IFN receptor signaling induces cell-autonomous immunity to infections with intracellular bacterial pathogens. Here, we demonstrate that IFN-inducible guanylate binding protein (Gbp) proteins stimulate caspase-11-dependent, cell-autonomous immunity in response to cytoplasmic LPS. Caspase-11-dependent pyroptosis is triggered in IFN-activated macrophages infected with the Gram-negative bacterial pathogen Legionella pneumophila. The rapid induction of pyroptosis in IFN-activated macrophages required a cluster of IFN-inducible Gbp proteins encoded on mouse chromosome 3 (Gbp(chr3)). Induction of pyroptosis in naive macrophages by infections with the cytosol-invading ΔsdhA L. pneumophila mutant was similarly dependent on Gbp(chr3), suggesting that these Gbp proteins play a role in the detection of bacteria accessing the cytosol. Cytoplasmic LPS derived from Salmonella ssp. or Escherichia coli has recently been shown to trigger caspase-11 activation and pyroptosis, but the cytoplasmic sensor for LPS and components of the caspase-11 inflammasome are not yet defined. We found that the induction of caspase-11-dependent pyroptosis by cytoplasmic L. pneumophila-derived LPS required Gbp(chr3) proteins. Similarly, pyroptosis induced by cytoplasmic LPS isolated from Salmonella was diminished in Gbp(chr3)-deficient macrophages. These data suggest a role for Gbp(chr3) proteins in the detection of cytoplasmic LPS and the activation of the noncanonical inflammasome.
Keywords: Nos2; cell death; immunity-related GTPases; interferon.