Immunity is a large network of organs, white blood cells and proteins that work together to protect the body from germs that cause infections and diseases. It also helps the body heal from injuries and other illnesses.
The immune system can distinguish between your own cells and those of a disease-causing germ, and it can respond quickly to kill the germs or limit how much damage they can do. Your immune system is made up of 2 parts: the innate immune system, which you are born with; and the adaptive immune system, which develops as the body encounters microbes or their toxins.
Anything that triggers the immune response is called an antigen, such as bacteria, viruses, fungi, or chemicals. The first time your immune system meets an antigen, B cells and T cells are activated and produce antibodies that attack the pathogen based on its characteristics (think of it as a lock and key). This is called the primary immune response. The immune system then “remembers” each specific pathogen that has been attacked, so it can respond more quickly the next time it sees that particular antigen.
The innate immune system also includes other barriers to infection, such as the closed surfaces of the skin and mucous membranes that line the inside of organs and body cavities, which prevent many germs from entering the body. In addition, substances such as acids, enzymes and sweat help keep germs from growing and causing illness.