Project description:This logical set encompases several 8hr timecourses (0,1,2,4,8 hrs) and their replicates. All correspond to treatments of bone marrow derived macrophages. Abstract: Innate and adaptive immunity depends critically on host recognition of pathogen-associated molecules. Toll-like receptors (TLRs) are key mediators of pathogen surveillance at the cell or phagocytic vacuole surface. However, mechanisms underlying recognition of pathogens in other cellular compartments remain unclear, and responses elicited by cytosolic challenge are poorly characterized. We therefore used mouse cDNA microarrays to investigate gene expression triggered by infection of bone marrow-derived macrophages with cytosol- and vacuole-localized Listeria monocytogenes (Lm), a model cytosolic pathogen. The resulting gene expression program included two basic categories of induced genes: an "early/persistent" cluster consistent with NF-kappaB-dependent responses downstream of TLRs, and a subsequent "late response" cluster largely composed of IFN-responsive genes (IRGs). The early/persistent cluster was observed upon infection with WT, heat-killed, or mutant Lm lacking listeriolysin O, the pore-forming hemolysin that promotes escape from phagocytic vacuoles. However, the IRG cluster depended on entry of WT Lm into the cytosol. Infection with listeriolysin O-expressing, cytosolic Bacillus subtilis (Bs) strikingly recapitulated the expression profile associated with WT Lm, including IRG induction. IRG up-regulation was associated with MyD88-independent induction of IFN-beta transcription and activity. Whereas Staphylococcus aureus (Sa) lipoteichoic acid treatment confirmed that many late-response genes could also be stimulated through TLRs, our study identified a cytosol-specific transcriptional program independent of TLR signaling through MyD88. Further characterization of cytosolic surveillance pathway(s) and their points of convergence with TLR- and IFN-dependent pathways will enhance our understanding of the means by which mammals detect and respond to pathogens. Set of arrays organized by shared biological context, such as organism, tumors types, processes, etc. Computed

Project description:The intracellular bacterial pathogen Legionella pneumophila causes an inflammatory pneumonia called Legionnaires’ Disease. For virulence, L. pneumophila requires a Dot/Icm type IV secretion system that translocates bacterial effectors to the host cytosol. L. pneumophila lacking the Dot/Icm system is recognized by Toll-like receptors (TLRs), leading to a canonical NF-κB-dependent transcriptional response. In addition, L. pneumophila expressing a functional Dot/Icm system potently induces unique transcriptional targets, including proinflammatory genes such as Il23a and Csf2. Here we demonstrate that this Dot/Icm-dependent response, which we term the effector-triggered response (ETR), requires five translocated bacterial effectors that inhibit host protein synthesis. Upon infection of macrophages with virulent L. pneumophila, these five effectors caused a global decrease in host translation, thereby preventing synthesis of IκB, an inhibitor of the NF-κB transcription factor. Thus, macrophages infected with wildtype L. pneumophila exhibited prolonged activation of NF-κB, which was associated with transcription of ETR target genes such as Il23a and Csf2. L. pneumophila mutants lacking the five effectors still activated TLRs and NF-κB, but because the mutants permitted normal IκB synthesis, NF-κB activation was more transient and was not sufficient to fully induce the ETR. L. pneumophila mutants expressing enzymatically inactive effectors were also unable to fully induce the ETR, whereas multiple compounds or bacterial toxins that inhibit host protein synthesis via distinct mechanisms recapitulated the ETR when administered with TLR ligands. Previous studies have demonstrated that the host response to bacterial infection is induced primarily by specific microbial molecules that activate TLRs or cytosolic pattern recognition receptors. Our results add to this model by providing a striking illustration of how the host immune response to a virulent pathogen can also be shaped by pathogen-encoded activities, such as inhibition of host protein synthesis. Three-condition experiment: macrophages left uninfected (negative control), or infected with wildtype Legionella pneumophila, or the mutant Δ5, which lacks five bacterial effectors involved in inhibition of host protein synthesis (lgt1, lgt2, lgt3, sidI, sidL) (two experimental conditions). Biological replicates: two, independently infected, harvested, and hybridized to arrays. One technical replicate per array.

Project description:The intracellular bacterial pathogen Legionella pneumophila causes an inflammatory pneumonia called Legionnaires’ Disease. For virulence, L. pneumophila requires a Dot/Icm type IV secretion system that translocates bacterial effectors to the host cytosol. L. pneumophila lacking the Dot/Icm system is recognized by Toll-like receptors (TLRs), leading to a canonical NF-κB-dependent transcriptional response. In addition, L. pneumophila expressing a functional Dot/Icm system potently induces unique transcriptional targets, including proinflammatory genes such as Il23a and Csf2. Here we demonstrate that this Dot/Icm-dependent response, which we term the effector-triggered response (ETR), requires five translocated bacterial effectors that inhibit host protein synthesis. Upon infection of macrophages with virulent L. pneumophila, these five effectors caused a global decrease in host translation, thereby preventing synthesis of IκB, an inhibitor of the NF-κB transcription factor. Thus, macrophages infected with wildtype L. pneumophila exhibited prolonged activation of NF-κB, which was associated with transcription of ETR target genes such as Il23a and Csf2. L. pneumophila mutants lacking the five effectors still activated TLRs and NF-κB, but because the mutants permitted normal IκB synthesis, NF-κB activation was more transient and was not sufficient to fully induce the ETR. L. pneumophila mutants expressing enzymatically inactive effectors were also unable to fully induce the ETR, whereas multiple compounds or bacterial toxins that inhibit host protein synthesis via distinct mechanisms recapitulated the ETR when administered with TLR ligands. Previous studies have demonstrated that the host response to bacterial infection is induced primarily by specific microbial molecules that activate TLRs or cytosolic pattern recognition receptors. Our results add to this model by providing a striking illustration of how the host immune response to a virulent pathogen can also be shaped by pathogen-encoded activities, such as inhibition of host protein synthesis. Four-condition experiment: macrophages left uninfected (negative control), or infected with wildtype Legionella pneumophila, the flagellin-deficient mutant ΔflaA, or the secretion-deficient mutant ΔdotA (three experimental conditions). Biological replicates: two, independently infected, harvested, and hybridized to arrays. One to two technical replicates per array, as indicated in file titles.

Project description:The intracellular bacterial pathogen Legionella pneumophila causes an inflammatory pneumonia called Legionnaires’ Disease. For virulence, L. pneumophila requires a Dot/Icm type IV secretion system that translocates bacterial effectors to the host cytosol. L. pneumophila lacking the Dot/Icm system is recognized by Toll-like receptors (TLRs), leading to a canonical NF-κB-dependent transcriptional response. In addition, L. pneumophila expressing a functional Dot/Icm system potently induces unique transcriptional targets, including proinflammatory genes such as Il23a and Csf2. Here we demonstrate that this Dot/Icm-dependent response, which we term the effector-triggered response (ETR), requires five translocated bacterial effectors that inhibit host protein synthesis. Upon infection of macrophages with virulent L. pneumophila, these five effectors caused a global decrease in host translation, thereby preventing synthesis of IκB, an inhibitor of the NF-κB transcription factor. Thus, macrophages infected with wildtype L. pneumophila exhibited prolonged activation of NF-κB, which was associated with transcription of ETR target genes such as Il23a and Csf2. L. pneumophila mutants lacking the five effectors still activated TLRs and NF-κB, but because the mutants permitted normal IκB synthesis, NF-κB activation was more transient and was not sufficient to fully induce the ETR. L. pneumophila mutants expressing enzymatically inactive effectors were also unable to fully induce the ETR, whereas multiple compounds or bacterial toxins that inhibit host protein synthesis via distinct mechanisms recapitulated the ETR when administered with TLR ligands. Previous studies have demonstrated that the host response to bacterial infection is induced primarily by specific microbial molecules that activate TLRs or cytosolic pattern recognition receptors. Our results add to this model by providing a striking illustration of how the host immune response to a virulent pathogen can also be shaped by pathogen-encoded activities, such as inhibition of host protein synthesis.

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Listeria host responses

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