Infectivity of Scrapie Prions Bound to a Stainless Steel Surface

Table 1 Infectivity of prion-coated wire

Treatment ^a	Incubation Time to Terminal Disease (no. mice sick/total)	Log LD ₅₀ Units ^b
Wire^c	72 ± 3 (4/4)	5 ± 0.3
Wire, formaldehyde-treated^d	87 ± 9 (4/4)	3.5 ± 1
1% scrapie-infected brain homogenate^e	65 ± 1 (4/4)	6 ± 0.1
PBS wash^f	>120 (0/4)	<1

^aWire segments were inserted into the brain of four Tga20 mice in deep anesthesia. Liquid samples (30 µl) were injected intracerebrally.
^bApparent infectivity titers were estimated from incubation times using the formula log LD₅₀ = 13 − 0.11 × (incubation time in days) (14).
^cStainless steel wire (diameter about 0.15 mm; 5 mm length) exposed to scrapie brain homogenate and washed five times with PBS, as described in Materials and Methods.
^dWire exposed to scrapie brain homogenate, washed four times with 50 ml PBS, and incubated in 10% formaldehyde for 1 hr at room temperature.
^eThirty microliters of RML4.1 diluted 10-fold in PBS containing 5% BSA.
^fThirty microliters of the 5th 50-ml PBS wash of wire segments exposed to scrapie homogenate.

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