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Binding and germination of Aspergillus fumigatus conidia on cultured A549 pneumocytes
D J DeHart1, D E Agwu, N C Julian
1Department of Internal Medicine, Wake Forest University Medical Center, Winston-Salem, North Carolina 27157-1042, USA.
Abstract:
Invasive pulmonary aspergillosis is acquired through inhalation of conidia. Little is known about early interactions between Aspergillus fumigatus conidia and alveolar epithelial cells, so an in vitro model was developed to study binding between conidia and A549 cells, a line of type II pneumocytes. Conidia rapidly became attached to confluent monolayers of A549 cells in serum-free medium, reaching a plateau within 40 min. Scanning electron microscopy (EM) showed a random pattern of early adherence; viable conidia subsequently became clustered on pneumocyte surfaces. Following germination of pneumocyte-adherent conidia for 12 h, direct penetration of epithelial cells by hyphae could be demonstrated by scanning and transmission EM. These data suggest that an early event following inhalation of A. fumigatus conidia may be binding of conidia to pneumocytes, followed by hyphal penetration of the epithelial cell layer.
Insights
Early interactions between Aspergillus fumigatus conidia and lung cells were studied. Conidia bind to alveolar epithelial cells, then penetrate them, suggesting a key step in invasive pulmonary aspergillosis.
Area of Science:
- Medical Mycology
- Cell Biology
- Pulmonary Medicine
Background:
- Invasive pulmonary aspergillosis results from inhaling Aspergillus fumigatus conidia.
- Early interactions between fungal conidia and host lung cells remain poorly understood.
Purpose of the Study:
- To investigate the initial binding and penetration of Aspergillus fumigatus conidia onto alveolar epithelial cells using an in vitro model.
- To elucidate the early cellular events following inhalation of fungal spores.
Main Methods:
- Development of an in vitro model using A549 cells (a type II pneumocyte cell line).
- Observation of conidia adherence to cell monolayers using microscopy techniques, including scanning and transmission electron microscopy (EM).
- Assessment of conidia germination and subsequent hyphal interaction with epithelial cells over time.
Main Results:
- Aspergillus fumigatus conidia rapidly adhered to A549 cell monolayers within 40 minutes in serum-free conditions.
- Scanning EM revealed initial random adherence followed by clustering of viable conidia on pneumocyte surfaces.
- Germinated conidia demonstrated direct penetration of the epithelial cell layer after 12 hours of incubation.
Conclusions:
- Conidia binding to pneumocytes is an early event after inhalation.
- Hyphal penetration of the epithelial cell layer follows conidia adherence.
- This in vitro model provides insights into the initial stages of invasive pulmonary aspergillosis pathogenesis.
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