Type C oncornavirus isolation studies in systemic lupus erythematosus. I. Attempted detection by isopycnic sedimentation of 3H-uridine-labelled virions.

Type C oncornavirus isolation was attempted from cell cultures of tissues from 7 patients with systemic lupus erythematosus. Detection was based on the characteristic sedimentation of 3H-uridine-labelled virions at a density of 1-16 g/ml. Cultures positive by this method were negative by two other criteria for type C viruses: characteristic virions by electron microscopy and the viral enzyme RNA-directed DNA polymerase. The positive results were probably due to cellular damage by prolonged radiolabelling, with release of organelles containing labelled RNA sedimenting at the same density as type C viruses.