Date Published: November 17, 2003
Publisher: Public Library of Science
Partial Text: Faced with all manner of potential threats in the form of billions of different viral, bacterial, and chemical pathogens, the mammalian immune system relies on a “safety in diversity” strategy for protection. With two distinct subsystems—one innate, the other adaptive—the immune system can recognize some 100 trillion antigens. The innate system deploys cells programmed to quickly recognize microbes with a particular set of conserved molecular structures. The adaptive system relies on billions of uniquely outfitted lymphocytes (white blood cells) to identify just as many pathogens through their protein fragments, or antigens. A human being grinds out billions of these cells every day. In the absence of threats, the immune system maintains a quiescent state and many of these cells are discarded. But for the immune system, doing nothing takes a concerted effort.