PHF1 and Alzheimer disease: We confirmed the presence of strong and selective concentrations of silver grains in tissue sections from AD cases, reflecting underlying [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 binding of these three tracers to neurofibrillary tangle containing regions in AD brains that closely matched the laminar distribution of tangles on adjacent slices as revealed by PHF-1 immunostaining but not the plaque distribution pattern revealed by Aβ immunostaining (Fig. 7a).