New tool for tracing blood cells’ ancestry might one day help predict disease risk
The human blood system is in a constant state of turnover. First-line immune defenders, like neutrophils, need to be replaced after just four to eight hours, platelets can last a week, red blood cells up to four months, and some white blood cells, like memory B cells, live for decades.
The heroic task of constantly replenishing these ranks, and making sure the balance of different types of blood cells is right, falls to a primitive reserve of stem cells that reside deep in the bone marrow. Humans have anywhere between 20,000 and 200,000 hematopoietic stem cells, or HSCs, but just 1,000 of them are active at any given time, giving rise to about 500 billion blood cells every day.
