P2RY12 and Alzheimer disease: P2RY12 is considered a homeostatic microglia marker because of its downregulation in neurogenerative and neuroinflammatory models, including amyotrophic lateral sclerosis, AD (Table 5) and MS (Table 6) [174, 179, 191, 214], which have been more extensively investigated than encephalitis (Table 3) and stroke (Table 4).