Immunohistochemistry of PrPsc within bovine spongiform encephalopathy brain samples with graded autolysis

Bovine spongiform encephalopathy (BSE) is a transmissible neurodegenerative disease of cattle. Clinical diagnosis can be confirmed by investigation of both spongiform changes and abnormal prion protein (PrPsc), a marker considered specific for the disease. Tissue autolysis, often unavoidable in routine field cases, is not compatible with histological examination of the brain even though PrPsc is still detectable by immunoblotting. To determine how autolysis might affect accurate diagnosis using PrPsc immunohistochemistry, we studied 50 field samples of BSE brainstem (obex) with various degrees of autolysis. We demonstrated that the antigen-unmasking pretreatments necessary for PrPsc immunohistochemistry were compatible with the preservation of autolyzed brain sections and that PrPsc detection was unaffected by autolysis, even though anatomic markers were sometimes lost. In tissue samples in which anatomic sites were still recognizable, PrPsc accumulation was detected in specific gray matter nuclei. In samples with advanced autolysis, PrPsc deposits were still observed, at least at the cellular level, as an intraneuronal pattern. We found that the sensitivity of PrPsc immunohistochemistry as a diagnostic method for BSE was undiminished even by severe tissue autolysis.