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Relative hyperoxia augments lipopolysaccharide-stimulated cytokine secretion by murine macrophages
Daren S Danielson1, Wyrta Heagy, Kimberly M Nieman
1Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
Background:
Increased systemic levels of inflammatory mediators are seen after open abdominal operations. Macrophages that are exposed to lipopolysaccharide secrete cytokines. Peritoneal macrophages normally reside in a pO(2) of 40 mm Hg. We hypothesize that exposure of lipopolysaccharide-stimulated macrophages to "non-physiologic" pO(2) augments cytokine secretion.
Method:
Murine macrophages were preconditioned to a pO(2) of 40 mm Hg for 24 hours. The medium then was discarded and exchanged for a medium containing a pO(2) of 40, 150, or 440 mm Hg. Macrophages were incubated in the desired pO(2) for 6 and 24 hours while stimulated with lipopolysaccharide (0 to 100 ng/mL). The effect of pO(2) was compared. Supernatant tumor necrosis factor (TNF) and interleukin-6 were measured with enzyme-linked immunosorbent assay. Statistics were performed with analysis of variance.
Results:
We found dose-dependent lipopolysaccharide-stimulated TNF and interleukin-6 production with macrophages incubated at physiologic pO(2). Higher pO(2) did not stimulate TNF and interleukin-6 in the absence of lipopolysaccharide. However, a pO(2) of 150 and 440 mm Hg significantly (P <.05) increased lipopolysaccharide-stimulated TNF and interleukin-6 production versus 45 mm Hg.
Conclusion:
Our data suggest synergy between increased pO(2) and lipopolysaccharide for macrophage TNF and interleukin-6 production. Similar pO(2) elevations may occur with an open peritoneum or high supplemental O(2). Cytokines from peritoneal macrophages may contribute to the increased systemic inflammation after open operations.
Insights
Elevated oxygen levels combined with lipopolysaccharide significantly increase inflammatory cytokine production by macrophages. This suggests a potential mechanism for post-operative systemic inflammation.
Area of Science:
- Immunology
- Cell Biology
- Surgical Inflammation
Background:
- Systemic inflammation increases after open abdominal surgery.
- Macrophages are key immune cells that secrete cytokines.
- Peritoneal macrophages typically exist at a lower oxygen tension (pO(2)) of 40 mm Hg.
Purpose of the Study:
- To investigate if non-physiologic oxygen levels augment cytokine secretion in lipopolysaccharide-stimulated macrophages.
- To understand the role of oxygen tension in macrophage inflammatory responses.
Main Methods:
- Murine macrophages were exposed to varying pO(2) levels (40, 150, 440 mm Hg) after preconditioning.
- Macrophages were stimulated with lipopolysaccharide (LPS) at different concentrations.
- Tumor necrosis factor (TNF) and interleukin-6 (IL-6) levels were quantified using ELISA.
Main Results:
- Lipopolysaccharide (LPS) dose-dependently stimulated TNF and IL-6 production at physiologic pO(2).
- Increased pO(2) (150 and 440 mm Hg) significantly enhanced LPS-stimulated TNF and IL-6 secretion compared to 40 mm Hg.
- Higher pO(2) alone did not induce cytokine production without LPS stimulation.
Conclusions:
- There is a synergistic effect between elevated oxygen tension and LPS in stimulating macrophage cytokine production.
- Increased pO(2) in the peritoneum during surgery or with oxygen therapy may exacerbate inflammation.
- Peritoneal macrophage-derived cytokines could contribute to systemic inflammation post-operation.