Table 1. Titration of sCJD and vCJD isolates in transgenic mice expressing the human or bovine prion protein*†.

Dilution	sCJD MM1 in tgHu			vCJD in tgBov
	Positive transmission in mice	Incubation period, d		Positive transmission in mice	Incubation period, d
Not diluted	6/6	186 ± 10		6/6	249 ± 2
10−1	6/6	213 ± 15		6/6	283 ± 15
10−2	6/6	240 ± 13		6/6	316 ± 21
10−3	6/6	263 ± 24		6/6	342 ± 10
10-4-	6/6	296 ± 26		6/6	453 ± 66
10−5	6/6	323 ± 29		4/6	499 ± 17
10−6	1/6	316		1/6	502
10−7	0/6	>650		0/6	>700
Infectious titer, ID50/g of brain (95% CI)	106.67 (106.33−106.97)			106.33 (105,84 −106.82)

*sCJD, sporadic Creutzfeld-Jakob Disease; tgHu, human PrP gene ;PrP, protease-resistant prion protein; vCJD, variant CJD; tgBov transgenic mice overexpressing bovine PrP, ID, infectious dose.
†Successive 1/10 dilutions of 10% brain homogenate (frontal cortex) from patients affected by vCJD and sCJD were injected intracerebrally to tgHu (n = 6) and tgBov (n = 6) mice, respectively. Those 2 patients were different from the 1 whose blood was tested in bioassay (Table 2). Mice were euthanized when they showed clinical signs of infection or after 650 days postinfection. Mice were considered infected when abnormal prion protein deposition was detected in the brain by western blot by using Sha31 monoclonal antibody, which recognizes amino acids 145–152 (YEDRYYRE) of the sheep prion protein. Infectious titers were estimated by the Spearman-Karber method (14).