A new study out of Harvard puts forward what the New York Times calls a "startling hypothesis" about Alzheimer's. The research published in Science Translational Medicine suggests that old infections in the brain—or, more specifically, the body's attempt to fight them off—may be at the root of the disease. The study revolves around the telltale plaque in the brain associated with Alzheimer's, which is caused by a buildup of a protein called amyloid beta. Scientists have never been sure why the protein begins to build up as people age. “Does it play a role in the brain, or is it just garbage that accumulates?" is how Harvard's Rudolph Tanzi frames the question per New Scientist. His study suggests that it does indeed play a role, and an important one: The body produces the protein to fight off infections that pass into the brain through the blood-brain barrier; the problem occurs when it doesn't get properly cleared away after the fight.
“It’s interesting and provocative,” an Alzheimer's researcher at the University of California, San Francisco, tells the Times of theory. It's been tested on mice and roundworms but not humans yet. "Most shocking of all," writes Scientific American, "was that when they injected bacteria into the brains of Alzheimer’s mouse models, amyloid plaques—the hallmark of the disease—formed within 48 hours." If further research backs up the notion, it could lead to new ways of treating the disease. For example, if this protein that eventually causes trouble comes into being originally as a way to fight pathogens, "you could vaccinate against those pathogens, and potentially prevent this problem arising later in life,” says Tanzi's co-author, Robert Moir of Massachusetts General Hospital. (Maybe memories lost to Alzheimer's aren't gone forever?)