Western Blot Detection of Scrapie-associated Fibril Protein in Tissues outside the Central Nervous System from Preclinical Scrapie-infected Mice

We describe a method of sample preparation to detect scrapie-associated fibril (SAF) proteins in small amounts of scrapie-infected mouse tissues by Western blot analysis using an antiserum to a synthetic peptide that corresponds tothe N-terminal region of hamster prion protein. SAF proteins were efficiently detected in brain tissue by this procedure. The proteins were also detected in preparations from spleen and lymph node. SAF proteins were detected in brain samples at 24 weeks after intraperitoneal infection. Using spleen samples, the proteins were detected from mice in the preclinical stage (from 4 weeks after infection), clinical symptoms of scrapie were observed in some mice from 22 weeks after infection. Scrapie is a spongiform encephalopathy of sheep and goats. The scrapie agent has been transmitted experimentally between its natural hosts and from the natural hosts to experimental animals such as mice and hamsters (Dickinson, 1976). Infected animals do not develop detectable immune responses to the scrapie agent (Kasper et al., 1981; Kingsbury et al., 1981) and therefore there is still no way of identifying infected animals before the clinical stage. Unique fibrillary structures of 4 to 6 nm width and 50 to 500 nm length designated scrapie-associated fibrils (SAF) (Merz et al., 1981) or prion rods (Prusiner et al., 1982) were found in fractions from brains of scrapie-infected animals. The concentration of SAF was directly proportional to the titre of infectivity; that is SAF co-purified with the serapie agent (Bolton e