PRNP and scrapie: In sheep and goats infected with natural scrapie, the disease-associated prion protein (PrPSc) has been detected in the lymphoreticular system (e.g., spleen, lymph nodes, palatine tonsils, gut-associated lymphoid tissues, etc.), prompting the development of biopsy tests for the antemortem diagnosis of scrapie using more accessible tissues, including recto-anal mucosa-associated lymphoid tissue (RAMALT) (12), third eyelid (13), or palatine tonsil (14) that are primarily analyzed after immunohistochemistry (IHC).