What amyloid beta normally does in the brain isn’t clear. Robert Moir, a neurologist at the MassGeneral Institute for Neurodegenerative Disease, says that many researchers have cast it as a villainous molecule with no beneficial function. “It’s just bad, bad, bad,” he says. “But it has become increasingly obvious that this isn’t true.” Moir thinks that amyloid beta has a more heroic role, as a foot soldier of our immune system. It protects neurons from infectious microbes—and from herpes viruses, in particular.
William Eimer, a member of Moir’s team, demonstrated this protection by injecting the common herpes virus HSV–1 into the brains of two kinds of mice: normal rodents and ones that were genetically engineered to produce high levels of amyloid beta in their brains. The latter were better at resisting the viruses. Eimer then got similar results when he injected a different herpes virus, HHV–6, into human cells growing in a dish.