Immune System Eyed as Cause of Alzheimer’s

A study involving mice has led to a new theory about the cause of Alzheimer’s disease. Researchers compared autopsy brain tissue from mice of various ages, a human baby and an older person. They focused on an immune system protein called C1q, which builds up even in healthy brains as they age. Levels of C1q were 300 times as high in older brains as in younger ones. C1q built up mostly at synapses, the junctions between nerve cells. This possibly could get in the way of signals between cells that allow the brain to function. C1q plays a role in the brain in childhood, when some synapses are “pruned” away to allow others to develop. In the immune system, C1q clings to foreign bodies, such as bacteria, or to pieces of dying cells. This sets off a chain reaction. Other proteins build up on top of the C1q. Then other immune system cells gulp down the object.