SURFACE LOCALIZATION OF VIRUS PRODUCTION ON A GLUCOCORTICOID-STIMULATED ONCORNAVIRUS-PRODUCING MOUSE MAMMARY-TUMOR CELL LINE BY SCANNING ELECTRON-MICROSCOPY

  • 1 January 1976
    • journal article
    • research article
    • Vol. 36  (3) , 1084-1093
Abstract
A chronically infected continuous mouse mammary tumor cell line containing virus particles of type B morphology, free of contaminating type C virions, was grown in tissue culture. These cells were treated with dexamethasone, a synthetic glucocorticoid potent stimulator of mouse mammary tumor virus expression. Surfaces of untreated and dexamethasone-treated cells were investigated by scanning electron microscopy. Untreated cells demonstrated a moderate expression of mouse mammary tumor virus (80 particles/cell) distributed diffusely over the cell surface. Virions on dexamethasone-treated cells were localized in clusters of 100-2000 virus particles, often with >1 cluster/cell. Dexamethasone-treated cells typically showed a 10-fold increase in cell-associated virus over untreated cells. Concentrated extracellular fluids from untreated and dexamethasone-treated cultures were quantitated for free virus. Dexamethasone-treated culture fluids demonstrated a similar 10-fold increase of extracellular particles. This increase in virus particles on the cell surfaces and in extracellular fluid supports that dexamethasone has a stimulatory effect on viral replication, not just on the release of budding particles. The ultrastructure of budding mouse mammary tumor virus during dexamethasone stimulation, determined by scanning and transmission electron microscopy, and the significance of such an in vitro system for viral immunodiagnosis are discussed.

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