Accumulation of mono-glycosylated form-rich, plaque-forming PrPSc in the second atypical bovine spongiform encephalopathy case in Japan

Abstract

The recent identification of several atypical cases of bovine spongiform encephalopathy (BSE) has raised the possibility of the existence of distinct strains of BSE agents, arguing against the previous notion that BSE is caused by a single strain. To date, at least, two atypical types (L and H) of agent have been reported based on the molecular sizes of the proteinase K-resistant forms of prion protein (PrP(Sc)). These atypical agents were identified first in Japan, Italy, France, and Germany, and later in other European countries. Here, we have identified a case of BSE in a 169-month-old cow (designated as BSE/JP24), in which predominant deposition of the mono-glycosylated form of PrP(Sc) was observed by Western-blot analysis, and plaques of PrP(Sc) were detected in the brain by immunohistochemical analysis. The glycoform ratio of PrP(Sc) was different from that of the typical BSE agent, in which the di-glycosylated form is dominant; instead, the ratio resembled that of type-2 human sporadic Creutzfeldt-Jakob disease and that reported for the L-type BSE. The characteristic glycoform ratio and plaques of PrP(Sc) suggested that the agent in BSE/JP24 was relevant, if not identical, to the agent in bovine amyloidotic spongiform encephalopathy (BASE), an L-type BSE identified in Italy. It was of interest that at the level of the obex, the medulla oblongata was devoid of plaques of PrP(Sc), and a pathological phenotype similar to that of typical BSE specimens with vacuolations and coarse granular/linear deposition of PrP(Sc) were observed.