Studies on a Virus ("Polyoma") Inducing Multiple Tumors in Animals.

Abstract

Mouse embryo cells grown in vitro and derived from 2 strains NIH-Swiss and Af/Dm, were treated with polyoma virus preparations. Following the observation of the characteristic cytopathogenic effect the cells of these mouse embryos were examined in the electron microscope. Spherical particles of 270 A in diameter and of low electron density have been observed mostly in the nucleus, occasionally in the cytoplasm and outside the cells. Some of the particles show an internal structure, composed of a more dense center of 50 A in diameter, surrounded by an electron translucent outer zone with outlines of a limiting membrane. Similar particles have not been observed in uninfected control cultures which failed to hemagglutinate guinea pig red blood corpuscles, while the infected cultures hemagglutinated the red blood corpuscles in a high titer. The infected tissue culture fluids induced parotid gland neoplasms and mammary tumors in NIH-Swiss mice. Similar particles were found in the nuclei of the cells from these 2 types of tumors but much less frequently than in the cells of the infected mouse embryos.