Figure 2.

Histoblot analysis of PrP expression. Frozen sections from brains engrafted with PrP-overexpressing neuroectodermal tissue were mounted on nitrocellulose, and PrP was displayed immunochemically without (a, c, and e) or with (b, d, and f) previous protease digestion (25). Arrows pinpoint the position of grafts. Intracerebrally infected grafts (c) consistently show stronger total PrP immunoreactivity than uninfected (a) and intraocularly inoculated (e) grafts. Protease-resistant PrP was formed only in intracerebrally infected PrP^C-expressing grafts (d) and migrated into the surrounding structures as described earlier (19). Uninfected (b) and intraocularly inoculated (f) mice did not accumulate protease-resistant PrP (PrP^Sc). As previously reported (19), myelinated structures show faint homogeneous background staining even in noninoculated Prnp^o/o mice. no inf., No infection; d, days; i.c., intracerebrally infected; i.o., intraocularly inoculated.