Three different host-PrP/strain combinations were studied: the 127S cloned scrapie prion strain in ovine PrP tg338 transgenic mice29, the 139A cloned mouse scrapie prion strain in murine PrP tga20 mice42 and the vCJD cloned human prion strain in human PrP tg650 mice43,44. Here, PRNP is linked to scrapie.