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Deactivation of macrophage oxidative burst in vitro by different strains of Histoplasma capsulatum
1Department of Veterinary Microbiology, Azabu University, Kanagawa, Japan.
Abstract:
It was previously reported that Histoplasma capsulatum (Hc) yeast not only failed to stimulate a murine macrophage oxidative burst (OB), but they also blunted or abolished OB stimulation by a subsequent encounter with potent stimuli such as zymosan or phorbol 12-myristate 13-acetate (PMA). The present studies show that macrophage deactivation is proportional to the time of incubation and the dose of Hc yeast that induce the deactivated state. Hc yeast derived from a virulent strain (G217B) are more efficient inducers of macrophage deactivation than similar preparations derived from the avirulent Downs Hc strain. Yeast cells of two other pathogenic fungi, Candida albicans and Cryptococcus neoformans are shown to stimulate rather than deactivate a macrophage OB.
Insights
Histoplasma capsulatum yeast deactivates macrophage oxidative burst (OB) in a dose- and time-dependent manner. Virulent Hc strains more effectively induce this deactivation compared to avirulent strains.
Area of Science:
- Immunology
- Microbiology
- Cellular Biology
Background:
- Histoplasma capsulatum (Hc) yeast is known to evade macrophage immune responses.
- Previous studies indicated Hc yeast suppresses macrophage oxidative burst (OB) and subsequent stimulation by other agents.
Purpose of the Study:
- To investigate the dose- and time-dependency of Hc-induced macrophage deactivation.
- To compare the deactivating potential of virulent versus avirulent Hc strains.
- To assess the effect of other pathogenic fungi on macrophage OB.
Main Methods:
- Incubation of murine macrophages with varying concentrations and durations of Hc yeast.
- Measurement of macrophage oxidative burst (OB) response to Hc yeast and subsequent stimuli (zymosan, PMA).
- Comparison of deactivation by virulent (G217B) and avirulent (Downs) Hc strains.
- Assessment of OB stimulation by Candida albicans and Cryptococcus neoformans.
Main Results:
- Macrophage deactivation by Hc yeast was found to be proportional to incubation time and yeast dose.
- Virulent Hc strain (G217B) induced a more pronounced deactivation than the avirulent strain.
- Candida albicans and Cryptococcus neoformans stimulated, rather than deactivated, the macrophage OB.
Conclusions:
- Histoplasma capsulatum yeast actively suppresses macrophage oxidative burst, a mechanism dependent on dose and duration of exposure.
- Strain virulence influences the efficacy of Hc-mediated macrophage deactivation.
- Other pathogenic fungi like Candida albicans and Cryptococcus neoformans exhibit contrasting effects, stimulating macrophage immune activity.