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      Cytoplasmic flagellin activates caspase-1 and secretion of interleukin 1beta via Ipaf.

      Nature immunology

      Animals, Apoptosis Regulatory Proteins, genetics, physiology, Bacterial Proteins, immunology, Calcium-Binding Proteins, Caspase 1, metabolism, Cytoplasm, microbiology, Enzyme Activation, Flagellin, Interleukin-1, Macrophages, enzymology, Mice, Mice, Mutant Strains, Mutation, Protein Transport, Salmonella Infections, Salmonella typhimurium, pathogenicity, Toll-Like Receptor 5

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          Abstract

          Macrophages respond to Salmonella typhimurium infection via Ipaf, a NACHT-leucine-rich repeat family member that activates caspase-1 and secretion of interleukin 1beta. However, the specific microbial salmonella-derived agonist responsible for activating Ipaf is unknown. We show here that cytosolic bacterial flagellin activated caspase-1 through Ipaf but was independent of Toll-like receptor 5, a known flagellin sensor. Stimulation of the Ipaf pathway in macrophages after infection required a functional salmonella pathogenicity island 1 type III secretion system but not the flagellar type III secretion system; furthermore, Ipaf activation could be recapitulated by the introduction of purified flagellin directly into the cytoplasm. These observations raise the possibility that the salmonella pathogenicity island 1 type III secretion system cannot completely exclude 'promiscuous' secretion of flagellin and that the host capitalizes on this 'error' by activating a potent host-defense pathway.

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          Author and article information

          Journal
          16648853
          10.1038/ni1344

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