Linking T cells to Alzheimer's disease: from neurodegeneration to neurorepair

•AD-specific T cell populations indicate a role for adaptive immune responses.•T cell infiltration into the brain occurs in AD and models of AD.•A role for the choroid plexus in immune surveillance has been identified.•Contrasting effects of adoptive transfer of T cells in models of AD are reported.•Evidence suggests that regulatory T cells (Tregs) play an immune regulatory role in the brain.

The overly-simplistic view that inflammatory and anti-inflammatory influences in the brain were respectively detrimental and advantageous in Alzheimer's disease (AD) is being challenged by advances in methodologies, and a debate relating to immune surveillance mechanisms in the brain. In contrast with previous findings, increasing interleukin (IL)-4 and IL-10 in brain by a recently-developed adenoviral delivery method, had detrimental effects in an animal model of AD, and the ability to isolate the choroid plexus has opened the debate on the role of this specialized tissue in immune surveillance. Delivery of polarized T cells to animal models of AD by different routes has yielded contrasting results; analysis of these diverse responses is vital to understand the role of T cells in the brain in AD, first reported over 25 years ago.