Properties of a Transmissible Agent Capable of Inducing Marked DNA Degradation and Thymine Catabolism in a Human Cell.

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Abstract
The appearance of a transmissible cytopathic agent during the first blind passage of pooled human “liver” cultures previously infected with 4 acute infectious hepatitis bloods is described. The infectivity of this agent in the “liver” culture was cell-associated. The infective degenerated “liver” cells retained their infectivity for at least 16 weeks at 4°C and 8 weeks at 36°C. Heating for 1 hour at 56°C failed to destroy completely the infectivity of infected mouse fibroblasts. One cycle of freeze-thawing or homogenizing, however, abolished the infectivity with occasional exceptions. Characteristic cytopathology consisted of cytoplasmic granularity, cell rounding followed by diminution of cell volume leading to morphologic picture of shrunken cells. During an intermediate stage of degeneration, characteristic intranuclear basophilic globules were seen regularly; the globules were Feulgen positive. The established cell line was more susceptible to the destructive action of this agent than primary cells. Preliminary immunological study failed to establish the identity of this agent.