To confirm that TSPO radioligand binding determined with PET in PSP reflects microglial reactivity, we assessed the regional association between histologically determined microgliosis in post-mortem brain tissue and 11C-PK11195 binding potential (BPND) from the same PSP donors during life.8,10 ‘Phagocytic’ microglia were quantified using CD68 immunohistochemistry across eight cortical and 11 subcortical regions. This evidence concerns the gene TSPO and supranuclear palsy, progressive, 1.