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Fungicidal activity of IFN-gamma-activated macrophages. Extracellular killing of Cryptococcus neoformans
I E Flesch1, G Schwamberger, S H Kaufmann
1Department of Medical Microbiology and Immunology, University of Ulm, FRG.
Abstract:
Cryptococcus neoformans is an encapsulated yeast-form fungus which causes pulmonary and meningeal infections preferentially in the immunocompromised host. It is thought that cell-mediated immunity is important for acquired resistance against cryptococcosis with activated macrophages as the final effector cells. However, specific polysaccharides in the capsule of C. neoformans protect the fungus from adherence to phagocytes and from subsequent phagocytosis. We have studied extracellular killing of C. neoformans by IFN-gamma-activated macrophages and their products. Murine bone marrow-derived macrophages stimulated with rIFN-gamma for 24 h were able to effectively suppress the growth of C. neoformans and the effect of IFN-gamma was augmented by LPS. Killing of C. neoformans was also achieved by cell-free supernatants from bone marrow-derived macrophages stimulated with IFN-gamma plus LPS. Our results indicate that killing of C. neoformans by activated macrophages is independent from toxic oxygen radicals and mediated by secreted protein(s) of apparent molecular mass of 15 and 30 kDa. These findings indicate that activated macrophages play a major role in host defense, although the fungus resists phagocytosis and remains in the extracellular milieu.
Insights
Activated macrophages kill Cryptococcus neoformans extracellularly using secreted proteins, not oxygen radicals. This finding is crucial for understanding host defense against fungal infections in immunocompromised individuals.
Area of Science:
- Immunology
- Mycology
- Infectious Diseases
Background:
- Cryptococcus neoformans causes serious infections, especially in immunocompromised individuals.
- The fungus's capsule protects it from phagocytosis by immune cells.
- Cell-mediated immunity, involving macrophages, is key to fighting cryptococcosis.
Purpose of the Study:
- To investigate the extracellular killing of C. neoformans by activated macrophages.
- To identify the mechanisms and factors involved in macrophage-mediated killing.
Main Methods:
- Murine bone marrow-derived macrophages were activated with recombinant interferon-gamma (rIFN-gamma).
- The effect of rIFN-gamma was studied alone and in combination with lipopolysaccharide (LPS).
- Cell-free supernatants from activated macrophages were used to assess secreted killing factors.
Main Results:
- IFN-gamma-activated macrophages suppressed C. neoformans growth.
- LPS augmented the growth-suppressive effect of IFN-gamma.
- Extracellular killing was mediated by secreted proteins (15 and 30 kDa), independent of toxic oxygen radicals.
Conclusions:
- Activated macrophages are effective in controlling C. neoformans growth extracellularly.
- Secreted proteins, not oxygen radicals, are the primary mediators of this killing.
- These findings highlight a critical macrophage function in host defense against C. neoformans infections.