New clue about what causes Alzheimer's disease

New research is shedding light on the possible cause of Alzheimer's disease and the surprising role a person's immune system may play in protecting the brain from dementia.

A study in lab mice, conducted by researchers at Duke University, suggests that when Alzheimer's develops, certain immune cells called microglia that normally protect the brain instead start a pattern of activity that dampens the immune system.

The study, published today in the Journal of Neuroscience, opens up the possibility that two of the main suspects in Alzheimer's development -- amyloid plaques and tangles of tau proteins in the brain -- are not acting alone.

"You're finding a molecular pathway that we hadn't thought of at all that might be important for the development of Alzheimer's," said CBS News chief medical correspondent Dr. Jon LaPook.

Instead of just focusing on amyloid plaques and tau proteins, "now they're looking at something new. They're looking at these supportive cells called microglia that are inside the brain, they help to support the surrounding neurons."

What happens next -- in mice, anyway -- is that "there's an increase of an enzyme called arginase that comes out of these microglia cells. And arginase lowers the level of an important amino acid called arginine. Arginine is important for the health of neurons of nerve cells," especially in regions of the brain associated with memory.

LaPook explains that this could provide a target for future research and potential drug treatments.

"If they were able to block the enzyme -- can you prevent the development of memory loss and of the amyloid plaques and the nerve death in mice? And they were able to. Somehow this arginine seems to be very important in maintaining the normal health of nerve cells."

Does that mean people should start taking arginine dietary supplements to ward off Alzheimer's? Unfortunately, it doesn't work that way. Arginine in the diet would not get through the blood-brain barrier to the cells that need it.

Much more research is needed, and LaPook points out that studies in mice don't always translate into treatments that work in humans. Still, he calls this "very interesting, exciting research."