C3 and prion disease: This microglia-induced A1 astrocytic subtype is characterized by increased expression of complement component 3 (C3) and has been identified in human patients and mouse models of Alzheimer’s disease (AD), Huntington’s disease, amyotrophic lateral sclerosis, multiple sclerosis, Parkinson’s disease, prion disease and frontotemporal dementia6,8–10.