We next assessed the expression of PrP from exosome lysates by Western blotting using the anti-PrP mAb P4 (R-Biopharm), routinely used due to its high sensitivity and specificity in confirmatory Western blotting assays for active scrapie outbreak surveillance, as described previously (Arsac et al., 2007; Baron et al., 2007; Harmeyer et al., 1998; Mazza et al., 2010). The gene discussed is PRNP; the disease is scrapie.