Brief Communication: Small, Virus-Like Particles Detected in Bovine Sera by Electron Microscopy2

Abstract

Twenty-two samples of bovine sera were examined by ultracentrifugation and electron microscopy for the presence of virus-like structures. All samples, including those of “virus-screened” fetal bovine serum (FBS) and agamma calf serum, had such structures. When pellets of FBS were resuspended in buffer and spun to equilibrium on a continuous 1.1–1.3 glcc CsCI gradient, virus-like particles identical to tJ:tose seen in the FBS pellets were observed in fractions with a density of 1.16–1.18 g/cc. In samples of FBS used to support the growth of 2 human Iymphoblastoid cell lines from patients with acute infectious mononucleosis, peak incorporation of radioactive uridine was observed in the 1.17–1.18 glcc densities; fractions with the highest radioactivity also contained the most small, virus-like particles.