PRNP and scrapie: After four successive rounds of PMCA, no proteinase K (PK)-resistant abnormal PrP could be detected by Dot blot or Western blot in any sample, whereas the brain homogenate from scrapie sheep included on each run to check the amplification performance displayed positivity in reactions seeded with a 10−7–10−8 dilution, suggesting that the presence of PrPres in plasma-derived sEVs, if any, is at least 8 log10-fold lower than that detected in sheep brains (Figure S1).