IFNB1 and Creutzfeldt Jacob disease: In SEP cells the 68-fold increase in IFN-β mRNA was provoked only by the highest titer 33-day re-arrested cells, not low titer persistently infected cells, and FU-CJD proliferating and arrested cells with low infectivity, but visible PrP-res bands, produced no change in IFN-β mRNA.