Involvement of Toll-like receptor 5 in the recognition of flagellated bacteria

Role of pattern recognition receptors in the development of MASLD and potential therapeutic applications

Metabolic dysfunction-associated steatotic liver disease (MASLD) has become one of the most prevalent liver diseases worldwide, and its occurrence is strongly associated with obesity, insulin resistance (IR), genetics, and metabolic stress. Ranging from simple fatty liver to metabolic dysfunction-associated steatohepatitis (MASH), even to severe complications such as liver fibrosis and advanced cirrhosis or hepatocellular carcinoma, the underlying mechanisms of MASLD progression are complex and involve multiple cellular mediators and related signaling pathways. Pattern recognition receptors (PRRs) from the innate immune system, including Toll-like receptors (TLRs), C-type lectin receptors (CLRs), NOD-like receptors (NLRs), RIG-like receptors (RLRs), and DNA receptors, have been demonstrated to potentially contribute to the pathogenesis for MASLD. Their signaling pathways can induce inflammation, mediate oxidative stress, and affect the gut microbiota balance, ultimately resulting in hepatic steatosis, inflammatory injury and fibrosis. Here we review the available literature regarding the involvement of PRR-associated signals in the pathogenic and clinical features of MASLD, in vitro and in animal models of MASLD. We also discuss the emerging targets from PRRs for drug developments that involved agent therapies intended to arrest or reverse disease progression, thus enabling the refinement of therapeutic targets that can accelerate drug development.

Exosomes derived from olive flounders infected with Streptococcus parauberis: Proteomic analysis, immunomodulation, and disease resistance capacity

Multidrug-resistant Streptococcus parauberis causes high fish mortality in aquaculture, necessitating an urgent need for innovative control strategies. This study aimed to develop an immunizing agent against S. parauberis using exosomes isolated from the plasma of olive flounders infected experimentally with S. parauberis (Sp-Exo). Initially, we tested the in vitro immunomodulatory effect of Sp-Exo in murine macrophage RAW264.7 cells and compared it to that of exosomes isolated from naïve fish (PBS-Exo-treated). Notably, Sp-Exo treatment significantly (p < 0.05) upregulated pro-and anti-inflammatory cytokines (Il1β, Tnfα, and Il10), antimicrobial peptide, defensin isoforms (Def-rs2 and Def-ps1), and antiviral (Ifnβ1 and Isg15) genes. In vivo studies in larval and adult zebrafish revealed similar patterns of immunomodulation. Furthermore, larval and adult zebrafish exhibited significantly (p < 0.05) enhanced resistance to S. parauberis infection following treatment with Sp-Exo compared to that with PBS-Exo. Proteomic analysis using isobaric tags for relative and absolute quantitation (iTRAQ) approach revealed the presence of 77 upregulated and 94 downregulated differentially expressed proteins (DEPs) in Sp-Exo, with 22 and 37 significantly (p < 0.05) upregulated and downregulated DEPs, respectively. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Search Tool for the Retrieval of Interacting Genes/Proteins analyses revealed that these genes are associated with key pathways, such as innate immune responses, complement system, acute phase responses, phospholipid efflux, and chylomicron remodeling. In conclusion, Sp-Exo demonstrated superior immunomodulatory activity and significant resistance against S. parauberis infection relative to that on treatment with PBS-Exo. Proteomic analysis further verified that most DEPs in Sp-Exo were associated with immune induction or modulation. These findings highlight the potential of Sp-Exo as a promising vaccine candidate against S. parauberis and other bacterial infections in olive flounder.

Decoding Toll-like receptors: Recent insights and perspectives in innate immunity

Toll-like receptors (TLRs) are an evolutionarily conserved family in the innate immune system and are the first line of host defense against microbial pathogens by recognizing pathogen-associated molecular patterns (PAMPs). TLRs, categorized into cell surface and endosomal subfamilies, recognize diverse PAMPs, and structural elucidation of TLRs and PAMP complexes has revealed their intricate mechanisms. TLRs activate common and specific signaling pathways to shape immune responses. Recent studies have shown the importance of post-transcriptional regulation in TLR-mediated inflammatory responses. Despite their protective functions, aberrant responses of TLRs contribute to inflammatory and autoimmune disorders. Understanding the delicate balance between TLR activation and regulatory mechanisms is crucial for deciphering their dual role in immune defense and disease pathogenesis. This review provides an overview of recent insights into the history of TLR discovery, elucidation of TLR ligands and signaling pathways, and their relevance to various diseases.

TLR5-deficiency controls dendritic cell subset development in an autoimmune diabetes-susceptible model

Introduction

The incidence of the autoimmune disease, type 1 diabetes (T1D), has been increasing worldwide and recent studies have shown that the gut microbiota are associated with modulating susceptibility to T1D. Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and is widely expressed on many cells, including dendritic cells (DCs), which are potent antigen-presenting cells (APCs). TLR5 modulates susceptibility to obesity and alters metabolism through gut microbiota; however, little is known about the role TLR5 plays in autoimmunity, especially in T1D.

Methods

To fill this knowledge gap, we generated a TLR5-deficient non-obese diabetic (NOD) mouse, an animal model of human T1D, for study.

Results

We found that TLR5-deficiency led to a reduction in CD11c+ DC development in utero, prior to microbial colonization, which was maintained into adulthood. This was associated with a bias in the DC populations expressing CD103, with or without CD8α co-expression, and hyper-secretion of different cytokines, both in vitro (after stimulation) and directly ex vivo. We also found that TLR5-deficient DCs were able to promote polyclonal and islet antigen-specific CD4+ T cell proliferation and proinflammatory cytokine secretion. Interestingly, only older TLR5-deficient NOD mice had a greater risk of developing spontaneous T1D compared to wild-type mice.

Discussion

In summary, our data show that TLR5 modulates DC development and enhances cytokine secretion and diabetogenic CD4+ T cell responses. Further investigation into the role of TLR5 in DC development and autoimmune diabetes may give additional insights into the pathogenesis of Type 1 diabetes.

MARCKS Inhibition Alters Bovine Neutrophil Responses to Salmonella Typhimurium

Neutrophils are innate immune cells that respond quickly to sites of bacterial infection and play an essential role in host defense. Interestingly, some bacterial pathogens benefit from exuberant neutrophil inflammation. Salmonella is one such pathogen that can utilize the toxic mediators released by neutrophils to colonize the intestine and cause enterocolitis. Because neutrophils can aid gut colonization during Salmonella infection, neutrophils represent a potential host-directed therapeutic target. Myristoylated alanine-rich C-kinase substrate (MARCKS) is an actin-binding protein that plays an essential role in many neutrophil effector responses. We hypothesized that inhibition of MARCKS protein would alter bovine neutrophil responses to Salmonella Typhimurium (STm) ex vivo. We used a MARCKS inhibitor peptide to investigate the role of MARCKS in neutrophil responses to STm. This study demonstrates that MARCKS inhibition attenuated STm-induced neutrophil adhesion and chemotaxis. Interestingly, MARCKS inhibition also enhanced neutrophil phagocytosis and respiratory burst in response to STm. This is the first report describing the role of MARCKS protein in neutrophil antibacterial responses.

Tlr5 deficiency exacerbates lupus-like disease in the MRL/lpr mouse model

Introduction

Leaky gut has been linked to autoimmune disorders including lupus. We previously reported upregulation of anti-flagellin antibodies in the blood of lupus patients and lupus-prone mice, which led to our hypothesis that a leaky gut drives lupus through bacterial flagellin-mediated activation of toll-like receptor 5 (TLR5).

Methods

We created MRL/lpr mice with global Tlr5 deletion through CRISPR/Cas9 and investigated lupus-like disease in these mice.

Result

Contrary to our hypothesis that the deletion of Tlr5 would attenuate lupus, our results showed exacerbation of lupus with Tlr5 deficiency in female MRL/lpr mice. Remarkably higher levels of proteinuria were observed in Tlr5 -/- MRL/lpr mice suggesting aggravated glomerulonephritis. Histopathological analysis confirmed this result, and Tlr5 deletion significantly increased the deposition of IgG and complement C3 in the glomeruli. In addition, Tlr5 deficiency significantly increased renal infiltration of Th17 and activated cDC1 cells. Splenomegaly and lymphadenopathy were also aggravated in Tlr5-/- MRL/lpr mice suggesting impact on lymphoproliferation. In the spleen, significant decreased frequencies of regulatory lymphocytes and increased germinal centers were observed with Tlr5 deletion. Notably, Tlr5 deficiency did not change host metabolism or the existing leaky gut; however, it significantly reshaped the fecal microbiota.

Conclusion

Global deletion of Tlr5 exacerbates lupus-like disease in MRL/lpr mice. Future studies will elucidate the underlying mechanisms by which Tlr5 deficiency modulates host-microbiota interactions to exacerbate lupus.

The distinct translational landscapes of gram-negative Salmonella and gram-positive Listeria

Translational control in pathogenic bacteria is fundamental to gene expression and affects virulence and other infection phenotypes. We used an enhanced ribosome profiling protocol coupled with parallel transcriptomics to capture accurately the global translatome of two evolutionarily distant pathogenic bacteria-the Gram-negative bacterium Salmonella and the Gram-positive bacterium Listeria. We find that the two bacteria use different mechanisms to translationally regulate protein synthesis. In Salmonella, in addition to the expected correlation between translational efficiency and cis-regulatory features such as Shine-Dalgarno (SD) strength and RNA secondary structure around the initiation codon, our data reveal an effect of the 2nd and 3rd codons, where the presence of tandem lysine codons (AAA-AAA) enhances translation in both Salmonella and E. coli. Strikingly, none of these features are seen in efficiently translated Listeria transcripts. Instead, approximately 20% of efficiently translated Listeria genes exhibit 70 S footprints seven nt upstream of the authentic start codon, suggesting that these genes may be subject to a novel translational initiation mechanism. Our results show that SD strength is not a direct hallmark of translational efficiency in all bacteria. Instead, Listeria has evolved additional mechanisms to control gene expression level that are distinct from those utilised by Salmonella and E. coli.

Transcriptome analysis of the hepatopancreas from the Litopenaeus vannamei infected with different flagellum types of Vibrio alginolyticus strains

Vibrio alginolyticus, one of the prevalently harmful Vibrio species found in the ocean, causes significant economic damage in the shrimp farming industry. Its flagellum serves as a crucial virulence factor in the invasion of host organisms. However, the processes of bacteria flagella recognition and activation of the downstream immune system in shrimp remain unclear. To enhance comprehension of this, a ΔflhG strain was created by in-frame deletion of the flhG gene in V. alginolyticus strain HN08155. Then we utilized the transcriptome analysis to examine the different immune responses in Litopenaeus vannamei hepatopancreas after being infected with the wild type and the mutant strains. The results showed that the ΔflhG strain, unlike the wild type, lost its ability to regulate flagella numbers negatively and displayed multiple flagella. When infected with the hyperflagella-type strain, the RNA-seq revealed the upregulation of several immune-related genes in the shrimp hepatopancreas. Notably, two C-type lectins (CTLs), namely galactose-specific lectin nattectin and macrophage mannose receptor 1, and the TNF receptor-associated factor (TRAF) 6 gene were upregulated significantly. These findings suggested that C-type lectins were potentially involved in flagella recognition in shrimp and the immune system was activated through the TRAF6 pathway after flagella detection by CTLs.

Commensal bacteria signal through TLR5 and AhR to improve barrier integrity and prevent allergic responses to food

The increasing prevalence of food allergies has been linked to reduced commensal microbial diversity. In this article, we describe two features of allergy-protective Clostridia that contribute to their beneficial effects. Some Clostridial taxa bear flagella (a ligand for TLR5) and produce indole (a ligand for the aryl hydrocarbon receptor [AhR]). Lysates and flagella from a Clostridia consortium induced interleukin-22 (IL-22) secretion from ileal explants. IL-22 production is abrogated in explants from mice in which TLR5 or MyD88 signaling is deficient either globally or conditionally in CD11c+ antigen-presenting cells. AhR signaling in RORγt+ cells is necessary for the induction of IL-22. Mice deficient in AhR in RORγt+ cells exhibit increased intestinal permeability and are more susceptible to an anaphylactic response to food. Our findings implicate TLR5 and AhR signaling in a molecular mechanism by which commensal Clostridia protect against allergic responses to food.

Extracellular vesicles of the probiotic bacteria E. coli O83 activate innate immunity and prevent allergy in mice

BACKGROUND

E. coli O83 (Colinfant Newborn) is a Gram-negative (G-) probiotic bacterium used in the clinic. When administered orally, it reduces allergic sensitisation but not allergic asthma. Intranasal administration offers a non-invasive and convenient delivery method. This route bypasses the gastrointestinal tract and provides direct access to the airways, which are the target of asthma prevention. G- bacteria such as E. coli O83 release outer membrane vesicles (OMVs) to communicate with the environment. Here we investigate whether intranasally administered E. coli O83 OMVs (EcO83-OMVs) can reduce allergic airway inflammation in mice.

METHODS

EcO83-OMVs were isolated by ultracentrifugation and characterised their number, morphology (shape and size), composition (proteins and lipopolysaccharide; LPS), recognition by innate receptors (using transfected HEK293 cells) and immunomodulatory potential (in naïve splenocytes and bone marrow-derived dendritic cells; BMDCs). Their allergy-preventive effect was investigated in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

EcO83-OMVs are spherical nanoparticles with a size of about 110 nm. They contain LPS and protein cargo. We identified a total of 1120 proteins, 136 of which were enriched in OMVs compared to parent bacteria. Proteins from the flagellum dominated. OMVs activated the pattern recognition receptors TLR2/4/5 as well as NOD1 and NOD2. EcO83-OMVs induced the production of pro- and anti-inflammatory cytokines in splenocytes and BMDCs. Intranasal administration of EcO83-OMVs inhibited airway hyperresponsiveness, and decreased airway eosinophilia, Th2 cytokine production and mucus secretion.

CONCLUSIONS

We demonstrate for the first time that intranasally administered OMVs from probiotic G- bacteria have an anti-allergic effect. Our study highlights the advantages of OMVs as a safe platform for the prophylactic treatment of allergy. Video Abstract.

Bacterial Outer Membrane Vesicles and Immune Modulation of the Host

This article reviews the role of outer membrane vesicles (OMVs) in mediating the interaction between Gram-negative bacteria and their human hosts. OMVs are produced by a diverse range of Gram-negative bacteria during infection and play a critical role in facilitating host-pathogen interactions without requiring direct cell-to-cell contact. This article describes the mechanisms by which OMVs are formed and subsequently interact with host cells, leading to the transport of microbial protein virulence factors and short interfering RNAs (sRNA) to their host targets, exerting their immunomodulatory effects by targeting specific host signaling pathways. Specifically, this review highlights mechanisms by which OMVs facilitate chronic infection through epigenetic modification of the host immune response. Finally, this review identifies critical knowledge gaps in the field and offers potential avenues for future OMV research, specifically regarding rigor and reproducibility in OMV isolation and characterization methods.

From Pathogenesis to Intervention: The Importance of the Microbiome in Oral Mucositis

Oral mucositis (OM) is a common and impactful toxicity of standard cancer therapy, affecting up to 80% of patients. Its aetiology centres on the initial destruction of epithelial cells and the increase in inflammatory signals. These changes in the oral mucosa create a hostile environment for resident microbes, with oral infections co-occurring with OM, especially at sites of ulceration. Increasing evidence suggests that oral microbiome changes occur beyond opportunistic infection, with a growing appreciation for the potential role of the microbiome in OM development and severity. This review collects the latest articles indexed in the PubMed electronic database which analyse the bacterial shift through 16S rRNA gene sequencing methodology in cancer patients under treatment with oral mucositis. The aims are to assess whether changes in the oral and gut microbiome causally contribute to oral mucositis or if they are simply a consequence of the mucosal injury. Further, we explore the emerging role of a patient's microbial fingerprint in OM development and prediction. The maintenance of resident bacteria via microbial target therapy is under constant improvement and should be considered in the OM treatment.

Application of Lactobacillus reuteri B1/1 (Limosilactobacillus reuteri) Improves Immunological Profile of the Non-Carcinogenic Porcine-Derived Enterocytes

In our previous studies, Lactobacillus reuteri B1/1, which was renamed Limosilactobacillus reuteri (L. reuteri), was able to modulate the production of pro-inflammatory cytokines and other components of the innate immune response in vitro and in vivo. In this study, we evaluated the effect of Lactobacillus reuteri B1/1 in two concentrations (1 × 10⁷ and 1 × 10⁹ CFU) on the metabolic activity, adherence ability and relative gene expression of pro-inflammatory interleukins (IL-1β, IL-6, IL-8, IL-18), lumican and olfactomedin 4 produced by non-carcinogenic porcine-derived enterocytes (CLAB). CLAB cells were cultured in a 12-well cell culture plate at a concentration of 4 × 10⁵ cells/well in DMEM medium in a controlled humidified atmosphere for 48 h. A 1 mL volume of each probiotic bacterial suspension was added to the CLAB cells. Plates were incubated for 2 h and 4 h. Our results revealed that L. reuteri B1/1 was able to adhere to CLAB cells in sufficient numbers in both concentrations. In particular, the concentration of 10⁹L. reuteri B1/1 allowed to modulate the gene expression of pro-inflammatory cytokines, as well as to increase the metabolic activity of the cells. In addition, administration of L. reuteri B1/1 in both concentrations significantly stimulated gene expression for both proteins in the CLAB cell line after 4 h of incubation.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

flgC gene is involved in the virulence regulation of Pseudomonas plecoglossicida and affects the immune response of Epinephelus coioides

As a pathogen of cultured teleosts, Pseudomonas plecoglossicida has caused significant economic losses. flgC plays an important role in encoding flagellar basal-body rod proteins. Our previous studies revealed the high expression of P. plecoglossicida flgC in infected Epinephelus coioides. To explore the role of flgC in the virulence of P. plecoglossicida and the immune response of E. coioides to the infection of P. plecoglossicida, flgC gene of P. plecoglossicida was knocked down by RNA interference (RNAi). The results showed that the flgC gene in all four mutants of P. plecoglossicida was significantly knocked down, and the mutant with the best knockdown efficiency of 94.3% was selected for subsequent studies. Compared with the NZBD9 strain of P. plecoglossicida, the flgC-RNAi strain showed a significantly decrease in chemotaxis, motility, adhesion, and biofilm formation. Furthermore, compared with the E. coioides infected with the NZBD9 strain, the infection of flgC-RNAi strain resulted in the infected E. coioides a 1.5-day delay in the time of first death and an 80% increase in survival rate, far fewer white nodules upon the spleen surfaces, and lower pathogen load in the spleens. RNAi of flgC significantly influenced the metabolome and transcriptome of the spleen in infected E. coioides. KEGG enrichment analysis exhibited that the Toll-like receptor signaling pathway was the most enriched immune pathway; the most significantly enriched metabolic pathways were associated with Linoleic acid metabolism, Choline metabolism in cancer, and Glycerophospholipid metabolism. Further combined analysis of transcriptome and metabolome indicated significant correlations among pantothenate and CoA biosynthesis, beta-alanine metabolism, lysosome metabolites, and related genes. These results suggested that flgC was a pathogenic gene of P. plecoglossicida; flgC was associated with the regulation of chemotaxis, motility, biofilm formation, and adhesion; flgC influenced the immune response of E. coioides to the infection of P. plecoglossicida.

Intravenous anti-P. aeruginosa IgY-antibodies do not decrease pulmonary bacterial concentrations in a porcine model of ventilator-associated pneumonia

Ventilator associated pneumonia (VAP) caused by P. aeruginosa is a cause of morbidity and mortality in critically ill patients. The spread of pathogens with anti-microbial resistance mandates the investigation of novel therapies. Specific polyclonal anti-P. aeruginosa IgY-antibodies (Pa-IgY) might be effective for VAP caused by P. aeruginosa. The objective of this study was to investigate if intravenous Pa-IgY decreases the lower airway concentration of P. aeruginosa in VAP. We used a double blind randomized placebo controlled porcine model of VAP caused by P. aeruginosa. Eighteen pigs were randomized to either receive intravenous Pa-IgY or placebo. Repeated registration of physiological parameters and sampling was performed for 27 h. Concentration of P. aeruginosa in BAL-cultures was similar in both groups with 104.97 ± 102.09 CFU/mL in the intervention group vs 104.37 ± 102.62 CFU/mL in the control group at the end of the experiment. The intervention group had higher heart rate, cardiac index, oxygen delivery and arterial oxygen tension/fraction of inspired oxygen-ratio, but lower plasma lactate and blood hemoglobin levels than the control group. In summary, in an anesthetized and mechanically ventilated porcine model of VAP, Pa-IgY at the dose used did not decrease concentrations of P. aeruginosa in the lower airways.

Immunogenic Modification of Ligilactobacillus agilis by Specific Amino Acid Substitution of Flagellin

Ligilactobacillus agilis is a flagellated motile commensal microbe that resides in the gastrointestinal tract of mammals and birds. Flagellin, the major subunit protein of flagellar filament, from pathogenic bacteria is generally a proinflammatory molecule that stimulates immune cells via Toll-like receptor 5 (TLR5). Interestingly, the flagellins of L. agilis are known to be immunologically attenuated despite the fact that the structure of the proteins, including the TLR5 recognition site, is highly conserved among bacteria. The results of our previous study suggested that this is attributed to the differences in three specific amino acids within the conserved TLR5 recognition site; however, this hypothesis remains to be confirmed. In this study, a series of recombinant L. agilis flagellins, with amino acid substitutions at the TLR5 recognition site, were constructed, and their immunogenic activity was evaluated in vitro. Then, an L. agilis strain with an active immunogenic TLR5 recognition site was generated. In vitro and in vivo immunological studies revealed that the mutant L. agilis strain with the modified flagellin was more immunogenic than the wild-type strain. In conclusion, the specific amino acid residues in L. agilis flagellins likely contribute to the discrimination between pathogens and commensals by the host defense system. Additionally, the immunogenically potent L. agilis mutants may serve as a useful platform for oral vaccine delivery. IMPORTANCE The interactions between gut microbes and immune cells play an important role in the health and disease of hosts. Ligilactobacillus agilis is a flagellated commensal bacterium found in the gut of mammals and birds. However, the flagellin proteins of L. agilis are immunologically attenuated and barely induce TLR5-dependent inflammation, unlike the flagellins of several pathogenic bacteria. This study demonstrated that three specific amino acids in the flagellin protein are responsible for this low immunogenicity in L. agilis. The results obtained herein improve our understanding of the symbiosis between gut microbes and their hosts.

Nutritional immunomodulation of Atlantic salmon response to Renibacterium salmoninarum bacterin

We investigated the immunomodulatory effect of varying levels of dietary ω6/ω3 fatty acids (FA) on Atlantic salmon (Salmo salar) antibacterial response. Two groups were fed either high-18:3ω3 or high-18:2ω6 FA diets for 8 weeks, and a third group was fed for 4 weeks on the high-18:2ω6 diet followed by 4 weeks on the high-18:3ω3 diet and termed “switched-diet”. Following the second 4 weeks of feeding (i.e., at 8 weeks), head kidney tissues from all groups were sampled for FA analysis. Fish were then intraperitoneally injected with either a formalin-killed Renibacterium salmoninarum bacterin (5 × 10⁷ cells mL⁻¹) or phosphate-buffered saline (PBS control), and head kidney tissues for gene expression analysis were sampled at 24 h post-injection. FA analysis showed that the head kidney profile reflected the dietary FA, especially for C₁₈ FAs. The qPCR analyses of twenty-three genes showed that both the high-ω6 and high-ω3 groups had significant bacterin-dependent induction of some transcripts involved in lipid metabolism (ch25ha and lipe), pathogen recognition (clec12b and tlr5), and immune effectors (znrf1 and cish). In contrast, these transcripts did not significantly respond to the bacterin in the “switched-diet” group. Concurrently, biomarkers encoding proteins with putative roles in biotic inflammatory response (tnfrsf6b) and dendritic cell maturation (ccl13) were upregulated, and a chemokine receptor (cxcr1) was downregulated with the bacterin injection regardless of the experimental diets. On the other hand, an inflammatory regulator biomarker, bcl3, was only significantly upregulated in the high-ω3 fed group, and a C-type lectin family member (clec3a) was only significantly downregulated in the switched-diet group with the bacterin injection (compared with diet-matched PBS-injected controls). Transcript fold-change (FC: bacterin/PBS) showed that tlr5 was significantly over 2-fold higher in the high-18:2ω6 diet group compared with other diet groups. FC and FA associations highlighted the role of DGLA (20:3ω6; anti-inflammatory) and/or EPA (20:5ω3; anti-inflammatory) vs. ARA (20:4ω6; pro-inflammatory) as representative of the anti-inflammatory/pro-inflammatory balance between eicosanoid precursors. Also, the correlations revealed associations of FA proportions (% total FA) and FA ratios with several eicosanoid and immune receptor biomarkers (e.g., DGLA/ARA significant positive correlation with pgds, 5loxa, 5loxb, tlr5, and cxcr1). In summary, dietary FA profiles and/or regimens modulated the expression of some immune-relevant genes in Atlantic salmon injected with R. salmoninarum bacterin. The modulation of Atlantic salmon responses to bacterial pathogens and their associated antigens using high-ω6/high-ω3 diets warrants further investigation.

Virulence Factors of Pseudomonas Aeruginosa and Antivirulence Strategies to Combat Its Drug Resistance

Pseudomonas aeruginosa is an opportunistic pathogen causing nosocomial infections in severely ill and immunocompromised patients. Ubiquitously disseminated in the environment, especially in hospitals, it has become a major threat to human health due to the constant emergence of drug-resistant strains. Multiple resistance mechanisms are exploited by P. aeruginosa, which usually result in chronic infections difficult to eradicate. Diverse virulence factors responsible for bacterial adhesion and colonization, host immune suppression, and immune escape, play important roles in the pathogenic process of P. aeruginosa. As such, antivirulence treatment that aims at reducing virulence while sparing the bacterium for its eventual elimination by the immune system, or combination therapies, has significant advantages over traditional antibiotic therapy, as the former imposes minimal selective pressure on P. aeruginosa, thus less likely to induce drug resistance. In this review, we will discuss the virulence factors of P. aeruginosa, their pathogenic roles, and recent advances in antivirulence drug discovery for the treatment of P. aeruginosa infections.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Mechanisms for the Invasion and Dissemination of Salmonella

Salmonella enterica is a gastroenteric Gram-negative bacterium that can infect both humans and animals and causes millions of illnesses per year around the world. Salmonella infections usually occur after the consumption of contaminated food or water. Infections with Salmonella species can cause diseases ranging from enterocolitis to typhoid fever. Salmonella has developed multiple strategies to invade and establish a systemic infection in the host. Different cell types, including epithelial cells, macrophages, dendritic cells, and M cells, are important in the infection process of Salmonella. Dissemination throughout the body and colonization of remote organs are hallmarks of Salmonella infection. There are several routes for the dissemination of Salmonella typhimurium. This review summarizes the current understanding of the infection mechanisms of Salmonella. Additionally, different routes of Salmonella infection will be discussed. In this review, the strategies used by Salmonella enterica to establish persistent infection will be discussed. Understanding both the bacterial and host factors leading to the successful colonization of Salmonella enterica may enable the rational design of effective therapeutic strategies.

Immunoinformatics Approach Toward the Introduction of a Novel Multi-Epitope Vaccine Against Clostridium difficile

Clostridium difficile (C.difficile) is an exclusively anaerobic, spore-forming, and Gram-positive pathogen that is the most common cause of nosocomial diarrhea and is becoming increasingly prevalent in the community. Because C. difficile is strictly anaerobic, spores that can survive for months in the external environment contribute to the persistence and diffusion of C. difficile within the healthcare environment and community. Antimicrobial therapy disrupts the natural intestinal flora, allowing spores to develop into propagules that colonize the colon and produce toxins, thus leading to antibiotic-associated diarrhea and pseudomembranous enteritis. However, there is no licensed vaccine to prevent Clostridium difficile infection (CDI). In this study, a multi-epitope vaccine was designed using modern computer methods. Two target proteins, CdeC, affecting spore germination, and fliD, affecting propagule colonization, were chosen to construct the vaccine so that it could simultaneously induce the immune response against two different forms (spore and propagule) of C. difficile. We obtained the protein sequences from the National Center for Biotechnology Information (NCBI) database. After the layers of filtration, 5 cytotoxic T-cell lymphocyte (CTL) epitopes, 5 helper T lymphocyte (HTL) epitopes, and 7 B-cell linear epitopes were finally selected for vaccine construction. Then, to enhance the immunogenicity of the designed vaccine, an adjuvant was added to construct the vaccine. The Prabi and RaptorX servers were used to predict the vaccine's two- and three-dimensional (3D) structures, respectively. Additionally, we refined and validated the structures of the vaccine construct. Molecular docking and molecular dynamics (MD) simulation were performed to check the interaction model of the vaccine-Toll-like receptor (TLR) complexes, vaccine-major histocompatibility complex (MHC) complexes, and vaccine-B-cell receptor (BCR) complex. Furthermore, immune stimulation, population coverage, and in silico molecular cloning were also conducted. The foregoing findings suggest that the final formulated vaccine is promising against the pathogen, but more researchers are needed to verify it.

IL-17 Aggravates Pseudomonas aeruginosa Airway Infection in Acute Exacerbations of Chronic Obstructive Pulmonary Disease

Pseudomonas aeruginosa airway infection increases risks of exacerbations and mortality in chronic obstructive pulmonary disease (COPD). We aimed to elucidate the role of IL-17 in the pathogenesis. We examined the expression and influences of IL-23/IL-17A in patients with stable COPD (n = 33) or acute COPD exacerbations with P. aeruginosa infection (n = 34). A mouse model of COPD (C57BL/6) was used to investigate the role of IL-17A in host inflammatory responses against P. aeruginosa infection through the application of IL-17A–neutralizing antibody or recombinant IL-17A. We found that P. aeruginosa infection increased IL-23/17A signaling in lungs of both COPD patients and COPD mouse models. When COPD mouse models were treated with neutralizing antibody targeting IL-17A, P. aeruginosa induced a significantly less polymorphonuclear leukocyte infiltration and less bacterial burden in their lungs compared to those of untreated counterparts. The lung function was also improved by neutralizing antibody. Furthermore, IL-17A-signaling blockade significantly reduced the expression of pro-inflammatory cytokine IL-1β, IL-18, TNF-α, CXCL1, CXCL15 and MMP-9, and increased the expression of anti-inflammatory cytokine IL-10 and IL-1Ra. The application of mouse recombinant IL-17A exacerbated P. aeruginosa-mediated inflammatory responses and pulmonary dysfunction in COPD mouse models. A cytokine protein array revealed that the expression of retinol binding protein 4 (RBP4) was down-regulated by IL-17A, and exogenous RBP4-recombinant protein resulted in a decrease in the severity of P. aeruginosa-induced airway dysfunction. Concurrent application of IL-17A-neutralizing antibody and ciprofloxacin attenuated airway inflammation and ventilation after inoculation of P. aeruginosa in COPD mouse models. Our results revealed that IL-17 plays a detrimental role in the pathogenesis of P. aeruginosa airway infection during acute exacerbations of COPD. Targeting IL-17A is a potential therapeutic strategy in controlling the outcomes of P. aeruginosa infection in COPD patients.

Self-Assembly of Flagellin into Immunostimulatory Ring-like Nanostructures as an Antigen Delivery System

Proteinaceous nanoparticles represent attractive antigen carriers for vaccination as their size and repetitive antigen displays that mimic most viral particles enable efficient immune processing. However, these nanocarriers are often unable to stimulate efficiently the innate immune system, requiring coadministration with adjuvants to promote long-lasting protective immunity. The protein flagellin, which constitutes the primary constituent of the bacterial flagellum, has been widely evaluated as an antigen carrier due to its intrinsic adjuvant properties involving activation of the innate immune receptor Toll-like receptor 5 (TLR5). Although flagellin is known for its ability to self-assemble into micron-scale length nanotubes, few studies have evaluated the potential usage of flagellin-based nanostructures as immunostimulatory antigen carriers. In this study, we reported for the first time a strategy to guide the self-assembly of a flagellin protein from Bacillus subtilis, Hag, into lower aspect ratio nanoparticles by hindering non-covalent interactions responsible for its elongation into nanotubes. We observed that addition of an antigenic sequence derived from the influenza A virus (3M2e) at the C-terminus of this flagellin, as opposed to positioning the epitope into mid-sequence, precluded filament elongation and resulted in low aspect ratio ring-like nanostructures upon salting-out-induced self-assembly. These nanostructures displayed the antigen at their surface and shared morphological and structural characteristics with flagellin nanotubes, with a diameter of approximately 12 nm, and an α-helix-rich secondary structure. Flagellin ring-like nanostructures were efficiently internalized by antigen-presenting cells, and avidly activated the TLR5 in vitro as well as the innate and adaptive immune responses. Intranasal immunization of mice with these nanostructures resulted in the potentiation of the antigen-specific antibody response and protection against a lethal infection with the influenza A virus, illustrating the potential of these intrinsically immunostimulatory nanostructures as antigen carriers.

Shoc2 recognizes bacterial flagellin and mediates antibacterial Erk/Stat signaling in an invertebrate

Flagellin is a key bacterial virulence factor that can stimulate molecular immune signaling in both animals and plants. The detailed mechanisms of recognizing flagellin and mounting an efficient immune response have been uncovered in vertebrates; however, whether invertebrates can discriminate flagellin remains largely unknown. In the present study, the homolog of human SHOC2 leucine rich repeat scaffold protein in kuruma shrimp (Marsupenaeus japonicus), designated MjShoc2, was found to interact with Vibrio anguillarum flagellin A (FlaA) using yeast two-hybrid and pull-down assays. MjShoc2 plays a role in antibacterial response by mediating the FlaA-induced expression of certain antibacterial effectors, including lectin and antimicrobial peptide. FlaA challenge, via MjShoc2, led to phosphorylation of extracellular regulated kinase (Erk), and the subsequent activation of signal transducer and activator of transcription (Stat), ultimately inducing the expression of effectors. Therefore, by establishing the FlaA/MjShoc2/Erk/Stat signaling axis, this study revealed a new antibacterial strategy in shrimp, and provides insights into the flagellin sensing mechanism in invertebrates.

Flagellin sensing has been proven as a general antibacterial strategy. Recognition of bacterial flagellin by the transmembrane receptor toll like receptor 5 (TLR5) leads to the activation of nuclear factor kappa B (NF-κB) pathway and induction of proinflammatory cytokines, while recognition by the intracellular nucleotide-binding leucine-rich (NLR) receptor leads to caspase-activation and cytokines-expression. Although flagellin is an effective immune stimulator that induces antimicrobial peptides in Drosophila and in crustaceans, how an invertebrate host senses flagellin and mounts an immune response is poorly understood. Here, we used the flagellin (FlaA) from Vibrio anguillarum, a pathogen of shrimp, as a bait protein to screen a yeast two-hybrid library derived from kuruma shrimp (Marsupenaeus japonicus). We found a scaffold protein, MjShoc2, able to interact with FlaA. We also found that FlaA could effectively induce the expression of certain recognized antibacterial effectors in shrimp depending on MjShoc2. We revealed that extracellular regulated kinase (Erk) phosphorylation occurred downstream of FlaA/MjShoc2, and led to signal transducer and activator of transcription (Stat) activation, resulting in transcription of certain effectors. Therefore our study provides new insights into the FlaA-induced molecular immunity in invertebrates.

Recombinant Bacillus subtilis flagellin Hag is a potent immunostimulant with reduced proinflammatory properties compared to Salmonella enterica serovar Typhimurium FljB

Flagellin constitutes a potential adjuvant for vaccines owing to its robust immunostimulatory properties. However, clinical trials have revealed that flagellin derived from Salmonella enterica serovar Typhimurium induces high levels of proinflammatory markers and substantial adverse effects. The flagellin from Bacillus subtilis, Hag, shares high sequence homology with Salmonella FljB within the D0 and D1 domains responsible for TLR5 engagement, while the D2 and D3 domains associated with an off-target immune response are absent. Accordingly, we compared the immunostimulatory and proinflammatory properties of Hag with FljB by harnessing an epitope from the matrix 2 protein (M2e) of the influenza virus. Both flagellins engaged TLR5, with FljB showing a 2.5-fold higher potency than Hag. Mice inoculation showed a robust FljB- or Hag-induced M2e-specific antibody response, with Hag demonstrating a decreased secretion of proinflammatory markers and reduced weight loss. This study revealed that flagellin Hag is a potent immunoadjuvant with reduced proinflammatory properties.

Immunometabolites Drive Bacterial Adaptation to the Airway

Pseudomonas aeruginosa and Staphylococcus aureus are both opportunistic pathogens that are frequently associated with chronic lung infections. While bacterial virulence determinants are critical in initiating infection, the metabolic flexibility of these bacteria promotes their persistence in the airway. Upon infection, these pathogens induce host immunometabolic reprogramming, resulting in an airway milieu replete with immune-signaling metabolites. These metabolites are often toxic to the bacteria and create a steep selection pressure for the emergence of bacterial isolates adapted for long-term survival in the inflamed lung. In this review, we discuss the main differences in the host immunometabolic response to P. aeruginosa and S. aureus, as well as how these pathogens alter their own metabolism to adapt to airway metabolites and cause persistent lung infections.

The Impact of Di-Isononyl Phthalate Exposure on Specialized Epithelial Cells in the Colon

Di-isononyl phthalate (DiNP) is a high-molecular-weight phthalate commonly used as a plasticizer for polyvinyl chloride and other end products, such as medical devices and construction materials. Most of our initial exposure to DiNP occurs by ingestion of DiNP-contaminated foods. However, little is known about the effects of DiNP on the colon. Therefore, the goal of this study was to test the hypothesis that DiNP exposure alters immune responses and impacts specialized epithelial cells in the colon. To test this hypothesis, adult female mice were orally dosed with corn-oil vehicle control or doses of DiNP ranging from 20 µg/kg/d to 200 mg/kg/d for 10-14 days. After the dosing period, mice were euthanized in diestrus, and colon tissues and sera were collected for histological, genomic, and proteomic analysis of various immune factors and specialized epithelial cells. Subacute exposure to DiNP significantly increased protein levels of Ki67 and MUC2, expression of a Paneth cell marker (Lyz1), and estradiol levels in sera compared with control. Gene expression of mucins (Muc1, Muc2, Muc3a, and Muc4), Toll-like receptors (Tlr4 and Tlr5), and specialized epithelial cells (ChgA, Lgr5, Cd24a, and Vil1) were not significantly different between treatment groups and control. Cytokine levels of IL-1RA and CXCL12 were also not significantly different between DiNP treatment groups and control. These data reveal that DiNP exposure increases circulating estradiol levels and gene expression in specialized epithelial cells with immune response capabilities (eg, goblet and Paneth cells) in the mouse colon, which may initiate immune responses to prevent further damage in the colon.

Salmonella flagella confer anti-tumor immunological effect via activating Flagellin/TLR5 signalling within tumor microenvironment

mediated cancer therapy has achieved remarkable anti-tumor effects in experimental animal models, but the detailed mechanism remains unsolved. In this report, the active involvement of the host immune response in this process was confirmed by comparing the tumor-suppressive effects of Salmonella in immunocompetent and immunodeficient mice bearing melanoma allografts. Since flagella are key inducers of the host immune response during bacterial infection, flagella were genetically disrupted to analyse their involvement in Salmonella-mediated cancer therapy. The results showed that flagellum-deficient strains failed to induce significant anti-tumor effects, even when more bacteria were administered to offset the difference in invasion efficiency. Flagella mainly activate immune cells via Flagellin/Toll-like receptor 5 (TLR5) signalling pathway. Indeed, we showed that exogenous activation of TLR5 signalling by recombinant Flagellin and exogenous expression of TLR5 both enhanced the therapeutic efficacy of flagellum-deficient Salmonella against melanoma. Our study highlighted the therapeutic value of the interaction between Salmonella and the host immune response through Flagellin/TLR5 signalling pathway during Salmonella-mediated cancer therapy, thereby suggesting the potential application of TLR5 agonists in the cancer immune therapy.

In silico designing of vaccine candidate against Clostridium difficile

Clostridium difficile is a spore-forming gram-positive bacterium, recognized as the primary cause of antibiotic-associated nosocomial diarrhoea. Clostridium difficile infection (CDI) has emerged as a major health-associated infection with increased incidence and hospitalization over the years with high mortality rates. Contamination and infection occur after ingestion of vegetative spores, which germinate in the gastro-intestinal tract. The surface layer protein and flagellar proteins are responsible for the bacterial colonization while the spore coat protein, is associated with spore colonization. Both these factors are the main concern of the recurrence of CDI in hospitalized patients. In this study, the CotE, SlpA and FliC proteins are chosen to form a multivalent, multi-epitopic, chimeric vaccine candidate using the immunoinformatics approach. The overall reliability of the candidate vaccine was validated in silico and the molecular dynamics simulation verified the stability of the vaccine designed. Docking studies showed stable vaccine interactions with Toll‐Like Receptors of innate immune cells and MHC receptors. In silico codon optimization of the vaccine and its insertion in the cloning vector indicates a competent expression of the modelled vaccine in E. coli expression system. An in silico immune simulation system evaluated the effectiveness of the candidate vaccine to trigger a protective immune response.

Reverse vaccinology approach for the identifications of potential vaccine candidates against Salmonella

Salmonella is a leading cause of foodborne pathogen which causes intestinal and systemic diseases across the world. Vaccination is the most effective protection against Salmonella, but the identification and design of an effective broad-spectrum vaccine is still a great challenge, because of the multi-serotypes of Salmonella. Reverse vaccinology is a new tool to discovery and design vaccine antigens combining human immunology, structural biology and computational biology with microbial genomics. In this study, reverse vaccinology, an in-silico approach was established to screen appropriate immunogen targets by calculating the immunogenicity score of 583 non-redundant outer membrane and secreted proteins of Salmonella. Herein among 100 proteins identified with top-ranked scores, 15 representative antigens were selected randomly. Applying the sequence conservation test, four proteins (FliK, BcsZ, FhuA and FepA) remained as potential vaccine candidates for in vivo evaluation of immunogenicity and immunoprotection. All four candidates were capable to trigger the immune response and stimulate the production of antiserum in mice. Furthermore, top-ranked proteins including FliK and BcsZ provided wide antigenic coverage among the multi-serotype of Salmonella. The S. Typhimurium LT2 challenge model used in mice immunized with FliK and BcsZ showed a high relative percentage survival (RPS) of 52.74 % and 64.71 % respectively. In conclusion, this study constructed an in-silico pipeline able to successfully pre-screen the vaccine targets characterized by high immunogenicity and protective immunity. We show that reverse vaccinology allowed screening of appropriate broad-spectrum vaccines for Salmonella.

Bronchially instilled IgY-antibodies did not decrease pulmonary p. aeruginosa concentration in experimental porcine pneumonia

BACKGROUND

P. aeruginosa possesses antibiotic resistance, making treatment difficult. Polyclonal anti-P. aeruginosa IgY-antibodies (Pa-IgY) have antibacterial effects, but have not been studied in large animal pneumonia.

OBJECTIVES

To test if Pa-IgY decreases the concentration of P. aeruginosa in bronchoalveolar lavage in experimental porcine pneumonia over 27 hours.

METHOD

Norwegian landrace pigs were anesthetized, mechanically ventilated, and subject to invasive monitoring. The animals were randomized to receive either P. aeruginosa (control, n = 12) or P aeruginosa + Pa-IgY antibodies with a repeated dose of Pa-IgY after 12 hours (intervention, n = 12) in the right lower pulmonary lobe. Bronchoalveolar lavage (BAL) cultures and physiological measurements were obtained repeatedly for 27 hours after which the pigs were sacrificed.

RESULTS

BAL bacterial concentration increased in both groups and peaked at 107.28  ± 100.21  CFU/mL in the intervention group vs 107 .36  ± 100.50  CFU/mL in the control group (n.s.). BAL bacterial concentration decreased during the experiment to 105.35  ± 100 .39  CFU/mL in the intervention group vs 105.19  ± 100.37 in the control group (n.s.). The intervention group had lower heart rate (P < .001), lower cardiac index (P < .01), and lower arterial lactate (P < .001) compared to the control group. The core temperature was lower in the intervention group than in the control group (P < .001).

CONCLUSION

The chosen dose of Pa-IgY did not decrease concentrations of P. aeruginosa in BAL over 27 hours. We conclude that it is unlikely that there is a large effect of this specific dose and route of administration of Pa-IgY in this type of model.

Anesthetics isoflurane and sevoflurane attenuate flagellin-mediated inflammation in the lung

Isoflurane and sevoflurane are volatile anesthetics (VA) widely used in clinical practice to provide general anesthesia. We and others have previously shown that VAs have immunomodulatory effects and may have a significant impact on the progression of disease states. Flagellin is a component of Gram negative bacteria and plays a significant role in the pathophysiology of bacterial pneumonia through its binding to Toll-like Receptor 5 (TLR5). Our results showed that VAs, not an intravenous anesthetic, significantly attenuated the activation of TLR5 and the release of the neutrophil chemoattractant IL-8 from lung epithelial cells. Furthermore, flagellin-induced lung injury was significantly attenuated by VAs by inhibiting neutrophil migration to the bronchoalveolar space. The lungs of cystic fibrosis (CF) patients are highly colonized by Pseudomonas aeruginosa, which causes inflammation. The retrospective study of oxygenation in patients with CF who had received VA versus intravenous anesthesia suggested that VAs might have the protective effect for gas exchange. To understand the interaction between VAs and TLR5, a docking simulation was performed, which indicated that isoflurane and sevoflurane docked into the binding interphase between TLR5 and flagellin.

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.

Convergent Losses of TLR5 Suggest Altered Extracellular Flagellin Detection in Four Mammalian Lineages

Toll-like receptors (TLRs) play an important role for the innate immune system by detecting pathogen-associated molecular patterns. TLR5 encodes the major extracellular receptor for bacterial flagellin and frequently evolves under positive selection, consistent with coevolutionary arms races between the host and pathogens. Furthermore, TLR5 is inactivated in several vertebrates and a TLR5 stop codon polymorphism is widespread in human populations. Here, we analyzed the genomes of 120 mammals and discovered that TLR5 is convergently lost in four independent lineages, comprising guinea pigs, Yangtze river dolphin, pinnipeds, and pangolins. Validated inactivating mutations, absence of protein-coding transcript expression, and relaxed selection on the TLR5 remnants confirm these losses. PCR analysis further confirmed the loss of TLR5 in the pinniped stem lineage. Finally, we show that TLR11, encoding a second extracellular flagellin receptor, is also absent in these four lineages. Independent losses of TLR5 and TLR11 suggest that a major pathway for detecting flagellated bacteria is not essential for different mammals and predicts an impaired capacity to sense extracellular flagellin.

Going, Toll-like receptors in skin inflammation and inflammatory diseases

The Indian Ayurvedic physicians knew the concept of inflammation dating back to 1500 BC. The continuous progress in the immunology of inflammation has explained its undiscovered mechanisms. For example, the discovery of Toll-like receptor 4 (TLR4) in humans (1997) has revolutionized the field of infection biology and innate immunity. The laboratory mice have shown twelve TLRs and express TLR10 (CD290) as a disrupted pseudogene, and humans have ten functional TLRs. Now, it is well established that TLRs play a significant role in different infectious and inflammatory diseases. Skin inflammation and other associated inflammatory diseases, including atopic dermatitis (AD), acne vulgaris, and psoriasis, along with many skin cancers are major health problems all over the world. The continuous development in the immunopathogenesis of inflammatory skin diseases has opened the window of opportunity for TLRs in studying their role. Hence, the manuscript explores the role of different TLRs in the pathogenesis of skin inflammation and associated inflammatory diseases. The article starts with the concept of inflammation, its origin, and the impact of TLRs discovery on infection and inflammation biology. The subsequent section describes the burden of skin-associated inflammatory diseases worldwide and the effect of the geographical habitat of people affecting it. The third section explains skin as an immune organ and explains the expression of different TLRs on different skin cells, including keratinocytes, Langerhans cells (LCs), skin fibroblasts, and melanocytes. The fourth section describes the impact of TLRs on these cells in different skin-inflammatory conditions, including acne vulgaris, AD, psoriasis, and skin cancers. The article also discusses the use of different TLR-based therapeutic approaches as specific to these inflammatory skin diseases.

Fusion of Bacterial Flagellin to a Dendritic Cell-Targeting αCD40 Antibody Construct Coupled With Viral or Leukemia-Specific Antigens Enhances Dendritic Cell Maturation and Activates Peptide-Responsive T Cells

Conventional dendritic cell (DC) vaccine strategies, in which DCs are loaded with antigens ex vivo, suffer biological issues such as impaired DC migration capacity and laborious GMP production procedures. In a promising alternative, antigens are targeted to DC-associated endocytic receptors in vivo with antibody–antigen conjugates co-administered with toll-like receptor (TLR) agonists as adjuvants. To combine the potential advantages of in vivo targeting of DCs with those of conjugated TLR agonists, we generated a multifunctional antibody construct integrating the DC-specific delivery of viral- or tumor-associated antigens and DC activation by TLR ligation in one molecule. We validated its functionality in vitro and determined if TLR ligation might improve the efficacy of such a molecule. In proof-of-principle studies, an αCD40 antibody containing a CMV pp65-derived peptide as an antigen domain (αCD40^CMV) was genetically fused to the TLR5-binding D0/D1 domain of bacterial flagellin (αCD40.Flg^CMV). The analysis of surface maturation markers on immature DCs revealed that fusion of flagellin to αCD40^CMV highly increased DC maturation (3.4-fold elevation of CD80 expression compared to αCD40^CMV alone) by specifically interacting with TLR5. Immature DCs loaded with αCD40.Flg^CMV induced significantly higher CMV_NLV-specific T cell activation and proliferation compared to αCD40^CMV in co-culture experiments with allogeneic and autologous T cells (1.8-fold increase in % IFN-γ/TNF-α⁺ CD8⁺ T cells and 3.9-fold increase in % CMV_NLV-specific dextramer⁺ CD8⁺ T cells). More importantly, we confirmed the beneficial effects of flagellin-dependent DC stimulation using a tumor-specific neoantigen as the antigen domain. Specifically, the acute myeloid leukemia (AML)-specific mutated NPM1 (mNPM1)-derived neoantigen CLAVEEVSL was delivered to DCs in the form of αCD40^mNPM1 and αCD40.Flg^mNPM1 antibody constructs, making this study the first to investigate mNPM1 in a DC vaccination context. Again, αCD40.Flg^mNPM1-loaded DCs more potently activated allogeneic mNPM1_CLA-specific T cells compared to αCD40^mNPM1. These in vitro results confirmed the functionality of our multifunctional antibody construct and demonstrated that TLR5 ligation improved the efficacy of the molecule. Future mouse studies are required to examine the T cell-activating potential of αCD40.Flg^mNPM1 after targeting of dendritic cells in vivo using AML xenograft models.

Signal Transduction Pathways Activated by Innate Immunity in Mast Cells: Translating Sensing of Changes into Specific Responses

Mast cells (MCs) constitute an essential cell lineage that participates in innate and adaptive immune responses and whose phenotype and function are influenced by tissue-specific conditions. Their mechanisms of activation in type I hypersensitivity reactions have been the subject of multiple studies, but the signaling pathways behind their activation by innate immunity stimuli are not so well described. Here, we review the recent evidence regarding the main molecular elements and signaling pathways connecting the innate immune receptors and hypoxic microenvironment to cytokine synthesis and the secretion of soluble or exosome-contained mediators in this cell type. When known, the positive and negative control mechanisms of those pathways are presented, together with their possible implications for the understanding of mast cell-driven chronic inflammation. Finally, we discuss the relevance of the knowledge about signaling in this cell type in the recognition of MCs as central elements on innate immunity, whose remarkable plasticity converts them in sensors of micro-environmental discontinuities and controllers of tissue homeostasis.

Early Cytokine Induction Upon Pseudomonas aeruginosa Infection in Murine Precision Cut Lung Slices Depends on Sensing of Bacterial Viability

Breathing allows a multitude of airborne microbes and microbial compounds to access the lung. Constant exposure of the pulmonary microenvironment to immunogenic particles illustrates the need for proper control mechanisms ensuring the differentiation between threatening and harmless encounters. Discrimination between live and dead bacteria has been suggested to be such a mechanism. In this study, we performed infection studies of murine precision cut lung slices (PCLS) with live or heat-killed P. aeruginosa, in order to investigate the role of viability for induction of an innate immune response. We demonstrate that PCLS induce a robust transcriptomic rewiring upon infection with live but not heat-killed P. aeruginosa. Using mutants of the P. aeruginosa clinical isolate CHA, we show that the viability status of P. aeruginosa is assessed in PCLS by TLR5-independent sensing of flagellin and recognition of the type three secretion system. We further demonstrate that enhanced cytokine expression towards live P. aeruginosa is mediated by uptake of viable but not heat-killed bacteria. Finally, by using a combined approach of receptor blockage and genetically modified PCLS we report a redundant involvement of MARCO and CD200R1 in the uptake of live P. aeruginosa in PCLS. Altogether, our results show that PCLS adapt the extent of cytokine expression to the viability status of P. aeruginosa by specifically internalizing live bacteria.

Entolimod as a radiation countermeasure for acute radiation syndrome

High doses of total-body or partial-body radiation exposure can result in a life-threatening acute radiation syndrome as manifested by severe morbidity. Entolimod (CBLB502) is effective in protecting against, and mitigating the development of, the hematopoietic and gastrointestinal subsyndromes of the acute radiation syndrome in rodents and nonhuman primates. Entolimod treatment reduces radiation-induced apoptosis and accelerates the regeneration of progenitors in radiation-damaged tissues. The drug has been evaluated clinically for its pharmacokinetics (PK), toxicity, and biomarkers. The US Food and Drug Administration (FDA) has granted investigational new drug, fast-track, and orphan drug statuses to entolimod. Its safety, efficacy, and animal-to-human dose conversion data allowed its progression with a pre-emergency use authorization application submission.

Toll-like receptors in sepsis-associated cytokine storm and their endogenous negative regulators as future immunomodulatory targets

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Sepsis infects more than 48.9 million people world-wide, with 19.7 million deaths.

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Cytokine storm plays a significant role in sepsis, along with severe COVID-19.

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TLR signaling pathways plays a crucial role in generating the cytokine storm.

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Endogenous negative regulators of TLR signaling are crucial to regulate cytokine storm.

Cytokine storm generates during various systemic acute infections, including sepsis and current pandemic called COVID-19 (severe) causing devastating inflammatory conditions, which include multi-organ failure or multi-organ dysfunction syndrome (MODS) and death of the patient. Toll-like receptors (TLRs) are one of the major pattern recognition receptors (PRRs) expressed by immune cells as well as non-immune cells, including neurons, which play a crucial role in generating cytokine storm. They recognize microbial-associated molecular patterns (MAMPs, expressed by pathogens) and damage or death-associate molecular patterns (DAMPs; released and/expressed by damaged/killed host cells). Upon recognition of MAMPs and DAMPs, TLRs activate downstream signaling pathways releasing several pro-inflammatory mediators [cytokines, chemokines, interferons, and reactive oxygen and nitrogen species (ROS or RNS)], which cause acute inflammation meant to control the pathogen and repair the damage. Induction of an exaggerated response due to genetic makeup of the host and/or persistence of the pathogen due to its evasion mechanisms may lead to severe systemic inflammatory condition called sepsis in response to the generation of cytokine storm and organ dysfunction. The activation of TLR-induced inflammatory response is hardwired to the induction of several negative feedback mechanisms that come into play to conclude the response and maintain immune homeostasis. This state-of-the-art review describes the importance of TLR signaling in the onset of the sepsis-associated cytokine storm and discusses various host-derived endogenous negative regulators of TLR signaling pathways. The subject is very important as there is a vast array of genes and processes implicated in these negative feedback mechanisms. These molecules and mechanisms can be targeted for developing novel therapeutic drugs for cytokine storm-associated diseases, including sepsis, severe COVID-19, and other inflammatory diseases, where TLR-signaling plays a significant role.

Polymorphisms in Toll-like receptors 1, 2, 5, and 10 are associated with predisposition to Helicobacter pylori infection

OBJECTIVE

Toll-like receptors (TLRs) are significant receptors to the innate immune system which symbolizes a family of pattern recognition receptors. We aimed to investigate associations between rs4833095 polymorphism of TLR1, rs3804099 polymorphism of TLR2, rs5744174 polymorphism of TLR5, and rs10004195 polymorphism of TLR10 in dyspeptic individuals with Helicobacter pylori infection.

METHODS

Genomic DNA was isolated and genotyping of rs4833095 polymorphism in TLR1, rs3804099 polymorphism in TLR2, rs5744174 polymorphism in TLR5, and rs10004195 polymorphism in TLR10 were investigated in 400 individuals (205 in dyspeptic individuals with H. pylori-positive subjects and 195 dyspeptic individuals with H. pylori-negative subjects) by real-time PCR. Statistical analysis was performed by Pearson's Chi-square test.

RESULTS

According to our study; rs4833095 polymorphism in TLR1 C allele, rs3804099 polymorphism in TLR2 C allele, rs5744174 polymorphism in TLR5 C allele, and rs10004195 polymorphism in TLR10 A allele increased the risk of H. pylori infection [odds ratio (OR), 2.01; 95% confidence interval (CI), 1.39-3.16; OR, 1.78; 95% CI, 1.19-2.6; OR, 1.87; 95% CI, 1.25-2.78; OR, 2.66; 95% CI, 1.72-4.099, respectively].

CONCLUSION

This is the first study that investigates TLRs in H. pylori infection in Turkey. Our findings may support the hypothesis that polymorphisms in certain TLRs may cause a genetic predisposition to H. pylori-related gastric problems.

Mannheimia haemolytica and lipopolysaccharide induce airway epithelial inflammatory responses in an extensively developed ex vivo calf model

Pulmonary infection is associated with inflammation and damage to the bronchial epithelium characterized by an increase in the release of inflammatory factors and a decrease in airway barrier function. Our objective is to optimize a method for the isolation and culture of primary bronchial epithelial cells (PBECs) and to provide an ex vivo model to study mechanisms of epithelial airway inflammation. PBECs were isolated and cultured from the airways of calves in a submerged cell culture and liquid-liquid interface system. A higher yield and cell viability were obtained after stripping the epithelium from the bronchial section compared to cutting the bronchial section in smaller pieces prior to digestion. Mannheimia haemolytica and lipopolysaccharide (LPS) as stimulants increased inflammatory responses (IL-8, IL-6 and TNF-α release), possibly, by the activation of "TLR-mediated MAPKs and NF-κB" signaling. Furthermore, M. haemolytica and LPS disrupted the bronchial epithelial layer as observed by a decreased transepithelial electrical resistance and zonula occludens-1 and E-cadherin expression. An optimized isolation and culture method for calf PBECs was developed, which cooperated with animal use Replacement, Reduction and Refinement (3R's) principle, and can also contribute to the increased knowledge and development of effective therapies for other animal and humans (childhood) respiratory diseases.

Boosting the IL-22 response using flagellin prevents bacterial infection in cigarette smoke-exposed mice

The progression of chronic obstructive pulmonary disease (COPD), a lung inflammatory disease being the fourth cause of death worldwide, is marked by acute exacerbations. These episodes are mainly caused by bacterial infections, frequently due to Streptococcus pneumoniae. This susceptibility to infection involves a defect in interleukin (IL)-22, which plays a pivotal role in mucosal defense mechanism. Administration of flagellin, a Toll-like receptor 5 (TLR-5) agonist, can protect mice and primates against respiratory infections in a non-pathological background. We hypothesized that TLR-5-mediated stimulation of innate immunity might improve the development of bacteria-induced exacerbations in a COPD context. Mice chronically exposed to cigarette smoke (CS), mimicking COPD symptoms, are infected with S. pneumoniae, and treated in a preventive and a delayed manner with flagellin. Both treatments induced a lower bacterial load in the lungs and blood, and strongly reduced the inflammation and lung lesions associated with the infection. This protection implicated an enhanced production of IL-22 and involved the recirculation of soluble factors secreted by spleen cells. This is also associated with higher levels of the S100A8 anti-microbial peptide in the lung. Furthermore, human mononuclear cells from non-smokers were able to respond to recombinant flagellin by increasing IL-22 production while active smoker cells do not, a defect associated with an altered IL-23 production. This study shows that stimulation of innate immunity by a TLR-5 ligand reduces CS-induced susceptibility to bacterial infection in mice, and should be considered in therapeutic strategies against COPD exacerbations.

The Role of Endophytic/Epiphytic Bacterial Constituents in the Immunostimulatory Activity of the Botanical, Astragalus membranaceus

Astragalus membranaceus is a staple of Traditional Chinese Medicine being one of the oldest medicinal herbs listed in the material medica of Chinese herbal medicine. Chinese herbalists have used Astragalus to help the human body fight a variety of diseases. Modern herbalists utilize Astragalus primarily as an immunostimulant to prevent common infection and aid in the recovery following infection. Historically, the biological activities associated with Astragalus have been accounted for, at least in part, to several constituents present in the botanical including saponins and polysaccharides. We propose that in addition to these constituents, compounds from endophytic (or epiphytic) bacteria present in (or on) the roots of Astragalus may have an important biological role. Lipopolysaccharides and lipoproteins are major components of Gram-negative bacteria and highly potent activators of the innate immune response. Our data supports a direct correlation between the level of immune gene induction and the level of lipopolysaccharides/lipoproteins present in the Astragalus extract. We demonstrate that extracts from Astragalus specifically activate Toll-like and NOD-like receptors involved in the recognition and response to bacterial constituents and that removal of the lipopolysaccharide/lipoprotein from the Astragalus extract reduced the level of this response. The results support that many immune enhancing botanicals have established a symbiotic relationship with Gram-negative bacteria and that the immune enhancing effect of these botanical extracts on the body may not only be due to endogenous plant compounds, but endophytic (or epiphytic) bacterial components as well.

Innate and Adaptive Immune Responses during Listeria monocytogenes Infection

It could be argued that we understand the immune response to infection with Listeria monocytogenes better than the immunity elicited by any other bacteria. L. monocytogenes are Gram-positive bacteria that are genetically tractable and easy to cultivate in vitro, and the mouse model of intravenous (i.v.) inoculation is highly reproducible. For these reasons, immunologists frequently use the mouse model of systemic listeriosis to dissect the mechanisms used by mammalian hosts to recognize and respond to infection. This article provides an overview of what we have learned over the past few decades and is divided into three sections: "Innate Immunity" describes how the host initially detects the presence of L. monocytogenes and characterizes the soluble and cellular responses that occur during the first few days postinfection; "Adaptive Immunity" discusses the exquisitely specific T cell response that mediates complete clearance of infection and immunological memory; "Use of Attenuated Listeria as a Vaccine Vector" highlights the ways that investigators have exploited our extensive knowledge of anti-Listeria immunity to develop cancer therapeutics.

Characterisation and functional analysis of canine TLR5

In this study, we characterised the single exon TLR5 gene of the Chinese rural dog. Sequence analysis revealed a 2577 nucleotide-long open reading frame of canine TLR5, encoding an 858 amino acid-long protein. The putative amino acid sequence of canine TLR5 consisted of a signal peptide sequence, 15 LRR domains, a LRR C-terminal domain, a transmembrane domain and an intracellular Toll-IL-1 receptor domain. The amino acid sequence of the canine TLR5 protein shared 95.4% identity with vulpine, 72.2% with feline and 64.7% with human TLR5. Plasmids expressing canine TLR5 and NF-κB-luciferase were constructed and transfected into HEK293T cells. Expression was confirmed by indirect immunofluorescence assay. These HEK293T cells transfected with the canine TLR5- and NF-κB-luciferase plasmids significantly responded to flagellin from Salmonella enteritidis serovar Typhimurium, indicating that it is a functional TLR5 homolog. In response to stimulation with Salmonella enteritidis, the level of TLR5 mRNA significantly increased over the control in PBMCs at 4 h. The levels of IL-8, IL-6 and IL-1β also increased after exposure. The highest levels of TLR5, IL-8 and IL-1β expression were detected at 8, 4 and 12 h after stimulation, respectively. These results imply that the expression of canine TLR5 may participate in the immune response against bacterial pathogens.

Multiomics analyses reveal that NOD-like signaling pathway plays an important role against Streptococcus agalactiae in the spleen of tilapia

Streptococcus aglactiae(GBS) infection in tilapia is a serious global disease that causes significant production loss. Here, we studied the role of GBS in the spleen and the spleen's response against the pathogen through dual RNA-seq and proteome technology. Animals were divided into three groups: control, virulent treated (HN016), and attenuated treated (YM001). Spleen samples were collected and analysis when a disease outbreak. Dual RNA-seq result showed the virulence factor genes of GBS, included CAMP factor, PGK, OCT, enolase, scpB, Sip, bca, were upregulation. downregulation of GapA, cylE, OCT, scpB, C5AP, rlmB, hly, FBP, in HN016 and YM001. But for proteomic, OCT and bca were downregulation, the others were upregulation. For host transcriptome KEGG analysis showed, the NOD-like receptor signaling pathway (NLRs) and TOLL-like receptor signaling pathway (TLRs) were upreguoation in HN016 infected fish than the control fish; But for proteome KEGG, only the NLRS was up, the TLRS was not change. Compared with YM001 infected fishes, for transcriptome, NLRs and TLRs in infected HN016 fishes were significance rise (p < 0.01); for proteome, the NLRs was up (p < 0.05), but TLRs was no change.Analysis of pathogen-host interaction showed that the peptidoglycan (PNG), CD2, LCK, and host's Zap70 were involved in the regulation of NLRs; PNG, LCK, and ZAP70 were involved in the regulation of TRLs. Conclusion: the virulent strain HN016 and attenuated strainYM001 differed in the quantity of virulence factors. In tilapia's innate immune system, NLRs was the main defense factors, but bacteria avoided the host defense through TLRs.

Insights into flagellar function and mechanism from the squid-vibrio symbiosis

Flagella are essential and multifunctional nanomachines that not only move symbionts towards their tissue colonization site, but also play multiple roles in communicating with the host. Thus, untangling the activities of flagella in reaching, interacting, and signaling the host, as well as in biofilm formation and the establishment of a persistent colonization, is a complex problem. The squid-vibrio system offers a unique model to study the many ways that bacterial flagella can influence a beneficial association and, generally, other bacteria-host interactions. Vibrio fischeri is a bioluminescent bacterium that colonizes the Hawaiian bobtail squid, Euprymna scolopes. Over the last 15 years, the structure, assembly, and functions of V. fischeri flagella, including not only motility and chemotaxis, but also biofilm formation and symbiotic signaling, have been revealed. Here we discuss these discoveries in the perspective of other host-bacteria interactions.