Micrograph of Chlamydia pneumoniae in an epithelial cell in acute bronchitis: 1 – infected epitheliocyte, 2 – uninfected epitheliocytes, 3 – chlamydial inclusion bodies in cell, 4 – cell nuclei
Chlamydia pneumoniae—a common bacterium that causes pneumonia and sinus infections—can linger in the eye and brain for years and may aggravate Alzheimer’s disease, according to a new study.
The study shows for the first time that Chlamydia pneumoniae can reach the retina—the tissue lining the back of the eye—where it triggers immune responses linked to inflammation, nerve cell death and cognitive decline.
For the study, published in Nature Communications, researchers used advanced imaging, genetic testing and protein analysis to examine retinal tissue from 104 individuals, some with normal cognition, some with mild cognitive impairment and some with Alzheimer’s disease.
They found significantly higher levels of Chlamydia pneumoniae in the retinas and brains of people with Alzheimer’s disease than they found in those with normal cognition. The higher the bacterial levels, the more severe the brain changes and cognitive decline. Additionally, the researchers discovered that higher levels of the bacterium were more common in people who carried the APOE4 gene variant, a known risk factor for Alzheimer’s disease.
The researchers also studied human neurons in the lab and in laboratory mice with Alzheimer’s disease. In both, infection with Chlamydia pneumoniae increased inflammation, nerve cell death and cognitive decline, showing the bacterium can accelerate disease processes. The infection triggered production of amyloid-beta, the protein that accumulates in the brains of people with Alzheimer’s.
These findings suggest that targeting chronic bacterial infection—and the inflammation it triggers—could represent a new treatment strategy. The research also supports potential use of the retina as a noninvasive way to help diagnose and monitor Alzheimer’s disease.
Data from Cedars Sinai Medical Center