Toll-like receptors in the host defense against Pseudomonas aeruginosa respiratory infection and cystic fibrosis

Seasonal and climatic influence on respiratory infections in children with cystic fibrosis

Pseudomonas aeruginosa (Pa) and Methicillin susceptible Staphylococcus aureus (MSSA) are the predominant bacteria found in the airways of people with cystic fibrosis (pwCF), significantly contributing to lung disease progression. While various factors influencing the initial acquisition (IA) of these pathogens are known, the impact of environmental conditions remains understudied. This epidemiological study assessed the risk of MSSA and Pa initial acquisitions in relation to seasonality and climatic zones among 1,184 French pwCF under 18 years old. The age at IA for Pa (Pa-IA) and MSSA (MSSA-IA) was estimated using the Kaplan-Meier method. Seasonality and climatic zones were analysed as risk factors using time-varying Cox regression models. The median age at MSSA-IA was notably earlier (2.0 years) than that at Pa-IA (5.1 years). MSSA-IA occurred increasingly younger in more recent birth cohorts, while the age at Pa-IA remained stable over time. The risk of Pa-IA was consistently higher in all seasons compared with spring, peaking in autumn (HR = 1.53), irrespective of climatic zones. In Oceanic and Continental climates, the highest risk for MSSA-IA was in winter (HRs = 1.45 and 1.20 respectively). In the Mediterranean climate, the risk of MSSA-IA was lower in winter compared to spring (HRs = 0.68 and 0.61 respectively), and the median age at MSSA-IA later than for Pa-IA. This study demonstrates that seasonality and meteorological factors may influence acquisition of MSSA and Pa in pwCF. These findings suggest that environmental factors play a role in pathogen acquisition dynamics in CF and could inform the development of preventive strategies.

Pseudomonas aeruginosa: metabolic allies and adversaries in the world of polymicrobial infections

Pseudomonas aeruginosa (PA), an opportunistic human pathogen that is frequently linked with chronic infections in immunocompromised individuals, is also metabolically versatile, and thrives in diverse environments. Additionally, studies report that PA can interact with other microorganisms, such as bacteria, and fungi, producing unique metabolites that can modulate the host immune response, and contribute to disease pathogenesis. This review summarizes the current knowledge related to the metabolic interactions of PA with other microorganisms (Staphylococcus, Acinetobacter, Klebsiella, Enterococcus, and Candida) and human hosts, and the importance of these interactions in a polymicrobial context. Further, we highlight the potential applications of studying these metabolic interactions toward designing better diagnostic tools, and therapeutic strategies to prevent, and treat infections caused by this pathogen.

Pseudomonas aeruginosa in chronic lung disease: untangling the dysregulated host immune response

Pseudomonas aeruginosa is a highly adaptable opportunistic pathogen capable of exploiting barriers and immune defects to cause chronic lung infections in conditions such as cystic fibrosis. In these contexts, host immune responses are ineffective at clearing persistent bacterial infection, instead driving a cycle of inflammatory lung damage. This review outlines key components of the host immune response to chronic P. aeruginosa infection within the lung, beginning with initial pathogen recognition, followed by a robust yet maladaptive innate immune response, and an ineffective adaptive immune response that propagates lung damage while permitting bacterial persistence. Untangling the interplay between host immunity and chronic P. aeruginosa infection will allow for the development and refinement of strategies to modulate immune-associated lung damage and potentiate the immune system to combat chronic infection more effectively.

A Bacterial Quorum Sensing Regulated Protease Inhibits Host Immune Responses by Cleaving Death Domains of Innate Immune Adaptors

Innate immune adaptor proteins are critical components of the innate immune system that propagate pro-inflammatory responses from their upstream receptors, and lead to pathogen clearance from the host. Bacterial pathogens have developed strategies to survive inside host cells without triggering the innate immune surveillance in ways that are still not fully understood. Here, it is reported that Pseudomonas aeruginosa induces its quorum sensing mechanism after macrophage engulfment. Further investigation of its secretome identified a quorum sensing regulated product, LasB, is responsible for innate immune suppression depending on the MyD88-mediated signaling. Moreover, it is showed that this specific type of pathogen-mediated innate immune suppression is due to the enzymatic digestion of the death domains of the innate immune adaptors, mainly MyD88, and attributed to LasB's large substrate binding groove. Lastly, it is demonstrated that the secretion of LasB from P. aeruginosa directly contributed to MyD88 degradation within macrophages. Hence, it is discovered an example of bacterial quorum sensing-regulated cellular innate immune suppression by direct cleavage of immune adaptors.

Masking of typical TLR4 and TLR5 ligands modulates inflammation and resolution by Helicobacter pylori

Helicobacter pylori is a paradigm of chronic bacterial infection and is associated with peptic ulceration and malignancies. H. pylori uses specific masking mechanisms to avoid canonical ligands from activating Toll-like receptors (TLRs), such as lipopolysaccharide (LPS) modification and specific flagellin sequences that are not detected by TLR4 and TLR5, respectively. Thus, it was believed for a long time that H. pylori evades TLR recognition as a crucial strategy for immune escape and bacterial persistence. However, recent data indicate that multiple TLRs are activated by H. pylori and play a role in the pathology. Remarkably, H. pylori LPS, modified through changes in acylation and phosphorylation, is mainly sensed by other TLRs (TLR2 and TLR10) and induces both pro- and anti-inflammatory responses. In addition, two structural components of the cag pathogenicity island-encoded type IV secretion system (T4SS), CagL and CagY, were shown to contain TLR5-activating domains. These domains stimulate TLR5 and enhance immunity, while LPS-driven TLR10 signaling predominantly activates anti-inflammatory reactions. Here, we discuss the specific roles of these TLRs and masking mechanisms during infection. Masking of typical TLR ligands combined with evolutionary shifting to other TLRs is unique for H. pylori and has not yet been described for any other species in the bacterial kingdom. Finally, we highlight the unmasked T4SS-driven activation of TLR9 by H. pylori, which mainly triggers anti-inflammatory responses.

Identification of Key TRIM Genes Involved in Response to Pseudomonas aeruginosa or Chlamydia spp. Infections in Human Cell Lines and in Mouse Organs

Bacterial infections represent an unsolved problem today since bacteria can evade antibiotics and suppress the host's immune response. A family of TRIM proteins is known to play a role in antiviral defense. However, the data on the involvement of the corresponding genes in the antibacterial response are limited. Here, we used RT-qPCR to profile the transcript levels of TRIM genes, as well as interferons and inflammatory genes, in human cell lines (in vitro) and in mice (in vivo) after bacterial infections caused by Pseudomonas aeruginosa and Chlamydia spp. As a result, the genes were identified that are involved in the overall immune response and associated primarily with inflammation in human cells and in mouse organs when infected with both pathogens (TRIM7, 8, 14, 16, 17, 18, 19, 20, 21, 47, 68). TRIMs specific to the infection (TRIM59 for P. aeruginosa, TRIM67 for Chlamydia spp.) were revealed. Our findings can serve as a basis for further, more detailed studies on the mechanisms of the immune response to P. aeruginosa and Chlamydia spp. Studying the interaction between bacterial pathogens and the immune system contributes to the search for new ways to successfully fight bacterial infections.

The study of NF-κB transcription factor activation by Pseudomonas aeruginosa recombinant proteins in eukaryotic cell culture

The transcription factor NF-κB is a key factor in the activation of immune responses; it is in turn activated by pattern recognition receptors, such as TLR and NLR receptors. The search for ligands activating innate immunity receptors is an important scientific problem due to the possibility of their use as adjuvants and immunomodulators. In this study the effect of recombinant Pseudomonas aeruginosa OprF proteins and a toxoid (a deletion atoxic form of exotoxin A) on the activation of TLR4, TLR9, NOD1, and NOD2 receptors has been investigated. The study was carried out using free and co-adsorbed on Al(OH)₃ P. aeruginosa proteins and eukaryotic cells encoding these receptors and having NF-κB-dependent reporter genes. The enzymes encoded by the reported genes are able to cleave the substrate with the formation of a colored product, the concentration of which indicates the degree of receptor activation. It was found that free and adsorbed forms of the toxoid were able to activate the TLR4 surface receptor for lipopolysaccharide. OprF and the toxoid activated the intracellular NOD1 receptor, but only in the free form. This may be due to the fact that the cell lines used were not able to phagocytize aluminum hydroxide particles with protein adsorbed on them.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

SLAMF7 regulates the inflammatory response in macrophages during polymicrobial sepsis

Uncontrolled inflammation occurred in sepsis results in multiple organ injuries and shock, which contributes to the death of patients with sepsis. However, the regulatory mechanisms that restrict excessive inflammation are still elusive. Here, we identified an Ig-like receptor called signaling lymphocyte activation molecular family 7 (SLAMF7) as a key suppressor of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes/macrophages was significantly elevated in patients with sepsis and in septic mice. SLAMF7 attenuated TLR-dependent MAPK and NF-κB signaling activation in macrophages by cooperating with Src homology 2-containing inositol-5'‑phosphatase 1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor-associated factor 6 (TRAF6) to inhibit K63 ubiquitination of TRAF6. In addition, we found that tyrosine phosphorylation sites within the intracellular domain of SLAMF7 and the phosphatase domain of SHIP1 were indispensable for the interaction between SLAMF7, SHIP1, and TRAF6 and SLAMF7-mediated modulation of cytokine production. Finally, we demonstrated that SLAMF7 protected against lethal sepsis and endotoxemia by downregulating macrophage proinflammatory cytokines and suppressing inflammation-induced organ damage. Taken together, our findings reveal a negative regulatory role of SLAMF7 in polymicrobial sepsis, thus providing sights into the treatment of sepsis.

CLEC5A is critical in Pseudomonas aeruginosa-induced acute lung injury

Pseudomonas aeruginosa is one of the most common nosocomial infections worldwide, and it frequently causes ventilator-associated acute pneumonia in immunocompromised patients. Abundant neutrophil extracellular traps (NETs) contribute to acute lung injury, thereby aggravating ventilator-induced lung damage. While pattern recognition receptors (PRRs) TLR4 and TLR5 are required for host defense against P. aeruginosa invasion, the PRR responsible for P. aeruginosa–induced NET formation, proinflammatory cytokine release, and acute lung injury remains unclear. We found that myeloid C-type lectin domain family 5 member A (CLEC5A) interacts with LPS of P. aeruginosa and is responsible for P. aeruginosa–induced NET formation and lung inflammation. P. aeruginosa activates CLEC5A to induce caspase-1–dependent NET formation, but it neither causes gasdermin D (GSDMD) cleavage nor contributes to P. aeruginosa–induced neutrophil death. Blockade of CLEC5A attenuates P. aeruginosa–induced NETosis and lung injury, and simultaneous administration of anti-CLEC5A mAb with ciprofloxacin increases survival rate and decreases collagen deposition in the lungs of mice challenged with a lethal dose of P. aeruginosa. Thus, CLEC5A is a promising therapeutic target to reduce ventilator-associated lung injury and fibrosis in P. aeruginosa–induced pneumonia.

High prevalence of Merkel cell polyomavirus is associated with dysregulation in transcript levels of TLR9 and type I IFNs in a large cohort of CF patients from the Italian (Lazio) reference center for cystic fibrosis

Merkel cell polyomavirus (MCPyV) has been detected in respiratory specimens including those from Cystic Fibrosis (CF) patients, raising questions about its immunological and clinical relevance in the respiratory tract. MCPyV might promote an inappropriate antiviral response contributing to a chronic inflammatory response and resulting in detrimental effects in CF. Respiratory samples (n = 1138) were randomly collected from respiratory tract of CF patients (n = 539) during July 2018-October 2019. MCPyV-DNA detection was performed by real time PCR and positive samples were characterized by sequencing of the NCCR genomic region. The transcript levels of Toll-like receptor 9 (TLR9) and type I interferon (IFN-I) genes (IFNα, IFNβ and IFNε) were examined by real-time RT-PCR assays. MCPyV-DNA was detected in 268 out of 1138 respiratory specimens (23.5%) without any difference in the prevalence of MCPyV-DNA according to age, gender or bacteriological status of CF individuals. Thirteen out of 137 CF patients remained positive for MCPyV-DNA over the time (a median follow-up period of 8.8 months). Detection of MCPyV-DNA in respiratory specimens was not associated with the occurrence of exacerbation events. Both MCPyV positive adolescents (11-24 years) and adults (≥25 years) had lower mRNA levels of TLR9, IFNβ, IFNε and IFNα than the negative patients of the same age group, while MCPyV positive children produced increased levels of TLR9 and IFN-I genes (p < 0.05 for TLR9, IFNβ, IFNε) with respect to the negative ones. There were significant differences in TLR9 levels (p < 0.01), but not in those of IFNs, between MCPyV-DNA positive and negative patients with S. aureus, P. aeruginosa or both. Overall, these results indicate that MCPyV-DNA is frequently detected in the respiratory samples of CF patients and might influence the expression levels of IFN-related genes in an age dependent manner. The concomitant detection of MCPyV together with S. aureus and/or P. aeruginosa correlated with alterations in TLR9 levels suggesting that virus-bacteria coinfections might contribute to affect antiviral immunity in CF patients.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

Antioxidant and Anti-Inflammatory Effects of Thyme (Thymus vulgaris L.) Essential Oils Prepared at Different Plant Phenophases on Pseudomonas aeruginosa LPS-Activated THP-1 Macrophages

Thyme (Thymus vulgaris L.) essential oil (TEO) is widely used as an alternative therapy especially for infections of the upper respiratory tract. TEO possesses antiviral, antibacterial, and antifungal properties. The emerging antibiotic resistance of bacterial strains, including Pseudomonas aeruginosa, has prompted the urge to find alternative treatments. In the present study, we examined the anti-inflammatory and antioxidant effects of thymol, the main compound of TEO, and two TEOs prepared at the beginning and at the end of the flowering period that may make these oils promising candidates as complementary or alternative therapies against P. aeruginosa infections. The activity measurements of the antioxidant enzymes peroxidase (PX), catalase (CAT), and superoxide dismutase (SOD) as well as the determination of total antioxidant capacity of P. aeruginosa-activated THP-1 cells revealed that thymol and both TEOs increased CAT and SOD activity as well as the antioxidant capacity of the THP-1 cells. The measurements of the proinflammatory cytokine mRNA expression and secreted protein level of LPS-activated THP-1 cells showed that from the two TEOs, only TEO prepared at the beginning of the flowering period acted as a potent inhibitor of the synthesis of IL-6, IL-8, IL-β, and TNF-α. Our results suggest that not only thymol, but also the synergism or the antagonistic effects of the additional compounds of the essential oils are responsible for the anti-inflammatory activity of TEOs.

Pseudomonas aeruginosa: pathogenesis, virulence factors, antibiotic resistance, interaction with host, technology advances and emerging therapeutics

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen that infects patients with cystic fibrosis, burn wounds, immunodeficiency, chronic obstructive pulmonary disorder (COPD), cancer, and severe infection requiring ventilation, such as COVID-19. P. aeruginosa is also a widely-used model bacterium for all biological areas. In addition to continued, intense efforts in understanding bacterial pathogenesis of P. aeruginosa including virulence factors (LPS, quorum sensing, two-component systems, 6 type secretion systems, outer membrane vesicles (OMVs), CRISPR-Cas and their regulation), rapid progress has been made in further studying host-pathogen interaction, particularly host immune networks involving autophagy, inflammasome, non-coding RNAs, cGAS, etc. Furthermore, numerous technologic advances, such as bioinformatics, metabolomics, scRNA-seq, nanoparticles, drug screening, and phage therapy, have been used to improve our understanding of P. aeruginosa pathogenesis and host defense. Nevertheless, much remains to be uncovered about interactions between P. aeruginosa and host immune responses, including mechanisms of drug resistance by known or unannotated bacterial virulence factors as well as mammalian cell signaling pathways. The widespread use of antibiotics and the slow development of effective antimicrobials present daunting challenges and necessitate new theoretical and practical platforms to screen and develop mechanism-tested novel drugs to treat intractable infections, especially those caused by multi-drug resistance strains. Benefited from has advancing in research tools and technology, dissecting this pathogen's feature has entered into molecular and mechanistic details as well as dynamic and holistic views. Herein, we comprehensively review the progress and discuss the current status of P. aeruginosa biophysical traits, behaviors, virulence factors, invasive regulators, and host defense patterns against its infection, which point out new directions for future investigation and add to the design of novel and/or alternative therapeutics to combat this clinically significant pathogen.

Isthmin 1 is Expressed by Progenitor-Like Cells in the Lung: Phenotypical Analysis of Isthmin 1+ Hematopoietic Stem-Like Cells in Homeostasis and during Infection

The process by which blood cells are generated has been widely studied in homeostasis and during pathogen-triggered inflammatory response. Recently, murine lungs have been shown to be a significant source of hematopoietic progenitors in a process known as extramedullary hematopoiesis. Using multiparametric flow cytometry, we have identified mesenchymal, endothelial, and hematopoietic progenitor cells that express the secreted small protein Isthmin 1 (ISM1). Further characterization of hematopoietic progenitor cells indicated that ISM1⁺ Lineage⁻ Sca-1⁺ c-kit⁺ (ISM1⁺ LSK) cells are enriched in short-term hematopoietic stem cells (ST-HSCs). Moreover, most Sca-1⁺ ISM1⁺ cells express the residence marker CD49a, and this correlated with their localization in the extravascular region of the lung, indicating that ISM1⁺ cells are lung-resident cells. We also observed that ISM1⁺ cells express TLR4, TLR5, and TLR9, and, in a mouse model of sepsis induced by P. aeruginosa, we observed that all the LSK and ISM1⁺LSK cells were affected. We conclude that ISM1 is a novel biomarker associated with progenitor-like cells. ISM1⁺ cells are involved in the response to a bacterial challenge, suggesting an association between ISM1-producing cells and dangerous inflammatory responses like sepsis.

Participation of Acyl-Coenzyme A Synthetase FadD4 of Pseudomonas aeruginosa PAO1 in Acyclic Terpene/Fatty Acid Assimilation and Virulence by Lipid A Modification

The pathogenic bacterium Pseudomonas aeruginosa possesses high metabolic versatility, with its effectiveness to cause infections likely due to its well-regulated genetic content. P. aeruginosa PAO1 has at least six fadD paralogous genes, which have been implicated in fatty acid (FA) degradation and pathogenicity. In this study, we used mutagenesis and a functional approach in P. aeruginosa PAO1 to determine the roles of the fadD4 gene in acyclic terpene (AT) and FA assimilation and on pathogenicity. The results indicate that fadD4 encodes a terpenoyl-CoA synthetase utilized for AT and FA assimilation. Additionally, mutations in fadD paralogs led to the modification of the quorum-sensing las/rhl systems, as well as the content of virulence factors pyocyanin, biofilm, rhamnolipids, lipopolysaccharides (LPS), and polyhydroxyalkanoates. In a Caenorhabditis elegans in vivo pathogenicity model, culture supernatants from the 24-h-grown fadD4 single mutant increased lethality compared to the PAO1 wild-type (WT) strain; however, the double mutants fadD1/fadD2, fadD1/fadD4, and fadD2/fadD4 and single mutant fadD2 increased worm survival. A correlation analysis indicated an interaction between worm death by the PAO1 strain, the fadD4 mutation, and the virulence factor LPS. Fatty acid methyl ester (FAME) analysis of LPS revealed that a proportion of the LPS and FA on lipid A were modified by the fadD4 mutation, suggesting that FadD4 is also involved in the synthesis/degradation and modification of the lipid A component of LPS. LPS isolated from the fadD4 mutant and double mutants fadD1/fadD4 and fadD2/fadD4 showed a differential behavior to induce an increase in body temperature in rats injected with LPS compared to the WT strain or from the fadD1 and fadD2 mutants. In agreement, LPS isolated from the fadD4 mutant and double mutants fadD1/fadD2 and fadD2/fadD4 increased the induction of IL-8 in rat sera, but IL1-β cytokine levels decreased in the double mutants fadD1/fadD2 and fadD1/fadD4. The results indicate that the fadD genes are implicated in the degree of pathogenicity of P. aeruginosa PAO1 induced by LPS-lipid A, suggesting that FadD4 contributes to the removal of acyl-linked FA from LPS, rendering modification in its immunogenic response associated to Toll-like receptor TLR4. The genetic redundancy of fadD is important for bacterial adaptability and pathogenicity over the host.

Antagonistic Roles of Gallates and Ascorbic Acid in Pyomelanin Biosynthesis of Pseudomonas aeruginosa Biofilms

Primarily synthesized for chelating metal ions from the surrounding media, the pyomelanin plays an important role in bacterial virulence where it is needed for infection and biofilm formation as well as protection from host immune response. In this study, two out of three phenolic acids, gallic acid, and propyl gallate induced pyomelanin in two clinical isolates of Pseudomonas aeruginosa and inhibited biofilm formation. Ascorbic acid treatment reversed the gallic acid and propyl gallate mediated pyomelanin synthesis without reversing the inhibition of the biofilm formation. mRNA expression study revealed the upregulation of homogentisic acid oxidase enzyme by ascorbic acid treatment, possibly contributing towards the inhibition of pyomelanin synthesis. Tannic acid did not show any antibacterial or pyomelanin-induction activities. The synergistic effect of gallates and ascorbic acid in the inhibition of biofilm formation and associated pyomelanin synthesis was evidenced which needs further studies to establish their antibacterial efficacies, especially against the clinical isolates of Pseudomonas sp.

Designing multi-epitope vaccine candidates against functional amyloids in Pseudomonas aeruginosa through immunoinformatic and structural bioinformatics approach

Pseudomonas aeruginosa (P. aeruginosa) displays high drug resistance and biofilm-mediated adaptability, which makes its infections difficult to treat. Alternative intervention methods and targets have made such infections treatment manageable. One of the biofilm components, functional amyloids of Pseudomonas (Fap) is correlated positively with virulence and mucoidy phenotype found in infection in cystic fibrosis (CF) patients. Extracellular accessibility, conservation across P. aeruginosa isolates and linkage with lung infections phenotype in CF patients, makes Fap a promising intervention target. Furthermore, the reported effect of bacterial amyloid on neuronal function and immune response makes it a targetable candidate. In the current study, Fap C protein and its immediate interactions were explored to extract antigenic T-cell and B-cell epitopes. A combination of epitopes and peptide adjuvants has been linked to derive vaccine candidate structures. The vaccine candidates were validated for antigenicity, allergenicity, physiochemical properties, stability and interactions with TLRs and MHC alleles. Immunosimulation studies have demonstrated that vaccines elicit Th1 dominated response, which can assist in good prognosis of infection in CF patients.

Lipopolysaccharide from biofilm-forming Pseudomonas aeruginosa PAO1 induces macrophage hyperinflammatory responses

Introduction. Macrophages polarization is essential in infection control. Llipopolysaccharide (LPS) plays an essential role in host innate immune system-pathogen interaction. The LPS structure of Pseudomonas aeruginosa modifies in the adaptation of this pathogen to biofilm-related chronic infection.Gap statement. There have been several studies on LPS induced polarization of human and mouse macrophages with different results. And it was reported that the lipid A structure of the LPS derived from biofilm-forming Pseudomonas aeruginosa strain PAO1 was modified.Aim. This study aimed to investigate the effect and the involved pathway of LPS from biofilm-forming PAO1 on human and murine macrophage polarization.Methodology. LPS was isolated from biofilm-forming and planktonic PAO1 and quantified. Then the LPS was added to PMA-differentiated human macrophage THP-1 cells and Raw264.7 murine macrophage cells. The expression of iNOS, Arg-1, IL4, TNF-α, CCL3, and CCL22 was analysed in the different cell lines. The expression of TICAM-1 and MyD88 in human THP-1 macrophages was quantified by Western blot. PAO1 infected macrophages at different polarization states, and the intracellular bacterial growth in macrophages was evaluated.Results. LPS from biofilm-forming PAO1 induced more marked hyperinflammatory responses in THP-1 and Raw264.7 macrophages than LPS derived from planktonic PAO1, and these responses were related to the up-regulation of MyD88. Intracellular growth of PAO1 was significantly increased in THP-1 macrophages polarized by LPS from biofilm-forming PAO1, but decreased both in THP-1 and Raw264.7 macrophages polarized by LPS from planktonic PAO1.Conclusion. The presented in vitro study indicates that LPS derived from biofilm-forming PAO1 induces enhanced M1 polarization in human and murine macrophage cell lines than LPS from planktonic PAO1.

mTOR-driven glycolysis governs induction of innate immune responses by bronchial epithelial cells exposed to the bacterial component flagellin

Human bronchial epithelial (HBE) cells play an essential role during bacterial infections of the airways by sensing pathogens and orchestrating protective immune responses. We here sought to determine which metabolic pathways are utilized by HBE cells to mount innate immune responses upon exposure to a relevant bacterial agonist. Stimulation of HBE cells by the bacterial component flagellin triggered activation of the mTOR pathway resulting in an increased glycolytic flux that sustained the secretory activity of immune mediators by HBE cells. The mTOR inhibitor rapamycin impeded glycolysis and limited flagellin-induced secretion of immune mediators. The role of the mTOR pathway was recapitulated in vivo in a mouse model of flagellin-triggered lung innate immune responses. These data demonstrate that metabolic reprogramming via the mTOR pathway modulates activation of the respiratory epithelium, identifying mTOR as a potential therapeutic target to modulate mucosal immunity in the context of bacterial infections.

de Vos A, Sirard JC, J. T. H. Roelofs J, P. Scicluna B, van der Poll T. Bronchial epithelial DNA methyltransferase 3b dampens pulmonary immune responses during Pseudomonas aeruginosa infection

DNA methyltransferase (Dnmt)3b mediates de novo DNA methylation and modulation of Dnmt3b in respiratory epithelial cells has been shown to affect the expression of multiple genes. Respiratory epithelial cells provide a first line of defense against pulmonary pathogens and play a crucial role in the immune response during pneumonia caused by Pseudomonas (P.) aeruginosa, a gram-negative bacterium that expresses flagellin as an important virulence factor. We here sought to determine the role of Dntm3b in respiratory epithelial cells in immune responses elicited by P. aeruginosa. DNMT3B expression was reduced in human bronchial epithelial (BEAS-2B) cells as well as in primary human and mouse bronchial epithelial cells grown in air liquid interface upon exposure to P. aeruginosa (PAK). Dnmt3b deficient human bronchial epithelial (BEAS-2B) cells produced more CXCL1, CXCL8 and CCL20 than control cells when stimulated with PAK, flagellin-deficient PAK (PAKflic) or flagellin. Dnmt3b deficiency reduced DNA methylation at exon 1 of CXCL1 and enhanced NF-ĸB p65 binding to the CXCL1 promoter. Mice with bronchial epithelial Dntm3b deficiency showed increased Cxcl1 mRNA expression in bronchial epithelium and CXCL1 protein release in the airways during pneumonia caused by PAK, which was associated with enhanced neutrophil recruitment and accelerated bacterial clearance; bronchial epithelial Dnmt3b deficiency did not modify responses during pneumonia caused by PAKflic or Klebsiella pneumoniae (an un-flagellated gram-negative bacterium). Dnmt3b deficiency in type II alveolar epithelial cells did not affect mouse pulmonary defense against PAK infection. These results suggest that bronchial epithelial Dnmt3b impairs host defense during Pseudomonas induced pneumonia, at least in part, by dampening mucosal responses to flagellin.

Low-Dose Exposure to Ganglioside-Mimicking Bacteria Tolerizes Human Macrophages to Guillain-Barré Syndrome-Associated Antigens

Early in life, commensal bacteria play a major role in immune development, helping to guide the host response toward harmful stimuli while tolerating harmless antigens to prevent autoimmunity. Guillain-Barré syndrome (GBS) is an autoimmune disease caused by errant immune attack of antibody-bound ganglioside receptors on host nerve cells, resulting in paralysis. Lipooligosaccharides enveloping the prevalent enteric pathogen, Campylobacter jejuni, frequently mimic human gangliosides and can trigger GBS by stimulating the autoimmune response. In low- to middle-income countries, young children are consistently exposed to C. jejuni, and it is not known if this impacts GBS susceptibility later in life. Using a macrophage model, we examined the effect of training these cells with low doses of ganglioside-mimicking bacteria prior to challenge with GBS-associated antigens. This training caused decreased production of proinflammatory cytokines, suggesting tolerance induction. We then screened Campylobacter isolates from 154 infant fecal samples for GM1 ganglioside mimicry, finding that 23.4% of strains from both symptomatic and asymptomatic infants displayed GM1-like structures. Training macrophages with one of these asymptomatic carrier isolates also induced tolerance against GBS-associated antigens, supporting that children can be exposed to the tolerizing antigen early in life. RNA interference of Toll-like receptor 2 (TLR2) and TLR4 suggests that these receptors are not involved in tolerance associated with decreases in tumor necrosis factor (TNF), interleukin-6 (IL-6), or IL-1β levels. The results of this study suggest that exposure to ganglioside-mimicking bacteria early in life occurs naturally and impacts host susceptibility to GBS development. IMPORTANCE In this study, we demonstrated that it is possible to tolerize immune cells to potentially dampen the autoreactive proinflammatory immune response against Guillain-Barré syndrome (GBS)-associated antigens. The innate immune response functions to arm the host against bacterial attack, but it can be tricked into recognizing the host's own cells when infectious bacteria display sugar structures that mimic human glycans. It is this errant response that leads to the autoimmunity and paralysis associated with GBS. By presenting immune cells with small amounts of the bacterial glycan mimic, we were able to suppress the proinflammatory immune response upon subsequent high exposure to glycan-mimicking bacteria. This suggests that individuals who have already been exposed to the glycan mimics in small amounts are less sensitive to autoimmune reactions against these glycans, and this could be a factor in determining susceptibility to GBS.

PTP1B negatively regulates STAT1-independent Pseudomonas aeruginosa killing by macrophages

Pseudomonas aeruginosa is the main conditional pathogen of immunodeficiency individuals. The mechanisms governing immune response to P. aeruginosa infection by macrophages remain incompletely defined. Herein, we demonstrate that protein tyrosine phosphatase-1B (PTP1B) is a critical negative regulator of P. aeruginosa infection response by macrophages. PTP1B-deficient macrophages display greatly enhanced bacterial phagocytosis and killing, accompanied by increased lysosome formation during P. aeruginosa infection. We also found that PTP1B repressed nitric oxide (NO) production and nitric oxide synthase (iNOS) induction following P. aeruginosa infection. PTP1B deficiency tended to upregulate the production of TRIF-interferon (IFN) pathway cytokines and chemokines, including IFN-β and interferon γ-inducible protein 10 (CXCL10, IP-10). Unexpectedly, the phosphorylation level of STAT1 was not regulated by PTP1B. In vivo experiments also confirmed that the regulatory function of PTP1B was not dependent on STAT1. These findings demonstrate that STAT1 is dispensable for negative regulation of P. aeruginosa clearance by macrophages.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.

Influence of Pseudomonas autoinducer N-3-oxododecanoyl homoserine lactone on human corneal epithelial cells

The quorum-sensing (QS) signaling-dependent extracellular virulence factors of Pseudomonas aeruginosa can cause infections such as P. aeruginosa keratitis. P. aeruginosa communicates by secreting and sensing small chemical molecules called autoinducers in QS system. The key QS signal molecule, N-3-oxododecanoyl-homoserine lactone (3OC12HSL), can affect the behavior of host cells and initiate immune response. In this report we investigated the influence of 3OC12HSL on human corneal epithelial cells (HCECs) and the mechanisms of 3OC12HSL on activated toll-like receptor 2 (TLR2)-dependent interleukin-8 (IL-8) secretion in HCECs. Cells were cultured under different concentrations of 3OC12HSL. Cell viability was assessed using Crystal violet staining and the cell counting kit-8 assay. We demonstrated the administration of 3OC12HSL decreased HCEC viability and survival in a concentration- and time-dependent manner. At high concentrations, 3OC12HSL rapidly promoted a time-dependent increase in the expressions of TLR2 and TLR4. It was found that the nuclear translocation and expression of nuclear factor-κB (NF-κB) were also increased in response to 3OC12HSL treatment. The significantly elevated expressions of TLR2, TLR4, and NF-κB, encouraged us to further test their mechanisms that cause inflammatory response. Among the inflammatory factors examined (IL-6, IL-8, IL-10, and TNF-α), we found that IL-8 was significantly increased after treatment with 3OC12HSL and its expression was inhibited when TLR2 was specifically blocked or silenced. These results indicated that the QS signaling molecule 3OC12HSL could be recognized by the host innate immune system in HCECs. This recognition then triggered an immune inflammatory response involving the activation of TLR2 and an increase in expression of IL-8. This crosstalk between 3OC12HSL and host immunity in HCECs contributes to the development and progression of P. aeruginosa keratitis.

Role of Lung Microbiome in Innate Immune Response Associated With Chronic Lung Diseases

Respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), lung fibrosis, and lung cancer, pose a huge socio-economic burden on society and are one of the leading causes of death worldwide. In the past, culture-dependent techniques could not detect bacteria in the lungs, therefore the lungs were considered a sterile environment. However, the development of culture-independent techniques, particularly 16S rRNA sequencing, allowed for the detection of commensal microbes in the lung and with further investigation, their roles in disease have since emerged. In healthy individuals, the predominant commensal microbes are of phylum Firmicutes and Bacteroidetes, including those of the genera Veillonella and Prevotella. In contrast, pathogenic microbes (Haemophilus, Streptococcus, Klebsiella, Pseudomonas) are often associated with lung diseases. There is growing evidence that microbial metabolites, structural components, and toxins from pathogenic and opportunistic bacteria have the capacity to stimulate both innate and adaptive immune responses, and therefore can contribute to the pathogenesis of lung diseases. Here we review the multiple mechanisms that are altered by pathogenic microbiomes in asthma, COPD, lung cancer, and lung fibrosis. Furthermore, we focus on the recent exciting advancements in therapies that can be used to restore altered microbiomes in the lungs.

High-throughput nucleotide sequencing for bacteriome studies in oral squamous cell carcinoma: a systematic review

PURPOSE

Dysbiosis has been identified in oral squamous cell carcinoma (OSCC). The aim of this study was to carry out a systematic review of an electronic research that was carried out on articles published between January 2008 and September 2018.

METHODS

Eight studies were selected after applying the inclusion and exclusion criteria.

RESULTS

All articles targeted the hypervariable regions of the 16S rRNA gene. At the phylum level, it was found reduction of Bacteroidetes (2/8 studies) and increase of Firmicutes (2/8 studies). At the genus level, Rothia increased (1/8 studies) and decreased (2/8 studies) in tumor samples, and Streptococcus also was found increased (3/8 studies) and reduced (3/8 studies). Fusobacterium only increased in OSCC samples (3/8 studies). At species level, an increase in F. nucleatum subsp. polymorphum was more associated to OSCC (2/8 studies) than with controls, as was P. aeruginosa (3/8 studies).

CONCLUSION

In summary, the results corroborated dysbiosis in OSCC patients, with enrichment of microbial taxa that are associated with inflammation and production of acetaldehyde. However, variations of study design and sample size were observed among the studies, as well as a shortage of more detailed analyses of possible correlations between risk habits and OSCC. This lack of more detailed analysis may be the cause of the inconsistencies in regard of the alterations reported for certain genera and species. In conclusion, there is an association between OSCC and oral microbiota dysbiosis, but its role in oral carcinogenesis needs to be clarified in more detail.

Intranasal Peptide-Based FpvA-KLH Conjugate Vaccine Protects Mice From Pseudomonas aeruginosa Acute Murine Pneumonia

Pseudomonas aeruginosa is an opportunistic pathogen causing acute and chronic respiratory infections associated with morbidity and mortality, especially in patients with cystic fibrosis. Vaccination against P. aeruginosa before colonization may be a solution against these infections and improve the quality of life of at-risk patients. To develop a vaccine against P. aeruginosa, we formulated a novel peptide-based P. aeruginosa subunit vaccine based on the extracellular regions of one of its major siderophore receptors, FpvA. We evaluated the effectiveness and immunogenicity of the FpvA peptides conjugated to keyhole limpet hemocyanin (KLH) with the adjuvant curdlan in a murine vaccination and challenge model. Immunization with the FpvA-KLH vaccine decreased the bacterial burden and lung edema after P. aeruginosa challenge. Vaccination with FpvA-KLH lead to antigen-specific IgG and IgM antibodies in sera, and IgA antibodies in lung supernatant. FpvA-KLH immunized mice had an increase in recruitment of CD11b⁺ dendritic cells as well as resident memory CD4⁺ T cells in the lungs compared to non-vaccinated challenged mice. Splenocytes isolated from vaccinated animals showed that the FpvA-KLH vaccine with the adjuvant curdlan induces antigen-specific IL-17 production and leads to a Th17 type of immune response. These results indicate that the intranasal FpvA-KLH conjugate vaccine can elicit both mucosal and systemic immune responses. These observations suggest that the intranasal peptide-based FpvA-KLH conjugate vaccine with curdlan is a potential vaccine candidate against P. aeruginosa pneumonia.

Infection of Dendritic Cells With Mycobacterium avium subspecies hominissuis Exhibits a Functionally Tolerogenic Phenotype in Response to Toll-Like Receptor Agonists via IL-10/Cox2/PGE2/EP2 Axis

Mycobacterium avium subspecies hominissuis (MAH) is the most common agent causing nontuberculous mycobacterial disease in humans. It mainly causes chronic and slowly progressive pulmonary disease (PD), which requires a long-term treatment and allows opportunistic co-infection by common pulmonary pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, and Aspergillus spp., thereby resulting in alteration of host immune response. In the present study, we investigated the phenotypical and functional alterations of dendritic cells (DCs), a bridge antigen-presenting cell between innate and adaptive immunity, following MAH infection in response to various toll-like receptor (TLR) agonists mimicking co-infection conditions, along with subsequent T cell response. Interestingly, MAH-infected DCs produced interleukin (IL)-10 significantly and decreased the level of IL-12p70 in response to Poly I:C and LPS, although not so in response to Pam3CSK4, imiquimod, or CpG oligodeoxynucleotide, thereby indicating that the TLR3 and TLR4 agonists functionally altered MAH-infected DCs toward a tolerogenic phenotype. Moreover, IL-10-producing tolerogenic DCs were remarkably induced by MAH and P. aeruginosa co-infection. To precisely elucidate how these TLR agonists induce tolerogenic DCs upon MAH infection, we sought to clarify the major mechanisms involved, using LPS, which caused the greatest increase in IL-10 production by the TLR agonists. Increased IL-10 stimulated the creation of tolerogenic DCs by significantly reducing MHC class II expression and MHC class II-antigen presentation, eventually inhibiting CD4⁺ T cell proliferation, along with decreased IFN-γ and IL-2. The tolerogenic phenotypes of MAH/LPS-treated DCs were restored by anti-IL-10 neutralization, validating the induction of tolerogenicity by IL-10. Interestingly, IL-10-producing-tolerogenic DCs were observed after infection with live MAH, rather than with inactivated or dead MAH. In addition, TLR2^-/- and TLR4^-/- DCs confirmed the association of IL-10 production with TLR2 and TLR4 signaling; IL-10 production synergistically increased when both TLR4 and TLR2 were involved. Expression of Cox2 and PGE2 increased along with IL-10 while that of IL-10 was inhibited by their selective inhibitors celecoxib and anti-EP2 antibody, respectively. Thus, the tolerogenic phenotypes of MAH/LPS-treated DCs were proven to be induced by Cox-2/PGE2-dependent EP2 signaling as the main mechanism. These findings may provide important clues that the tolerogenic cascade in MAH-infected DCs induced by TLR 4 signaling can alter host immune response.

Triggering Receptors Expressed on Myeloid Cells 2 Promotes Corneal Resistance Against Pseudomonas aeruginosa by Inhibiting Caspase-1-Dependent Pyroptosis

Triggering receptors expressed on myeloid cells 2 (TREM2) is a novel cell surface receptor and functions as an immunomodulatory receptor in infectious diseases. In this study, we investigated the function and regulatory mechanism of TREM2 in Pseudomonas aeruginosa (P. aeruginosa) keratitis. We found that P. aeruginosa keratitis was more severe in Trem2^−/− versus wild type C57BL/6 mice as indicated by the increased clinical scores, bacterial load, and cornea pathology. The exacerbated disease progression caused by TREM2 deficiency was associated with boosted activation of caspase-1 and subsequent pyroptosis as well as increased expression of IL-1β. In addition, blockage of pyroptosis by caspase-1 inhibitor not only recovered the severe cornea pathology developed in Trem2^−/− mice but also restored the P. aeruginosa clearance suppressed by TREM2 deficiency. Our study demonstrated that TREM2 promotes host resistance against P. aeruginosa keratitis by inhibiting caspase-1-dependent pyroptosis, which provides new insights of TREM2-mediated anti-bacterial immunity.

Membrane lipids and cell signaling

PURPOSE OF REVIEW

Reception and transmission of signals across the plasma membrane has been a function generally attributed to transmembrane proteins. In the last 3 years, however, a growing number of reports have further acknowledged important contributions played by membrane lipids in the process of signal transduction.

RECENT FINDINGS

In particular, the constituency of membrane lipids can regulate how proteins with SH2 domains and molecules like K-Ras expose their catalytic domains to the cytosol and interact with effectors and second messengers. Recent reports have also shown that the degree of saturation of phospholipids can reduce the activation of certain G-protein-coupled receptors, and signaling downstream to Toll-like receptor 4 with consequences to nuclear factor kappa B activation and inflammation. Levels of specific gangliosides in the membrane were reported to activate integrins in a cell-autonomous manner affecting tumor cell migration. Furthermore, high resolution of the association of cholesterol with the smoothened receptor has clarified its participation in sonic hedgehog signaling. These are some of the key advancements that have further propelled our understanding of the broad versatile contributions of membrane lipids in signal transduction.

SUMMARY

As we gain definitive detail regarding the impact of lipid-protein interactions and their consequences to cell function, the options for therapeutic targeting expand with the possibility of greater specificity.

Progranulin Inhibits Human T Lymphocyte Proliferation by Inducing the Formation of Regulatory T Lymphocytes

We have examined the effect of progranulin (PGRN) on human T cell proliferation and its underlying mechanism. We show that PGRN inhibits the PHA-induced multiplication of T lymphocytes. It increases the number of iTregs when T lymphocytes are activated by PHA but does not do so in the absence of PHA. PGRN-mediated inhibition of T lymphocyte proliferation, as well as the induction of iTregs, was completely reversed by a TGF-β inhibitor or a Treg inhibitor. PGRN induced TGF-β secretion in the presence of PHA whereas it did not in the absence of PHA. Our findings indicate that PGRN suppresses T lymphocyte proliferation by enhancing the formation of iTregs from activated T lymphocytes in response to TGF-β.

Lyn prevents aberrant inflammatory responses to Pseudomonas infection in mammalian systems by repressing a SHIP-1-associated signaling cluster

The pleiotropic Src kinase Lyn has critical roles in host defense in alveolar macrophages against bacterial infection, but the underlying mechanism for Lyn-mediated inflammatory response remains largely elusive. Using mouse Pseudomonas aeruginosa infection models, we observed that Lyn^-/- mice manifest severe lung injury and enhanced inflammatory responses, compared with wild-type littermates. We demonstrate that Lyn exerts this immune function through interaction with IL-6 receptor and cytoskeletal protein Ezrin via its SH2 and SH3 domains. Depletion of Lyn results in excessive STAT3 activation, and enhanced the Src homology 2-containing inositol-5-phopsphatase 1 (SHIP-1) expression. Deletion of SHIP-1 in Lyn^-/- mice (double knockout) promotes mouse survival and reduces inflammatory responses during P. aeruginosa infection, revealing the rescue of the deadly infectious phenotype in Lyn deficiency. Mechanistically, loss of SHIP-1 reduces NF-κB-dependent cytokine production and dampens MAP kinase activation through a TLR4-independent PI3K/Akt pathway. These findings reveal Lyn as a regulator for host immune response against P. aeruginosa infection through SHIP-1 and IL-6/STAT3 signaling pathway in alveolar macrophages.

PcToll2 positively regulates the expression of antimicrobial peptides by promoting PcATF4 translocation into the nucleus

Drosophila Toll and mammalian Toll-like receptors (TLRs) are a family of evolutionarily conserved immune receptors that play a crucial role in the first-line defense against intruded pathogens. Activating transcription factor 4 (ATF4), a member of the ATF/CREB transcription factor family, is an important factor that participates in TLR signaling and other physiological processes. However, in crustaceans, whether ATF4 homologs were involved in TLR signaling remains unclear. In the current study, we identified a Toll homolog PcToll2 and a novel ATF4 homolog PcATF4 from Procambarus clarkii, and analyzed the likely regulatory activity of PcATF4 in PcToll2 signaling. The complete cDNA sequence of PcToll2 was 4175 bp long containing an open reading frame of 2820 bp encoding a 939-amino acid protein, and the cDNA sequence of PcATF4 was 2027 bp long with an open reading frame of 1296 bp encoding a 431-amino acid protein. PcToll2 and human TLR4 shared the high identity and they were grouped into a cluster. Furthermore, PcToll2 had a close relationship with other shrimp TLRs that possessed potential antibacterial activity. PcToll2 was highly expressed in the hemocytes, heart and gills, while PcATF4 mainly distributed in gills. Upon challenge with Vibrio parahemolyticus, PcToll2 and PcATF4 together with the antimicrobial peptides of ALF1 and ALF2 were significantly up-regulated in the hemocytes, and the PcATF4 was translocated into the nucleus. After PcToll2 silencing and challenge with Vibrio, the translocation of PcATF4 into the nucleus was inhibited and the expression of ALF1 and ALF2 was reduced, but the expression of PcDorsal and PcSTAT was not affected. Furthermore, after PcATF4 knockdown and challenge with or without Vibrio, the expression of ALF1 and ALF2 was also decreased while the expression of PcToll2 was upregulated. These results suggested that PcToll2 might regulate the expression of ALF1 and ALF2 by promoting the import of PcATF4, instead of the routine transcription factor PcDorsal, into the nucleus participating in the immune defense against Gram-negative bacteria.

Current Concepts and Controversies in Innate Immunity of Cystic Fibrosis Lung Disease

Cystic fibrosis (CF) lung disease is characterized by chronic infection and inflammation. The inflammatory response in CF is dominated by the activation of the innate immune system. Bacteria and fungi represent the key pathogens chronically colonizing the CF airways. In response, innate immune pattern recognition receptors, expressed by airway epithelial and myeloid cells, sense the microbial threat and release chemoattractants to recruit large numbers of neutrophils into CF airways. However, neutrophils fail to efficiently clear the invading pathogens, but instead release harmful proteases and oxidants and finally cause tissue injury. Here, we summarize and discuss current concepts and controversies in the field of innate immunity in CF lung disease, facing the ongoing questions of whether inflammation is good or bad in CF and how innate immune mechanisms could be harnessed therapeutically.

Pseudomonas aeruginosa promotes autophagy to suppress macrophage-mediated bacterial eradication

OBJECTIVES

To explore the role of autophagy on macrophage-mediated phagocytosis and intracellular killing of Pseudomonas aeruginosa (PA), a common extracellular bacterium which often causes various opportunistic infections.

METHODS

Macrophages were infected with PA or stimulated with zymosan bioparticles. Autophagy was tested by fluorescent microscopy and Western blot for LC3. Phagocytosis and killing efficiency were assessed by plate count assay, flow cytometry or immunofluorescent staining. Phagocytic receptor expression, ROS generation and NO production were examined by PCR, flow cytometry and Griess reaction, respectively.

RESULTS

PA infection induced autophagy activation in both mouse and human macrophages. Induction of autophagy by rapamycin or starvation significantly inhibited PA internalization by downregulating phagocytosis receptor expression, and suppressed intracellular killing of PA via reducing ROS and NO production in macrophages. While knockdown of autophagy molecules ATG7 or Beclin1 enhanced macrophage-mediated phagocytosis and intracellular killing of PA. Additionally, confocal microscopy data showed that induction of autophagy reduced the number of phagosomes and phagolysosomes in macrophages after stimulation with zymosan bioparticles.

CONCLUSIONS

Our study suggested that PA promotes autophagy to suppress macrophage-mediated bacterial phagocytosis and intracellular killing. These insights demonstrated a novel immune evasion mechanism employed by PA, which may provide potential therapeutic strategies of PA infectious diseases.

Lung epithelial MyD88 drives early pulmonary clearance of Pseudomonas aeruginosa by a flagellin dependent mechanism

Pseudomonas aeruginosa is a flagellated pathogen frequently causing pneumonia in hospitalized patients and sufferers of chronic lung disease. Here we investigated the role of the common Toll-like receptor (TLR) adaptor myeloid differentiation factor (MyD)88 in myeloid vs. lung epithelial cells in clearance of P. aeruginosa from the airways. Mice deficient for MyD88 in lung epithelial cells (Sftpccre-MyD88-lox mice) or myeloid cells (LysMcre-MyD88-lox mice) and bone marrow chimeric mice deficient for TLR5 (the receptor recognizing Pseudomonas flagellin) in either parenchymal or hematopoietic cells were infected with P. aeruginosa via the airways. Sftpccre-MyD88-lox mice demonstrated a reduced influx of neutrophils into the bronchoalveolar space and an impaired early antibacterial defense after infection with P. aeruginosa, whereas the response of LysMcre-MyD88-lox mice did not differ from control mice. The immune-enhancing role of epithelial MyD88 was dependent on recognition of pathogen-derived flagellin by epithelial TLR5, as demonstrated by an unaltered clearance of mutant P. aeruginosa lacking flagellin from the lungs of Sftpccre-MyD88-lox mice and an impaired bacterial clearance in bone marrow chimeric mice lacking TLR5 in parenchymal cells. These data indicate that early clearance of P. aeruginosa from the airways is dependent on flagellin-TLR5-MyD88-dependent signaling in respiratory epithelial cells.

TLR2 and TLR4 mediated host immune responses in major infectious diseases: a review

During the course of evolution, multicellular organisms have been orchestrated with an efficient and versatile immune system to counteract diverse group of pathogenic organisms. Pathogen recognition is considered as the most critical step behind eliciting adequate immune response during an infection. Hitherto Toll-like receptors (TLRs), especially the surface ones viz. TLR2 and TLR4 have gained immense importance due to their extreme ability of identifying distinct molecular patterns from invading pathogens. These pattern recognition receptors (PRRs) not only act as innate sensor but also shape and bridge innate and adaptive immune responses. In addition, they also play a pivotal role in regulating the balance between Th1 and Th2 type of response essential for the survivability of the host. In this work, major achievements rather findings made on the typical signalling and immunopathological attributes of TLR2 and TLR4 mediated host response against the major infectious diseases have been reviewed. Infectious diseases like tuberculosis, trypanosomiasis, malaria, and filariasis are still posing myriad threat to mankind. Furthermore, increasing resistance of the causative organisms against available therapeutics is also an emerging problem. Thus, stimulation of host immune response with TLR2 and TLR4 agonist can be the option of choice to treat such diseases in future.

LPS- or Pseudomonas aeruginosa-mediated activation of the macrophage TLR4 signaling cascade depends on membrane lipid composition

It is well known that PUFA impede the LPS-mediated activation of the transcription factor NFkappaB. However, the underlying mode of action has not been clarified yet. To address this issue in a comprehensive approach, we used the monocyte/macrophage cell line RAW264.7 to investigate the consequences of a PUFA supplementation on the TLR4 pathway with a focus on (i) the gene expression of TLR4 itself as well as of its downstream mediators, (ii) the membrane microdomain localization of TLR4 and CD14, (iii) the stimulation-induced interaction of TLR4 and CD14. Our data indicate that the impairment of the TLR4-mediated cell activation by PUFA supplementation is not due to changes in gene expression of mediator proteins of the signaling cascade. Rather, our data provide evidence that the PUFA enrichment of macrophages affects the TLR4 pathway at the membrane level. PUFA incorporation into membrane lipids induces a reordering of membrane microdomains thereby affecting cellular signal transduction. It is important to note that this remodeling of macrophage rafts has no adverse effect on cell viability. Hence, microdomain disruption via macrophage PUFA supplementation has a potential as non-toxic strategy to attenuate inflammatory signaling.

Possible mechanisms of Pseudomonas aeruginosa-associated lung disease

Pseudomonas aeruginosa is an opportunistic bacterium causing lung injury in immunocompromised patients correlated with high morbidity and mortality. Many bacteria, including P. aeruginosa, use extracellular signals to synchronize group behaviors, a process known as quorum sensing (QS). In the P. aeruginosa complex QS system controls expression of over 300 genes, including many involved in host colonization and disease. P. aeruginosa infection elicits a complex immune response due to a large number of immunogenic factors present in the bacteria or released during infection. Here, we focused on the mechanisms by which P. aeruginosa triggers lung injury and inflammation, debating the possible ways that P. aeruginosa evades the host immune system, which leads to immune suppression and resistance.

A lectin S-domain receptor kinase mediates lipopolysaccharide sensing in Arabidopsis thaliana

The sensing of microbe-associated molecular patterns (MAMPs) triggers innate immunity in animals and plants. Lipopolysaccharide (LPS) from Gram-negative bacteria is a potent MAMP for mammals, with the lipid A moiety activating proinflammatory responses via Toll-like receptor 4 (TLR4). Here we found that the plant Arabidopsis thaliana specifically sensed LPS of Pseudomonas and Xanthomonas. We isolated LPS-insensitive mutants defective in the bulb-type lectin S-domain-1 receptor-like kinase LORE (SD1-29), which were hypersusceptible to infection with Pseudomonas syringae. Targeted chemical degradation of LPS from Pseudomonas species suggested that LORE detected mainly the lipid A moiety of LPS. LORE conferred sensitivity to LPS onto tobacco after transient expression, which demonstrated a key function in LPS sensing and indicated the possibility of engineering resistance to bacteria in crop species.

Enhanced immune response of BMDCs pulsed with H9N2 AIV and CpG

Dendritic cells (DCs), professional antigen presenting cells, have demonstrated effective in controlling the initial of innate immune, while CpG could improve the performance of immune system. To explore the mechanism of CpG enhancing the immune response, we compared different stimulated mouse DCs with systemic approach microarrays. Analysis revealed 1840 differentially expressed genes in H9N2 stimulated group, more than 1728 altered genes in inactive H9N2 group. Investigation also proved that CpG/inactive H9N2 co-stimulation changed 2140 genes, more than that in H9N2 group, strongly demonstrated that CpG improved the performance of inactive H9N2 vaccination. Pathways analysis founded that DCs response rapid to shift in their maturation state, which involved Toll-like receptor (TLR) pathway significantly. Microarrays results were also verified by qRT-PCR with 14 elected representative genes. Further analysis proved that co-stimulatory molecules (CD40, CD80, CD86 and MHC-II), regulatory protein (IRF-7 and TRAF-6) and pro-inflammatory cytokines (IL-1, IL-6 and IL-12) were all changed and involved in DCs maturation. At last we demonstrated TLR signalling pathway in chicken bone marrow-derived dendritic cells (chBM-DCs) stimulated with CpG. The distinct transcriptional profiles of DCs pulsed with various stimuli expanded our understanding of how DCs respond and recognize influenza.

Zingerone suppresses liver inflammation induced by antibiotic mediated endotoxemia through down regulating hepatic mRNA expression of inflammatory markers in Pseudomonas aeruginosa peritonitis mouse model

Antibiotic-induced endotoxin release is associated with high mortality rate even when appropriate antibiotics are used for the treatment of severe infections in intensive care units. Since liver is involved in systemic clearance and detoxification of endotoxin hence it becomes a primary target organ for endotoxin mediated inflammation. Currently available anti-inflammatory drugs give rise to serious side effects. Hence, there is an urgent need for safe and effective anti-inflammatory therapy. It is likely that anti-inflammatory phytochemicals and neutraceutical agents may have the potential to reduce the endotoxin mediated inflammation and complications associated with endotoxin release. Keeping this in mind, the present study was planned to evaluate the hepatoprotective potential of zingerone (active compound of zingiber officinale) against liver inflammation induced by antibiotic mediated endotoxemia. The selected antibiotics capable of releasing high content of endotoxin were employed for their in vivo efficacy in P.aeruginosa peritonitis model. Released endotoxin induced inflammation and zingerone as co-anti-inflammatory therapy significantly reduced inflammatory response. Improved liver histology and reduced inflammatory markers MDA, RNI, MPO, tissue damage markers (AST, ALT, ALP) and inflammatory cytokines (MIP-2, IL-6 and TNF-α) were indicative of therapeutic potential of zingerone. The mechanism of action of zingerone may be related to significant inhibition of the mRNA expression of inflammatory markers (TLR4, RelA, NF-kB2, TNF- α, iNOS, COX-2) indicating that zingerone interferes with cell signalling pathway and suppresses hyper expression of cell signaling molecules of inflammatory pathway. Zingerone therapy significantly protected liver from endotoxin induced inflammatory damage by down regulating biochemical as well as molecular markers of inflammation. In conclusion, this study provides evidence that zingerone is a potent anti-inflammatory phytomedicine against hepatic inflammation induced by antibiotic mediated endotoxemia. These results thus suggest that zingerone treatment can be used as a co-therapy with antibiotics to reduced endotoxin induced inflammation during treatment of severe P.aeruginosa infections.

Flagellin concentrations in expectorations from cystic fibrosis patients

Background

The aim was to measure flagellin concentrations in the expectorations of CF patients and to examine whether there are correlations with the level of respiratory insufficiency and inflammation.

Methods

Sputum samples from 31 adult patients chronically colonized with P. aeruginosa were collected and analysed for their content of flagellin and IL-8. Clinical data were extracted from patient files.

Results

Regardless of whether patients are colonized with mucoid strains or not, they carry clones of P. aeruginosa that express flagellin. While flagellin was present in airways of all of our CF patients, it is difficult to ascertain its contribution to inflammation (IL-8) and lung function deterioration.

Conclusions

This is the first demonstration that flagellin is present in the sputum of patients. Thus, attempts to down regulate inflammation by the use of TLR5 (flagellin receptor) antagonists remain a possibility. However, this result needs to be extended to a larger number of patients to validate it for future research on this subject.

Use of lipolanthionine peptide, a toll-like receptor 2 inhibitor, enhances transdermal delivery efficiency

The transdermal delivery system (TDS) is able to obtain a systemic therapeutic effect by administration through the skin, which has low side effects and is able to maintain a sustained blood concentration. However, due to the barrier presented by the stratum corneum, numerous drugs have poor percutaneous permeability. Therefore, the improvement of skin permeability is key to TDS. The main method of promoting transdermal absorption is through the usage of penetration enhancers. Dimethyl sulfoxide (DMSO) is a commonly used penetration enhancer, which has anti-inflammatory analgesic effects and is able to penetrate the skin. Retinoic acid (RA) and lipolanthionine peptide (LP) may also benefit the permeation efficiency of TDS. Therefore, the present study examined the function of DMSO, RA and LP as penetration enhancers in TDS. Firstly, the optimum concentration of DMSO was confirmed by detecting the expression of the LacZ gene in vitro. Secondly, different combinations of LP, RA and DMSO were applied to mouse skin to analyze the penetration enhancer combination with the greatest efficacy. All the animals were divided into five groups: The RA + LP + DMSO + pORF-LacZ group, the RA + DMSO + pORF-LacZ group, the LP + DMSO + pORF-LacZ group, the DMSO + pORF-LacZ group and the control group. Skin was soaked in combinations of LP, RA and DMSO for seven days and then the pORF-LacZ plasmids were daubed onto the skin once daily three days. On the 11th day, all the animals were sacrificed by cervical dislocation and the skin and blood samples were collected. The blood samples were used to detect the expression of the LacZ gene by quantitative polymerase chain reaction and the skin samples were used to detect the expression of claudin-4 and zonula occluden-1 (ZO-1) proteins by immunohistochemistry and western blot analysis. The results demonstrated that the combination of LP, RA and DMSO exhibited the greatest transdermal delivery efficiency, which verified that RA and LP were able to increase the penetration effects. Following treatment with LP, the symptoms of dermal edema were relieved and the capillaries contracted, which suggested that LP was a safe and effective penetration enhancer able to reduce the side-effects caused by DMSO. The present study provides a guideline for the synthesis of novel penetration enhancers.

TREM-2 promotes macrophage-mediated eradication of Pseudomonas aeruginosa via a PI3K/Akt pathway

Triggering receptor expressed on myeloid cells 2 (TREM-2) is a cell surface receptor abundantly expressed on myeloid lineage cells such as macrophages and dendritic cells. It is reported that TREM-2 functions as an inflammatory inhibitor in macrophages and dendritic cells. However, the role of TREM-2 in bacterial killing remains unclear. This study explored the role of TREM-2 in bacterial eradication of Pseudomonas aeruginosa (PA), a Gram-negative bacterium which causes various opportunistic infections. Phagocytosis assay assessed by flow cytometry suggested that TREM-2 was not involved in the uptake of PA by macrophages, while bacterial plate count data showed that TREM-2 was required for macrophage-mediated intracellular killing of PA. Moreover, our results demonstrated that TREM-2 promoted macrophage killing by enhancing reactive oxygen species (ROS), but not nitric oxygen (NO) production. Treatment with N-acetylcysteine, a ROS scavenger, diminished the TREM-2-mediated intracellular killing of PA. To further investigate the underlined mechanisms of TREM-2-promoted bacterial killing, we examined the activation of downstream mitogen-activated protein kinases and PI3K/Akt pathway. Western blot data showed that silencing of TREM-2 inhibited phosphorylation of Akt, but not ERK, JNK or P38. In addition, pretreatment with PI3K active product PIP3 DiC16 reversed the elevation of intracellular bacterial load in TREM-2-silenced macrophages, while PI3K inhibitor wortmannin restored the decline of bacterial load in TREM-2-overexpressed macrophages. These data together suggested that the TREM-2-mediated bacterial killing is dependent on the activation of PI3K/Akt signalling, which may provide a better understanding of the host antibacterial immune defence.

Phagocytic and signaling innate immune receptors: are they dysregulated in cystic fibrosis in the fight against Pseudomonas aeruginosa?

Cystic fibrosis (CF) is a genetic disease that affects mainly the lung and the digestive system, causing progressive disability and organ failure. The most prevalent CFTR mutation dF508 (which constitutes 70% of all mutations) results in an incorrect targeting of the CFTR molecule to the membrane. It is now a well-accepted concept that mucosal innate immune responses are dysregulated in cystic fibrosis through a cycle of infectious and inflammatory episodes. However, although much work has focused on the late consequences of chronic lung inflammation in CF, very little is known on the early events leading to infection and colonization, such as that of Pseudomonas aeruginosa (P.a). We review here the involvement of a range of innate phagocytic/signaling receptors in the control of this pathogen (mannose receptor, complement receptor-3, Toll-like receptors, etc.) and evaluate the possibility that the activity of some of these receptors may be dysregulated in cystic fibrosis, potentially explaining the florid infections encountered in this disease.

Elevated paracellular glucose flux across cystic fibrosis airway epithelial monolayers is an important factor for Pseudomonas aeruginosa growth

People with cystic fibrosis (CF) who develop related diabetes (CFRD) have accelerated pulmonary decline, increased infection with antibiotic-resistant Pseudomonas aeruginosa and increased pulmonary exacerbations. We have previously shown that glucose concentrations are elevated in airway surface liquid (ASL) of people with CF, particularly in those with CFRD. We therefore explored the hypotheses that glucose homeostasis is altered in CF airway epithelia and that elevation of glucose flux into ASL drives increased bacterial growth, with an effect over and above other cystic fibrosis transmembrane conductance regulator (CFTR)-related ASL abnormalities. The aim of this study was to compare the mechanisms governing airway glucose homeostasis in CF and non-CF primary human bronchial epithelial (HBE) monolayers, under normal conditions and in the presence of Ps. aeruginosa filtrate. HBE-bacterial co-cultures were performed in the presence of 5 mM or 15 mM basolateral glucose to investigate how changes in blood glucose, such as those seen in CFRD, affects luminal Ps. aeruginosa growth. Calu-3 cell monolayers were used to evaluate the potential importance of glucose on Ps. aeruginosa growth, in comparison to other hallmarks of the CF ASL, namely mucus hyperviscosity and impaired CFTR-dependent fluid secretions. We show that elevation of basolateral glucose promotes the apical growth of Ps. aeruginosa on CF airway epithelial monolayers more than non-CF monolayers. Ps. aeruginosa secretions elicited more glucose flux across CF airway epithelial monolayers compared to non-CF monolayers which we propose increases glucose availability in ASL for bacterial growth. In addition, elevating basolateral glucose increased Ps. aeruginosa growth over and above any CFTR-dependent effects and the presence or absence of mucus in Calu-3 airway epithelia-bacteria co-cultures. Together these studies highlight the importance of glucose as an additional factor in promoting Ps. aeruginosa growth and respiratory infection in CF disease.