Polymorphisms in the TLR4 and TLR5 gene are significantly associated with inflammatory bowel disease in German shepherd dogs

Inflammatory bowel disease (IBD) is considered to be the most common cause of vomiting and diarrhoea in dogs, and the German shepherd dog (GSD) is particularly susceptible. The exact aetiology of IBD is unknown, however associations have been identified between specific single-nucleotide polymorphisms (SNPs) in Toll-like receptors (TLRs) and human IBD. However, to date, no genetic studies have been undertaken in canine IBD. The aim of this study was to investigate whether polymorphisms in canine TLR 2, 4 and 5 genes are associated with IBD in GSDs. Mutational analysis of TLR2, TLR4 and TLR5 was performed in 10 unrelated GSDs with IBD. Four non-synonymous SNPs (T23C, G1039A, A1571T and G1807A) were identified in the TLR4 gene, and three non-synonymous SNPs (G22A, C100T and T1844C) were identified in the TLR5 gene. The non-synonymous SNPs identified in TLR4 and TLR5 were evaluated further in a case-control study using a SNaPSHOT multiplex reaction. Sequencing information from 55 unrelated GSDs with IBD were compared to a control group consisting of 61 unrelated GSDs. The G22A SNP in TLR5 was significantly associated with IBD in GSDs, whereas the remaining two SNPs were found to be significantly protective for IBD. Furthermore, the two SNPs in TLR4 (A1571T and G1807A) were in complete linkage disequilibrium, and were also significantly associated with IBD. The TLR5 risk haplotype (ACC) without the two associated TLR4 SNP alleles was significantly associated with IBD, however the presence of the two TLR4 SNP risk alleles without the TLR5 risk haplotype was not statistically associated with IBD. Our study suggests that the three TLR5 SNPs and two TLR4 SNPs; A1571T and G1807A could play a role in the pathogenesis of IBD in GSDs. Further studies are required to confirm the functional importance of these polymorphisms in the pathogenesis of this disease.     

Role of MyD88 in phosphatidylinositol 3-kinase activation by flagellin/toll-like receptor 5 engagement in colonic epithelial cells

Bacterial flagellin, recognized by Toll-like receptor (TLR) 5, is suggested to be involved in colonic inflammation. However, the detailed signaling mechanisms mediated by flagellin/TLR5 engagement are not clear. Here we dissected the biochemical mechanism by which TLR5 engagement mediates phosphatidylinositol 3-kinase (PI3K) activation in colonic epithelial cells. We demonstrate that silencing TLR5 expression in nontransformed human colonic epithelial cells blocks flagellin-induced PI3K activation, indicating specific activation of PI3K by flagellin/TLR5 engagement. Moreover, we determine that TLR5 recruits the p85 regulatory subunit of PI3K to its cytoplasmic TIR domain in response to flagellin. However, the Src homology binding "YXXM" motif in the cytoplasmic TIR domain of TLR5 is not involved in p85 recruitment, implying that TLR5 indirectly recruits p85. Indeed, we demonstrate that the adaptor molecule MyD88 associates with TLR5 and silencing MyD88 expression blocks PI3K activation by disrupting the association between TLR5 and p85. Furthermore, we show that MyD88 associates with p85 in response to flagellin. Additionally, we determine that blocking PI3K activation reduces interleukin-8 production induced by flagellin in human colonic epithelial cells. Together, MyD88 bridges TLR5 engagement to PI3K activation in response to flagellin.     

The Toll-like receptor 5 stimulus bacterial flagellin induces maturation and chemokine production in human dendritic cells

Toll-like receptors (TLRs) are pattern recognition receptors that serve an important function in detecting pathogens and initiating inflammatory responses. Upon encounter with foreign Ag, dendritic cells (DCs) go through a maturation process characterized by an increase in surface expression of MHC class II and costimulatory molecules, which leads to initiation of an effective immune response in naive T cells. The innate immune response to bacterial flagellin is mediated by TLR5, which is expressed on human DCs. Therefore, we sought to investigate whether flagellin could induce DC maturation. Immature DCs were cultured in the absence or presence of flagellin and monitored for expression of cell surface maturation markers. Stimulation with flagellin induced increased surface expression of CD83, CD80, CD86, MHC class II, and the lymph node-homing chemokine receptor CCR7. Flagellin stimulated the expression of chemokines active on neutrophils (IL-8/CXC chemokine ligand (CXCL)8, GRO-alpha/CXCL1, GRO-beta/CXCL2, GRO-gamma/CXCL3), monocytes (monocyte chemoattractant protein-1/CC chemokine ligand (CCL)2), and immature DCs (macrophage-inflammatory protein-1 alpha/CCL3, macrophage-inflammatory protein-1 beta/CCL4), but not chemokines active on effector T cells (IFN-inducible protein-10 kDa/CXCL10, monokine induced by IFN-gamma/CXCL9, IFN-inducible T cell alpha chemoattractant/CXCL11). However, stimulating DCs with both flagellin and IFN-inducible protein-10 kDa, monokine induced by IFN-gamma, and IFN-inducible T cell alpha chemoattractant expression, whereas stimulation with IFN-beta or flagellin alone failed to induce these chemokines. In functional assays, flagellin-matured DCs displayed enhanced T cell stimulatory activity with a concomitant decrease in endocytic activity. Finally, DCs isolated from mouse spleens or bone marrows were shown to not express TLR5 and were not responsive to flagellin stimulation. These results demonstrate that flagellin can directly stimulate human but not murine DC maturation, providing an additional mechanism by which motile bacteria can initiate an acquired immune response.     

Genetic diversity of Toll-like receptor 5 among pig populations

The Toll-like receptor 5 (TLR5) recognizes flagellin of Gram-positive and -negative bacteria and plays an important role in the host defense system. Here, we surveyed single nucleotide polymorphisms (SNPs) in the coding sequence of the porcine TLR5 gene in 83 individuals from five pig breeds, these including Chinese local populations and Western commercial pig breeds. A total of 19 medium polymorphic SNPs (0.25 < PIC < 0.5) were identified, three of which were missense mutations that clustered within the extracellular domain of TLR5. One of the non-synonymous SNPs fell within a 228-amino acid region which has been shown to be important for flagellin recognition. Four SNPs were only found with high frequencies in Oriental pig breeds. The 19 SNPs were found in 30 haplotypes, one of which segregated at high frequency in all samples. Compared with Western pig breeds, Chinese local populations had higher genetic diversity and more haplotypes. Tajima’s test showed no evidence for deviation from neutrality. The data provide useful information for future genetic marker characterization by means of disease association analysis and/or stimulating the mutation carrier with relevant ligands.     

Induction of macrophage nitric oxide production by Gram-negative flagellin involves signaling via heteromeric Toll-like receptor 5/Toll-like receptor 4 complexes

The induction of cytokine synthesis by flagellin is mediated by a Toll-like receptor 5 (TLR5) signaling pathway. Although flagellin activation of the IL-1R-associated kinase and induction of TNF-alpha synthesis are dependent on TLR5 and not TLR4, we have found that flagellin stimulates NO in macrophages via a pathway that requires TLR5 and TLR4. Flagellin induced NO synthesis in HeNC2 cells, a murine macrophage cell line that expresses wild-type TLR4, but not in TLR4-mutant or -deficient GG2EE and 10ScNCr/23 cells. Flagellin stimulated an increase in inducible NO synthase (iNOS) mRNA and activation of the iNOS promoter. TLR5 forms heteromeric complexes with TLR4 as well as homomeric complexes. IFN-gamma permitted GG2EE and 10ScNCr/23 cells to produce NO in response to flagellin. Flagellin stimulated IFN-beta synthesis and Stat1 activation. The effect of flagellin on iNOS gene expression was inhibited by a Stat1 mutant protein. Taken together, these results support the conclusions that flagellin induces distinct patterns of inflammatory mediators depending on the nature of the TLR5 signaling complex and that the induction of NO by flagellin involves signaling via TLR5/TLR4 complexes.     

TRIF Mediates Toll-like Receptor 5-induced Signaling in Intestinal Epithelial Cells

Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. Here, we found that TRIF is involved in mediating TLR5-induced nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), specifically JNK1/2 and ERK1/2, activation in intestinal epithelial cells. TLR5 activation by flagellin permits the physical interaction between TLR5 and TRIF in human colonic epithelial cells (NCM460), whereas TLR5 does not interact with TRAM upon flagellin stimulation. Both primary intestinal epithelial cells from TRIF-KO mice and TRIF-silenced NCM460 cells significantly reduced flagellin-induced NFκB (p105 and p65), JNK1/2, and ERK1/2 activation compared with control cells. However, p38 activation by flagellin was preserved in these TRIF-deficient cells. TRIF-KO intestinal epithelial cells exhibited substantially reduced inflammatory cytokine (keratinocyte-derived cytokine, macrophage inflammatory protein 3α, and IL-6) expression upon flagellin, whereas control cells from TRIF-WT mice showed robust cytokine expression by flagellin. Compare with TRIF-WT mice, TRIF-KO mice were resistant to in vivo intestinal inflammatory responses: flagellin-mediated exacerbation of colonic inflammation and dextran sulfate sodium-induced experimental colitis. We conclude that in addition to MyD88, TRIF mediates TLR5-dependent responses and, thereby regulates inflammatory responses elicited by flagellin/TLR5 engagement. Our findings suggest an important role of TRIF in regulating host-microbial communication via TLR5 in the gut epithelium.     

Human corneal epithelial cells respond to ocular-pathogenic, but not to nonpathogenic-flagellin

In this study, we investigated the expression of TLR5 in human corneal epithelial cells (CEC), and the functional outcome of TLR5 triggering by flagellins of pathogenic- and nonpathogenic bacteria. Flagellins derived from Pseudomonas aeruginosa, Salmonella typhimurium, Serratia marcescense or Bacillus subtilis were used. The TLR5 protein and TLR5 specific mRNA expression was evident on human CEC. In human corneal epithelium tissues, TLR5 protein was detected at the basal and wing cells of the tissues. Ocular pathogenic bacteria, namely P. aeruginosa and S. marcescense, derived flagellin induced the significantly increased level of gene activation and IL-6 and IL-8 production. In contrast, ocular nonpathogenic S. typhimurium- and B. subtilis-derived flagellin induced neither the gene activation nor the increased production of IL-6 and IL-8 in human CEC. Human CEC would respond only to flagellin derived of ocular pathogenic bacteria, but not to those derived of ocular nonpathogenic bacteria, to generate pro-inflammatory cytokines.     

Flagellin-induced tolerance of the Toll-like receptor 5 signaling pathway in polarized intestinal epithelial cells

Salmonella typhimurium is a gram-negative enteric pathogen that invades the mucosal epithelium and is associated with diarrheal illness in humans. Flagellin from S. typhimurium and other gram-negative bacteria has been shown to be the predominant proinflammatory mediator through activation of the basolateral Toll-like receptor 5 (TLR5). Recent evidence has shown that prior exposure can render immune cells tolerant to subsequent challenges by TLR ligands. Accordingly, we examined whether prior exposure to purified flagellin would render human intestinal epithelial cells insensitive to future contact. We found that flagellin-induced tolerance is common to polarized epithelial cells and prevents further activation of proinflammatory signaling cascades by both purified flagellin and Salmonella bacteria but does not affect TNF-alpha stimulation of the same pathways. Flagellin tolerance is a rapid process that does not require protein synthesis, and that occurs within 1 to 2 h of flagellin exposure. Prolonged flagellin exposure blocks activation of the NF-kappaB, MAPK, and phosphoinositol 3-kinase signaling pathways and results in the internalization of a fraction of the basolateral TLR5 without affecting the polarity or total expression of TLR5. After removal of flagellin, cells require more than 24 h to fully recover their ability to mount a normal proinflammatory response. We have found that activation of phosphoinositol 3-kinase and Akt by flagellin has a small damping effect in the early stages of flagellin signaling but is not responsible for tolerance. Our study indicates that inhibition of TLR5-associated IL-1 receptor-associated kinase-4 activity occurs during the development of flagellin tolerance and is likely to be the cause of tolerance.     

Bacterial flagellin inhibits T cell receptor-mediated activation of T cells by inducing suppressor of cytokine signalling-1 (SOCS-1)

Flagellin, the structural component of bacterial flagella, is secreted by pathogenic and commensal bacteria, and is recognized by Toll-like receptor (TLR) 5. Flagellin is a common bacterial antigen present on most motile bacteria and is speculated to contribute to the activation of CD4+ T cells in the intestine. However, molecular mechanisms by which flagellin regulate T cell activation remains to be determined. Using Jurkat T cells or human primary T cell, we showed that flagellin stimulation induced tyrosine phosphorylation of TLR5 and activation of both mitogen-activated protein kinases and nuclear factor kappaB. In addition, stimulation by flagellin did not induce nuclear factor of activated T cells (NFAT) activation, while stimulation via the T cell receptor (TCR) leads to activation of NFAT. However, TCR-mediated NFAT activation and tyrosine phosphorylation of zeta-associated protein 70 (Zap-70) were inhibited in cells pre-stimulated by flagellin. Furthermore, flagellin stimulation induced suppressor of cytokine signalling-1 (SOCS-1), which formed a complex with Zap-70 after stimulation via TCR, and inhibition of SOCS-1 expression by SOCS-1-specific small interfering RNA reinstated TCR-mediated activation of NFAT in cells pre-stimulated with flagellin. These results collectively indicate that bacterial flagellin inhibits TCR-mediated activation of T cells by inducing SOCS-1.     

Protein kinase D interaction with TLR5 is required for inflammatory signaling in response to bacterial flagellin

Protein kinase D (PKD), also called protein kinase C (PKC)mu, is a serine-threonine kinase that is involved in diverse areas of cellular function such as lymphocyte signaling, oxidative stress, and protein secretion. After identifying a putative PKD phosphorylation site in the Toll/IL-1R domain of TLR5, we explored the role of this kinase in the interaction between human TLR5 and enteroaggregative Escherichia coli flagellin in human epithelial cell lines. We report several lines of evidence that implicate PKD in TLR5 signaling. First, PKD phosphorylated the TLR5-derived target peptide in vitro, and phosphorylation of the putative target serine 805 in HEK 293T cell-derived TLR5 was identified by mass spectrometry. Furthermore, mutation of serine 805 to alanine abrogated responses of transfected HEK 293T cells to flagellin. Second, TLR5 interacted with PKD in coimmunoprecipitation experiments, and this association was rapidly enhanced by flagellin treatment. Third, pharmacologic inhibition of PKC or PKD with G?6976 resulted in reduced expression and secretion of IL-8 and prevented the flagellin-induced activation of p38 MAPK, but treatment with the PKC inhibitor G?6983 had no significant effects on these phenotypes. Finally, involvement of PKD in the p38-mediated IL-8 response to flagellin was confirmed by small hairpin RNA-mediated gene silencing. Together, these results suggest that phosphorylation of TLR5 by PKD may be one of the proximal elements in the cellular response to flagellin, and that this event contributes to p38 MAPK activation and production of inflammatory cytokines in epithelial cells.     

Sensing bacterial flagellin by membrane and soluble orthologs of Toll-like receptor 5 in rainbow trout (Onchorhynchus mikiss)

Rainbow trout (Onchorhynchus mikiss) possess two genes encoding putative leucine-rich repeat (LRR)-containing proteins similar to human TLR5. Molecular cloning of these two LRR proteins suggested the presence of a TLR5-like membrane form (rtTLR5M) and a soluble form (rtTLR5S). Here we elucidated the primary structures and the unique combinational functions of these fish versions of TLR5. The LRR regions of rtTLR5S and rtTLR5M exhibited 81% homology and relatively high (35.6 and 33.7%) homology to the extracellular domains of human TLR5 (huTLR5). Thus, two distinct genes encode the TLR5 orthologs in fish, one of which has a consensus intracellular domain (TIR). In order to test their functions, we constructed fusion proteins with the LRR region of rtTLR5S (S-chimera) or that of rtTLR5M and the TIR of huTLR5 (M-chimera). The S- and M-chimeras expressed in HeLa or CHO cells signaled the presence of Vibrio anguillarum flagellin, resulting in NF-kappaB activation. rtTLR5M was ubiquitously expressed, whereas rtTLR5S was predominantly expressed in the liver. In the hepatoma cell lines of the rainbow trout RTH-149, stimulation of rtTLR5M with V. anguillarum or its flagellin allowed the up-regulation of rtTLR5S. Flagellin-mediated NF-kappaB activation was more significant in the presence of or simultaneous expression of rtTLR5S. Therefore, a two-step flagellin response occurred for host defense against bacterial infection in fish: (a) flagellin first induced basal activation of NF-kappaB via membrane TLR5, facilitating the production of soluble TLR5 and minimal acute phase proteins, and (b) the inducible soluble TLR5 amplifies membrane TLR5-mediated cellular responses in a positive feedback fashion.     

Gangliosides inhibit flagellin signaling in the absence of an effect on flagellin binding to toll-like receptor 5

A recent study (Ogushi, K., Wada, A., Niidome, T., Okuda, T., Llanes, R., Nakayama, M., Nishi, Y., Kurazono, H., Smith, K. D., Aderem, A., Moss, J., and Hirayama, T. (2004) J. Biol. Chem. 279, 12213-12219) concluded that gangliosides serve as co-receptors for flagellin signaling via toll-like receptor 5 (TLR5). In view of several findings in this study that were inconsistent with a role for gangliosides as co-receptors, we re-examined this important issue. Using TLR5-negative RAW 264.7 cells and a TLR5-enhanced yellow fluorescent protein chimera, we established an assay for specific binding of flagellin to cells. Inhibition of clatherin-mediated internalization of flagellin.TLR5-enhanced yellow fluorescent protein complexes did not impair flagellin activation of IRAK-1. Thus flagellin signal occurs at the cell surface and not intracellularly. Exogenous addition of mixed gangliosides (GM1, GD1a, and GT1b) as well as GD1a itself inhibited flagellin-induced interleukin-1 receptor-associated kinase activation as well as tumor necrosis factor alpha production in HeNC2, THP-1, and RAW 264.7 cells. Gangliosides inhibited flagellin signaling in the absence of an effect on flagellin binding to TLR5. Depletion of gangliosides in RAW 264.7 cells did not alter the concentration dependence or magnitude of flagellin signaling as measured by interleukin-1 receptor-associated kinase activation or tumor necrosis factor alpha production. Our findings are consistent with the conclusions that gangliosides are not essential co-receptors for flagellin and that the inhibitory effect of gangliosides is mediated by at least one mechanism that is distinct from any effect on the binding of flagellin to TLR5.     

Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin

Bacterial flagellin has recently been identified as a ligand for Toll-like receptor 5 (TLR5). Human sites known to specifically express TLR5 include macrophages and gastric and intestinal epithelium. Because infection of intestinal epithelial cells with Salmonella leads to an active transport of flagellin to the subepithelial compartment in proximity to microvessels, we hypothesized that human intestinal endothelial cells functionally express TLR5, thus enabling an active inflammatory response upon binding of translocated flagellin. Endothelial expression of TLR5 in human macro- and microvascular endothelial cells was examined by RT-PCR, immunoblot analysis, and immunofluorescence. Endothelial expression of TLR5 in vivo was verified by immunohistochemistry. Endothelial modulation of ICAM-1 expression was quantitated using flow cytometry, and leukocyte transmigration in vitro was assessed by an endothelial transmigration assay. Epithelial-endothelial cellular interactions upon infection with viable Salmonella were investigated using a coculture system in vitro. We found that Salmonella-infected intestinal epithelial cells induce endothelial ICAM-1 expression in cocultured human endothelial cells. Both macro- (HUVEC) and microvascular endothelial cells derived from human skin (human dermal microvascular endothelial cell 1) and human colon (human intestinal microvascular endothelial cells) were found to express high constitutive amounts of TLR5 mRNA and protein. These findings were paralleled by strong immunoreactivity for TLR5 of normal human colonic microvessels in vivo. Furthermore, incubation of human dermal microvascular endothelial cells with flagellin from clinical isolates of Escherichia and Salmonella strains led to a marked up-regulation of ICAM-1, as well as to an enhanced leukocyte transendothelial cell migration. These results suggest that endothelially expressed TLR5 might play a previously unrecognized role in the innate immune response toward bacterial Ags.     

Identification of a sequence in human toll-like receptor 5 required for the binding of Gram-negative flagellin

Flagellins from Gram-negative bacteria activate inflammatory cells by a toll-like receptor 5 (TLR5)-dependent signaling pathway. We have examined the interaction between flagellin and TLR5 using an in vitro binding assay. Purified recombinant His-tagged flagellin from Salmonella enteritidis bound to TLR5 in detergent lysates from COS-1 cells transiently transfected with a human TLR5 expression plasmid. Flagellins from Salmonella typhimurium and Escherichia coli also bound to TLR5. The specificity of this interaction was demonstrated by its concentration dependence and lack of TLR5 binding to a biologically inactive form of flagellin or to a His-tagged non-flagellar protein. Flagellin bound to the extracellular domain of TLR5 expressed on the surface of COS-1 cells and to a soluble, monomeric form of the extracellular domain (amino acids 1-636). Although a TLR5 extracellular domain containing amino acids 1-407 retained flagellin binding activity, binding was not evident with a TLR5 peptide encoding residues 1-386. Conversely, a peptide containing amino acid residues 386-636 retained flagellin binding. Thus it is likely that amino acids 386-407 is a binding site for flagellin. This sequence contains a putative leucine-rich repeat. These results support the conclusion that flagellin signaling via TLR5 involves a direct interaction between flagellin and a leucine-rich region in TLR5. We also show that the NH2-terminal 358 amino acids of TLR5 play an important role in its signaling activity. Our results provide, for the first time, a molecular basis for the agonist specificity of a TLR.     

Flagellin/TLR5 responses in epithelia reveal intertwined activation of inflammatory and apoptotic pathways

Flagellin, the primary structural component of bacterial flagella, is recognized by Toll-like receptor 5 (TLR5) present on the basolateral surface of intestinal epithelial cells. Utilizing biochemical assays of proinflammatory signaling pathways and mRNA expression profiling, we found that purified flagellin could recapitulate the human epithelial cell proinflammatory responses activated by flagellated pathogenic bacteria. Flagellin-induced proinflammatory activation showed similar kinetics and gene specificity as that induced by the classical endogenous proinflammatory cytokine TNF-alpha, although both responses were more rapid than that elicited by viable flagellated bacteria. Flagellin, like TNF-alpha, activated a number of antiapoptotic mediators, and pretreatment of epithelial cells with this bacterial protein could protect cells from subsequent bacterially mediated apoptotic challenge. However, when NF-kappaB-mediated or phosphatidylinositol 3-kinase/Akt proinflammatory signaling was blocked, flagellin could induce programmed cell death. Consistently, we demonstrate that flagellin and viable flagellate Salmonella induces both the extrinsic and intrinsic caspase activation pathways, with the extrinsic pathway (caspase 8) activated by purified flagellin in a TLR5-dependant fashion. We conclude that interaction of flagellin with epithelial cells induces caspase activation in parallel with proinflammatory responses. Such intertwining of proinflammatory and apoptotic signaling mediated by bacterial products suggests roles for host programmed cell death in the pathogenesis of enteric infections.     

Interleukin-18 secretion and Th1-like cytokine responses in human peripheral blood mononuclear cells under the influence of the toll-like receptor-5 ligand flagellin

Flagellin is the major protein component of the flagella from motile bacteria and was identified as the ligand for toll-like receptor (TLR)-5. Whereas its effects on epithelial cells have been studied in detail, activation of human peripheral blood mononuclear cells (PBMC) by flagellin is characterized only partially. By using the recombinant protein of Salmonella muenchen we confirm the proinflammatory nature of flagellin as detected by nuclear factor-kappaB activation and interleukin (IL)-8 production. Aim of the current study was to elucidate in PBMC effects of flagellin on IL-18 and Th1-like cytokine responses. We report that flagellin in pathophysiologically relevant concentrations augmented release of mature IL-18 by THP-1 monocytes, PBMC, and whole blood stimulated with nigericin or by ATP-mediated P2X7 purinergic receptor activation. Further key functions of the IL-18/IL-12/interferon-gamma (IFNgamma) pathway were upregulated by flagellin. Flagellin synergized with IL-12 for production of IFN-gamma and augmented secretion of interferon-inducible protein-10, a CXC-chemokine that is key to the generation of Th1-type responses. In contrast, neither IL-18-binding protein nor IL-4 was affected. Taken together, the present data demonstrate for the first time that flagellin at concentrations that are detectable in the blood compartment during sepsis efficiently enhances the IL-18/IL-12/IFNgamma pathway and thus Th1-like cytokine responses in PBMC.     

Characterization of the canine desmin (DES) gene and evaluation as a candidate gene for dilated cardiomyopathy in the Dobermann

Canine-dilated cardiomyopathy (DCM) in dogs is a disease of the myocardium associated with dilatation and impaired contraction of the ventricles and is suspected to have a genetic cause. A missense mutation in the desmin gene (DES) causes DCM in a human family. Human DCM closely resembles the canine disease. In the present study, we evaluated whether DES gene mutations are responsible for DCM in Dobermann dogs. We have isolated bacterial artificial chromosome clones (BACs) containing the canine DES gene and determined the chromosomal location by fluorescence in situ hybrizidation (FISH). Using data deposited in the NCBI trace archive and GenBank, the canine DES gene DNA sequence was assembled and seven single nucleotide polymorphisms (SNPs) were identified. From the canine DES gene BAC clones, a polymorphic microsatellite marker was isolated. The microsatellite marker and four informative desmin SNPs were typed in a Dobermann family with frequent DCM occurrence, but the disease phenotype did not associate with a desmin haplotype.

We concluded that mutations in the DES gene do not play a role in Dobermann DCM. Availability of the microsatellite marker, SNPs and DNA sequence reported in this study enable fast evaluation of the DES gene as a DCM candidate gene in other dog breeds with DCM occurrence.     

Gram-negative flagellin-induced self-tolerance is associated with a block in interleukin-1 receptor-associated kinase release from toll-like receptor 5

Flagellin from a number of Gram-negative bacteria induces cytokine and nitric oxide production by inflammatory cell types. In view of the evidence that flagellin responsiveness is subject to modulation, we explored the possibilities that a prior exposure to flagellin might result in a state of reduced flagellin responsiveness or tolerance and that lipopolysaccharide (LPS) and flagellin may induce a state of cross-tolerance to each other. Our results demonstrate that a prior exposure to flagellin results in a subsequent state of flagellin tolerance in human monocytes, THP1 cells, Jurkat cells, and COS-1 cells. Tolerance occurs within 2 h after addition of flagellin and does not require protein synthesis. Flagellin did not induce tolerance to LPS in monocytes and THP1 cells; however, LPS treatment of monocytes and THP1 cells resulted in a state of flagellin cross-tolerance. Flagellin-induced self-tolerance is not the result of a decrease in the steady-state level of toll-like receptor 5 (TLR5) or interleukin-1 receptor associated kinase (IRAK), but it is associated with a block in the release of IRAK from the TLR5 complex in flagellin-tolerant cells. Release is essential for IRAK activity because the TLR5-associated IRAK lacks kinase activity. LPS-induced cross-tolerance to flagellin is also associated with a block in IRAK release from TLR5. These results provide evidence for a novel mechanism of TLR signaling control.     

Engineered expression of the TLR5 ligand flagellin enhances paramyxovirus activation of human dendritic cell function

The paramyxovirus simian virus 5 (SV5) is a poor activator of human dendritic cell (DC) maturation pathways in vitro, and infected DC do not upregulate cell surface costimulatory proteins or secretion of immunomodulatory cytokines. We evaluated the hypothesis that activation of SV5-infected DC would be enhanced by engineering SV5 to express a Toll-like-receptor (TLR) ligand. To test this hypothesis, a novel virus was engineered such that the gene encoding an intracellular form of the TLR5 ligand flagellin was expressed from the genome of wild-type (WT) SV5 (SV5-flagellin). Cells infected in vitro with the flagellin-expressing virus released low levels of biologically active flagellin, which was capable of stimulating TLR5 signaling. Infection of human peripheral blood mononuclear cell-derived immature DC with SV5-flagellin resulted in enhanced levels of interleukin-6 (IL-6) and IL-12 compared to infection with DC with the parental virus, WT SV5. In contrast to cytokine induction, the flagellin-expressing virus did not appreciably increase DC surface expression of the costimulatory molecule CD80 or CD86 above the level seen with WT SV5 alone. In mixed-culture assays, DC infected with the flagellin-expressing virus were more effective at activating gamma interferon secretion from both CD8⁺ and CD4⁺ allogeneic T cells than DC infected with WT SV5. Our results with SV5-directed intracellular expression of flagellin may be applicable to other vectors or pathogenic viruses where overcoming impairment of DC activation could contribute to the development of safer and more effective vaccines.