Carlson College of Veterinary Medicine

Previous studies have shown that recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates human and murine macrophages to inhibit growth and kill intracellularly. This study shows the effect of GM-CSF on Mycobacterium avium complex (MAC) infection in vivo using a C57BL/6 beige mouse model of disseminated MAC infection. Furthermore, it examined the activity of the combination of GM-CSF and amikacin or azithromycin, two antimicrobials active against MAC, on the survival of MAC within macrophages in vitro and in the mouse model of disseminated infection. Although GM-CSF (25 mg/kg) induced mycobactericidal and mycobacteriostatic activity in macrophages in vitro and in vivo, the combination of GM-CSF and amikacin (50 mg/kg) or azithromycin (250 mg/kg) was associated with a significant increase in killing of MAC both within cultured macrophages and in the beige mouse model. Therefore, a significant reduction in the number of viable bacteria was observed in blood, liver, and spleen of mice treated with a combination of GM-CSF and azithromycin or amikacin compared with control mice and those treated with GM-CSF or antimicrobials alone.