Purification of scrapie agent from infected animal brains and raising of antibodies to the purified fraction.

The fraction (P4) containing scrapie infectivity was obtained by treatment of scrapie-infected mouse brains with the detergent sarcosyl, differential centrifugation, and proteolytic enzyme digestion. Scrapie infectivity in the P4 fraction was purified 239-2,390 times with respect to protein. Similar fractions were also prepared from the brain of a sheep naturally infected with scrapie. Morphological observation of the P4 fractions revealed that the main components were unique rods of 3-5 X 60-200 nm, which resembled scrapie-associated fibrils (SAF) or prion rods. The P4 fractions formed three major broad bands of polypeptides with molecular weights (MWs) of about 24.5K, 21K, and 17K dalton (Kd) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and some low MW polypeptides were also present in the fraction. Rabbits immunized with this fraction prepared from mouse brains raised antibodies against the three major polypeptides.