Atypical status of bovine spongiform encephalopathy in Poland: a molecular typing study.

The aim of this study was to analyze molecular features of protease-resistant prion protein (PrP(res)) in Western blots of BSE cases diagnosed in Poland with respect to a possible atypical status. Confirmed cases were analyzed by Western blotting with several monoclonal antibodies directed at N-terminal and core epitopes of prion protein (PrP). Most cases showed the classical glycoprofile characterized by the dominance of the di- over the monoglycosylated PrP(res) band, yielding di-/mono- ratios well above 2 and by reactivity with antibodies having their epitopes in bovine PrP region 110-242 (C-type cases). Surprisingly, seven cases of BSE were atypical. Six were classified as L-type based on a slightly lower molecular mass (M(r)) of the non- glycosylated band with respect to C-types and a conspicuously low di-/mono- ratio of glycosylated PrP(res) bands approaching unity. One case was classified as H-type because of a higher M(r) of PrP(res) bands on the blot when compared with C-type cases. A characteristic epitope of H-type PrP(res) occurred in the 101-110 region of PrP for which only antibody 12B2 had a sufficient affinity. The occurrence of atypical cases only in animals 9 years of age and older raises questions about the mechanisms of prion diseases and the origin of BSE.