The PrP^Sc-ferritin complex coimmunoprecipitates with anti-ferritin and anti-PrP antibodies. Mock-treated or DE-treated NH and CJDH samples were immunoprecipitated (I.P.) with anti-ferritin or 8H4 antibodies, and coimmunoprecipitated proteins were detected by immunoblotting with specific antibodies. A, I.P. with anti-ferritin, followed by probing with 3F4, shows no coimmunoprecipitation of PrP^C from NH and NH-DE samples (lanes 1, 2). In contrast, full-length PrP^Sc and a significantly greater amount of protease-resistant PrP^Sc from CJDH and CJDH-DE immunoprecipitate with anti-ferritin (lanes 3, 4). Reprobing of the same membrane with anti-ferritin shows the H and L chains of ferritin migrating at 21 and 20 kDa in both NH and CJDH samples (lanes 5, 7). The H chain comigrates with the L chain at 20 kDa after DE treatment of NH and CJDH (lanes 6, 8). The identity of additional ferritin-immunoreactive bands in the CJDH-DE sample is unclear (lane 8, ^*). I.P. of CJDH-DE with 8H4, followed by probing with 3F4, shows PrP^Sc bands similar to the ones detected with anti-ferritin I.P. (compare lanes 9, 4). Reprobing with anti-ferritin reveals the 20 kDa ferritin band (lane 10). Silver staining of proteins immunoprecipitated with anti-ferritin or 8H4 shows bands comigrating with ferritin at 20 kDa and several other minor species (lanes 11-14). Note that the IgG band in 8H4 immunoprecipitates is negligible because the antibody was conjugated to protein A beads. A similar conjugation of anti-ferritin reduced the amount of coimmunoprecipitated PrP^Sc significantly. B, No PrP bands are detected in the absence of primary antibody either with protein A beads or BSA-coated protein A beads (lanes 1-8).