Accumulation of a short peptide, called amyloid beta, within the brain is an early event thought to lead to Alzheimer’s disease. To identify the trigger for this accumulation, we explored the function of this peptide, which could lead to earlier diagnosis and much needed therapeutic opportunities. In this study we found evidence that amyloid beta is part of our innate immune system. amyloid beta may have evolved as an antibiotic to protect the brain from invading microorganisms, and can effectively form a web to trap microbes. With this in mind, we can now start to explore the earliest events that initiate amyloid beta accumulation.

This paper represents a major advance, and possibly a breakthrough, in our understanding of Alzheimer’s disease. It shows that the amyloid protein, which has been previously viewed as a culprit in Alzheimer’s disease, actually has a function in immunity. This raises the possibility that Alzheimer’s might be a disease that is set up as an abnormal response to infection. It also means that attempts to cure Alzheimer’s disease by removing amyloid may be set back by harming natural immunity and may explain why such therapeutic approaches have not worked well in clinical trials. There is still much to learn, but these discoveries change our thinking about the cause of Alzheimer’s disease and challenge certain dogmatic assumptions about the disease.

The substance that is in the brain in patients with Alzheimer’s called amyloid has long been though to be the cause of Alzheimer’s disease. Yet no one knows why amyloid is found in the brain of these patients. It seems from this paper that one of the effects of amyloid may be to stop the spread of bacteria and yeast - i.e. one of its properties is that it is an anti-bacterial/anti-fungal produced by the brain as a defence mechanism. This is interesting since Alzheimer’s is very common and there have been suggestions for a while that infection may contribute to Alzheimer’s. So it seems amyloid may have a function that can protect the brain against infection but when amyloid continues in the brain in excess, it may over time also damage the brain, leading to Alzheimer’s. This is an extraordinarily interesting paper