Standard Scrapie Cell Assay of swa-resistant and swa-dependent RML prions propagated in the presence or absence of swa.

<p>AMO10 and 2E4 cells were infected with RML prions, cultured in the presence of swa, and prions secreted into the conditioned medium (CM) were concentrated (CCM) and used to infect fresh batches of cells, also in the constant presence of swa. This cycle was repeated once more; the infected cells were cultured in the presence of swa for an extended period of time and then divided into two batches, of which one continued to be propagated in the presence of swa for nine splits while the other was propagated in parallel in the absence of swa (see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003158#ppat-1003158-g002" target="_blank">Figure 2B, C</a>). CCM from these cultures was then analyzed by the SSCA on PK1 cells in the absence (blue line) or presence (red, dashed line) of swa. RIs are the reciprocals of the dilutions required to yield 1000 PrP^res positive cells per 20000 cells. Q_swa = RI_cell/RI_cell+swa indicates the inhibitory effect of swa. <b>A.</b> Swa-resistant AMO10-derived prions that were constantly propagated in the presence of swa (<13>) remained swa resistant, but reverted to semi-resistance when propagated for nine splits in the absence of swa (<12>). <b>B.</b> Swa-dependent 2E4-derived prions remained swa dependent whether propagated for 9 splits in the presence of swa (<16>) or in its absence (<17>). <b>C.</b> Swa-sensitive, brain-derived RML prions. Q_swa for RML^brain was unusually high in this assay and that of <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003158#ppat-1003158-g005" target="_blank">Figure 5B</a>, leading to the low Q_rel values shown in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003158#ppat-1003158-t001" target="_blank">Table 1</a>.