PRNP and scrapie: To determine if the increased level of PrP in the cellular medium of NIH3T3-22L/F-MuLV cells correlated with an increase in scrapie infectivity in the medium, scrapie-susceptible murine neuroblastoma cells (N2a#58) were exposed to 100 K centrifugation pellets from the medium of either NIH3T3-22L or NIH3T3-22L/F-MuLV cells.