Chronic inflammation early in life may leave the brain vulnerable to Alzheimer's disease, research suggests.
Scientists made the discovery after triggering persistent inflammation in unborn mice.
A single infection during late pregnancy was enough to induce long-term neurological changes and memory problems in old age.
The mice developed boosted levels of immune system signalling molecules linked to inflammation.
If the immune system challenge was repeated in adulthood the effect was strongly amplified, resulting in changes similar to those seen in Alzheimer's patients.
Mice genetically modified to produce a human version of the Alzheimer's-associated brain protein amyloid-beta showed the most striking reaction.
"It seems likely that chronic inflammation due to infection could be an early event in the development of Alzheimer's disease," said study leader Dr Irene Knuesel, from the University of Zurich in Switzerland.
The research is published in the Journal of Neuroinflammation.
If the findings can be shown to apply to humans, it would suggest a role for anti-inflammatory drugs in treating Alzheimer's.
Dr Marie Janson, from the charity Alzheimer's Research UK, said: "The results of this study suggest that repeated or severe infections may contribute to the development of Alzheimer's disease in mice.
"While we know that the immune system plays a role in human Alzheimer's disease, clinical trials with anti-inflammatory drugs have not yet shown conclusive benefits in treating the disease and so more research is needed to fit these pieces of the puzzle together.
"Understanding the risk factors for Alzheimer's disease is essential, especially if some of these factors are things that we can actively change or avoid. This understanding can only come through research, yet research into dementia remains hugely underfunded."