Answer:
When germs enter the body, a powerful defense system may turn on. Known as the immune system, it calls in cells that serve as combat troops, snipers and medics. Some of these cells take on invaders. Others clean out sick and dead cells. Still more trigger healing. Genes hold instructions for making many of those immune troops and their weapons. But a study now finds that the environment may play a bigger role than genes do in revving up the immune system and shutting it down when the battle is over.
