PRNP and prion disease: All the brains from the mice in each infection group that developed clinical signs of prion disease displayed the characteristic spongiform pathology (neuronal vacuolation), microgliosis, astrogliosis and accumulations of prion disease-specific PrP (referred to as PrPd) that are associated with a terminal, clinical, infection with ME7 scrapie prions (Fig. 3B).