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In vitro interaction of alveolar macrophages and Aspergillus fumigatus
K Nessa1, C Jarstrand, A Johansson
1Division of Inhalation Toxicology, Karolinska Institute, Stockholm, Sweden.
Abstract:
In vitro interaction of alveolar macrophages (AM) from rats with conidia from Aspergillus fumigatus and Aspergillus candidus as well as inert control particles (amorphous silica) of similar diameter (about 3 microns), was studied. Experimental observations showed that both kinds of conidia were phagocytized significantly faster by AM than were the control particles due to a faster rate of attachment, but even more so due to a faster rate of ingestion. Quantitative nitroblue tetrazolium reduction by AM reflecting their oxidative metabolism and oxygen radical release was increased in response to both kinds of conidia by a factor of 2-3 during the process of phagocytosis, as well as 24 hr after the onset of phagocytosis, compared to corresponding conditions with inert particles and to resting macrophages. The mean pH in phagolysosomes with each of the conidia tended to be higher after 3 hr but was significantly lower after 24 hr than in the phagolysosomes with the control particles. After 3 hr there was a considerable percentage (around 8%) of phagolysosomes with pH > or = 6.5 and after 24 hr there was still a small percentage (0.7%) of such phagolysosomes for each of the conidia. Such a fraction was not observed for the control particles. Electron microscopic studies showed passages between phagolysosomes and AM surface with both kinds of conidia. The occurrence of such unsealed phagolysosomes might explain the percentage of phagolysosomes with high pH. Hence, Aspergillus conidia in unsealed macrophage vacuoles mediate an increased oxygen radical release from the macrophages, a process which in the long run might cause lung damage.
Insights
Aspergillus fungal spores are rapidly engulfed by rat alveolar macrophages (AM). This interaction triggers increased oxidative metabolism and oxygen radical release, potentially leading to lung damage.
Area of Science:
- Immunology
- Cell Biology
- Mycology
Background:
- Alveolar macrophages (AM) are crucial for lung immunity.
- Aspergillus species are common airborne fungi.
- Fungal spore-macrophage interactions influence host defense and pathology.
Purpose of the Study:
- To investigate the in vitro interaction between rat AM and Aspergillus conidia.
- To compare the phagocytosis and oxidative response to Aspergillus conidia versus inert particles.
- To elucidate the mechanisms underlying macrophage activation by fungal spores.
Main Methods:
- In vitro phagocytosis assays using rat AM and Aspergillus conidia (A. fumigatus, A. candidus) or amorphous silica particles.
- Measurement of oxidative metabolism via nitroblue tetrazolium reduction.
- Phagolysosomal pH determination at different time points (3 hr, 24 hr).
- Electron microscopy to visualize macrophage-conidia interactions.
Main Results:
- AM phagocytized Aspergillus conidia significantly faster than inert particles, with enhanced attachment and ingestion rates.
- Nitroblue tetrazolium reduction, indicating oxidative metabolism and oxygen radical release, increased 2-3 fold in response to conidia.
- Phagolysosomes containing conidia exhibited higher pH initially, with a persistent fraction of alkaline phagolysosomes (pH ≥ 6.5) at 24 hr, unlike those with inert particles.
- Electron microscopy revealed passages between phagolysosomes and the AM surface (unsealed phagolysosomes) when interacting with conidia.
Conclusions:
- Aspergillus conidia are efficiently phagocytized by AM, leading to heightened oxidative burst.
- Unsealed phagolysosomes formed during Aspergillus conidia interaction may contribute to sustained high phagolysosomal pH.
- This interaction, characterized by increased oxygen radical release from macrophages, could contribute to lung damage in the long term.