Enhancement of immunohistochemical staining of scrapie proteins and immune cells within lymph nodes of early scrapie-infected sheep.

Transmissible spongiform encephalopathies (TSE) are a group of fatal neurodegenerative diseases that affect animals as well as humans. The oldest of these diseases is Scrapie seen in sheep. Scrapie is caused by an altered form (PrP(sc)), capable of inducing "self-replication" of the normal host prion protein (PrP(c)). There is currently no universal standard for antigen retrieval when using immunohistochemistry to simultaneously stain the PrP(c) protein and other cellular markers. The use of formalin-fixed tissue creates a challenge by concealing the antigenic sites where an antibody would bind, and lengthy antigen retrieval methods must be applied in order to facilitate staining. Further complicating sheep tissue immunohistochemistry is a significant lack of commercial antibodies to sheep cell markers available in research. Here we developed a novel immunohistochemical technique using trypsin, formic acid, and hydrated autoclaving using citraconic anhydride buffer to increase sensitivity of staining for scrapie proteins and immune cell subsets. This allowed us to stain and identify cells within lymphoid tissue associated with early lymphoid pathogenesis in scrapie.