Overexpression of PrP^C does not influence the transport of sCJD-PrP^Sc across Caco-2 monolayers. Lysates of M17 neuroblastoma cells, Caco-2 cells, and transfected Caco-2^PrP cells were immunoblotted with 3F4 to assess the level of PrP expression. A, Transfected Caco-2^PrP expresses significantly more PrP compared with M17 and nontransfected Caco-2 cells (lane 3 vs lanes 1, 2). B, Quantitative estimation shows 2.5- and 1.5-fold PrP expression in Caco-2^PrP cells compared with nontransfected Caco-2 and M17 cells, respectively [lane 3 vs lanes 1 (^*p < 0.05; n = 3) and lane 3 vs lane 2 (^Δp < 0.01; n = 3)]. C, Transport of PK-resistant PrP^Sc across Caco-2 and Caco-2^PrP cell monolayers was measured as in Figure 2. There is no significant difference in the amount of PrP^Sc transported to the BL chamber of Caco-2^PrP cells compared with nontransfected Caco-2 cells (lanes 3, 4 vs lanes 1, 2). D, Quantitative estimation shows transport of 10 and 11.2% of PrP^Sc to the BL chamber of Caco-2 and Caco-2^PrP cell monolayers, respectively. Each bar represents the mean ± SD of three experiments. ^*p < 0.05.