Scientists believe they may have discovered why the immune system attacks the body triggering diseases like Alzheimer's.

The immune system protects the body by attacking and hopefully killing viruses and diseases.

However, in certain circumstances it can also turn on the body killing vital cells.

It is possibly too simple to suggest that too much glutamate is responsible for the disease

Dr Paul Francis, Guy's, King's & St Thomas' School of Biomedical Sciences

Researchers in the United States believe that damage to just a few brain cells can cause this to happen.

Dr Zhi-Qi Xiong and Dr James McNamara of Duke University, North Carolina, examined the effects of glutamate on brain cells.

Key chemical

Glutamate is a chemical which is released in the brain following many kind of injuries.

This includes a seizure or a trauma to the head. It can also occur when blood flow to the brain is reduced as a result of a stroke, for instance.

The researchers found that too much of the chemical reduced the ability of some brain cells to protect themselves from the body's immune system.

This, they suggested, left the body vulnerable to attack and to brain diseases like Alzheimer's.

They believe the discovery could help scientists to develop new drugs to protect against the disease by blocking or reducing levels of glutamate after an injury.

"[It] may prove to be a clinically feasible approach for reducing the rate of neurological deterioration in diverse diseases of the human nervous system," said Dr McNamara.

Complex mechanism

However, Dr Paul Francis a senior lecturer at Guy's, King's and St Thomas' School of Biomedical Sciences in London, suggested the problem was more complex.

"Glutamate is an important, crucial substance in the brain which provides the chemical neurotransmitters for most of the activity in the brain, such as cognition, learning and memory and motor function," he said.

"The majority of brain cells use glutamate and these cells die in Alzheimer's disease. However, they die through a variety of mechanisms.

"It is possibly too simple to suggest that too much glutamate is responsible for the disease."

The study is published in the journal Neuron.