A subpopulation of adaptive immune cells patrols the brain and cerebrospinal fluid in people who have Alzheimer’s disease. This discovery should broaden our understanding of how the immune system can influence neurodegeneration.
By Michael T. Heneka
For decades, research into Alzheimer’s disease has centred on neurons. Only in the past few years have scientists identified a role for immune cells in the progression of this neurodegenerative disorder1. Most research has focused on the nonspecific, innate branch of the immune system. But writing in Nature, Gate et al.2 report that an immune-cell subpopulation belonging to the adaptive immune system — which remembers and responds to specific foreign invaders — might also have a role in Alzheimer’s disease.
The authors isolated and analysed immune cells from the blood of healthy people and people who had Alzheimer’s disease or a precursor of the disease known as mild cognitive impairment (MCI). They discovered an immune-cell subpopulation called CD8+ T effector memory CD45RA+ (TEMRA) cells that was associated with MCI and Alzheimer’s disease. TEMRA cells have previously been linked to immunological memory, and they release inflammatory and cytotoxic (cell-death-promoting) molecules3.
Analysis of a separate cohort of people who had Alzheimer’s disease revealed that an increased presence of TEMRA cells in the blood was associated with compromised cognitive performance. This finding could indicate that TEMRA cells contribute to neuronal dysfunction by secreting inflammatory and cytotoxic molecules in the brain (Fig. 1). Alternatively, a damaging mechanism that causes cognitive dysfunction might also elicit an inflammatory TEMRA-cell response in the blood.
