The Innate Immune System
One of the two immune systems is the innate immune system. It is a nonspecific defense mechanism that comes into play immediately or within hours of an antigen’s appearance in the body. This system is part of you from birth and is built, so it recognizes an invader. When this happens, the cells surround the unwanted bacteria or other foreign cells and work to get rid of them.
The cells specific to this system are known as phagocytes. They include physical barriers such as chemicals in the blood, skin, and other external and internal surfaces of the human body.