SPI1 and Alzheimer disease: We demonstrated that CD28, a well-known T cell co-stimulatory signalling protein3,4, which is induced by PU.1 downregulation and in response to plaque-associated cues in mouse (Figs. 2a,d, 3b,d and 4d and Extended Data Figs. 4e, 5, 9b and 10a,b) and human microglia (Fig. 2e), contributes to microglial activation during AD.