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Live-cell Video Microscopy of Fungal Pathogen Phagocytosis
Published on: January 9, 2013
Escherichia coli and Candida albicans induced macrophage extracellular trap-like structures with limited microbicidal
Pan Liu1, Xiuping Wu1, Chengshui Liao1
1Key Laboratory for Zoonosis Research, Ministry of Education, Institute of Zoonosis, Jilin University, Changchun, China.
Abstract:
The formation of extracellular traps (ETs) has recently been recognized as a novel defense mechanism in several types of innate immune cells. It has been suggested that these structures are toxic to microbes and contribute significantly to killing several pathogens. However, the role of ETs formed by macrophages (METs) in defense against microbes remains little known. In this study, we demonstrated that a subset of murine J774A.1 macrophage cell line (8% to 17%) and peritoneal macrophages (8.5% to 15%) form METs-like structures (METs-LS) in response to Escherichia coli and Candida albicans challenge. We found only a portion of murine METs-LS, which are released by dying macrophages, showed detectable killing effects on trapped E. coli but not C. albicans. Fluorescence and scanning electron microscopy analyses revealed that, in vitro, both microorganisms were entrapped in J774A.1 METs-LS composed of DNA and microbicidal proteins such as histone, myeloperoxidase and lysozyme. DNA components of both nucleus and mitochondrion origins were detectable in these structures. Additionally, METs-LS formation occurred independently of ROS produced by NADPH oxidase, and this process did not result in cell lysis. In summary, our results emphasized that microbes induced METs-LS in murine macrophage cells and that the microbicidal activity of these METs-LS differs greatly. We propose the function of METs-LS is to contain invading microbes at the infection site, thereby preventing the systemic diffusion of them, rather than significantly killing them.
Insights
Murine macrophages form extracellular traps (METs-LS) that trap microbes like E. coli and C. albicans. These structures primarily contain invaders, with limited killing activity, suggesting a role in infection containment.
Area of Science:
- Immunology
- Cell Biology
Background:
- Extracellular traps (ETs) are a defense mechanism of innate immune cells.
- The role of macrophage-derived extracellular traps (METs) in microbial defense is not well understood.
Purpose of the Study:
- To investigate the formation and function of METs-like structures (METs-LS) in murine macrophages against microbial challenges.
- To determine the microbicidal activity and composition of METs-LS.
Main Methods:
- Murine J774A.1 macrophage cell line and peritoneal macrophages were challenged with Escherichia coli and Candida albicans.
- Fluorescence and scanning electron microscopy were used to analyze METs-LS.
- Detection of DNA components and microbicidal proteins within METs-LS.
Main Results:
- A subset of macrophages formed METs-LS in response to E. coli and C. albicans.
- METs-LS entrapped both microbes and contained DNA from nuclear and mitochondrial origins.
- Limited killing effects were observed for E. coli, but not C. albicans.
- METs-LS formation was independent of ROS and did not cause cell lysis.
Conclusions:
- Microbial challenge induces METs-LS formation in murine macrophages.
- The microbicidal activity of METs-LS is variable and microbe-dependent.
- METs-LS likely function to contain microbes at infection sites, preventing systemic spread, rather than direct killing.
