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Updated: Jul 7, 2026
10:23
Evaluation of Caspase Activation to Assess Innate Immune Cell Death
Published on: January 20, 2023
Pseudomonas aeruginosa activates caspase 1 through Ipaf
Edward A Miao1, Robert K Ernst, Monica Dors
1Institute for Systems Biology, Seattle, WA 98103, USA.
Summary
Macrophages detect bacterial flagellin using the NLR Ipaf protein, activating caspase 1 and inflammatory cytokine secretion. This conserved innate immune pathway identifies pathogens employing type III secretion systems.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- The innate immune system utilizes cytosolic Nod-like receptors (NLRs) to detect pathogens.
- Several NLRs, like Ipaf, trigger caspase 1 activation, leading to IL-1beta and IL-18 secretion.
- Macrophages activate caspase 1 in response to Salmonella typhimurium via cytosolic flagellin and type III secretion systems (T3SS).
Purpose of the Study:
- To investigate the role of Pseudomonas aeruginosa in activating caspase 1 and IL-1beta secretion in macrophages.
- To determine if P. aeruginosa flagellin and T3SS are involved in this activation pathway.
- To elucidate the contribution of Naip5 in P. aeruginosa-induced immune responses.
Main Methods:
- Infection of macrophages with wild-type and mutant P. aeruginosa strains (T3SS and flagellin mutants).
- Assessment of caspase 1 activation and IL-1beta secretion.
- Delivery of P. aeruginosa flagellin directly into the macrophage cytosol.
- Comparison of immune responses in Naip5-deficient (A/J) and Naip5-sufficient (C57BL/6, BALB/c) macrophages.
Main Results:
- Live, virulent P. aeruginosa induced caspase 1-dependent IL-1beta secretion.
- Mutations in P. aeruginosa T3SS or flagellin abolished IL-1beta secretion.
- Reconstitution of caspase 1 activation by delivering flagellin to the cytosol confirmed its role.
- Naip5-deficient macrophages showed slightly reduced, but still present, IL-1beta secretion against various pathogens and flagellin.
Conclusions:
- Ipaf-dependent recognition of cytosolic flagellin is a conserved mechanism for macrophages to detect pathogens utilizing T3SS.
- Flagellin delivered via T3SS is a key P. aeruginosa component triggering innate immune activation.
- Naip5 plays a role, but other pathways also contribute to flagellin sensing in macrophages.
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