Formation of large vacuoles induced by cooperative effects of oncostatin M and dexamethasone in human fetal liver cells

The morphology of human fetal liver cells treated with both oncostatin M and dexamethasone was strikingly different from those of cells treated with either oncostatin M or dexamethasone alone. Cotreatment with oncostatin M and dexamethasone resulted in the appearance of numerous large vacuoles. The size of the vacuoles varied among individual cells, ranging from 0.05 to 20 μm depending on the cell. Electron microscopy indicated that swollen large vacuoles in the human fetal liver cells were generally electron lucent. On the other hand, relatively small vacuoles about 2 μm in diameter were discrete structures that contained electron-dense material, such as partially degraded cytoplasmic membrane, cytoplasm, or organelle components. An autophagosome-like organelle was formed in cytoplasm. Electron microscopic analysis indicated direct fusion among the vacuoles formed in the cytoplasm of human fetal liver cells. To our knowledge, this is the first report of large swollen vacuoles formed in cells by the cooperative effects of oncostatin M and dexamethasone.