Human prion protein, PrP, selectively presents the epitope MDEYSNQNN (SEQ ID No. 14) when PrP misfolds. The misfolded form of human PrP is associated with various disease states. The present invention provides an antibody useful to detect and treat such diseases, including cancer such as ovarian cancer and lymphomas, and transmissible spongiform encephalopathies such as CJD. Also provided is an immunoconjugate in which the antibody is conjugated with urease as cytotoxin.