Wikijunior:Biology/Systems/Immune System

Immune System
The immune system protects our bodies from disease. Cells called white blood cells found in our blood are able to kill bad things such as bacteria and viruses.

There are many different types of white blood cells. Some of them make things called antibodies that stick to things that enter our bodies, making them easy to find. Other white blood cells get rid of bacteria and stop viruses like the flu. When our immune system does not work well, we are vulnerable to diseases caused by bacteria and viruses.

Problems with the immune system include allergies; when someone has allergies, their white blood cells attack things that are not harmful to the body. When someone sneezes or their eyes water because of pollen or cat dander, it is because of the immune system's reaction to those things.

AIDS (Acquired Immunodeficiency Syndrome) is a disease caused by a virus that kills some white blood cells, which hurts the immune system and leaves our bodies vulnerable to bacteria or viruses.

Covid-19 is a virus that attacks humans. Some people have damaged immune systems after being infected with the virus.