Kinetics of Abnormal Prion Protein in Blood of Transgenic Mice Experimentally Infected by Multiple Routes with the Agent of Variant Creutzfeldt–Jakob Disease

Transmissible spongiform encephalopathies (TSEs) or prion diseases are characterized by the accumulation in affected tissues of the abnormal prion protein PrP(TSE). We previously demonstrated PrP(TSE) in the blood of macaques experimentally infected with variant Creutzfeldt–Jakob disease (vCJD), a human TSE, months to years prior to clinical onset. That work supported the prospect of using PrP(TSE) as a blood biomarker to detect vCJD and possibly other human TSEs before the onset of overt illness. However, our results also raised questions about the origin of PrP(TSE) detected in blood early after inoculation and the effects of dose and route on the timing of the appearance of PrP(TSE). To investigate these questions, we inoculated vCJD-susceptible transgenic mice and non-infectable prion protein-knockout mice under inoculation conditions resembling those used in macaques, with additional controls. We assayed PrP(TSE) in mouse blood using the protein misfolding cyclic amplification (PMCA) method. PrP(TSE) from the inoculum cleared from the blood of all mice before 2 months post-inoculation (mpi). Mouse PrP(TSE) generated de novo appeared in blood after 2 mpi. These results were consistent regardless of dose or inoculation route. We also demonstrated that a commercial ELISA-like PrP(TSE) test detected and quantified PMCA products and provided a useful alternative to Western blots.