Detection of characteristic proteinase K resistant three isoforms of PrPScfrom hemal nodes and retropharyngeal lymph nodes by western blot assays. Western blot analysis was performed with retropharyngeal lymph node (A) and abdominal hemal node (B) homogenates prepared from experimentally and naturally scrapie-infected sheep. Lanes 1 – 6, experimentally (blood transfusion recipient) scrapie-infected sheep (ID 4489, 4493, 4494, 4495, 4496, and 4498 respectively); lanes 7 -9 naturally scrapie-infected sheep (ID 3349, 3779 and 3781 respectively). Lane 10, scrapie uninfected control sheep (ID 4492). To concentrate PrPSc, proteinase K treated samples were incubated with sodium phosphotungstic acid and PrPSc was detected using F99/97.6.1 mAb. The positions of the molecular mass markers (in kDa) are shown to the left of the blots.