Alzheimer's is starting to look less like a plaque disease and more like an immune-cell-decided one

The category line for Alzheimer's has been wrong for a generation. It was framed as a plaque disease: clear the amyloid, slow the decline. What's left is a sharper question. If many older brains carry full amyloid and tau burden without symptoms, what actually decides who tips into dementia?

A Nature Medicine paper this week, from VIB, KU Leuven, UK-DRI, and Muna Therapeutics, points to microglia, the brain's resident immune cells, as the gate. Microglia don't clear pathology in resilient brains. They shift cellular state at the amyloid-tau inflection point, and that shift looks different in people who progress to dementia than in cognitively healthy centenarians who carry the same plaques without decline. The decision to develop dementia, on this evidence, tracks with an immune-state transition, not with how much pathology sits in the brain. This is an interpretive inference from the observed divergence in microglial transition patterns; causal mechanism is not yet established.

That reframes the next therapeutic decade. A pipeline aimed at retuning microglial state, rather than only lowering amyloid, would target the gate instead of the debris. It also reframes the goal: not "prevent plaques," but "preserve cognitive state in the presence of plaques." Centenarians, who carried the pathology and never paid the symptom price, become the protocol. Patients gain a target that survives amyloid failure.