TSPO and Alzheimer disease: In a previous quantitative neuropathological study, we found that the purported PET imaging biomarker of reactive microglia translocator protein 18 kDa (TSPO) is not only expressed by microglia but also by astrocytes, endothelial cells, and vascular smooth muscle cells, and that its expression level is not dramatically different between AD and control (CTRL) donors, nor does it correlate with the number of reactive microglia in AD [20].