The method for production of the PrP2/2 mice was described in detail elsewhere (43, 44). The cultures were incubated at 37°C in a 5% CO2/95% air incubator in Dulbecco’s modified
Eagle’s medium supplemented with 10% fetal bovine serum, 100 U/ml penicillin, and 100 µg/ml streptomycin (feeding medium).