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PubMed2002

Responsiveness of intestinal epithelial cell lines to lipopolysaccharide is correlated with Toll-like receptor 4 but not Toll-like receptor 2 or CD14 expression.

BACKGROUND AND AIMS: Luminal bacteria have been implicated in the pathogenesis of inflammatory bowel diseases. Exposure of intestinal epithelial cells (IEC) to bacterial components potentially initiates intestinal inflammation by release of chemokines and recruitment of inflammatory cells. We analyzed receptor expression and signaling pathways involved in activation of human primary IEC and carcinoma-derived cell lines by lipopolysaccharide (LPS). MATERIALS AND METHODS: HT-29/p, HT-29/MTX, and Caco-2 cells were stimulated by LPS. IL-8 content in supernatants was analyzed by ELISA, and expression of CD14, Toll-like receptor (TLR) 2 and TLR 4 was determined by RT-PCR. Presence of TLR 4 protein was assessed by western blot analysis. LPS response was modulated by sCD14, LPS-binding protein, neutralization of CD14, and inhibitors of early signal activation. RESULTS: LPS dose-dependently induced secretion of IL-8 in undifferentiated HT-29/p cells while Caco-2 and permanently differentiated HT-29/MTX cells were unresponsive. Differently to HT-29/MTX, both HT-29/p and Caco-2 cells constitutively expressed transcripts for CD14. However, CD14 was not required for LPS-mediated induction of IL-8 in HT-29/p cells since neutralizing anti-CD14 antibodies left IL-8 levels unchanged. Unresponsiveness of Caco-2 and HT-29/MTX cells to LPS persisted in the presence of sCD14 and/or LPS-binding protein. Neither cell line expressed TLR 2 transcripts while only responsive HT-29/p cells expressed TLR 4 mRNA and TLR 4 protein. Butyrate down-regulated TLR 4 expression and significantly diminished LPS-dependent IL-8 secretion. Inhibition of G protein dependent kinase activation reduced IL-8 levels to 50%; the phosphatidyl-inositol-3'-kinase inhibitor LY294002 abrogated the response. CONCLUSION: Responsiveness of IEC lines to LPS is positively correlated with TLR 4 expression. Strategies targeting TLR 4 expression or TLR 4 mediated signaling may antagonize IEC activation by LPS.

Cross Reactions↗
PubMed2002

HSP70 as endogenous stimulus of the Toll/interleukin-1 receptor signal pathway.

Human heat-shock protein (HSP)70 activates innate immune cells and hence requires no additional adjuvants to render bound peptides immunogenic. Here we tested the assumption that endogenous HSP70 activates the Toll/IL-1 receptor signal pathway similar to HSP60 and pathogen-derived molecular patterns. We show that HSP70 induces interleukin-12 (IL-12) and endothelial cell-leukocyte adhesion molecule-1 (ELAM-1) promoters in macrophages and that this is controlled by MyD88 and TRAF6. Furthermore, HSP70 causes MyD88 relocalization and MyD88-deficient dendritic cells do not respond to HSP70 with proinflammatory cytokine production. Using the system of genetic complementation with Toll-like receptors (TLR) we found that TLR2 and TLR4 confer responsiveness to HSP70 in 293T fibroblasts. The expanding list of endogenous ligands able to activate the ancient Toll/IL-1 receptor signal pathway is in line with the "danger hypothesis" proposing that the innate immune system senses danger signals even if they originate from self.

Animals↗
PubMed2005

Tpl2 (tumor progression locus 2) phosphorylation at Thr290 is induced by lipopolysaccharide via an Ikappa-B Kinase-beta-dependent pathway and is required for Tpl2 activation by external signals.

The serine-threonine protein kinase encoded by the tumor progression locus 2 (Tpl2) proto-oncogene transduces Toll-like receptor and death receptor signals in a variety of cell types. Here we show that Tpl2 undergoes phosphorylation at Thr(290) both in cells overexpressing Tpl2 and in cells stimulated with lipopolysaccharide (LPS) or tumor necrosis factor-alpha and that phosphorylation on this site parallels Tpl2 activation. Reconstitution of Tpl2(-/-) macrophages with wild type Tpl2 or Tpl2 T290D restored ERK activation by LPS, whereas reconstitution of the same cells with Tpl2 T290A did not, suggesting that phosphorylation at Thr(290) is required for the physiological activation of Tpl2 by external signals. Both the wild type Tpl2 and the kinase-inactive mutant Tpl2 K167M undergo Thr(290) phosphorylation, suggesting that Thr(290) may be a site of trans-phosphorylation rather than auto-phosphorylation. Pretreatment of 293 cells and primary macrophages with the Ikappa-B kinase-beta (IKKbeta) inhibitor PS-1145 blocked Tpl2 phosphorylation at Thr(290), suggesting that phosphorylation depends on IKKbeta, an obligatory positive regulator of Tpl2. We conclude that Tpl2 phosphorylation at Thr(290) is induced by LPS, depends on IKKbeta, and is required for the physiological activation of Tpl2 by external signals.

Animals↗
PubMed2003

Toll-like receptor-dependent production of IL-12p40 causes chronic enterocolitis in myeloid cell-specific Stat3-deficient mice.

Stat3 plays an essential role in IL-10 signaling pathways. A myeloid cell-specific deletion of Stat3 resulted in inflammatory cytokine production and development of chronic enterocolitis with enhanced Th1 responses in mice. In this study, we analyzed the mechanism by which a Stat3 deficiency in myeloid cells led to the induction of chronic enterocolitis in vivo. Even in the absence of Stat1, which is essential for IFN-gamma signaling pathways, Stat3 mutant mice developed chronic enterocolitis. TNF-alpha/Stat3 double-mutant mice developed severe chronic enterocolitis with enhanced Th1 cell development. IL-12p40/Stat3 double-mutant mice, however, showed normal Th1 responses and no inflammatory change in the colon. RAG2/Stat3 double-mutant mice did not develop enterocolitis, either. These findings indicate that overproduction of IL-12p40, which induces potent Th1 responses, is essential for the development of chronic enterocolitis in Stat3 mutant mice. Furthermore, enterocolitis was significantly improved and IFN-gamma production by T cells was reduced in TLR4/Stat3 double-mutant mice, indicating that TLR4-mediated recognition of microbial components triggers aberrant IL-12p40 production by myeloid cells, leading to the development of enterocolitis. Thus, this study clearly established a sequential innate and acquired immune mechanism for the development of Th1-dependent enterocolitis.

Animals↗
PubMed2004

Toll-like receptors involved in the response to microbial pathogens: development of agonists for toll-like receptor 9.

Upon microbial infection, a host has to mount a multiplicity of immune responses that target the invading pathogen. This is achieved in part by the use of particular receptors expressed on mammalian innate immune cells, the toll-like receptors (TLRs). Recognition of a given microbial molecular structure, such as bacterial or viral DNA, leads to the activation of signaling pathways that result in distinct sets of immune responses. The pathogen structures that are recognized by TLR9 in bacterial or viral DNA are deoxycytidyl-deoxyguanosine dinucleotides (CpGs) in specific sequence contexts (CpG motifs). The stimulatory activity of pathogen DNA can be mimicked by synthetic oligodeoxynucleotides (ODNs) containing such motifs (CpG ODNs). The TLR9-mediated stimulation of the vertebrate innate immune system, and subsequently of the adaptive immune system, allows the use of TLR9 agonists as highly effective vaccine adjuvants for infectious diseases, and as stand-alone therapies or in combination with other therapies in cancer.

Adjuvants, Immunologic↗
PubMed2006

HSP70 enhances macrophage phagocytosis by interaction with lipid raft-associated TLR-7 and upregulating p38 MAPK and PI3K pathways.

BACKGROUND: Exogenous Heat Shock Protein-70 (HSP70), a product of necrotic cell death, binds the lipid raft microdomains of macrophages and, within minutes, stimulates the phagocytosis and presentation of internalized antigens. The aim of this study was to identify (a) the receptor on the lipid raft microdomain that interacts with HSP70 and (b) the subsequent signaling pathways that mediate HSP70-enhanced phagocytosis. METHODS: Cells including RAW264.7, bone-marrow-derived macrophages from TLR7-/- mice or controls and cells subjected to genetic methods reducing the mRNA expression of TLR7 were used to examine the interaction of HSP70 with TLR7. The effect of HSP70-TLR7 interaction on phagocytosis was assessed using phagocytosis assays described earlier. RESULTS: HSP70 binds Toll-like receptor-7 (TLR7) on the lipid raft microdomain of macrophage plasma membrane. Subsequent signaling is mediated through phosphoinositide 3-kinase (PI3K) and the up-regulation of the p38 MAP kinase pathways, both known activators of the phagocytic mechanisms. Reduced expression of TLR7 either via short interfering RNA for TLR7 (siRNA-TLR7) or using bone-marrow derived macrophages from TLR7-/- mice show that, as macrophages lose expression of TLR7, their ability to mediate HSP70-induced phagocytosis undergoes a corresponding diminution. Similarly, disruption of lipid rafts or blocking HSP70-TLR7-interaction or treatment with wortmannin and SB203580, inhibitors of PI3K or p38 MAPK, respectively, abrogates HSP70-induced macrophage phagocytosis. CONCLUSIONS: The interaction of HSP70 and LR-associated TLR7, two phylogenetically conserved molecules, activates a rapid, membrane-bound signaling pathway that enhances phagocytosis, a vital innate defense mechanism. This study elucidates critical mechanistic elements that mediate HSP70-enhanced phagocytosis by macrophages.

Animals↗
PubMed2006

Effects of Scutellaria baicalensis Georgi on macrophage-hepatocyte interaction through cytokines related to growth control of murine hepatocytes.

The aim of this study is to elucidate the effects of Scutellaria baicalensis Georgi (SbG) extract and its constituents on macrophage-hepatocyte interaction in primary cultures. By using trans-well primary Kupffer cell culture or conditioned medium (CM) from murine macrophage RAW264.7 cell line (RAW cells), effects of SbG on hepatocyte growth were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and trypan blue exclusion assay. Cytokine production, antibody-neutralization studies, and molecular mechanisms of transforming growth factor (TGF)-beta1 gene expression were elucidated on SbG-treated RAW264.7 cells. In addition, recombinant human TGF-beta1 (r-human TGF-beta1) was added to elucidate the mechanisms of SbG effects on cultured hepatocytes. Immunohistochemistry using anti-NF-kappaB antibody was used to determine the possible signal transduction pathways in primary hepatocyte culture. The results showed that SbG stimulated the proliferation of cultured hepatocytes, possibly through NF-kappaB, but not of Toll-like receptor 4 activation; whereas SbG-RAW-CM and SbG in trans-well significantly suppressed the proliferation of hepatocytes. Antibody-neutralization studies revealed that TGF-beta1 was the main antimitotic cytokine in SbG-treated RAW cells CM. The growth stimulation effect of SbG on cultured hepatocytes was inhibited by exogenous administration of r-human TGF-beta1. Furthermore, SbG induced NF-kB translocation into the nuclei of cultured cells. In the RAW264.7 line, SbG and baicalin stimulated TGF-beta1 gene expression via NF-kappaB and protein kinase C activation. We conclude that SbG stimulates hepatocyte growth via activation of the NF-kappaB pathway and induces TGF-beta1 gene expression through the Kupffer cell-hepatocyte interaction, which subsequently results in the inhibition of SbG-stimulated hepatocyte growth.

Animals↗
PubMed2001

Evidence for an innate immune response in the immature human intestine: toll-like receptors on fetal enterocytes.

The intestinal epithelium is an active participant in the mucosal immune response against luminal pathogens. Microorganisms and their cell wall products, i.e. lipopolysaccharide (LPS), can stimulate the enterocyte to produce an innate immune response with the increased production of IL-8 via an activation of the transcription factor NFkappaB. The innate response mechanism, however, has not been understood until the recent description of a family of human toll-like receptors (hTLR) on immune cells that interact with LPS and modulate the IL-8 response via an intracellular signal transduction pathway similar to that of the IL-1 receptor family. Accordingly, in this study we have sought to determine the constitutive and regulated expression of hTLR on a nonmalignant human fetal primary small intestinal cell line (H4 cells) and on small intestinal samples of ileum from human fetuses (age 18-21 wk). Specimens were examined by reverse-transcription PCR, Western blot analysis, and immunofluorescence for hTLR2 and hTLR4 mRNA and protein and to determine whether their expression was regulated by LPS or by an endogenous inflammatory stimulus, IL-1beta. hTLR2 and hTLR4 were expressed constitutively on H4 cells and on human fetal small intestinal enterocytes, predominantly on the basolateral surface of crypt enterocytes. Inflammatory stimuli appeared to regulate hTLR transcription (IL-1beta increased both hTLR2 and hTLR4 whereas LPS decreased hTLR4) and possibly translation (qualitative observations). The presence of hTLR on human fetal enterocyte suggests a mechanism for the innate immune response to pathogens and could provide the basis for further study of the accentuated inflammatory response in age-dependent gastrointestinal diseases such as necrotizing enterocolitis.

Base Sequence↗
PubMed1998

Phosphorylation modulates direct interactions between the Toll receptor, Pelle kinase and Tube.

Determination of dorsal/ventral polarity in Drosophila requires 12 genetically defined, maternally encoded proteins. These include Toll, a transmembrane receptor, Pelle, a ser/thr protein kinase and Tube, all of which function intracytoplasmically to initiate the cascade that ultimately activates Dorsal, an NF-kappaB family transcription factor. Here we describe biochemical interactions between recombinant Toll, Pelle and Tube that provide insights into early events in activation of the signaling cascade. We first show that Pelle binds directly to a region within the Toll intracytoplasmic domain, providing the first evidence that these two evolutionarily conserved molecules physically interact. We then demonstrate that Pelle can be autophosphorylated, and that this prevents binding to Toll as well as Tube. Autophosphorylation occurs in the N-terminal, death-domain-containing region of Pelle, which is dispensable for binding to Toll but required for enzymatic activity. We also show that Pelle phosphorylates Toll, within the region required for Pelle interaction, but this phosphorylation can be blocked by a previously characterized inhibitory domain at the Toll C terminus. These and other results allow us to propose a model by which multiple phosphorylation-regulated interactions between these three proteins lead to activation of the Dorsal signaling pathway.

Animals↗
PubMed2006

Toll-like receptor 3 and TICAM genes in catfish: species-specific expression profiles following infection with Edwardsiella ictaluri.

Toll-like receptors (TLRs) are a family of transmembrane proteins that recognize specific pathogen-associated molecular patterns and use conserved signaling pathways to activate proinflammatory cytokines and type-1 interferons to fight infection. TLR3 in mammals is best known for its recognition of dsRNA as ligand and its MyD88-independent signaling. TLR3, upon recognition of dsRNA, recruits and binds its adaptor protein TIR domain-containing adapter molecule (TICAM) 1. Here we report the genomic sequences and structures of TLR3 and a TICAM adaptor from channel catfish (Ictalurus punctatus). Whereas a partial TLR3 cDNA sequence has been reported from channel catfish, and complete TLR3 genes are known from other teleost fish species, a complete TICAM sequence has not been previously reported from a nonmammalian species. Analysis of catfish TLR3 and TICAM expression after infection with Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC), suggested a conserved TLR3-TICAM receptor-adaptor relation in catfish. Comparison of TLR3 and TICAM expression profiles in channel catfish with those from the closely related blue catfish species (Ictalurus furcatus), which exhibits strong resistance to ESC, revealed a striking pattern of species-specific expression. A dramatic downregulation of TLR3 and TICAM gene expression was observed in blue catfish head kidney and spleen, which we speculate may be the result of maturation and migration of different cell types to and from the lymphoid tissues following infection.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Airway peptidoglycan and immunostimulatory DNA exposures have divergent effects on the development of airway allergen hypersensitivities.

BACKGROUND: Environmental exposures to toll-like receptor (TLR) ligands have been suggested to provide immunologic protection against allergic diseases. However, some TLRs use unique intracellular signaling pathways, suggesting that ambient TLR ligand exposures might induce a range of host responses. OBJECTIVE: These investigations compared peptidoglycan (PGN; TLR2)-induced and immunostimulatory sequence DNA oligodeoxynucleotide (ISS-ODN; TLR9)-induced innate responses and determined how airway exposures to these TLR ligands affect adaptive immunity and the asthmatic phenotype. METHODS: In in vitro and in vivo studies innate responses to PGN and ISS-ODN were compared. Alternatively, mice were intranasally immunized with ovalbumin (OVA) alone or OVA plus PGN or ISS-ODN, and adaptive immune profiles and responses to airway OVA challenge were assessed. RESULTS: PGN and ISS-ODN induced divergent innate responses predictive of their having TH2- and TH1-biasing adjuvant potential, respectively. Consistent with these findings, mice intranasally immunized with OVA alone had relatively weak adaptive responses, whereas intranasal OVA/PGN- and OVA/ISS-ODN-coimmunized mice had much stronger humoral and cellular responses that were TH2 and TH1 biased, respectively. Finally, on airway allergen challenge, mice intranasally immunized with OVA alone had modest TH2-biased airway hypersensitivity responses, whereas airway responses were greatly exaggerated for intranasal OVA/PGN-immunized mice. In contrast, intranasal OVA/ISS-ODN-immunized mice had little evidence of airway hypersensitivity after airway allergen challenge. CONCLUSIONS: Considered in a larger context, these results suggest that inspired air is likely to contain TLR ligands capable of both preventing and precipitating the asthmatic phenotype.

Adjuvants, Immunologic↗
PubMed2005

Distinct poly(I-C) and virus-activated signaling pathways leading to interferon-beta production in hepatocytes.

Innate cellular antiviral defenses are likely to influence the outcome of infections by many human viruses, including hepatitis B and C viruses, agents that frequently establish persistent infection leading to chronic hepatitis, cirrhosis, and liver cancer. However, little is known of the pathways by which hepatocytes, the cell type within which these hepatitis agents replicate, sense infection, and initiate protective responses. We show that cultured hepatoma cells, including Huh7 cells, do not activate the interferon (IFN)-beta promoter in response to extracellular poly(I-C). In contrast, the addition of poly(I-C) to culture media activates the IFN-beta promoter and results in robust expression of IFN-stimulated genes (ISG) in PH5CH8 cells, which are derived from non-neoplastic hepatocytes transformed with large T antigen. Small interfering RNA knockdown of TLR3 or its adaptor, Toll-interleukin-1 receptor domain-containing adaptor inducing IFN-beta (TRIF), blocked extracellular poly(I-C) signaling in PH5CH8 cells, whereas poly(I-C) responsiveness could be conferred on Huh7 hepatoma cells by ectopic expression of Toll-like receptor 3 (TLR3). In contrast to poly(I-C), both cell types signal the presence of Sendai virus infection through a TLR3-independent intracellular pathway requiring expression of retinoic acid-inducible gene I (RIG-I), a putative cellular RNA helicase. Silencing of RIG-I expression impaired only the response to Sendai virus and not extracellular poly(I-C). We conclude that hepatocytes contain two distinct antiviral signaling pathways leading to expression of type I IFNs, one dependent upon TLR3 and the other dependent on RIG-I, with little cross-talk between these pathways.

Animals↗
PubMed2026

Coordinated inflammatory macrophage and vascular smooth muscle cell remodeling signatures in human atherosclerosis: An integrative single-cell and bulk transcriptomic analysis.

Atherosclerotic plaque progression is shaped by coordinated inflammatory and remodeling programs involving immune cells and vascular wall cells. Inflammatory macrophage activation and vascular smooth muscle cell (VSMC) phenotypic remodeling are central features of human atherosclerosis, but their transcriptomic relationships during plaque progression remain incompletely characterized. This study integrated single-cell and bulk transcriptomic datasets to examine highly inflammatory macrophage states, VSMC remodeling-related transcriptional programs, and candidate ligand-receptor expression patterns in human atherosclerotic plaques. Human atherosclerotic plaque single-cell RNA sequencing data from GSE260657 and bulk transcriptomic data from GSE28829 were analyzed. After quality control, 7628 cells were retained for single-cell analysis. Major cell types were annotated using canonical markers, followed by reclustering of macrophages and VSMC-related cells. Functional module scoring, differential expression analysis, Gene Ontology biological process enrichment, and Kyoto Encyclopedia of Genes and Genomes pathway analyses were performed to characterize macrophage transcriptional states. Slingshot was applied to infer VSMC pseudotime ordering. CellChat and NicheNet were used to prioritize candidate ligand-receptor expression patterns and ligand-associated VSMC target gene programs. External bulk transcriptomic analysis was performed to examine whether single-cell-derived inflammatory and remodeling signatures were represented at the tissue-transcriptome level during plaque progression. Macrophage reclustering identified a highly inflammatory macrophage state characterized by prominent inflammatory activation, cytokine-response, and stress-response features. Genes upregulated in this population were enriched in pathways related to tumor necrosis factor (TNF) response, nuclear factor kappa B signaling, leukocyte activation, cytokine signaling, lipid and atherosclerosis, toll-like receptor signaling, and inflammasome-associated inflammation. VSMC reclustering revealed contractile VSMCs, PTHLH+ synthetic VSMCs, KRT7+ VSMC-like cells, interferon-responsive VSMCs, pericyte-like mural cells, and osteogenic/modulated VSMCs. Pseudotime analysis showed a broad contractile-to-osteogenic/modulated transcriptional continuum accompanied by increased expression of remodeling-associated genes and selected inflammatory or remodeling-associated receptor genes. CellChat and NicheNet analyses prioritized candidate ligand-receptor and ligand-associated target gene expression patterns involving SPP1-CD44, TNF-TNFRSF1A, IL1B-IL1R1/IL1RAP, MIF-ACKR3, PDGFB-PDGFRB, and FN1-SDC1/ITGB1. In GSE28829, inflammatory macrophage-, osteogenic/modulated VSMC-, candidate ligand-receptor expression-, SPP1-CD44 candidate axis-, and NicheNet-prioritized target program-related signatures were more prominent in advanced plaques and were positively correlated with each other. This integrative transcriptomic analysis identified a highly inflammatory macrophage state and a VSMC remodeling continuum in human atherosclerotic plaques. Candidate ligand-receptor and ligand-associated target gene expression patterns linked inflammatory macrophage activation with osteogenic/modulated VSMC remodeling at the computational level. External bulk data further showed coordinated enrichment of inflammatory and remodeling signatures in advanced plaques. These findings provide a descriptive and hypothesis-generating transcriptomic framework for understanding inflammatory macrophage activation and VSMC remodeling in human atherosclerosis.

atherosclerosis↗
PubMed2026

Transcriptomic insights into the coordinated regulation of signaling, apoptosis, immunity, and metabolism during Sinonovacula constricta larval metamorphosis.

Metamorphosis is a critical ontogenetic transition for marine bivalves, marking the shift from planktonic to benthic lifestyles, where successful transformation dictates survival. The razor clam Sinonovacula constricta is economically important; however, low larval metamorphosis rates remain a major bottleneck in seedling production. To elucidate the mechanisms governing this process, we performed a comparative transcriptome analysis of S. constricta larvae at pre- and post-metamorphosis stages using Illumina sequencing. A total of 3701 differentially expressed genes (DEGs) were identified, including 3254 up-regulated and 447 down-regulated genes. Functional annotation of the respective top 20 significantly up-regulated and down-regulated DEGs indicated their potential pivotal roles in signal transduction (e.g., up-regulated: CAV1, CHRNA2; down-regulated: APP, NOTCH1), cellular proliferation and differentiation (e.g., up-regulated: TUBA, EGF1; down-regulated: KIF23, TTC25), transcriptional and epigenetic regulation (e.g., up-regulated: NFIL3; down-regulated: OVO, HMX1), substance transport (e.g., up-regulated: LRP2, LRP1B; down-regulated: SLC51A, Slc33a1), substance metabolism (e.g., up-regulated: CPK3, CYP26A1; down-regulated: RDMT1, ADAC), immunomodulation (e.g., up-regulated: CPN2, CRISP2), and protein homeostasis (e.g., up-regulated: HSP27, NAS-27). Functional enrichment analysis further revealed that DEGs were significantly enriched in pathways related to signal transduction and developmental regulation (e.g., Ras, TNF), cell death and homeostasis (e.g., apoptosis), immune responses (e.g., Toll-like receptor), energy metabolism (e.g., lipid), cardiovascular related (e.g., Fluid shear stress), cell junction and architecture (e.g., Tight junction), and infectious disease (e.g., measles). These results suggest a synergistic interplay between signaling, apoptosis, immunity, and metabolism during S. constricta metamorphosis. This study advances our understanding of marine bivalve metamorphosis and offers candidate genes for further mechanistic studies.

Animals↗
PubMed2003

Helicobacter pylori infection: pathogenesis.

This review covers progress in identifying Helicobacter pylori-derived factors that are involved in survival and virulence of the organism and in elucidating host response pathways that can limit the infection but are also susceptible to dysregulation. Recent work has identified genes of the cytotoxin-associated gene (cag) pathogenicity island (PAI) involved in regulating signaling, interleukin-8 secretion, and phenotypic events in epithelial cells. New roles in pathogenesis have been recognized for vacuolating toxin A (VacA) and urease, H. pylori membrane and secreted factors, and host epithelial surface molecules. Molecular pathways involved in H. pylori-induced apoptosis in epithelial cells, T cells, and macrophages are being dissected. Activation of toll-like receptors and bacterial factors involved in nitric oxide (NO) and reactive oxygen species induction were also described. The ability of H. pylori to limit NO production by several mechanisms may be an important part of its ability to evade the host immune response.

Journal Article↗
PubMed2005

Dissemination of Toxoplasma gondii to immunoprivileged organs and role of Toll/interleukin-1 receptor signalling for host resistance assessed by in vivo bioluminescence imaging.

Toxoplasma gondii infection can lead to life-threatening systemic disease in the immunocompromised individual and in the developing fetus. Despite intensive investigation in animal models of toxoplasmosis, the processes leading to systemic dissemination remain poorly characterized. In the present study, in vivo bioluminescence imaging (BLI) was applied to the Toxoplasma mouse model to study the dynamics of infection in real time. Photon emission analyses revealed rapid dissemination of parasites in the organism and dissemination to immunoprivileged organs (brain, eyes and testes). Spatio-temporal analysis by BLI in individual mice showed that the virulent RH strain (type I) and the non-virulent ME49/PTG strain (type II) disseminate widely, but the virulent RH strain (type I) exhibits a more dramatic expansion of parasite biomass. Assessment by BLI of the Toll/interleukin-1 receptor (TIR) signalling pathway in host resistance to T. gondii revealed that signal transduction to the adaptor protein MyD88 is probably mediated by Toll-like receptor(s) rather than by IL-1R or IL-18R signalling. However, TLR1(-/-), TLR2(-/-), TLR4(-/-), TLR6(-/-) and TLR9(-/-) animals did not exhibit increased susceptibility to infection. These results suggest that intricate mechanisms regulate TIR-mediated responses during Toxoplasma infection.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Microbial recognition by Toll-like receptors.

Toll-like receptors (TLRs) sense invasion of microorganisms by detecting microbial components that are conserved among pathogens. Recognition of microbial components by TLRs triggers activation of the innate immune system. Signaling pathways via TLRs originate from conserved cytoplasmic Toll/IL-1 receptor (TIR) domains. Recent accumulating evidence demonstrates that TIR domain-containing adaptors, such as MyD88, TIRAP/Mal, TRIF, and TRAM, regulate TLR-mediated signaling pathways. MyD88 is common to all TLR-mediated pathways, which lead to the production of inflammatory cytokines, whereas TRIF mediates induction of IFN-beta in TLR3 and TLR4 signaling pathways. TIRAP/Mal is implicated in the TLR2- and TLR4-mediated MyD88-dependent signaling pathway. TRAM is specifically involved in the TLR4-mediated TRIF-dependent pathway. Thus, TIR domain-containing adaptors play a pivotal role in TLR signaling pathways, which culminate in pathogen-specific immune responses.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Toll receptors and pathogen resistance.

Toll receptors in insects, mammals and plants are key players that sense the invasion of pathogens. Toll-like receptors (TLRs) in mammals have been established to detect specific components of bacterial and fungal pathogens. Furthermore, recent evidence indicates that TLRs are involved in the recognition of viral invasion. Signalling pathways via TLRs originate from the conserved Toll/IL-1 receptor (TIR) domain. The TIR domain-containing MyD88 acts as a common adaptor that induces inflammatory cytokines; however, there exists a MyD88-independent pathway that induces type I IFNs in TLR4 and TLR3 signalling. Another TIR domain-containing adaptor, TIRAP/Mal has recently been shown to mediate the MyD88-dependent activation in the TLR4 and TLR2 signalling pathway. Thus, individual TLRs may have their own signalling systems that characterize their specific activities.

Animals↗