Scientists explain sits at the center of this dementia and brain health question.

Scientists have made a significant breakthrough in understanding how lecanemab, an FDA-approved Alzheimer’s drug, effectively clears toxic amyloid plaques from the brain. The drug works by activating the brain’s immune cells, called microglia, through a specific component called the Fc fragment, which triggers these cells to engulf and remove accumulated plaques. This discovery reveals that the drug’s effectiveness depends on two critical cellular processes: phagocytosis, where cells physically engulf the plaques, and lysosomal activity, which breaks down the material once it’s inside the cell.

For patients with early Alzheimer’s disease who receive lecanemab, this mechanism offers a direct biological explanation for the modest cognitive improvements observed in clinical trials—the drug is literally removing some of the brain’s toxic protein accumulation. Beyond lecanemab, researchers have identified multiple pathways by which existing and experimental drugs can interfere with amyloid-beta plaque formation and clearance. This article explores the detailed mechanisms of how current Alzheimer’s drugs work at the cellular level, examines an unexpectedly promising anti-seizure medication, and discusses emerging targets that may lead to even more effective treatments. Understanding these mechanisms is important not just for patients considering treatment options, but for families navigating the complex decision of whether these drugs might help their loved ones.

How Does Lecanemab Activate Brain Immune Cells to Remove Plaques?
What Happens Inside Microglia When Plaques Are Cleared?
Can Older Anti-Seizure Drugs Prevent Plaques From Forming in the First Place?
How Do Researchers Identify Which Drug Target Will Actually Work?
What Genetic or Biological Factors Limit How Well These Drugs Work?
How Do These Drug Mechanisms Compare to What Happens Naturally in Healthy Brains?
What Do These Discoveries Tell Us About Future Alzheimer’s Treatments?
Conclusion

How Does Lecanemab Activate Brain Immune Cells to Remove Plaques?

Lecanemab operates through a surprisingly elegant biological mechanism centered on the brain’s resident immune cells. When lecanemab binds to amyloid-beta plaques, its Fc fragment—a portion of the antibody structure—interacts with receptors on microglia, essentially sending a “clear this away” signal to the brain’s cleanup crew. This activation is not random or generic; researchers have identified a specific microglial gene program that drives effective plaque clearance, marked by strong expression of the SPP1 gene. Microglia expressing this gene program appear to be the most efficient at clearing the plaques, which suggests that one reason lecanemab works for some patients better than others may relate to individual differences in this immune gene expression.

The phagocytosis step—the actual engulfment of plaques—requires the microglia to physically wrap around and internalize the plaque material. Once inside the cell, the second critical process begins: lysosomal activity breaks down the engulfed plaques into harmless components that the cell can eliminate. If either process fails or is impaired, the drug cannot work effectively. This dual-requirement explains why lecanemab’s clinical benefit is modest in many patients; it requires both a robust immune response and healthy cellular machinery. Additionally, the brain’s blood-brain barrier creates a hurdle; lecanemab must cross into the brain tissue to reach plaques, which limits how much drug can reach its target, even when injected intravenously.

How Does Lecanemab Activate Brain Immune Cells to Remove Plaques?

What Happens Inside Microglia When Plaques Are Cleared?

Once phagocytosis occurs and plaques are inside the microglial cell, the lysosomal system takes over—this is the cell’s waste disposal unit, filled with enzymes that break down proteins and other cellular material. For lecanemab to work, these lysosomes must remain functionally active and responsive. In some patients with advanced Alzheimer’s disease or other complicating factors, lysosomal function may be impaired, meaning that even if lecanemab successfully activates microglia and triggers plaque engulfment, the lysosomes cannot fully break down and clear the material.

In these cases, the plaques may be removed from the extracellular space but still accumulate inside immune cells, potentially limiting the drug’s benefit. However, if lysosomal function is intact, the cleared plaques are broken down into lipids and amino acids that the cell can safely handle. This is why lecanemab requires a healthy, functioning immune and cellular system to work effectively—a limitation that highlights why the drug is most beneficial in early-stage Alzheimer’s disease, when cellular systems are less compromised. Patients with advanced disease, severe cellular damage, or those with genetic conditions affecting immune function may not benefit as much from this immune-activation approach.

Can Older Anti-Seizure Drugs Prevent Plaques From Forming in the First Place?

While lecanemab targets existing plaques, researchers recently discovered that levetiracetam—an inexpensive anti-seizure medication that has been used for decades—takes a different approach: it prevents the formation of amyloid-beta 42, the specific form of amyloid most toxic to neurons. Levetiracetam works by binding to a protein called SV2A, which is involved in the recycling process of amyloid precursor protein (APP). By binding to SV2A, the drug pauses this recycling process, causing APP to remain on the cell’s surface longer than normal.

This detours the APP molecule away from the enzymatic pathway that would otherwise cleave it into amyloid-beta 42, the toxic protein fragment that aggregates into plaques. This mechanism represents a fundamentally different strategy from plaques-removal: instead of cleaning up accumulated damage, levetiracetam prevents the damage from occurring in the first place. The drug’s advantages are significant—it is inexpensive, has a decades-long safety record in treating seizures, and may be preventive rather than just symptomatic. The limitation is that preventing plaques from forming may be most effective before significant accumulation has already occurred, suggesting levetiracetam might be most valuable as a preventive treatment in people at high genetic risk for Alzheimer’s, rather than as a treatment for those already showing symptoms.

Can Older Anti-Seizure Drugs Prevent Plaques From Forming in the First Place?

How Do Researchers Identify Which Drug Target Will Actually Work?

One emerging target that researchers have identified is the protein LRP1, which acts as a molecular gatekeeper controlling how much amyloid-beta enters and leaves the brain. Supramolecular drugs—a new class of therapeutic designed to mimic LRP1 ligands—can bind directly to amyloid-beta and trigger its clearance across the blood-brain barrier, moving toxic plaques out of the brain and into the bloodstream for elimination. This approach has the advantage of restoring vascular function, not just clearing plaques locally, and represents a way to enhance the brain’s natural clearance systems. Comparing these different approaches reveals important tradeoffs.

Lecanemab activates immune cells, which requires them to be present and functional. LRP1-targeting drugs enhance the brain’s natural vascular drainage system, which may be more broadly applicable across patient populations. Levetiracetam prevents new plaques from forming, which requires early intervention. No single approach is optimal for all patients; the most effective future treatments may combine multiple mechanisms—for example, using levetiracetam to prevent new plaques while simultaneously using lecanemab or LRP1-targeting drugs to clear existing damage.

What Genetic or Biological Factors Limit How Well These Drugs Work?

Beyond the mechanisms of action themselves, individual genetic variation significantly affects drug effectiveness. Researchers have found that removing specific enzymes from brain neurons substantially reduces amyloid plaques, suggesting that genetic differences affecting these enzymes may explain why lecanemab works better in some patients than others. Additionally, the presence of the APOE4 genetic variant—a major Alzheimer’s risk gene—may impair both the immune activation triggered by lecanemab and the clearance mechanisms that LRP1-targeting drugs rely on. Patients carrying the APOE4 variant may have intrinsically less effective microglial responses or impaired vascular drainage, limiting the benefit of these drugs.

Another important limitation is inflammation. While lecanemab’s immune activation is designed to clear plaques, excessive or uncontrolled immune activation can cause inflammation-related side effects, including amyloid-related imaging abnormalities (ARIA)—microhemorrhages or microinfarcts that appear on brain imaging. This is not just an imaging finding; in some patients, ARIA causes headaches, confusion, or other symptoms. The warning here is that more immune activation is not always better; the goal is calibrated, targeted clearance, not systemic neuroinflammation. Patients with baseline brain inflammation, stroke history, or blood vessel abnormalities face higher risk for these adverse effects.

What Genetic or Biological Factors Limit How Well These Drugs Work?

How Do These Drug Mechanisms Compare to What Happens Naturally in Healthy Brains?

In healthy brains, microglia naturally clear amyloid-beta and other protein debris as part of ongoing maintenance, and the vascular system continuously clears proteins through the glymphatic system—a recently discovered brain-cleaning network that uses cerebrospinal fluid to flush out waste. The problem in Alzheimer’s disease is that this natural clearance becomes insufficient; plaques accumulate faster than they can be removed. Lecanemab essentially amplifies the brain’s natural immune response by tagging plaques with an antibody that microglia recognize more readily.

LRP1-targeting drugs enhance the vascular drainage system, boosting another natural clearance pathway. A key insight from understanding these mechanisms is that Alzheimer’s-preventing drugs may work best when they support the brain’s natural systems rather than completely replacing them. Levetiracetam, by preventing plaques from forming in the first place, reduces the burden on these natural clearance systems, making it potentially sustainable long-term without overwhelming the immune response.

What Do These Discoveries Tell Us About Future Alzheimer’s Treatments?

The emerging picture suggests that future Alzheimer’s treatments will likely combine multiple drug mechanisms—perhaps a plaque-prevention drug like levetiracetam combined with plaque-clearance drugs like lecanemab or LRP1-targeting agents, potentially supported by anti-inflammatory medications to prevent excessive immune activation. Clinical trials are beginning to test such combinations, and early results suggest they may be more effective than single drugs alone. The specificity being discovered—such as the importance of SPP1-expressing microglia for plaque clearance, or the role of specific enzymes in plaque formation—opens the door for even more targeted, personalized treatments based on individual genetic profiles.

Another promising direction involves earlier intervention. As these mechanisms are understood, it becomes clearer that waiting for Alzheimer’s symptoms to appear may be too late; the brain’s clearance systems may be overwhelmed by then. This supports the emerging consensus toward treating asymptomatic people with amyloid accumulation, ideally with combinations of preventive (levetiracetam-like) and clearance-enhancing drugs (lecanemab-like) before cognitive symptoms develop. The challenge ahead is not just developing new drugs, but identifying which people will benefit from which combinations, and ensuring treatments remain tolerable during years of preventive use.

Conclusion

Scientists now understand that lecanemab clears amyloid plaques by activating the brain’s immune cells through the Fc fragment of the antibody, triggering phagocytosis and lysosomal breakdown of the engulfed plaques. This explanation reveals why the drug’s benefit is modest in many patients—it requires both robust immune activation and intact cellular machinery, both of which may be compromised in advanced Alzheimer’s disease. Complementing this approach, levetiracetam prevents plaque formation entirely by pausing protein recycling, and emerging LRP1-targeting drugs enhance the brain’s natural vascular clearance systems. Together, these mechanisms represent three different biological strategies for addressing amyloid accumulation.

For patients and families considering Alzheimer’s treatments, understanding these mechanisms helps contextualize what these drugs can and cannot do. Lecanemab and similar immune-activating drugs work best in early disease with intact cellular systems; levetiracetam may be most valuable as a preventive therapy; and future combination treatments will likely target multiple pathways simultaneously. If you are considering these options for a loved one, discuss with your neurologist which mechanism might best match the stage of disease and individual health factors. As research continues to refine our understanding of these processes, more effective and personalized treatment strategies will emerge—but today, these drugs represent the most direct scientific proof that Alzheimer’s plaques can be actively removed from the brain.