The paraffin-embedded tissue blot detects PrPSC early in the incubation time in prion diseases

With the appearance of bovine spongiform encephalopathy (BSE) and a new variant of Creutzfeldt-Jakob disease (nvCJD) that seems to be caused by BSE, thence is an increased need for improvement of diagnostic techniques and recognition of all variants of prion diseases in humans and animals. Publications on the immunohistochemical identification of PrPSc in the tonsils and appendix in the incubation period of nvCJD indicate that new and more sensitive techniques for the detection of PrPSc in various tissues may be a valuable tool for early diagnosis in prion diseases. We developed a new and sensitive technique to detect PrPSc in formalin-fixed and paraffin-embedded tissue, the paraffin-embedded tissue blot (PET blot), and reinvestigated archival brain material from CJD as well as BSE and scrapie. In addition, C57/B16 mice experimentally infected with the ME7 strain were investigated sequentially during the incubation time to compare this new technique with conventional methodologies. The PET blot detects PrPSc in idiopathic (sporadic) and acquired prion diseases, even in cases with equivocal or negative immunohistochemistry, and is more sensitive than the conventional Western blot and histoblot techniques. The PET blot makes possible the detection of PrPSc during the incubation period long before the onset of clinical disease and in prion disease variants with very low levels of PrPSc. In mice experimentally infected with the ME7 strain, the PET blot detects PrPSc in the brain 30 days after intracerebral inoculation-145 days before the onset of clinical signs, Its anatomical resolution is superior to that of the histoblot technique. It may therefore be of particular interest in biopsy diagnosis. Thus it complements other tissue-based techniques for the diagnosis of prion diseases in humans and animals.