Related Experiment Video
Updated: Aug 18, 2026
Intravenous Endotoxin Challenge in Healthy Humans: An Experimental Platform to Investigate and Modulate Systemic Inflammation
Published on: May 16, 2016
Stimulus-specific effects of endotoxin on superoxide production by rabbit polymorphonuclear leukocytes
1Oregon Health Sciences University, Portland 97201.
Abstract:
The release of superoxide (O2-) by polymorphonuclear leukocytes (PMN) is an important function that contributes to microbial death. Controversy exists as to the effect of bacterial endotoxin (lipopolysaccharide, or LPS) on the production of O2-. We have injected rabbits with 25 micrograms Escherichia coli LPS intravenously and studied PMN function 18 to 24 hours later. Relative to PMN from saline-injected controls, PMN from LPS-treated rabbits released markedly greater amounts of O2- in response to 10 ng/ml phorbol myristate acetate (PMA) as measured by nmol cytochrome C reduced in 20 minutes (40.8 +/- 7.8 for LPS-treated PMN versus 10.1 +/- 1.6 for control, p less than 0.01). LPS injection, however, significantly reduced O2- release in response to C (complement) 5a (1.4 +/- 0.6 nmole/20 minutes for LPS-treated PMN versus 5.6 +/- 1.3 nmole/20 minutes for control, p less than 0.01). O2- release in response to a third stimulus, n-formyl-methionyl-leucyl-phenylalanine (10(-7) to 10(-9) M), was not affected by LPS. O2- release in response to PMA was enhanced over a wide range of PMA concentrations (10 to 300 ng/ml). Kinetic studies over 30 minutes indicated that, after a brief initial latency in measurable response, LPS enhanced responsiveness to PMA at all time points observed. The reduced responsiveness to C5a corresponds to a previously reported down regulation of receptors for this ligand after intravenous LPS. The observations indicate that intravenous LPS can alter a critical function of PMN for at least 24 hours in a stimulus-specific manner.
Insights
Bacterial endotoxin (lipopolysaccharide, or LPS) alters polymorphonuclear leukocyte (PMN) superoxide production. LPS enhances PMN response to phorbol myristate acetate but reduces response to complement C5a, indicating stimulus-specific effects.
Area of Science:
- Immunology
- Cellular Biology
- Microbiology
Background:
- Polymorphonuclear leukocytes (PMNs) are crucial for microbial defense through superoxide (O2-) release.
- The impact of bacterial endotoxin, specifically lipopolysaccharide (LPS), on PMN O2- production is debated.
- Understanding LPS effects on PMN function is vital for host defense mechanisms.
Purpose of the Study:
- To investigate the stimulus-specific effects of intravenous Escherichia coli lipopolysaccharide (LPS) on rabbit polymorphonuclear leukocyte (PMN) superoxide production.
- To determine how LPS influences PMN O2- release in response to different stimuli, including phorbol myristate acetate (PMA), complement C5a, and n-formyl-methionyl-leucyl-phenylalanine (fMLP).
Main Methods:
- Rabbits were intravenously injected with Escherichia coli LPS (25 micrograms).
- PMN function was assessed 18 to 24 hours post-injection by measuring O2- release.
- Superoxide production was quantified using cytochrome c reduction in response to PMA, C5a, and fMLP.
Main Results:
- LPS-treated rabbits showed significantly enhanced O2- release from PMNs in response to phorbol myristate acetate (PMA) compared to controls (40.8 vs. 10.1 nmol/20 min).
- Conversely, LPS significantly reduced PMN O2- release in response to complement C5a (1.4 vs. 5.6 nmol/20 min).
- PMN O2- release in response to n-formyl-methionyl-leucyl-phenylalanine (fMLP) was not affected by LPS.
Conclusions:
- Intravenous LPS administration alters PMN superoxide production in a stimulus-dependent manner for at least 24 hours.
- Enhanced PMA responsiveness and reduced C5a responsiveness suggest complex modulatory effects of LPS on PMN signaling pathways.
- The findings highlight LPS's capacity to selectively modulate critical PMN functions, impacting host defense against microbial challenges.
