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Fate of Histoplasma capsulatum in guinea pig polymorphonuclear leukocytes
Abstract:
Guinea pig polymorphonuclear leukocytes (PMN) were parasitized in vitro with yeast cells of Histoplasma capsulatum. Preparations stained after 3 h at 37 C with May Greenwald-Giemsa revealed that 87% of the yeasts were tinctorially altered. Such alterations corresponded to those displayed by fungus cells intentionally killed by heat or other means and thus the altered yeast were presumed to be dead. A combination of 10(-5) M H(2)O(2), 10(-5) M KI, and horseradish peroxidase killed H. capsulatum. Death was assessed by the eosin-y dye exclusion test. All of the listed components were required for death of the fungus. A granule lysate preparation derived from guinea pig PMN leukocytes could replace the horseradish peroxidase in the fungicidal system. The granule lysates behaved in keeping with the attributes of a myeloperoxidase. Thus, PMN leukocytes and certain extracellular peroxidase systems kill the yeast cell phase of the dimorphic fungus H. capsulatum.
Insights
Guinea pig polymorphonuclear leukocytes (PMN) utilize a myeloperoxidase system to kill Histoplasma capsulatum yeast cells. This process requires hydrogen peroxide and iodide, demonstrating an effective innate immune response against fungal pathogens.
Area of Science:
- Immunology
- Mycology
- Biochemistry
Background:
- Histoplasma capsulatum is a dimorphic fungus causing opportunistic infections.
- Polymorphonuclear leukocytes (PMN) are crucial immune cells involved in combating fungal pathogens.
- The precise mechanisms by which PMN eliminate H. capsulatum yeast cells are not fully elucidated.
Purpose of the Study:
- To investigate the fungicidal activity of guinea pig PMN against Histoplasma capsulatum in vitro.
- To identify the key components of the PMN-mediated killing system.
- To explore the role of extracellular peroxidase systems in H. capsulatum killing.
Main Methods:
- In vitro incubation of guinea pig PMN with H. capsulatum yeast cells.
- Microscopic examination using May Greenwald-Giemsa staining to assess yeast viability.
- Fungicidal assays using hydrogen peroxide (H2O2), potassium iodide (KI), and horseradish peroxidase (HRP).
- Eosin-Y dye exclusion test to confirm fungal cell death.
- Analysis of guinea pig PMN granule lysates for peroxidase activity.
Main Results:
- After 3 hours of incubation, 87% of H. capsulatum yeasts showed tinctorial alterations indicative of cell death.
- A combination of H2O2, KI, and HRP was required to kill H. capsulatum, with all components being essential.
- Guinea pig PMN granule lysates, possessing myeloperoxidase-like activity, could substitute for HRP in the fungicidal system.
- PMN leukocytes and extracellular peroxidase systems effectively kill the yeast phase of H. capsulatum.
Conclusions:
- Guinea pig PMN possess an effective mechanism to kill H. capsulatum yeast cells.
- The myeloperoxidase system, involving H2O2 and iodide, plays a critical role in PMN-mediated fungal killing.
- Extracellular peroxidase systems share similarities with PMN's innate immune response against H. capsulatum.