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Updated: May 10, 2026
Visualization of Bacterial Toxin Induced Responses Using Live Cell Fluorescence Microscopy
Published on: October 1, 2012
Reduction of streptolysin O (SLO) pore-forming activity enhances inflammasome activation
Peter A Keyel1, Robyn Roth, Wayne M Yokoyama
1Department of Immunology, University of Pittsburgh, Pittsburgh, PA 15260, USA. pak55@pitt.edu
Abstract:
Pore-forming toxins are utilized by bacterial and mammalian cells to exert pathogenic effects and induce cell lysis. In addition to rapid plasma membrane repair, macrophages respond to pore-forming toxins through activation of the NLRP3 inflammasome, leading to IL-1β secretion and pyroptosis. The structural determinants of pore-forming toxins required for NLRP3 activation remain unknown. Here, we demonstrate using streptolysin O (SLO) that pore-formation controls IL-1β secretion and direct toxicity. An SLO mutant incapable of pore-formation did not promote direct killing, pyroptosis or IL-1β production. This indicated that pore formation is necessary for inflammasome activation. However, a partially active mutant (SLO N402C) that was less toxic to macrophages than wild-type SLO, even at concentrations that directly lysed an equivalent number of red blood cells, enhanced IL-1β production but did not alter pyroptosis. This suggests that direct lysis may attenuate immune responses by preventing macrophages from successfully repairing their plasma membrane and elaborating more robust cytokine production. We suggest that mutagenesis of pore-forming toxins represents a strategy to enhance adjuvant activity.
Insights
Pore-forming toxins trigger cell lysis and immune responses like IL-1β secretion. This study shows pore formation is essential for activating the NLRP3 inflammasome and subsequent cell death pathways.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Pore-forming toxins (PFTs) are virulence factors used by pathogens and endogenous molecules.
- Macrophages detect PFTs, activating the NLRP3 inflammasome, leading to IL-1β secretion and pyroptosis.
- The specific structural features of PFTs required for NLRP3 inflammasome activation are not well understood.
Purpose of the Study:
- To investigate the role of pore formation by streptolysin O (SLO) in NLRP3 inflammasome activation, IL-1β secretion, and pyroptosis.
- To determine if PFTs can be modified to enhance immune responses for use as adjuvants.
Main Methods:
- Site-directed mutagenesis of streptolysin O (SLO) to generate pore-deficient and partially pore-forming mutants.
- Treatment of macrophages with wild-type SLO and mutant variants.
- Assessment of cell viability, pyroptosis, and IL-1β production.
Main Results:
- A non-pore-forming SLO mutant failed to induce cell lysis, pyroptosis, or IL-1β production, confirming pore formation is necessary for inflammasome activation.
- A partially pore-forming SLO mutant (SLO N402C) enhanced IL-1β production without inducing pyroptosis, even at concentrations causing red blood cell lysis.
- Reduced direct toxicity of the partially active mutant suggests that excessive membrane damage may impair macrophage immune signaling.
Conclusions:
- Pore formation is a critical determinant for streptolysin O-induced NLRP3 inflammasome activation and subsequent IL-1β secretion and pyroptosis.
- Modulating the pore-forming activity of toxins, like SLO, could be a viable strategy for developing enhanced vaccine adjuvants.
- Understanding the interplay between pore formation, membrane repair, and immune activation is crucial for PFTs' pathogenic and therapeutic roles.
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