The brain has its own set of immune cells, called microglia, which can secrete C1q, a protein that has been implicated in diseases such as Alzheimer’s and Parkinson’s. This protein appears to lodge in synapses (the point between neurons) and is associated with cell death when a brain injury occurs. Levels of C1q appear to increase with age. According to professor and chair of neurobiology and senior author of the study, Ben Barres MD, PhD: “The first regions of the brain to show a dramatic increase in C1q are places like the hippocampus and substantia nigra, the precise brain regions most vulnerable to neurodegenerative diseases like Alzheimer’s and Parkinson’s disease, respectively.” Children don’t get Alzheimer’s and Parkinson’s and these findings may help to explain that phenomenon. (Source)