Cloning and characterization of the murine toll-like receptor 5 (Tlr5) gene: sequence and mRNA expression studies in Salmonella-susceptible MOLF/Ei mice

Membrane orthologs of TLR5 of tongue sole Cynoglossus semilaevis: Expression patterns, signaling pathway and antibacterial property

Mammalian toll-like receptor 5 (TLR5) is crucial for recognizing bacterial flagellin and initiating the inflammatory signaling cascades via myeloid differentiation factor 88 (MyD88) signaling pathway, which plays vital roles in innate immune against pathogenic bacteria. Herein, we reported the signaling pathway and antibacterial property of tongue sole (Cynoglossus semilaevis) membrane forms of TLR5 (i.e. CsTLR5M1and CsTLR5M2). CsTLR5M1/M2 contain 936 and 885 amino acid residues respectively. CsTLR5M1 shares 86.7% overall sequence identities with CsTLR5M2. CsTLR5M1/M2 possess the same extracellular domain (ECD) and transmembrane domain (TMD), but the different toll-interleukin-1 receptor (TIR) domain. CsTLR5M1/M2 expression occurred constitutively in multiple tissues and regulated by bacterial stimulation. Recombinant CsTLR5M1/M2 (rCsTLR5M) could bind to flagellin and Gram-negative/positive bacteria, which could suppress bacterial growth. Stimulation of the CsTLR5M pathway by flagellin resulted in increased expression of MyD88-dependent signaling molecules and inflammatory cytokines. Blocking rCsTLR5M by antibody markedly reduced the phagocytosis and ROS production of peripheral blood leukocytes (PBLs), which in turn in vivo promoted the dissemination of bacteria. Overall, these observations add new insights into the signaling pathway and immune function of teleost TLR5M.

Molecular cloning and functional studies on magang goose toll-like receptor 5

Disease outbreaks heavily impact the economic viability of animal industries. Little is known about the mechanisms of immune system-related diseases in geese. Toll-like receptors (TLRs) play a major role in the anti-inflammatory immunity process in most animal species, but they have not been studied in the Magang goose. To elucidate the role of TLRs, reverse transcription polymerase chain reaction (RT-PCR) and PCR amplification of cDNA ends (Smart RACE) were used to clone the Magang goose TLR5 gene (mgTLR5). The full-length cDNA of mgTLR5 was 2967 bp in length, including a 5'-terminal untranslated region (UTR) of 215 bp, a 3'-terminal UTR of 384 bp, and an open reading frame of 2583 bp that encodes a protein of 860 amino acids. Structurally, mgTLR5 has a toll/interleukin-receptor (TIR) domain, a transmembrane domain, and seven leucine-rich repeats (LRRs) domains. Homology alignment of TLR5 and its TIR domains with other species revealed that mgTLR5 shared 98 % and 81.3 % of sequence similarity with white goose TLR5 and chicken TLR5, respectively. Quantitative RT-PCR showed that the mgTLR5 gene of the goose is widely expressed in all tested tissues, with the highest expression in the kidney and spleen. The increase in NF-κB promoter activity stimulated by flagellin was dependent on mgTLR5 expression in 293 T cells. Salmonella pullorum and flagellin significantly upregulated the expression of TLR5, IL-8, and IL-1 mRNA in peripheral blood mononucleotide cells of Magang goose cultured in vitro. Stimulation by S. pullorum for 24 h upregulated mgTLR5 expression in the cecum and kidney. We conclude that Magang goose TLR5 is a functional TLR5 homologue of the protein in other species and plays an important role in bacterial recognition.

Molecular Characterization and Evolution Analysis of Two Forms of TLR5 and TLR13 Genes Base on Larimichthys crocea Genome Data

TLRs (Toll-like receptors) are essential in host defense against pathogens. There are two types of TLR5, namely, membrane form of TLR5 (TLR5M) and soluble form of TLR5 (TLR5S), both of which perform a crucial role in flagellin response. TLR13 is a TLR that localizes to endosomes and recognizes nucleic acids released by internal microorganisms, including viruses, bacteria, and fungi. Here, the full-length coding sequence (CDS), protein structure, and immune response and subcellular localization of TLR5 (TLR5S) and TLR13 were characterized in large yellow croaker (Larimichthys crocea). These TLRs share high sequence homology with other ichthyic TLRs, while also having their own characters; qtPCR was determined and the results found that the three genes were constitutively expressed in all examined tissues: TLR5M was highly expressed in the spleen and liver; TLR13 expression was high in the kidney, liver, and spleen. And TLRs were upregulated following stimulation with Vibrio parahaemolyticus in the liver, spleen, and kidney. Immunofluorescence staining revealed that TLR5M were localized in the cytoplasm, while TLR5S and TLR13 were in the endosome. The evolutionary analysis has shown that TLR13 was clustered with TLR11, 19, 20, 21, and 22, while TLR5 and TLR3 were classified into a group; these results suggest that TLRs are vital in the defense of L. crocea against bacterial infection and further increase our understanding of TLR function in innate immunity in teleosts.

Isolation and expression of four Megalobrama amblycephala toll-like receptor genes in response to a bacterial infection

Toll-like receptors (TLRs) are a category of pattern recognition receptors (PRRs), which recognize pathogen associated molecular patterns (PAMPs) and participate in the immune responses. We identified tlr5a, tlr5b, tlr9 and tlr21 from the genome of blunt snout bream (Megalobrama amblycephala). All four tlrs were constitutively expressed in all examined tissues. After an immune bacterial challenge with Aeromonas hydrophila, their expressionwas up-regulated in lymphoid organs and tissues. Recombinant eukaryotic plasmid pEGFP-N1 was transfected into the common carp (Cyprinus carpio) EPC (epithelioma papulosum cyprini) cells for the purpose of subcellular localization. pcDNA3.1(+) recombinant eukaryotic plasmid was used to investigate the effects of overexpression of tlrs on the expression of downstream interferon-associated immune factors. The four Tlrs were distributed in the cytoplasm of transfected cells and appeared as filamentous or reticular. The expression of irf3, irf7, isg15, mx1, pkr and viperin at 0, 6, 12, 18, 24, 36, 48 and 72 h post-transfection in transfected EPC cells was quantified by qPCR. Overexpression of tlrs upregulated the expression of viperin, isg15, irf3, irf7, mx1 and pkr (in that order of magnitude). We also cloned the following promoters of irfs: Irf1-p, irf2-p, irf6-p, irf7-p, irf8-p and irf9-p. Results of the dual luciferase reporter assay suggested that tlr5a, tlr5b and tlr9 enhanced the activities of irf7-p, while tlr5b enhanced the activities of irf1-p and irf7-p. This suggests that they all play a role in the innate immunity. The experiments also indicated that TLRs activate irf3 or irf7 signaling to induce IFN secretion and subsequent upregulation of IFN-stimulated genes. These results indicate that tlrs and irfs play an important immune role in response to A. hydrophila infection in blunt snout bream, and pave the way for further studies of immune mechanisms mediated by TLRs in fish.

Role of Toll-Like Receptor 5 (TLR5) in Experimental Melioidosis

The Gram-negative intracellular pathogen Burkholderia pseudomallei is the causative agent of melioidosis, an important cause of sepsis in Southeast Asia. Recognition of pathogen-associated molecular patterns by Toll-like receptors (TLRs) is essential for an appropriate immune response during pathogen invasion. In patients with melioidosis, TLR5 is the most abundantly expressed TLR, and a hypofunctional TLR5 variant has been associated with improved survival. Here, we studied the functional role of TLR5 and its ligand flagellin in experimental melioidosis. First, we observed differential TLR5 expression in the pulmonary and hepatic compartments upon infection with B. pseudomallei Next, we found that B. pseudomallei-challenged TLR5-deficient (Tlr5^-/- ) mice were more susceptible to infection than wild-type (WT) mice, as demonstrated by higher systemic bacterial loads, increased organ injury, and impaired survival. Lung bacterial loads were not different between the two groups. The phenotype was flagellin independent; no difference in in vivo virulence was observed for the flagellin-lacking mutant MM36 compared to the wild-type B. pseudomallei strain 1026b. Tlr5^-/- mice showed a similar impaired antibacterial defense when infected with MM36 or 1026b. Ex vivo experiments showed that TLR5-deficient macrophages display markedly impaired phagocytosis of B. pseudomallei In conclusion, these data suggest that TLR5 deficiency has a detrimental flagellin-independent effect on the host response against pulmonary B. pseudomallei infection.

Molecular cloning and expression study on Toll-like receptor 5M in turbot, Scophthalmus maximus

Toll-like receptor 5 (TLR5) is responsible for the recognition of bacterial flagellin in mammals and play an important role in innate immunity. In the present study, a TLR5M gene was cloned from turbot, Scophthalmus maximus, and its immune responsive expression was subsequently studied in vivo. The Scophthalmus maximus (Sm)TLR5M gene is 4268 bp in length, consists of four exons and three introns and encodes a peptide of 892 amino acids (aa). The deduced protein possesses a signal peptide sequence, a leucine-rich repeat (LRR) domain composed of 23 LRR motifs, a transmembrane (TM) domain and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis grouped SmTLR5M with other teleost TLR5Ms. A number of binding sites for transcription factors involved in immune response regulation were predicted in the 5'-flanking region of SmTLR5M. Quantitative real-time PCR (qPCR) analysis demonstrated that SmTLR5M mRNA was expressed ubiquitously with higher levels in head kidney and spleen. Its expression following stimulation with flagellin and lipopolysaccharide (LPS) was further tested in gills, spleen, head kidney and muscle. The maximum increases of SmTLR5M transcript levels ranged from 1.3 to 6.8-fold and appeared at 3 h to 5 day post-injection depending on different organs and stimuli. These findings suggest that SmTLR5M may play an important role in immune responses to infections with bacterial pathogens.

Genetics of metabolic syndrome: potential clues from wild-derived inbred mouse strains

The metabolic syndrome (MetS) is a complex constellation of metabolic abnormalities including obesity, abnormal glucose metabolism, dyslipidemia, and elevated blood pressure that together substantially increase risk for cardiovascular disease and Type 2 diabetes. Both genetic and environmental factors contribute to the development of MetS, but this process is still far from understood. Human studies have revealed only part of the underlying basis. Studies in mice offer many strengths that can complement human studies to help elucidate the etiology and pathophysiology of MetS. Here we review the ways mice can contribute to MetS research. In particular, we focus on the information that can be obtained from studies of the inbred strains, with specific focus on the phenotypes of the wild-derived inbred strains. These are newly derived inbred strains that were created from wild-caught mice. They contain substantial genetic variation that is not present in the classical inbred strains, have phenotypes of relevance for MetS, and various mouse strain resources have been created to facilitate the mining of this new genetic variation. Thus studies using wild-derived inbred strains hold great promise for increasing our understanding of MetS.

Characterization, expression, and evolutionary analysis of new TLR3 and TLR5M genes cloned from the spiny eel Mastacembelus armatus

Toll-like receptors (TLRs) play an important role in innate and adaptive immunity. Here, we identify two new TLRs from the spiny eel Mastacembelus armatus (TLR3 and membrane TLR5M). Both MaTLR3 and MaTLR5M were expressed in all tested tissues; expression was highest in liver and spleen, respectively. After infection with Vibrio parahaemolyticus, expression of both TLRs fluctuated and differed significantly from controls at several time points. The predicted three-dimensional model of the MaTLR3 and MaTLR5M proteins indicates that most sites under positive selection were located in the extracellular domains of TLRs. Evolutionary analysis detected positively selected sites in the ancestral lineages of vertebrates, amphibians and reptiles. Multiple ML methods recovered 10 positively selected sites in teleost TLR3 and 24 in TLR5M, and most sites were located in leucine-rich repeat domain, possibly related to an "arms-race" co-evolution with pathogens.

Polymorphism of TLR5 rs5744174 is associated with disease progression in Chinese patients with chronic HBV infection

Toll-like receptors (TLRs) play a crucial role in innate and adaptive immunity, protecting the host from viral pathogens. Studies have implicated that TLR5 is associated with various diseases such as autoimmune and inflammation related diseases. However, little is known about the relationship between TLR5 and hepatitis B virus (HBV) infection. We studied the effect of TLR5 gene polymorphisms on susceptibility to and disease progression of chronic hepatitis B (CHB) infection in Chinese. Blood samples were taken from 636 patients with CHB, HBV-related liver cirrhosis (LC) or hepatocellular carcinoma (HCC) and 273 controls. Polymorphisms of TLR5 (1775A>G rs2072493 and 1846T>C rs5744174) were analyzed by PCR-based sequencing. No difference in genotypic and allelic frequencies of TLR5 rs2072493 and rs5744174 was observed between patients and controls. Significant difference was found in frequency of TLR5 rs5744174 TT genotype between men with CHB and LC (p = 0.035). Frequency of TT genotype of TLR5 rs5744174 in patients positive for HBeAg was increased from 53.2% in patients with CHB to 74.1% in those with HCC (p = 0.024). Our results indicate that in Chinese genetic variation of TLR5 may be not a determinant of susceptibility to HBV-related diseases but may play a role in development of HBV-related severe liver diseases.

Functional expression of TLR5 in murine salivary gland epithelial cells

Toll-like receptors (TLR) recognize microbe-associated molecular patterns and induce the innate immune response. Among them, TLR5 recognizes the Gram-negative bacterial component flagellin. The aim of this study was to examine the expression of TLR5 in mouse salivary gland (SG). The SG was excised from 8- to 10-week-old female C57BL/6 mice. Salivary gland epithelial cells (SGECs) were purified and subjected to reverse transcription polymerase chain reaction (RT-PCR). Western blotting was performed to detect TLR5 expression at the protein level in several organs. The localization of TLR5 in SG was examined using immunohistochemical staining. The responsiveness of SGECs to flagellin was further examined by evaluating the induction of CXCL1 by real-time PCR and immunoprecipitation followed by Western blotting. TLR5 expression in SG was confirmed at the gene and protein levels. Immunohistochemical staining detected TLR5 in both acinic and ductal cells of the sublingual gland, but not in serous acinic cells of the submandibular gland. Although TLR5 was detected throughout the cytoplasm in ductal cells, positive staining was observed on the basal side of the mucous acinic cells. The purified SGECs responded to flagellin and induced the production of CXCL1. These findings suggest that TLR5 is functionally expressed in the SG and responds to its cognate ligand flagellin. (J Oral Sci 58, 317-323, 2016).

Molecular identification and expression analysis of TLR5M and TLR5S from orange-spotted grouper (Epinepheluscoioides)

Toll-like receptor 5 (TLR5) is an important receptor that interacts with bacterial flagellin and regulates host immune response in mammal. Recent studies demonstrate that piscine contains two types of TLR5, namely membrane form of TLR5 (TLR5M) and soluble form of TLR5 (TLR5S), and both of which perform crucial role in flagellin response. In the present study, a TLR5M and a TLR5S sequence was cloned from orange-spotted grouper (Epinepheluscoioides), and their ORFs are respectively 2466 bp (821 aas) and 1935 bp (644 aas). EcTLR5M has the typical TLR structure of a LRR domain, a transmembrane region and a TIR domain, while EcTLR5S only contains a LRR domain like other species' TLR5S. Both molecules have 23 LRR motifs, a LRR-NT and a LRR-CT in the LRR domain, similar to those of other species. Phylogenetic and sequence alignment indicated that both EcTLR5s respectively displayed closer relationship and higher sequence identity with those in other fish species. In healthy grouper, EcTLR5M was highly expressed in the skin, head kidney and spleen, while EcTLR5S was mainly detected in the liver. Ciliate Cryptocaryon irritans infection could significantly up-regulate the expression level of EcTLR5s in the gill and spleen from day 1 to day 3, and higher expression fold change was observed in the spleen. Taken together, the present studies contributed to understanding the function of piscine TLR5M/S and clarify their possible role in fish immune response against ciliate infection.

Imiquimod has strain-dependent effects in mice and does not uniquely model human psoriasis

BACKGROUND

Imiquimod (IMQ) produces a cutaneous phenotype in mice frequently studied as an acute model of human psoriasis. Whether this phenotype depends on strain or sex has never been systematically investigated on a large scale. Such effects, however, could lead to conflicts among studies, while further impacting study outcomes and efforts to translate research findings.

METHODS

RNA-seq was used to evaluate the psoriasiform phenotype elicited by 6 days of Aldara (5% IMQ) treatment in both sexes of seven mouse strains (C57BL/6 J (B6), BALB/cJ, CD1, DBA/1 J, FVB/NJ, 129X1/SvJ, and MOLF/EiJ).

RESULTS

In most strains, IMQ altered gene expression in a manner consistent with human psoriasis, partly due to innate immune activation and decreased homeostatic gene expression. The response of MOLF males was aberrant, however, with decreased expression of differentiation-associated genes (elevated in other strains). Key aspects of the IMQ response differed between the two most commonly studied strains (BALB/c and B6). Compared with BALB/c, the B6 phenotype showed increased expression of genes associated with DNA replication, IL-17A stimulation, and activated CD8+ T cells, but decreased expression of genes associated with interferon signaling and CD4+ T cells. Although IMQ-induced expression shifts mirrored psoriasis, responses in BALB/c, 129/SvJ, DBA, and MOLF mice were more consistent with other human skin conditions (e.g., wounds or infections). IMQ responses in B6 mice were most consistent with human psoriasis and best replicated expression patterns specific to psoriasis lesions.

CONCLUSIONS

These findings demonstrate strain-dependent aspects of IMQ dermatitis in mice. We have shown that IMQ does not uniquely model psoriasis but in fact triggers a core set of pathways active in diverse skin diseases. Nonetheless, our findings suggest that B6 mice provide a better background than other strains for modeling psoriasis disease mechanisms.

Molecular characterization and analysis of TLR-1 in rabbit tissues

The rabbit has great commercial importance as a source of meat and fur, as well as its uses as a laboratory animal for the production of antibodies, used to detect the presence or absence of disease and for research in infectious diseases and immunology. One of the most critical problems in immunology is to understand how the immune system detects the presence of infectious agents and disposes the invader without destroying the self-tissues. Genetic characterization of Toll-like receptors has established that innate immunity is a skillful system that detects invasion of microbial pathogens. Our work aimed to identify, clone and express the Oryctolagus cuniculus (rabbit) TLR-1 mRNA and its encoding protein. We cloned the complete mRNA sequence of Oryctolagus cuniculus TLR-1 and deposit it in the GenBank under accession number (KC349941), which has 2388 base pair and it encodes encode an open reading frame (ORF) translated into 796 amino acids mRNA and consist of 20 types of amino acids. The analysis of amino acid sequence revealed that the rabbit TLR-1 has a typical protein components belonging to the TLR family. Rabbit TLR-1 was expressed in a wide variety of rabbit tissues, which indicate an important role in immune system in different organs.

Isolation and expression of grass carp toll-like receptor 5a (CiTLR5a) and 5b (CiTLR5b) gene involved in the response to flagellin stimulation and grass carp reovirus infection

Toll-like receptor 5 (TLR5), a member of Toll-like receptors (TLRs) family and is responsible for the bacterial flagellin recognition in vertebrates, play an important role in innate immunity. In the study, two TLR5 genes of grass carp (Ctenopharyngodon idellus), named CiTLR5a and CiTLR5b, were cloned and analyzed. Both CiTLR5a and CiTLR5b are typical TLR proteins, including LRR motif, transmembrane region and TIR domain. The full-length cDNA of CiTLR5a is 3054 bp long, with a 2646 bp open reading frame (ORF), 78 bp 5' untranslated regions (UTR), and 330 bp 3' UTR. The full-length cDNA of CiTLR5b is 3326 bp, with a 2627 bp ORF, 95 bp 5' UTR, and 594 bp 3' UTR. Phylogenetic analysis showed that CiTLR5a and CiTLR5b were closed to the TLR5 of cirrhinus mrigala, cyprinus_carpio, and danio rerio. Subcellular localization indicated that CiTLR5a and CiTLR5b shared similar localization pattern and may locate in the plasma membrane of transfected cells. Real-time quantitative PCR revealed CiTLR5a and CiTLR5b were constitutively expressed in all examined tissues, whereas the highest expressed tissue differed. Following exposure to flagellin and GCRV, CiTLR5a and CiTLR5b were up-regulated significantly. Moreover, the downstream genes of TLR5 signal pathway such as MyD88, NF-κB, IRF7, IL-1β, and TNF-α also up-regulated significantly, whereas the IκB gene was down-regulated, suggesting that CiTLR5a and CiTLR5b involved in response to flagellin stimulation and GCRV infection. The results obtained in the study would provide a new insight for further understand the function of TLR5 in teleost fish.

Over-activation of TLR5 signaling by high-dose flagellin induces liver injury in mice

Flagellin is a potent activator of a broad range of cell types that are involved in innate and adaptive immunity. Therefore, it is a good adjuvant candidate for vaccines, and it might function as a biological protectant against both major acute radiation syndrome during cancer radiotherapy and a mitigator of radiation emergencies. However, accumulating evidence has implicated flagellin in the occurrence of some inflammatory diseases, such as acute lung inflammation, cardiovascular collapse and inflammatory bowel disease. The aim of this study was to elucidate whether only flagellin-TLR5 signaling activation plays a role in the pathophysiology of liver or whether some other flagellin activity also contributes to liver injury either via bacterial infections or during clinical applications. Recombinant flagellin proteins with or without TLR5-stimulating activity were used to evaluate the role of flagellin-TLR5 signaling in liver injury in wild-type and TLR5 KO mice. Gross lesions and large areas of hepatocellular necrosis were observed in liver tissue 12 h after the intraperitoneal administration of 100 or 200 µg flagellin (FliC) in a dose- and time-dependent manner in wild-type mice, but not in TLR5 KO mice. Deletion of the N-terminal or TLR5 binding domain of flagellin inhibited flagellin-induced inflammatory responses and the subsequent acute liver function abnormality and damage. These data confirmed that flagellin is an essential determinant of liver injury and demonstrated that the over-activation of TLR5 signaling by high-dose flagellin caused acute inflammatory responses, neutrophil accumulation and oxidative stress in the liver, which contributes to the progression and severity of flagellin-induced liver injury.

Redundant and cooperative interactions between TLR5 and NLRC4 in protective lung mucosal immunity against Pseudomonas aeruginosa

Flagellin is the major structural component of flagella expressed by Pseudomonas aeruginosa (PA) and other bacteria. This protein has been shown to activate the Toll-like receptor TLR5 and the Nod-like receptor Nlrc4/Ipaf, culminating in the expression of innate cytokines and antimicrobial molecules. In this study, we tested the hypothesis that TLR5 and Nlrc4 in combination are required for maximal protective lung innate mucosal immunity against PA. To test this hypothesis, we compared innate immune responses in wild-type (WT) C57B6 mice challenged with PA intratracheally to those observed in mice genetically deficient in TLR5 (TLR5(-/-)) or Nlrc4 (Nlrc4(-/-)) alone or in combination (TLR5/Nlrc4(-/-)). As compared to WT, TLR5(-/-) and Nlrc4(-/-) mice, we observed a significant increase in mortality in TLR5/Nlrc4(-/-) mice, which was associated with a >5,000-fold increase in lung PA colony-forming units and systemic bacterial dissemination. The increased mortality observed in double-deficient mice was not attributable to differences in lung leukocyte influx or lung injury responses. Levels of biologically active IL-1β and IL-18 were reduced in the bronchoalveolar lavage fluid from PA-infected Nlrc4(-/-) and TLR5/Nlrc4(-/-) but not TLR5(-/-) mice, indicating the requirement for Nlrc4-dependent caspase-1 activation. Similarly, decreased production of biologically active IL-1β and activation of caspase-1 was observed in PA-stimulated pulmonary macrophages isolated from Nlrc4(-/-) and TLR5/Nlrc4(-/-) but not TLR5(-/-) mice, whereas the expression of iNOS and the production of NO were significantly reduced in cells from double-mutant but not single-mutant mice. Collectively, our findings indicate that TLR5 and Nlrc4 have both unique and redundant roles in lung antibacterial mucosal immunity, and the absence of both pathogen recognition receptors results in an increase in susceptibility to invasive lung infection.

Toll-like receptors in central nervous system injury and disease: a focus on the spinal cord

Toll-like receptors (TLRs) are best known for recognizing pathogens and initiating an innate immune response to protect the host. However, they also detect tissue damage and induce sterile inflammation upon the binding of endogenous ligands released by stressed or injured cells. In addition to immune system-related cells, TLRs have been identified in central nervous system (CNS) neurons and glial subtypes including microglia, astrocytes and oligodendrocytes. Direct and indirect effects of TLR ligands on neurons and glial subtypes have been documented in vitro. Likewise, the effects of TLR ligands have been demonstrated in vivo using animal models of CNS trauma and disease including spinal cord injury (SCI), amyotrophic lateral sclerosis (ALS) and neuropathic pain. The indirect effects are most likely mediated via microglia or immune system cells that infiltrate the diseased or injured CNS. Despite considerable progress over the past decade, the role of TLRs in the physiological and pathological function of the spinal cord remains inadequately defined. Published reports collectively highlight TLRs as promising targets for therapeutic interventions in spinal cord pathology. The findings also underscore the complexity of TLR-mediated mechanisms and the necessity for further research in this field. The goals of the current review are to recapitulate the studies that investigated the role of TLRs in the spinal cord, to discuss potential future research directions, and to examine some of the challenges associated with pre-clinical studies pertinent to TLRs in the injured or diseased spinal cord.

Genetic dissection of the ity3 locus identifies a role for ncf2 co-expression modules and suggests selp as a candidate gene underlying the ity3.2 locus

Typhoid fever and salmonellosis, which are caused by Salmonella typhi and typhimurium, respectively, are responsible for significant morbidity and mortality in both developed and developing countries. We model typhoid fever using mice infected with Salmonella typhimurium, which results in a systemic disease, whereby the outcome of infection is variable in different inbred strains of mice. This model recapitulates several clinical aspects of the human disease and allows the study of the host response to Salmonella typhimurium infection in vivo. Previous work in our laboratory has identified three loci (Ity, Ity2, and Ity3) in the wild-derived MOLF/Ei mice influencing survival after infection with Salmonella typhimurium. Fine mapping of the Ity3 locus indicated that two sub-loci contribute collectively to the susceptibility of B6.MOLF-Ity/Ity3 congenic mice to Salmonella infection. In the current paper, we provided further evidence supporting a role for Ncf2 (neutrophil cytosolic factor 2 a subunit of NADPH oxidase) as the gene underlying the Ity3.1 sub-locus. Gene expression profiling indicated that the Ity3.1 sub-locus defined a global gene expression signature with networks articulated around Ncf2. Furthermore, based on differential expression and complementation analysis using Selp (selectin-P) knock-out mice, Selp was identified as a strong candidate gene for the Ity3.2 sub-locus.

Innate immunity of finfish: primordial conservation and function of viral RNA sensors in teleosts

During the past decade, huge progress has been made in research into teleost PAMPs (pathogen-associated molecule patterns) recognition receptors (PRRs). Numerous fish PRR genes have been identified, and the primordial functions of PRRs involved in the innate immune response to viral infection (especially those responsible for sensing viral RNA) have been increasingly clarified in teleosts. Particular progress has been made in our understanding of Toll-like receptors (TLRs) and retinoic acid inducible gene I (RIG-I)-like receptors (RLRs). However, there are important evolutionary differences between teleosts and mammals; for instance, seven TLR repertoires (TLR5S, -14, -19, -20, -21, -22 and -23) are present in teleosts but not in mammals, indicating that some TLRs likely possess different functions. Thus, comparison of PRRs in teleosts and mammals may help us understand the immune responses triggered by host-pathogen interactions in teleosts. In this article, the evolutionary conservations and divergences in the PRR mechanisms of teleosts and mammals are examined, with a focus on their molecular features and the recognition of viral RNA by fish TLRs and RLRs. In addition, the mechanism of type I interferon gene expression in teleosts, which is enhanced after the recognition of viral RNA by fish TLRs and RLRs, is also introduced.

Caprine Toll-like receptor 8 gene sequence characterization reveals close relationships among ruminant species

TLR8 mediates antiviral immunity by recognizing ssRNA viruses and triggers potent antiviral and antitumor immune responses. In this study, approximately 3.5 Kb nucleotide sequence data of caprine TLR8 gene were generated from one sample each of twelve different Indian goat breeds belonging to different geographical regions. Cloning and characterization of cDNA synthesized from RNA purified from goat spleen revealed TLR8 ORF to be of 3102 nucleotides long coding for 1033 amino acids similar to other ruminant species, that is sheep, buffalo and cattle. The sequence analysis at nucleotide level revealed goat TLR8 to be closer to buffalo sharing 99.6% homology, followed by cattle and sheep. Simple Modular Architecture Research Tool (SMART) used for the structural analysis of goat TLR8 showed the presence of 16 leucine-rich repeats (LRRs) along with single Toll/interleukin-1 receptor (TIR) domain. TIR domain when compared with other livestock species was found to be conserved in ruminant species goat, sheep, cattle and buffalo. The phylogenetic analysis also revealed grouping of all ruminant species together, goat being closer to buffalo followed by cattle and sheep. Total 4 polymorphic sites were observed in TLR8 gene of one specimen goat representing each of 12 different breeds studied, all of which were synonymous and present within the coding region. Of these 4 SNPs, two were in ectodomains, one in TIR domain and one was found to be present in transmembrane domain. PCR-RFLP genotyping of two of the SNPs indicated variations in allele frequencies among different goat breeds. The expression profiling in 13 tissues of goat showed maximum expression of TLR8 gene in kidney followed by spleen, lung and lymph node. Overall, our results indicate conservation of TLR8 gene among the ruminant species and low variation within Indian goat breeds.

Molecular cloning, characterization, and expression analysis of the Muscovy duck Toll-like receptor 3 (MdTLR3) gene

Toll-like receptor 3 (TLR3) is an important membrane-bound receptor for recognizing double-stranded RNA in innate immunity. In this study, we described the cloning and characterization of the Muscovy duck TLR3 (MdTLR3) gene. The full-length MdTLR3 cDNA (2,836 bp) encoded a polypeptide of 895 amino acids. The deduced amino acid sequence contained 4 main structural domains: a signal peptide, an extracellular leucine rich repeats domain, a transmembrane domain, and a Toll/IL-1 receptor domain. Quantitative real-time PCR analysis indicated that MdTLR3 mRNA was constitutively expressed in all sampled tissues of uninfected Muscovy duck except muscle. Expression of MdTLR3 in brain was significantly upregulated at 24 h (1.94-fold, P < 0.05), reached a peak at 48 h (4.64-fold, P < 0.05), and recovered to normal levels at 72 h postinfection with the H5N1 highly pathogenic avian influenza virus. In contrast, MdTLR3 expression was downregulated during the test period in spleen and lung. These results implicated MdTLR3 was a novel member of the TLR family, which is involved in the early stage of antiviral innate immunity.

Regulation of Toll-like receptor 5 gene expression and function on mucosal dendritic cells

Toll-like receptor (TLR) 5 has been shown to maintain intestinal homeostasis and regulate host defense against enterobacterial infection. However, how TLR5 expression is regulated and its function in the intestine have not been fully elucidated. Here we demonstrate that mucosal dendritic cells (DCs), but not splenic DCs, express high levels of TLR5 protein. Alternatively spliced Tlr5 transcripts were identified but it did not explain the selective expression of TLR5 on mucosal DCs. Treatment with various bacterial ligands downregulated BMDC TLR5 expression, while retinoic acid and host stromal cell-derived signals promoted TLR5 expression in a TGF-β-independent mechanism. Signaling through TLR5 restrained regulatory T (Treg) cell generation, and accordingly, TLR5^−/− mice displayed increased frequencies of Foxp3⁺ Treg cells in the intestinal lamina propria. Our data indicate that bacterial and host factors differentially regulate DC TLR5 expression. TLR5 signaling regulates immune responses towards the microbiota via modulation of the Treg/effector T cell balance.

Linkage mapping of toll-like receptors (TLRs) in Japanese flounder, Paralichthys olivaceus

Toll-like receptors (TLRs) are responsible for the recognition of specific pathogen-associated molecular patterns and consequently activate signal pathways leading to inflammatory and interferon responses. The region surrounding several TLRs was previously found to be associated with resistance to specific disease. Hence, we determined the location of 11 TLRs in Japanese flounder (Paralichthys olivaceus) using polymorphic microsatellite markers. TLR1 and TLR3 were located on linkage group (LG) 21 and 7, respectively. Membrane TLR5 and soluble TLR5 were mapped to LG22. TLR7 and TLR8 were mapped to LG3. TLR9 was found on LG1 and TLR14 and TLR21 were located on the same linkage group, LG10. TLR22 was found on LG8. Interestingly, TLR2 was mapped with the previously reported Poli9-8TUF microsatellite marker which is tightly associated with lymphocystis virus disease resistance. Therefore, TLR2 is a candidate gene for resistance to lymphocystis disease. These results imply that the location of a TLR associated with a particular disease may be valuable for the research on the relationship between host immune response and disease resistance.

A TLR5 agonist inhibits acute renal ischemic failure

Reperfusion of ischemic organs induces a potent inflammatory response initiated by the generation of reactive oxygen species that directly damage tissue and promote leukocyte infiltration and activation that also mediate tissue injury. We recently found that radiation-induced tissue injury, which is caused by radiation-induced reactive oxygen species, is attenuated by administration of CBLB502, a pharmacologically optimized derivative of the TLR5 agonist flagellin. Therefore, we tested the ability of CBLB502 to attenuate injury in a murine model of acute ischemic renal failure. CBLB502 given 30 min before imposition of bilateral renal pedicle occlusion provided marked protection against the renal dysfunction and inflammation that follows reperfusion of ischemic kidneys, including marked decreases in leukocyte infiltration, proinflammatory cytokine production, and tubular injury. Importantly, CBLB502 given within 30 min after ischemic kidney reperfusion reproduced the protective effects of pretreatment with the TLR5 agonist, indicating a window following reperfusion in which CBLB502 administration abrogates acute renal ischemic failure. Bone marrow-reconstituted chimeras were used to show that the protective effects of CBLB502 could be delivered by intact MyD88 signaling on renal parenchymal cells. Consistent with this, Ab staining of kidney sections indicated that cells lining the renal vasculature expressed TLR5. Overall, these results indicate the use of TLR5 agonists as mitigators and protectants of acute renal ischemic failure.

Flagellin stimulates protective lung mucosal immunity: role of cathelicidin-related antimicrobial peptide

TLRs are required for generation of protective lung mucosal immune responses against microbial pathogens. In this study, we evaluated the effect of the TLR5 ligand flagellin on stimulation of antibacterial mucosal immunity in a lethal murine Pseudomonas aeruginosa pneumonia model. The intranasal pretreatment of mice with purified P. aeruginosa flagellin induced strong protection against intratracheal P. aeruginosa-induced lethality, which was attributable to markedly improved bacterial clearance, reduced dissemination, and decreased alveolar permeability. The protective effects of flagellin on survival required TLR5 and were observed even in the absence of neutrophils. Flagellin induced strong induction of innate genes, most notably the antimicrobial peptide cathelicidin-related antimicrobial peptide. Finally, flagellin-induced protection was partially abrogated in cathelicidin-related antimicrobial peptide-deficient mice. Our findings illustrate the profound stimulatory effect of flagellin on lung mucosal innate immunity, a response that might be exploited therapeutically to prevent the development of gram-negative bacterial infection of the respiratory tract.

Immune responses of TLR5(+) lamina propria dendritic cells in enterobacterial infection

Toll-like receptors (TLRs) recognize distinct microbial components and induce innate immune responses. TLR5 has been shown to recognize bacterial flagellin. Unlike other TLRs, TLR5 is not expressed on conventional dendritic cells or macrophages. By contrast, TLR5 is mainly expressed on intestinal CD11c(+) lamina propria cells (LPCs), which do not express TLR4. These cells detect pathogenic bacteria and secreted proinflammatory cytokines, mainly in a TLR5-dependent manner. Notably, transport of pathogenic Salmonella typhimurium from the intestinal tract to mesenteric lymph nodes was impaired in Tlr5 (-/-) mice, suggesting that CD11c(+) LPCs expressing TLR5 are used by S. typhimurium for systemic infection. CD11c(+) LPCs consist of four subsets distinguished by differential expression patterns of CD11c and CD11b. CD11c(hi)CD11b(hi) LPDCs have been identified as TLR5-expressing cells. In response to flagellin, these LPDCs induce the differentiation of naive B cells into IgA(+) plasma cells via a mechanism independent of gut-associated lymphoid tissue (GALT), and trigger the differentiation of antigen-specific Th17 and Th1 cells. These LPDCs have unique properties in that they can induce acquired immunity as well as innate immunity via TLR5 in the intestine.

Role of Toll-like receptor 5 in the innate immune response to acute P. aeruginosa pneumonia

Pseudomonas aeruginosa is a leading cause of hospital-acquired pneumonia and an important pathogen in patients with chronic lung disease, such as cystic fibrosis and bronchiectasis. The contribution of Toll-like receptor 5 (TLR5) to the innate immune response to this organism is incompletely understood. We exposed wild-type and TLR5-deficient (Tlr5(-/-)) mice to aerosolized P. aeruginosa at low and high inocula and assessed bacterial clearance, lung inflammation, and cytokine production 4 and 24 h after infection. Bacterial clearance was impaired in Tlr5(-/-) mice after low-inoculum, but not high-inoculum, infection. Early bronchoalveolar accumulation of neutrophils was reduced in Tlr5(-/-) mice after low- and high-dose infection. Cytokine responses, including markedly impaired monocyte chemoattractant protein-1 production 4 h after low- and high-inoculum challenge, were selectively altered in Tlr5(-/-) mice. In contrast, there was no impairment of bacterial clearance, neutrophil recruitment, or monocyte chemoattractant protein-1 production in Tlr5(-/-) mice after infection with a nonflagellated isotypic strain of P. aeruginosa. Thus TLR5-mediated recognition of flagellin is involved in activating pulmonary defenses against P. aeruginosa and contributes to antibacterial resistance in a manner that is partially inoculum dependent. These data are the first to demonstrate a unique role for TLR5 in the innate immune response to P. aeruginosa lung infection.

Differential expression of toll-like receptor mRNA in selected tissues of goat (Capra hircus)

Pattern recognition receptors (PRRs) expressed by various immune cells and tissues have been shown to play a pivotal role in the recognition of pathogens by the host. The present study was carried out to identify toll-like receptors (TLRs) 1-10 mRNA in goat peripheral blood mononuclear cells (PBMCs) and selected tissues including jejunum, lung, lymph node, skin, spleen and uterus using reverse transcriptase polymerase chain reaction (RT-PCR). Our results confirm earlier reports regarding the evolutionarily conserved nature of these receptors as successful amplification of the goat TLR mRNAs could be obtained with bovine TLR mRNA-specific primers. The partial sequences of the purified TLR PCR amplicons had 93.8-99.7% nucleotide identity with sheep TLR cDNA sequences available in the GenBank. Semi-quantification of the expression levels of the TLR mRNAs was done using densitometric analysis of band intensities. All the TLR mRNAs (1-10) were expressed in high amounts in the lymph node while spleen showed lower expression of TLR 6 and 10 mRNAs. PBMC and lung expressed all TLR mRNAs in high amounts except TLR 10 mRNA. In uterus and jejunum, lower expression of TLR 3, 4 and 10 mRNAs was seen. Skin had the lowest repertoire of TLR mRNA expression with lower or no expression of TLR 2, 3, 4, 8, 9 and 10 mRNAs. Another interesting observation was that tissues such as uterus, lung and skin that exhibited lower levels of TLR 2 had higher levels of TLR 6 mRNAs.

Innate immune receptors on neutrophils and their role in chronic lung disease

Neutrophils, the prototypic cells of the innate immune system, are recruited to infected sites to protect the human body from invading pathogens. To accomplish this function, neutrophils sense pathogens and endogenous damage-associated molecules via innate immune receptors, such as Toll-like receptors (TLRs) and other pattern recognition receptors. This defence function is essential for the pulmonary microenvironment where the host is faced with millions of particles and pathogens inhaled daily. Chronic lung diseases, such as cystic fibrosis or chronic obstructive pulmonary disease are characterized by a neutrophil accumulation and chronic bacterial colonization of the airways. Consequently, insights into the role of TLRs on neutrophils in chronic lung diseases are of high relevance for further diagnostic and therapeutic approaches. Here we summarize and discuss recent advances in the expression, regulation and functional role of TLRs on neutrophils in chronic lung diseases.

Immune interventions of human diseases through toll-like receptors

Toll-like receptors (TLRs) are the immune sensors for infections, triggering robust innate immune activation followed by protective adaptive immunity against various infectious diseases. Recent evidence, however, has suggested that TLRs are involved in the pathogenesis of many diseases, including not only infectious diseases but also autoimmune diseases, allergy and atherosclerosis. Therefore, prophylactic or therapeutic application of TLR-based immune interventions should be potent, but their safety must be demonstrated using experimental animal models as well as human resources, including analysis of single nucleotide polymorphisms. Here, we focus on recent advances in understanding of the protective and pathogenic roles of TLRs in human diseases.

TLR4-mediated activation of dendritic cells by the heat shock protein DnaK from Francisella tularensis

Francisella tularensis is the causative agent of tularemia, a severe, debilitating disease of humans and other mammals. As this microorganism is also classified as a "category-A pathogen" and a potential biowarfare agent, there is a need for an effective vaccine. Several antigens of F. tularensis, including the heat shock protein DnaK, have been proposed for use in a potential subunit vaccine. In this study, we characterized the innate immune response of murine bone marrow-derived dendritic cells (DC) to F. tularensis DnaK. Recombinant DnaK was produced using a bacterial expression system and purified using affinity, ion-exchange, and size-exclusion chromatography. DnaK induced the activation of MAPKs and NF-kappaB in DC and the production of the proinflammatory cytokines IL-6, TNF-alpha, and IL-12 p40, as well as low levels of IL-10. DnaK induced phenotypic maturation of DC, as demonstrated by an up-regulation of costimulatory molecules CD40, CD80, and CD86. DnaK stimulated DC through TLR4 and the adapters MyD88 and Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) that mediated differential responses. DnaK induced activation of MAPKs and NF-kappaB in a MyD88- or TRIF-dependent manner. However, the presence of MyD88- and TRIF-dependent signaling pathways was essential for an optimal, DnaK-induced cytokine response in DC. In contrast, DnaK induced DC maturation in a TRIF-dependent, MyD88-independent manner. These results provide insight about the molecular interactions between an immunodominant antigen of F. tularensis and host immune cells, which is crucial for the rational design and development of a safe and efficacious vaccine against tularemia.

An agonist of toll-like receptor 5 has radioprotective activity in mouse and primate models

The toxicity of ionizing radiation is associated with massive apoptosis in radiosensitive organs. Here, we investigate whether a drug that activates a signaling mechanism used by tumor cells to suppress apoptosis can protect healthy cells from the harmful effects of radiation. We studied CBLB502, a polypeptide drug derived from Salmonella flagellin that binds to Toll-like receptor 5 (TLR5) and activates nuclear factor-kappaB signaling. A single injection of CBLB502 before lethal total-body irradiation protected mice from both gastrointestinal and hematopoietic acute radiation syndromes and resulted in improved survival. CBLB502 injected after irradiation also enhanced survival, but at lower radiation doses. It is noteworthy that the drug did not decrease tumor radiosensitivity in mouse models. CBLB502 also showed radioprotective activity in lethally irradiated rhesus monkeys. Thus, TLR5 agonists could potentially improve the therapeutic index of cancer radiotherapy and serve as biological protectants in radiation emergencies.

Effects of flagellin on innate and adaptive immunity

Flagella are locomotive organelles present on a wide range of bacteria and are important for the pathogenesis of many species. Cells of the innate immune system lack memory per se, but recognize conserved pathogen-associated molecular patterns (PAMPs) through a family of type I membrane receptors known as Toll-like receptors (TLRs). Flagellin, the major structural component of flagella, is a highly conserved protein recognized in hosts by TLR5. Signaling of flagellin via TLR5/TLR4 heteromeric complexes enhances the diversity of the response, likely by engaging MyD88-independent adaptors to activate the interferon pathway. Flagellin is a potent immune activator, stimulating diverse biologic effects that mediate both innate inflammatory responses as well as the development of adaptive immunity. Binding of flagellin to the extracellular domain of TLR5 rapidly induces a signal cascade that culminates in the production of proinflammatory mediators such as cytokines, chemokines, and costimulatory molecules. This review focuses on the mechanisms of action of flagellin and its effects on both innate and adaptive immunity.

Genetic analysis of resistance to infections in mice: A/J meets C57BL/6J

Susceptibility to infectious diseases has long been known to have a genetic component in human populations. This genetic effect is often complex and difficult to study as it is further modified by environmental factors including the disease-causing pathogen itself. The laboratory mouse has proved a useful alternative to implement a genetic approach to study host defenses against infections. Our laboratory has used genetic analysis and positional cloning to characterize single and multi-gene effects regulating inter-strain differences in the susceptibility of A/J and C57BL/6J mice to infection with several bacterial and parasitic pathogens. This has led to the identification of several proteins including Nrampl (Slc11a1), Birc1e, Icsbp, C5a, and others that play critical roles in the antimicrobial defenses of macrophages against intracellular pathogens. The use of AcB/BcA recombinant congenic strains has further facilitated the characterization of single gene effects in complex traits such as susceptibility to malaria. The genetic identification of erythrocyte pyruvate kinase (Pklr) and myeloid pantetheinase enzymes (Vnn1/3) as key regulators of blood-stage parasitemia has suggested that cellular redox potential may be a key biochemical determinant of Plasmodium parasite replication. Expanding these types of studies to additional inbred strains and to emerging stocks of mutagenized mice will undoubtedly continue to unravel the molecular basis of host defense against infections.

Expression of Toll/IL-1R domain-containing adaptor protein (TIRAP) is detrimental to primary clearance of Salmonella and is not required for the generation of protective immunity

Salmonella infection triggers activation of innate immune cells through the interaction of bacterial products with Toll-like receptors (TLRs). Toll/IL-1R domain-containing adaptor protein (TIRAP) is an adaptor protein involved in downstream signaling through TLRs 1, 2, 4, and 6. We examined the role of TIRAP during infection with attenuated Salmonella. Surprisingly, TIRAP-deficient mice were fully capable of resolving primary infection with Salmonella and actually exhibited accelerated clearance of bacteria at a late stage of the infection. Consistent with enhanced bacterial clearance, TIRAP-deficient mice resolved bacterial-associated splenic inflammation more rapidly than wild-type (Wt) mice and splenocytes from Salmonella-infected TIRAP-deficient mice produced more IFN-gamma upon in vitro re-stimulation. Upon secondary challenge, TIRAP-deficient and Wt mice displayed a similar level of protective immunity against virulent Salmonella. Together these data indicate that TIRAP-mediated signaling is completely dispensable for clearance of Salmonella infection, and actually has a mild deleterious effect upon the resolution of primary infection.

Differential expression of pattern recognition receptors in sheep tissues and leukocyte subsets

The various members of the different pattern recognition receptor families are now recognized as playing a crucial role in the initial interactions between a pathogen and the host. This paper identifies all 10 members of the TLR family in sheep as well as key members of the C-type lectin and NLR families. Our data show that sheep possess the 'human' and not the 'mouse' pattern of TLRs and confirm the high degree of sequence identity between orthologous genes in the different species. In the absence of definitive antibodies, qRT-PCR assays were developed to quantify PRR transcript expression patterns in a range of normal sheep tissues as well as isolated dendritic cell (DC) and leukocyte subsets. These data show that the lymphoid organs (spleen and lymph nodes) express the widest range of PRRs and that organs such as the lung and kidney have distinctive arrays of PRRs that reflect their potential risk of pathogen exposure. In addition we show that the two DC subsets, defined by the differential expression of CD172a/CD45RA and their cytokine expression profiles, have different and characteristic PRR complements again possibly reflecting their distinctive function. These data are important for future studies on the role of PRRs in disease pathogenesis and control.

Molecular genetic analysis of two loci (Ity2 and Ity3) involved in the host response to infection with Salmonella typhimurium using congenic mice and expression profiling

Numerous genes have been identified to date that contribute to the host response to systemic Salmonella Typhimurium infection in mice. We have previously identified two loci, Ity2 and Ity3, that control survival to Salmonella infection in the wild-derived inbred MOLF/Ei mouse using a (C57BL/6J x MOLF/Ei)F(2)cross. We validated the existence of these two loci by creating congenic mice carrying each quantitative trait locus (QTL) in isolation. Subcongenic mice generated for each locus allowed us to define the critical intervals underlying Ity2 and Ity3. Furthermore, expression profiling was carried out with the aim of identifying differentially expressed genes within the critical intervals as potential candidate genes. Genomewide expression arrays were used to interrogate expression differences in the Ity2 congenics, leading to the identification of a new candidate gene (Havcr2, hepatitis A virus cellular receptor 2). Interval-specific oligonucleotide arrays were created for Ity3, identifying one potential candidate gene (Chi3l1, chitinase 3-like 1) to be pursued further. The combination of the use of congenics in QTL confirmation and fine mapping and in the identification of candidate genes by expression profiling has been successful and represents a step toward quantitative gene(s) identification.

Aggregating phenotype in Lactobacillus crispatus determines intestinal colonization and TLR2 and TLR4 modulation in murine colonic mucosa

The colonic microbiota is a major modulator of the mucosal immune system; therefore, its manipulation through supplementation with probiotics may significantly affect the host's immune responses. Since different probiotics seem to exert various effects in vivo, we tested the relevance of the autoaggregation phenotype on the intestinal persistence of lactobacilli and their ability to modulate the host's innate immune responses. After 14 days of diet supplementation, the aggregating strain Lactobacillus crispatus M247 but not aggregation-deficient isogenic mutant MU5 was recovered from the feces and colonic mucosa of mice. This observation was confirmed by strain-specific PCR amplification and by Lactobacillus-specific denaturing gradient gel electrophoresis analysis. Indeed, L. crispatus M247 increased Toll-like receptor 2 (TLR2) mRNA levels, while it reduced TLR4 mRNA and protein levels in the colonic mucosa, whereas MU5 was ineffective. In colonic epithelial cells (CMT-93 cells) L. crispatus M247 but not MU5 induced time-dependent extracellular signal-regulated kinase-1 (ERK1) tyrosine phosphorylation and TLR modulation, which were abolished in the presence of PD98059 (an ERK1 inhibitor). To assess the functional relevance of probiotic-induced TLR modulation, we determined the consequences of L. crispatus preexposure on TLR4 (lipopolysaccharide [LPS]) and TLR2 [Pam3Cys-Ser-(Lys)4] ligand-mediated effects in intestinal epithelial cells. Preexposure to L. crispatus M247 blunted LPS-induced interleukin-6 (IL-6) release and inhibition of CMT-93 migration over a wound edge, whereas it enhanced TLR2-mediated IL-10 up-regulation. In summary, the aggregation phenotype is required for L. crispatus persistence in the colon and for modulation of TLR2/TLR4 expression through an ERK-dependent pathway. We speculate that the aggregation phenotype in L. crispatus M247 is required to temper epithelial cell responsiveness to bacterial endotoxins, which thus affects the evolution of intestinal inflammatory processes.

Complex genetic control of susceptibility to Mycobacterium bovis (Bacille Calmette-Guérin) infection in wild-derived Mus spretus mice

Susceptibility to Mycobacterium bovis Bacille Calmette-Guérin (BCG) is genetically controlled by Nramp1 (Slc11a1). Inbred mouse strains harbor either the resistance (Nramp1(G169)) or the susceptibility (Nramp1(D169)) allele at Nramp1. Mus spretus (Nramp1(G169); SPRET/EiJ) is shown to display an intermediate level of BCG replication in the spleen (log(10) colony-forming units (CFU) approximately 5), compared to resistant A/J (log(10)CFU approximately 4.0) and susceptible C57BL/6J (log(10)CFU approximately 6.0) mice. The presence of genetic modifiers of Nramp1-dependent susceptibility to M. bovis (BCG) infection in Mus spretus was analyzed by whole-genome scanning in 175 mice of an informative (C57BL/6J x SPRET/EiJ) x C57BL/6J backcross. Nramp1 showed a major effect (D1Mcg4, P<1e(-4)), but additional single marker effects were identified on chromosomes 4 (D4Mit150) and x (DXMit249) in male mice, and on chromosome 9 (D9Mit77) and 17 (D17Mit81) in female mice. A strong interaction between Nramp1 and the major histocompatibility locus was also noted in female mice. The mapped loci may act as modifiers of Nramp1 action, and constitute novel entry points for the parallel search of loci regulating susceptibility to mycobacterial infections in humans.

Vaccination with recombinant fusion proteins incorporating Toll-like receptor ligands induces rapid cellular and humoral immunity

Recognition of specific pathogen associated molecular patterns (PAMPs) is mediated primarily by members of the Toll-like receptor (TLR) family. Stimulation through these receptors results in quantitative and qualitative changes in antigen presentation and cellular activation, thereby linking innate and adaptive immunity. Consequently, the incorporation of TLR-ligands into vaccines could result in more potent and efficacious vaccines. To test this hypothesis, we employed a recombinant fusion protein strategy using the TLR5 ligand flagellin fused to specific antigens to promote protective immunity. These purified recombinant fusion proteins demonstrated potent TLR5-specific NF-kappaB dependent activity in vitro. Immunization of mice with the recombinant-flagellin-OVA fusion protein STF2.OVA resulted in potent antigen-specific T and B cell responses that were equal to or better than responses induced by OVA emulsified in Complete Freund's adjuvant. These included rapid and consistent antigen-specific IgG(1) and IgG(2a) antibody responses that were detectable within 7 days of immunization, and the development of protective CD8 T cell responses. Moreover, the enhanced immunogenicity to OVA is dependant on the direct fusion to flagellin, as co-delivery of OVA with flagellin unlinked failed to augment antigen-specific responses in vivo. Similar results were obtained using a recombinant fusion protein comprised of flagellin and a novel polypetide sequence containing two immuno-protective epitopes derived from the Listeria monocytogenes antigens p60 and listeriolysin O. Animals immunized with this recombinant protein demonstrated significant antigen-specific CD8 T cell responses and protection upon challenge with virulent L. monocytogenes. We conclude that immunization with PAMP:antigen fusion proteins induce rapid and potent antigen-specific responses in the absence of supplemental adjuvants. Collectively our data demonstrate that PAMP:antigen fusion proteins offer significant promise for developing recombinant protein vaccines.

TIR, CARD and PYRIN: three domains for an antimicrobial triad

Innate immunity to microorganisms in mammals has gained a substantial interest during the last decade. The discovery of the Toll-like receptor (TLR) family has allowed the identification of a class of membrane-spanning receptors dedicated to microbial sensing. TLRs transduce downstream signaling via their intracellular Toll-interleukin-1 receptor (TIR) domain. More recently, the role of intracellular microbial sensors has been uncovered. These molecules include the Nod-like receptors Nod1, Nod2, Ipaf and Nalps, together with the helicase domain-containing antiviral proteins RIG-I and Mda-5. The intracellular microbial sensors lack the TIR domain, but instead transduce downstream signals via two domains also implicated in homophilic protein-protein interactions, the caspase activation and recruitment domain (CARD) and PYRIN domains. In light with these recent findings, we propose that TIR, CARD and PYRIN domains represent the three arms of innate immune detection of microorganisms in mammals.

The expression patterns of Toll-like receptors in the ileal pouch mucosa of postoperative ulcerative colitis patients

The aim of this study was to evaluate the expression pattern of Toll-like receptors (TLRs) in the pouch mucosa of ulcerative colitis patients in comparison with that in the ileum mucosa of noninflammatory bowel disease patients. Pouch mucosal biopsy specimens were collected from postoperative patients who had undergone surgery for ulcerative colitis. Normal ileum specimens were collected from colon cancer patients. The specimens were assessed by immunofluorescence histochemistry using TLR2, TLR3, TLR4, and TLR5 polyclonal antibodies. The normal ileal mucosa constitutively expressed TLR3 and TLR5, whereas TLR2 and TLR4 were barely detectable. In the mucosa of active pouchitis, TLR2 and TLR4 was strongly upregulated, and TLR4 was upregulated even in a noninflamed pouch. No TLR3 or TLR5 expression was detectable. These data suggest that pouchitis may be associated with distinctive changes in selective TLR expression in the pouch mucosa, and that TLR4 alterations in the innate response system may contribute to the pathogenesis of these disorders in particular.

Tlr5 is not primarily associated with susceptibility to Salmonella Typhimurium infection in MOLF/Ei mice

The extreme susceptibility to infection with Salmonella Typhimurium of wild-derived MOLF/Ei mice has been linked to one genomic region on Chromosome 1 (Ity3). A member of the Toll-like receptors family, Tlr5, located on distal Chromosome 1, was previously shown to be a candidate gene for Ity3 based on expression studies and sequencing analysis. The candidacy of Tlr5 as a Salmonella-susceptibility gene was evaluated functionally by comparing Tlr5 C57BL/6J and MOLF/Ei alleles in vitro and in vivo. In vitro studies showed that the MOLF/Ei Tlr5 allele is more transcriptionally active when the gene is removed from its natural genomic environment. This observation was supported by in vivo studies in B6.MOLF-Ity3 congenic mice that showed that mice homozygous for the MOLF/Ei allele at Ity3, including Tlr5, had an increased response to flagellin as measured by IL-6 and CXCL-1 secretion in the serum compared with parental MOLF/Ei mice. Despite the fact that both MOLF/Ei and B6.MOLF-Ity/Ity3 mice are more susceptible to Salmonella Typhimurium infection than B6.MOLF-Ity mice, they exhibit a different phenotype with respect to Tlr5 expression and Tlr5 signaling, supporting the prediction that Tlr5 is not primarily involved in the disease phenotype underlying the Ity3 locus in MOLF/Ei mice.

Detection of pathogenic intestinal bacteria by Toll-like receptor 5 on intestinal CD11c+ lamina propria cells

Toll-like receptors (TLRs) recognize distinct microbial components and induce innate immune responses. TLR5 is triggered by bacterial flagellin. Here we generated Tlr5-/- mice and assessed TLR5 function in vivo. Unlike other TLRs, TLR5 was not expressed on conventional dendritic cells or macrophages. In contrast, TLR5 was expressed mainly on intestinal CD11c+ lamina propria cells (LPCs). CD11c+ LPCs detected pathogenic bacteria and secreted proinflammatory cytokines in a TLR5-dependent way. However, CD11c+ LPCs do not express TLR4 and did not secrete proinflammatory cytokines after exposure to a commensal bacterium. Notably, transport of pathogenic Salmonella typhimurium from the intestinal tract to mesenteric lymph nodes was impaired in Tlr5-/- mice. These data suggest that CD11c+ LPCs, via TLR5, detect and are used by pathogenic bacteria in the intestinal lumen.

Antitumor Activity of the TLR-5 Ligand Flagellin in Mouse Models of Cancer

Flagellin, the structural protein subunit of the bacterial flagellum, is specifically recognized by TLR-5 and has potent immunomodulatory effects. The antitumor effects of purified Salmonella typhimurium flagellin were evaluated in mice transplanted s.c. with a weakly immunogenic murine tumor or with its variant stably transfected to express the highly antigenic human HER-2 oncoprotein. Peritumoral administration of flagellin 8-10 days after tumor implantation did not affect the growth rate of the weakly immunogenic tumor but significantly inhibited growth of the antigenic variant tumor. In contrast, flagellin administered at the time of implantation of the antigenic tumor led to accelerated tumor growth. These contrasting effects of flagellin on tumor growth correlated with the type of immune response induced; i.e., late flagellin administration was associated with an increased IFN-gamma:IL-4 ratio and the decreased frequency of CD4+CD25+ T regulatory cells, whereas flagellin treatment at the time of tumor implantation decreased the IFN-gamma:IL-4 ratio and increased CD4+CD25+ T cell frequency. When the early flagellin treatment was combined with administration of CpG-containing oligodeoxynucleotides, tumor growth was completely suppressed, indicating synergy between flagellin and CpG-containing oligodeoxynucleotides. Together, these data provide evidence that flagellin can have contrasting effects on tumor growth.

Mucosal interplay among commensal and pathogenic bacteria: lessons from flagellin and Toll-like receptor 5

Toll-like receptors (TLR) detect pathogen-associated molecular patterns (PAMP) and play a crucial role in triggering immunity. Due to their large surfaces in direct contact with the environment, mucosal tissues are the major sites of PAMP-TLR signalling. How innate and adaptive immunity are triggered through flagellin-TLR5 interaction is the main focus of the review. In view of recent reports on genetic polymorphism, we will summarize the impact of TLR5 on the susceptibility to mucosal infections and on various immuno-pathologies. Finally, the contribution of TLRs in the induction and maintenance of mucosal homeostasis and commensal discrimination is discussed.

Role of Toll-like receptors in health and diseases of gastrointestinal tract

The human gastrointestinal (GI) tract is colonized by non-pathogenic commensal microflora and frequently exposed to many pathogenic organisms. For the maintenance of GI homeostasis, the host must discriminate between pathogenic and non-pathogenic organisms and initiate effective and appropriate immune and inflammatory responses. Mammalian toll-like receptors (TLRs) are members of the pattern-recognition receptor (PRR) family that plays a central role in the initiation of innate cellular immune responses and the subsequent adaptive immune responses to microbial pathogens. Recent studies have shown that gastrointestinal epithelial cells express almost all TLR subtypes characterized to date and that the expression and activation of TLRs in the GI tract are tightly and coordinately regulated. This review summarizes the current understanding of the crucial dual roles of TLRs in the development of host innate and adaptive immune responses to GI infections and the maintenance of the immune tolerance to commensal bacteria through down-regulation of surface expression of TLRs in intestinal epithelial cells.