Fig. 3.
A compares the human vCJD agent and the hamster 263k agent inoculated in mice of different genotypes at primary and progressive serial passages. All vCJD inoculated mice showed an incubation time that rapidly falls, and then levels off between passages 2 and 3; (the 2nd passage days are the mean of a3 and a6 mouse recipients). In contrast to the sudden drop in incubation time in the 2nd passage of vCJD, the 263K scrapie agent shows only a small decrease in the 2nd passage. Even after 4 passages, the 263K scrapie incubation time is still very prolonged at 300 days in both CD-1 and Tga20 mice in stark contrast to vCJD-Tga20 mice. Only the NZW mice infected with the 263K scrapie agent displayed significantly shorter incubation times than parallel inoculated CD-1 mice. These agent differences in the same host genotypes demonstrate host-agent interactions that cannot be determined by PrP sequence or amount. Figs. 3B and 3C show Western blot PrP bands from representative brain samples in the different mouse genotypes; the agent strain and serial passage are labeled. Lanes digested with PK (+) as well as relative loads in each lane are also indicated. Only the vCJD samples showed the lower 19kd band. The very different sCJD (SY), Japanese CJD (FU), and 263k scrapie agents all show the same PrP pattern in infected mouse brain, and could not be distinguished from each other on this basis.