Fig. 2. Elongation and structural features of fibril-like PrP^d aggregates and crypticity of PrP^d epitopes.

A Time-dependent growth of 5B2-positive PrP^d fibrils in primary astrocytes of FVB-wt (Prnp^+/+), but not in those of FVB-ko (Prnp ^-/-) mice, following infection with RML. B Lengths of fibril-like PrP^d aggregates in FVB-wt versus FVB-ko mice. Significance levels for time-dependent fibril growth in FVB-wt (Prnp^+/+) mice and for FVB-wt versus FVB-ko were assessed from 2 independent experiments with at least 30 replicates per group using Kruskal–Wallis test with Dunn’s multiple comparisons with **p < 0.001. The statistical difference in rod length between FVB-wt versus FVB-ko mice at 3 weeks was determined by unpaired Mann–Whitney U Test; ** denotes a p-value < 0.001. For definition of boxplot elements see “Methods” section. C SIM images of fibril-like PrP^d aggregates at the ECM of prion-infected S7 cells, cultured according to “standard TC protocol” in “Methods” section, labelled with 5B2 and 6D11 after guanidinium thiocyanate (GTC) treatment. Magnified area (a) denoted by dashed box. D Identification of cryptic epitopes in PrP^d-bearing cells. Prion-infected S7 cells were incubated with anti-PrP mAbs in absence and presence of GTC. For complete image data set see Supplementary Fig. 4. Scale bars are 5 µm. E Summary of anti-PrP mAb binding to PrP^d aggregates under native (-GTC) and denaturing (+GTC) conditions with corresponding PrP domains (for abbreviations of PrP regions see Supplementary Fig. 4). F Detection of intracellular 5B2-positive PrP^d aggregates following a 16 h incubation with 6 nM bafilomycin A1 (BafA1) and 16 mM ammonium chloride (NH₄Cl), respectively. Arrows denote intracellular 5B2-positive PrP^d aggregates. G Model depicting cryptic, exposed and putative PrP-cleavage sites, respectively (modified from Rouvinski et al.¹⁴). Source data are provided as a Source Data file.