PRNP and Creutzfeldt Jacob disease: Since homology between PrPSc in the inoculum and PrPC in the recipient mice may increase the chance of disease transmission,20,21 the brain homogenates from Tg(FFI) and Tg(CJD) mice expressing 3F4-tagged mutant PrP were also inoculated into Tg(WT-E1) mice overexpressing 3F4-tagged moPrP WT, and into Tg mice, which express low levels of 3F4-tagged moPrP D177N and do not spontaneously become ill.6,8