Here's how it works. Your immune system protects you from all kinds of nasty bugs and helps repair tissue that has been damaged by injury or surgery. When a problem develops somewhere, your body does the equivalent of calling 911. The alarm sounds, and the immune system springs into action. The first responders, the white blood cells, travel to the site of the problem. As weapons, some of the cells released a shower of powerful free radicals (called an oxidative burst) that aids in the destruction of invading microorganisms and damaged tissue.