PRNP and Alzheimer disease: Moreover, immunohistochemical analysis could not detect any cystatin F in the frontal cortex of these patients with Creutzfeldt-Jakob disease and Alzheimer’s disease, despite the presence of microgliosis as detected by Iba1 stainings (S5 Fig) and the presence of partially protease-resistant PrP in the former and amyloid β deposits and neurofibrillary tangles in the latter (Fig 5C).