Immune cells in the blood drive brain ageing - blocking them improves memory

"T cells have many jobs, chiefly destroying pathogens. But as people age, a group of T cells called CD8+ cells begin to infiltrate the brain tissue, where they secrete an enzyme that causes inflammation and prevents brain cells from regenerating. Many more CD8+ cells remain in the bloodstream, but their role in ageing wasn't known until now."

"In the latest study, researchers show that this large population of 'non-infiltrating' T cells actively contributes to cognitive decline. Blocking these effects in the blood might be a more realistic treatment strategy than targeting the cells in the brain, say researchers. "We don't even have to get into the brain to start treating cognitive decline," says study co-author Saul Villeda, a neuroscientist at the University of California, San Francisco. "We can actually block things in blood to have an impact on memory.""

"To understand the factors that influence cognitive ageing, Villeda's team used a surgical technique called parabiosis to join the circulatory systems of two mice - one old, one young. The researchers wanted to see whether the young immune cells aged in the presence of older blood, and vice versa. They found no changes in how the cells behaved, which Villeda says suggested that the older non-infiltrating CD8+ cells were somehow driving the ageing process, rather than being influenced by other factors."

CD8+ T cells infiltrate brain tissue with age and secrete an enzyme that promotes inflammation and blocks brain cell regeneration. A larger population of CD8+ cells remains in the bloodstream, and its role in cognitive ageing was previously unclear. A mouse study using parabiosis joined the circulatory systems of young and old mice to test whether blood factors drive ageing. The young immune cells did not change, indicating that aged non-infiltrating CD8+ cells actively contribute to cognitive decline. Blocking the effects of these blood-borne cells reversed ageing-related changes, suggesting a treatment strategy focused on blood rather than targeting brain-infiltrating cells.

Read at Nature