Characterization of scrapie infection in mouse neuroblastoma cells.

A mouse neuroblastoma cell line was successfully infected with scrapie agent. Agent derived from infected mouse brain or spleen infected cultures. However, agent from infected hamsters did not infect mouse cell cultures, suggesting that species specificity influenced the infection process in vitro. Positive cultures supported scrapie replication for as many as 47 passages in vitro. Agent was shown to be cell-associated and between 631 and 7943 unselected culture cells constituted 1 mouse LD50. However, fluctuation analysis indicated that only one of 144 cells in unselected cultures was actually infected. Thus, agent was confined to a small percentage of cells and only 4.4 to 55.1 positive cells were needed to confer a mouse LD50.