In order to determine if rPrP-res could induce the conversion of mammalian PrPC into PrPSc either acutely or persistently, the scrapie susceptible septal neuron cell line SN56 [31], [45] was plated at different densities and exposed to either 15 ng of rPrP-res, a 1% brain homogenate from mice infected with 22L scrapie, or cell-culture medium alone. Here, PRNP is linked to scrapie.