PRNP and Creutzfeldt Jacob disease: Western blotting for protease-resistant PrP (PrPRes), which is an indicator of propagation and accumulation of infectious prions, showed increased detection in the unseeded CJD-infected compared with the NPC-seeded CJD-infected COs (Fig. 4A & B, uncropped blots are shown in Additional file 1: Fig. S6).