Explore the vast range of titles available.

Infection with Burkholderia pseudomallei or B. thailandensis triggers activation of the NLRP3 and NLRC4 inflammasomes leading to release of IL-1β and IL-18 and death of infected macrophages by pyroptosis, respectively. The non-canonical inflammasome composed of caspase-11 is also activated by these bacteria and provides protection through induction of pyroptosis. The recent generation of bona fide caspase-1-deficient mice allowed us to reexamine in a mouse model of pneumonic melioidosis the role of caspase-1 independently of caspase-11 (that was also absent in previously generated Casp1-/- mice). Mice lacking either caspase-1 or caspase-11 were significantly more susceptible than wild type mice to intranasal infection with B. thailandensis. Absence of caspase-1 completely abolished production of IL-1β and IL-18 as well as pyroptosis of infected macrophages. In contrast, in mice lacking caspase-11 IL-1β and IL-18 were produced at normal level and macrophages pyroptosis was only marginally affected. Adoptive transfer of bone marrow indicated that caspase-11 exerted its protective action both in myeloid cells and in radio-resistant cell types. B. thailandensis was shown to readily infect mouse lung epithelial cells triggering pyroptosis in a caspase-11-dependent way in vitro and in vivo. Importantly, we show that lung epithelial cells do not express inflammasomes components or caspase-1 suggesting that this cell type relies exclusively on caspase-11 for undergoing cell death in response to bacterial infection. Finally, we show that IL-18's protective action in melioidosis was completely dependent on its ability to induce IFNγ production. In turn, protection conferred by IFNγ against melioidosis was dependent on generation of ROS through the NADPH oxidase but independent of induction of caspase-11. Altogether, our results identify two non-redundant protective roles for caspase-1 and caspase-11 in melioidosis: Caspase-1 primarily controls pyroptosis of infected macrophages and production of IL-18. In contrast, caspase-11 mediates pyroptosis of infected lung epithelial cells.

Pyroptosis, a lytic form of programmed cell death dependent on cleavage of gasdermin-D by inflammatory caspase-1 and caspase-11 following inflammasome activation, is known to be protective against intracellular infection by a number of pathogens. The intracellular, Gram-negative bacterium Burkholderia pseudomallei causes the disease melioidosis. B. pseudomallei and the closely related B. thailandensis, which is used to model melioidosis in mice, triggers the canonical NLRC4, NLRP3, and non-canonical caspase-11 inflammasomes, resulting in secretion of IL-1β and IL-18, and pyroptosis of infected cells. Mice deficient in inflammasome components, inflammatory caspases, or IL-18 are highly susceptible to melioidosis. Previously, while investigating the roles of inflammatory caspases in a mouse model of pneumonic melioidosis, our laboratory found that caspase-1 is crucial for induction of pyroptosis in macrophages and dendritic cells. Utilizing in situ lung staining, our laboratory demonstrated that caspase-11 is the primary mediator of pyroptosis in cells of the lung epithelium but not macrophages. Here, we further examined the role of gasdermin-D in pneumonic melioidosis. Our results show that gasdermin-D-deficient (Gsdmd-/-) mice, which are incapable of inducing pyroptosis downstream of inflammatory caspase activity, have increased susceptibility to B. thailandensis compared to wild-type mice. Although it has been shown that in vitro IL-1β secretion by macrophages and dendritic cells depends on gasdermin-D, our results indicate that neutrophils are likely the major cell population contributing to gasdermin-D-independent IL-1β secretion during B. thailandensis infection. While we observed comparable IL-1β secretion between Gsdmd-/- mice and wild-type mice, IL-18 was significantly decreased in Gsdmd-/- mice. Although IL-18 protection is mediated primarily through induction of IFNγ production, we observed no reduction of IFNγ in Gsdmd-/- mice, suggesting that gasdermin-D mediates protection against melioidosis primarily through a mechanism independent of protective IFNγ. Based on previous evidence that active gasdermin-D can target and damage the bacterial cell membrane, we investigated the capacity of gasdermin-D to lyse B. thailandensis bacteria directly. We found that B. thailandensis bacteria had significantly decreased viability following in vitro exposure to the lytic N-terminal fragment of recombinant gasdermin-D. Moreover, bacteria harvested from infected wild-type macrophages experienced decreased viability when exposed to hydrogen peroxide or human β-defensin-3 while bacteria from infected Gsdmd-/- macrophages were not sensitive to treatment with these agents. In summary, we found that gasdermin-D plays a protective role by damaging bacterial cell membranes and mediating host cell pyroptosis and that neutrophils are a major source of IL-1β in Gsdmd-/- mice during pneumonic melioidosis.