Immunohistochemical investigations of the prion protein accumulation in human spongiform encephalopathies. Special report II.

Creutzfeldt-Jakob disease (CJD) in a proportion of cases may have nonspecific clinical signs and symptoms and no characteristic neuroimaging and EEG picture. Thus, neuropathological studies are mandatory for a diagnosis. However, spongiform change, neuronal loss and astrocyte proliferation--the hallmarks of prion diseases, may also be absent or variable. In such cases, the diagnosis should be supported by the detection of prion protein (PrP) by Western blotting or immunohistochemistry (ICC). PrP may not be visualised under "regular" conditions, but it is unmasked following pretreatment procedures: incubation in formic acid or guanidine thiocyanate, microwave treatment, and hydrated or hydrolytic autoclaving, and these methods were included in standard diagnostic procedures in several different protocols. The aim of this study was to compare the effectiveness of these pretreatment methods and to introduce an optimal protocol for our laboratory. For this purpose, we used brain sections of 11 cases of CJD, 1 case of Gerstmann-Sträussler-Scheinker syndrome (GSS), 1 case of kuru and 3 control brains. For pretreatment we used the hydrated and hydrolytic autoclaving and incubation with formic acid. Immunostaining was performed with monoclonal 3F4 antibody against PrP. The best results were achieved with hydrolytic autoclaving. By this procedure we were able to detect the "synaptic" type of PrP accumulation in all CJD cases, as well as in GSS and kuru, while with other two methods the signal was weaker or even absent.