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J Med Microbiol. 2018 Aug;67(8):1168-1180. doi: 10.1099/jmm.0.000782. Epub 2018 Jun 29.

ASC acts in a caspase-1-independent manner to worsen acute pneumonia caused by Pseudomonas aeruginosa.

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1​Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
†​Present address: Academy for Quality and Safety Improvement, Northwestern Medicine, Chicago, IL, USA.
2​Department of Medicine, Division of Infectious Diseases, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.



Pseudomonas aeruginosa expresses a type III secretion system (T3SS) that activates the host inflammasome-mediated immune response. We examined the role of inflammasome activation in severe infection outcomes.


We infected C57BL/6 (B6) mice lacking inflammasome components ASC or caspase-1/11 with a highly virulent strain of P. aeruginosa, PSE9, using a mouse model of pneumonia. We evaluated inflammasome activation in vitro by infecting bone marrow-derived macrophages (BMDMs) with PSE9 and measuring cell death and release of inflammasome-dependent cytokines IL-18 and IL-1β. A bioluminescent reporter assay was used to detect activity of caspase-1 and caspase-3/7 in BMDMs from B6 and ASC-deficient mice.Results/Key Findings. ASC-/- mice exhibited significantly improved survival relative to caspase-1/11-/- mice and B6 mice, demonstrating that ASC and caspase-1/11 play differential roles in P. aeruginosa infection. We found that ASC-/- BMDMs exhibited significantly reduced cell death relative to B6 BMDMs, while caspase-1/11-/- BMDMs were resistant to cell death. IL-18 and IL-1β were both detected from supernatants of infected B6 BMDMs, but cytokine release was abrogated in both ASC-/- and caspase-1/11-/- BMDMs. We detected a 2.5-fold increase in the activation of caspase-3/7 in PSE9-infected B6 BMDMs, but no increase in infected ASC-/- BMDMs. Cell death, cytokine release and caspase-3/7 activity were dependent on a functional T3SS.


Collectively, these results are consistent with a model whereby the T3SS apparatus of P. aeruginosa activates the caspase-1-dependent inflammasome and caspase-3/7 through an ASC-dependent mechanism. This activation may have implications for the outcomes of P. aeruginosa infections.


Pseudomonas aeruginosa; T3SS; apoptosis; caspase-1; caspase-3; inflammasome; pyroptosis; type III secretion

[Available on 2019-08-01]
[Indexed for MEDLINE]

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