For years, we’ve treated Amyloid-beta (Aβ) as if it were simply metabolic waste. But the repeated failure of anti-amyloid therapies—which often spike infection rates without helping the patient—suggests we’re actually stripping away a functional part of the innate immune system. Since Aβ acts as a potent antimicrobial peptide (AMP), I’m proposing the Systemic-Sequestration Hypothesis. In this model, Aβ plaques aren't the root cause of neurodegeneration; they're compensatory "immune sinks." They're designed to trap systemic inflammatory triggers, like microbial PAMPs and retrotransposon cDNA, that leak into the CNS when peripheral barriers break down.

The Mechanistic Cascade

1. Peripheral Barrier Failure: As we age, the "GALT-Gut-Vascular Axis" wears down. This immunosenescence leads to a leaky gut, allowing microbial products to slip into systemic circulation.
2. The CNS Influx: In a younger brain, the blood-brain barrier and glymphatic system keep the environment pristine. However, age-related stiffening of the extracellular matrix—what I've called the ‘ECM-IgG Lock’—shuts down glymphatic outflow. This creates a stagnant environment where systemic toxins, including LINE-1 retrotransposons, begin to accumulate.
3. Aβ as a Sacrificial Filter: To shield neurons from these toxins, the brain ramps up Aβ production. We've seen this in Candida-infected AD models, where Aβ fibrils physically cage pathogens in a protective matrix. This fibrillization is a deliberate sequestration strategy to keep these threats away from synaptic receptors.
4. Tau as a Metabolic Brake: Tau hyperphosphorylation might not be inherently toxic. Instead, it looks like a "hibernation" signal. By decoupling microtubules, the neuron lowers its metabolic demand and limits the spread of sequestration sinks, preventing the mechanical collapse of the axonal network until the systemic threat is dealt with.

Why Clinical Trials Fail

Removing Aβ without fixing the upstream leak is like pulling the filter out of a polluted stream while the factory is still dumping waste. When anti-Aβ antibodies dissolve plaques, they likely dump the trapped pathogens, PAMPs, and pro-inflammatory cDNA back into the neural tissue. This explains why Aβ blockade can actually impair memory and fails to stop the decline: the trap is gone, but the poison remains.

Testable Predictions

If this hypothesis is correct, we should see:

• Higher PAMP-to-Aβ ratios in early AD: High-sensitivity proteomics should show that plaques in early-stage patients are packed with gut-derived markers like LPS or peptidoglycan and LINE-1 cDNA.
• Glymphatic-Mucosal Correlation: There should be a measurable inverse link between intestinal barrier integrity (via zonulin/IFABP) and the rate of glymphatic clearance.

Synthesis

We need to stop viewing Alzheimer’s as a localized protein problem and start seeing it as a systemic failure of compartmentalization. The "scar tissue" of Aβ is the brain’s desperate attempt to maintain homeostasis against a rising tide of metabolic and microbial noise. Future treatments shouldn't focus on dismantling the brain’s final line of defense, but on reinforcing the gut-vascular barrier and restoring glymphatic drainage.