Protease-resistant prion protein in brain and lymphoid organs of sheep within a naturally scrapie-infected flock

The hallmark of transmissible spongiform encephalopathies (TSE), such as scrapie in sheep, is the accumulation in tissues of an insoluble and protease resistant form (PrPres) of the cellular prion protein. In this study, we evaluated whether the diversity in both the clinical pattern and the PrP genotypes of scrapied sheep from the same flock was connected with different levels and/or glycoform patterns of the PrPres in the brain and lymphoid organs of the animals. Whereas the PrPres levels in spleen, lymph nodes and tonsils from sheep of different PrP genotypes and clinical status appeared comparable, they were highly variable in brain, particularly in the brain stem and the cerebellum. PrPres was only detected in sheep bearing at least one VRQ allele, including three asymptomatic sheep and the highest PrPres load was found in the cerebellum of VRQ/VRQ animals. All together, levels of PrPres in brain did not necessarily correlate with the severity of the clinical disease but might depend on the PrP genotype of the animals. Different brain regions from a given sheep displayed a similar glycopattern of PrPres, whereas the apparent molecular sizes of the unglycosylated and diglycosylated forms of the protein differed between brain and lymphoid tissues. We did not find any notifiable differences in the glycopattern of PrPres in brain from sheep of different PrP genotypes or different clinical status and this PrPres glycotype was also similar to that found in brain from four cattle BSE.