Fortress Brain

Host-parasite interactions are species specific. This may explain the rarity of AD-like pathology in most other older mammals. Over evolutionary timescales, the human brain should be adapted to predation by neurotropic agents. Viewed from this perspective, the prion-like pro-inflammatory and pro-apoptotic properties of β-amyloid and other proteins may be adaptive, and anti-microbial. Reductions in synaptic density may slow the progress of invading pathogens, while perineuronal nets and other structures may guard the gates. This suggests a defense in depth of a structure, the brain, that is inherently vulnerable to invasion along its neural networks.