Figure 3.

Detection of immune response in sera of mock- and scrapie-inoculated grafted and control mice. Immunoblots containing purified recombinant PrP (lane r), brain homogenate derived from Prnp^o/o (lane o) and tg20 (lane +) mice were incubated with sera from mock- and scrapie-inoculated grafted and control mice (dilution 1:100), respectively, and visualized by enhanced chemiluminescence. Presence of PrP-specific antibodies in the serum is indicated by 27- to 30-kDa bands in lane r and by a cluster of bands present in lane + but absent from lane o. tg20-engrafted Prnp^o/o mice developed a strong humoral immune response to PrP both before (a) and after (b) inoculation with scrapie prions, whereas engrafted tg33 mice (Prnp^o/o, lck-PrP) did not develop antibodies to PrP even after intraocular inoculation (c and d). (e–g) As positive controls, we used both polyclonal antibody generated in Prnp^o/o mice (KO2) and polyclonal rabbit antiserum 1B3 to mouse PrP (24).