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Updated: Aug 9, 2026
Depletion and Reconstitution of Macrophages in Mice
Published on: August 1, 2012
Drug potentiation of macrophage function
1Cancer Research Institute and Department of Medicine, University of California School of Medicine, San Francisco, California 94122.
Abstract:
The mechanism by which macrophages kill facultative intracellular parasites is not known. A test system is described utilizing human macrophages derived from blood monocytes and the opportunistic pathogen Listeria monocytogenes. In this system, bacterial killing was impaired under hypoxic conditions. Under aerobic conditions, addition of Clofazimine (B663), a phenazine derivative effective in the treatment of human leprosy, potentiated the killing of Listeria by macrophages. Potentiation occurred at drug concentrations usually attainable in man and which are not directly injurious to the bacteria. The enhanced bactericidal activity occurred only in the presence of oxygen; the drug induced increased leukocyte oxygen consumption which was insensitive to cyanide.
Insights
Macrophages kill bacteria like Listeria monocytogenes more effectively with the drug Clofazimine under oxygen-rich conditions. This immune response enhancement occurs without directly harming the bacteria, offering potential therapeutic insights.
Area of Science:
- Immunology
- Microbiology
- Pharmacology
Background:
- The precise mechanisms by which macrophages eliminate facultative intracellular parasites remain incompletely understood.
- Macrophages play a crucial role in the innate immune system's defense against various pathogens.
- Facultative intracellular parasites, such as Listeria monocytogenes, pose significant challenges to host immune responses.
Purpose of the Study:
- To investigate the role of oxygen levels in macrophage-mediated bacterial killing.
- To evaluate the potential of Clofazimine (B663) in enhancing macrophage bactericidal activity against Listeria monocytogenes.
- To elucidate the mechanism underlying Clofazimine's effect on macrophage function.
Main Methods:
- Development of a test system using human macrophages derived from blood monocytes.
- Infection of macrophages with the opportunistic pathogen Listeria monocytogenes.
- Assessment of bacterial killing under both hypoxic and aerobic conditions, with and without Clofazimine.
Main Results:
- Bacterial killing by macrophages was significantly impaired under hypoxic conditions.
- Addition of Clofazimine potentiated the killing of Listeria by macrophages under aerobic conditions.
- The enhanced bactericidal activity was oxygen-dependent and associated with increased leukocyte oxygen consumption, insensitive to cyanide.
Conclusions:
- Oxygen availability is critical for effective macrophage-mediated killing of Listeria monocytogenes.
- Clofazimine potentiates macrophage bactericidal activity against Listeria in an oxygen-dependent manner.
- The drug's mechanism involves enhancing host cell oxygen consumption rather than direct antibacterial effects.
