Prion protein immunocytochemistry: reliable protocols for the investigation of Creutzfeldt-Jakob disease.

Current criteria for the histological diagnosis of Creutzfeldt-Jakob disease (CJD) include features such as spongiform change, neuronal loss and reactive gliosis which are shared to a varying extent with other neuro-degenerative disorders. Reliable visualization of prion protein (PrP) has substantial potential value in diagnostic practice and as a research tool, since accumulation of the disease-associated isoform of this protein is apparently specific for spongiform encephalopathies. A number of antisera against PrP have previously been employed in conjunction with a range of pre-treatments designed to optimize the specificity of immunostaining; such varied usage makes the comparison and interpretation of results difficult. This study was undertaken to identify optimal combinations of each of three PrP antisera and five pre-treatments designed to specifically demonstrate disease-specific PrP in a series of seven CJD cases, six cases of Alzheimer-type dementia and six non-demented control cases. Specific staining of amyloid plaques, spongiform neuropil, neurons and, occasionally, astrocytes was achieved in CJD cases. Alzheimer and control cases were unstained. Use of formic acid with guanidine thiocyanate, and hydrolytic autoclaving with IB3 and SP30 antisera proved most effective and can be recommended for future immunocytochemical studies. PrP immunocytochemistry revealed a greater extent of subcortical neural involvement than routine histological techniques in CJD; the relationship between classical neuropathology in CJD and PrP accumulation as revealed by immunocytochemistry is not clear cut and requires further investigation. These findings may help to broaden our understanding of human spongiform encephalopathies, and have implications for diagnostic practices in neuropathology.