Caspase-1 Activation of IL-1β and IL-18 Are Essential for Shigella flexneri–Induced Inflammation

Caspases are intracellular proteases that mediate mammalian cell apoptosis. Caspase-1 (Casp-1) is a unique caspase because it activates the proinflammatory cytokines interleukin (IL)-1β and IL-18. Shigella flexneri, the etiological agent of bacillary dysentery, induces macrophage apoptosis, which requires Casp-1 and results in the release of mature IL-1β and IL-18. Here we show that casp-1−/− mice infected with S. flexneri do not develop the acute inflammation characteristic of shigellosis and are unable to resolve the bacterial infection. Using casp-1−/− mice supplemented with recombinant cytokines and experiments with IL-1β−/− and IL-18−/− mice, we show that IL-1β and IL-18 are both required to mediate inflammation in S. flexneri infections. Together, these data demonstrate the importance of Casp-1 in acute inflammation and show the different roles of its substrates, IL-1β and IL-18, in this response.