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Two functionally independent pathways for lipopolysaccharide-dependent activation of mouse peritoneal macrophages
C R Amura1, L C Chen, N Hirohashi
1Department of Microbiology, Molecular Genetics, and Immunology, The University of Kansas Medical Center, Kansas City 66160, USA.
Abstract:
We have investigated the effects of human LPS-binding protein (LBP) and human bactericidal/permeability-increasing protein (BPI) on LPS-dependent activation of mouse thioglycolate-elicited peritoneal macrophages in vitro, in comparison with human PBMCs. Confirming earlier published studies, BPI inhibited, and LBP enhanced, the ability of LPS to stimulate PBMC production of the cytokines TNF-alpha and IL-6. In marked contrast to these results, under identical conditions of in vitro culture, both LBP and BPI suppressed, in a dose-dependent manner, the ability of LPS to stimulate cytokine production in mouse macrophages. Further, while human BPI also suppressed LPS-dependent NO secretion in mouse macrophages, human LBP had no inhibitory effect on NO secretion under conditions that inhibited TNF-alpha secretion. These data provide the first direct evidence that mouse macrophages may utilize two independent pathways in response to LPS, thus leading to different phenotypic responses.
Insights
Human LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI) differentially regulate lipopolysaccharide (LPS)-induced cytokine production in mouse macrophages compared to human cells, suggesting distinct immune response pathways.
Area of Science:
- Immunology
- Cell Biology
Background:
- Lipopolysaccharide (LPS) is a key component of Gram-negative bacteria that triggers immune responses.
- LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI) are crucial host proteins involved in modulating LPS-mediated immune activation.
- Differential responses to LPS exist across species, necessitating comparative studies.
Purpose of the Study:
- To investigate the distinct effects of human LBP and BPI on LPS-induced activation of mouse macrophages.
- To compare these effects with those observed in human peripheral blood mononuclear cells (PBMCs).
- To elucidate potential differences in LPS signaling pathways between mouse and human immune cells.
Main Methods:
- In vitro culture of mouse thioglycolate-elicited peritoneal macrophages and human PBMCs.
- Stimulation with LPS in the presence or absence of human LBP and BPI.
- Quantification of cytokine production (TNF-alpha, IL-6) and nitric oxide (NO) secretion.
Main Results:
- Human LBP enhanced and BPI inhibited LPS-induced cytokine production in human PBMCs, consistent with prior research.
- Both LBP and BPI dose-dependently suppressed LPS-induced cytokine production in mouse macrophages.
- Human BPI suppressed LPS-induced NO secretion in mouse macrophages, while LBP did not inhibit NO secretion despite suppressing TNF-alpha.
Conclusions:
- Mouse macrophages exhibit distinct responses to LPS compared to human PBMCs when treated with LBP and BPI.
- These findings suggest that mouse macrophages may employ independent signaling pathways for LPS recognition, leading to varied phenotypic outcomes.
- The differential effects of LBP and BPI highlight species-specific mechanisms in innate immune responses to bacterial components.