Occurrence of minute ring-shaped nucleoprotein particles in culture media conditioned by mammalian cells.

Conditioned media of 21 mammalian cell lines have been examined by electron microscopic and biochemical techniques for the presence of a minute ring-shaped nucleoprotein particle (RSP). Electron microscopy showed the presence of RSP in 20 of the 21 cell lines tested. Comparative analyses of sex cell cultures for radioactive RSP, following 3H-thymidine incorporation, suggested that quantitative differences exist in the amount of RSP detectable in conditioned media of normal and pathologic cells. The cell lines tested included cells of different morphologies, origin and function