Listeria monocytogenes engineered to activate the Nlrc4 inflammasome are severely attenuated and are poor inducers of protective immunity

Abstract

Inflammasomes are intracellular multiprotein signaling complexes that activate Caspase-1, leading to the cleavage and secretion of IL-1β and IL-18, and ultimately host cell death. Inflammasome activation is a common cellular response to infection; however, the consequences of inflammasome activation during acute infection and in the development of long-term protective immunity is not well understood. To investigate the role of the inflammasome in vivo, we engineered a strain of Listeria monocytogenes that ectopically expresses Legionella pneumophila flagellin, a potent activator of the Nlrc4 inflammasome. Compared with wild-type L. monocytogenes , strains that ectopically secreted flagellin induced robust host cell death and IL-1β secretion. These strains were highly attenuated both in bone marrow-derived macrophages and in vivo compared with wild-type L. monocytogenes . Attenuation in vivo was dependent on Nlrc4, but independent of IL-1β/IL-18 or neutrophil activity. L. monocytogenes strains that activated the inflammasome generated significantly less protective immunity, a phenotype that correlated with decreased induction of antigen-specific T cells. Our data suggest that avoidance of inflammasome activation is a critical virulence strategy for intracellular pathogens, and that activation of the inflammasome leads to decreased long-term protective immunity and diminished T-cell responses.

The adaptor ASC exacerbates lethal Listeria monocytogenes infection by mediating IL‐18 production in an inflammasome‐dependent and ‐independent manner

“…Thus, findings of our present study extended the mechanistic understanding of the IL-18 function. The NLRC4 inflammasome has been shown to contribute to host defense against a L. monocytogenes strain engineered to secrete Legionella pneumophila flagellin, which strongly and rapidly induces inflammasome activation and host cell death in an NLRC4-dependent manner, while this inflammasome is dispensable for defense against its parental strain [21]. This suggests that hyperactivation of the inflammasome is deleterious to L. monocytogenes.…”

“…A protective role of caspase-1 in systemic L. monocytogenes infection has been demonstrated [20]. Moreover, a recent study has shown that a L. monocytogenes strain engineered to secrete Legionella flagellin, an NLRC4 agonist, strongly induces inflammasome activation and is severely attenuated in vivo in an NLRC4-dependent manner [21]. It has also been reported that the impact of IL-1R deficiency on resistance of mice to L. monocytogenes varies with the genetic background of the host and infection route.…”

LysPGS formation inListeria monocytogeneshas broad roles in maintaining membrane integrity beyond antimicrobial peptide resistance

“…While motility in the host is advantageous for navigation of the gastrointestinal tract and host-cell targeting, secretion of flagellin or the presence of a flagellum triggers the inflammasome and can result in subsequent clearance by the immune system. 30,31 In L. monocytogenes, flagellar motility is thermo-regulated by the action of an anti-repressor protein called GmaR, which is also an O-linked N-acetylglucosamine transferase responsible for posttranslational modification of flagellin with up to six molecules of β-O-GlcNAc. 32 GmaR becomes unstable at the non-permissive growth temperature (37 °C) and dissociates from the motility operon repressor, MogR, thus resulting in downregulation of motility.…”

Listeria monocytogenes-Induced Cell Death Inhibits the Generation of Cell-Mediated Immunity

“…Thus, we are able to study how preferential activation of cell death pathways in myeloid-derived antigen-presenting cells influences the development of immunity. To activate pyroptosis, we utilized a previously described strain of L. monocytogenes (Lm-pyro) that triggers the Nlrc4 inflammasome via the ectopic secretion of flagellin (34). Upon infection of wild-type bone marrow-derived macrophages (BMDMs) or granulocyte-macrophage colony-stimulating factor (GM-CSF)-stimulated cells (referred to as bone marrow-derived dendritic cells [BMDCs]), strain Lm-pyro triggered robust lytic host cell death as measured by lactate dehydrogenase (LDH) release (Fig.…”