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Does endotoxin play a major role in inducing the depression of macrophage function during polymicrobial sepsis?
A Ayala1, Z K Deol, D L Lehman
1Department of Surgery, Michigan State University, East Lansing, USA.
Background:
Endotoxin (ETX) is thought to be the primary inducer of proinflammatory mediator release associated with bacterial sepsis. Furthermore, a number of studies indicate that preexposure of animals to high doses of ETX produces macrophages (M luminal diameters) that are refractory to ex vivo stimulation with ETX. However, it is unknown if levels of ETX comparable to those typically encountered in sepsis induce a similar refractory state in M luminal diameters.
Design:
To assess this, peritoneal M luminal diameters (PM luminal diameters) were harvested from C3H/HeN mice (ETX sensitive) at 1 hour (early) or 24 hours (late) following cecal ligation and puncture (CLP) to induce polymicrobial sepsis, sham CLP, or laparotomy followed by peritoneal implantation of a minipump delivering either saline or ETX (0.025 microgram/g of body weight, every 24 hours). Peritoneal M luminal diameter cultures were incubated with ETX, either 0 or 10 micrograms/mL, for 24 hours, and their ability to release interleukin-1, interleukin-6, and tumor necrosis factor was assessed by bioassay.
Results:
Chronic low-dose ETX with 0 microgram of ETX media added produced early (at 1 hour) in vivo activation of PM luminal diameter interleukin-1 release, which was comparable to that seen in mice subjected to CLP. However, unlike PM luminal diameter taken from CLP mice, PM luminal diameters from mice implanted with the ETX minipump at 1 or 24 hours showed no marked decline in their ability to respond to ETX (10 micrograms). Comparable changes were seen for interleukin-6 and tumor necrosis factor release.
Conclusions:
Bacterial component(s) other than ETX per se induces the sustained dysfunction in PM luminal diameter capacity to produce proinflammatory cytokines during sepsis and/or peritonitis. Thus, agents directed against ETX alone may not be adequate in the treatment of polymicrobial sepsis.
Insights
Bacterial sepsis involves more than just endotoxin (ETX). While ETX can activate macrophages, other bacterial factors cause sustained dysfunction in cytokine production during sepsis, suggesting ETX-targeted treatments may be insufficient.
Area of Science:
- Immunology
- Microbiology
- Sepsis Pathophysiology
Background:
- Endotoxin (ETX) is a primary trigger for proinflammatory mediator release in bacterial sepsis.
- High-dose ETX pre-exposure can render macrophages refractory to further ETX stimulation.
- The effect of sepsis-relevant ETX levels on macrophage refractoriness remains unclear.
Purpose of the Study:
- To investigate whether ETX levels encountered during sepsis induce macrophage refractoriness.
- To compare the effects of endotoxin and other bacterial components on macrophage function during sepsis.
Main Methods:
- Peritoneal macrophages were harvested from mice 1 or 24 hours after inducing polymicrobial sepsis via cecal ligation and puncture (CLP).
- Macrophages were also obtained from sham CLP or CLP mice implanted with minipumps delivering saline or low-dose ETX.
- Macrophage cytokine release (IL-1, IL-6, TNF) was assessed after ex vivo ETX stimulation.
Main Results:
- Low-dose chronic ETX activated interleukin-1 release in vivo, similar to CLP.
- Unlike macrophages from CLP mice, those from ETX-minipump mice did not show significant refractoriness to ex vivo ETX stimulation.
- Similar patterns were observed for interleukin-6 and tumor necrosis factor release.
Conclusions:
- Sustained macrophage dysfunction in sepsis is induced by bacterial components other than endotoxin.
- Endotoxin alone does not appear to cause the observed refractory state in macrophages during sepsis.
- Targeting only endotoxin may be inadequate for treating polymicrobial sepsis.