Prions of Ruminants Show Distinct Splenotropisms in an Ovine Transgenic Mouse Model

BACKGROUND Transmissible agents involved in prion diseases differ in their capacities to target different regions of the central nervous system and lymphoid tissues, which are also host-dependent. METHODOLOGY/PRINCIPAL FINDINGS Protease-resistant prion protein (PrP(res)) was analysed by Western blot in the spleen of transgenic mice (TgOvPrP4) that express the ovine prion protein under the control of the neuron-specific enolase promoter, after infection by intra-cerebral route with a variety of transmissible spongiform encephalopathies (TSEs) from cattle and small ruminants. Splenic PrP(res) was consistently detected in classical BSE and in most natural scrapie sources, the electrophoretic pattern showing similar features to that of cerebral PrP(res). However splenic PrP(res) was not detected in L-type BSE and TME-in-cattle, or in the CH1641 experimental scrapie isolate, indicating that some TSE strains showed reduced splenotropism in the ovine transgenic mice. In contrast with CH1641, PrP(res) was also consistently detected in the spleen of mice infected with six natural "CH1641-like" scrapie isolates, but then showed clearly different molecular features from those identified in the brains (unglycosylated PrP(res) at approximately 18 kDa with removal of the 12B2 epitope) of ovine transgenic mice or of sheep. These features included different cleavage of the main PrP(res) cleavage product (unglycosylated PrP(res) at approximately 19 kDa with preservation of the 12B2 epitope) and absence of the additional C-terminally cleaved PrP(res) product (unglycosylated form at approximately 14 kDa) that was detected in the brain. CONCLUSION/SIGNIFICANCE Studies in a transgenic mouse model expressing the sheep prion protein revealed different capacities of ruminant prions to propagate in the spleen. They showed unexpected features in "CH1641-like" ovine scrapie suggesting that such isolates contain mixed conformers with distinct capacities to propagate in the brain or lymphoid tissues of these mice.