Could Alzheimer's Be a Reaction to Infection?

A theory is gaining credence that Alzheimer's may be a response to infections by pathogens like viruses, bacteria, and fungi, reports Scientific American . One pathogen of particular interest is herpes simplex virus type 1 (HSV-1), with a 1997 study finding HSV-1-infected persons with the Alzheimer's-affiliated APOE E4 gene have a much higher risk of developing the disorder. More recent research demonstrated that HSV-1 induces a dramatic increase in amyloid beta production in infected cell cultures, while 90 percent of amyloid beta plaques contain the viral DNA of HSV-1. Another study showed amyloid beta binds to the surface of HSV-1 and forms fibrils to corral the virus before it adheres to brain cells. Mice that expressed higher concentrations of amyloid beta were more effective at combating HSV-1, which aligns with the antimicrobial protection hypothesis (APH). According to the APH, amyloid beta, when generated at normal concentrations, shields the brain from pathogenic infections.