Pseudomonas aeruginosa pilin activates the inflammasome

Area of Science:

• Microbiology
• Immunology
• Molecular Biology

Background:

• Interleukin-1β (IL-1β) production relies on caspase-1 activation by inflammasomes.
• Flagellin from bacteria like Pseudomonas aeruginosa is a known inflammasome activator via NLRC4.
• Some P. aeruginosa strains lacking flagellin still induce inflammasome activation.

Purpose of the Study:

• To identify non-flagellin components of P. aeruginosa responsible for inflammasome activation.
• To investigate the role of bacterial pilin in triggering immune responses.

Main Methods:

• Mass spectrometry to identify inflammasome-activating factors in P. aeruginosa.
• Liposomal delivery of purified pilin to mouse macrophages.
• Infection of macrophages with wild-type and mutant P. aeruginosa strains.
• Assessment of caspase-1 activation and IL-1β secretion.

Main Results:

• Pilin, the major component of type IV pili, was identified as an inflammasome-activating factor.
• Purified pilin activated caspase-1 and induced IL-1β secretion in macrophages.
• Inflammasome activation by pilin was caspase-1 dependent but independent of NLRC4, NLRP3, and ASC.
• P. aeruginosa mutants lacking pilin failed to activate the inflammasome.

Conclusions:

• Pilin is a novel activator of the inflammasome, distinct from flagellin.
• Bacterial pilin contributes to inflammasome activation and subsequent IL-1β secretion.
• This discovery expands the repertoire of bacterial triggers for innate immune pathways.