Early appearance but lagged accumulation of detergent-insoluble prion protein in the brains of mice inoculated with a mouse-adapted Creutzfeldt-Jakobdisease agent

1. To elucidate mechanisms for the generation of the detergent-insoluble, p roteinase K-resistant prion protein (PrPSc) from the detergent-soluble, pro teinase K-sensitive PrP (PrPC) and the replication of the infectious agent in prion diseases, we followed the kinetics of detergent-insoluble PrP and PrPSc levels, infectious liters, and associated pathological changes in the brains of mice inoculated with a mouse-adapted Creutzfeldt-Jakob disease a gent. 2. Prp(Sc) in brain homogenate and detergent-insoluble PrP enriched by two- cycle ultracentrifugation were detected by immunoblotting and their relativ e amounts were estimated according to a standard curve plotted between the amount of PrP and signal intensity on immunoblotting. The titer of infectiv ity was determined by the incubation periods of mice inoculated with the un -fractionated homogenate on the basis of a standard curve plotted between t he titer and incubation period. 3. Detergent-insoluble PrP became detectable 4 weeks postinoculation (p.i.) well before the detection of PrPSc. The low level of detergent-insoluble P rP continued until dramatic accumulation occurred at 14 weeks p.i., correla ting well with the accumulation of PrPSc and development of pathological ch anges. The infectious titer was undetectable at 4 weeks p.i. and its logari thmic increase occurred 10 weeks p.i. preceding the logarithmic accumulatio n of PrPs. 4. The lag time of detergent-insoluble PrP accumulation and the discrepancy between infectious titers and PrPs observed during the early period after inoculation suggest a slow and rate-limiting step for the detergent-insolub le PrP to become the infectious agent-associated PrPSc.