Inflammasomes are signaling hubs that activate inflammatory caspases to drive cytokine maturation and cell lysis. Inflammasome activation by Salmonella Typhimurium infection or Salmonella-derived molecules is extensively studied in murine myeloid cells. Salmonella-induced inflammasome signaling in human innate immune cells, is however, poorly characterized. Here, we show that Salmonella mutation to inactivate the Salmonella pathogenicity island-2 type III secretion system (SPI2 T3SS) potentiates S. Typhimurium-induced inflammasome responses from primary human macrophages, resulting in strong IL-1β production and macrophage death. Inactivation of the SPI1 T3SS diminished human macrophage responses to WT and ΔSPI2 Salmonella. Salmonella ΔSPI2 elicited a mixed inflammasome response from human myeloid cells, in which NLR family CARD-domain containing protein 4 (NLRC4) and NLR family PYRIN-domain containing protein 3 (NLRP3) perform somewhat redundant functions in generating IL-1β and inducing pyroptosis. Our data suggest that Salmonella employs the SPI2 T3SS to subvert SPI1-induced NLRP3 and NLRC4 inflammasome responses in human primary macrophages, in a species-specific immune evasion mechanism.
Bibliographical note©2018 Society for Leukocyte Biology.
- CARD Signaling Adaptor Proteins/metabolism
- Calcium-Binding Proteins/metabolism
- Cell Death
- Genomic Islands
- Mice, Inbred C57BL
- Myeloid Cells/metabolism
- NLR Family, Pyrin Domain-Containing 3 Protein/metabolism
- Salmonella typhimurium/genetics