"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."
"The discovery that these cells influence the brain from the outside "reveals something entirely new", says Paloma Navarro Negredo, a neuroimmunologist at the Swiss Federal Institute of Technology in Lausanne. Old blood meets young"
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+ T cells remains in the bloodstream, and its role in cognitive ageing was previously unclear. A mouse study used parabiosis to connect the circulatory systems of young and old mice and found that young cells did not change in behavior in older blood, suggesting aged non-infiltrating CD8+ cells actively drive ageing. Blocking the effects of these blood-borne cells reversed cognitive decline and related brain changes, indicating that targeting blood rather than brain infiltration may be a more realistic treatment strategy.
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