Role of granulocyte/macrophage colony-stimulating factor in zymocel-induced hepatic granuloma formation.

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.

Effects of granulocyte/macrophage colony-stimulating factor on the development and differentiation of CD5-positive macrophages and their potential derivation from a CD5-positive B-cell lineage in mice.

In co-cultures of either the murine pre-B cell line J13, fetal liver cells, or adult peritoneal or bone marrow cells with ST2 mouse bone marrow stromal cells in the presence of granulocyte/macrophage colony-stimulating factor (GM-CSF), the development of CD5+ macrophages was demonstrated by immunohistochemical staining and flow cytometry. Although CD5+ macrophages were not present in the peritoneal cavities of normal mice, approximately 30% of the peritoneal macrophages in viable motheaten (mev/mev) mice, deficient in SHP-1 protein tyrosine phosphatase, expressed cell surface CD5 and B220, markers for B cells. In the mev/mev mice, GM-CSF level in peritoneal fluid was increased significantly. At 5 days after daily intravenous injection with GM-CSF, many CD5+ macrophages appeared in the peritoneal cavity and in omental milky spots of normal mice but fewer in osteopetrosis (op) mutant mice, deficient in macrophage (M)-CSF. These results indicate that GM-CSF, in combination with M-CSF, induces the development and differentiation of CD5+ macrophages in the peritoneal cavity, particularly in the omental milky spots of mice. In the peritoneal cavity of GM-CSF-treated mice, the percentages of hematopoietic progenitor cells doubly positive for CD5 and CD34 or c-kit and of macrophage precursor cells doubly positive for CD5 and ER-MP58 or ER-MP20 were increased significantly during the development of CD5+ macrophages and CD5 B cells, suggesting that CD5+ macrophages and B cells may share a bipotential progenitor in vivo.