Effect of macrophage colony-stimulating factor on anticryptococcal activity of bronchoalveolar macrophages: Synergy with fluconazole for killing

The anticryptococcal activity of murine bronchoalveolar macrophages (BAM) and their synergy with fluconazole (FCZ) was studied. BAM cultured with tissue culture medium for 48 to 72 h were fungicidal (24 to 39%) in a 3-h killing assay. However, net killing of Cryptococcus neoformans did not continue when culture time was extended to 24 h, although BAM were fungistatic (88 to 98%). Treatment with macrophage colony-stimulating factor (M-CSF; 5,000 U/ml, 48 h) did not significantly increase BAM killing of a low challenge dose in 3-h assays compared with control BAM. However, M-CSF- treated BAM were significantly more fungistatic against higher challenge doses in the 3-h assays. FCZ was not fungicidal at 5 μg/ml but was highly fungistatic (98 and 99% at 24 and 48 h, respectively). M-CSF-treated BAM acted synergistically with FCZ (2.5 μg/ml) for significantly greater killing than control BAM, 55% versus 20% and 96% versus 45% at 24 h and 48 h, respectively. Killing by M-CSF BAM and FCZ (5.0 μg/ml) was significantly (P < 0.01) greater than that by control BAM and FCZ at 48 h. These findings indicate an important collaborative role for BAM and FCZ in killing C. neoformans, and this is enhanced by M-CSF.