In vitro studies with the scrapie agent.

Persistent infection with the scrapie agent has been established in L cells. The agent was propagated in homogenates of the cell line designated L-S. The L-S cells showed slower growth rate and morphological changes like pycnosis of nuclei and vacuolization of their cytoplasm. Cytogenetic analysis revealed rearrangement of chromosomes in L-S cells. In the course of passaging the number of cells with the characteristic marker chromosome decreased. Along with this cells were found with deletion of one arm of the marker chromosome. In addition, 3 new marker chromosomes were detected in infected cells, suggesting the influence of the scrapie agent on cytogenetic processes in scrapie-carrier cultures. The infectious activity of nucleic acids isolated from L-S cells was determined in BALB/c mice inoculated with untreated, DNase-treated and pronase-treated nucleic acid preparations. A slightly decreased infectious activity has been noted after DNase and pronase treatments.