Related Experiment Videos
Neutrophils undergo apoptosis following ingestion of Escherichia coli
R W Watson1, H P Redmond, J H Wang
1Royal College of Surgeons in Ireland, Beaumont Hospital, Dublin.
Abstract:
Apoptosis is a distinct mechanism by which eukaryotic cells die. Neutrophils (PMN) play a fundamental role in the systemic inflammatory response syndrome. Clearance of PMN during resolution of the acute inflammatory process occurs by apoptosis, but factors inducing this process are unknown. The aims of this study were to determine whether PMN ingestion of Escherichia coli would result in PMN apoptosis and whether the mechanism was related to the respiratory burst. PMN from 10 healthy volunteers were cultured with different ratios of PMN:E. coli (1:0 to 1:25) for 12 h. Apoptosis was then assessed by propidium iodide DNA staining, morphology, gel electrophoresis, and Fc gamma RIII expression. There was a significant induction of PMN apoptosis on incubation with E. coli at a ratio of 1:10 and 1:25 PMN:E. coli as well as decreases in Fc gamma RIII. This correlated with increased ingestion of FITC-labeled E. coli and intracellular reactive oxygen intermediates after a 2-h coculture. To clarify the role of reactive oxygen intermediates in E. coli-induced PMN apoptosis, we assessed the effects of the antioxidants catalase, DMSO, glutathione, and N-acetylcysteine. There was a significant decrease in E. coli-induced PMN apoptosis on incubation with DMSO (1.0%), glutathione (25 mM), and N-acetylcysteine (25 mM) compared with control PMN:E. coli. This study demonstrates for the first time that E. coli induces PMN apoptosis through an oxygen-dependent mechanism. The removal of effete PMN by the process of apoptosis rather than necrosis may be teleologically beneficial during Gram-negative septicemia.
Insights
Escherichia coli (E. coli) ingestion triggers programmed cell death (apoptosis) in neutrophils (PMN) via an oxygen-dependent pathway. This finding is crucial for understanding inflammatory resolution during infections.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Neutrophils (PMN) are key immune cells involved in inflammation.
- Apoptosis, or programmed cell death, is essential for resolving inflammation by clearing spent PMN.
- The specific triggers and mechanisms of PMN apoptosis during bacterial infections remain largely unknown.
Purpose of the Study:
- To investigate if Escherichia coli (E. coli) ingestion induces apoptosis in human neutrophils.
- To determine if the respiratory burst, a key inflammatory response, is involved in E. coli-induced PMN apoptosis.
- To explore the role of reactive oxygen intermediates in this process.
Main Methods:
- Human neutrophils were cultured with varying ratios of E. coli.
- Apoptosis was assessed using propidium iodide DNA staining, morphology, gel electrophoresis, and Fc gamma RIII expression.
- The effects of antioxidants (catalase, DMSO, glutathione, N-acetylcysteine) on E. coli-induced apoptosis were evaluated.
Main Results:
- E. coli significantly induced PMN apoptosis at high bacterial ratios (1:10, 1:25).
- This induction correlated with increased E. coli uptake and intracellular reactive oxygen intermediates.
- Antioxidants like DMSO, glutathione, and N-acetylcysteine significantly reduced E. coli-induced PMN apoptosis.
Conclusions:
- E. coli ingestion triggers neutrophil apoptosis through an oxygen-dependent mechanism.
- Reactive oxygen intermediates play a critical role in mediating E. coli-induced PMN apoptosis.
- Apoptotic clearance of PMN, rather than necrosis, may be advantageous during Gram-negative septicemia.