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Bacterial ingestion, tumor necrosis factor-alpha, and heat induce programmed cell death in activated neutrophils
R W Watson1, H P Redmond, J H Wang
1Department of Surgery, Royal College of Surgeons in Ireland, Dublin.
Abstract:
Resolution of acute inflammation requires the removal of sequestered neutrophils (PMN) from the inflammatory site by apoptosis and ingestion by tissue macrophages; however, sequestered PMN are prevented from undergoing programmed cell death by some of the mediators of the acute inflammatory process, including lipopolysaccharide (LPS), granulocyte-macrophage colony-stimulating factor, and interleukin 2. This delay in apoptosis could lead to necrosis resulting in tissue damage. Tumor necrosis factor-alpha (TNF-alpha), Escherichia coli ingestion resulting in a respiratory burst, and heat have been shown to induce PMN apoptosis. The effects of TNF-alpha, E. coli ingestion, and heat shock on the one hand and LPS on the other, on PMN apoptosis are unknown. The aim of this study was to determine if TNF-alpha, E. coli ingestion, and heat shock, which have been shown to induce PMN apoptosis, could override the delay in apoptosis associated with LPS. PMN (10(6)) isolated from 10 healthy volunteers were cultured in either medium alone or PMN cultured with LPS (10 ng/mL/1 h). PMN activation was assessed subsequently by phagocytosis of E. coli and CD11b expression. PMN were then further studied under four culture conditions: medium alone, TNF-alpha (100 U/mL), E. coli (1:25, PMN:E. coli), and heat shock (42 degrees C for 45 min). Apoptosis was assessed over time by propidium iodide staining of DNA and Fc gamma RIII receptor expression. The results demonstrate, for the first time, that the mechanisms by which LPS delays PMN apoptosis are overridden by the mechanisms by which TNF-alpha, E. coli ingestion, and heat shock induce programmed cell death. Factors regulating PMN apoptosis have an important role to play in the resolution of acute inflammation. Identification of these factors and their interaction have important implications for the development of therapeutic strategies aimed at modulating the acute inflammatory response.
Insights
Lipopolysaccharide (LPS) delays neutrophil apoptosis, hindering inflammation resolution. However, tumor necrosis factor-alpha (TNF-alpha), E. coli ingestion, and heat shock can override this delay, promoting programmed cell death and aiding inflammatory response modulation.
Area of Science:
- Immunology
- Cell Biology
- Inflammation Research
Background:
- Resolution of acute inflammation depends on neutrophil (PMN) apoptosis and clearance by macrophages.
- Mediators like lipopolysaccharide (LPS) can delay PMN apoptosis, potentially causing tissue damage.
- Factors such as TNF-alpha, E. coli ingestion, and heat shock are known to induce PMN apoptosis.
Purpose of the Study:
- To investigate if TNF-alpha, E. coli ingestion, and heat shock can overcome the LPS-induced delay in PMN apoptosis.
- To understand the mechanisms regulating PMN apoptosis in the context of inflammatory mediators.
Main Methods:
- Human neutrophils (PMN) were isolated and cultured with LPS.
- PMN activation was assessed via E. coli phagocytosis and CD11b expression.
- Apoptosis was measured under conditions with TNF-alpha, E. coli, or heat shock, alongside LPS exposure.
Main Results:
- TNF-alpha, E. coli ingestion, and heat shock were demonstrated to override the LPS-mediated delay in PMN apoptosis.
- This suggests distinct pathways for apoptosis induction and delay.
- The study provides the first evidence of these specific interactions.
Conclusions:
- Factors inducing PMN apoptosis can counteract the inhibitory effects of LPS.
- Understanding these regulatory mechanisms is crucial for developing therapeutic strategies for acute inflammation.
- Modulating PMN apoptosis holds significant therapeutic potential for inflammatory conditions.