A limited population of 87V PrPSc aggregates is preferentially taken up and rapidly disaggregated by CF10 cells. (A and B) Brain homogenates from an 87V scrapie-infected mouse (A) or cell lysates from CF10 cells exposed to the 87V brain homogenate for up to 24 h (B) were fractionated by discontinuous sucrose gradient centrifugation. Eleven fractions (fractions 1 to 11) were collected from the top of the gradient, digested with PK, and analyzed by Western blotting using anti-PrP mouse monoclonal antibody 6D11. In panels A and B, molecular mass markers in kilodaltons are indicated on the left. (C) Quantitation of the relative amount of PrPSc in individual sucrose gradient fractions derived from either the 87V scrapie-infected brain homogenate or CF10 cell lysates after exposure to the 87V scrapie brain homogenate for 2 h, 8 h, and 24 h. The values represent averages ± standard errors of the percentage of PrPSc in each fraction for 3 experiments.