Transmission of atypical bovine prions to mice transgenic for human prion protein

Abstract

To assess risk for cattle-to-human transmission of prions that cause uncommon forms of bovine spongiform encephalopathy (BSE), we inoculated mice expressing human PrP Met129 with field isolates. Unlike classical BSE agent, L-type prions appeared to propagate in these mice with no obvious transmission barrier. H-type prions failed to infect the mice.

Figure 1

Protease-resistant prion protein (PrP^res) in the brains of human PrP transgenic mice infected with atypical or zoonotic bovine spongiform encephalopathy (BSE) agents. A) Representative Western blot analysis of PrP^res extracted (for detailed protocol, see 7) from brain homogenates of mice at terminal stage of disease or at end of lifespan after serial transmission of atypical (L-type and H-type) or classical BSE isolates. The amount of equivalent brain tissue loaded onto the gels was 0.01 mg (BSE; Fr3 isolate, 2nd and 3rd passage), 0.3 mg (L-type and 1st passage of BSE), and 10 mg (PrP^res-negative samples). Anti-PrP monoclonal antibody Sha31 was used for PrP^res detection. Immunoreactivity was determined by chemiluminescence. B) Ratio of diglycosylated and monoglycosylated PrP^res species in the brains of mice after serial transmission of L-type or BSE isolates (data plotted as means ± standard error of the mean). Primary passage of L-type isolates are represented as triangles (orange, It; blue, Fr7; green, Fr10; pink, Fr11) and BSE as squares (light blue, Fr3; red, Ge). Passages are indicated by unfilled symbols of the same color (solid line, second passage; broken line, third passage). The ratio was determined after acquisition of PrP^res chemiluminescent signals with a digital imager as previously described (7). Note the distinct glycoform ratio between L-type and BSE groups. It, Italy; Fr, France; Ge, Germany.

Figure 2

Representative histoblots in 4 different anteroposterior sections showing the distribution of disease-specific PrP^res deposits in the brains of tg650 mice infected with bovine spongiform encephalopathy (BSE) or L-type BSE. Panels A–D show infection with BSE (second passage of France 3). Panels E–H show infection with L-type BSE (first passage of France 7). Panels I–L show infection with L-type BSE (second passage of Italy). Panels M–P show brain sections of an age-matched, mock-infected mouse, euthanized while healthy at 700 days postinfection, for comparison. Note the differing aspect and distribution of PrP^res deposits between brain of mice infected with BSE and BSE-L (arrowheads). Assignment of the positive brain regions has been made according to a mouse brain atlas after digital acquisition.