IMMUNOHISTOCHEMICAL DETECTION AND LOCALIZATION OF PRION PROTEIN IN BRAIN-TISSUE OF SHEEP WITH NATURAL SCRAPIE

A converted form of the normal cellular prion protein (PrP) accumulate s in the brains of sheep with scrapie. We describe an immunohistochemi cal method for identifying scrapie-associated PrP (PrPSc) in periodate -lysine-paraformaldehyde-fixed brain tissue, which provides adequate p reservation of tissue morphology. After pretreatment of tissue section s with formic acid and hydrated autoclaving, we located PrPSc in the b rains of 50 sheep with natural scrapie by use of antipeptide antisera raised against ovine PrP. No PrP was seen in 20 sheep without histopat hologic signs of scrapie. PrPSc that did not stain for amyloid was pre sent in the cytoplasm and at the cell membrane of both neurons and ast rocytes. Large amounts of PrPSc were seen at the cell membrane of neur ons in the medulla oblongata and pens, whereas PrPSc accumulated at th e cell membrane of astrocytes of the glial limitans in all brain regio ns. PrPSc that stained for amyloid was located in the walls of blood v essels and perivascularly in the brains of 32 (64%) of 50 sheep, mainl y in the thalamus and never in the pens or medulla oblongata. No appar ent topographic relationship existed between PrPSc that stained for am yloid and PrPSc accumulation associated with neurons or astrocytes. In all scrapie-affected sheep, PrPSc was present in brain regions with v acuolation, but it could also be detected in regions with minimal or n o vacuolation. We conclude that the immunohistochemical detection of P rP can be an important confirmative test in scrapie diagnosis.