PRNP and nervous system disorder: Intracerebral inoculation of brain homogenates from sick ki-3F4-FFI mice induced neurological disease in ki-3F4-WT mice expressing 3F4-tagged WT PrP, and in Tga20 mice, but not in nontransgenic mice [41], arguing that homology between mutant PrP and the recipient’s PrPC at residues 108 and 111 (which constitute the 3F4 epitope), or overexpression of untagged PrP by the recipient mice, is required for disease transmission.