Salmonella pathogenicity island 2-dependent macrophage death is mediated in part by the host cysteine protease caspase-1.
Salmonella typhimurium invades host macrophages and can either induce a rapid cell death or establish an intracellular niche within the phagocytic vacuole. Rapid cell death requires the Salmonella pathogenicity island (SPI)1 and the host protein caspase-1, a member of the pro-apoptotic caspase family of proteases. Salmonella that do not cause this rapid cell death and instead reside in the phagocytic vacuole can trigger macrophage death at a later time point. We show here that the human pathogen Salmonella typhi also triggers both rapid, caspase-1-dependent and delayed cell death in human monocytes. The delayed cell death has previously been shown with S. typhimurium to be dependent on SPI2-encoded genes and ompR. Using caspase-1(-/-) bone marrow-derived macrophages and isogenic S. typhimurium mutant strains, we show that a large portion of the delayed, SPI2-dependent death is mediated by caspase-1. The two known substrates of activated caspase-1 are the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and IL-18, which are cleaved to produce bioactive cytokines. We show here that IL-1beta is released during both SPI1- and SPI2-dependent macrophage killing. Using IL-1beta(-/-) bone marrow-derived macrophages and a neutralizing anti-IL-18 antibody, we show that neither IL-1beta nor IL-18 is required for rapid or delayed macrophage death. Thus, both rapid, SPI1-mediated killing and delayed, SPI2-mediated killing require caspase-1 and result in the secretion of IL-1beta, which promotes inflammation and may facilitate the spread of Salmonella beyond the gastrointestinal tract in systemic disease.
Monack
D M
DM
Department of Microbiology and Immunology, Stanford University School of Medicine, 299 Campus Drive, Stanford, CA 94305, USA. dmonack@stanford.edu
Detweiler
C S
CS
Falkow
S
S
D000818:Animals; D017209:Apoptosis; D001426:Bacterial Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D007375:Interleukin-1 / Q000096:biosynthesis / Q000378:metabolism; D020382:Interleukin-18 / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000276:immunology / Q000382:microbiology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012485:Salmonella typhi / Q000378:metabolism / Q000472:pathogenicity*; D012486:Salmonella typhimurium / Q000378:metabolism / Q000472:pathogenicity*; D013997:Time Factors; D020298:U937 Cells
D001426:Bacterial Proteins; D007375:Interleukin-1; D020382:Interleukin-18; D008565:Membrane Proteins; C440638:SPI-2 protein, Salmonella; C419942:Spi1 protein, Salmonella; D020170:Caspase 1