Which prion?


By Jonathan Knight in San Francisco A NEW antibody test can distinguish one strain of prion disease from another, say researchers in San Francisco. So far the test has been shown to work with hamsters infected with scrapie, which normally affects sheep. Eventually it might reveal whether BSE has crossed from cows into sheep, as some researchers fear it may have done. Current techniques for identifying strains of prion disease are very slow. Tissue must be injected into mice and left to incubate for a year or more. Only in this way can BSE be distinguished from the various strains of scrapie, each of which has a unique delay from infection to the onset of symptoms. Now a team at the University of California, San Francisco, led by the Nobel prizewinner Stanley Prusiner, has devised a rapid test that can distinguish between eight strains of scrapie. Prions, which are a rogue versions of the protein PrP, form clumps to which antibodies against normal PrP don’t easily bind. But by adding a chemical called guanidinium to brain samples taken from infected hamsters, the researchers partly broke up the clumps, allowing antibodies to bind. They found that the ratio of the quantity of antibodies binding to the PrP before and after treatment with guanidinium was unique to each strain (Nature Medicine, vol 4, p 1157). Whether the test will work in sheep remains to be seen, says Jeffrey Almond of the University of Reading,
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