To examine the role of
granulocyte/macrophage colony-stimulating factor (
GM-CSF) in inflammatory
granuloma formation, we injected
GM-CSF-deficient (
GM-CSF(-/-)) mice and wild-type (
GM-CSF(+/+)) mice intravenously with 2 mg of
zymocel, and mice were killed at various intervals for examination. In
GM-CSF(-/-) mice, we demonstrated a marked delay of
zymocel-induced hepatic
granuloma formation until 5 days after
zymocel injection with a rapid reduction in numbers of
granulomas at 10 days until their disappearance. In the early phase of
granuloma formation, monocyte infiltration and differentiation of monocytes into macrophages were impaired in
GM-CSF(-/-) mice compared with
GM-CSF(+/+) mice. The percentages of [(3)H]
thymidine-labeled macrophages at 2 days after
zymocel injection were lower in the
GM-CSF(-/-) mice than in the
GM-CSF(+/+) mice. The DNA nick-end-labeling method demonstrated increased numbers of apoptotic cells in and around hepatic
granulomas of
GM-CSF(-/-) mice from 8 days after
zymocel injection, and electron microscopy detected apoptotic bodies.
Granuloma macrophage digestion of
glucan particles and activation of macrophages were similar in the two types of mice. In situ hybridization demonstrated expression of
GM-CSF mRNA in the endothelial cells, hepatocytes, and some
granuloma cells in the
GM-CSF(+/+) mice but not in the
GM-CSF(-/-) mice. These results provide evidence that
GM-CSF is important for the influx of monocytes into hepatic
granulomas, for differentiation of monocytes into macrophages, and for proliferation and survival of macrophages within hepatic
granulomas.