There is currently no cure for Alzheimer's disease
The body's immune system could be harnessed to fight back against Alzheimer's disease, research suggests.
Turning off a part of the immune system cleared away harmful brain deposits and improved memory, the mouse study found.
US scientists, reporting their discovery in the journal Nature Medicine, said it was like a "vacuum cleaner" had been working in the brain.
The Alzheimer's Society said more research would reveal if the process also worked in humans.
Alzheimer's disease patients are gradually deprived of their memories and their ability to live normally.
The damage is caused by the formation of "amyloid plaques" in their brain cells.
Scientists have been searching for ways to break up and dispose of these plaques, and perhaps halting or even reversing the symptoms.
So far, while there are some drugs which can delay the progress of the disease in some patients, there is no cure.
One of the biggest obstacles to a successful treatment is the blood-brain barrier, which stops large molecules getting into the brain, ruling out many complex drugs which might otherwise be used.
The researchers from Yale University took a different approach.
They used genetic engineering to block an immune system response in mice, but only in cells outside the brain.
Researchers had expected the change to worsen the Alzheimer's by sending the immune response into overdrive, causing too much inflammation inside the brain.
But they found up to 90% of the plaque material disappeared from the brains of the mice.
And when the animals' memories were tested using mazes, significant improvements were found.
Tests revealed that immune cells called macrophages, whose normal role is to roam around engulfing harmful bacteria or cell debris, were entering the brain and turning their attention to the plaques.
One of the authors, Professor Richard Flavell, said: "It was like a vacuum cleaner had removed the plaques."
Another of the researchers, Dr Terence Town, said that it raised the possibility of a drug in humans to try to reproduce this effect.
He said: "If results from our study in mice engineered to develop Alzheimer's-like dementia are supported by studies in humans, we may be able to develop a drug that could be introduced into the bloodstream to cause peripheral immune cells to target the amyloid plaques."
Dr Susanne Sorenson, head of research at the Alzheimer's Society, said there was increasing research into inflammation in the brain and Alzheimer's.
"These inflammatory reactions could play an important role in the development of Alzheimer's, which may have previously been overlooked.
"Further research is now required to find the best potential drug to stop this reaction and to investigate whether the same effects will occur in people with the disease."