Table 4.

Attack rate and incubation period in tg338 mice intracerebrally inoculated with WBC and PBMC prepared at different stages of the incubation period of sheep orally inoculated with PG127 scrapie^a

Donor and sample type	Result on dpi:
	30			60			90			130			190
	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)
D4
WBC	5.3 × 106	0/6	>250	1.2 × 107	0/6	>250	107	1/6	137	6.7 × 106	1/6	115	1.7 × 107	6/6	85 ± 3
PBMC	2 × 107	0/6	>250	2.8 × 107	1/6	115	2.3 × 107	0/6	>250	3.8 × 107	3/6	113 ± 14	8.1 × 106	6/6	81 ± 3
D5
WBC	7.4 × 106	0/6	>250	1.7 × 107	1/6	85	7.2 × 106	2/6	126, 134	7.2 × 106	6/6	112 ± 3	8.2 × 106	6/6	91 ± 7
PBMC	1.3 × 107	0/6	>250	2.8 × 107	0/6	116	9.2 × 106	0/5	>250	9.2 × 106	6/6	102 ± 8	1.2 × 107	6/6	86 ± 7
D6
WBC	2.7 × 106	0/6	>250	3.6 × 106	0/6	>250	4.4 × 106	0/5	>250	6.4 × 106	1/5	124	7.5 × 106	6/6	97 ± 5
PBMC	6 × 106	0/6	>250	5.3 × 106	0/6	>250	4.2 × 106	1/5	116	7.8 × 106	4/5	122 ± 15	6.3 × 106	6/6	85 ± 2
C1
WBC	8.3 × 106	0/6	>250	1.2 × 107	0/6	>250	9.6 × 106	0/6	>250	2.1 × 107	0/6	>250	9.3 × 106	0/6	>250

^aThree susceptible VRQ/VRQ sheep (identified as D4, D5, and D6) and one resistant ARR/ARR sheep (C1) were orally challenged with 2 g of brain homogenate (10^6.6 ID₅₀/g IC in tg338 mice). The three VRQ/VRQ sheep died 217, 206, and 217 dpi, respectively, whereas the ARR/ARR sheep is still alive (>1,500 days). At different time points of the incubation period, whole blood (150 to 180 ml) was collected from each donor and WBC and PBMC were prepared, counted, and pelleted. Each pellet was resuspended in 200 μl of a 5% glucose solution and inoculated intracerebrally into tg338 mice (n = 6; 20 μl per mouse). Mice then were observed until the occurrence of clinical signs or killed after 250 days postinoculation. Mice were considered positive when abnormal PrP deposition was detected in the brain. Incubation periods are shown as means ± SD, except when less than 50% of mice were positive. In those cases, incubation times of the positive mice are individually presented.