A new study from Cedars-Sinai has identified a surprising connection: the common bacterium Chlamydia pneumoniae, known for causing pneumonia and sinus infections, can persist in the eye and brain, contributing to chronic inflammation, nerve cell death, and accelerated cognitive decline, particularly in Alzheimer’s disease.
Published January 30, 2026, in Nature Communications, the research shows for the first time that Chlamydia pneumoniae reaches the retina – the light-sensitive tissue at the back of the eye – where it triggers immune responses linked to neurodegeneration. Higher levels of the bacterium in retinal and brain tissues correlated with more severe Alzheimer’s pathology and greater cognitive impairment.
The study examined retinal tissue from 104 individuals, including those with normal cognition, mild cognitive impairment, and Alzheimer’s disease. Researchers also tested human neurons in culture and used mouse models of Alzheimer’s to demonstrate the effects of infection.
Led by senior authors Maya Koronyo-Hamaoui, PhD, professor of Neurosurgery, Neurology, and Biomedical Sciences at Cedars-Sinai, and Timothy Crother, PhD, with co-first authors Bhakta Gaire, PhD, and Yosef Koronyo, MSc, the team found Chlamydia pneumoniae in higher amounts in the retinas and brains of Alzheimer’s patients compared to controls.
The bacterium appears to linger for years, amplifying inflammation and driving processes central to Alzheimer’s, including increased production of amyloid-beta – the protein that forms plaques in the brain – and heightened nerve cell death.
“Seeing Chlamydia pneumoniae consistently across human tissues, cell cultures and animal models allowed us to identify a previously unrecognized link between bacterial infection, inflammation and neurodegeneration,” said Maya Koronyo-Hamaoui, PhD. “The eye is a surrogate for the brain, and this study shows that retinal bacterial infection and chronic inflammation can reflect brain pathology and predict disease status, supporting retinal imaging as a noninvasive way to identify people at risk for Alzheimer’s.”
The findings were particularly pronounced among individuals carrying the APOE4 gene variant, a major genetic risk factor for Alzheimer’s disease, who exhibited higher bacterial loads.
“This discovery raises the possibility of targeting the infection-inflammation axis to treat Alzheimer’s,” said Timothy Crother, PhD.
The research suggests potential new strategies for Alzheimer’s, including early antibiotic interventions or therapies to reduce chronic inflammation. Importantly, retinal changes detectable through routine eye examinations could serve as noninvasive biomarkers for earlier detection of disease risk or progression than current methods.
While the study establishes strong associations and mechanistic links in models, it highlights the need for further research to confirm causality and explore therapeutic applications in larger human populations.
LincolnCitizen.com continues to cover emerging research on aging, brain health, and potential impacts on wellness and healthcare in Lincoln and Nebraska communities. Stay informed on how national breakthroughs may influence local approaches to cognitive health.
