A bacterium behind ordinary pneumonia and sinus infections can settle into the retina and the brain and stay there for years, and it appears to make Alzheimer's disease worse. That is the central finding of a Cedars-Sinai study published in Nature Communications, which reports the first evidence that Chlamydia pneumoniae reaches the retina - the light-sensing tissue at the back of the eye - and sets off immune responses tied to inflammation, nerve cell death and cognitive decline.
What gives the result weight is the range of evidence behind it. The team traced the same bacterium across human tissue samples, cell cultures and animal models. "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, professor of neurosurgery, neurology and biomedical sciences at Cedars-Sinai Health Sciences University and the study's senior author.
The practical interest here is that infections and inflammation are, at least in principle, treatable. The researchers suggest their findings point toward possible interventions such as therapies that limit inflammation and early antibiotic treatment - approaches aimed at a contributing factor rather than at amyloid plaques, the target of most current Alzheimer's drugs.
The work describes the bacterium as amplifying Alzheimer's disease rather than causing it outright, and the leap from laboratory and animal findings to treatments that help patients is a long one. Whether antibiotics or anti-inflammatory strategies can slow cognitive decline in people carrying this infection remains to be tested.