Table 6.
Intracerebral inoculation of tg338 mice with PK-treated or untreated PG127 scrapie brain homogenate and WBC from PG127-infected VRQ/VRQ sheepa
| PK treatment status | Results for PG127 brain homogenate at dose (ID50/IC tg338) of: |
Results for WBC from sheep: |
||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 103 |
102 |
10 |
D7 |
D8 |
D9 |
D10 |
D11 |
|||||||||
| No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | No. of mice positive for abnormal PrP | Length of incubation (days) | |
| Untreated | 6/6 | 83 ± 6 | 6/6 | 102 ± 5 | 6/6 | 122 ± 14 | 5/5 | 111 ± 13 | 6/6 | 109 ± 5 | 6/6 | 98 ± 7 | 6/6 | 101 ± 3 | 6/6 | 99 ± 4 |
| Treated | 6/6 | 87 ± 3 | 6/6 | 107 ± 10 | 5/6 | 127 ± 18 | 6/6 | 123 ± 17 | 5/6 | 121 ± 16 | 6/6 | 107 ± 8 | 6/6 | 117 ± 15 | 6/6 | 111 ± 12 |
Aliquots of PG127 scrapie brain homogenate (previously titrated in tg338 mice) and WBC homogenate prepared from five susceptible VRQ/VRQ sheep (identified as D7, D8, D9, D10, and D11) orally challenged with the same scrapie agent (collected 224 dpi) were prepared. The blood donors died at 228, 248, 256, 242, and 244 dpi, respectively, and classical scrapie occurrence was confirmed by histopathology (vacuolar changes in the central nervous system) and the detection of abnormal PrP deposits in the central nervous system and lymphoid tissues. Aliquots of the brain material and WBC homogenate were submitted to PK digestion under standard conditions (4 μg of PK per mg of protein for 2 h at 37°C) that allow the complete digestion of PrPC. Aliquots of both PK-treated and untreated material then were inoculated in tg338 mice (n = 6; 20 μl per mice). Mice then were observed until the occurrence of clinical signs or killed after 200 dpi. Mice were considered positive when abnormal PrP deposition was detected in the brain. Incubation periods are presented as means ± SD except when less than 50% of mice were positive. For brain material dilutions, the infectivity amount (number of ID50/IC in tg338) inoculated in each mouse is indicated.