Scientists at Cedars-Sinai have discovered that a common type of bacteria called Chlamydia pneumoniae may stay hidden in the eye and brain for years—and could make Alzheimer’s disease worse.
The study, published in Nature Communications, suggests that this infection may increase brain inflammation and damage, and that treating it early might help slow down the disease.
Chlamydia pneumoniae is known for causing lung and sinus infections, but this new study shows it can travel to the retina—the part of the eye that sends signals to the brain.
Once there, it triggers inflammation and other problems linked to nerve damage and memory loss.
Dr. Maya Koronyo-Hamaoui, the senior author of the study, said they found this bacteria not only in human eyes but also in lab-grown cells and animals.
This helped them understand the connection between infection, inflammation, and brain diseases like Alzheimer’s. She said that because the eye reflects what’s happening in the brain, looking at the retina may be a noninvasive way to detect early signs of Alzheimer’s.
To explore this link, researchers looked at the retinal tissue from 104 people. Some had normal brain function, some had mild memory problems, and others had Alzheimer’s. The team used advanced imaging and tests to look for the bacteria.
They discovered that people with Alzheimer’s had more of this bacteria in their eyes and brains than those with normal memory. The more bacteria they found, the more damage they saw in the brain. This was even more common in people with the APOE4 gene, which already raises the risk of Alzheimer’s.
In lab tests on human brain cells and mice with Alzheimer’s, the bacteria caused more inflammation and brain cell death. It also led to a buildup of amyloid-beta, a sticky protein that collects in the brains of people with Alzheimer’s. These changes made memory and brain function worse.
Dr. Timothy Crother, another author of the study, said this discovery suggests that we might be able to treat Alzheimer’s by targeting the infection and the inflammation it causes. Reducing this inflammation or using antibiotics early could help protect the brain.
The study also supports using the retina as a way to check for Alzheimer’s. Since eye exams are noninvasive and easy to do, this could be a helpful tool for early diagnosis.
The findings raise hope for new ways to treat or prevent Alzheimer’s. While more studies are needed, the research shows that fighting certain bacterial infections and controlling inflammation may help slow down brain damage.
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