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E11 Multiple inflammasomes direct innate immune responses against Salmonella
Extended abstracts of the lectures organ-specific inflammation. These studies show that the role of the IEC in regulating luminal microbiota and the responsiveness of IECs to environmental stimuli can determine the propensity of the intestines to develop dysregulated inflammation. These studies also support a model in which the genetically-endowed ability to manage ER stress and the highly related autophagy pathway are important factors in determining an host’s ability at the cellular level to appropriately respond to numerous ERstress inducing signals derived from environmental stimuli (e.g. dietary, microbial and inflammation per se). E10 Autophagy R. Xavier. Center for Computational and Integrative Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA Crohn’s disease (CD) and ulcerative colitis (UC) are debilitating, inflammatory diseases of the gastrointestinal tract, collectively known as the inflammatory bowel diseases (IBD). Among complex diseases, genetics has been particularly successful in the identification of genes for IBD, with recent efforts in genomewide association bringing the total number of genes confirmed as associated to more than 30. One of the most unexpected findings that has come from Crohn’s disease genome-wide association studies is that autophagy has an important role in disease pathogenesis. Autophagy involves the concerted action of cytoplasmic proteins that generate curved isolation membranes to envelop cytoplasm, cytoplasmic organelles and intracellular pathogens. Autophagy requires the action of two ubiquitin like conjugation (Atg5/12/16L1 and Atg8) systems. This relationship is supported by the finding that two genes involved in autophagic processes ATG16L1 and IRGM are significantly associated with disease. Among the associated genes, recent studies have demonstrated that ATG16L1 is essential for classic and microbe induced autophagy and this, along with association of variation at IRGM with CD, confirms that autophagy is a key process in CD susceptibility. We will review the functional implications of ATG16L1 and IRGM in murine models of colitis and human IBD. Autophagy has also been identified as a key process in host resistance to bacterial infection, as well as being exploited by some pathogens to generate their intracellular niche. So far, little is known of the steps by which pathogens manipulate the cell to evade, or establish themselves within, the autophagy pathway. However, given the established role for type III secretion in host pathogen interactions, we postulated that bacterial effectors secreted by such systems might have uncharacterized roles in modulating the mammalian autophagic machinery. We will present data on the effects of type III effectors upon basal autophagy, as well as a systems-level analysis of screen hits and the biological context in which the bacterial modulation of autophagy operates. E11 Multiple inflammasomes direct innate immune responses against Salmonella P. Broz, M. Lamkanfi, K. Newton, S. Mariathasan, V.M. Dixit, D.M. Monack. Department of Microbiology and Immunology, Stanford University Stanford School of Medicine, Stanford, CA, USA NOD-like receptors (NLRs) sense intracellular pathogens and endogenous danger signals in the cytosol. Activated NLR’s assemble a multiprotein complex called inflammasome that matures caspase-1, which triggers release of proinflammatory
9 cytokines IL-1b and IL-18. However, the NLRs involved in host defense against microbial pathogens remain poorly defined. Here we show that two inflammasome receptors, Nalp3 and Ipaf, are necessary to fully activate caspase-1 in response to an intracellular pathogen, Salmonella typhimurium. In addition, the assembly of a large cytoplasmic structure termed the pyroptosome, which mediated the majority of IL-1b processing, was dependent on Nalp3 and Ipaf. Unexpectedly, mice deficient for both Nalp3 and Ipaf were markedly more susceptible to S. typhimurium infection, demonstrating redundancy among inflammasome receptors during infection with an intracellular pathogen. Session 5
Innate immunity
E12 Role of innate immune signaling pathways in the development of colitis S. Nish, D. Schenten, N. Hoshi, R. Medzhitov. HHMI and Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA Inflammatory Bowel Diseases are characterized by disregulated immune responses in the intestine [1]. The mechanisms responsible for the induction of pathogenic T cell responses are still poorly defined, although the recent progress has highlighted the critical roles of commensal bacteria, innate immune system, myeloid cells (dendritic cells and macrophages), Th17 cells and regulatory T cells (Treg). These recent findings have brought up a new focus of investigation, including characterization of the key innate immune signaling pathways and their roles in the development of pathogenic T cell responses. In particular, analyses of Th17 responses in the intestine have elucidated both pathogenic and protective roles of cytokines produced by these cells in the development of colitis. Similarly, accumulating evidence indicates that different innate signaling pathways (for example, IL-23-driven, versus TGF-b and IL-6-driven) may have differential roles in the generation of pathogenic versus non-pathogenic, or protective Th17 responses [2]. Finally, development of commensaldependent colitis in IL-10 deficient mice was previously shown to be dependent on the TLR and IL-1R signaling adapter MyD88 [3]. The focus of this presentation will be on the role of innate immune signaling pathways in the initiation of pathogenic T cell responses in the intestine. Specifically, the role of IL-6 and TGF-b signaling in T cells in the generation of pathogenic Th1 and Th17 responses will be discussed. Our previous study indicated that IL-6 produced by dendritic cells upon stimulation with bacterial TLR ligands is necessary for activation of naïve T cells in the presence, but not in the absence of Treg cells. We have now extended these findings to demonstrate that IL-6 signaling in CD4 T cells is required for the systemic Th1 and Th17 responses. However, only Th1 but not Th17 response can be recovered by the depletion of Treg cells, consistent with the role of IL-6 in Th17 differentiation. The role of IL-6 signaling in T cells in the IL-10 / and naïve T cell transfer models of colitis will be discussed in the context of these findings. In addition, we have generated conditional knock-out of MyD88 and investigate the role of MyD88 in dendritic cells, macrophages and T cells in the development of colitis in various models (IL-10 / and naïve T cell transfer models). Recent studies have suggested an important role of Th17 responses in intestinal inflammation [2]. The current view on the role of Th17 responses in the development of colitis is complicated however, by the fact that Th17 produced cytokines (IL-17A, IL-17F and IL-22) do not appear to play a pathogenic
9 cytokines IL-1b and IL-18. However, the NLRs involved in host defense against microbial pathogens remain poorly defined. Here we show that two inflammasome receptors, Nalp3 and Ipaf, are necessary to fully activate caspase-1 in response to an intracellular pathogen, Salmonella typhimurium. In addition, the assembly of a large cytoplasmic structure termed the pyroptosome, which mediated the majority of IL-1b processing, was dependent on Nalp3 and Ipaf. Unexpectedly, mice deficient for both Nalp3 and Ipaf were markedly more susceptible to S. typhimurium infection, demonstrating redundancy among inflammasome receptors during infection with an intracellular pathogen. Session 5
Innate immunity
E12 Role of innate immune signaling pathways in the development of colitis S. Nish, D. Schenten, N. Hoshi, R. Medzhitov. HHMI and Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA Inflammatory Bowel Diseases are characterized by disregulated immune responses in the intestine [1]. The mechanisms responsible for the induction of pathogenic T cell responses are still poorly defined, although the recent progress has highlighted the critical roles of commensal bacteria, innate immune system, myeloid cells (dendritic cells and macrophages), Th17 cells and regulatory T cells (Treg). These recent findings have brought up a new focus of investigation, including characterization of the key innate immune signaling pathways and their roles in the development of pathogenic T cell responses. In particular, analyses of Th17 responses in the intestine have elucidated both pathogenic and protective roles of cytokines produced by these cells in the development of colitis. Similarly, accumulating evidence indicates that different innate signaling pathways (for example, IL-23-driven, versus TGF-b and IL-6-driven) may have differential roles in the generation of pathogenic versus non-pathogenic, or protective Th17 responses [2]. Finally, development of commensaldependent colitis in IL-10 deficient mice was previously shown to be dependent on the TLR and IL-1R signaling adapter MyD88 [3]. The focus of this presentation will be on the role of innate immune signaling pathways in the initiation of pathogenic T cell responses in the intestine. Specifically, the role of IL-6 and TGF-b signaling in T cells in the generation of pathogenic Th1 and Th17 responses will be discussed. Our previous study indicated that IL-6 produced by dendritic cells upon stimulation with bacterial TLR ligands is necessary for activation of naïve T cells in the presence, but not in the absence of Treg cells. We have now extended these findings to demonstrate that IL-6 signaling in CD4 T cells is required for the systemic Th1 and Th17 responses. However, only Th1 but not Th17 response can be recovered by the depletion of Treg cells, consistent with the role of IL-6 in Th17 differentiation. The role of IL-6 signaling in T cells in the IL-10 / and naïve T cell transfer models of colitis will be discussed in the context of these findings. In addition, we have generated conditional knock-out of MyD88 and investigate the role of MyD88 in dendritic cells, macrophages and T cells in the development of colitis in various models (IL-10 / and naïve T cell transfer models). Recent studies have suggested an important role of Th17 responses in intestinal inflammation [2]. The current view on the role of Th17 responses in the development of colitis is complicated however, by the fact that Th17 produced cytokines (IL-17A, IL-17F and IL-22) do not appear to play a pathogenic