Flagellar Motility Is a Key Determinant of the Magnitude of the Inflammasome Response to Pseudomonas aeruginosa

Abstract

eWe previously demonstrated that bacterial flagellar motility is a fundamental mechanism by which host phagocytes bind and ingest bacteria. Correspondingly, loss of bacterial motility, consistently observed in clinical isolates from chronic Pseudomonas aeruginosa infections, enables bacteria to evade association and ingestion of P. aeruginosa by phagocytes both in vitro and in vivo. Since bacterial interactions with the phagocyte cell surface are required for type three secretion system-dependent NLRC4 inflammasome activation by P. aeruginosa, we hypothesized that reduced bacterial association with phagocytes due to loss of bacterial motility, independent of flagellar expression, will lead to reduced inflammasome activation. Here we report that inflammasome activation is reduced in response to nonmotile P. aeruginosa. Nonmotile P. aeruginosa elicits reduced IL-1␤ production as well as caspase-1 activation by peritoneal macrophages and bone marrow-derived dendritic cells in vitro. Importantly, nonmotile P. aeruginosa also elicits reduced IL-1␤ levels in vivo in comparison to those elicited by wild-type P. aeruginosa. This is the first demonstration that loss of bacterial motility results in reduced inflammasome activation and antibacterial IL-1␤ host response. These results provide a critical insight into how the innate immune system responds to bacterial motility and, correspondingly, how pathogens have evolved mechanisms to evade the innate immune system.

Differential ASC requirements reveal a key role for neutrophils and a noncanonical IL-1β response toPseudomonas aeruginosa

“…G. O'Toole and D. Hogan (Dartmouth Medical School, Hanover, NH). The popB mutant has been previously described (35).…”

“…This leads to pro-IL-1␤ processing and release as mature IL-1␤. Loss of a functional bacterial T3SS or any of the NLRC4 inflammasome components, namely NLRC4, caspase-1, and ASC, leads to a deficit in IL-1␤ production by macrophages in response to P. aeruginosa (16,28,35,43).…”

“…Since loss of ASC leads to a deficit in IL-1␤ release from macrophages in vitro (5,6,16,35,43), we hypothesized that ASC Ϫ/Ϫ mice would exhibit reduced IL-1␤ production and inflammation-driven pathology in vivo, resulting in reduced mortality. Here we report that loss of ASC expression in vivo does not phenocopy the effects previously derived in vitro with macrophages.…”

Clinical Isolates of Pseudomonas aeruginosa from Chronically Infected Cystic Fibrosis Patients Fail To Activate the Inflammasome during Both Stable Infection and Pulmonary Exacerbation

“…2). Flagellar motility is important for inflammasome activation independently of the flagellin protein, and pilin may also activate the inflammasome in P. aeruginosa (33,34). To analyze the motility phenotypes of the chronic, acute, and environmental isolates in our study, we performed swimming (flagellar-based) and twitching (pili-based) motility assays.…”

Pseudomonas aeruginosaflagellar motility activates the phagocyte PI3K/Akt pathway to induce phagocytic engulfment

“…Multiple reports have demonstrated that flagellar function is a critical virulence factor for the establishment, persistence, and inflammatory profile of P. aeruginosa infection (1,2,19,28). P. aeruginosa swims via a single, polar, monotrichous flagellum, which it rotates by proton motive force (33).…”