Immunohistochemical comparison of anti-prion protein (PrP) antibodies in the CNS of mice infected with scrapie.

One of the pathological changes characteristic of the transmissible spongiform encephalopathies (TSEs) is the accumulation of disease-specific PrP (PrP(sc)). Immunolabeling of PrP(sc) was compared using a panel of monoclonal and polyclonal antibodies. To determine the effects of tissue fixation on immunostaining, we performed a supplementary investigation reviewing the fixatives formol saline and periodate-lysine-paraformaldehyde (PLP). The main target sites of the antibodies were similar. However the monoclonal antibodies (MAbs) 6H4, 7A12 and 8H4 revealed targeted PrP(sc) labeling with no background labeling. Although 7A12 and 8H4 did not detect early PrP deposition, we propose that during the later stages of disease 7A12 and 8H4 can be used with equal effectiveness in place of 6H4. Tissues taken during the early stages of disease that had been fixed in PLP displayed more PrP immunolabeling than tissues that had undergone formol fixation. PLP fixation on 6H4-immunostained tissue revealed interweaving granular linear PrP deposits in the hippocampus. This labeling was not observed in tissue that had undergone formol fixation, suggesting that PLP fixation might enhance the sensitivity of the immunohistochemical (IHC) detection of PrP. In the two scrapie mouse models studied here, PLP fixation and immunolabeling with the anti-PrP antibody 6H4 gave superior results.