Y Sun

In the bone marrow, as in a barracks, there is a constant roll call. Rookie T cells wait for their first assignment, and for a while they all look alike. But with age, soldiers with a special mark on their uniform start to appear among them: the protein annexin A1. This mark is not a decoration but a brake shoe that keeps the cell from charging into battle.

In a house where no one has done repairs for years, old junk doesn't just take up space. It starts to smell, shed dust, and spoil the air for everyone living there. Senescent cells behave much the same way in our bodies: they can no longer divide, but they reliably broadcast inflammatory signals around them, accelerating the aging of neighboring tissues.