Change in the molecular properties of CH1641 prions after transmission to wild-type mice: Evidence for a single strain.

Aim: CH1641 was discovered in 1970 as a scrapie isolate that was unlike all other classical strains of scrapie isolated so far. We performed bio-assays of CH1641 in mice in order to further characterise this specific isolate.

Methods: We inoculated the original CH1641 isolate into ovine and bovine prion protein (PrP) transgenic mice as well as wild-type mice. In addition, we performed cross- and back passages between the various mouse lines to examine if one identical prion strain was isolated in all mouse lines or whether multiple prion strains exist in CH1641.

Results: We report the first successful transmission of CH1641 to wild-type RIII mice and via RIII mice to wild-type VM mice. Unexpectedly, analysis of the protease-resistant prion protein (PrP^res ) in wild-type mice showed a classical scrapie banding pattern differing from the banding pattern of the original CH1641 isolate. Cross- and back passages of CH1641 between the various mouse lines confirmed that the same prion strain had been isolated in all mouse lines.

Conclusions: The CH1641 isolate consists of a single prion strain but its molecular banding pattern of PrP^res differs between wild-type mice and PrP transgenic mice. Consequently, molecular banding patterns of PrP^res should be used with caution in strain typing since they do not solely depend on the properties of the prion strain but also on the host prion protein.