We next investigated how different stimuli affect microglial Cd83 expression. To this end, we established an in vitro cultivation protocol since microglia tend to change their gene expression profile upon removal from their native environment5. Microglia that were treated for 7 days with M-CSF and TGF-β acquired a distinctive phenotype with branched membrane protrusions, which dynamically interact with the environment (Supplementary Fig. 2a, Supplementary Movie 1 and 2). These cultured cells express the microglial marker P2RY12 and also exhibit CD83 promoter activity, highlighted by eGFP-reporter expression (Supplementary Fig. 2b). As microglia depend on intact TGF-β signaling both in vivo and in vitro5,7,31, we assessed whether this cytokine affects the phenotype of our cultured cells and the expression of Cd83. Microglia cultured in the presence of TGF-β had a substantially increased expression of the homeostatic gene Tmem119 when compared to cultivation with M-CSF alone, while the activation marker Msr1 was less expressed (Supplementary Fig. 2c). Interestingly, also Cd83 expression was considerably increased by the addition of TGF-β, thus resembling a homeostatic, less activated phenotype. To assess the effect of cellular activation,
