Besides glial cells, C1q, C3, and C5 are also expressed in neurons, specifically in the synaptic compartments [3, 8, 12], where they accumulate upon exposure to developmental cues during the entire life [30] or in the course of neurodegenerative (Parkinson’s or Alzheimer’s disease) and autoimmune (multiple sclerosis, optic neuritis) diseases [12, 29, 31]. This evidence concerns the gene C3 and early-onset autosomal dominant Alzheimer disease.