Oral Presentation Lorne Infection and Immunity 2018

Salmonella Typhimurium employs SPI2 virulence factors to evade inflammasome activation in human macrophages (#14)

Damien Bierschenk 1 , Mercedes Monteleone 1 , Paul Baker 2 3 , Fiona Moghaddas 2 3 , Seth Masters 2 3 , Dave Boucher 1 , Kate Schroder 1
  1. Institute for Molecular Bioscience, and IMB Centre for Inflammation and Disease Research, The University of Queensland, Brisbane, Queensland, Australia
  2. Inflammation Division, The Walter and Eliza Hall Institute of Medical Research, The University of Melbourne, Parkville, Victoria, Australia
  3. Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia

Salmonella activates various host pro-inflammatory cascades to limit and resolve infection. One such cascade is mediated by inflammasomes, large cytosolic complexes that activate inflammatory caspases (-1/-11 in mouse, -1/-4/-5 in human). Inflammasome activation drives a form of lytic cell death, pyroptosis, and cytokine maturation. Salmonella-induced inflammasome activation has been extensively studied in murine innate immune cells, however inflammasome signalling in human innate immune cells is poorly characterised. Here we show that Salmonella Typhimurium-infected human primary macrophages induce a weak pyroptotic response, unlike the robust pyroptotic response observed in Salmonella-infected murine primary macrophages. In contrast, Salmonella infection induces a potent cytokine maturation response in both murine and human macrophages. We found that S. Typhimurium utilises virulence effectors encoded on the Salmonella pathogenicity island-2 (SPI2) to limit pyroptosis in human macrophages. Mutation of Salmonella SPI2 virulence factors induce increased pyroptosis, cytokine maturation and caspase activation in Salmonella-infected human macrophages. We found, using CRISPR/Cas9 gene editing of THP-1 monocytic cells, that caspase-1 and caspase-4 drive SPI2 mutant-induced pyroptosis and cytokine maturation. These responses occur independently of the NLRP3 inflammasome, while the inflammasome adaptor protein ASC is required for cytokine maturation but not pyroptosis. Together our data suggests that Salmonella Typhimurium employs injection of SPI2 virulence factors in to the host cell cytosol as a species-specific inflammasome evasion mechanism.