Like a home security system that guards against intruders and sounds the alarm, your immune system tracks and destroys germs and other invaders that could make you sick. The cells and organs that make up your immune system work together to help you stay healthy throughout life. It is made up of two major systems: the innate immune system and the adaptive immune system.
Your innate immune system includes skin, body hair and natural barriers such as stomach acid and saliva. It also includes defense mechanisms such as inflammation and killing cells that have become damaged or infected.
Immunity is your body’s defense against disease-causing microbes, such as bacteria, viruses, parasites and fungi. Your body is constantly monitoring your surroundings for these harmful pathogens, locating them in blood and tissues throughout the body.
Upon finding a harmful pathogen, white blood cells (including lymphocytes such as B-cells and T-cells) attack the pathogen. Antibodies made by B-cells bind to a specific part of the pathogen and kill it or prevent its spread. This is called humoral immunity.
After fighting off a disease-causing pathogen, some of the B cells that attacked it become memory B cells. These cells keep a record of the germ and are ready to quickly activate the adaptive immune system if the same germ enters the body again. This is known as immunological memory.
A person can acquire active immunity either naturally or through immunization. Natural immunity results from infection with a disease organism and is often life-long. Vaccines can be inactivated or live, attenuated, and can be administered by mouth or intravenously.
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