Prion protein immunocytochemistry – UK five centre consensus report

Creutzfeldt‐Jakob disease (CJD) and other prion diseases are associated with the deposition of insoluble prion protein (PrP^CJD) in the central nervous system (CNS). Antibodies raised against PrP^CJD also react with its precursor protein, a soluble form of PrP (PrP^C), which is widely distributed in the normal CNS. This cross‐reactivity has in the past raised doubts as to the specificity and diagnostic reliability of PrP immunolocalization, especially in familial cases which are atypical clinically and which lack characteristic pathology findings. Following an MRC‐funded workshop which focused on this problem, a multicentre prospective study was set up to identify a reliable protocol for PrP^CJD immunocytochemistry. Five UK centres took part in this study and demonstrated consistent staining of plaques, vacuolar deposits in severe spongiform change, and perineuronal deposits using a variety of antibodies and enhancement procedures. A protocol using formic acid, guanidine thiocyanate, and hydrated autoclaving pre‐treatment in conjunction with a monoclonal PrP^CJD antibody produced the clearest immunochemical results and is presented as the consensus UK recommendation for PrP^CJD immunocytochemical procedures.