A team of researchers from Harvard has presented evidence that suggests a mechanism for fighting infections in the brain may be a contributing factor to the development of Alzheimer’s disease. The research, reported in Science Translational Medicine, opens up a new and surprising window into the possible causes of Alzheimer’s.

According to the new research, the process that results in Alzheimer’s goes something like this. The blood-brain barrier keeps many bacterial pathogens that are present in the bloodstream out of the brain. As people age, the blood-brain barrier weakens and viruses, bacteria and fungi that were previously contained within the bloodstream begin to enter the brain.