Immune cells called T cells, which normally hunt down infected or foreign cells, pile up in the brains of people with Alzheimer's disease and related disorders at far higher levels than in healthy brains, and they appear to contribute to the loss of neurons. What has been missing is an explanation of where those cells come from and what tells them to gather there in the first place.
Researchers at Washington University School of Medicine in St. Louis report that, in mice, the instructions come from lymph nodes outside the brain entirely. When the team interfered with that signaling, neurodegeneration was dramatically reduced. The work points to a pathway nobody had suspected in primary tauopathies, the family of diseases - Alzheimer's among them - defined by twisted clumps of tau protein building up in brain tissue.
David M. Holtzman, MD, the study's senior author and a professor of neurology at WashU Medicine, framed the appeal of a disease driver that sits outside the skull in practical terms. Drug developers working on neurological disease have to engineer compounds that cross the blood-brain barrier, a persistent obstacle. If the damaging signal originates in peripheral lymph nodes, a treatment may not need to reach the central nervous system at all to slow the damage.
That opens a door to an existing pharmacological toolkit. Methods of manipulating T cells have been studied at length and several are already approved therapies for other conditions, though Holtzman noted that many of them have not been tested against neurodegenerative disease. The findings so far come from mice, and translating an immune-targeting strategy into human tauopathy treatment remains the next step.