To be immune (say: ih-MYOON) means to be protected. So it makes sense that the body system that helps fight off sickness is called the immune system. The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. White blood cells, also called leukocytes (say: LOO-kuh-sytes), are part of this defense system. There are two basic types of these germ-fighting cells: phagocytes (say: FAH-guh-sytes), which chew up invading germs lymphocytes (say: LIM-fuh-sytes), which allow the body to remember and recognize previous invaders Leukocytes are found in lots of places, including your spleen, an organ in your belly that filters blood and helps fight infections. Leukocytes also can be found in bone marrow, which is a thick, spongy jelly inside your bones. So you have this great system in place. Is it enough to keep you from getting sick? Well, everyone gets sick sometimes. But your immune system helps you get well again. And if you've had your shots (also called vaccines), your body is extra-prepared to fight off serious illnesses that your immune system alone might not handle very well. If you get the shot that covers measles, for instance, it can protect you from getting measles, if you're ever exposed to it. Healthy kids can help their immune systems by washing their hands regularly to prevent infections, eating nutritious foods, getting plenty of exercise, getting enough sleep, and getting regular medical checkups. And if you feel great today, thank your immune system! Back to Articles Related Articles Activity: Immune System Do you know your immune system? Label the parts of the system that keeps you well. Read More Why Do I Need to Wash My Hands? Washing your hands is the best way to stop germs from spreading. Learn all about the best way to wash your hands in this article for kids. Read More Movie: Immune System Watch this movie about your immune system - the system that keeps you healthy. Read More Quiz: Immune System Take this quiz about the immune system, the system that keeps you healthy. Read More What Are Germs? You know they can hurt you, but what are these invisible creatures? Find out in this article for kids. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.