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Updated: Jul 23, 2026
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Published on: April 19, 2017
Inhibition of different phases of Coccidioides immitis by human neutrophils or hydrogen peroxide
Abstract:
As arthroconidia of Coccidioides immitis transform into spherules, the fungal particles progressively become more resistant to the inhibitory effects of human polymorphonuclear leukocytes (PMNLs) as measured by PMNL inhibition of fungal incorporation of N-acetylglucosamine. Similar changes were noted when leucine incorporation was measured. When H2O2, at a concentration of 2.0 mM, was substituted for PMNLs, an equivalent inhibition of arthroconidia was produced and, as with PMNL effects, was lost with spherule maturation. The results from these studies indicate that C. immitis may evade natural inhibition by PMNLs by transformation into the spherule phase.
Insights
Coccidioides immitis arthroconidia evade human immune cells by transforming into spherules. This developmental change increases fungal resistance to polymorphonuclear leukocytes (PMNLs) and hydrogen peroxide.
Area of Science:
- Medical Mycology
- Immunology
- Microbial Pathogenesis
Background:
- Coccidioides immitis is a fungus causing Valley fever.
- The human immune system, particularly polymorphonuclear leukocytes (PMNLs), attempts to clear fungal infections.
- Fungal developmental stages may influence immune evasion strategies.
Purpose of the Study:
- To investigate the resistance of Coccidioides immitis developmental stages to immune cell inhibition.
- To determine if fungal transformation confers resistance to human polymorphonuclear leukocytes (PMNLs).
Main Methods:
- Measuring PMNL inhibition of fungal nutrient uptake (N-acetylglucosamine and leucine incorporation).
- Assessing fungal resistance to hydrogen peroxide (H2O2) at a concentration of 2.0 mM.
- Comparing inhibition effects on arthroconidia versus mature spherules.
Main Results:
- Arthroconidia of Coccidioides immitis showed increased resistance to PMNL inhibition as they matured into spherules.
- This increased resistance correlated with reduced fungal incorporation of N-acetylglucosamine and leucine.
- Hydrogen peroxide (2.0 mM) mimicked PMNL inhibitory effects, which were also lost upon spherule maturation.
Conclusions:
- Coccidioides immitis transformation into the spherule phase is a mechanism for evading host immune defenses.
- The spherule stage of Coccidioides immitis is inherently more resistant to innate immune components like PMNLs and oxidative stress.
