Scrapie-infected spleens: analysis of infectivity, scrapie-associated fibrils, and protease-resistant proteins.

Scrapie-associated fibrils (SAF) and protease-resistant proteins (PrP) were isolated from spleens and brains of clinical animals (mice and hamsters) from three scrapie agent-host strain combinations, and their concentrations were compared with infectivity levels. The spleens of infected animals contained lower levels of infectivity, PrP, and SAF than did brains. Regardless of the route of infection, both SAF and infectivity were detected in spleen before brain. Infectivity increased in brains and spleens of 139A-infected mice before the detection and increase in SAF, suggesting that the synthesis of SAF and PrP may not be the limiting factor in agent replication. In contrast to those in ME7- and 263K-infected animals, the Western blot profiles for PrP from brain and spleen of 139A-infected mice exhibited distinct differences. Results indicate that SAF and PrP found in the spleens are both organ- and scrapie strain-specific.