This study investigates the three-dimensional morphology of microglia and the intracellular localization of phosphorylated SMAD proteins as downstream effectors of transforming growth factor β (TGF-β) signaling in the amyloid precursor protein and presenilin-1 (APP/PS1) transgenic mouse model of Alzheimer's disease. This evidence concerns the gene TGFB1 and Alzheimer disease.