A type VI secretion system in species and triggers distinct macrophage death pathways independent of the pyrin inflammasome.

The complex contains opportunistic pathogens that cause chronic infections and inflammation in the lungs of people with cystic fibrosis. Two closely related species within this complex are and the recently classified and encode a type VI secretion system and the effector TecA, which is detected by the pyrin/caspase-1 inflammasome, and triggers macrophage inflammatory death. We previously showed that the pyrin inflammasome was dispensable for lung inflammation in mice infected with AU1054 indicating this species activates an alternative pathway of macrophage inflammatory death. Notably, strains J2315 and K56-2 can damage macrophage phagosomes, and K56-2 triggers activation of the caspase-11 inflammasome, which detects cytosolic lipopolysaccharide. Here, we investigated inflammatory cell death in pyrin- () or caspase-1/caspase-11- () deficient mouse macrophages infected with J2315 or K56-2 or AU1054 or PC184. Macrophage inflammatory death was measured by cleavage of gasdermin D protein, the release of cytokines IL-1α and IL-1β, and plasma membrane rupture. We found that J2315 and K56-2 are detected by the caspase-11 inflammasome in macrophages, resulting in IL-1β release. By contrast, inflammasome activation was not detected in macrophages infected with AU1054 or PC184. Instead, AU1054 triggered an alternative macrophage inflammatory death pathway that required TecA and resulted in plasma membrane rupture and IL-1α release. Structural modeling of TecA orthologs in and suggested that amino acid changes in the latter may underlie its ability to trigger a non-inflammasome macrophage death pathway.