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Further studies on the inhibition of Histoplasma capsulatum within macrophages from immunized animals
Abstract:
Mononuclear phagocytes freshly harvested from immunized animals restrict the intracellular growth of Histoplasma capsulatum. The fate of the inhibited fungus is the subject of this report. Macrophages harvested from mice immunized by sublethal infection were parasitized in vitro with yeast cells of H. capsulatum. The subsequent fate of the fungus was assessed by staining characteristics, viability on subculture, and radioisotopic techniques. No tinctorial distinction could be made between yeasts within normal or immune phagocytes stained by the May Greenwald-Giemsa or by the Gridley techniques. Yeast cells recovered after 24 h of residence within the cytoplasm of immune monocytes excluded the dye eosin-Y, germinated on Casamino Acid agar incubated at 30 C, and initiated growth at a normal rate within phagocytes from normal animals. Thus even though the growth of H. capsulatum was inhibited within macrophages from immunized animals, the fungus was not killed by the encounter. However, autoradiographic studies established that protein synthesis by the fungus in situ was impaired.
Insights
Immune macrophages inhibit Histoplasma capsulatum growth but do not kill it. The fungus remains viable, though its protein synthesis is impaired within these immune cells.
Area of Science:
- Immunology
- Mycology
- Infectious Diseases
Background:
- Mononuclear phagocytes play a crucial role in host defense against fungal infections.
- Immunity developed through sublethal infection can enhance macrophage function.
- Understanding the fate of intracellular pathogens within immune cells is vital for developing effective treatments.
Purpose of the Study:
- To investigate the survival and viability of Histoplasma capsulatum within immune macrophages.
- To determine if growth inhibition equates to fungal killing.
- To elucidate the specific mechanisms affecting fungal viability after phagocytosis by immune cells.
Main Methods:
- Macrophages were harvested from immunized mice and infected in vitro with Histoplasma capsulatum.
- Fungal viability was assessed using staining techniques (May Greenwald-Giemsa, Gridley), dye exclusion (eosin-Y), and subculture on agar.
- Autoradiographic studies were employed to evaluate fungal protein synthesis.
Main Results:
- Histoplasma capsulatum yeast cells within immune macrophages showed no tinctorial differences with standard staining.
- Recovered yeast cells excluded eosin-Y, germinated on culture media, and initiated normal growth in non-immune macrophages.
- Autoradiography revealed impaired protein synthesis by the fungus residing within immune macrophages.
Conclusions:
- Macrophage-mediated inhibition of Histoplasma capsulatum growth does not result in fungal death.
- The immune response restricts fungal proliferation but does not eliminate the pathogen intracellularly.
- Impaired fungal protein synthesis is a key mechanism by which immune macrophages control Histoplasma capsulatum.