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Growth inhibition of Cryptococcus neoformans by human alveolar macrophages
P B Weinberg1, S Becker, D L Granger
1Center for Environmental Medicine, University of North Carolina at Chapel Hill.
Abstract:
Macrophage cytotoxicity for Cryptococcus neoformans was investigated by culturing human alveolar macrophage (AM) with a thin-capsuled clone of C. neoformans in a polypropylene culture tube assay system. Yeast replication was quantitated by electronic particle counting after detergent lysis of AM and viability by quantitative plate counts. Under appropriate conditions, fungal replication was inhibited in the presence of human AM. This effect persisted over the 48-h time course that was evaluated. During this period, organisms in medium alone proliferated rapidly, doubling their number every 4 h. Human AM did not require endotoxin, fetal calf serum, or specific rabbit anticryptococcal antibody for fungistasis. Under these conditions, microscopic evaluation of a cytocentrifuge preparation of AM-yeast cocultures, stained by a modified Giemsa technique, revealed all the fungi to be extracellular. In the presence of 10% fresh human serum, AM phagocytized C. neoformans and exhibited fungicidal activity. Tumor necrosis factor did not affect the replication rate of the yeast. These findings suggest that there may be at least 2 mechanisms by which human AM protect against C. neoformans. One is serum-independent and extracellular and results in fungistasis, and the other is dependent on a serum factor and leads to intracellular inhibition of growth and possibly killing of the organism.
Insights
Human alveolar macrophages (AM) inhibit Cryptococcus neoformans replication through two distinct mechanisms. One is serum-independent and extracellular, while the other requires serum for intracellular fungicidal activity.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Cryptococcus neoformans is an opportunistic fungal pathogen that can cause life-threatening infections, particularly in immunocompromised individuals.
- Macrophages play a critical role in the innate immune response against microbial infections, including fungal pathogens.
Purpose of the Study:
- To investigate the mechanisms by which human alveolar macrophages (AM) exert cytotoxic effects against Cryptococcus neoformans.
- To determine if AM require specific factors like serum or antibodies for anti-cryptococcal activity.
Main Methods:
- Human alveolar macrophages were co-cultured with a thin-capsuled clone of C. neoformans in a polypropylene tube assay.
- Yeast replication was quantified using electronic particle counting after cell lysis.
- Fungal viability was assessed by quantitative plate counts.
- Microscopic evaluation of Giemsa-stained co-cultures was performed to determine fungal location (intracellular vs. extracellular).
Main Results:
- Human AM inhibited C. neoformans replication over a 48-hour period, while yeast proliferated rapidly in medium alone.
- This serum-independent, extracellular fungistasis was observed without the need for endotoxin, fetal calf serum, or specific antibodies.
- In the presence of fresh human serum, AM phagocytized C. neoformans and demonstrated intracellular fungicidal activity.
Conclusions:
- Human AM employ at least two distinct mechanisms to combat C. neoformans infection.
- A serum-independent, extracellular mechanism results in fungistasis.
- A serum-dependent mechanism leads to intracellular growth inhibition and potential killing of the yeast.