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Human neutrophil degranulation stimulated by Aspergillus fumigatus
1Evans Memorial Department of Clinical Research, University Hospital, Boston University Medical Center, MA 02118.
Abstract:
Previous studies have established that human neutrophils (PMN) are unable to kill resting conidia (RC) of Aspergillus fumigatus but can kill conidia that have been preincubated in culture medium until swollen but not yet germinated. Compared with swollen conidia (SC), RC stimulate a relatively weak PMN respiratory burst. In the present study, we further examined the mechanisms of resistance of RC to neutrophil killing by comparing neutrophil degranulation and phagocytosis following stimulation by RC and SC opsonized in pooled human serum. RC, compared with SC, stimulated significantly less release of both the primary granule marker beta-glucuronidase and the secondary granule marker lactoferrin. PMN also phagocytosed significantly greater numbers of SC, although the differences in phagocytosis were not great enough to account for the differences in degranulation. Suboptimal stimulation of degranulation and phagocytosis may thus contribute to the inability of neutrophils to kill RC. Moreover, reagent lactoferrin bound avidly to both RC and SC, raising the possibility that PMN-released lactoferrin may contribute to antifungal activity at the conidial surface by competing for iron or catalyzing the formation of oxygen radicals.
Insights
Human neutrophils struggle to kill resting Aspergillus fumigatus conidia. This resistance is linked to reduced neutrophil degranulation and phagocytosis of resting conidia compared to swollen ones.
Area of Science:
- Immunology
- Mycology
- Cell Biology
Background:
- Human neutrophils (PMN) can kill swollen conidia (SC) of Aspergillus fumigatus but not resting conidia (RC).
- Resting conidia (RC) elicit a weaker PMN respiratory burst compared to swollen conidia (SC).
Purpose of the Study:
- To investigate the mechanisms behind the resistance of resting conidia (RC) to neutrophil-mediated killing.
- To compare neutrophil degranulation and phagocytosis when stimulated by opsonized resting conidia (RC) versus swollen conidia (SC).
Main Methods:
- Human neutrophils (PMN) were stimulated with resting conidia (RC) and swollen conidia (SC) of Aspergillus fumigatus, both opsonized in pooled human serum.
- Neutrophil degranulation was assessed by measuring the release of primary (beta-glucuronidase) and secondary (lactoferrin) granule markers.
- Phagocytosis of conidia by neutrophils was quantified.
Main Results:
- Resting conidia (RC) stimulated significantly less release of beta-glucuronidase and lactoferrin compared to swollen conidia (SC).
- Neutrophils phagocytosed significantly more swollen conidia (SC) than resting conidia (RC), though this difference alone did not fully explain degranulation disparities.
- Reagent lactoferrin demonstrated avid binding to both resting conidia (RC) and swollen conidia (SC).
Conclusions:
- Suboptimal neutrophil degranulation and phagocytosis contribute to the resistance of resting conidia (RC) to neutrophil killing.
- Neutrophil-derived lactoferrin may exert antifungal activity by competing for iron or catalyzing oxygen radical formation on the conidial surface.