Figure 5

Measuring the infectivity of RML prion rods bound to mica supports for AFM. (a) Schematic diagram showing how prion infectivity of purified RML PrP rods was measured in cell culture. Identical aliquots of purified RML prion rods were either applied to cells as solution or dried onto sections of mica before application of cells. Infectivity was measured using methods based upon the Scrapie Cell Assay⁴⁵. (b) Levels of infectivity (spot count) plotted against the concentration of purified RML prion rods (0.001–1x relative concentration range) after drying onto mica (green) or applied to cells in-solution (red). Data points show mean spot count ± SEM n = 18; 3 independent experiments using three different preparations of purified RML PrP rods. 1x relative concentration of RML prion rods in this experiment corresponds to about 2,500 intracerebral LD₅₀ units in Tg20 mice. Recombinant PrP fibrils or purified P4 fractions from normal mouse brain showed no detectable prion infectivity when applied either in-solution or after drying onto mica.