FIGURE 4.

Distribution of “rPrP^Sc granules” outside and inside cells at various times after infection with RML or 22L, in the absence or presence of swa. PK1 cells were grown for 3 days with or without 2 μg of swa/ml and exposed to a 10⁻³ dilution of RML or 22L brain homogenate for various times. At 4, 24, and 48 h post-infection, cells were digested with thermolysin to remove PrP^C, biotinylated to visualize the cell surface, fixed, and fluorescently stained for rPrP^Sc (green) and biotin (blue). A thick layer of biotinylated material coated the surface of infected cells, as compared with a faint layer on uninfected cells. External and internal granules of rPrP^Sc were quantified by confocal imaging (supplemental Table S1). Relatively few rPrP^Sc granules were internalized, but uptake was not affected by swa. White bar, 10 μm.