Effect of cellular components or detergent present in the gradient top fractions on infectivity of the LA21K PK-resistant PrP<sup>Sc</sup>–richest fractions.

<p>LA21K PK-resistant PrP<sup>Sc</sup>-richest fractions 11 to 13 (fr11–13) were mixed together and incubated (vol∶vol) with either the upper fractions 1 to 3 (fr1–3) of a gradient made with uninfected <i>tg338</i> mouse brain (NI) or with dodecyl maltoside (DDM) at 2% (wt/vol.) final concentration. The specific influence of sarkosyl was not tested since the gradients were prepared in a solution containing this detergent (see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000859#s4" target="_blank">methods</a>). The resulting mixture was inoculated to recipient mice. Their relative infectious titer was estimated by an incubation time bioassay, and compared to that of the fractions 1 to 3 of the same gradient pooled and diluted in 5% glucose (vol∶vol). The infectious titers are expressed as relative infectious doses as in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000859#ppat-1000859-g003" target="_blank">Figure 3</a>.</p>