Scientists are developing a vaccine which could treat Alzheimer's disease.
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Injecting antibodies into mice was found to prevent the build-up of the brain-clogging plaques characteristic of the disease.
University of California at Irvine researchers also found it stopped "tangles" of another protein forming within brain cells.
UK experts said the research, published in the journal Neuron, showed this kind of treatment had "enormous potential".
In Alzheimer's disease, deposits of a protein called beta amyloid (Ab) form in the brain.
There is a theory that this then leads to the development of tangles of another protein, tau, which destroy brain cells from the inside.
In this study, researchers looked at mice which had been genetically modified so they had human genes, allowing them to develop the plaques.
They administered anti-beta-amyloid antibodies into the mice's hippocampus - a part of the brain involved in learning and memory.
It was found that the plaques cleared within three days.
The researchers also looked at tau tangles, which were found to have cleared two days after the plaques had been destroyed.
When the mice were examined a third time, 30 days after the treatment, the plaques had started to reform, but the tau tangles had not - suggesting they occurred at a later stage in the process than the formation of amyloid plaques.
To check this, the researchers gave the mice a drug that blocked the action of an enzyme which is key to producing the Ab protein. They found doing this also led to the clearance of tau.
Writing in Neuron, the researchers led by Dr Frank LaFerla, said their results "indicate that immunisation may be useful for clearing both hallmark lesions of Alzheimer's, provided that intervention occurs early in the disease course."
Professor Clive Ballard, director of research for the Alzheimer's Society, told BBC News Online the US study was unique because it was the first study to look at this kind of treatment in mice genetically modified to develop the signs of Alzheimer's.
He added: "Importantly this suggests that this type of 'vaccine' treatment approach, in addition to clearing amyloid from the brain, can prevent the development of tangles."
Other research looking at using a vaccine just to destroy beta-amyloid was stopped after a number of patients developed the potentially fatal brain inflammation meningoencephalitis.
But Dr Ballard said of the latest study: "This is very exciting and further emphasises the enormous potential of this type of approach if the difficulties of brain inflammation can be overcome."
The US team are now investigating whether a combination therapy, where one treatment is aimed at clearing plaques and the other the tangles - would be most effective.