A common bacterium known for causing pneumonia and sinus infections may contribute to the progression of Alzheimer’s disease, according to new research from Cedars-Sinai Medical Center. The study, published on February 21, 2026, in *Nature Communications*, reveals that Chlamydia pneumoniae can invade both the retina and brain, leading to inflammation, nerve cell death, and the accumulation of amyloid-beta, a protein closely associated with Alzheimer’s.
Researchers discovered that individuals diagnosed with Alzheimer’s showed significantly higher levels of the bacterium compared to those with normal cognitive function. The presence of Chlamydia pneumoniae was particularly pronounced in patients carrying the high-risk APOE4 gene variant, which is known to elevate the likelihood of developing Alzheimer’s.
Implications for Alzheimer’s Treatment Strategies
The findings suggest that chronic infection and inflammation may play a critical role in Alzheimer’s pathology. By identifying a connection between bacterial infection and neurodegeneration, researchers propose that addressing these infections could pave the way for innovative treatment approaches. This could potentially include early antibiotic intervention and therapies that target inflammation.
The research team utilized advanced imaging techniques to analyze retinal tissue from 104 participants, encompassing individuals with normal cognition, mild cognitive impairment, and Alzheimer’s disease. They found that elevated levels of Chlamydia pneumoniae were linked not only to the severity of brain damage but also to cognitive decline, underscoring the need for further investigation into the bacterium’s role in neurodegenerative processes.
Maya Koronyo-Hamaoui, PhD, a professor of Neurosurgery, Neurology, and Biomedical Sciences at Cedars-Sinai and the study’s senior author, emphasized the significance of these findings. “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,” she stated. This insight supports the use of retinal imaging as a noninvasive method to identify individuals at risk for Alzheimer’s.
Research Findings and Future Directions
To further explore the connection, researchers conducted laboratory studies involving human nerve cells and Alzheimer’s disease models in mice. Their investigations revealed that infection with Chlamydia pneumoniae triggered increased inflammation and nerve cell death, alongside the heightened production of amyloid-beta protein.
Co-first authors of the study, Bhakta Gaire, PhD, and Yosef Koronyo, MSc, noted that the results indicate a potential therapeutic pathway focusing on the infection-inflammation axis to combat Alzheimer’s disease. Timothy Crother, PhD, a co-corresponding author and research professor at Cedars-Sinai, added that targeting long-standing bacterial infections could represent a novel approach to treatment.
The research was funded by several grants from the National Institutes of Health/National Institute on Aging, alongside contributions from the Alzheimer’s Association. Additional authors from Cedars-Sinai include Jean-Philippe Vit, Alexandre Hutton, and Natalie Swerdlow, among others.
As the scientific community continues to seek effective treatments for Alzheimer’s, these findings underscore a promising link between bacterial infections and cognitive impairment, potentially reshaping future therapeutic strategies.
