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Expression and regulation of macrophage inflammatory protein-1 alpha by murine alveolar and peritoneal macrophages
G M VanOtteren1, T J Standiford, S L Kunkel
1Department of Medicine, University of Michigan Medical School, Ann Arbor 48109-0360.
Abstract:
A number of disease states are characterized by the accumulation of inflammatory cells at the site of tissue injury. Mononuclear phagocytes (M phi) represent key cellular mediators of inflammation via the production of regulatory and chemokinetic cytokines. One such cytokine, macrophage inflammatory protein-1 alpha (MIP-1 alpha), has been shown to be one of the major inducible chemotaxins expressed from murine macrophage cell lines (RAW 264.7). We postulated that MIP-1 alpha is a major monocyte chemoattractant produced by resident M phi, and the magnitude of production of this chemotaxin may depend upon the specific population of M phi studied. To test this hypothesis, we isolated alveolar macrophages (AM phi) and peritoneal macrophages (PM phi) from CD-1 mice by bronchoalveolar and peritoneal lavage, respectively. Recombinant murine MIP-1 alpha accounted for significant neutrophil chemokinetic rather than chemotactic activity, as assessed by checkerboard analysis. LPS-stimulated AM phi-derived monocyte chemotactic activity (MCA) was significantly neutralized by specific rabbit anti-murine MIP-1 alpha serum. In contrast, PM phi-derived conditioned media failed to produce MCA attributable to MIP-1 alpha. The production of MIP-1 alpha was then characterized from both AM phi and PM phi. While unstimulated AM phi and PM phi failed to express MIP-1 alpha mRNA, both AM phi and PM phi challenged with lipopolysaccharide (LPS) expressed MIP-1 alpha mRNA in a time-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is a key cytokine in inflammation. Alveolar macrophages produce more MIP-1 alpha than peritoneal macrophages, influencing monocyte chemotactic activity.
Area of Science:
- Immunology
- Cell Biology
Background:
- Inflammatory diseases involve immune cell accumulation.
- Mononuclear phagocytes (M phi) mediate inflammation through cytokine production.
- Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is a key chemotactic cytokine.
Purpose of the Study:
- To investigate the role of MIP-1 alpha in monocyte chemoattractant activity.
- To compare MIP-1 alpha production by different macrophage populations (alveolar vs. peritoneal).
Main Methods:
- Isolation of alveolar macrophages (AM phi) and peritoneal macrophages (PM phi) from mice.
- Assessment of neutrophil chemokinetic and chemotactic activity using recombinant MIP-1 alpha.
- Neutralization assays using anti-MIP-1 alpha serum to determine its contribution to monocyte chemotactic activity (MCA).
- Analysis of MIP-1 alpha mRNA expression in response to lipopolysaccharide (LPS) stimulation.
Main Results:
- Recombinant MIP-1 alpha primarily induced neutrophil chemokinesis, not chemotaxis.
- LPS-stimulated AM phi produced MCA that was neutralized by anti-MIP-1 alpha serum.
- PM phi-derived conditioned media showed minimal MCA attributable to MIP-1 alpha.
- Both AM phi and PM phi expressed MIP-1 alpha mRNA in a time-dependent manner after LPS challenge.
Conclusions:
- Alveolar macrophages are a significant source of MIP-1 alpha, contributing to monocyte chemotactic activity.
- Peritoneal macrophages produce less MIP-1 alpha and contribute less to MCA.
- MIP-1 alpha production by both macrophage types is inducible by LPS.