Brain sections from 16 different mouse
scrapie models were immunostained with
antisera to
scrapie-associated fibrils (
SAF) from three experimental
scrapie sources (hamster 263K, mouse ME7 and mouse 22L). These models involved seven strains of
scrapie injected intracerebrally or intraperitoneally into a range of inbred mouse strains, producing a wide variety of neuropathological changes. The only brain structures which were positively immunostained were
amyloid plaque cores in those models in which plaques could be readily identified using traditional
amyloid stains. The intensity of immunostaining correlated with the density of
amyloid in the cores, as detected by
Congo red and
thioflavine S staining. No differences in immunostaining specificity were found between
antisera or between plaques in different combinations of
scrapie strain and mouse genotype. There were also no differences in immunoreactivity between plaques in different parts of the brain. These results strongly suggest that
SAF and histologically detectable
amyloid in
scrapie mice are derived from the same precursor
protein.
Scrapie-associated cerebrovascular
amyloid and plaques in sheep and goats also gave positive immunostaining with
SAF antisera, although the lesions in the natural disease could only be stained after
formic acid pretreatment.
Senile plaques in
Alzheimer's disease and
Down's syndrome, although structurally similar to
scrapie amyloid plaques, were found to be completely negative for
SAF, in agreement with previous biochemical and immunocytochemical findings.