Scrapie strains retain their distinctive characteristics following passages of homogenates from different brain regions and spleen.

The molecular basis of differences among scrapie strains is unknown. The prion theory posits that there are differences in the conformation of the host protease-resistant protein (PrP) molecules and that these differences are responsible for scrapie strains. A corollary of this theory is that the origin of host PrP variation resides in different neuronal cell types. To assess this concept, preparations from three brain regions (cerebrum, cerebellum and olfactory bulb) and from spleen were passaged in C57BL mice by intracerebral injection. After three passages of three scrapie strains in this manner, homogenates of each brain region and spleen were tested for several of the characteristics that distinguish the three strains: (1) the rank order of incubation periods in C57BL mice, (2) induction of obesity in SJL mice and (3) comparative incubation periods in mice with three genotypes for the scrapie incubation period marker. Analysis revealed that virtually all of the criteria that distinguished the three strains prior to passages of the three brain regions and spleen were retained after this series of passages. This finding argues against cellular-based PrP differences providing a basis for strain specificity.