TSPO and Alzheimer disease: The main findings of the present study are: (1) sTREM2, TSPO and amyloidosis progressively increase with age in the PS2APP mouse model of AD; (2) sTREM2 levels, TSPO μPET and Aβ μPET uptake are all strongly associated with each other, and still after exclusion of age; and (3) there is widespread microgliosis in young PS2APP mice, along with early punctate fibrillar Aβ deposition, which progresses to extensive overlap of microglial activation and amyloidosis in the 16 month old mice.