http://www.sciencemag.org/news/2020/05/defective-immune-cells-could-make-us-old

Compared with a normal mouse (left), a mouse with defective mitochondria in its T cells appears old.

T cells are supposed to defend us from pathogens, but a new mouse study suggests they may also speed aging. Blocking inflammation caused by the cells or boosting their supply of a key metabolic molecule lessened the severity of some aging-related symptoms in rodents, raising the possibility these treatments could benefit older people.