Y Li

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.

Water in a sink spirals down the drain. A cell caught in the whirlpool of aging is much the same: it can no longer climb out, and every turn pulls it deeper. Scientists have found what sets this whirlpool spinning: the ApoD protein, which old cells release into their surroundings like a distress signal that actually drowns the neighbors.