Figure 3. High splenic prion titers at early stages after prion infection.

Groups of four 129/Sv×C57BL/6 and Prnp ^0/0 mice were inoculated i.p. with 100 µl 1% (w/v) RML I6200 (9.3 log LD₅₀ units/g brain). At various time points after inoculation spleens and mesenteric lymph nodes were dissected and prion titers and PrP^Sc levels determined. (A) Infectious titers of spleens (closed circles) and mesenteric lymph nodes (open circles) of 129/Sv×C57BL/6 mice. To account for residual inoculum infectious titers of spleens of RML-inoculated Prnp^0/0 mice (closed square) were determined. Prion titers were estimated by a GLM with binomial family complementary log-log link. Data represent mean infectious titers ± SD of four repeats. (B) Spleen homogenates were analyzed for levels of PK-resistant PrP (PrP^Sc) by Western blotting after NaPTA precipitation as described in Materials and Methods. (C) Detection of PrP^Sc-positive deposits in spleens of prion-infected 129/Sv×C57BL/6 mice. At 3 dpi less than 5% of the total number of follicles was weakly PrP^Sc-positive. An increase in the number of immunopositive follicles, but overall a weak immunostaining for abnormal PrP was observed at 7 dpi. At 14 dpi, the number of positive follicles was similar, but the staining intensity increased to ‘moderate’ in two animals. At 30 dpi 90% of lymphoid follicles showed moderate or strong labeling. The scale bar corresponds to 100 µm (20 µm in the inserts).