Fast and ultrasensitive method for quantitatingprion infectivity titre

摘要

Bioassay by end-point dilution has been used for decades for routine determination of prioninfectivity titre. Here we show that the new protein misfolding cyclic amplification with beads(PmCAb) technique can be used to estimate titres of the infection-specific forms of the prionprotein with a higher level of precision and in 3–6 days as opposed to 2 years, when comparedwith the bioassay. For two hamster strains, 263K and ssLoW, the median reactive dosesdetermined by PCmAb (PmCAb50) were found to be 10~(12.8) and 10~(12.2) per gram of brain tissue,which are 160- and 4,000-fold higher than the corresponding median infectious dose (ID50)values measured by bioassay. The 102- to 103-fold differences between ID50 and PmCAb50values could be due to a large excess of PmCAb-reactive prion protein seeds with little or noinfectivity. Alternatively, the differences between ID50 and PmCAb50 could be due to higherrate of clearance of infection-specific prion protein seeds in animals versus PmCAb reactions.A well-calibrated PmCAb reaction can be an efficient and cost-effective method for theestimation of infection-specific prion protein titre.