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Pro-inflammatory interactions of streptolysin O toxin with human neutrophils in vitro
D Joseph1, A J Theron2, C Feldman3
1Department of Internal Medicine, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa.
Abstract:
The recent global resurgence of severe infections caused by the Group A streptococcus (GAS) pathogen, Streptococcus pyogenes, has focused attention on this microbial pathogen, which produces an array of virulence factors, such as the pore-forming toxin, streptolysin O (SOT). Importantly, the interactions of SOT with human neutrophils (PMN), are not well understood. The current study was designed to investigate the effects of pretreatment of isolated human PMN with purified SOT on several pro-inflammatory activities, including generation of reactive oxygen species (ROS), degranulation (elastase release), influx of extracellular calcium (Ca2+) and release of extracellular DNA (NETosis), using chemiluminescence, spectrophotometric and fluorimetric procedures, respectively. Exposure of PMN to SOT alone caused modest production of ROS and elastase release, while pretreatment with the toxin caused significant augmentation of chemoattractant (fMLP)-activated ROS generation and release of elastase by activated PMN. These effects of treatment of PMN with SOT were associated with both a marked and sustained elevation of cytosolic Ca2+concentrations and significant increases in the concentrations of extracellular DNA, indicative of NETosis. The current study has identified a potential role for SOT in augmenting the Ca2+-dependent pro-inflammatory interactions of PMN, which, if operative in a clinical setting, may contribute to hyper-activation of PMN and GAS-mediated tissue injury.
Insights
Group A Streptococcus toxin streptolysin O (SOT) primes human neutrophils (PMN) to overreact. This priming enhances pro-inflammatory responses, potentially worsening tissue damage during severe infections.
Area of Science:
- Microbiology and Immunology
- Infectious Diseases
- Cellular Biology
Background:
- Global resurgence of severe Group A Streptococcus (GAS) infections highlights the need to understand pathogen virulence factors.
- Streptolysin O (SOT), a GAS pore-forming toxin, plays a role in pathogenesis, but its interaction with human neutrophils (PMN) is poorly understood.
- Understanding SOT-PMN interactions is crucial for elucidating mechanisms of GAS-induced tissue injury.
Purpose of the Study:
- To investigate the effects of purified SOT on pro-inflammatory activities of isolated human PMN.
- To examine SOT's impact on reactive oxygen species (ROS) generation, degranulation (elastase release), calcium influx, and NETosis in PMN.
- To determine if SOT pretreatment potentiates chemoattractant-activated PMN responses.
Main Methods:
- Isolated human PMN were pretreated with purified SOT.
- Pro-inflammatory activities including ROS generation, elastase release, cytosolic Ca2+ concentration, and NETosis were measured.
- Chemiluminescence, spectrophotometry, and fluorimetry were employed for quantitative analysis.
Main Results:
- SOT alone induced modest ROS production and elastase release in PMN.
- SOT pretreatment significantly augmented chemoattractant (fMLP)-activated ROS generation and elastase release.
- SOT-treated PMN exhibited sustained elevation of cytosolic Ca2+ and increased extracellular DNA release (NETosis).
Conclusions:
- SOT primes human PMN, enhancing their pro-inflammatory responses.
- SOT-induced potentiation of PMN activity is linked to increased cytosolic Ca2+ and NETosis.
- SOT may contribute to hyper-activated PMN responses and tissue injury in GAS infections.
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