What is the Immune System?

Your immune system prevents infection and defends your body against foreign invaders. You are constantly exposed to millions of organisms like bacteria, viruses and other microbes waiting to enter your body. Any organism that enters your body and provokes your immune system is known as an antigen. Since bacteria and viruses are always evolving and changing, your body could be exposed to essentially an infinite variety of antigens. For this reason there are a variety of mechanisms the immune system uses to accomplish the same thing, but in different ways.