Preventing new transmissions of the prion protein (PrP) isoforms that cause spongiform encephalopathies requires reliable diagnostic tests. In October 21 Nature Biotechnology, Jiri G. Safar and colleagues from the University of California, San Francisco, describe a new test, based on conformation-dependent immunoassay (CDI), that can detect the PrP isoforms that cause bovine spongiform encephalopathy or chronic wasting disease in deer and elk (Nature Biotechnology, doi:10.1038/nbt748, October 21, 2002).

The assay uses high-affinity recombinant antibody fragments (recFab) that react with residues 95–105 of bovine PrP for detection, and another recFab that recognizes residues 132–156 for capture of PrP. Using this CDI, Safar et al were able to measure the disease-causing PrP isoform (PrPSc) in bovine brainstems with a sensitivity similar to that of end-point titrations in transgenic mice expressing bovine PrP.

Furthermore, the assay was able to discriminate between PrPSc from BSE-infected cattle and...

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