag challenge. Finally, the intratracheal reconstitution of IL-23 in TLR9(-/-) mice recapitulated the immunopathology observed in WT mice. In conclusion, our studies suggest that TLR9 is critical for the development of Th17-mediated granulomatous inflammation in the lung in response to S. chartarum.

Host defenses against bacterial lower respiratory tract infection

Bacterial pneumonia continues to be a significant cause of morbidity and mortality worldwide. Recent studies have shown that lung epithelia signal through pattern recognition receptors to initiate the innate immune response. Other mediators of innate immunity against bacterial pneumonia include transepithelial dendritic cells, alveolar macrophages, and innate produces of IL-17. CD4+ T cells and B cells play a key role in eliminating and preventing the development of bacterial pneumonias. B cell development and maturation can be modulated by the lung epithelia through BAFF and APRIL, furthering our current understanding of the role of epithelial cells in the immune response.

Sterile inflammatory response in acute pancreatitis

The initial injury in acute pancreatitis is characteristically sterile and results in acinar cells necrosis. Intracellular contents released from damaged cells into the extracellular space serve as damage-associated molecular patterns (DAMPs) that trigger inflammation. There is increasing evidence that this sterile inflammatory response mediated through DAMPs released from necrotic acinar cells is a key determinant of further pancreatic injury, remote organ injury, and disease resolution in experimental models. A number of DAMPS, including high-mobility group box protein 1, DNA, adenosine triphosphate and heat shock protein 70, have been shown to have a role in experimental pancreatitis. Many of these DAMPs are also detectable in the human pancreatitis. Genetic deletion and pharmacologic antagonism demonstrate that specific DAMP receptors, including Toll-like receptor (TLR) 4, TLR9, and P2X7, are also required for inflammation in experimental acute pancreatitis. Downstream DAMP-sensing components include nod-like receptor protein 3, caspase 1, interleukin-1β (IL-1), IL-18, and IL-1 receptor, and also are required for full experimental pancreatitis. These DAMP-mediated pathways provide novel therapeutic targets using antagonists of TLRs and other receptors.

Protective role of Toll-like receptor 4 in experimental gonococcal infection of female mice

Neisseria gonorrhoeae is a common bacterial sexually transmitted infection. Like all Gram-negative bacteria, the outer membrane of the gonococcus is rich in endotoxin, a known ligand for Toll-like receptor (TLR)4. However, the role of endotoxin and that of its cognate receptor TLR4 in the mucosal response to acute gonococcal infection in the genital tract of women is unclear. To test this, we examined the course of infection after vaginal inoculation of N. gonorrhoeae in mice carrying the Lps(d) mutation in Tlr4, which renders them unresponsive to endotoxin. Although there was no difference in the duration of colonization, Lps(d) mice had a significantly higher peak bacterial burden which coincided with a massive polymorphonuclear cell influx and concomitant upregulation of a subset of inflammatory cytokine and chemokine markers. Notably, infected Lps(d) mice showed a decrease in interleukin-17, suggesting that Th17 responses are more dependent on TLR4 signaling in vivo. Defective polymorphonuclear cell-mediated and complement-independent serum killing of gonococci in Lps(d) mice was also observed and may account for the increased bacterial burden. This is the first in vivo evidence that TLR4-regulated factors modulate early inflammatory responses to gonococcal infection in the female reproductive tract and control bacterial replication.

TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia

Toll-like receptors (TLRs) are required for protective host defense against bacterial pathogens. However, the role of TLRs in regulating lung injury during Gram-negative bacterial pneumonia has not been thoroughly investigated. In this study, experiments were performed to evaluate the role of TLR4 in pulmonary responses against Klebsiella pneumoniae (Kp). Compared with wild-type (WT) (Balb/c) mice, mice with defective TLR4 signaling (TLR4(lps-d) mice) had substantially higher lung bacterial colony-forming units after intratracheal challenge with Kp, which was associated with considerably greater lung permeability and lung cell death. Reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein was noted in lungs and bronchoalveolar lavage fluid of TLR4 mutant mice postintratracheal Kp compared with WT mice, and primary alveolar epithelial cells (AEC) harvested from TLR4(lps-d) mice produced significantly less GM-CSF in vitro in response to heat-killed Kp compared with WT AEC. TLR4(lps-d) AEC underwent significantly more apoptosis in response to heat-killed Kp in vitro, and treatment with GM-CSF protected these cells from apoptosis in response to Kp. Finally, intratracheal administration of GM-CSF in TLR4(lps-d) mice significantly decreased albumin leak, lung cell apoptosis, and bacteremia in Kp-infected mice. Based on these observations, we conclude that TLR4 plays a protective role on lung epithelium during Gram-negative bacterial pneumonia, an effect that is partially mediated by GM-CSF.

T(H)17 cells in asthma and inflammation

BACKGROUND

The chronic airway disease asthma causes significant burden to patients as well as the healthcare system with limited options for prevention or cure. Inadequate treatment strategies are most likely due to the complex heterogeneous nature of asthma. Furthermore, the severe asthma phenotype is characterized by the lack of a response to standard medication, namely, corticosteroids.

SCOPE OF REVIEW

In the last several years it has been shown that the eosinophilic/atopic phenotype of asthma driven by T(H)2 mechanisms is not the only immunologic pathway contributing to disease. In fact, there has been evidence revealing that severe asthmatics in particular have neutrophilic inflammation, and this is associated with corticosteroid resistance. T(H)17 cells, a recently discovered lineage of T helper cells, play an important role in lung host defense against multiple pathogens via production of the cytokine IL-17. IL-17 promotes neutrophil production and chemotaxis via multiple factors.

MAJOR CONCLUSIONS

Mouse and human studies provide robust evidence that T(H)17 cells and IL-17 play a role in severe asthma and may contribute to corticosteroid resistance.

GENERAL SIGNIFICANCE

As we learn more about T(H)17 cells in severe asthma, the goal is to potentially target this pathway for treatment in the hope of significantly improving the quality of life for those children and adults affected with this disease. This article is part of a Special Issue entitled: Biochemistry of Asthma.

Toll like receptors in diseases of the lung

The lung is in continuous contact with a diverse array of infectious agents, foreign antigens, and host-derived danger signals. To sample this expansive internal and external milieu, both resident myeloid and stromal/structure cells of the lung express a full complement of toll like receptors (TLRs) which recognize pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs). TLRs play a vital role in immune host defense against bacterial, mycobacterial, fungal, and viral pathogens of the lung. Additionally, TLRs contribute to disease pathogenesis in non-infectious pulmonary disorders, including airway disease, acute lung injury, and interstitial lung disease. In this review, TLR biology in the context of experimental infectious and non-infectious lung disease is discussed, and correlates to human lung disease, including therapeutic implications of these findings, are defined.

IL-23 in infections, inflammation, autoimmunity and cancer: possible role in HIV-1 and AIDS

The growing family of interleukin (IL)-12-like cytokines produced by activated macrophages and dendritic cells became the important players in the control of infections, development of inflammation, autoimmunity and cancer. However, the role of one of them-heterodimer IL-23, which consists of IL12p40 and the unique p19 subunit in HIV-1 infection pathogenesis and progression to AIDS, represent special interest. We overviewed findings of IL-23 involvement in control of peripheral bacterial pathogens and opportunistic infection, central nervous system (CNS) viral infections and autoimmune disorders, and tumorogenesis, which potentially could be applicable to HIV-1 and AIDS.

Receptor-interacting protein 2 controls pulmonary host defense to Escherichia coli infection via the regulation of interleukin-17A

Recognition of microbial patterns by host receptors is the first step in a multistep sequence leading to neutrophil-dependent host resistance. Although the role of membrane-bound sensors in bacterial recognition has been examined in detail, the importance of cytosolic sensors in the lungs is largely unexplored. In this context, there is a major lack of understanding related to the downstream signaling mediators, such as cells and/or molecules, during acute extracellular Gram-negative bacterial pneumonia. In order to determine the role of NOD-like receptors (NLRs), we used an experimental Escherichia coli infection model using mice deficient in the gene coding for the NLR adaptor, receptor-interacting protein 2 (RIP2). RIP2(-/-) mice with E. coli infection displayed higher bacterial burden and reduced neutrophil recruitment and tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), macrophage inflammatory protein 2 (MIP-2), and CXCL5/LIX expression, along with attenuated histopathological changes in the lungs. Decreased IL-17A levels were observed, along with lower numbers of IL-17A-producing T cells, in RIP2(-/-) mice after infection. RIP2(-/-) mice also show reduced IL-6 and IL-23 levels in the lungs, along with decreased activation of STAT3 after infection. Furthermore, activation of NF-κB and mitogen-activated protein kinases (MAPKs) and expression of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) in the lungs of infected RIP2(-/-) mice were attenuated following infection. Although neutrophil mobilization to the blood was impaired in RIP2(-/-) mice following infection, the expression of CD62P, CD11a/18, CD11b, and CXCR2 on blood and lung neutrophils was not altered between infected wild-type (WT) and RIP2(-/-) mice. Thus, RIP2 contributes to neutrophil-dependent host defense against an extracellular Gram-negative pathogen via (i) IL-17A regulation and (ii) neutrophil mobilization to the blood.

Interleukin-17A is involved in development of spontaneous pulmonary emphysema caused by Toll-like receptor 4 mutation

AIM

To explore the pathogenic role of Th17 cells and interleukin-17A (IL-17A)-associated signaling pathways in spontaneous pulmonary emphysema induced by a Toll-like receptor 4 mutant (TLR4(mut)).

METHODS

Lungs were obtained from wild-type (WT) or TLR4mut mice that were treated with or without recombinant mouse IL-17A (1 μg·kg(-1)·d(-1), ip) from the age of 3 weeks to 3 months. Pulmonary emphysema was determined using histology, immunochemistry, and biochemical analysis. T cell polarization was determined with flow cytometry, the levels of cytokines were measured using ELISA, and the levels of IL-17A-associated signaling molecules were detected using Western blot.

RESULTS

Compared to WT mice, 3 month-old TLR4(mut) mice were characterized by significantly reduced infiltration of Th17 cells into lungs (2.49%±1.13 % νs 5.26%±1.39%), and significantly reduced expression levels of IL-17A (3.66±0.99 pg/μg νs 10.67±1.65 pg/μg), IL-23 (12.43±1.28 pg/μg νs 28.71±2.57 pg/μg) and IL-6 (51.82±5.45 pg/μg νs 92.73±10.91 pg/μg) in bronchoalveolar lavage fluid. In addition, p38 MAPK phosphorylation and AP-1 expression were decreased to 27%±9% and 51%±8%, respectively, of that in WT mice. Treatment of TLR4(mut) mice with IL-17A increased the infiltration of Th17 cells into lungs and expression levels of IL-17A, IL-6, and IL-23 in bronchoalveolar lavage fluid, attenuated MDA and apoptosis, and improved emphysema accompanied with increased phosphorylation of p38 MAPK and expression of AP-1.

CONCLUSION

Th17 cells, in particular the cytokine IL-17A, play a crucial role in the pathogenesis of TLR4(mut)-induced spontaneous pulmonary emphysema. Both of them are potential targets for therapeutic strategies for pulmonary emphysema.

Defending the mucosa: adjuvant and carrier formulations for mucosal immunity

A majority of infectious microorganisms either colonize or cross mucosal surfaces to enter the host. A major goal in vaccine design is to induce a protective, lasting immune response against potential pathogens at mucosal surfaces. In addition, mucosal vaccines can offer needle-free delivery, thereby improving accessibility, safety, and cost-effectiveness. Challenges to successful mucosal vaccination include poor induction of mucosal immunity, limited understanding of protective mechanisms and crosstalk between mucosal compartments, and the availability of safe, effective mucosal adjuvants and delivery systems. This review focuses on some key advances in the field of mucosal vaccinology within the past 2-3 years, including reports on promising new formulations and investigations into the mechanisms of established mucosal adjuvants and/or particulate carrier systems.