The impact of systemic infection on the progression of neurodegenerative disease

In multiple sclerosis — the archetypal inflammatory response in the central nervous system — T cells and macrophages invade the brain and damage the myelin and neurons. In other chronic neurodegenerative diseases, there is an atypical inflammatory response that is characterized by large numbers of activated microglia. These macrophages are primed by components of the neuropathology but might be further activated by systemic infection, which in turn has pronounced effects on inflammation in the brain and perhaps on neurological function. There is emerging evidence to support the idea that nonspecific systemic infection or inflammation in people with existing inflammation in the brain contributes to the rate of disease progression through further activation of these already primed macrophages.