Immunological characterization of abnormal prion protein from atypical scrapie cases in sheep using a panel of monoclonal antibodies

After the implementation of an active surveillance programme for scrapie in sheep in the EU, the number of diagnosed classical scrapie cases rose sharply and a novel kind of so-called atypical scrapie case was discovered. These atypical scrapie cases display unusual features concerning the distribution of the abnormal prion protein (PrP(Sc)) in the brain, a distinct electrophoretic profile of PrP(Sc) and an inconsistent reaction pattern in the currently used rapid tests. In this report, PrP(Sc) of two German atypical sheep scrapie cases was characterized by epitope mapping using a panel of 18 monoclonal antibodies that were directed against epitopes located throughout the prion protein. This analysis suggests that PrP(Sc) derived from atypical scrapie cases and treated with proteinase K is largely composed of an 11 kDa fragment (previously referred to as the 12 kDa band) and of polymeric fragments thereof. The 11 kDa band corresponds to a prion protein fragment spanning approximately aa 90-153 and may therefore represent a novel PrP(Sc) type.