immune system disorder
(ih-MYOON SIS-tem dis-OR-der)
A condition
that affects the immune system. The immune system is made
up of cells, tissues, and organs that help the body fight
infections and other diseases. There are many different
types of immune system disorders, including
immunodeficiency disease, autoimmune disorders, and
allergic disorders. Immunodeficiency disease occurs when a
part of the immune system is missing or not working
properly. Autoimmune disorders occur when the immune system
recognizes its own tissues as foreign and attacks them.
Allergic disorders occur when the immune system overreacts
to substances that are usually not harmful, such as pollen,
molds, and certain foods. Cancers of the immune system
(such as leukemia and lymphoma) are also immune system
disorders.