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Antibody response in mice to scrapie-associated fibril proteins (protease-resistant proteins [PrPs]) was generated to different epitopes depending on the source of antigen. Mice responded differently to PrPs isolated from scrapie-infected animals of homologous (mouse) versus heterologous (hamster) species. An enzyme-linked immunosorbent assay established to monitor this antibody response in mice immunized with PrPs was unable to detect such a response in scrapie-infected mice. A monoclonal antibody (MAb), 263K 3F4, derived from a mouse immunized with hamster 263K PrPs reacted with hamster but not mouse PrPs. MAb 263K 3F4 also recognized normal host protein of 33 to 35 kilodaltons in brain tissue from hamsters and humans but not from bovine, mouse, rat, sheep, or rabbit brains. This is the first demonstration of epitope differences on this host protein in different species. The defining of various epitopes on PrP through the use of MAbs will lead to a better understanding of the relationship of PrPs to their host precursor protein and to the infectious scrapie agent.

Abnormal fibrillary structures, designated "scrapie-associated fibrils" (SAF), have been observed using negative stain techniques in subfractions of brains from scrapie-affected animals. SAF have been observed in all combinations of strain of scrapie agent and strain or species of host examined, regardless of their histopathology, in particular the presence or absence of amyloid plaques. SAF consist either of two or four filaments. They are morphologically dissimilar to the normal brain fibrils--microtubules, neurofilaments, glial filaments, and F actin. However, SAF do bear a resemblance to amyloid.

No abstract

SUMMARYScrapie-associated fibrils (SAF) were isolated and purified from animals infected with three different scrapie agents: ME7 and 139A in mice, and 263K in hamsters. Mouse ME7 and 139A SAF differed from hamster 263K SAF in morphology, sedimentation rate and protein composition. SAF from the three scrapie agents were distinguishable from each other by their sensitivity to proteinase K digestion. SAF copurified with infectivity in both the hamster and mouse systems. SAF appear to be a unique class of structures which are related but specific for each individual scrapie agent. These properties may correlate with the biological and pathological differences seen among these agents.