Transmission of Scrapie by Steel-surface-bound Prions

Table 3 Infectivity of prion-coated wire after exposure to brain homogenate, PBS or brain of uninfected mice

Inoculation	Sick/Total	Incubation Time ± s.d. (days)
Infectious wire	3/4	62 ± 3
Experiment 1: *In vitro* exposure of infectious wire to:
(a) Prnp ^0/0 brain homogenate
Wire	4/4	89 ± 3
Homogenate	1/4*	108
(b) PBS
Wire	3/3	85 ± 6
PBS	0/4	>260
Experiment 2: *In vivo* exposure of infectious wire to:
(a) Brain of Prnp ^+/+ mice, 1 day
Wire	3/3	104 ± 20
Surrounding tissue	0/8^†	>260
(b) Brain of Prnp ^+/+ mice, 5 days
Wire	2/3	86 ± 4
Surrounding tissue	0/8^†	>260
(c) Brain of Prnp ^0/0 mice, 1 day
Wire	3/3	79 ± 4
Surrounding tissue	1/8^†,*	101
(d) Brain of Prnp ^0/0 mice, 5 days
Wire	3/3	91 ± 5
Surrounding tissue	0/8^†	>260

Infectious wires were prepared with centrifuged 10% brain homogenate from terminally sick CD1 mice (11). For the in vitro assay (expt.1), 20 wires were shaken in Eppendorf tubes for 24 h at 37°C, either with 0.2 ml freshly prepared brain homogenate (10% w/v in PBS) of uninfected Prnp^0/0 mice or with 0.2 ml PBS/0.1% albumin, on a thermomixer (1400 rpm). After washing with 0.2 ml of the cognate solution, wires were assayed for infectivity. Thirty-µl samples of each preparation (0.4 ml) were assayed for infectivity in Tga20 indicator mice. For the in vivo experiment (expt.2), infectious wires were implanted into the brain of uninfected Prnp^+/+ (C57Bl6) or Prnp^0/0 mice. After 1 and 5 days, respectively, the mice were culled and the brain tissue immediately surrounding the wire was dissected out. Wires were washed in 1 ml PBS and assayed. The brain samples (each about 80 mg) were homogenised in PBS to give a 10% homogenate and centrifuged samples were injected i.c. into 3 indicator mice each.
*Scrapie diagnosis was confirmed by histopathology or histoblotting (24)
^†One of 9 mice died during or after injection.

ISSN: 1528-3658