CD8⁺T cells are present at low levels in the white matter with physiological and pathological aging

The presence and functional role of T cell infiltration in human brain parenchyma with normal aging and neurodegeneration is still under intense debate. Recently, CD8(+) cells have been shown to infiltrate the subventricular zone in humans and mice with a deleterious effect on neural stem cells. However, to which extent T cell infiltration in humans also occurs in other regions such as cortical areas and, especially, white matter (WM) has not yet been addressed. In this work, we report a low-grade infiltration of T cells (CD3(+), CD4(+) and CD8(+)) in the WM of aged individuals that is also observed at similar levels in patients with neurodegenerative disorders (Alzheimer's disease). In particular, CD3(+) and CD8(+) cells were increased in perivascular and parenchymal WM and cortical regions (enthorinal cortex). These results reveal that T cell infiltration in brain parenchyma occurs with physiological and pathological aging in several regions, but it seems to be lower than in the subventricular zone neurogenic niche.