Macrophage colony-stimulating factor (M-CSF) induction of enhanced anticryptococcal activity in human monocyte-derived macrophages: Synergy with fluconazole for killing

Induction of enhanced anticryptococcal activity in human monocyte-derived macrophages (HMM) by macrophage colony-stimulating factor (M-CSF) and possible synergy with fluconazole (FCZ) for killing of Cryptococcus neoformans (CN) was studied. Fungistasis by HMM cultured in medium for 3, 5, or 7 days was minimal, 0-17%. The fungistasis of HMM cocultured with M-CSF at 1000, 5000, or 20,000 U/ml for 3, 5, or 7 days was increased significantly (P < 0.02) at all study times and by all concentrations. The optimal M-CSF concentration for HMM treatment for enhanced fungistasis was 5000 U/ml for Day 3 (84%), whereas 1000 U/ml was sufficient with more prolonged HMM culture and M-CSF treatment (Days 5-7). The enhancement by M-CSF was seen with four different donors and three patient isolates of CN. FCZ at 5 μg/ml was fungicidal, 28 ± 17% (n = 8). Killing by FCZ was enhanced by HMM treated with M-CSF 5000 or 20,000 U/ml for 5 days compared to control HMM, 58% (P = 0.001) and 60% (P = 0.002) vs 48%, respectively. This was also seen with HMM cultured with 1000 U/ml M-CSF for 7 days (P < 0.05). M-CSF also induced in HMM enhancement of fungistasis by lower, fungistatic, concentrations of FCZ. These results demonstrate enhancement of anticryptococcal activity by HMM treated with M-CSF and synergy with FCZ for inhibition and killing. These findings may provide a rationale for combined treatment of FCZ and M-CSF against cryptococcosis.