rodentium stimulation . The different results may depend on the assay employed (microscopy versus immunoblot), the type of cells (primary versus immortalized macrophages) or the bacteria used. Further studies are needed to clarify whether ASC speck formation and oligomerization
are essential for noncanonical inflammasome signaling. While it is unclear how caspase-11 interacts with the inflammasome components to support IL-1β and IL-18 release, caspase-11 circumvents the requirement for NLRP3 for the production of IL-1α . Indeed, IL-1α selleck products release was suppressed in Casp11−/− or in double Casp1−/− Casp11−/− macrophages, but not in Nlrp3−/− or Asc−/− macrophages, upon noncanonical stimuli (CTB, E. coli) (Table 1).
As caspase-11 activation depends on the TRIF/IFNs pathway, similar to IL-1β, IL-1α release was severely impaired in Trif−/−, Irf3−/−, Ifnra1−/−, Stat1−/−, and Irf9−/− macrophages stimulated with EHEC or C. rodentium . However, IL-1α remains fully dependent on caspase-1 when canonical stimuli (ATP, C. difficile toxin B) are employed . Many of the studies discussed so far have relied upon in vitro experiments to elucidate the roles of inflammasome pathway molecules, but the real importance of these interactions becomes apparent in in vivo models of human disease. In a mouse model of acute septic shock induced by LPS, serum IL-1β and IL-18 levels were markedly reduced in Casp11−/−, double Casp1−/− Casp11−/− and Casp1−/− Casp11Tg animals click here . IL-1α serum levels were similarly low in mice lacking caspase-11 (Casp11−/−, double Casp1−/− Casp11−/−), but in contrast were unaffected in Casp1−/− Casp11Tg mice. These results confirm that both caspase-1 and caspase-11 are necessary for IL-1β/IL-18
release, whereas IL-1α production is fully dependent on caspase-11. Canonical activation of caspase-1 by NLRP3 and NLRC4 inflammasomes induces a form of programmed GPX6 cell death known as pyroptosis, a genetically regulated form of cell death that acts as an innate immune effector mechanism against intracellular bacteria . Therefore, attention turned to the potential role of the caspase-11-mediated noncanonical inflammasome activation pathway in this mechanism of cell death. Early studies showed that caspase-11 was upregulated during cell death and that its overexpression per se induced cell death [5, 7]. Consequently, cell survival was markedly increased in spleens from Casp11−/− mice injected with LPS compared with wild-type controls . Caspase-11 directly controls the activation of the effector caspases 3 and 7 of the apoptotic pathway independent of caspase-1 . Recently it was shown that caspase-11, but not caspase-1, NLRC4 or ASC, was responsible for cell lethality in macrophages following application of noncanonical stimuli (Table 1) [3, 10, 20].