The immune system is like a police force. It patrols everywhere, and if it finds a disturbance, it calls for back-up. In this way, it is different from other systems in that it has to be able to react in any part of the body. The immune system provides two levels of defense: innate and adaptive immunity. This discussion will begin with a brief description of the organs and tissues associated with the immune system and then focus on the cells that provide innate and adaptive immunity.
Reviewed on April 22, 2019