Hidden restructuring of brain immunity begins around age 50

Local microglia gradually decrease, and their place is taken by cells with a more inflammatory character, similar to immune cells from the blood.

This may explain why the brain becomes more sensitive to inflammation with age and the risk of neurodegeneration increases.

It is not yet clear why local microglia decrease or whether this replacement directly triggers Alzheimer's disease. However, the fact of a hidden immune restructuring in middle age provides a new point for seeking interventions that could preserve a "calmer" immune profile of the brain.

Sources:

1. NIH/Office of the Director. "Scientists discover a hidden brain shift that begins around age 50." ScienceDaily (August 6, 2026).
2. Zemke N.R. et al. "Epigenetic and 3D genome reprogramming during the aging of the human hippocampus." Science (2026). DOI: 10.1126/science.adt8307.