Immumohistochemical Detection and Localization of Prion Protein in Brain Tissue of Sheep With Natural Scrapie

Abstract

A converted form of the normal cellular prion protein (PrP) accumulates in the brains of sheep with scrapie. We describe an immunohistochemical method for identifying scrapie-associated PrP (PrP^Sc) in periodate-lysine-paraformaldehyde-fixed brain tissue, which provides adequate preservation of tissue morphology. After pretreatment of tissue sections with formic acid and hydrated autoclaving, we located PrP^Sc in the brains of 50 sheep with natural scrapie by use of antipeptide antisera raised against ovine PrP. No PrP was seen in 20 sheep without histopathologic signs of scrapie. PrP⁸⁰ that did not stain for amyloid was present in the cytoplasm and at the cell membrane of both neurons and astrocytes. Large amounts of PrP^Sc were seen at the cell membrane of neurons in the medulla oblongata and pons, whereas PrP^Sc accumulated at the cell membrane of astrocytes of the glial limitans in all brain regions. PrP^Sc that stained for amyloid was located in the walls of blood vessels and perivascularly in the brains of 32 (64%) of 50 sheep, mainly in the thalamus and never in the pons or medulla oblongata. No apparent topographic relationship existed between PrP^Sc that stained for amyloid and PrP^Sc accumulation associated with neurons or astrocytes. In all scrapie-affected sheep, PrP^Sc was present in brain regions with vacuolation, but it could also be detected in regions with minimal or no vacuolation. We conclude that the immunohistochemical detection of PrP can be an important confirmative test in scrapie diagnosis.