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Effect of granulocyte-macrophage colony-stimulating factor on rat alveolar macrophage anticryptococcal activity in
G H Chen1, J L Curtis, C H Mody
1Pulmonary Section, Department of Veterans Affairs Medical Center, Ann Arbor, MI.
Abstract:
Cryptococcus neoformans, a pathogenic fungus usually acquired by inhalation, causes the most common lethal mycosis in AIDS. The resident lung phagocytes, alveolar macrophages (AM phi), inhibit growth of C. neoformans poorly unless activated by cytokines such as IFN-gamma. In this study, we examined the effect of rat AM phi of the potent hematopoietic and M phi-activating cytokine, granulocyte-macrophage CSF (GM-CSF), alone and in combination with other cytokines. Rat AM phi monolayers were preincubated with 0.1 to 1000 U/ml GM-CSF without or with other recombinant cytokines, and then were incubated with viable C. neoformans (strain H99/C3D). Growth inhibition was assessed by counting cryptococcal CFU at 24 and 48 h of coculture; AM phi proliferation was assessed by measuring both uptake of [3H]TdR and AM phi numbers. AM phi preincubated with GM-CSF for 5 days (but not for shorter periods) inhibited growth of C. neoformans. Anticryptococcal activity required direct contact of AM phi with C. neoformans, but once induced by preincubation, did not require continued exposure to GM-CSF. Induction of anticryptococcal activity by GM-CSF was dose dependent (maximal induction at 250 U/ml), and was due to both increased ingestion and killing. GM-CSF induced AM phi proliferation, but anticryptococcal activity was not due totally to increases in AM phi numbers, indicating AM phi activation by GM-CSF. GM-CSF-induced AM phi proliferation was increased by IL-6, unchanged by IL-8, and abolished by LPS or IFN-gamma. However, IL-6 did not increase GM-CSF-induced anticryptococal activity. The combination of GM-CSF and IFN-gamma showed rapid and sustained anticryptococcal activity, unlike either cytokine alone. Our in vitro data suggest that the combination of GM-CSF and IFN-gamma may have beneficial effects on host defense against C. neoformans in vivo.
Insights
Granulocyte-macrophage colony-stimulating factor (GM-CSF) activates rat alveolar macrophages to inhibit Cryptococcus neoformans growth. Combining GM-CSF with IFN-gamma enhances this antifungal activity, suggesting a potential therapeutic strategy.
Area of Science:
- Immunology
- Mycology
- Cell Biology
Background:
- Cryptococcus neoformans is a major cause of lethal fungal infections in AIDS patients.
- Alveolar macrophages (AM phi) normally exhibit limited ability to inhibit C. neoformans growth.
- Cytokines like IFN-gamma can activate AM phi to enhance antifungal activity.
Purpose of the Study:
- To investigate the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on rat AM phi's ability to inhibit C. neoformans.
- To evaluate the combined effects of GM-CSF and other cytokines, including IFN-gamma, on AM phi's anticryptococcal activity.
Main Methods:
- Rat AM phi monolayers were pre-incubated with varying concentrations of GM-CSF, alone or with other cytokines.
- Pre-treated AM phi were co-cultured with viable C. neoformans.
- Anticryptococcal activity was assessed by quantifying fungal colony-forming units (CFU), and AM phi proliferation was measured.
Main Results:
- GM-CSF pre-incubation for 5 days significantly inhibited C. neoformans growth, mediated by increased fungal ingestion and killing.
- GM-CSF induced AM phi proliferation, but the anticryptococcal activity was attributed to macrophage activation, not just increased cell numbers.
- The combination of GM-CSF and IFN-gamma demonstrated rapid and sustained anticryptococcal activity, superior to either cytokine alone.
Conclusions:
- GM-CSF activates rat alveolar macrophages to inhibit C. neoformans growth in vitro.
- Combined GM-CSF and IFN-gamma treatment offers enhanced and sustained anticryptococcal effects.
- These findings suggest a potential therapeutic benefit of combining GM-CSF and IFN-gamma for managing C. neoformans infections in vivo.