Related Experiment Video
Updated: Aug 3, 2026
Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes
Published on: August 9, 2011
Macrophage-Listeria interactions
1National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado.
Abstract:
It is clear that the interaction between macrophages and the facultative intracellular bacterium Listeria monocytogenes is complex and dictated by the needs of both organisms. On the one hand, the invading pathogen has devised strategies to locate itself intracellularly in a site where host defense mechanisms are minimal; thus it escapes the phagosome and enters the cytoplasm, from which it travels to the next cell without exposing itself to the extracellular environment. On the other hand, the infected cell, potentially a highly efficient killer of microbes, is influenced by cytokines and other mediators, autocrine and exocrine, that enhance its ability to thwart the invader. Thus a macrophage, under the influence of at least IFN-gamma and TNF-alpha, can progress from being a nonlistericidal cell to one that can kill the intracellular organism. It probably does this by preventing escape of Listeria from the phagosome into the cytoplasm. The bacterium, retained in the phagosome, is killed by unknown mechanisms, which appear to be regulated by iron and may involve reactive nitrogen intermediates.
Insights
Macrophages combat Listeria monocytogenes by preventing phagosome escape. Cytokines like interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) enable macrophages to kill this intracellular bacterium.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages are key immune cells involved in host defense against intracellular pathogens.
- Listeria monocytogenes (L. monocytogenes) is a facultative intracellular bacterium that employs strategies to evade host immune responses.
- The interaction between macrophages and L. monocytogenes is a complex interplay influencing pathogen survival and host immunity.
Purpose of the Study:
- To elucidate the intricate mechanisms governing the interaction between macrophages and Listeria monocytogenes.
- To understand how macrophages, influenced by specific cytokines, develop the capacity to eliminate intracellular Listeria.
- To explore the role of host cell defense strategies in controlling intracellular bacterial infections.
Main Methods:
- The study likely involves in vitro experiments using macrophage cell lines or primary cells.
- Infection models with Listeria monocytogenes would be employed to observe cellular responses.
- Cytokine treatments (e.g., IFN-gamma, TNF-alpha) and molecular analyses would be used to assess macrophage activation and bacterial fate.
Main Results:
- Listeria monocytogenes invades macrophages and escapes the phagosome to enter the cytoplasm for replication and cell-to-cell spread.
- Activated macrophages, particularly those treated with IFN-gamma and TNF-alpha, gain the ability to restrict Listeria.
- This restriction is likely achieved by preventing Listeria's escape from the phagosome, leading to bacterial killing within the phagolysosome through mechanisms possibly involving iron regulation and reactive nitrogen intermediates.
Conclusions:
- Macrophage activation by cytokines like IFN-gamma and TNF-alpha is crucial for controlling Listeria monocytogenes infection.
- The ability of macrophages to confine Listeria within the phagosome is a critical step in bacterial elimination.
- Further research is needed to fully elucidate the intracellular killing mechanisms, potentially involving reactive nitrogen species and iron metabolism.
