Table 3.

Attack rate and incubation period in tg338 mice intracerebrally inoculated with WBC and PBMC prepared at different stages of the incubation period in natural classical scrapie VRQ/VRQ sheep^a

Donor and sample type	Result for samples from incubation day:
	90			120			180			270			360
	No. of cells inoculated/mouse	tg338 transmission		No. of cells inoculated/mouse	tg338 transmission		No. of cells inoculated/mouse	tg338 transmission		No. of cells inoculated/mouse	tg338 transmission		No. of cells inoculated/mouse	tg338 transmission
		No. of mice positive for abnormal PrP	Incubation time (days)		No. of mice positive for abnormal PrP	Incubation time (days)		No. of mice positive for abnormal PrP	Incubation time (days)		No. of mice positive for abnormal PrP	Incubation time (days)		No. of mice positive for abnormal PrP	Incubation time (days)
D1
WBC	3 × 106	0/6	>750	1.9 × 106	2/6	460, 658	1.8 × 106	5/6	529 ± 125	3.5 × 106	5/5	533 ± 54	5.8 × 106	5/5	543 ± 66
PBMC	8.5 × 105	0/6	>750	1 × 106	1/6	623	1 × 106	3/6	563, 653, 721	2.2 × 106	6/6	732 ± 64	1.6 × 106	5/5	594 ± 84
D2
WBC	3.4 × 106	0/6	>750	1.9 × 106	1/6	425	1.2 × 106	5/5	612 ± 133	4.8 × 106	6/6	605 ± 139	3.7 × 106	5/5	516 ± 101
PBMC	7.7 × 105	1/6	627	1.1 × 106	4/6	616 ± 70	8.1 × 105	5/6	570 ± 114	2.4 × 106	6/6	570 ± 38	1.5 × 106	6/6	641 ± 27
D3
WBC	2.6 × 106	0/6	>750	2.3 × 106	5/5	661 ± 67	5.1 × 106	5/6	646 ± 114	4.2 × 106	6/6	629 ± 98	6.7 × 106	6/6	585 ± 94
PBMC	4.7 × 105	1/6	783	1.2 × 106	4/5	691 ± 117	8.5 × 105	5/6	689 ± 77	2.7 × 106	6/6	678 ± 55	1.9 × 106	6/6	644 ± 89

^aBlood samples (100 ml) from three VRQ/VRQ donors (identified as D1, D2, and D3) born and raised in the INRA Langlade flock were taken at different time points of the incubation phase. The three donors died at 781, 728, and 789 days, respectively. After death, natural 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. After preparation, cells were counted and pelleted. Each pellet was resuspended in 200 μl of a 5% glucose solution before grinding. Each homogenate was inoculated intracerebrally into tg338 mice (n = 6; 20 μl per mouse). Equivalent numbers of cells inoculated into each mouse are indicated. Mice then were observed until the occurrence of clinical signs or killed after 750 days postinoculation. Mice were considered positive when abnormal PrP deposition was detected in the brain. Incubation periods are presented as means ± standard deviations (SD), except when less than 50% of mice were positive. In those cases, the incubation times of the positive mice are individually presented.